Method for producing polylactide blow film

Abstract

The present invention relates to a method for manufacturing a polylactide blown film. According to the present invention, a polylactide blown film having high transparency and excellent surface properties can be provided without a plasticizer additive or the like, and process stability can be improved.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0028617 filed in the Korean Intellectual Property Office on March 3, 2023, and Korean Patent Application No. 10-2024-0029918 filed in the Korean Intellectual Property Office on February 29, 2024, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to a method for producing a polylactide blown film having excellent transparency and surface properties without a plasticizer. Background Art

[0004] Polylactide polymer (hereinafter referred to as "PLA") is a biodegradable environmentally friendly material, which has been extensively studied in recent years. Unless modified, PLA is generally a linear molecule and has thermoplastic polymer-like properties, and is used as a material for various films, fibers and other molded products.

[0005] It is known that films, especially blown films, comprising PLA are difficult to manufacture and therefore require the addition of additives such as plasticizers during manufacture. However, plasticizers are generally undesirable in films for food-related applications and have poor compatibility with PLA and thus are sometimes leached out. In order to avoid such problems, solution casting is used, but in the case of PLA films manufactured by solution casting, only films with limited uses can be produced and the process costs are very high.

[0006] Therefore, a new manufacturing method for producing PLA blown films with excellent properties without plasticizers is needed. Summary of the invention

[0007] Technical issues

[0008] An object of the present invention is to provide a method for producing a polylactide blown film, which can provide a polylactide blown film having high transparency and excellent surface properties and can improve process stability.

[0009] Technical Solution

[0010] Therefore, according to one embodiment of the present invention, there is provided a method for manufacturing a polylactide blown film, the method comprising the steps of: preparing a mixture comprising a polylactide polymer and an epoxy-containing acrylate terpolymer (step 1); subjecting the mixture to reactive extrusion to prepare a branched polylactide polymer in the form of pellets (step 2); and subjecting the pellets to blow extrusion to manufacture a blown film (step 3), wherein the epoxy-containing acrylate terpolymer comprises 30 to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other, and the mixture of step 1 comprises the epoxy-containing acrylate terpolymer in an amount of 0.1 to 1.0 parts by weight based on 100 parts by weight of the polylactide polymer.

[0011] The epoxy-containing acrylate terpolymer may include 30 wt % to 45 wt % of repeating units derived from a first alkyl (meth)acrylate monomer, 30 wt % to 45 wt % of repeating units derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of repeating units derived from a second alkyl (meth)acrylate monomer.

[0012] The epoxy-containing acrylate terpolymer may have 30 to 80 epoxy groups per molecule.

[0013] The first alkyl (meth)acrylate and the second alkyl (meth)acrylate may each independently be at least one selected from methyl (meth)acrylate, butyl acrylate, and 2-(ethylhexyl) acrylate.

[0014] The polylactide membrane may have a weight average molecular weight of 200,000 to 500,000 g / mol when measured by gel permeation chromatography using polystyrene standards.

[0015] The mixture of step 1 includes the epoxy acrylate terpolymer in an amount of 0.5 to 0.75 parts by weight based on 100 parts by weight of the polylactide polymer.

[0016] The mixture of step 1 may further include one or more selected from the group consisting of a slip agent and an anti-blocking agent.

[0017] The reactive extrusion of step 2 may be performed at a temperature of 150°C to 220°C.

[0018] In the reactive extrusion of step 2, the screw speed of the extruder may be 100 rpm to 300 rpm.

[0019] The blow extrusion of step 3 may be performed at a temperature of 200° C. to 230° C.; and a pressure of 10 bar to 50 bar.

[0020] Beneficial Effects

[0021] According to the present invention, a polylactide blown film having high transparency and excellent surface properties can be provided without additives such as plasticizers, and process stability can be improved without increasing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The measurement results of the molecular weights of the pellets prepared in Examples and Comparative Examples are shown.

[0023] Figure 2 The measurement results of the molecular weights of the blown films produced in Examples and Comparative Examples are shown.

[0024] Figure 3 The appearance of the blown films prepared in Examples and Comparative Examples, and the bubble shape during extrusion blown film are shown. DETAILED DESCRIPTION

[0025] The terms used herein are only for explaining specific implementations and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular expressions used herein may include plural expressions, and the terms "including", "equipped with" or "having" used in the specification mean the existence of the features, steps, structural elements and / or their combinations practiced, and do not exclude the possibility of other features, steps, structural elements or their combinations.

[0026] Although various modifications can be made to the invention, and the invention can have various forms, specific embodiments will be described and explained in detail below. However, it should be understood that these are not intended to limit the invention to a specific invention, and the invention includes all modifications, equivalents or alternatives thereof without departing from the spirit and technical scope of the invention.

[0027] As used herein, the term "long chain branch (LCB)" refers to a long chain having a carbon number similar to that of the main chain, and thus cannot be distinguished from the main chain.

[0028] As used herein, the terms "unit derived from" and "repeating unit derived from" may refer to a component, a unit and a structure from any material or the material itself, respectively.

[0029] Hereinafter, the present invention will be described in detail.

[0030] The present invention relates to a method for producing a polylactide blown film having high transparency and excellent surface properties without a plasticizer.

[0031] Specifically, according to one embodiment of the present invention, there is provided a method for manufacturing a polylactide blown film, the method comprising the following steps:

[0032] preparing a mixture comprising a polylactide polymer and an epoxy-containing acrylate terpolymer (step 1);

[0033] Reactively extruding the mixture to produce a branched polylactide polymer in the form of pellets (step 2); and

[0034] The pellets are blown extruded to produce a blown film (step 3),

[0035] wherein the epoxy-containing acrylate terpolymer comprises 30 wt % to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 wt % to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, and

[0036] The first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other, and the mixture of step 1 includes the epoxy-containing acrylate terpolymer in an amount of 0.1 parts by weight or more and 1.0 parts by weight or less based on 100 parts by weight of the polylactide polymer.

[0037] Previously, plasticizers were required when preparing polylactide blown films, but they are generally not suitable for food-related films due to their harmful effects on the human body, and there are also leaching problems due to poor compatibility with PLA. In addition, in the case of making PLA films by solution casting, only films with limited uses can be produced, and the process cost is very high.

[0038] Therefore, the inventors of the present invention studied a method for producing a PLA blown film having excellent properties without additives such as plasticizers, and as a result, confirmed that a PLA blown film having excellent properties can be produced by reactively extruding and blow-molding a mixture comprising PLA and an epoxy-containing acrylate terpolymer, thereby completing the present invention.

[0039] Specifically, epoxy-containing acrylate terpolymer is used as a branching agent for PLA. Therefore, in the process of reactive extrusion of the mixture, long chain branching (LCB) is introduced into PLA, and the linear structure of PLA polymer is modified to form a sufficient branched structure. Therefore, PLA polymer with branched structure has increased elasticity and can stably form film bubbles when blow molding is extruded, thereby being able to produce a blown film with smooth surface and uniform thickness. In addition, when epoxy-containing acrylate terpolymer is used as a branching agent, the blown film produced has high transparency and shows excellent appearance characteristics.

[0040] Hereinafter, a method for manufacturing a polylactide blown film will be described in detail according to steps.

[0041] (Step 1)

[0042] In the production method according to one embodiment of the present invention, first, a mixture including a polylactide polymer and an epoxy-containing acrylate-based terpolymer is prepared.

[0043] Polylactide polymers are thermoplastic polyesters obtained by polymerization of lactide or lactic acid, including polymers having -[OC(O)CH(CH3)]- repeating units.

[0044] In addition, the polylactide polymer may be one or more selected from the group consisting of poly-L-lactide, poly-D-lactide, and poly-L,D-lactide.

[0045] In addition, the polylactide polymer may also have repeating units derived from alkylene oxide, or repeating units derived from other monomers copolymerizable with lactide, and in this case, the repeating units derived from alkylene oxide, or repeating units derived from other monomers copolymerizable with lactide may be present in the form of blocks and / or random arrangements. In addition, in the case where the polylactide polymer contains repeating units derived from alkylene oxide or repeating units derived from other monomers copolymerizable with lactide, the content of the repeating units may be 10% by weight or less, specifically 5% by weight or less.

[0046] In addition, the relative weight average molecular weight of the polylactide polymer measured by gel permeation chromatography using a polystyrene standard can be 50,000 g / mol or more, or 100,000 g / mol or more, and 300,000 g / mol or less, or 250,000 g / mol or less, and the molecular weight distribution can be 1.2 or more, or 1.5 or more, and 4 or less, or 3 or less.

[0047] As the polylactide polymer, those generally known in the art may be purchased and used, and the polylactide polymer may be prepared and used, and in the case of preparing the polylactide polymer, the polylactide polymer may be prepared by a conventional polymerization method using lactide or lactic acid as a monomer.

[0048] The epoxy-containing acrylate terpolymer is used to react with the polylactide polymer to introduce long chain branches (LCB) in the following step 2. Thus, a branched structure is formed in the polylactide polymer to improve elasticity, and bubbles can be stably formed during blow extrusion, thereby providing a polylactide blown film with excellent quality.

[0049] The epoxy-containing acrylate terpolymer comprises 30 to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other.

[0050] In one embodiment, the epoxy-containing acrylate terpolymer may include 30 wt % to 45 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 wt % to 45 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer.

[0051] The epoxy-containing acrylate terpolymer comprises 40 to 45 wt % of repeating units derived from a first alkyl (meth)acrylate monomer, 40 to 45 wt % of repeating units derived from a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of repeating units derived from a second alkyl (meth)acrylate monomer.

[0052] Wherein, the first (meth) alkyl acrylate monomer and the second (meth) alkyl acrylate monomer may be independently selected from one or more of the group consisting of methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate and 2-ethylhexyl acrylate, and they may be different from each other. Specifically, the first (meth) alkyl acrylate monomer and the second (meth) alkyl acrylate monomer may be independently selected from methyl methacrylate, methyl acrylate, butyl methacrylate or butyl acrylate, and they may be different from each other. More specifically, the first (meth) alkyl acrylate monomer may be methyl methacrylate, and the second (meth) alkyl acrylate monomer may be butyl methacrylate.

[0053] In addition, the glycidyl (meth)acrylate monomer may be a glycidyl methacrylate monomer or a glycidyl acrylate monomer.

[0054] The epoxy-containing acrylate terpolymer may be prepared by polymerizing a first alkyl (meth)acrylate monomer, a glycidyl (meth)acrylate monomer, and a second alkyl (meth)acrylate monomer different from the first alkyl (meth)acrylate monomer in the presence of an emulsifier.

[0055] Specifically, the epoxy-containing acrylate terpolymer can be prepared by polymerizing 30 to 50 wt % of a first alkyl (meth)acrylate monomer, 30 to 60 wt % of a glycidyl (meth)acrylate monomer, and 10 to 20 wt % of a second alkyl (meth)acrylate monomer different from the first alkyl (meth)acrylate monomer in a solvent in the presence of an emulsifier, wherein the polymerization can be performed at 70 to 80° C. for 3 to 10 hours.

[0056] Furthermore, the polymerization may be carried out in an aqueous solvent, in which case the solvent is distilled water.

[0057] The emulsifier may be one or more selected from anionic emulsifiers, cationic emulsifiers and nonionic emulsifiers, for example, it may be one or more selected from the group consisting of alkyl aryl sulfonates, alkali methyl alkyl sulfates, fatty acid soaps, oleic acid alkali salts, rosin acid alkali salts, lauric acid alkali salts, diethylhexyl sodium phosphate, alcohol polyoxyethylene phosphonates and phenol polyoxyethylene phosphonates. In addition, based on 100 parts by weight of the total monomers, the amount of the emulsifier may be 5 parts by weight or less, specifically 3.0 parts by weight or less, or 0.5 to 2.5 parts by weight.

[0058] Furthermore, if necessary, polymerization can be carried out using a polymerization initiator, wherein an inorganic peroxide or an organic peroxide can be used as the initiator, for example, a water-soluble polymerization initiator such as potassium persulfate, sodium persulfate and ammonium persulfate, and an oil-soluble polymerization initiator such as cumene hydroperoxide and benzoyl peroxide can be used.

[0059] Furthermore, in order to promote the initiation reaction to peroxide together with the polymerization initiator, an activator may be additionally used, and one or more selected from sodium formaldehyde sulfoxylate, sodium ethylenediaminetetraacetate, ferrous sulfate, and glucose may be used as the activator.

[0060] In addition, the polymerization initiator may be used in an amount of 0.1 to 10 parts by weight, specifically 0.1 to 5 parts by weight, based on 100 parts by weight of the total monomers.

[0061] In addition, in order to improve the efficiency of the polymerization reaction, a chain transfer agent can be further used, and as the chain transfer agent, a C5 to 20 straight or branched alkyl mercaptan compound can be used, for example, it can be one or more selected from the group consisting of hexanethiol, cyclohexanethiol, adamantanethiol, heptanethiol, octanethiol, nonanethiol, decanethiol, undecanethiol, dodecanethiol, hexadecanethiol and octadecanethiol.

[0062] In addition, the epoxy-containing acrylate terpolymer may be prepared by further performing one or more steps selected from washing, dehydration and drying, wherein washing, dehydration and drying may be performed by methods known in the art.

[0063] Meanwhile, the content of the epoxy acrylate terpolymer in the mixture is 0.1 parts by weight or more to less than 1.0 parts by weight based on 100 parts by weight of the polylactide polymer. Specifically, the content of the epoxy acrylate terpolymer in the mixture is 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, or 0.4 parts by weight or more, or 0.5 parts by weight or more, and 0.9 parts by weight or less, 0.8 parts by weight or less, 0.75 parts by weight or less, or 0.7 parts by weight or less, based on 100 parts by weight of the polylactide polymer.

[0064] If the mixture contains less than 0.1 parts by weight of the epoxy acrylate terpolymer based on 100 parts by weight of the polylactide polymer, sufficient branching cannot be achieved during reactive extrusion, and thus, it is difficult to form bubbles in subsequent blow extrusion. On the contrary, if the mixture contains more than 1.0 parts by weight of the epoxy acrylate terpolymer based on 100 parts by weight of the polylactide polymer, gel may be formed during extrusion of the blown film due to excessive branching, and thus, bubbles cannot be normally maintained and blow extrusion cannot be smoothly performed.

[0065] The mixture may contain, in addition to the polylactide polymer and the epoxy-containing acrylate terpolymer explained above, one or more additives selected from the group consisting of a slip agent and an anti-blocking agent.

[0066] Slip agents are used to reduce the friction coefficient between films. As slip agents, for example, one or more selected from the group consisting of oleamide, erucamide, stearamide, behenamide, oleyl palmitamide, stearyl erucamide, ethylenebisoleamide and N,N'-ethylenebis(stearamide) (EBS) can be used. When a slip agent is used, its content can be less than 5 wt%, less than 3 wt%, or less than 1 wt%, and more than 0.1 wt%, more than 0.3 wt%, or more than 0.5 wt%, based on the total weight of the mixture.

[0067] Antiblocking agent can be used to prevent the adhesion of the film of manufacture and to increase processability, for example, one or more selected from the group consisting of natural silica, synthetic silica, talcum and calcium carbonate can be used. Based on the gross weight of the mixture, the content of antiblocking agent can be, for example, less than 10 % by weight, less than 8 % by weight, less than 5 % by weight or less than 3 % by weight, and more than 0.1 % by weight, more than 0.5 % by weight, more than 1 % by weight or more than 1.5 % by weight.

[0068] In one embodiment, the mixture comprises oleamide as a slip agent and talc as an anti-blocking agent, wherein the content of oleamide may be 0.1 wt % to 5 wt %, or 0.5 wt % to 1.0 wt %, based on the total weight of the mixture; the content of talc may be 0.1 wt % to 10 wt %, or 1.5 wt % to 3 wt %.

[0069] The method of preparing the mixture is not particularly limited, and the mixture may be prepared by dry mixing the above raw materials without a solvent. For mixing, a batch mixer, an extruder, etc. may be used, but is not limited thereto.

[0070] (Step 2)

[0071] Next, the mixture is subjected to reactive extrusion to prepare a branched polylactide polymer in the form of pellets.

[0072] Reactive extrusion is a chemical reaction process that uses an extruder as a reactor to initiate polymer modification, and in the present invention, it is used for branching of polylactide polymers. Reactive extrusion does not require solvents, is easy to move, knead, and mix high-viscosity reactants, and can set various reaction conditions.

[0073] Reactive extrusion can be carried out by a single-shaft extruder or a twin-shaft extruder, and a twin-shaft extruder can be preferably used. The twin-shaft extruder can control the residence time distribution in the extruder, has excellent kneading performance, thermal conductivity and polymer transfer ability, and is easy to combine the screw and barrel together.

[0074] The reactive extrusion is preferably performed at 150° C. to 220° C. If the extrusion temperature is low, modification of the polylactide polymer proceeds smoothly, whereas if the temperature is too high, the polylactide polymer and the epoxy-containing acrylate terpolymer may be modified.

[0075] In this regard, it is preferred that the extrusion temperature is 150°C or higher, 170°C or higher, or 180°C or higher, or 190°C or higher, and 220°C or lower, or 210°C or lower, or 200°C or lower.

[0076] Reactive extrusion temperature refers to the temperature at the reaction zone (barrel) of the extruder. The temperature of the raw material inlet and the die is about 20°C to 40°C lower than the temperature of the reaction zone.

[0077] Furthermore, it is preferred that during reactive extrusion, the screw speed of the extruder is 100 rpm or more, or 150 rpm or more, or 170 rpm or more and 300 rpm or less, or 250 rpm or less, or 200 rpm or less to allow for adequate mixing, prevent reactant modification, and prevent excessive branching.

[0078] Under the above conditions, the residence time in the reactive extrusion step may preferably be 1 minute or more, or 2 minutes or more, and 10 minutes or less, or 5 minutes or less.

[0079] The branched polylactide polymer in the form of pellets prepared by reactive extrusion may have an average number of long chain branches per molecule of 7 to 10, and may exhibit excellent melt strength and elasticity due to such branched properties.

[0080] (Step 3)

[0081] Next, the pellets are subjected to blown extrusion to produce blown films.

[0082] Blown extrusion can use a blown film extruder commonly used in polymer film production, and although a small single-screw extruder is used in the following examples, the present invention is not limited thereto.

[0083] Preferably, during blow extrusion, the barrel temperature is 200° C. to 230° C., and the barrel pressure is 10 bar to 50 bar. When the barrel temperature and pressure satisfy the above ranges, sufficient branching can be generated, so it is preferred in terms of melt elasticity. More preferably, the barrel temperature may be 200° C. or more, or 210° C. or more, and 230° C. or less, or 220° C. or less, and the barrel pressure may be 10 bar or more, or 15 bar or more, and 50 bar or less, or 30 bar or less.

[0084] The barrel pressure refers to the pressure of the entire barrel, and the barrel temperature refers to the temperature of the barrels except the first barrel connected to the raw material inlet. Since the first barrel is directly connected to the raw material hopper, it is preferred to maintain the temperature at 30°C to 100°C to prevent the raw material from melting.

[0085] Furthermore, in order to achieve sufficient branching, the screw rotation speed is preferably 10 rpm or more, or 15 rpm or more, and 50 rpm or less, or 30 rpm or less.

[0086] The branched polylactide membrane manufactured by the method has a weight average molecular weight of 200000 g / mol to 500000 g / mol measured by gel permeation chromatography using polystyrene standards, and a polydispersity index of 2.0 to 4.0, or 2.0 to 3.5. The method of measuring the weight average molecular weight and the polydispersity index by gel permeation chromatography will be described in detail in the following examples.

[0087] According to the above-mentioned manufacturing method, a polylactide blown film having high transparency, smooth surface and excellent appearance characteristics can be provided without additives such as plasticizers. In particular, the manufacturing method has significantly reduced manufacturing costs compared to the casting method, and has excellent process efficiency and process stability, and is therefore suitable for mass production. The polylactide blown film manufactured according to the manufacturing method can be used to replace existing non-degradable films, and has biodegradability, and is therefore environmentally friendly. The polylactide blown film can be suitable as a transparent film for packaging materials for foods such as meat, fish, vegetables, etc. and for toy packaging, etc.

[0088] In the following, preferred embodiments will be given to help understand the present invention, but these embodiments are only used as illustrations of the present invention. For ordinary technicians in the field, it is obvious that various changes and modifications can be made within the scope and technical concept of the present invention, and such changes and modifications fall within the scope of the attached claims.

[0089] [Example]

[0090] Preparation Example 1

[0091] In the reactor, 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzene sulfonate (SDBS) were added, and the temperature was raised to 70°C while stirring. 0.2 parts by weight of potassium persulfate (KPS) was added and stirred for 20 minutes, and then a mixture of 45 parts by weight of methyl methacrylate, 40 parts by weight of glycidyl methacrylate, 15 parts by weight of butyl methacrylate and 0.7 parts by weight of 1-octanethiol was continuously added to the reactor over 4 hours, and after the addition was completed, it was cooled to 25°C while stirring for 30 minutes to prepare an emulsion polymerized latex. The prepared emulsion polymerized latex was solidified with an aqueous solution of calcium acetate, heat-treated to 90°C, and then dehydrated and dried at 60°C for 16 hours to prepare an epoxy-containing acrylate terpolymer.

[0092] Preparation Example 2

[0093] In the reactor, 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzene sulfonate (SDBS) were added, and the temperature was raised to 70°C while stirring. 0.2 parts by weight of potassium persulfate (KPS) was added and stirred for 20 minutes, and then a mixture of 45 parts by weight of methyl methacrylate, 45 parts by weight of glycidyl methacrylate, 10 parts by weight of 2-ethylhexyl acrylate and 0.7 parts by weight of 1-octanethiol was continuously added to the reactor over 4 hours, and after the addition was completed, it was cooled to 25°C while stirring for 30 minutes to prepare an emulsion polymerized latex. The prepared emulsion polymerized latex was solidified with an aqueous solution of calcium acetate, heat-treated to 90°C, and then dehydrated and dried at 60°C for 16 hours to prepare an epoxy-containing acrylate terpolymer.

[0094] Preparation Example 3

[0095] In the reactor, 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzene sulfonate (SDBS) were added, and the temperature was raised to 70°C while stirring. 0.2 parts by weight of potassium persulfate (KPS) was added and stirred for 20 minutes, and then a mixture of 65 parts by weight of methyl methacrylate, 20 parts by weight of glycidyl methacrylate, 15 parts by weight of butyl methacrylate and 0.7 parts by weight of 1-octanethiol was continuously added to the reactor over 4 hours, and after the addition was completed, it was cooled to 25°C while stirring for 30 minutes to prepare an emulsion polymerized latex. The prepared emulsion polymerized latex was solidified with an aqueous solution of calcium acetate, heat-treated to 90°C, and then dehydrated and dried at 60°C for 16 hours to prepare an epoxy-containing acrylate terpolymer.

[0096] Example 1

[0097] The polylactide polymer (4032D, Natureworks) was dried at 80° C. for 24 hours. The “polylactide polymer” in the following Examples and Comparative Examples is the polylactide polymer prepared in this way.

[0098] To 97.5 parts by weight of the prepared polylactide polymer, 0.5 parts by weight of the epoxy-containing acrylate terpolymer prepared in Preparation Example 1, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc were mixed to prepare a mixture.

[0099] The mixture was extruded using a twin-screw extruder (Bautek, BA-19) under the conditions of the following Table 1 to prepare pellets.

[0100] [Table 1]

[0101]

[0102] Next, the prepared pellets were extruded using a blown film extruder (Collin Lab & Pilot Solutions, Blown Film Line E Entrance) under the conditions of the following Table 2 to produce a polylactide blown film.

[0103] [Table 2]

[0104]

[0105] Example 2

[0106] By the same method as Example 1, pellets were prepared using a mixture including 97.25 parts by weight of a polylactide polymer, 0.75 parts by weight of the epoxy-containing acrylate terpolymer prepared in Preparation Example 1, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0107] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 3 to produce a polylactide blown film.

[0108] [Table 3]

[0109]

[0110] Example 3

[0111] By the same method as Example 1, pellets were prepared using a mixture including 97.9 parts by weight of a polylactide polymer, 0.1 parts by weight of the epoxy-containing acrylate terpolymer prepared in Preparation Example 2, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0112] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 4 to produce a polylactide blown film.

[0113] [Table 4]

[0114]

[0115] Example 4

[0116] By the same method as Example 1, pellets were prepared using a mixture including 97.1 parts by weight of a polylactide polymer, 0.9 parts by weight of the epoxy-containing acrylate terpolymer prepared in Preparation Example 2, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0117] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 5 to produce a polylactide blown film.

[0118] [Table 5]

[0119]

[0120] Comparative Example 1

[0121] By the same method as Example 1, pellets were prepared using a mixture including 98.0 parts by weight of a polylactide polymer, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0122] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 6 to produce a polylactide blown film.

[0123] [Table 6]

[0124]

[0125] Comparative Example 2

[0126] By the same method as Example 1, pellets were prepared using a mixture including 97.0 parts by weight of a polylactide polymer, 1.0 parts by weight of the epoxy-containing acrylate terpolymer prepared in Preparation Example 1, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0127] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 7 to produce a polylactide blown film.

[0128] [Table 7]

[0129]

[0130] Comparative Example 3

[0131] In the same manner as in Example 1, a mixture containing 97.5 parts by weight of a polylactide polymer, 0.5 parts by weight of a chain extender Joncryl-ADR manufactured by BASF A mixture of 0.5 parts by weight of oleamide and 1.5 parts by weight of talc was used to prepare pellets.

[0132] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 8 to produce a polylactide blown film.

[0133] [Table 8]

[0134]

[0135] Comparative Example 4

[0136] By the same method as Example 1, pellets were prepared using a mixture including 97.5 parts by weight of a polylactide polymer, 0.5 parts by weight of the epoxy-containing acrylate terpolymer prepared in Preparation Example 3, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0137] Next, the prepared pellets were extruded using a blown film extruder under the conditions of the following Table 9 to produce a polylactide blown film.

[0138] [Table 9]

[0139]

[0140] Experimental example

[0141] (1) GPC (gel permeation chromatography) analysis of pellets

[0142] The number average molecular weight (Mn), weight average molecular weight (Mw), peak top molecular weight (Mp), Z average molecular weight (Mz) and polydispersity index (PDI) of each pellet prepared in Examples and Comparative Examples were measured using a gel permeation chromatograph (GPC, Tosoh ECO SEC Elite) equipped with a differential refractive index detector (RI). The results are shown in Tables 10 and 10 below. Figure 1 middle.

[0143] The peak top properties were confirmed by obtaining a differential molecular weight distribution curve, where the horizontal axis is the logarithmic molecular weight [log(M)] and the vertical axis is the differential of the concentration fraction w with respect to the logarithmic molecular weight, dw / dlog(M).

[0144] GPC measurement conditions are as follows.

[0145] Column: Two PLgelOlexis (Polymer Laboratories) columns

[0146] Solvent: Tetrahydrofuran (THF)

[0147] Flow rate: 1.0ml / min

[0148] Column temperature: 40°C

[0149] Sample: 1.5mg / 1.0mlTHF

[0150] Standard material: polystyrene (calibrated with cubic function, using 10 types with molecular weights of 580 / 3320 / 9310 / 29460 / 75050 / 128900 / 298600 / 739500 / 2327000 / 6545000)

[0151] [Table 10]

[0152]

[0153] With reference to Table 7, it can be confirmed that, unlike the pellets of Comparative Example 1 in which no branching agent was used, branching occurred in the pellets of Examples 1, 2 and Comparative Example 2 in which a branching agent was used.

[0154] (2) GPC (gel permeation chromatography) analysis of blown film

[0155] The blown films produced in the examples and comparative examples were subjected to GPC analysis in the same manner as in (1). The results are shown in Tables 11 and 11. Figure 2 shown.

[0156] [Table 11]

[0157]

[0158] (3) Measurement of thickness and haze of blown film

[0159] The thickness of the blown film was measured at 3 different points using a Mitutoyo thickness gauge, and the average value was obtained and determined as the thickness of the blown film.

[0160] According to ASTM D1003, using C / 2 as the light source, the haze of the blown film was measured with a colorimeter. The thickness of the samples was in the range of 70 μm to 80 μm (see Table 9 below), and the thickness of each sample was measured 10 times to take the average value.

[0161] The measurement results of thickness and haze are shown in Table 12 below.

[0162] [Table 12]

[0163] Blown Film Thickness(mm) Haze(%) Comparative Example 1 0.077 19.07 Example 1 0.080 21.03 Example 2 0.075 15.67 Comparative Example 2 0.079 32.84 Comparative Example 3 0.071 37.18

[0164] (4) Evaluation of bubble stability and blown film appearance during blown film production.

[0165] The bubble stability of each of the blown films of the Production Examples and Comparative Examples, and the appearance (smoothness) of the produced blown films were visually evaluated. Figure 3 An image of a film bubble when a blown film is produced, and the surface of the produced film are shown.

[0166] The bubble stability, i.e., the degree of maintaining the shape without tearing and the smoothness of the film surface when manufacturing the blown film were also excellent in Examples 1, 2 and Comparative Example 3. Meanwhile, in Comparative Example 2, in which the amount of the branching agent used in Preparation Example 1 was more than 1 part by weight based on 100 parts by weight of polylactide, the bubble was continuously torn and did not maintain the shape, and therefore, the bubble stability was the worst and the surface of the manufactured film was also very rough.

[0167] Taking these results and the results of molecular weight measurement of the blown film into consideration, it is judged that in Examples 1, 2 and Comparative Example 3 using a branching agent, a sufficient branching structure is formed and elasticity is increased, thereby showing excellent bubble stability, and the manufactured film has excellent appearance characteristics. At the same time, it is judged that in Comparative Example 2, due to excessive branching, a gel is formed during the extrusion process of the blown film, and thus the bubble cannot be maintained.

[0168] Meanwhile, comparing the blown films of Examples 1 and 2 with the blown film of Comparative Example 3, the haze values ​​in Examples 1 and 2 are significantly lower than that in Comparative Example 3, and therefore, the transparency in Examples 1 and 2 is very excellent.

[0169] According to the above experimental results, it can be confirmed that the polylactide blown film produced by the present invention exhibits processing properties similar to those of the polylactide blown film using the existing branching agent, and also has significantly excellent haze characteristics.

Claims

1. A method for producing a polylactide blown film, the method comprising the following steps: Step 1: preparing a mixture comprising a polylactide polymer and an epoxy-containing acrylate terpolymer; Step 2: subjecting the mixture to reactive extrusion to produce a branched polylactide polymer in the form of pellets; and Step 3: Blowing and extruding the pellets to produce a blown film, wherein the epoxy-containing acrylate terpolymer comprises 30 wt % to 50 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 wt % to 60 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer, and the first alkyl (meth)acrylate monomer and the second alkyl (meth)acrylate monomer are different from each other, and The mixture of step 1 includes the epoxy-containing acrylate terpolymer in an amount of 0.1 parts by weight or more and less than 1.0 parts by weight based on 100 parts by weight of the polylactide polymer.

2. The method for producing a polylactide blown film according to claim 1, wherein: The epoxy-containing acrylate terpolymer comprises 30 wt % to 45 wt % of a repeating unit derived from a first alkyl (meth)acrylate monomer, 30 wt % to 45 wt % of a repeating unit derived from a glycidyl (meth)acrylate monomer, and 10 wt % to 20 wt % of a repeating unit derived from a second alkyl (meth)acrylate monomer.

3. The method for producing a polylactide blown film according to claim 2, wherein: The epoxy-containing acrylate terpolymer has 30 to 80 epoxy groups per molecule.

4. The method for producing a polylactide blown film according to claim 2, wherein: The first alkyl (meth)acrylate and the second alkyl (meth)acrylate are each independently at least one selected from the group consisting of methyl (meth)acrylate, butyl acrylate, and 2-(ethylhexyl) acrylate.

5. The method for producing a polylactide blown film according to claim 1, wherein: The polylactide membrane has a weight average molecular weight of 200,000 g / mol to 500,000 g / mol when measured by gel permeation chromatography using a polystyrene standard.

6. The method for producing a polylactide blown film according to claim 1, wherein: The mixture of step 1 includes the epoxy-containing acrylate terpolymer in an amount of 0.5 to 0.75 parts by weight based on 100 parts by weight of the polylactide polymer.

7. The method for producing a polylactide blown film according to claim 1, wherein: The mixture of step 1 further comprises one or more selected from the group consisting of a slip agent and an anti-blocking agent.

8. The method for producing a polylactide blown film according to claim 1, wherein: The reactive extrusion of step 2 is performed at a temperature of 150°C to 220°C.

9. The method for producing a polylactide blown film according to claim 1 or 8, wherein: In the reactive extrusion of step 2, the screw speed of the extruder is 100 rpm to 300 rpm.

10. The method for producing a polylactide blown film according to claim 1, wherein: The blow extrusion of step 3 is performed at a temperature of 200° C. to 230° C.; and a pressure of 10 bar to 50 bar.

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