Method for manufacturing polylactide blown film

Abstract

The present invention relates to a manufacturing method capable of manufacturing a polylactide blow film. According to the present invention, it is possible to provide a polylactide blow film having high transparency and excellent surface characteristics without additives such as plasticizers, and it is possible to improve process stability.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0028617 filed on March 3, 2023 and Korean Patent Application No. 10 - 2024 - 0029918 filed on February 29, 2024, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a manufacturing method capable of providing a polylactic acid blow film having excellent transparency and surface properties without a plasticizer.

Background Art

[0003] A polylactic acid polymer (hereinafter referred to as "PLA") is an eco - friendly material having biodegradability, and many studies have been carried out recently. PLA is generally a linear molecule and shows the characteristics of a thermoplastic polymer unless deformed, and is usefully utilized as a material for various films, fibers and other molded products.

[0004] Films containing PLA, especially blow films, are known to be difficult to manufacture, and additives such as plasticizers must be added for production. However, plasticizers are often not preferable for films used in food - related applications and may be leached because they have poor compatibility with PLA. To avoid such problems, the solution casting method has been used. However, when manufacturing a PLA film by the solution casting method, only films for limited applications can be produced, and there is a demerit that the process cost is very high.

[0005] Therefore, there is a need for a new manufacturing method capable of manufacturing a PLA blow film with excellent physical properties without a plasticizer.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention aims to provide a method for manufacturing a polylactide blown film that can provide a polylactide blown film with high transparency and excellent surface properties, and that can enhance process safety. [Means for solving the problem]

[0007] Therefore, according to one embodiment of the present invention, a method for producing a polylactide blown film comprises the steps of: preparing a mixture containing a polylactide polymer and an epoxy group-containing acrylate ternary copolymer (step 1); reacting and extruding the mixture to produce a pellet-shaped branched polylactide polymer (step 2); and blow extruding the pellet to produce a blown film (step 3), wherein the epoxy group-containing acrylate ternary copolymer comprises 30% to 50% by weight of repeating units derived from a primary alkyl(meth)acrylate monomer. A method for producing a polylactide blown film is provided, comprising 30% to 60% by weight of repeating units derived from a glycidyl(meth)acrylate monomer and 10% to 20% by weight of repeating units derived from a second alkyl(meth)acrylate monomer, wherein the first alkyl(meth)acrylate monomer and the second alkyl(meth)acrylate monomer are different from each other, and the mixture in step 1 contains 0.1 parts by weight or more and less than 1.0 part by weight of epoxy acrylate ternary copolymer per 100 parts by weight of polylactide polymer.

[0008] The epoxy group-containing acrylate ternary copolymer may contain 30% to 45% by weight of repeating units derived from a primary alkyl(meth)acrylate monomer, 30% to 45% by weight of repeating units derived from a glycidyl(meth)acrylate monomer, and 10% to 20% by weight of repeating units derived from a secondary alkyl(meth)acrylate monomer.

[0009] The epoxy group-containing acrylate ternary copolymer may have 30 to 80 epoxy groups per molecule.

[0010] The first alkyl(meth)acrylate and the second alkyl(meth)acrylate may each be independently selected from the group consisting of methyl(meth)acrylate, butyl acrylate, and 2-(ethylhexyl)acrylate.

[0011] The polylactide film may have a weight-average molecular weight of 200,000 g / mol to 500,000 g / mol, as measured by gel permeation chromatography using a polystyrene standard.

[0012] The mixture in step 1 may contain 0.5 to 0.75 parts by weight of epoxy acrylate terpolymer per 100 parts by weight of polylactide polymer.

[0013] The mixture in step 1 may further include one or more selected from the group consisting of slip agents and anti-blocking agents.

[0014] The reaction extrusion in step 2 may be carried out at a temperature of 150°C to 220°C.

[0015] During the reaction extrusion in step 2, the screw rotation speed of the extruder may be 100 rpm to 300 rpm.

[0016] The blow extrusion in step 3 may be carried out at a temperature of 200°C to 230°C and a pressure of 10 bar to 50 bar. [Effects of the Invention]

[0017] According to the present invention, a polylactide blown film with high transparency and excellent surface properties can be provided without additives such as plasticizers, and process stability can be improved without increasing costs. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 shows the measurement results of the molecular weights of the pellets produced in each of the examples and comparative examples. [Figure 2] Figure 2 shows the measurement results of the molecular weights of the blown films produced in each of the examples and comparative examples. [Figure 3] Figure 3 shows the appearance of the blown films produced in each of the examples and comparative examples and the state of the bubbles during the extrusion of the blown films.

Mode for Carrying Out the Invention

[0019] The terms used in this specification are merely used for the purpose of explaining exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates a different meaning. In this specification, terms such as "comprising," "including," or "having" are intended to specify the presence of the implemented features, steps, components, or combinations thereof, and it should be understood that they do not preclude in advance the presence or addition possibility of one or more other features, steps, components, or combinations thereof.

[0020] Since the present invention can be subjected to various modifications and can have various forms, specific embodiments are exemplified and described in detail below. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0021] In this specification, the term "long chain branching (LCB)" means a long chain in which the number of carbon atoms in the branch is similar to that of the backbone chain to such an extent that it is indistinguishable from the backbone chain.

[0022] In this specification, the terms "derived unit and derived repeating unit" may each mean a component, unit body, structure, or the substance itself resulting from a certain substance.

[0023] The present invention will be described in detail below.

[0024] The present invention relates to a method for producing a polylactide blow film having high transparency and excellent surface properties without a plasticizer.

[0025] Specifically, according to an embodiment of the present invention, a step of preparing a mixture containing a polylactide polymer and an epoxy group-containing acrylate terpolymer (step 1); a step of producing a branched polylactide polymer in the form of pellets by reacting and extruding the mixture (step 2); a step of producing a blow film by blow-extruding the pellets (step 3), which is a method for producing a polylactide blow film, the epoxy group-containing acrylate terpolymer contains 30% to 50% by weight of repeating units derived from a first alkyl (meth)acrylate monomer, 30% to 60% by weight of repeating units derived from a glycidyl (meth)acrylate monomer, and 10% to 20% by weight of repeating units 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; a method for producing a polylactide blow film is provided, wherein the mixture in step 1 contains 0.1 part by weight or more and less than 1.0 part by weight of an epoxy acrylate terpolymer with respect to 100 parts by weight of the polylactide polymer.

[0026] Conventionally, a plasticizer has been required to produce a polylactide blow film. However, the plasticizer is often not suitable for films used in food-related applications due to its harmful effects on the human body, etc., and there are problems such as leaching because it has poor compatibility with PLA. Also, when producing a PLA film by the solution casting method, only films for limited applications can be produced, and there is a demerit that the process cost is very high.

[0027] Therefore, the present inventors researched a method for producing PLA blown films with excellent physical properties without additives such as plasticizers, and as a result found that PLA blown films with excellent physical properties can be produced by reaction extrusion and blow extrusion of a mixture containing PLA and an epoxy group-containing acrylate ternary copolymer, thus completing the present invention.

[0028] Specifically, the epoxy group-containing acrylate ternary copolymer acts as a branching agent for PLA. During the reaction extrusion process of the mixture, long-chain branching (LCB) is introduced into the PLA, modifying the linear structure of the PLA polymer and forming a sufficiently branched structure. The PLA polymer with this branched structure exhibits increased elasticity, allowing for stable bubble formation during blow extrusion. Therefore, a blow film with a smooth surface and uniform thickness can be produced. Furthermore, when the epoxy group-containing acrylate ternary copolymer is used as a branching agent, the produced blow film exhibits high transparency and excellent appearance characteristics.

[0029] The method for manufacturing the polylactide blown film will be described in more detail below, step by step.

[0030] (Step 1) In a manufacturing method according to one embodiment of the present invention, first, a mixture containing a polylactide polymer and an epoxy group-containing acrylate-based terpolymer is prepared.

[0031] The polylactide polymer is a thermoplastic polyester obtained by polymerizing lactide or lactic acid, and includes a polymer having repeating units of the -[OC(O)CH(CH3)]- structure.

[0032] Furthermore, 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.

[0033] Furthermore, the polylactide polymer may have repeating units derived from alkylene oxide or from other monomers copolymerizable with lactide, in which case the repeating units derived from alkylene oxide or from other monomers copolymerizable with lactide may be present in blocks and / or random arrangements. Also, if the polylactide polymer contains repeating units derived from alkylene oxide or from other monomers copolymerizable with lactide, it may contain them in an amount of 10% by weight or less, specifically 5% by weight or less.

[0034] Furthermore, the polylactide polymer may have a relative weight-average molecular weight measured by gel permeation chromatography using a polystyrene standard of 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 its molecular weight distribution may be 1.2 or more, or 1.5 or more, and 4 or less, or 3 or less.

[0035] The aforementioned polylactide polymer can be purchased or manufactured from those commonly known in the industry. If manufactured, it may be produced using lactide or lactic acid as monomers by conventional polymerization methods in the industry.

[0036] In step 2, described later, the epoxy group-containing acrylate ternary copolymer reacts with the polylactide polymer to introduce long-chain branching (LCB). This forms a branched structure in the polylactide polymer, improving elasticity, enabling stable bubble formation during blow extrusion, and providing a high-quality polylactide blow film.

[0037] The epoxy group-containing acrylate ternary copolymer comprises 30% to 50% by weight of repeating units derived from a first alkyl(meth)acrylate monomer, 30% to 60% by weight of repeating units derived from a glycidyl(meth)acrylate monomer, and 10% to 20% by weight of repeating units derived from a second alkyl(meth)acrylate monomer, characterized in that the first alkyl(meth)acrylate monomer and the second alkyl(meth)acrylate monomer are different from each other.

[0038] In one embodiment, the epoxy group-containing acrylate ternary copolymer may contain 30% to 45% by weight of repeating units derived from a primary alkyl(meth)acrylate monomer, 30% to 45% by weight of repeating units derived from a glycidyl(meth)acrylate monomer, and 10% to 20% by weight of repeating units derived from a secondary alkyl(meth)acrylate monomer.

[0039] Alternatively, the epoxy group-containing acrylate ternary copolymer may contain 40% to 45% by weight of repeating units derived from a primary alkyl(meth)acrylate monomer, 40% to 45% by weight of repeating units derived from a glycidyl(meth)acrylate monomer, and 10% to 20% by weight of repeating units derived from a secondary alkyl(meth)acrylate monomer.

[0040] In the foregoing, the first alkyl(meth)acrylate monomer and the second alkyl(meth)acrylate monomer are independently at least one selected from the group consisting of methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate, and 2-ethylhexyl acrylate, and may be different from each other. Specifically, the first alkyl(meth)acrylate monomer and the second alkyl(meth)acrylate monomer are independently methyl methacrylate, methyl acrylate, butyl methacrylate, or butyl acrylate, and may be different from each other. More specifically, the first alkyl(meth)acrylate monomer may be methyl methacrylate, and the second alkyl(meth)acrylate monomer may be butyl methacrylate.

[0041] Furthermore, the glycidyl(meth)acrylate monomer may be a glycidyl methacrylate monomer or a glycidyl acrylate monomer.

[0042] The epoxy group-containing acrylate ternary copolymer can be produced by polymerizing a primary alkyl(meth)acrylate monomer, a glycidyl(meth)acrylate monomer, and a secondary alkyl(meth)acrylate monomer different from the primary alkyl(meth)acrylate monomer in a solvent in the presence of an emulsifier.

[0043] Specifically, the epoxy group-containing acrylate ternary copolymer is produced by polymerizing 30% to 50% by weight of a primary alkyl(meth)acrylate monomer, 30% to 60% by weight of a glycidyl(meth)acrylate monomer, and 10% to 20% by weight of a secondary alkyl(meth)acrylate monomer different from the primary alkyl(meth)acrylate monomer in a solvent and in the presence of an emulsifier, wherein the polymerization may be carried out at 70°C to 80°C for 3 to 10 hours.

[0044] Furthermore, the polymerization may be carried out in an aqueous solvent, in which case the solvent is distilled water.

[0045] The emulsifier may be one or more selected from the group consisting of anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers, and examples include one or more selected from the group consisting of alkylaryl sulfonates, alkali methyl alkyl sulfates, fatty acid soaps, alkali oleate salts, alkali rosinate salts, alkali laurylate salts, sodium diethylhexyl phosphate, phosphonated polyoxyethylene alcohol, and phosphonated polyoxyethylene phenol. Furthermore, the emulsifier may be used in an amount of 5 parts by weight or less, specifically 3.0 parts by weight or less, or 0.5 to 2.5 parts by weight, based on the total monomer content of 100 parts by weight.

[0046] Furthermore, the polymerization may be carried out using a polymerization disclosing agent as needed. In this case, the disclosing agent may be an inorganic peroxide or an organic peroxide. For example, water-soluble polymerization disclosing agents such as potassium potassium persulfate, sodium potassium persulfate, and ammonium potassium persulfate, and oil-soluble polymerization disclosing agents such as cumene hydroperoxide and benzoyl peroxide can be used.

[0047] Furthermore, an activator can be used in conjunction with the polymerization disclosure agent to promote the initiation of the peroxide reaction. As such an activator, one or more selected from the group consisting of sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate, and dextrose can be used.

[0048] Furthermore, the polymerization disclosure agent may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the total monomer content, and more specifically, in an amount of 0.1 to 5 parts by weight.

[0049] As another example, a chain transfer agent (or chain transfer agent) may be used to increase the efficiency of the polymerization reaction. The chain transfer agent may be a linear or branched alkylthiol compound having 5 to 20 carbon atoms. Examples include one or more selected from hexanethiol, cyclohexanethiol, adamantanethiol, heptanethiol, octanthiol, nonanthiol, decanethiol, undecanethiol, todecanethiol, hexadecanethiol, and octadecanethiol.

[0050] Furthermore, the epoxy group-containing acrylate ternary copolymer may be manufactured by further performing one or more steps selected from washing, dehydration, and drying after polymerization, in which case washing, dehydration, and drying may be carried out by methods commonly known in the art. On the other hand, the mixture contains 0.1 parts by weight or more and less than 1.0 part by weight of epoxy acrylate terpolymer per 100 parts by weight of polylactide polymer. Specifically, the mixture may contain 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, per 100 parts by weight of polylactide polymer.

[0051] If the mixture contains less than 0.1 parts by weight of epoxy acrylate terpolymer per 100 parts by weight of polylactide polymer, sufficient branching may not occur during the reaction extrusion process, making it difficult to form bubbles during subsequent blow extrusion. Conversely, if the content of epoxy acrylate terpolymer is 1.0 part by weight or more per 100 parts by weight of polylactide polymer, excessive branching may lead to gel formation during blow film extrusion, resulting in poor bubble maintenance and hindering smooth blow extrusion.

[0052] The mixture may further contain, along with the aforementioned polylactide polymer and epoxy group-containing acrylate ternary copolymer, one or more additives selectively selected from the group consisting of slip agents and blocking inhibitors.

[0053] The slip agent can be used to reduce the coefficient of friction between the films. As the slip agent, for example, one or more selected from the group consisting of oleamide, erucamide, stearamide, behenamide, oleyl palmitamide, stearyl erucamide, ethylenebis-oleamide, and N,N'-ethylenebis(stearamide) (EBS) can be used. When the slip agent is used, its content may be 5% by weight or less, 3% by weight or less, or 1% by weight or less, and 0.1% by weight or more, 0.3% by weight or more, or 0.5% by weight or more, based on the total weight of the mixture.

[0054] The antiblocking agent can be used to prevent the manufactured films from sticking to each other and to improve processability. For example, one or more antiblocking agents selected from the group consisting of natural silica, synthetic silica, talc, and calcium carbonate can be used. The antiblocking agent may, as an example, be included in an amount of 10% by weight or less, 8% by weight or less, 5% by weight or less, or 3% by weight or less, and 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, or 1.5% by weight or more, based on the total weight of the mixture.

[0055] In one embodiment, the mixture may contain oleamide as a slip agent and talc as an anti-blocking agent, in which case the oleamide may be present in an amount of 0.1% to 5% by weight, or 0.5% to 1.0% by weight, and the talc in an amount of 0.1% to 10% by weight, or 1.5% to 3% by weight, relative to the total weight of the mixture.

[0056] The method for producing the aforementioned mixture is not particularly limited, and the mixture can be produced by dry compounding the aforementioned raw materials without a solvent. While equipment such as a mixing machine or extruder can be used for mixing, the method is not limited to these.

[0057] (Step 2) Next, the mixture is reacted and extruded to produce pelletized, branched polylactide polymers.

[0058] Reaction extrusion is a chemical reaction process that uses an extruder as a reactor to induce the modification of a polymer, and in this invention, it is performed for the branching of polylactide polymers. Reaction extrusion has the advantages of not requiring a solvent, facilitating the movement, kneading, and mixing of highly viscous reactants, and allowing for diverse setting of reaction conditions.

[0059] The reaction extrusion described above can be carried out through a single-screw extruder or a twin-screw extruder, and preferably a twin-screw extruder can be used. Twin-screw extruders have the advantages of allowing adjustment of the residence time distribution within the extruder, having excellent kneading performance, thermal conductivity and polymer transfer capacity, and being easy to combine with a screw barrel.

[0060] The reaction extrusion is preferably carried out at a temperature of 150°C to 220°C. If the extrusion temperature is too low, the modification of the polylactide polymer may not occur smoothly, and if the temperature is too high, the polylactide polymer and the epoxy group-containing acrylate terpolymer may be deformed.

[0061] From this perspective, the extrusion temperature is preferably 150°C or higher, 170°C or higher, 180°C or higher, or 190°C or higher, and 220°C or lower, 210°C or lower, or 200°C or lower.

[0062] The aforementioned reaction extrusion temperature refers to the temperature in the reaction region (barrel) of the extruder; the temperature in the raw material input area and the die area may be about 20°C to 40°C lower than the reaction region.

[0063] Furthermore, during the reaction extrusion, it is preferable that the screw rotation speed of the extruder be 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, as this ensures sufficient mixing and prevents denaturation of the reactants, and prevents excessive branching.

[0064] The preferred residence time in the reaction extrusion step is 1 minute or more, or 2 minutes or more, and may be 10 minutes or less, or 5 minutes or less, under the conditions described above.

[0065] The pelletized branched polylactide polymer produced by the reaction extrusion described above may have an average of 7 to 10 long-chain branches per molecule, and such branching characteristics allow it to exhibit excellent melt strength and elastic properties.

[0066] (Step 3) Next, the pellets are blow-extruded to produce a blown film.

[0067] The blow extrusion described above can be carried out using a blow film extruder, which is generally used in the production of polymer films. In the embodiments described later, a small single-screw extruder was used, but the present invention is not limited thereto.

[0068] The barrel temperature during blow extrusion is preferably 200°C to 230°C, and the pressure is preferably 10 bar to 50 bar. When the barrel temperature and pressure satisfy the above range, sufficient branching occurs, which is preferable from the viewpoint of melt elasticity. More preferably, the barrel temperature is 200°C or higher, or 210°C or higher, and 230°C or lower, or 220°C or lower, and the pressure is 10 bar or higher, or 15 bar or higher, and 50 bar or lower, or 30 bar or lower.

[0069] The barrel pressure is the pressure throughout the entire barrel, and the barrel temperature is the temperature of the remaining barrels, excluding the first barrel connected to the raw material input section. The first barrel is directly connected to the raw material hopper, and it is preferable to maintain a temperature of 30°C to 100°C to prevent the raw materials from fusing together.

[0070] Furthermore, for 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.

[0071] The branched polylactide film produced by the above method may have a weight-average molecular weight of 200,000 g / mol to 500,000 g / mol, as measured by gel permeation chromatography using a polystyrene standard, and a polydispersity index of 2.0 to 4.0, or 2.0 to 3.5. The method for measuring the weight-average molecular weight and polydispersity index by gel permeation chromatography will be specifically described in the examples below.

[0072] According to the manufacturing method described above, a polylactide blown film with high transparency, a smooth surface, and excellent appearance characteristics can be provided without the use of additives such as plasticizers. In particular, the manufacturing method has significantly lower manufacturing costs compared to the casting method, is superior in process efficiency and process stability, and is suitable for mass production. The polylactide blown film produced by the manufacturing method can be used as a substitute for conventional non-degradable films and has the advantage of being environmentally friendly because it is biodegradable. The polylactide blown film can be appropriately used as a transparent film for packaging food such as meat, fish, and vegetables, as well as for toy packaging.

[0073] The following examples illustrate the present invention, but these examples are merely illustrative, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such changes and modifications naturally fall within the scope of the appended claims.

[0074] [Examples] Manufacturing Example 1 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzenesulfonate (SDBS) were added to a reactor and heated to 70°C while stirring. 0.2 parts by weight of potassium persulfate (KPS) was added and stirred for 20 minutes. 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-octanthiol was continuously added to the reactor over 4 hours. After the addition was complete, the mixture was cooled to 25°C while stirring for 30 minutes to produce an emulsion polymerization latex. The produced emulsion polymerization latex was coagulated with an aqueous calcium acetate solution, heat-treated to 90°C, dehydrated, and dried at 60°C for 16 hours to produce an epoxy group-containing acrylate terpolymer.

[0075] Manufacturing Example 2 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzenesulfonate (SDBS) were added to a reactor and heated to 70°C while stirring. 0.2 parts by weight of potassium persulfate (KPS) was added and stirred for 20 minutes. 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-octanthiol was continuously added to the reactor over 4 hours. After the addition was complete, the mixture was cooled to 25°C while stirring for 30 minutes to produce an emulsion polymerization latex. The produced emulsion polymerization latex was coagulated with an aqueous calcium acetate solution, heat-treated to 90°C, dehydrated, and dried at 60°C for 16 hours to produce an epoxy group-containing acrylate terpolymer.

[0076] Manufacturing Example 3 200 parts by weight of distilled water and 0.5 parts by weight of sodium dodecylbenzenesulfonate (SDBS) were added to a reactor and heated to 70°C while stirring. 0.2 parts by weight of potassium persulfate (KPS) was added and stirred for 20 minutes. 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-octanthiol was continuously added to the reactor over 4 hours. After the addition was complete, the mixture was cooled to 25°C while stirring for 30 minutes to produce an emulsion polymerization latex. The produced emulsion polymerization latex was coagulated with an aqueous calcium acetate solution, heat-treated to 90°C, dehydrated, and dried at 60°C for 16 hours to produce an epoxy group-containing acrylate terpolymer.

[0077] Example 1 A polylactide polymer (4032D, manufactured by Natureworks) was prepared by drying at 80°C for 24 hours. In the following examples and comparative examples, "polylactide polymer" refers to the polylactide polymer prepared in this manner.

[0078] A mixture was prepared by mixing 97.5 parts by weight of the prepared polylactide polymer with 0.5 parts by weight of the epoxy group-containing acrylate ternary copolymer produced in Production Example 1, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0079] The mixture was extruded using a twin-screw extruder (Bautek BA-19) under the conditions shown in Table 1 below to produce pellets. [Table 1]

[0080] Subsequently, the manufactured pellets were extruded using a blow film extruder (Collin Lab & Pilot Solutions, Blown Film Line E Entrance) under the conditions shown in Table 2 below to produce polylactide blow film. [Table 2]

[0081] Example 2 Pellets were prepared in the same manner as in Example 1 using a mixture containing 97.25 parts by weight of polylactide polymer, 0.75 parts by weight of epoxy group-containing acrylate ternary copolymer produced in Production Example 1, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0082] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 3 below to produce polylactide blow film. [Table 3]

[0083] Example 3 Pellets were prepared in the same manner as in Example 1 using a mixture containing 97.9 parts by weight of polylactide polymer, 0.1 parts by weight of epoxy group-containing acrylate ternary copolymer prepared in Production Example 2, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0084] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 4 below to produce polylactide blow film. [Table 4]

[0085] Example 4 Pellets were prepared in the same manner as in Example 1 using a mixture containing 97.1 parts by weight of polylactide polymer, 0.9 parts by weight of epoxy group-containing acrylate ternary copolymer prepared in Production Example 2, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0086] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 5 below to produce polylactide blow film. [Table 5]

[0087] Comparative Example 1 Pellets were prepared in the same manner as in Example 1 using a mixture containing 98.0 parts by weight of polylactide polymer, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0088] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 6 below to produce polylactide blow film. [Table 6]

[0089] Comparative Example 2 Pellets were prepared in the same manner as in Example 1 using a mixture containing 97.0 parts by weight of polylactide polymer, 1.0 part by weight of epoxy group-containing acrylate terpolymer prepared in Production Example 1, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0090] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 7 below to produce polylactide blow film. [Table 7]

[0091] Comparative Example 3 Pellets and polylactide blown films were produced in the same manner as in Example 1 using a mixture containing 97.5 parts by weight of polylactide polymer, 0.5 parts by weight of BASF's chain extender Joncryl-ADR 4468 (registered trademark), 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0092] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 8 below to produce polylactide blow film. [Table 8]

[0093] Comparative Example 4 Pellets were prepared in the same manner as in Example 1 using a mixture containing 97.5 parts by weight of polylactide polymer, 0.5 parts by weight of epoxy group-containing acrylate ternary copolymer produced in Production Example 3, 0.5 parts by weight of oleamide, and 1.5 parts by weight of talc.

[0094] Subsequently, the manufactured pellets were extruded using a blow film extruder under the conditions shown in Table 9 below to produce polylactide blow film. [Table 9]

[0095] Experimental example (1) Analysis of pellets using GPC (gel permeation chromatography) 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 the pellets prepared in each of the above examples and comparative examples were measured using gel permeation chromatography (GPC: Tosoh ECO SEC Elite) equipped with a differential refractive index detector (RI). The results are shown in Table 10 and Figure 1 below. The peak-top characteristics were confirmed by obtaining a fine powder molecular weight distribution curve where the horizontal axis is logarithmic molecular weight [log(M)] and the vertical axis is dw / dlog(M), which is the derivative of the concentration fraction w with respect to the logarithmic molecular weight.

[0096] The GPC measurement conditions are as follows: Columns: PLgel Olexis (Polymer Laboratories) columns, 2 pieces Solvent: Tetrahydrofuran (THF) Flow rate: 1.0ml / min Column temperature: 40℃ Sample: 1.5 mg / 1.0 ml THF Standard material: Polystyrene (corrected to a cubic function; 10 types were used with molecular weights of 580 / 3,320 / 9,310 / 29,460 / 75,050 / 128,900 / 298,600 / 739,500 / 2,327,000 / 6,545,000) [Table 10]

[0097] Referring to Table 7 above, it can be confirmed that branching occurred in the pellets of Examples 1 and 2, and Comparative Example 2, which used a branching agent, unlike the pellets of Comparative Example 1, which did not use a branching agent.

[0098] (2) Analysis of blow film by GPC (gel permeation chromatography) GPC analysis was performed on the blown films produced in each of the above examples and comparative examples using the same method as described in (1) above, and the results are shown in Table 11 and Figure 2 below. [Table 11]

[0099] (3) Measurement of the thickness and haze of the blow film Using a Mitutoyo thickness gauge, the thickness of the blown film was measured at three different points, and the average value was calculated to determine the thickness of the blown film.

[0100] The haze of the blown film was measured using a colorimeter according to the ASTM D1003 standard, with a C / 2 light source. The thickness of each specimen was in the range of 70-80 μm (see Table 9 below), and each specimen was measured 10 times, with the average value taken.

[0101] The thickness and haze measurement results are shown in Table 12 below. [Table 12]

[0102] (4) Bubble stability and appearance evaluation of blown film during manufacturing The stability of the bubbles during blow film production and the appearance (smoothness) of the produced blow film were visually evaluated for each of the above embodiments and comparative examples. Figure 3 shows the state of the bubbles during blow film production and a photograph of the surface of the produced film.

[0103] In the production of blown film, the bubble stability—that is, the degree to which the bubbles maintain their shape without bursting—and the smoothness of the film surface were comparable between Examples 1 and 2 and Comparative Example 3, indicating the best performance. In contrast, in Comparative Example 2, where the branching agent used in Production Example 1 was 1 part by weight or more per 100 parts by weight of polylactide, the bubbles continuously burst and could not maintain their shape, resulting in the worst bubble stability, and the surface of the produced film was also rough.

[0104] Combining these results with the molecular weight measurement results of the blown film, it is judged that Examples 1 and 2 and Comparative Example 3, which used the branching agent, formed a sufficient branched structure and increased elasticity, resulting in excellent bubble stability, and therefore the manufactured film had excellent appearance characteristics. In contrast, in the case of Comparative Example 2, it is judged that excessive branching led to gel formation during blown film extrusion, and the bubbles were not well maintained.

[0105] On the other hand, when comparing the blow films of Examples 1 and 2 with those of Comparative Example 3, it can be confirmed that the haze values ​​of Examples 1 and 2 are significantly lower than those of Comparative Example 3, indicating superior transparency.

[0106] From the experimental results described above, it can be confirmed that the polylactide blown film produced by the present invention exhibits a similar level of processability to existing polylactide blown films using branching agents, while demonstrating significantly superior haze characteristics.

Claims

1. Step 1 involves preparing a mixture containing a polylactide polymer and an epoxy group-containing acrylate terpolymer, Step 2 involves reacting and extruding the mixture to produce a pellet-shaped branched polylactide polymer. A method for producing a polylactide blown film, comprising the step (step 3) of blow-extruding the pellets to produce a blown film, The epoxy group-containing acrylate ternary copolymer comprises 30% to 45% by weight of repeating units derived from a first alkyl(meth)acrylate monomer, 30% to 45% by weight of repeating units derived from a glycidyl(meth)acrylate monomer, and 10% to 20% by weight of repeating units derived from a second alkyl(meth)acrylate monomer, wherein the first alkyl(meth)acrylate monomer and the second alkyl(meth)acrylate monomer are distinct from each other. 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. The mixture of step 1 contains 0.1 parts by weight or more and less than 1.0 part by weight of epoxy group-containing acrylate terpolymer per 100 parts by weight of polylactide polymer. A method for manufacturing polylactide blown film.

2. The epoxy group-containing acrylate terpolymer has 30 to 80 epoxy groups per molecule. A method for producing a polylactide blown film according to claim 1.

3. The polylactide blown film has a weight-average molecular weight of 200,000 g / mol to 500,000 g / mol, as measured by gel permeation chromatography using a polystyrene standard. A method for producing a polylactide blown film according to claim 1.

4. The mixture of step 1 comprises 0.5 to 0.75 parts by weight of epoxy acrylate terpolymer per 100 parts by weight of polylactide polymer. A method for producing a polylactide blown film according to claim 1.

5. The mixture of step 1 further comprises one or more selected from the group consisting of slip agents and blocking inhibitors. A method for producing a polylactide blown film according to claim 1.

6. The reaction extrusion in step 2 is carried out at a temperature of 150°C to 220°C. A method for producing a polylactide blown film according to claim 1.

7. During the reaction extrusion in step 2, the screw rotation speed of the extruder is 100 rpm to 300 rpm. A method for producing a polylactide blown film according to claim 1 or claim 6.

8. The blow extrusion in step 3 is carried out at a temperature of 200°C to 230°C and a pressure of 10 bar to 50 bar. A method for producing a polylactide blown film according to claim 1.

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