PVDC (POLYVINYLIDENE CHLORIDE)-BASED COMPOSITE HAVING A CORE-SHELL STRUCTURE AND ITS PRODUCTION METHOD

Abstract

The present invention relates to a PVDC-based composite and a method for producing the same. The PVDC-based composite is characterized by comprising a core containing a PVDC (Polyvinylidene chloride) polymer and a shell surrounding the core and containing a wax, wherein the wax is in the form of nano-sized particles.

Description

[Technical Field]

[0001] The present invention relates to a PVDC composite having a core-shell structure, a method for producing the same, a resin composition containing the same, and a food packaging film. [Background technology]

[0002] In the food packaging industry, when packaging oxygen- or moisture-sensitive products, contact with oxygen and moisture must be prevented to prevent food deterioration, so most food packaging films have a barrier layer. PVDC (Polyvinylidene chloride) has excellent oxygen and moisture barrier properties. While barrier materials such as EVOH and nylon rapidly lose their oxygen barrier properties when the ambient humidity is high, PVDC maintains excellent barrier properties regardless of humidity, so it is used in food packaging films that require a water-based sterilization process, such as retort pouches, or are used in hot and humid climates.

[0003] Due to its structural characteristics, PVDC is very difficult to process thermally, such as by extrusion molding. The C-Cl bond energy is very low in the repeating structure of the polymer chain (CH2Cl2), so the HCl elimination reaction occurs easily. When HCl is eliminated, a double bond is formed at that position, forming an allyl chloride structure with Cl in the next repeating structure. This structure allows the HCl elimination reaction to occur more easily, accelerating the elimination reaction. As a result, a polyene with consecutive double bonds is formed, and the Diels-Alder reaction between polyenes occurs. a The 'lder' reaction ultimately results in the formation of black aromatic carbon, which adheres to the inside of the extruder and die, causing uneven film thickness or appears as black inclusions on the film, making film processing difficult.

[0004] Furthermore, the porous nature of PVDC particles can lead to uneven feeding due to reduced fluidity during the extrusion process, resulting in different extrudate volumes and resulting film thickness variations. More seriously, powder particle bridging can lead to feeding problems. This can accelerate the aforementioned PVDC decomposition reaction, as the PVDC melt that entered the extruder is unable to exit and remains there, exposing it to heat. This can lead to excessive accumulation of carbonized material inside the extruder, resulting in serious pollution. Furthermore, the generation and accumulation of large amounts of HCl gas can contaminate the work environment and pose a risk to worker safety. Furthermore, HCl gas is a heavy gas that sinks to the bottom and can cause explosions due to sparks from power supplies and machinery. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a PVDC-based composite having improved fluidity and a method for producing the same. Another object of the present invention is to provide a PVDC-based composite that can produce a film with a uniform thickness by preventing uneven supply of raw materials due to the high surface roughness of PVDC particles during the extrusion molding process for producing a PVDC film.

[0006] Another object of the present invention is to provide a PVDC-based composite that can suppress the acceleration of PVDC decomposition caused by uneven supply of PVDC raw materials during the production of PVDC films, and prevent the generation of HCl gas. [Means for solving the problem]

[0007] The present invention provides a PVDC-based composite comprising a core containing a PVDC (Polyvinylidene chloride)-based polymer and a shell surrounding the core and containing a wax, wherein the wax is in the form of nano-sized particles.

[0008] In one embodiment of the present invention, the particle size of the wax may be 30 to 280 nm. In one embodiment of the present invention, the wax may be one or more selected from the group consisting of petroleum / coal-derived waxes extracted from petroleum or coal, animal and vegetable waxes, amide-based synthetic waxes, olefin-based synthetic waxes, and modified waxes thereof.

[0009] In one embodiment of the present invention, the wax may be at least two types including an acrylic wax. In one embodiment of the present invention, the shell has a thickness of 30 nm to 10 μm or less.

[0010] In one embodiment of the present invention, the PVDC-based polymer may be at least one selected from the group consisting of homopolymers and copolymers containing vinylidene chloride (VDC).

[0011] In one embodiment of the present invention, the PVDC-based polymer may be a copolymer containing one or more comonomers selected from the group consisting of vinyl chloride (VC) and methyl acrylate (MA).

[0012] In one embodiment of the present invention, the PVDC-based polymer may contain 2 to 25% by weight of the comonomer. In one embodiment of the present invention, the core may be a spherical particle having a size of 150 to 350 μm.

[0013] In one embodiment of the present invention, the powder containing the plurality of PVDC-based composites may have an angle of repose of 28 or less. In one embodiment of the present invention, the PVDC-based composite is characterized by further satisfying the following relational formula 1:

[0014] [Equation 1] 0.8

[0015] In Relational Formula 1, A is the angle of repose of the powder containing the plurality of PVDC-based polymer particles that do not contain the shell layer, and B is the angle of repose of the powder containing the plurality of PVDC-based composites.

[0016] The present invention also provides a method for producing a PVDC-based composite, the method comprising the steps of: a) preparing a first mixture containing a PVDC (Polyvinylidene chloride)-based polymer; b) adding a wax to the first mixture to prepare a second mixture; and c) drying the second mixture, wherein the wax is in the form of nano-sized particles.

[0017] In one embodiment of the present invention, the wax may be at least two types including an acrylic wax. In one embodiment of the present invention, the step c) may be performed at a temperature higher than the glass transition temperature (Tg) of the acrylic wax. In one embodiment of the present invention, the drying temperature may be 80 to 140°C.

[0018] The present invention also provides a food packaging film comprising a PVDC-based composite according to one embodiment of the present invention. [Effects of the Invention]

[0019] The PVDC-based composite according to the present invention can maximize the fluidity of particles, thereby preventing uneven particle supply during the PVDC film manufacturing process and enabling the production of a film with a uniform thickness. In addition, it is possible to improve the fluidity of the PVDC-based composite particles, suppress the accelerated decomposition of PVDC, and prevent the generation of HCl gas. [Brief explanation of the drawings]

[0020] [Figure 1] ​1A and 1B are scanning electron microscope (SEM) images of a core-shell composite according to an embodiment of the present invention, in which (a) is a SEM image of a PVDC polymer core particle before wax coating, and (b) is a SEM image of a PVDC-based composite including a wax shell layer. [Figure 2] 1A to 1C are scanning electron microscope images of a core-shell composite according to one embodiment of the present invention, showing the thickness of the shell layer at different positions in the composite. DETAILED DESCRIPTION OF THE INVENTION

[0021] The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. The present embodiments are provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains. The present invention is defined only by the scope of the claims. Specific details for implementing the present invention will be described in detail below with reference to the accompanying drawings. The same element numbers refer to the same components regardless of the drawing, and "and / or" includes each and every combination of one or more of the referenced items.

[0022] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the same manner as commonly understood by a person of ordinary skill in the art to which this invention belongs. Throughout this specification, when a part "comprises" a certain element, this means that it may further include other elements, not excluding other elements, unless otherwise specified. Furthermore, the singular form includes the plural form unless otherwise specified in the phrase.

[0023] In this specification, when a layer, film, region, plate, or other part is said to be "on top of" or "on" another part, this includes not only when it is "directly on top of" the other part, but also when there is another part between them.

[0024] The present invention provides a PVDC-based composite comprising a core containing a PVDC (Polyvinylidene chloride)-based polymer and a shell surrounding the core and containing a wax, wherein the wax is in the form of nano-sized particles.

[0025] PVDC-based polymers are synthetic resins based on vinylidene chloride (VDC). They offer excellent gas and moisture barrier properties, particularly moisture resistance, and are suitable for sterilization at high temperatures of 120°C. They are therefore used in food packaging, including retort pouches. However, as previously mentioned, PVDC-based polymers are prone to carbonization during thermal processing due to their structural characteristics, which can lead to the formation of carbon carbides, resulting in uneven film thickness or even difficulty in film processing. The formation of carbon carbides is further accelerated by the reduced fluidity of PVDC-based particles, resulting in increased film thickness variation and reduced quality.

[0026] In the present invention, a PVDC-based composite in which a shell containing a nano-sized wax is introduced into a PVDC-based polymer core is used, thereby reducing the surface roughness of the composite particles and significantly improving the flowability of the particles.

[0027] The PVDC-based polymer may be one or more selected from the group consisting of homopolymers and copolymers containing vinylidene chloride (VDC), and specifically, may be a copolymer containing one or more comonomers selected from the group consisting of vinyl chloride (VC) and methyl acrylate (MA).

[0028] The PVDC copolymer may contain 2 to 25 wt% of the comonomer. Specifically, the VC content of the VDC-VC copolymer may be 10 to 23 wt%, preferably 13 to 20 wt%, and the MA content of the VDC-MA copolymer may be 2 to 12 wt%, preferably 3 to 9 wt%. Within these ranges, the PVDC copolymer exhibits sufficient crystallinity and crystallinity to maintain moisture and gas barrier properties, while also lowering its melting temperature, thereby improving thermal processability. Specifically, as the melting temperature of the PVDC copolymer decreases, the difference between the decomposition temperature and melting temperature of the PVDC-based polymer increases proportionally. In the present invention, the PVDC-based polymer contains a VDC-VC copolymer and / or a VDC-MA copolymer, ensuring a melt-processable temperature range of 30°C or higher, preferably 50°C or higher, below the decomposition temperature of the PVDC polymer, thereby improving process efficiency.

[0029] The core may be a spherical particle having a particle size of 150 to 350 μm, preferably 200 to 300 μm. The core particle may be a porous particle having a surface roughness of several μm to several tens of μm. In this case, the particle size may refer to D50, which refers to the particle diameter at which the cumulative volume reaches 50% from the smallest particle size in particle size distribution measurement by laser scattering. Here, D50 can be measured by collecting a sample and measuring the particle size distribution using a Malvern Mastersizer 3000 in accordance with KS A ISO 13320-1 standard. Specifically, in dry analysis, the sample is suspended in air for measurement. In wet analysis, the volume density can be measured after dispersion using an ultrasonic disperser, if necessary, in ethanol as a solvent.

[0030] The thickness of the wax-containing shell may be 10 nm to 20 μm, preferably 10 nm to 15 μm, and more preferably 30 nm to 10 μm. Within this range, it is possible to prevent a decrease in the surface roughness reduction effect due to a thin shell thickness, while also preventing the problem of reduced barrier performance due to an excessively thick shell.

[0031] The wax may be one or more selected from the group consisting of petroleum / coal-derived waxes extracted from petroleum or coal, animal and vegetable waxes, amide-based synthetic waxes, olefin-based synthetic waxes, organosilicon polymer waxes, and modified waxes thereof. Specific examples include, but are not limited to, paraffin, microcrystalline wax, montan wax, polyethylene wax, oxidized polyethylene wax (oxidized PE), polypropylene wax, oxidized polypropylene wax, organosilicon polymer (polysiloxane), polyoxyethylene glycol wax, halogenated hydrocarbon wax, hydrogenated wax, acrylic wax, and carnauba wax.

[0032] The wax according to one embodiment of the present invention may be of at least two or more types including an acrylic wax. The acrylic wax may have a glass transition temperature (Tg) similar to the drying temperature during the preparation of the PVDC-based composite. Specifically, the drying process is a step of drying a mixture of a PVDC-based polymer and wax. It can be performed at a temperature of 80 to 140°C, preferably 90 to 130°C, and therefore may include an acrylic wax with a Tg of 80 to 140°C, preferably 90 to 130°C. The drying process may be performed by fluidized-bed drying, which is commonly used to dry particulate polymer products. Specifically, fluidized-bed drying is a method in which dry gas is blown into the particles to suspend them in a drying state. During the drying process, collisions between particles and between particles and the dryer surface may occur. The dryer may have various shapes and structures, such as, but not limited to, a vertical type, horizontal type, batch type, or semi-batch type. By including the acrylic wax, the acrylic wax undergoes a softening process during the drying process, causing collisions between particles or between particles and the equipment surface (dryer surface), which can induce particle deformation. This wax particle deformation process flattens the surface coating of the PVDC-based polymer core, reducing the surface roughness of the core. As a result, the PVDC-based composite has a smooth surface, significantly improving its fluidity. The type of wax other than the acrylic wax is not particularly limited, but may be an olefin-based synthetic wax, an olefin oxide-based synthetic wax, a natural wax, or a silicone polymer wax.

[0033] The wax particle size may be 30 to 280 nm, preferably 30 to 250 nm, and more preferably 50 to 200 nm, where the particle size may refer to D50. As described above, the PVDC core particles are porous particles having a particle size of 150 to 350 μm and a surface roughness of several μm to several tens of μm. Therefore, wax particles having this particle size range can enter the grooves on the surface of the core particles or cover the groove surfaces, thereby reducing the surface roughness of the core particles.

[0034] The coating coverage of a PVDC-based composite according to one embodiment of the present invention may be 32 to 99%, preferably 60 to 99%, and more preferably 90 to 99%. In particular, when a wax having a particle size within the above-mentioned range is used for coating, an excellent coating rate and uniform coating properties can be achieved, resulting in a coating coverage of 97% or more, and thus improved particle fluidity. In contrast, when a wax having a particle size larger than the above-mentioned range is used for coating, the contact surface between the wax particles and the PVDC core particles is relatively reduced, making it impossible to fully fill the grooves on the core particle surface. This can result in relatively low coating coverage and poor particle fluidity.

[0035] The inclination angle, i.e., the angle of repose (angle of repose) of a powder containing a plurality of PVDC-based composites according to one embodiment of the present invention was measured by free fall evaluation. epoThe angle of repose (se) may be 28 or less, preferably 24 to 28. The angle of repose is the maximum inclination angle at which unconsolidated sediment can be deposited on an inclined surface without flowing. That is, it is the largest angle between the natural surface of the powder and a horizontal plate in a static equilibrium state. It is generally 5 to 10 degrees smaller than the internal friction of the material. The smaller the angle of repose, the better the powder's flowability. Specifically, the angle of repose was determined by placing 140 g of powder in a funnel, allowing it to fall freely from a height of 20 cm to the bottom, measuring the left and right inclination angles of the pile of powder that accumulated at the bottom, and calculating the average value three times in the same manner to calculate the final value. In this case, the angle of repose of the powder containing the shell-free PVDC-based polymer particles was 30.7, while the angle of repose of the powder containing the PVDC-based composite of the present invention can be reduced by about 9% under the above conditions. Generally, the flowability of a powder with an angle of repose in the range of 30 to 40 is evaluated as "fair to passable," and the flowability of a powder with an angle of repose in the range of 25 to 30 is evaluated as "good." Therefore, the fluidity of the powder containing the PVDC-based composite, which has an angle of repose of 28 or less, is very good, and such increased powder fluidity allows for smooth feeding and extrusion of raw materials during thermal processing such as extrusion, thereby enabling the production of films with uniform thickness.

[0036] The PVDC-based composite is characterized by further satisfying the following relational expression 1: [Equation 1] 0.8

[0037] In Relational Formula 1, A is the angle of repose of a powder containing a plurality of PVDC-based polymer particles without a shell layer, and B is the angle of repose of a powder containing a plurality of PVDC-based core-shell composite particles. In Relational Formula 1, A is the angle of repose of a powder containing only a plurality of PVDC-based polymer core particles without a shell layer, and can be 30.7 when measured using a method similar to the method for measuring the angle of repose described above.

[0038] ​When the PVDC-based composite according to one embodiment of the present invention satisfies Relational Formula 1, it exhibits crystallinity and crystallinity sufficient to maintain moisture and gas barrier properties while also increasing particle fluidity, thereby simultaneously exhibiting excellent barrier properties and fluidity.

[0039] The present invention also provides a method for producing a PVDC-based composite, the method comprising the steps of: a) preparing a first mixture containing a PVDC (Polyvinylidene chloride)-based polymer; b) adding a wax to the first mixture to prepare a second mixture; and c) drying the second mixture, wherein the wax is in the form of nano-sized particles.

[0040] The step a) is a step of preparing a first mixed solution, which may further include a stabilizer, a suspending agent, and a solvent. In this case, the step a) may be performed at 50 to 100°C, preferably 70 to 100°C, and with stirring at 100 to 500 rpm.

[0041] Specifically, based on 100 parts by weight of the PVDC-based polymer particles, the dispersion may contain 0.1 to 0.3 parts by weight, preferably 0.15 to 0.25 parts by weight, of a stabilizer; 0.03 to 0.12 parts by weight, preferably 0.05 to 0.10 parts by weight, of a suspending agent; and 70 to 250 parts by weight, preferably 100 to 200 parts by weight, of a solvent. The stabilizer stabilizes PVDC and may be an inorganic stabilizer, non-limiting examples of which include tetrasodium pyrophosphate (TSPP), magnesium hydroxide (Mg(OH)2), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2). Examples of the suspending agent include, but are not limited to, hydroxypropyl methylcellulose (HPMC). The solvent may be one or more selected from the group consisting of water, distilled water, and demi-(demineralized) water, but is not limited thereto. In this case, the pH value of the mixture may be adjusted to 6 to 7, and an acidic aqueous solution such as hydrochloric acid (HCl), sulfuric acid (H2SO4), or nitric acid (HNO3) may be used to adjust the pH, but is not limited thereto.

[0042] Step b) is a step of preparing a second mixture containing wax, which can be prepared by adding wax to the first mixture and mixing at 100 to 500 rpm. In this case, the wax may be added in an amount of 1 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 1 to 5 parts by weight, based on 100 parts by weight of the PVDC-based polymer particles.

[0043] The wax may have a particle size (D50) of 30 to 300 nm, preferably 30 to 280 nm, and more preferably 50 to 200 nm, and may contain at least two types of wax, including an acrylic wax. In this case, the acrylic wax may be present in an amount of 20 to 100 parts by weight, preferably 40 to 100 parts by weight, and more preferably 60 to 90 parts by weight, based on 100 parts by weight of the total wax. The type of wax other than the acrylic wax is not particularly limited, but may be an olefin-based synthetic wax or a natural wax. The wax may be used in a powder state or in a suspension state. The wax content may be 20 to 60 parts by weight, preferably 25 to 50 parts by weight, based on 100 parts by weight of the suspension.

[0044] After step b), an inorganic salt addition process may be performed to shorten the wax coating time. In this case, this process may be performed under the same temperature and stirring speed conditions as step a), and the stirring time may be 1 to 60 minutes, preferably 2 to 40 minutes.

[0045] The inorganic salt refers to a water-soluble substance that dissociates into cations and anions when dissolved in water, and non-limiting examples include sodium chloride (NaCl), potassium chloride (KCl), lithium chloride (LiCl), magnesium chloride (MgCl2), calcium chloride (CaCl2), etc. The inorganic substance may be included in an amount of 0.2 to 5 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the PVDC-based polymer particles.

[0046] After the inorganic salt addition process, stirring may be stopped and the resulting mixture may be subjected to a vacuum filtering process to separate it from water. In this case, the filter is not particularly limited as long as it has a commonly used hole size of several μm to several tens of μm.

[0047] Step c) is a drying step, which may be carried out at a temperature higher than the glass transition temperature (Tg) of the acrylic wax used in step b) under aeration conditions using an inert gas such as nitrogen or argon. Specifically, the drying temperature may be 80 to 140°C, preferably 90 to 130°C, and more preferably 90 to 120°C, for 4 to 15 hours, preferably 6 to 14 hours. Furthermore, by carrying out the drying process under the above conditions, the acrylic wax softens, inducing deformation of the coating layer of the acrylic wax and other wax particles, thereby significantly reducing the surface roughness of the PVDC-based composite particles and increasing the fluidity of the PVDC-based composite particles.

[0048] The present invention also provides a food packaging film comprising a PVDC-based composite according to one embodiment of the present invention. Specifically, the film may comprise an inner layer, a barrier layer, and an outer layer.

[0049] The inner layer, which comes into direct contact with food, can be made of any polymeric material commonly used in food packaging films, including polyethylene and polyethylene copolymers, polypropylene and polypropylene copolymers, polyester, and polyamide. The inner layer may further contain a rubber-based resin and an antistatic agent. The rubber-based resin may be one or more selected from the group consisting of latex, styrene-butadiene-styrene (SBS) rubber, styrene-butadiene (SB) rubber, styrene-isoprene-styrene (SIS) rubber, styrene-ethylene-butylene-styrene (SEBS) rubber, ethylene-propylene-diene (EPDM) rubber, ethylene-propylene (EP) rubber, and a tackifier. The inclusion of the rubber-based resin and tackifier can improve flexibility and sealing properties. The antistatic agent may be any known material in the art, but a low-molecular-weight antistatic agent may be used to reduce costs. The barrier layer is a layer that blocks gas and moisture, and may contain a resin composition including a PVDC-based composite according to one embodiment of the present invention.

[0050] The outer layer is the layer that comes into contact with the outside and serves to protect the contents packed inside by resisting external impact and friction. The outer layer may be made of a polymeric material commonly used as a film material, and is not particularly limited as long as it is a polymeric material commonly used in food packaging films, such as polyethylene and its copolymers, polypropylene and its copolymers, polyester, and polyamide. The outer layer may further include a rubber-based resin and an antistatic agent. The rubber-based resin may be one or more selected from the group consisting of latex, styrene-butadiene-styrene (SBS) rubber, styrene-butadiene (SB) rubber, styrene-isoprene-styrene (SIS) rubber, styrene-ethylene-butylene-styrene (SEBS) rubber, ethylene-propylene-diene (EPDM) rubber, and ethylene-propylene (EP) rubber. The rubber-based resin is not particularly limited as long as it is a polymeric material commonly used in food packaging films.

[0051] The film may be further subjected to post-processing, such as stretching or orientation to increase the mechanical strength of the film or to impart shrinkage properties, electron beam crosslinking, corona discharge to enhance printing properties, or thermal aging to impart dimensional stability. Any of the processing methods typically used for food packaging materials may be applied.

[0052] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples.

[0053] Example 1 350g of dry PVDC powder, 0.27g of Methocel, and 0.66g of TSPP were added to 486g of doubly distilled water, and several drops of 1N HCl were added to adjust the pH to 6.3. The mixture was stirred at 90°C and 400 rpm for 30 minutes to produce a dispersion. Next, wax was added according to the composition in Table 1 below, and the mixture was stirred for 10 minutes to produce a mixed solution.

[0054] A 21.30 wt% NaCl aqueous solution was added to the mixture, which was then stirred for 15 minutes and vacuum filtered. The resulting mixture was then dried. A glass tube with a diameter of 5 cm and a length of 30 cm was filled with glass wool at the bottom, and the resulting mixture was placed inside. The top was then sealed with glass wool, and nitrogen gas was blown into the bottom of the glass tube. The outside of the glass tube was wrapped with an electrically operated heating cable, and the mixture was dried at 100°C for 12 hours to produce a PVDC-based composite.

[0055] Examples 2 to 5 The same procedure as in Example 1 was carried out, except that wax was added according to the composition in Table 1 below.

[0056] Example 6 The same procedure was followed as in Example 1 above, except that the drying step was carried out at 60°C instead of 100°C.

[0057] (Comparative Example 1) The same procedure as in Example 1 was carried out except that no wax was added.

[0058] (Comparative Example 2) A mixture was obtained by dry blending 300 g of dry PVDC powder and 1.5 g of wax B (AC 619A).

[0059] (Evaluation method) 1. Scanning Electron Microscope (SEM) Analysis The PVDC composite prepared in Example 2 was subjected to SEM analysis, and the results are shown in Figures 1 and 2. An Apreo instrument manufactured by FEI was used to analyze the shape of the PVDC. The analysis was performed under the following conditions: voltage 2.0 to 2.5 kV, current 1.6 to 3.2 nA, and working distance 10 mm; however, the conditions were optimized depending on the condition of the test specimen.

[0060] Figure 1(a) shows an SEM image of a PVDC polymer core particle before wax coating, and (b) shows an SEM image of a PVDC-based composite containing a wax shell layer.

[0061] Figure 2 shows the thickness of the wax shell layer formed on the surface of a PVDC particle in a PVDC-based composite after wax coating, with (a) to (c) showing the shell layer thickness at different positions.

[0062] As shown in Figure 1, it can be seen that a shell layer containing wax was formed on the entire surface of the PVDC core particle, and as shown in Figure 2, it can be seen that a shell layer with a thickness of 55 nm to 10 μm was formed on the surface of the PVDC polymer core.

[0063] 2. Coating coverage measurement The coating coverage of the PVDC composites prepared in Examples 1 to 6 was measured using SEM images, and the results are shown in Table 1 below.

[0064] The coating coverage was calculated using the light / dark ratio of the SEM image of the PVDC-based composite after wax coating. In this case, if the wax coating was inefficient, a mixture of light and dark areas would be displayed, while if the coating was efficient, only a dark image would be displayed.

[0065] As shown in Table 1, in Examples 1 to 4, all showed a coverage of 97% or more, which confirms that the wax-containing shell layer was uniformly coated on the surface of the PVDC-based polymer core.

[0066] In Example 5, the particle size of Wax F mixed with Acrylic Wax A was 284 nm, which was significantly larger than in Examples 2 to 4. This resulted in a relatively small contact area with the PVDC core particles, and the grooves on the core particle surface could not be fully filled, which is believed to have resulted in relatively low coverage.In Example 6, the drying process was performed at 60°C instead of 100°C, which resulted in insufficient softening of Acrylic Wax A, which is believed to have resulted in low coverage.

[0067] 3. Measurement of angle of repose The angles of repose were measured for the powders containing the PVDC composites or mixtures produced in Examples 1 to 6 and Comparative Examples 1 and 2, and the results are shown in Table 1 below.

[0068] Specifically, 140 g of each powder was placed in a funnel and allowed to fall freely from a height of 20 cm to the bottom. The left / right tilt angles of the pile of powder piled at the bottom were measured and the average value was used. The same method was repeated three times to calculate the average value.

[0069] As shown in Table 1, the PVDC-based polymer core particles without a shell layer (Comparative Example 1) showed an angle of repose of 30.7, while the PVDC-based polymer core particles and Wax B were simply dry mixed (Comparative Example 2) and showed an angle of repose of 29.2, which was similar to that of Comparative Example 1.

[0070] In contrast, the PVDC composites produced in Examples 1 to 6 all showed a respiration value of 29 or less, which is believed to be due to the increased fluidity caused by the formation of a shell layer containing acrylic wax A on the surface of the PVDC polymer core. In particular, Examples 2 to 4, which contained a second wax with a particle size of 150 nm or less in addition to acrylic wax A (first wax), showed a respiration value of 26 or less, which is believed to be due to the fact that the second wax particles with a particle size of 150 nm or less were able to uniformly fill the grooves present on the surface of the PVDC polymer core, thereby reducing surface roughness and improving particle fluidity.

[0071] In the case of Example 5, a second wax (F) with a particle size of 284 nm was used, and therefore, compared to Examples 1 to 4 in which second waxes with a particle size of 150 nm or less were used, it is believed that the relatively high angle of repose was exhibited because the second wax was unable to sufficiently fill the grooves present on the surface of the PVDC-based polymer core.

[0072] In the case of Example 6, the drying process was carried out at 60°C instead of 100°C, so it is believed that the reduction in the surface roughness of the core due to the softening of acrylic wax A was insufficient, resulting in a higher angle of repose compared to Examples 1 to 5, which used a drying temperature of 100°C.

[0073] [Table 1]

[0074] In Table 1, the contents of the first wax and the second wax are expressed as weight percent of the first wax and the second wax relative to the total weight of the produced PVDC-based composite. A (Product name: Plaststrength L1000, Arkema), and as the second wax, B (Product name: AC 6 1The following materials were used: C (product name: ME93135, Michelman), D (product name: ME 61335, Michelman), E (product name: ML160, Michelman), and F (product name: ME98040, Michelman). PVDC (product name: XU 32034.03, SK Global Chemical) was used.

Claims

1. a core containing a PVDC (Polyvinylidene chloride) polymer; a shell surrounding the core and comprising wax; Including, The wax is a nano-sized particle, and the particle size of the wax is 30 to 280 nm; the core is a spherical particle having a size of 150 to 350 μm, the core is a porous particle having a surface roughness of several μm to several tens of μm, The PVDC composite is characterized in that the wax has a particle size that can enter the grooves on the surface of the core particle or cover the surface of the grooves to reduce the surface roughness of the core particle.

2. 2. The PVDC composite according to claim 1, wherein the wax is at least one selected from the group consisting of petroleum / coal-derived waxes extracted from petroleum or coal, animal and vegetable waxes, amide-based synthetic waxes, olefin-based synthetic waxes, organosilicon polymer waxes, and modified waxes thereof.

3. 3. The PVDC composite according to claim 2, wherein the wax comprises at least two types of waxes including an acrylic wax.

4. 2. The PVDC composite according to claim 1, wherein the shell has a thickness of 30 nm to 10 μm.

5. 2. The PVDC composite according to claim 1, wherein the PVDC polymer is at least one selected from the group consisting of homopolymers and copolymers containing vinylidene chloride (VDC).

6. 6. The PVDC composite according to claim 5, wherein the PVDC polymer is a copolymer containing one or more comonomers selected from the group consisting of vinyl chloride (VC) and methyl acrylate (MA).

7. 7. The PVDC composite of claim 6, wherein the PVDC polymer comprises 2 to 25 wt. % of the comonomer.

8. 2. The PVDC composite of claim 1, wherein a powder containing a plurality of PVDC composites has an angle of repose of 28 or less.

9. The PVDC composite according to claim 8, further satisfying the following relational expression 1: [Relationship 1] 0.8<B / A<0.92 (In Relational Formula 1, A is the angle of repose of the powder containing the plurality of PVDC polymer particles not containing the shell, and B is the angle of repose of the powder containing the plurality of PVDC composites.)

10. a) preparing a first mixture containing a PVDC (Polyvinylidene chloride) based polymer; b) adding wax to the first mixture to prepare a second mixture; c) drying the second mixture; Including, The method for producing the PVDC composite according to any one of claims 1 to 9, wherein the wax is in the form of nano-sized particles.

11. The method for producing a PVDC composite according to claim 10, wherein the wax comprises at least two types of wax including an acrylic wax.

12. The method for producing a PVDC composite according to claim 10, wherein the step c) is performed at a temperature higher than the glass transition temperature (Tg) of the acrylic wax.

13. The method for producing a PVDC composite according to claim 10, wherein the drying temperature is 80 to 140°C.

14. A food packaging film comprising the PVDC-based composite of any one of claims 1 to 9.

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