Core-shell-structured expanded polystyrene particle and polystyrene foam produced therefrom

Abstract

The present invention relates to a core-shell-structured expanded polystyrene particle and a polystyrene foam produced therefrom, and, more specifically, to a core-shell-structured expanded polystyrene particle and a polystyrene foam produced therefrom, the expanded polystyrene particle having physical properties, such as moisture content of the polystyrene foam produced therefrom, that are improved due to the density difference between a core and a shell, thereby having long-term product packaging performance.

Description

Core-shell structured expandable polystyrene particles and polystyrene foam produced therefrom

[0001] The present invention relates to core-shell structured expandable polystyrene particles and polystyrene foams manufactured therefrom, and more particularly, to core-shell structured expandable polystyrene particles and polystyrene foams manufactured therefrom, which have improved properties such as moisture content of polystyrene foams manufactured therefrom due to the difference in density between the core and the shell, thereby enabling long-term product packaging.

[0002]

[0003] Due to recent tightening environmental regulations, demand for eco-friendly packaging materials to reduce carbon emissions is steadily growing. Consequently, interest in eco-friendly cushioning materials for heavy, medium- to large-sized products is also growing significantly. The most representative cushioning material is Styrofoam, manufactured from Expanded Polystyrene (EPS) particles. Due to its superior cushioning properties, there is currently no comparable substitute. Therefore, there is a pressing need to develop technologies for recycling waste Styrofoam without degrading its physical properties.

[0004] Expanded polystyrene (EPS) particles are spherical plastic particles approximately 0.2 to 2 mm in diameter, made from a polymer of styrene monomer, the raw material for Styrofoam. These particles contain foaming gas, which allows them to expand up to 130 times their original size when heated with steam. These foamed particles are then injected into a mold and heated with steam to form a specific shape, which can then be used as packaging materials.

[0005] The cross-sectional structure of conventional expandable polystyrene particles consists of polystyrene with a uniform density throughout, without a core-shell distinction. This uniform density within the particle ensures uniform cushioning performance. However, when foaming the particles with a blowing agent, a certain amount of void space is inevitably formed between the particles, leading to moisture infiltration into the void space, increasing the moisture content.

[0006]

[0007] Polystyrene Styrofoam has a wide range of uses, resulting in massive amounts of waste Styrofoam being generated. Because it does not decompose or decompose, landfilling creates additional pollution. Furthermore, incineration produces harmful gases and smoke, which is detrimental to the environment. Therefore, it is known as a chemical product that is difficult to reprocess.

[0008] Recent attempts to recycle waste Styrofoam have been problematic, however, with the mechanical properties of the material deteriorating. Therefore, there is a pressing need to develop technologies that can meet both cost and processability requirements while maintaining the material's properties.

[0009]

[0010] The purpose of the present invention is to provide core-shell structured expandable polystyrene particles, in which a low-density shell is over-expanded relative to the core during foam formation to minimize the space between adjacent particles, thereby improving physical properties such as moisture content, a polystyrene foam manufactured therefrom, and a method for manufacturing each.

[0011] However, the technical problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

[0012]

[0013] In order to achieve the above object, the present invention is characterized in that the core has a density greater than the shell, and the core has a density greater than the shell, in an expandable polystyrene particle comprising a core made of polystyrene material and a shell made of polystyrene material coating the core.

[0014] The density of the core may be 1.2 to 2.0 times greater than the density of the shell.

[0015] The above core can be manufactured from waste polystyrene foam, and more specifically, can be formed by crushing or re-extruding an ingot formed through a reduction treatment that applies a certain amount of heat to polystyrene foam.

[0016] The above shell can be formed by polymerizing a styrene monomer into the above core.

[0017] Another invention for achieving the above object relates to a polystyrene foam formed by foaming the polystyrene particles.

[0018] The above polystyrene foam may have a moisture content of 5% or less.

[0019] Another invention for achieving the above object is a method for producing expandable polystyrene particles, comprising the steps of: producing an ingot through a volume reduction treatment that reduces the volume by applying a certain amount of heat or pressure to polystyrene foam; producing a core pelletized to a certain size by extruding the produced ingot; and producing polystyrene particles having a core-shell structure by introducing the core and a styrene monomer into a reactor and then subjecting the core and a styrene monomer to suspension polymerization.

[0020] In the above reduction treatment or pelletizing process, an antioxidant can be added to prevent a decrease in molecular weight.

[0021] Another invention for achieving the above object is a method for producing an expandable polystyrene molded article, characterized by including a step of pre-foaming and maturing expandable polystyrene particles produced according to the above method; and a step of foaming and molding the matured polystyrene particles at a constant pressure in a molding machine.

[0022]

[0023] The expandable polystyrene foam manufactured by the present invention has the effect of significantly improving the moisture content by minimizing the gap between adjacent particles due to over-foaming of the particle shells due to the difference in density through the core-shell structure compared to conventional expandable polystyrene foams, thereby preventing moisture penetration.

[0024] Accordingly, it can be used as a high-performance cushioning packaging material for medium and large home appliances with enhanced long-term product packaging properties.

[0025] In addition, when the core is manufactured from waste Styrofoam, it is not only environmentally friendly but also has the advantage of improving physical properties compared to new Styrofoam.

[0026]

[0027] Figure 1 is a conceptual diagram of an expanded polystyrene (EPS) particle having a core-shell structure according to the present invention.

[0028] Figure 2 is a flow chart comparing and explaining the manufacturing process of conventional EPS particles (single spherical particles) and EPS particles with a core-shell structure according to the present invention.

[0029]

[0030] The specific embodiments described herein are intended to represent preferred embodiments or examples of the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that variations and other uses of the present invention do not depart from the scope of the invention described in the claims of this specification.

[0031] Hereinafter, the present invention will be described in detail with reference to the drawings.

[0032] FIG. 1 is a conceptual diagram of a core-shell structured expandable polystyrene particle according to the present invention. It is formed by including a core (100) made of a polystyrene material and a shell (200) made of a polystyrene material coating the core, and the density of the core (100) is greater than the density of the shell (200). Preferably, the density of the core may be 1.2 to 2.0 times the density of the shell. (If the core / shell density ratio is less than 1.2, the difference in foaming between the core and the shell is not large, so that a large space may be formed between the particles during foaming. If the core / shell density ratio exceeds 2.0, there is a concern that the overall bead foaming property may be reduced because the core portion has a high density and foaming hardly progresses.

[0033] The above core is preferably manufactured from waste polystyrene styrofoam, because, in addition to the reason that the use of waste polystyrene styrofoam improves environmental friendliness, the core has a higher density than virgin polystyrene because the polystyrene polymer is degraded and densified in the volume reduction step of applying heat to waste polystyrene styrofoam to reduce its volume and in the extrusion step of crushing or re-extruding the ingot produced from the volume reduction step to make particles.

[0034] The high-density core particles (solid state) are dispersed in water and then polymerized into a core-shell structure by coating new styrene (liquid state), and after polymerization has progressed by more than 80%, a foaming agent (liquid state) is added and impregnated. At this time, the core part in the solid state is partially and unevenly impregnated with the liquid foaming agent, and the shell part in the liquid state, where polymerization is in progress, is uniformly and in large quantities impregnated with the liquid foaming agent. In this way, due to the difference in the material state (solid or liquid) of the core and the shell, a difference in the concentration of the absorbed foaming agent occurs, and further, due to the difference in density between the core and the shell, when foaming is performed under the same conditions and with the same amount of foaming agent as a conventional single spherical new polystyrene foam, foaming starts from the low-density part, the shell, and a foam having a different structure from the new expandable polystyrene foam is formed.

[0035] As shown in Fig. 2, since the core has a high density compared to the shell, foaming progresses until it comes into contact with adjacent particles due to over-foaming of the shell, which has a relatively low density, resulting in the formation of a foam having amorphous (close to polygonal) foam particles. Therefore, the gap between each amorphous particle is reduced, and the gap through which moisture can penetrate during the water cooling process of the foaming / molding process is reduced, thereby having the effect of reducing the moisture content. Due to the effect of reducing the moisture content according to the present invention, the moisture content (residual moisture content) may be 5% or less, and more preferably 3.5% or less.

[0036] On the other hand, since conventional single-spherical expanded polystyrene particles have the same density throughout, when the particles are foamed by introducing a foaming agent, spherical foam is formed, increasing the gap between the particles. This causes moisture to penetrate during the water cooling process during the foaming / molding process, increasing the moisture content.

[0037]

[0038] Hereinafter, a method for manufacturing an expandable polystyrene particle according to the present invention and an expandable polystyrene foam (molded product) manufactured therefrom will be described.

[0039] The method for producing expandable polystyrene particles according to the present invention is

[0040] It includes a step of manufacturing an ingot through a volume reduction treatment that reduces the volume by applying a certain amount of heat or pressure to polystyrene foam; a step of manufacturing a core pelletized to a certain size by extruding the manufactured ingot; and a step of manufacturing a polystyrene particle having a core-shell structure by introducing the core and a styrene monomer into a reactor and then performing suspension polymerization.

[0041] First, the core is preferably manufactured from waste polystyrene foam. More specifically, waste raw materials (waste polystyrene foam) are collected, washed, and reduced in volume (by heating or pressurizing to remove blowing agent gases) to produce an ingot.

[0042] Next, the manufactured ingot is crushed or re-extruded to pelletize it into a certain size to manufacture core (seed) particles.

[0043] Next, suspension polymerization is performed to manufacture a shell through coating from the core particles manufactured above. The suspension polymerization may include (1) a step of dispersing core particles in a solvent together with an inorganic surfactant, suspending agent, dispersing agent, emulsifier, etc., (2) a step of growing seed particles by coating and polymerizing monomers on seed particles using a styrene monomer, an initiator, an organic surfactant, etc., (3) a step of impregnating the produced polystyrene particles with a blowing agent under high temperature and high pressure to form expandable polystyrene, and (4) a step of adding a stabilizer, a reaction terminator, etc. and washing to obtain polystyrene impregnated with the blowing agent.

[0044] The foaming agent may include, but is not limited to, Nor-pentane, Cyclo-pentane, Iso-pentane, etc., and may be included in an amount of 1 to 10 wt%, preferably 3 to 8 wt%, based on the manufactured expandable polystyrene (EPS) particles.

[0045] After manufacturing expandable polystyrene (EPS) particles, pre-foaming (20 to 80 times foaming) is performed under appropriate vapor pressure conditions, and then beads suitable for the desired density are injected into a mold of a certain shape, and then foaming and molding are performed under appropriate vapor pressure conditions to manufacture expandable polystyrene foam (molded product).

[0046] For reference, in the volume reduction process of core manufacturing, heat or pressure, usually heat above the glass transition temperature (Tg), is applied to waste expanded polystyrene foam to remove pores and reduce the volume. During this process, the polystyrene deteriorates and the molecular weight decreases. In addition, the ingot formed through the volume reduction process is again melt-extruded by applying heat above the glass transition temperature (Tg) to form pellets. Generally, when the molecular weight decreases due to polymer deterioration, the mechanical strength decreases, so these pellets exhibit deteriorated physical properties compared to virgin polystyrene.

[0047] In addition, in the process of melting the pellets by heating them again at a temperature higher than the glass transition temperature (Tg), the molecular weight of polystyrene decreases again.

[0048] To prevent this molecular weight reduction, an antioxidant may be added during the above-described reduction treatment or pelletizing process.

[0049] Antioxidants include phenol compounds such as 2-6-di-tert-butyl-4-methylphenol, Styrenated phenol, n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenol)propionate, 2,2'-methylenebiz(4-methyl-6-tert-butylphenol), amine compounds such as phenyl-α-naphtylamine, Phenyl-β-naphtylamine, N,N'-Diphenyl-p-phenylenediamine, and phosphorus compounds such as Tris(2,4-di-tert-butylphenyl)phosphite, Bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, Bis(2,4-dicumylphenyl)pentaerythritol diphosphate. The compound may be selected from sulfur compounds such as Dilaurylthiodiprop-pionate, Distearylthiodiprop-pionate, Ditridecylthiodiprop-pionate, etc., but is not limited thereto.

[0050]

[0051] [Example]

[0052] Example 1: Preparation of regenerated expandable polystyrene (EPS) particles with a core-shell structure

[0053] (1) Manufacturing core seeds from waste Styrofoam

[0054] The collected waste Styrofoam was subjected to a reduction treatment (temperature 90-150 degrees, pressure 10-25 kg / cm2) to produce an ingot, which was then crushed to produce primary pellets with a diameter and length of approximately 3 mm. Subsequently, micro-pelletized core seeds with a diameter and length of approximately 0.85 mm were produced through an additional extrusion process (die hole size 1 mm or less).

[0055]

[0056] (2) Manufacturing of regenerative expandable polystyrene particles (beads)

[0057] 1.14 kg of distilled water (DI water), 0.66 kg of the above-mentioned manufactured regenerated expandable polystyrene core seed, 7.2 g of tricalcium phosphate, and 0.054 g of sodium dodecylbenzenesulfonate were added to the main reactor, and heated to 75°C while stirring. 120 g of styrene monomer, 240 g of distilled water, 0.78 g of polyvinylpyrrolidine, 0.12 g of azobicisobutyronitrile, and 1.74 g of benzoyl peroxide were added to the auxiliary reactor, and stirred (6,000 rpm) for 5 minutes to uniformly disperse the styrene monomer. Then, the styrene monomer emulsion prepared in the auxiliary reactor was continuously introduced into the main reactor at a rate of 3 g / min. Afterwards, 1.32 g of trimagnesium phosphate and 0.03 g of sodium dodecylbenzenesulfonate were additionally added to the main reactor, and the temperature was raised to 115°C and maintained for 2 hours to manufacture regenerated expandable polystyrene (EPS) particles with a final core-shell structure. The results of measuring the density of the core and shell of the manufactured expandable polystyrene particles are as shown in Table 1 below. For reference, the density ratio of the core and shell was 1.67.

[0058] Diameter (D) [mm] Radius (r) [mm] Volume (V = 4 / 3 * πr) 3 )[mm 3 ]Mass (M)[g]Density (d=M / V)[g / mm 3 ]Regenerated EPS particle (core + shell) 1.18 0.59 0.86 22.32 Core seed (regenerated) 0.85 0.42 50.32 13.11 Shell (new) 0.54 11.86

[0059] (3) Manufacturing of regenerative expandable polystyrene foam

[0060] In the main reactor, 336 g of iso-pentane and nor-pentane as blowing agents were pressurized (12 kgf / cm) in a nitrogen atmosphere. 2 ) and maintained for 10 hours for impregnation. After impregnation was completed, the temperature of the main reactor was cooled to room temperature (25-30 degrees), and the regenerated foamable styrene bead particles impregnated with the foaming agent were taken out and dehydrated and dried.

[0061] Afterwards, the manufactured regenerative foamable styrene bead particles are pre-foamed at a foaming ratio of 50 ml / g and aged at room temperature in a silo for 15 to 18 hours, and then a foaming styrene resin molding machine is used at a steam pressure of 2 kgf / cm. 2 A regenerated expandable polystyrene foam having a density of 20 g / L was manufactured by molding.

[0062]

[0063] 2. Experimental Evaluation

[0064] (1) Measurement of compressive stress and moisture content

[0065] [Correction under Rule 91 15.10.2024] As a comparative example, new Styrofoam foam (EPS B240NH 500KG FLECON) having the same expansion ratio (50 ml / g) and density (20 g / L) as the regenerated expandable polystyrene foam manufactured in Example 1 was used, and the enlarged photographs of the surface and particles, and the results of measurements of compressive stress and moisture content were summarized as in Fig. 3.

[0066] [Correction pursuant to Rule 91, October 15, 2024]

[0067] The compressive stress of Example 1 is 19 N / cm 2 It was found that the level was equivalent to that of the comparative example formed with a new material, and the function rate was 3.3%, which was significantly improved compared to the comparative example.

[0068] This is because the particles of the comparative example (new EPS) are close to spherical in shape, whereas the particles of Example 1 (recycled EPS) according to the present invention are polygonal, so that the low-density shell is over-foamed and foaming progresses until it comes into contact with adjacent particles, resulting in foamed particles having a shape close to polygonal, and as a result, the gaps between the polygonal particles are reduced, so that the gaps for moisture to penetrate during the water cooling process during the foaming and molding process are reduced, resulting in a decrease in the moisture content.

[0069]

[0070] (2) Measurement of moisture content according to core-shell density ratio

[0071] In order to determine the moisture content according to the core / shell density ratio of regenerated expandable polystyrene particles (beads) with a core-shell structure, regenerated expandable polystyrene (EPS) particles having the core seed and bead diameters shown in Table 2 were manufactured, and then the moisture content according to the core / density ratio was measured.

[0072] Core diameter (D) [mm] EPS bead diameter (D) [mm] Core density / Shell density [times] Moisture content (%) Comparative example - 1.00 1.00 9.1 Example 10.85 1.18 1.67 3.3 Example 21.00 1.40 1.74 3.1 Example 30.71 1.00 1.80 2.9 Example 40.60 0.85 1.84 3.0

[0073] As a result of the measurement, the difference in core density / shell density of Examples 1 to 4 was 1.67 to 1.84 times, which confirmed that Examples 1 to 4 according to the present invention had a significantly superior moisture content compared to the comparative example having a single circular shape.

Claims

1. In an expandable polystyrene particle comprising a core made of polystyrene material and a shell made of polystyrene material coating the core, Expandable polystyrene particles, characterized in that the density of the core is greater than the density of the shell.

2. In paragraph 1, Expandable polystyrene particles, characterized in that the density of the core is 1.2 to 2.0 times greater than the density of the shell.

3. In paragraph 1, Expandable polystyrene particles, characterized in that the core is manufactured from waste polystyrene foam.

4. In paragraph 3, The above core is an expandable polystyrene particle, characterized in that it is formed by crushing or re-extruding an ingot formed through a reduction treatment that applies a certain amount of heat to polystyrene foam.

5. In paragraph 3, An expandable polystyrene particle is characterized in that the shell is formed by polymerizing a styrene monomer into the core.

6. A polystyrene foam formed by foaming the polystyrene particles according to Article 1.

7. In paragraph 6, A polystyrene foam, characterized in that the polystyrene foam has a moisture content of 5% or less.

8. In the method for manufacturing expandable polystyrene particles according to Article 1, A step of manufacturing an ingot through a volume reduction treatment that reduces the volume by applying a certain amount of heat or pressure to polystyrene foam; A step of manufacturing a core pelletized to a certain size by extruding the manufactured ingot; and A step of producing polystyrene particles having a core-shell structure by introducing the core and styrene monomer into a reactor and then performing suspension polymerization; A method for producing expandable polystyrene particles, characterized by comprising:

9. In paragraph 8, A method for manufacturing expandable polystyrene particles, characterized in that an antioxidant is added during the above-mentioned reduction treatment or pelletizing process.

10. A step of pre-foaming and maturing the expandable polystyrene particles manufactured according to Article 9; and A step of foaming the matured polystyrene particles at a constant pressure within a mold; A method for producing an expandable polystyrene molded body, characterized by including:

Images