Method for manufacturing recycled polystyrene microseeds, recycled polystyrene microseeds manufactured thereby, and expanded polystyrene

Abstract

The present invention relates to a method for manufacturing recycled polystyrene microseeds, recycled polystyrene microseeds manufactured thereby, and an expanded polystyrene. The purposes of the present invention are to provide recycled expanded polystyrene microseeds which can be mixed with an antioxidant to prevent a molecular weight decrease during a polystyrene microseed manufacturing process using waste expanded polystyrene, and to provide an expanded polystyrene having at least a certain level of buffering performance by using the recycled expanded polystyrene microseeds manufactured thereby.

Description

Method for producing regenerated polystyrene micro-seeds and regenerated polystyrene micro-seeds and expandable polystyrene produced therefrom

[0001] The present invention relates to a method for manufacturing a regenerated polystyrene micro-seed and to regenerated polystyrene micro-seed and expandable polystyrene manufactured therefrom, and more particularly, to regenerated expandable polystyrene micro-seed capable of preventing a decrease in molecular weight by mixing an antioxidant during a process for manufacturing a polystyrene micro-seed using waste expandable polystyrene, and to expandable polystyrene manufactured therefrom having a buffering performance above a certain level.

[0002] 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). Due to its superior cushioning properties, there is currently no comparable substitute. Therefore, there is a pressing need to develop technologies that utilize recycled Styrofoam foam to recycle the material without degrading its physical properties.

[0003] Recycled expanded polystyrene is a cushioning packaging material manufactured by recycling waste expanded polystyrene. It can contribute to the environment by recycling waste expanded polystyrene, which has a high environmental pollution burden, and reusing it as a cushioning material.

[0004] Representative methods for manufacturing such recycled expandable polystyrene include melt polymerization, which melts waste expandable polystyrene into the raw material styrene monomer to polymerize it, and seed polymerization, which forms micro-seeds of waste expandable polystyrene and coats them with styrene monomer to polymerize it.

[0005] In particular, seed polymerization has the advantage of allowing the participation of waste expanded polystyrene in the form of particles in the reaction, enabling uniform synthesis with little increase in viscosity during polymer reaction, and thus manufacturing regenerated expanded polystyrene with a high yield and recycling rate (over 50%).

[0006] The process for manufacturing these waste expanded polystyrene micro seeds involves reducing the volume of the expanded polystyrene, forming waste expanded polystyrene pellets by melt extrusion or other methods, and then crushing them by strand cutting or underwater cutting to form micro seeds.

[0007] During the volume reduction process, heat or pressure, usually heat above the glass transition temperature (Tg), is applied to waste expandable polystyrene to remove pores and reduce the volume. This process causes a decrease in the molecular weight of the polystyrene. Generally, as the molecular weight of a polymer decreases, fluidity increases but mechanical strength decreases. Therefore, the physical properties of waste expandable polystyrene pellets decrease compared to virgin polystyrene. As a result, waste expandable polystyrene pellets cannot be reused as cushioning packaging materials, and are mainly recycled for use as picture frames and building materials.

[0008] In addition, there was a problem that the molecular weight of the waste expanded polystyrene was reduced again in the process of melting the pellets by heating them again to a temperature higher than the glass transition temperature (Tg) for micro-seeding, and when this was applied as a micro-seed for seed polymerization, the physical properties of the recycled expanded polystyrene were reduced.

[0009] Accordingly, there is an urgent need for a technology that prevents molecular weight reduction during the volume reduction and micro-seeding processes to recycle waste expanded polystyrene from regenerated expanded polystyrene.

[0010] <Related literature>

[0011] - Republic of Korea Patent No. 10-086937 (Registration date: November 12, 2008)

[0012] - Republic of Korea Patent Publication No. 10-2014-0033936 (Published: March 19, 2014)

[0013]

[0014] The present invention aims to provide a method for producing regenerated expandable polystyrene micro-seeds having a high molecular weight by mixing an antioxidant therein to prevent a problem of a decrease in molecular weight during the manufacturing process of polystyrene micro-seeds including a volume reduction and micro-seeding step of waste expandable polystyrene, and an expandable polystyrene having a certain or higher cushioning performance foamed using the regenerated expandable polystyrene micro-seeds manufactured thereby.

[0015] 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.

[0016] The present invention to achieve the above purpose

[0017] A method for producing pellets, comprising: a volume reduction / pelletizing step of extruding an ingot manufactured after a volume reduction treatment that reduces the volume by applying a certain amount of heat or pressure to a regenerated polystyrene foam; and a micro-seeding step of applying a certain amount of heat to the manufactured pellets and cutting and crushing them to produce micro-seeds.

[0018] The present invention relates to a method for producing regenerated polystyrene micro-seeds, characterized in that an antioxidant is added to at least one of the above-mentioned reduction / pelletization step and micro-seeding step.

[0019] The above antioxidant may be a primary antioxidant including a phenol or amine group, or a secondary antioxidant including a sulfur or phosphorus group.

[0020] Preferably, the antioxidant added in the above reduction / pelletization step may include at least a primary antioxidant for preventing molecular weight reduction by removing radicals of polystyrene chains, and the antioxidant added in the micro-seeding step may include at least a secondary antioxidant for preventing molecular weight reduction by suppressing peroxide generation.

[0021] It is preferable that the above antioxidant be included in an amount of 0.001 to 1 wt% based on the total mass of the manufactured micro seed.

[0022] Another invention relates to a regenerated polystyrene micro seed manufactured according to the above method, characterized in that it has a weight average molecular weight of 150,000 to 300,000 MW.

[0023] Another invention relates to expandable polystyrene produced by foaming core-shell structured polystyrene particles produced by suspension polymerizing regenerated polystyrene micro-seeds produced by the above method with a styrene monomer.

[0024] The regenerated polystyrene micro-seeds forming the core of the above polystyrene particles contain an antioxidant and may have a weight average molecular weight of 150,000 to 300,000 MW.

[0025] The polystyrene particles may have a core density greater than a shell density, preferably 1.2 to 2.0 times greater than a shell density.

[0026] The above-mentioned expandable polystyrene may have a moisture content of 5% or less.

[0027] The regenerated polystyrene micro-seed manufactured according to the present invention can prevent the reduction in molecular weight of the micro-seed by adding an antioxidant during the manufacturing process, and the expandable polystyrene manufactured using this through a seed polymerization process with styrene monomer has the advantages of being environmentally friendly and having excellent mechanical performance as well as excellent buffering performance.

[0028] In addition, the core-shell structure polystyrene particles manufactured by seed polymerizing the regenerated polystyrene micro-seeds according to the present invention with a styrene monomer have a core density higher than that of the shell, thereby minimizing the space between adjacent particles due to over-foaming of the shell, thereby preventing moisture penetration and greatly improving the moisture content.

[0029] Figure 1 is a flow chart illustrating a process for manufacturing regenerated polystyrene micro-seeds and regenerated polystyrene micro-particles according to the present invention.

[0030] Fig. 2(a) is a photographic image of a conventional regenerative expandable polystyrene pellet, and Fig. 2(b) is a photographic image of a expandable polystyrene micro seed according to the present invention.

[0031] Figure 3 is a conceptual diagram of core-shell structured polystyrene (EPS) particles manufactured by suspension polymerizing regenerated polystyrene micro-seeds according to the present invention with a styrene monomer.

[0032] 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.

[0033] Hereinafter, the present invention will be described in detail with reference to the drawings.

[0034] Figure 1 is a flow chart illustrating a process for manufacturing regenerated polystyrene micro-seeds and regenerated polystyrene micro-particles according to the present invention.

[0035] First, a method for manufacturing regenerated polystyrene micro seeds according to the present invention is described step by step.

[0036] 1) Preparation of expanded polystyrene waste

[0037] Expanded polystyrene foam is a suitable choice for home appliance packaging, building packaging and insulation, and food packaging, but it is preferable to use it for home appliance packaging, which minimizes contamination during distribution.

[0038] 2) Reduction / pelletization stage

[0039] This step involves applying heat or pressure to reduce the volume of waste expanded polystyrene (EPS). This ingot is then fed into an extruder, where it is extruded into strands and then cut into pellets of a certain size (approximately 3 mm). During this process, an antioxidant is mixed in at 0.001 to 1% of the total weight to eliminate radicals generated during the thermal extrusion process, thereby preventing degradation.

[0040] 3) Micro-seeding step through crushing

[0041] The crushing of waste expandable polystyrene pellets (Ф=3 mm) to produce waste expandable polystyrene microseeds (Ф<1 mm) can be performed using strand cutting, underwater cutting, grinders, ball mills, bead mills, refiners, vibration mills, homomixers, etc. In the past, in the waste expandable polystyrene recycling process, only the pelletization process as shown in Fig. 2(a) was applied, but in the case of the present invention, the particle size is reduced (Ф<1 mm) compared to the existing pellets (Ф=3 mm), and accordingly, it is possible to produce regenerated expandable polystyrene (Ф0.4~1.7) that is easy to foam mold.

[0042] The present invention can prevent a decrease in molecular weight and improve long-term stability by adding 0.001 to 1 wt% of a secondary antioxidant (sulfur-based or phosphorus-based antioxidant) to the waste expanded polystyrene pellets manufactured in the previous step based on the total weight.

[0043] In summary, in the volume reduction / pelletization step for reducing the volume of waste expanded polystyrene, heat or pressure, usually heat above the glass transition temperature (Tg), is applied to the waste expanded polystyrene foam to remove pores and reduce the volume. However, during this process, a decrease in molecular weight occurs due to deterioration of the polystyrene. 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 is reduced due to deterioration of the polymer, the mechanical strength is reduced, so these pellets exhibit deteriorated physical properties compared to virgin polystyrene.

[0044] In addition, during the micro-seeding process of melting the pellets by heating them again to a temperature higher than the glass transition temperature (Tg), the molecular weight of polystyrene decreases again.

[0045] To prevent such molecular weight reduction, the present invention is characterized by adding an antioxidant to at least one of the reduction / pelletization step and the micro-seeding step.

[0046] More specifically, in the above-mentioned volume reduction / pelletization step, a primary antioxidant (phenol-based or amine-based antioxidant) is added to remove radicals of polystyrene chains decomposed by heat, thereby preventing a decrease in molecular weight. Then, in the step for micro-seeding, the waste expandable polystyrene pellets manufactured by the above-mentioned process and a secondary antioxidant (sulfur-based or phosphorus-based antioxidant) are added to suppress the generation of peroxides, thereby preventing a decrease in molecular weight and improving long-term stability. However, it is not necessary to separately add the primary and secondary antioxidants, and it is also possible to apply them in combination to more clearly prevent a decrease in molecular weight.

[0047] The above primary antioxidant may be selected from 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), and amine compounds such as phenyl-α-naphtylamine, Phenyl-β-naphtylamine, N,N'-Diphenyl-p-phenylenediamine.

[0048] The above secondary antioxidant can be selected from 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, etc., and sulfur compounds such as Dilaurylthiodiprop-pionate, Distearylthiodiprop-pionate, Ditridecylthiodiprop-pionate, etc.

[0049] For reference, the reduction in molecular weight due to polymer degradation begins with an oxidation reaction in which the hydrogen bonds in the polymer chain are broken down by externally applied heat, forming radicals. This oxidation reaction is initiated by the release of hydrogen from the polymer resin (RH) to generate alkyl radicals (R·), which then form a peroxide and enter a growth reaction in which radicals are generated at an accelerated rate by heat or ultraviolet rays, resulting in a rapid decrease in molecular weight. Therefore, in order to prevent degradation during the volume reduction and microseeding of polymers, the formation of radicals must be suppressed.

[0050] Therefore, by adding an antioxidant during the above manufacturing process, the deterioration of the polymer can be prevented, thereby preventing a decrease in the molecular weight of the micro-seeds. In addition, when manufacturing expandable polystyrene by synthesizing waste expandable polystyrene micro-seed particles with new styrene monomers, excellent buffering performance can be secured.

[0051] 4) Manufacturing of regenerative expandable polystyrene microparticles

[0052] The regenerated expandable polystyrene micro-seeds manufactured above and the new styrene monomer can be mixed in a reactor to manufacture regenerated expandable polystyrene particles through suspension polymerization. More specifically, the suspension polymerization can be performed including the steps of dispersing core micro-seeds in a solvent together with an inorganic surfactant, suspending agent, dispersing agent, emulsifier, etc.; and the step of coating and polymerizing the monomer on the seed using a styrene monomer, an initiator, an organic surfactant, etc. to grow the seed.

[0053] It can be carried out by including a step of impregnating the core-shell polystyrene particles generated thereafter with a foaming agent under high temperature and high pressure; and a step of adding a stabilizer, a reaction terminator, etc. and washing to obtain polystyrene impregnated with the foaming agent.

[0054] 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.

[0055] After manufacturing expandable polystyrene (EPS) particles, pre-foaming (20 to 80 times foaming) is performed under appropriate steam 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 steam pressure conditions to manufacture expandable polystyrene (molded product).

[0056] For reference, the core-shell structured expandable polystyrene particle according to the present invention has a structure as shown in Fig. 3. It is formed by including a core which is a regenerated expandable polystyrene micro-seed and a virgin polystyrene shell coating the core, and the density of the core is greater than the density of the shell. Preferably, the density of the core may be 1.2 to 2.0 times the density of the shell. When 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, and when the core / shell density ratio is more than 2.0, the core portion may hardly foam due to its high density, so that the overall bead foamability may be reduced.

[0057] The core of the expandable polystyrene particle having a core-shell structure according to the present invention has a high density compared to the shell, so that the over-foaming of the shell, which has a relatively low density, progresses until it comes into contact with adjacent particles, resulting in the formation of a foam having amorphous (close to polygonal) foam particles. Accordingly, 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.

[0058] 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.

[0059] [Example]

[0060] 1. Example: Manufacturing of regenerated expandable polystyrene by adding antioxidant

[0061] (1) Manufacturing of regenerative expandable polystyrene micro seeds

[0062] When the collected waste Styrofoam was subjected to volume reduction treatment (temperature 90-150 degrees, pressure 10-25 kg / cm2 conditions), 0.1 wt% (based on the total weight of the final polystyrene) of a primary antioxidant [Tetrakis[methylene-3-(3,5-ditert-butyl-4-hydroxyphenyl) propionate] methane, SONGNOX1010, Songwon Industrial] (based on the total weight of the final polystyrene) was added to produce an ingot, which was then fed into an extruder and extruded into a strand shape, cut, and pulverized to produce primary pellets with a diameter and length of approximately 3 mm.

[0063] Afterwards, during the additional extrusion process for seeding (die hole size of 1 mm or less), 0.1 wt% (based on the total weight of the final polystyrene) of secondary antioxidant [Tris(2,4-di-tert-butylphenyl) phosphite, SONGNOX1680, Songwon Industrial] was added, and then regenerated expandable polystyrene micro seeds with a diameter and length of 0.85 mm were manufactured.

[0064] (2) Manufacturing of regenerative expandable polystyrene particles

[0065] 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 produce regenerative expandable polystyrene (EPS) particles with a final core-shell structure.

[0066] (3) Manufacturing of regenerative expandable polystyrene

[0067] In the main reactor, 336 g of iso-pentane and nor-pentane as blowing agents were pressurized in a nitrogen atmosphere (12 kgf / cm 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.

[0068] 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 having a density of 20 g / L was manufactured by molding.

[0069]

[0070] 2. Comparative example: Manufacturing of regenerated expanded polystyrene without adding antioxidants.

[0071] In the above example, a regenerated expandable polystyrene micro seed was manufactured using the same method as in the above example, except that no antioxidant was added during the manufacturing process.

[0072]

[0073] 3. Experimental Evaluation: Comparison of Cushioning Performance of Regenerated Expanded Polystyrene

[0074] In order to compare the cushioning performance of the regenerative expandable polystyrene of the examples and comparative examples according to the present invention, experiments on compressive stress and flexural failure load were conducted under the following conditions, and the results are as shown in Table 1.

[0075] o Measuring equipment

[0076] - Molecular weight: THF-GPC,

[0077] - Buffer performance: UTM (Yeonjin S-Tech)

[0078] o Buffer performance test conditions

[0079] - Molecular weight: Shodex HK-G + 2 x TSKgel Supermultipore HZ-M + TSKgel SuperHZ-2500 column, temperature: 40℃, flow rate 0.35mL / min, injection volume 20μL (concentration 3g / L)

[0080] - Buffer performance: KS M3808 standard

[0081] Molecular weight, foam density (g / L), buffering performance, compressive stress (N / cm) 2 ) Bending failure load (N) Comparative example 13.7 20 17.6 24 Example 15.4 20 20.5 34

[0082] As shown in Table 1, in the case of the comparative example of recycled expandable polystyrene without added antioxidant, the average molecular weight is 150,000 MW or less and the flexural fracture load of the recycled expandable polystyrene with a foam density of 20 g / L is 25 N or less, whereas in the case of the example according to the present invention, the average molecular weight is 150,000 MW or more and the flexural fracture load of the recycled expandable polystyrene is excellent at 30 N or more.

[0083] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be apparent to those skilled in the art that various modifications and variations are possible within a scope that does not depart from the technical spirit of the present invention described in the claims.

Claims

1. A volume reduction / pelletization step in which an ingot manufactured after volume reduction treatment by applying a certain amount of heat or pressure to the regenerated polystyrene foam is extruded to manufacture a pellet; and It includes a micro-seeding step of applying a certain amount of heat to the above-mentioned manufactured pellets and cutting and crushing them to manufacture micro-seeds; A method for producing regenerated polystyrene micro-seeds, characterized in that an antioxidant is added to at least one of the above-mentioned reduction / pelletization step and micro-seeding step.

2. In paragraph 1, A method for manufacturing regenerated polystyrene micro seeds, characterized in that the antioxidant is a primary antioxidant containing a phenol or amine group, or a secondary antioxidant containing a sulfur or phosphorus group.

3. In paragraph 1, A method for producing regenerated polystyrene micro-seeds, characterized in that the antioxidant added in the above reduction / pelletization step includes at least a primary antioxidant for preventing a decrease in molecular weight by removing radicals of a polystyrene chain.

4. In paragraph 1, A method for manufacturing regenerated polystyrene micro-seeds, characterized in that the antioxidant added in the above micro-seeding step includes at least a secondary antioxidant for suppressing the generation of peroxides and preventing a decrease in molecular weight.

5. In paragraph 1, A method for producing regenerated polystyrene micro seeds, characterized in that the antioxidant is contained in an amount of 0.001 to 1 wt % based on the total mass of the produced micro seeds.

6. In the regenerated polystyrene micro seed manufactured according to paragraph 1, A regenerated polystyrene micro seed comprising an antioxidant and having a weight average molecular weight of 150,000 to 300,000 MW.

7. Expandable polystyrene characterized by foaming core-shell structured polystyrene particles manufactured by suspension polymerizing the regenerated polystyrene micro-seed manufactured according to Article 1 with a styrene monomer.

8. In paragraph 7, Expandable polystyrene, characterized in that the regenerated polystyrene micro-seeds forming the core of the polystyrene particles have a weight average molecular weight of 150,000 to 300,000 MW.

9. In paragraph 7, The above polystyrene particles are expandable polystyrene, characterized in that the density of the core is greater than the density of the shell.

10. In paragraph 8, Expandable polystyrene, characterized in that the density of the core is 1.2 to 2.0 times greater than the density of the shell.

11. In paragraph 7, The above-mentioned expandable polystyrene is characterized in that it has a moisture content of 5% or less.

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