阅读说明：本技术 具有优异的泡孔形成均匀性的发泡片材及其制备方法 (Foamed sheet having excellent uniformity of cell formation and method for preparing the same ) 是由 金宇镇 咸镇洙 李光熙 许娓 崔钟汉 河相勳 于 2018-12-26 设计创作，主要内容包括：本发明的发泡片材由聚酯树脂形成,因而在价格上具有竞争力,且对人体无害并环保。并且,上述发泡片材的耐冲击性及成型性优异,在聚酯树脂内部均匀地分散有特定大小的无机颗粒,使得发泡片材的泡孔形成均匀性高,且可根据无机颗粒的大小来调节泡孔尺寸。(The foamed sheet of the present invention is formed of a polyester resin, and thus is competitive in price, and is harmless to the human body and environmentally friendly. The foamed sheet is excellent in impact resistance and moldability, and inorganic particles having a specific size are uniformly dispersed in the polyester resin, so that the foamed sheet has high uniformity of cell formation, and the cell size can be adjusted according to the size of the inorganic particles.)

1. A foamed sheet which is a foamed sheet of a polyester resin containing inorganic particles,

the inorganic particles have an average size of 0.05 to 60 μm,

the foamed sheet has an average cell size of 5 to 500 μm,

the foamed sheet satisfies the following numerical formula 1,

mathematical formula 1: 50% | V1-V0 |/V0 × 100 | -300%,

in the above-mentioned mathematical formula 1,

v0 is the volume of foamed sheet in cm3 before circular foamed sheet with a diameter of 10cm is exposed for 30 seconds in an oven at a temperature of 200c,

v1 is the volume in cm3 of a circular foamed sheet having a diameter of 10cm after exposure to a temperature of 200 ℃ oven for 30 seconds.

2. The foamed sheet according to claim 1, wherein the foamed sheet satisfies the following numerical formula 2,

mathematical formula 2: i SV 1-SV 0I/SV 0 × 100 equals 20%,

in the above-mentioned numerical expression 2,

SV0 is the volume of a foamed sheet before a ball having a diameter of 7cm and a weight of 500g was freely dropped from a height of 30cm to a foamed sheet having a length of 10cm and a width of 10cm, and has a unit of cm3,

SV1 is the volume in cm3 of a foamed sheet after free fall of a ball having a diameter of 7cm and a weight of 500g from a height of 30cm to a foamed sheet having a length of 10cm and a width of 10 cm.

3. The foamed sheet according to claim 1, wherein the content of the inorganic particles is 0.05 to 1.00 wt% based on the total weight of the foamed sheet.

4. The foamed sheet according to claim 1, wherein the inorganic particles are one or more selected from the group consisting of titanium dioxide, talc, silicon dioxide and zirconium dioxide.

5. The foamed sheet of claim 1, wherein the foamed sheet has an average cell density of from 800cells/cm2 to 25000cells/cm 2.

6. The foamed sheet according to claim 1, wherein the polyester resin is one or more selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polyethylene adipate, polylactic acid, and polyglycolic acid.

7. The foamed sheet according to claim 1, wherein the polyester resin further comprises carbon black in an amount of 0.05 to 5 wt% based on the total weight of the foamed sheet.

8. The foamed sheet according to claim 6, wherein the average size of carbon black is 10nm to 5000 nm.

9. A food container comprising the foamed sheet of claim 1,

the foamed sheet satisfies the following numerical formula 3,

mathematical formula 3: 15 percent of CV 1-CV 0/CV 0 multiplied by 100,

in the above-mentioned numerical expression 3,

CV0 is the volume of foamed sheet in cm3 before the food container is exposed to an oven at a temperature of 200 ℃ for 30 seconds,

CV1 is the volume of foamed sheet in cm3 after exposure of a food container to an oven at a temperature of 200 ℃ for 30 seconds.

10. A method for producing a foamed sheet, comprising a step of preparing a foamed sheet by extrusion foaming a resin mixture comprising a polyester resin and inorganic particles,

the inorganic particles have an average size of 0.05 to 60 μm,

the foamed sheet has an average cell size of 5 to 500 μm.

11. The method of producing a foamed sheet according to claim 10, wherein the polyester resin is obtained by polymerizing a dicarboxylic acid component and an ethylene glycol component, or by polymerizing a hydroxycarboxylic acid component.

12. The method of producing a foamed sheet according to claim 10, wherein in the step of producing a foamed sheet, a foamed sheet having an average thickness of 1mm to 10mm is formed.

13. The method of producing a foamed sheet according to claim 10, wherein the content of the inorganic particles is 0.05 to 1.00 wt% based on the total weight of the resin mixture.

14. The method of producing a foamed sheet according to claim 10, wherein the resin mixture further contains 0.05 to 5 wt% of carbon black based on the total weight of the resin mixture.

Technical Field

The present invention relates to a foamed sheet containing inorganic particles having excellent uniformity of cell formation and a method for preparing the same.

Background

Disposable food container products are generally classified into foamed and non-foamed types. In general, a foamed container is used in which polystyrene and a foaming gas are mixed and extruded, and the foamed container has advantages such as shape maintenance, thermal barrier property, and price advantage because the foamed container can maintain a large thickness, but has a problem of releasing substances harmful to the human body at a high temperature. Further, a product in a film form made of polypropylene which is stable to heat is used as a non-foamed container which has a low rate of change in shape at high temperature and in which harmful substances are not detected, but has disadvantages of high price and poor heat insulation effect.

A representative product most commonly used as a disposable heat-resistant container is a bowl-noodle container. Such a bowl-noodle container mostly uses the aforementioned polystyrene foam container, and an attempt is made to replace the container with a paper container. However, the paper container has a limitation in commercialization because of high manufacturing costs and a decrease in price competitiveness.

On the other hand, recently, with the increase of the population of the individual living, the demand for take-out foods and simple food products has been increasing, and the demand for economical disposable containers free of harmful substances has been increasing day by day.

Therefore, there is a need to develop a disposable container that is excellent in shape-maintaining property or thermal barrier property, convenient in design of appearance, excellent in visual effect, competitive in price, harmless to the human body, and environmentally friendly.

Disclosure of Invention

Technical problem

Accordingly, the present invention is to provide a material for disposable containers, which has excellent shape-maintaining ability or heat-insulating property, has price competitiveness, is harmless to the human body, and is environmentally friendly.

Technical scheme

In one embodiment of the present invention, the present invention provides a foamed sheet as a polyester resin containing inorganic particles, wherein the inorganic particles have an average size of 0.05 μm to 60 μm, the foamed sheet has an average cell size of 5 μm to 500 μm, the foamed sheet satisfies the following numerical formula 1,

mathematical formula 1: 50% ═ V₁－V₀|/V₀×100＝300％，

In the above mathematical formula 1, V₀Is the volume of a circular foamed sheet having a diameter of 10cm in cm before exposure to an oven having a temperature of 200 ℃ for 30 seconds³，V₁Is the volume of a circular foamed sheet with a diameter of 10cm in a baking oven at a temperature of 200 ℃ after being exposed for 30 seconds and has a unit of cm³。

Further, in one embodiment of the present invention, the present invention provides a food container comprising the above foamed sheet, wherein the foamed sheet satisfies the following numerical formula 3,

mathematical formula 3: [ CV ] of₁－CV₀|/CV₀×100＝15％，

In the above mathematical formula 3, CV₀Is the volume of the foamed sheet in cm before the food container is exposed in an oven at a temperature of 200 deg.C for 30 seconds³，CV₁Is the volume of the foamed sheet in cm after exposing the food container to an oven at a temperature of 200 deg.C for 30 seconds³。

Further, in one embodiment of the present invention, the present invention provides a method for preparing a foamed sheet, comprising the step of extrusion foaming a resin mixture comprising a polyester resin and inorganic particles to prepare a foamed sheet, wherein the inorganic particles have an average size of 0.05 μm to 60 μm, and the foamed sheet has an average cell size of 5 μm to 500 μm.

Advantageous effects

The foamed sheet of the present invention is formed of a polyester resin, and thus has a competitive price, is harmless to the human body, and is environmentally friendly. Further, the above foamed sheet is excellent in impact resistance and moldability, inorganic particles of a specific size are uniformly dispersed inside the polyester resin, so that the uniformity of cell formation of the foamed sheet is high, and the cell size can be adjusted according to the size of the inorganic particles.

Drawings

Fig. 1 is a picture taken by a Scanning Electron Microscope (SEM) with respect to examples and comparative examples.

Detailed Description

The present invention relates to a foamed sheet and a method for producing the same.

Recently, in order to replace foamed containers using polystyrene or non-foamed containers using polypropylene, foamed containers using polyester are being actively developed. However, when polyester is prepared into a foamed sheet, particularly polyethylene terephthalate (PET), foaming is induced by charging a nucleating agent base particle, but when a nucleating agent is charged alone, the dispersibility of the added nucleating agent is insufficient, which may cause a decrease in the uniformity of cells (cells) formed, and the content may become uneven due to an erroneous operation. Furthermore, the conventional polyethylene terephthalate foamed sheet has a lower melting point than the polystyrene foamed sheet, and therefore has a problem that it is difficult to mold the sheet at a molding temperature of polystyrene.

In order to improve such a problem, the present invention provides a foamed sheet comprising a polyester resin and a method for producing the same.

The foamed sheet of the present invention is formed of a polyester resin, and thus has a competitive price, is harmless to the human body, and is environmentally friendly. Further, the above foamed sheet is excellent in impact resistance and moldability, inorganic particles of a specific size are uniformly dispersed inside the polyester resin, so that the uniformity of cell formation of the foamed sheet is high, and the cell size can be adjusted according to the size of the inorganic particles.

The present invention will be described in more detail below.

Foamed sheet

In one embodiment of the present invention, as the foamed sheet of the polyester resin containing inorganic particles, the inorganic particles have an average size of 0.05 to 60 μm, the foamed sheet has an average cell size of 5 to 500 μm, and the foamed sheet satisfies the following numerical formula 1,

mathematical formula 1: 50% ═ V₁－V₀|/V₀×100＝300％，

In the above-mentioned mathematical formula 1,

V₀the volume of a circular foamed sheet having a diameter of 10cm, in cm, before exposure to an oven at a temperature of 200 ℃ for 30 seconds, is used as the volume of the foamed sheet³，

V₁The volume of a circular foamed sheet with a diameter of 10cm after exposure for 30 seconds in an oven at a temperature of 200 ℃ is expressed in cm³。

The foamed sheet of the present invention is a foamed sheet containing a polyester resin as a main component, and can have a structure in which inorganic particles are uniformly dispersed in a layer made of the polyester resin.

At this time, the content of the above inorganic particles accounts for 0.05 wt% to 1.00 wt% of the total weight of the foamed sheet, and more specifically, the content of the inorganic particles accounts for 0.05 wt% to 0.80 wt%, 0.05 wt% to 0.60 wt%, 0.05 wt% to 0.40 wt%, 0.10 wt% to 0.50 wt%, 0.15 wt% to 0.45 wt%, or 0.20 wt% to 0.40 wt% of the total weight of the foamed sheet.

Further, the above inorganic particles may be selected from titanium dioxide (TiO)₂) Talc powder (Talc), silicon dioxide (silica) and zirconium dioxide (ZrO)₂) One or more of the above substances. For example, the inorganic particles may be titanium dioxide, talc, or silica. The above inorganic particles have a role in increasing cell density by decreasing cell size when foaming a polyester resin.

Furthermore, the size of the above inorganic particles may be 0.05 to 60 μm, specifically 0.05 to 50 μm, 0.05 to 40 μm, 0.05 to 30 μm, 0.05 to 20 μm, 0.05 to 15 μm, 0.05 to 5 μm, 0.05 to 1 μm, 0.05 to 0.6 μm, 0.05 to 0.2 μm, 0.15 to 0.6 μm, 0.4 to 6 μm, 0.4 to 11 μm, 0.08 to 40 μm, 0.1 to 35 μm, 1 to 15 μm, 1 to 9 μm, 1 to 5 μm, 8 to 20 μm, 8 to 15 μm, 8 to 12 μm, 12 to 25 μm, 25 to 30 μm, or 45 μm. The present invention can easily control the foamability of cells and the cell size when foaming the polyester resin by controlling the size of the inorganic particles within the above range. For example, by uniformly dispersing the above inorganic particles in a polyester resin, the foamability of the resin is kept constant, and thus the uniformity of cells of the extruded sheet can be maintained, i.e., the dispersion of cell size is kept uniform. In addition, the smaller the size of the inorganic particles uniformly dispersed in the polyester resin, the smaller the cell size becomes, so that the cell density can be increased.

For example, the foamed sheet can have an average cell size of 5 μm to 500 μm, specifically 10 μm to 400 μm, 15 μm to 450 μm, 20 μm to 400 μm, 50 μm to 370 μm, 15 μm to 200 μm, 80 μm to 350 μm, 100 μm to 300 μm, 70 μm to 120 μm, 30 μm to 110 μm, 250 μm to 370 μm, 290 μm to 410 μm, 280 μm to 320 μm, 330 μm to 380 μm, 5 μm to 50 μm, or 5 μm to 30 μm.

In addition, since the cell size of the foamed sheet has excellent uniformity (formation uniformity), the average cell size and the deviation between the maximum cell size and the minimum cell size can be reduced. Specifically, for the foamed sheet of the present invention, the deviation between the largest cells and the smallest cells may be ± 65% or less, ± 60% or less, ± 50% or less, or ± 45% or less, based on the average cell size. As an example, in the case where the average cell size of the above foamed sheet is 10 μm, the maximum cell size may be 15 μm or less, and the minimum cell size may be 5 μm or more; in the case where the average cell size is 350 μm, the maximum cell size may be 500 μm or less, and the minimum cell size may be 200 μm or more.

Further, the foamed sheet may have an average cell density of 800cells/cm²To 25000cells/cm²Specifically 800cells/cm²To 23000cells/cm²、800cells/cm²Up to 20000cells/cm²、800cells/cm²To 15000cells/cm²、800cells/cm²To 11000cells/cm²、800cells/cm²To 8000cells/cm²、1000cells/cm²To 5500cells/cm²、4500cells/cm²To 6000cells/cm²、15000cells/cm²To 25000cells/cm²、20000cells/cm²To 2450 cells/cm²、21000cells/cm²To 2450 cells/cm²、900cells/cm²To 2000cells/cm²、900cells/cm²To 1800cells/cm²Or 1200cells/cm²To 1600cells/cm²。

Further, the foamed sheet satisfies mathematical formula 1.

Mathematical formula 1: 50% ═ V₁－V₀|/V₀×100＝300％，

In the above-mentioned mathematical formula 1,

V₀the volume of a circular foamed sheet having a diameter of 10cm, in cm, before exposure to an oven at a temperature of 200 ℃ for 30 seconds, is used as the volume of the foamed sheet³，

V₁The volume of a circular foamed sheet with a diameter of 10cm after exposure for 30 seconds in an oven at a temperature of 200 ℃ is expressed in cm³。

Specifically, when the volume change of the foamed sheet of the present invention is evaluated by measuring the dimensional change rate of the diameter and thickness before and after exposure to an oven at a temperature of 200 ℃ for 30 seconds, the dimensional change rate according to mathematical formula 1 may be in the range of 50% to 280%, 50% to 250%, 50% to 200%, 50% to 150%, 50% to 100%, 50% to 90%, 50% to 80%, 50% to 70%, 100% to 300%, 150% to 300%, 200% to 300%, 250% to 300%, 80% to 120%, 80% to 140%, 150% to 200%, 180% to 300%, 220% to 290%, 270% to 300%, 90% to 150%, 90% to 160%, 110% to 170%, 130% to 170%, 140% to 160%, 140% to 190%, 190% to 230%, 170% to 210%, 190% to 210%, 220% to 280%, 240% to 260%, or 230% to 280%.

Further, the above foamed sheet can achieve impact resistance suitable for food containers or food and drink containers by exhibiting a high average cell density. For example, the foamed sheet of the present invention has excellent impact resistance and satisfies the following equation 2.

Mathematical formula 2: | SV₁－SV₀|/SV₀×100＝20％，

In the above-mentioned numerical expression 2,

SV₀the volume of a foamed sheet before a ball having a diameter of 7cm and a weight of 500g was freely dropped from a height of 30cm to a length of 10cm and a width of 10cm, in cm³，

SV₁The volume of a foamed sheet after a ball having a diameter of 7cm and a weight of 500g was freely dropped from a height of 30cm to a foamed sheet having a length of 10cm and a width of 10cm, in cm³。

According to the above equation 2, the shape change rate is a value corresponding to the foamed sheet when it receives an external impact, and the volume represents a value obtained by multiplying the length, width, and thickness of the foamed sheet. When 500g of balls (diameter: 7cm) are freely dropped from a height of 30cm from the foamed sheet to the foamed sheet after cutting the foamed sheet (average thickness: 2.5mm) of the present invention at a length of 10cm and a width of 10cm, the rate of change in shape of the foamed sheet based on mathematical formula 2 may be in the range of 0.01 to 20%, 0.05 to 18%, 0.1 to 15%, 0.1 to 10%, or 0.1 to 5%, and may approach 0% as the case may be. The foamed sheet of the present invention can improve impact resistance by satisfying equation 2, i.e., does not deform or has a significantly low rate of shape change when subjected to external impact.

Further, the polyester resin of the foamed sheet contains carbon black (carbon black) in addition to the inorganic particles. At this time, the above carbon black may be present in an amount of 0.05 wt% to 5 wt%, specifically 0.05 wt% to 4.5 wt%, 0.05 wt% to 3.5 wt%, 0.05 wt% to 2.5 wt%, 0.05 wt% to 1.5 wt%, 0.05 wt% to 0.6 wt%, 0.05 wt% to 0.2 wt%, 0.4 wt% to 3.5 wt%, 0.4 wt% to 2.5 wt%, 0.4 wt% to 1.5 wt%, 0.8 wt% to 3.5 wt%, 0.8 wt% to 2.5 wt%, 0.8 wt% to 1.5 wt%, 0.8 wt% to 1.2 wt%, 1.2 wt% to 2.5 wt%, 1.8 wt% to 2.2 wt%, 2.2 wt% to 3.2 wt%, 2.3 wt% to 2.8 wt%, 2.7 wt% to 3.3 wt%, 0.3 wt% to 3.5 wt%, 0.8 wt%, 0.2 wt% to 3 wt%, or 0.5 wt% to 15 wt% of the total weight of the foamed sheet.

Further, the above carbon black may have an average size of 10nm to 5000nm, more specifically 20nm to 3500nm, 20nm to 2500nm, 20nm to 2000nm, 20nm to 1500nm, 20nm to 1000nm, 20nm to 800nm, 20nm to 400nm, 20nm to 200nm, 20nm to 80nm, 20nm to 50nm, 80nm to 3500nm, 80nm to 2500nm, 100nm to 1000nm, 80nm to 130nm, 400nm to 600nm, 450nm to 550nm, 800nm to 1200nm, 1000nm to 3000nm, 15nm to 200nm, or 25nm to 550 nm.

For example, the polyester resin of the present invention may comprise 1 ± 0.5 wt% of carbon black having an average size of 25nm to 35nm, relative to the total weight of the foamed sheet.

The present invention can shorten the working time at the time of molding by controlling the average size and content of carbon black in the polyester resin within the above ranges while improving the thermal properties and moldability of the foamed sheet comprising the polyester resin.

In addition, the foamed sheet of the present invention may have a certain specific resistance when measured. Specifically, the foamed sheet may have an average resistivity of 10⁷To 10¹⁴And more specifically 10⁷To 10¹³、5×10⁷To 10¹³、5×10⁷To 5 × 10¹²、10⁸To 10¹²Or 10⁹To 10¹²。

On the other hand, as described above, the foamed sheet of the present invention is advantageous in that it is price competitive as a polyester resin foamed sheet which does not discharge substances harmful to the human body at high temperatures.

The polyester resin may be an aromatic polyester resin or an aliphatic polyester resin obtained by polymerizing a dicarboxylic acid component and an ethylene glycol component or synthesized from a hydroxycarboxylic acid. For example, the polyester resin may include one or more selected from the group consisting of Polyethylene Terephthalate (PET), polybutylene Terephthalate (PBT), Polytrimethylene Terephthalate (PTT), Polyethylene naphthalate (PEN), Polyethylene adipate (PEA), polylactic acid (PLA), and Polyglycolic acid (PGA), and may specifically include Polyethylene Terephthalate.

Further, the foamed sheet of the present invention may have an average thickness of 1mm to 10 mm. Specifically, the thickness of the above foamed sheet may be 1.5mm to 9.0mm, 2.0mm to 8.0mm, 1.5mm to 5.0mm, or 2.0mm to 7.0 mm.

Food container

In addition, in one embodiment of the present invention, the present invention provides a food container including the above foamed sheet, and the foamed sheet satisfies the following equation 3.

Mathematical formula 3: [ CV ] of₁－CV₀|/CV₀×100＝15％，

In the above-mentioned numerical expression 3,

CV₀the volume of the foamed sheet in cm before the food container was exposed to an oven at a temperature of 200 ℃ for 30 seconds³，

CV₁The volume of the foamed sheet after exposure of the food container to an oven at a temperature of 200 ℃ for 30 seconds is expressed in cm³。

The food container of the present invention, which comprises the above foamed sheet, exhibits only a small change in volume even when exposed to an oven at a temperature of 200 ℃ for 30 seconds, because of its excellent heat resistance.

Specifically, the dimensional change rate of the above food container was measured before and after 30 seconds of exposure to an oven at a temperature of 200 ℃. The rate of change may be a rate of dimensional change measured under conditions corresponding to the actual environment in which the food container is used or under more severe conditions. The volume is, for example, a value obtained by multiplying the length, width and thickness of the food container. The food container of the present invention may have a dimensional change rate based on math figure 3 in the range of 0.01% to 10%, 0.01% to 5%, 0.01% to 3%, or 0.01% to 1%. By satisfying the value obtained by the equation 3 in the above range, it is understood that the foamed sheet of the present invention hardly undergoes a change in shape even when used in a high-temperature environment. In summary, the food container of the present invention has excellent heat resistance.

Method for producing foamed sheet

Further, in one embodiment of the present invention, the present invention provides a method for preparing a foamed sheet, comprising the step of extrusion foaming a resin mixture comprising a polyester resin and inorganic particles to prepare a foamed sheet, wherein the inorganic particles have an average size of 0.05 μm to 60 μm, and the foamed sheet has an average cell size of 5 μm to 500 μm.

In the method for producing a foamed sheet of the present invention, when extrusion foaming is performed, inorganic particles having a specific size are uniformly mixed to a polyester resin to increase the uniformity of cell expression of the foamed sheet and control the cell size to be small.

In this case, the polyester resin may be prepared from raw material components generally used in the art. Specifically, the polyester resin can be obtained by reacting a dicarboxylic acid component and an ethylene glycol component or by reacting a hydroxycarboxylic acid component.

Among them, as the dicarboxylic acid component, one or more selected from terephthalic acid (terephthalic acid), naphthalenedicarboxylic acid (naphthalene dicarboxylic acid) and adipic acid (adipic acid) may be used.

The ethylene glycol component may be one or more selected from ethylene glycol (ethylene glycol), butylene glycol (butylene glycol), and propylene glycol (propylene glycol).

In addition, as the hydroxycarboxylic acid component, one or more selected from lactic acid (lactic acid) and glycolic acid (glycolic acid) can be used, but not limited thereto.

According to one embodiment, the polyester resin used in the present invention may be polyethylene terephthalate obtained by reacting terephthalic acid and ethylene glycol.

In addition, the inorganic particles contained in the above resin mixture may be one or more selected from the group consisting of titanium dioxide, talc, silicon dioxide and zirconium dioxide, and the content of the inorganic particles may be 0.05 wt% to 1.00 wt% based on the total weight of the resin mixture. Meanwhile, the average size of the above inorganic particles may be 0.05 μm to 60 μm. The present invention can improve the uniformity of cells of a foamed sheet by including inorganic particles having the above composition in a resin mixture, and when a polyester resin is foamed, the cell size can be reduced according to the average size of the inorganic particles to improve the cell density.

In one aspect, the resin mixture may further contain carbon black in addition to the inorganic particles. At this time, the above carbon black may be contained in an amount of 0.05 wt% to 5 wt% of the total weight of the resin mixture, specifically, 0.05 wt% to 4.5 wt%, 0.05 wt% to 3.5 wt%, 0.05 wt% to 2.5 wt%, 0.05 wt% to 1.5 wt%, 0.05 wt% to 0.6 wt%, 0.05 wt% to 0.2 wt%, 0.4 wt% to 3.5 wt%, 0.4 wt% to 2.5 wt%, 0.4 wt% to 1.5 wt%, 0.8 wt% to 3.5 wt%, 0.8 wt% to 2.5 wt%, 0.8 wt% to 1.5 wt%, 0.8 wt% to 1.2 wt%, 1.2 wt% to 2.5 wt%, 1.8 wt% to 2.2 wt%, 2.2 wt% to 3.2 wt%, 2.3 wt% to 2.8 wt%, 2.7 wt% to 3.2 wt%, 0.5 wt% to 3.5 wt%, or 0.05 wt% to 3.5 wt% of the total weight of the resin mixture.

In another aspect, the carbon black can have an average size of 10nm to 5000nm, more specifically 20nm to 3500nm, 20nm to 2500nm, 20nm to 2000nm, 20nm to 1500nm, 20nm to 1000nm, 20nm to 800nm, 20nm to 400nm, 20nm to 200nm, 20nm to 80nm, 20nm to 50nm, 80nm to 3500nm, 80nm to 2500nm, 100nm to 1000nm, 80nm to 130nm, 400nm to 600nm, 450nm to 550nm, 800nm to 1200nm, 1000nm to 3000nm, 15nm to 200nm, or 25nm to 550 nm.

According to the present invention, when extrusion foaming is performed on a resin mixture, by uniformly mixing carbon black to the resin mixture, thermal properties and moldability of a foamed sheet are simultaneously improved, and working time can also be shortened.

On the other hand, the polyester resin may be introduced in the form of pellets (pellet), granules (grain), beads (bead), chips (chip), powder (powder), or the like, and may be introduced in a molten state in some cases.

According to one embodiment, the polyester resin may be introduced into the extruder in a chip form, and in this case, in order to melt the resin chips (resin chips), the melting process of the resin chips may be performed at a temperature of 260 to 300 ℃.

In the step of preparing the foamed sheet, in order to realize the function of the foamed sheet, when the polyester resin is introduced into the extruder, additives in various forms may be added to the fluid connection line or added in the foaming step as necessary.

Specifically, the above-mentioned additive may impart Barrier (Barrier) properties, hydrophilization functions or waterproofing functions to the foamed sheet, and may include a substance containing one or more selected from the group consisting of a thickener, a surfactant, a hydrophilizing agent, a heat stabilizer, a water repellent, a cell size enlarging agent, an infrared ray attenuating agent, a plasticizer, a fire-retardant chemical, a pigment, an elastic polymer, an extrusion aid, an antioxidant, a nucleating agent, an air discharge preventing agent and an Ultraviolet (UV) absorbing agent.

According to one embodiment, in the method for producing a foamed sheet of the present invention, one or more of a thickener, a nucleating agent, a heat stabilizer, and a foaming agent may be added, and one or more of the above-exemplified functional additives may be further included.

The thickener is not particularly limited, and pyromellitic dianhydride (PMDA) can be used in the present invention.

Further, the heat stabilizer may be an organic phosphorus compound or an inorganic phosphorus compound. For example, the above-mentioned organic phosphorus compound or inorganic phosphorus compound may be phosphoric acid and organic esters thereof, phosphorous acid and organic esters thereof. For example, the heat stabilizer may be a commercially available one, and the heat stabilizer may be phosphoric acid, alkyl phosphate ester or aryl phosphate ester, and more specifically, the heat stabilizer of the present invention may be triphenyl phosphate, but is not limited thereto.

Further, an example of the blowing agent is nitrogen (N)₂) Carbon dioxide (CO)₂) Physical blowing agents such as freon, butane, pentane, neopentane, hexane, isohexane, n-heptane, isoheptane and chloromethane, azodicarbonamide (azodicarbonamide), p '-oxo (benzenesulfonylhydrazide) [ p, p' -oxy bis (phenyl sulfonyl hydrazide) ]]Chemical foaming agents such as N, N '-dinitrosopentamethylene tetramine (N, N' -dinitrosopentamethylene tetramine) compounds. Specifically, carbon dioxide may be used in the present invention.

Meanwhile, the present invention can be realized by using extruders of various forms. The foaming step can be usually carried out by bead foaming or extrusion foaming, but in the present invention, extrusion foaming is preferably employed. Since the extrusion foaming enables the resin mixture to be continuously extruded and foamed, the process steps can be simplified, mass production can be achieved, and phenomena such as cracks between beads and particle breakage generated during bead foaming can be prevented, thereby achieving more excellent bending strength and compression strength.

Further, the foamed sheet prepared in the present invention may be a foamed board and/or a foamed sheet, and the average thickness may be 1mm to 10mm, 1.5mm to 9.0mm, 2.0mm to 8.0mm, 1.5mm to 5.0mm, or 2mm to 7.0 mm.