JP3080208B2 - Method for producing polyester resin foam sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foamed polyester resin sheet, and more particularly to a method for producing a resin sheet without roughening the surface of the sheet and without adhering resin decomposition products to the sheet surface.
The present invention relates to a method for producing a polyester resin foam sheet having excellent appearance.

[0002]

2. Description of the Related Art As a method for producing a polyester resin foam sheet, an extrusion foaming method has been widely used. This extrusion foaming method is applied not only to a polyester-based resin but also to other thermoplastic resins such as a polystyrene-based resin, and is widely known as a method for producing a resin foamed sheet. Briefly, this method is as follows: a thermoplastic resin is melt-mixed together with a foaming agent in an extruder, and the molten mixture (hereinafter, also simply referred to as a resin melt) is formed into an annular shape of a die attached to a tip end of the extruder. Is extruded from the gap to an external low-pressure region and foamed. Thereafter, the tubular foamed sheet obtained by the foaming is cooled and cut to obtain a product. FIG. 3 is a schematic cross-sectional view showing the configuration of a main part of a conventional apparatus used in the extrusion foaming method. In the drawing, reference numeral 10 denotes a die, which is constituted by a core 1 and an out ring 2; An annular gap (hereinafter, also simply referred to as a resin flow path) 3 is formed between the outer ring 2 and the outer ring 2. Reference numeral 4 denotes a cylindrical foam sheet, and reference numeral 5 denotes a cylindrical cooling mandrel for expanding the inner diameter of the cylindrical foam sheet 4 and cooling the cylindrical foam sheet 4.

Here, the die 10 is generally obtained by processing a metal lump such as iron, copper, or the like into a required shape, and such a die 10 is conventionally used for producing a polyester resin foam sheet. Metal dies are used. still,
Although the extruder is not shown in the drawing, the die 10 is attached to the tip of the extruder, and a resin melt is supplied to the resin flow path 3 from the extruder.

When a foamed sheet is manufactured by the extrusion foaming method, the resin melt flowing through the resin flow path 3 in the die 10 is supplied from the outlet of the resin flow path 3 to an external low-pressure region. When extruded, it is necessary that a pressure necessary for foaming the resin melt is applied. Polyester resin is a crystalline resin, has the property that it melts rapidly by heating, and the melt becomes a low-viscosity liquid material.When using a polyester resin, for example, a polystyrene resin is used. By increasing the flow rate of the resin melt flowing in the resin flow path 3, that is, by increasing the extrusion speed, as compared with the case where a resin having a higher viscosity of the melt than that of the polyester resin is used, In particular, a sufficient pressure is applied to the resin melt near the outlet of the resin flow path 3.

[0005]

However, if the resin melt of the polyester resin is extruded at a high speed, it is necessary to apply a sufficient pressure to the resin melt so that the resin melt can foam. While it is possible to produce the foamed sheet with high production efficiency, the wall surface forming the out ring 2 of the die 10 and the resin flow path 3 of the core 1 has a metal surface obtained by processing metal. If left as it is, the frictional resistance between the wall surface and the resin melt flowing at a high speed becomes too large, and heat is generated between them to generate a decomposed product of the resin (hereinafter, referred to as a metal mold). As a result, However, the eye mold adheres to the surface of the foamed sheet, causing a problem that the appearance of the sheet is deteriorated.

On the other hand, Japanese Patent Application Laid-Open No. 4-345820 discloses that in a method for producing a polystyrene-based resin foam sheet, the frictional resistance between a wall constituting a resin flow path of a die and a resin melt flowing through the resin flow path is reduced. In order to reduce the size, there has been proposed a configuration in which the surface of the core forming the die and / or the resin flow path of the out ring is formed of zirconia ceramic (hereinafter, simply referred to as zirconia) having an extremely small friction coefficient. ing.

[0007] However, using a die described in this publication, in which the walls constituting both the core and the outer ring resin flow paths are formed of zirconia having an extremely small friction coefficient, a resin melt of the polyester resin is formed. When extruded, the frictional resistance between the wall of the resin flow path and the resin melt becomes too small. Therefore, even if the resin melt is extruded at a high speed, an opening (outlet) toward the outside (low-pressure region) of the resin flow path.
In the resin melt can not apply sufficient pressure, as a result, the resin melt foams in the resin flow path,
Only sheets with a rough appearance could be obtained.
In addition, when using a die in which the wall forming one of the resin flow paths of the core or the out ring is formed of zirconia ceramic, foaming of the resin melt does not occur in the resin flow path, but the resin flow path Since the difference in frictional resistance applied to the resin melt between the core side and the outer ring side becomes too large, the flow state of the resin melt is disturbed, causing melt fracture and obtaining only a sheet having a rough appearance. could not. In particular, in the case of using a die in which only the wall forming the resin flow path of the out ring is formed of zirconia ceramic, FIG.
A, that is, the space surrounded by the foam sheet 4 between the cooling mandrel 5 and the core 1 tends to trap heat, and the temperature of the core 1 itself increases with the elapse of the manufacturing time. When frictional heat is generated between the resin melt and the wall surface constituting the resin flow path of the core 1 in the state of the metal surface, a decomposition product of the resin is generated with the lapse of the manufacturing time, and the surface of the foamed sheet still remains. However, there is a problem that the eyes and the eyes are adhered to the surface.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is a polyester resin having an excellent appearance without causing roughness on the sheet surface and without adhering of resin decomposed products to the sheet surface. An object of the present invention is to provide a method for manufacturing a foamed sheet.

[0009]

According to a method of manufacturing a polyester resin foam sheet according to the present invention, a wall constituting a resin flow path of a core is made of one of zirconia, alumina and titania, or two or more of them. The mixture was melt-mixed with a polyester resin and a foaming agent at a temperature higher than the melting point of the polyester resin by at least 10 ° C. using a die formed by plating the wall surface constituting the resin channel of the out ring. The resin melt is extruded through the resin flow path so that the flow rate per 1 cm ² of the opening area of the resin flow path becomes 30 liter / hr or more.

[0010]

According to the present invention, by adopting the above structure, a resin melt of a polyester resin is foamed into a cylindrical shape without causing decomposition, foaming, and melt fracture of the resin in the resin flow path. Can be.
Such a configuration has been obtained by many experiments such as the test examples described below, and its operation is presumed as follows.

That is, the wall constituting the resin flow path of the core is formed of one of zirconia, alumina and titania having an extremely small coefficient of friction, or a mixture of two or more of these, and the resin flow path of the out ring is formed. The plating of the constituting wall has a coefficient of friction smaller than that of a metal surface obtained by processing a metal lump, and is larger than that of one of the above-mentioned zirconia, alumina, titania, or a mixture of two or more thereof. , A moderate frictional resistance can be applied to the resin melt of the low-viscosity polyester resin flowing at a high speed in the resin flow path, and the entire resin melt is formed in the resin flow path. And an appropriate pressure that does not cause foaming can be applied.

Further, the above resin melt and the above zirconia,
Friction resistance generated between a core-side wall surface formed of either alumina or titania or a mixture of two or more thereof, and an out-ring-side wall surface formed by the resin melt and the plating Since the difference between the frictional resistance and the frictional resistance does not become large, the flow state of the resin melt is not disturbed, and no melt fracture occurs.

Further, since the wall surface of the resin flow path of the core is formed of one of zirconia, alumina, and titania having a very small coefficient of friction, or a mixture of two or more of them. The frictional heat generated between the wall surface and the resin melt is extremely small, so that even if the temperature of the core itself increases with the elapse of the manufacturing time, no heat is generated to cause the decomposition of the resin.

[0014]

Embodiments of the present invention will be described below.
FIG. 1 is a schematic sectional view showing the configuration of a main part including a die of an apparatus applied to the method of the present invention. In the figure, the same reference numerals as those in FIG. 3 indicate the same or corresponding parts.
20 is a die, 1 is a core, and this is a core body 1a.
And a layer 1b that forms the wall surface of the resin flow path 3 and is made of any one of zirconia, alumina, and titania, or a mixture of two or more of them. 2a is an out ring, which is composed of an out ring main body 2a and a plating layer 2b forming a wall surface of the resin flow path 3. Here, the layer 1b made of any one of zirconia, alumina, titania, or a mixture of two or more of them is, for example, a plate-like zirconia, alumina obtained by firing to a thickness of 0.05 mm or more. , Titania, or a mixture of two or more of them is fixed to the core body 1a by baking, bonding, caulking, or the like, or the core body 1a has a thickness of 0.0
It is formed by spraying any one of zirconia, alumina, and titania, or a mixture of two or more of them so as to have a thickness of 5 mm or more.

When the layer 1b made of any of the above-mentioned zirconia, alumina, titania, or a mixture of two or more of them is formed by thermal spraying, air bubbles are involved in the thermal spraying, so that a plate-like shape such as shrink fit is used. The surface becomes rougher and the coefficient of friction increases (but smaller than the coefficient of friction of the plating layer) as compared with the case where any one of zirconia, alumina and titania or a mixture of two or more of them is fixed. ). The plating layer 2b is formed by electrolytic plating or electroless plating, and has a surface with a higher coefficient of friction than that of the zirconia layer 1b.
It is much smaller than a metal surface obtained by processing a metal lump such as iron or copper. The type of plating is not particularly limited, but chromium plating is preferred in terms of workability and cost. It is sufficient that the thickness of the plating layer 2b is 0.03 mm or more, and its surface finish is 6.3S (JIS standard II).
Ii) It is better to do above. The size of the resin flow path 3, that is, the size of the annular gap is not particularly limited. It is preferred in that respect.

The polyester resin used in the practice of the present invention is a chain polymer obtained by polycondensation of an aromatic dicarboxylic acid component and a diol component.
Examples thereof include polyethylene terephthalate, polybutylene terephthalate, polycyclohexane terephthalate, and polynaphthalene terephthalate. Since these polyester resins are generally easily hydrolyzed resins, they are preferably dried in advance by a dehumidifying dryer or the like before being melted and mixed by an extruder.

Examples of the foaming agent include inert gas, saturated aliphatic hydrocarbon, saturated alicyclic hydrocarbon, aromatic hydrocarbon, halogenated hydrocarbon, ether, ketone, water, alcohol and the like. . Specifically, carbon dioxide, nitrogen, methane, ethane, normal butane, isobutane, isopentane, neopentane, normal hexane,
2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, methylcyclopropane, cyclopentane, 1,1-dimethylcyclopropane, cyclohexane, methylcyclopentane, ethylcyclobutane, 1, 1,2-trimethylcyclopropane, benzene, trichloromonofluoromethane, dichlorofluoromethane, monochlorodifluoromethane, trichlorotrifluoroethylene, dichlorotetrafluoroethylene, dimethyl ether, methyl tert-butyl ether, acetone, ethyl methyl ketone, acetylacetone, etc. Can be mentioned. Among them, preferred foaming agents include normal butane, isobutane, normal pentane, isopentane, nitrogen, dimethyl ether, methyl tert-butyl ether and the like. These foaming agents are used in an amount of 0.1 to 100 parts by weight of the polyester resin.
It is used in a proportion of 1 to 5.0 parts by weight. When a resin having a high foaming rate such as nitrogen or carbon dioxide gas is used, the resin melt easily foams in the resin flow path 3 of the die 20. In order to increase the pressure (friction resistance) applied to the resin melt, the core 1
It is preferable to use any one of zirconia, alumina, and titania constituting the wall surface of the resin channel 3 or a layer formed by spraying a layer 1b made of a mixture of two or more of them.

In the practice of the present invention, not only the foaming agent but also other additives besides the foaming agent can be added to the melt of the polyester resin, if necessary. For example, as a viscosity modifier, an acid dianhydride such as pyromellitic anhydride, a metal compound of Group Ia of the periodic table such as sodium carbonate, or the like is added in an amount of 0.1 to 100 parts by weight of the polyester resin.
２．０2.0 parts by weight, or a small amount of talc powder as a foam control agent (foam nucleating agent).

In the embodiment of the present invention, the temperature of the molten mixture is set to a temperature higher than the melting point of the polyester resin by 10 ° C. or more, and the molten mixture is cooled per 1 cm ² of the opening area of the outlet of the resin flow path 3 of the die 20. Flow rate 30 liter / hr
Extrusion is performed as described above. However, if the extrusion speed is lower than this, the pressure applied to the molten mixture in the resin flow path 3 becomes too small, and foaming tends to occur in the resin flow path 3. Further, the temperature of the molten mixture is from the melting point of the polyester resin to the melting point of the polyester resin + 1.
When the temperature is in the range of 0 ° C., the viscosity of the molten mixture increases, and when the molten mixture is extruded so that the flow rate per 1 cm ² of the opening area of the outlet of the resin flow path 3 becomes 30 liters / hr or more, Such shear stress becomes too large, and tends to easily generate melt fracture.

FIG. 2 schematically shows an example of the overall configuration of an apparatus applied to the method of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts. In operation, the polyester resin and an additive such as a viscosity modifier charged into the single screw extruder 30 from the hopper 30a are melt-mixed in the extruder 30, and the molten mixture is mixed with an extruder (not shown). The foaming agent is press-fitted from the portion and mixed. This mixture is then transferred to the die 20
To the resin flow path 3. Then, the molten mixture guided to the resin flow path 3 is formed into a cylindrical shape in the atmosphere with an extrusion amount of 30 liters / hr or more per 1 cm ² of the opening area of the exit of the die 20, that is, the resin flow path 3. And foamed at the same time. Here, the molten mixture extruded into the air in a cylindrical shape is maintained at a temperature higher than the melting point of the polyester resin by 10 ° C. or more. Next, the cylindrical polyester resin foam sheet 4 obtained by the foaming is used.
After being cooled by the cooling mandrel 5, a predetermined portion thereof is cut by a cutter 6, developed in a planar shape, pulled by a take-up roll 7, and wound up in a roll shape to form a product 4a.

[0021]

Test Examples Hereinafter, the present invention will be described in more detail with reference to test examples of the present invention.

Test Example 1 First, PET with a melting point of 255 ° C
After drying (polyethylene terephthalate) resin TR8580 (trade name, manufactured by Teijin Limited) with a dehumidifying dryer,
ET resin TR8580 (100 parts by weight), talc (1.
0 parts by weight), sodium carbonate (0.05 parts by weight), and pyromellitic anhydride (0.35 parts by weight) were mixed with a tumbler.

Next, the obtained mixture was mixed with a single screw extruder (diameter: 65 mm, L / D: 3) of the apparatus shown in FIG.
5) Put into the inside, screw rotation speed is about 30 rpm, extruder supply section temperature is 280 ° C, extruder compression section temperature is 285 ° C, extruder melting section temperature is 267 ° C, extruder head Was sufficiently mixed at a temperature of 267 ° C., and 0.8 part by weight of butane as a foaming agent was injected into the molten mixture from the middle of the barrel.

Then, the molten mixture into which butane has been pressed is passed through the head portion of an extruder, and the core body is formed by processing an iron lump. A core made of a zirconia layer having a thickness of 0.1 mm formed by thermal spraying of zirconia, and an outring body made of an iron lump formed by processing an iron lump, and a wall surface constituting the resin flow path is formed on the outring body. thickness was formed by electroplating 0.02 mm, constituted by an out ring made of chromium-plated layer on the surface finish R _MAX 0.8S (JIS standard ▽▽▽▽), bore diameter 80φ
mm, an annular gap (resin flow path) was supplied to a resin flow path of a die having a diameter of 0.5 mm, and was extruded from the resin flow path into the atmosphere to form a cylindrical foamed sheet. At this time, the extrusion speed is 1 cm of opening area of the resin flow path outlet of the die per hour.
The temperature of the resin melt flowing out from the exit of the resin flow path of the die was 277 ° C. at an extrusion speed at which the extrusion amount per ² became 37.6 liters.

Then, the foam extruded from the die proceeds along the outer peripheral surface of a cooling mandrel having an outer diameter of 205 mm, is cooled, cut by a cutter, and cut into a polyester resin foam sheet. Was wound up.

The obtained foam sheet has a thickness of 1.0 mm,
At a density of 0.3 g / cc, the foamed sheet was observed for 2 hours from 4 hours after the start of extrusion. The sheet had no external stains and had a beautiful appearance.

Test Example 2 A foamed sheet was obtained in exactly the same manner as in Test Example 1, except that 0.20 part by weight of nitrogen was used as a foaming agent instead of butane in Test Example 1 per 100 parts by weight of the PET resin.

The obtained foam sheet has a thickness of 0.8 mm,
At a density of 0.38 g / cc, the foamed sheet was observed for 2 hours from 4 hours after the start of extrusion, but the sheet was beautiful with no eyes and tans.

Test Example 3 In the die of Test Example 2, the core whose wall constituting the resin flow path was formed of a zirconia layer was replaced with the core whose wall constituting the resin flow path was formed of an alumina layer having a thickness of 0.1 mm. A foamed sheet was obtained in exactly the same manner as in Test Example 2, except that the core body obtained by processing was sprayed with alumina to form an alumina layer having a thickness of 0.1 mm.

The obtained foam sheet has a thickness of 0.8 mm,
At a density of 0.38 g / cc, the foamed sheet was observed for 2 hours from 4 hours after the start of extrusion, but the sheet was beautiful with no eyes and tans.

Test Example 4 In the die of Test Example 2, a core whose wall constituting the resin flow path was formed of a zirconia layer was replaced with a core whose wall constituting the resin flow path was formed of a titania layer having a thickness of 0.1 mm. A foamed sheet was obtained in exactly the same manner as in Test Example 2, except that the core body obtained by processing was sprayed with titania to form a titania layer having a thickness of 0.1 mm).

The obtained foam sheet has a thickness of 0.8 mm,
At a density of 0.38 g / cc, the foamed sheet was observed for 2 hours from 4 hours after the start of extrusion, but the sheet was beautiful with no eyes and tans.

Test Example 5 The core of the die in Test Example 2 whose wall constituting the resin flow path was formed of a zirconia layer was a mixture of 13% by weight of titania and 8713% by weight of alumina having a wall thickness of 0.1 mm. (A core body obtained by processing an iron lump is sprayed with a mixture of 13% by weight of titania and 8713% by weight of alumina to form a 0.1 mm thick layer of a mixture of titania and alumina. A foamed sheet was obtained in exactly the same manner as in Test Example 2 except that the foamed sheet was changed to that formed.

The obtained foam sheet has a thickness of 0.8 mm.
At a density of 0.38 g / cc, the foamed sheet was observed for 2 hours from 4 hours after the start of extrusion, but the sheet was beautiful with no eyes and tans.

Test Example 6 In the die of Test Example 1, a core having a resin flow path formed by a zirconia layer was used as a core, and a resin flow path being formed by a chrome-plated core (obtained by processing an iron lump). The core body has a thickness of 0.02 mm by electroplating and a surface finish of R _MAX 0.
A foamed sheet was obtained in exactly the same manner as in Test Example 1 except that the chromium plating layer of 8S (JIS standard II) was used.

The obtained foamed sheet was 1.0 mm thick and had a density of 0.3 g / cc. The foamed sheet was observed for 2 hours from 4 hours after the start of extrusion.

Test Example 7 In the die of Test Example 1, the out ring having the resin flow path formed of a chrome plated layer on the wall forming the resin flow path, and the out ring having the 0.1 mm thick zirconia layer formed on the wall forming the resin flow path were used. A foam sheet was obtained in exactly the same manner as in Test Example 1, except that zirconia was sprayed on the outring body obtained by processing an iron lump to form a zirconia layer having a thickness of 0.1 mm. .

The obtained foamed sheet was 1.0 mm thick and had a density of 0.4 g / cc. The foamed sheet was observed for 2 hours after 4 hours from the start of extrusion. It was a bad foam sheet.

Test Example 8 A core whose wall constituting the resin flow path is formed of a chromium plating layer (a core body obtained by processing an iron lump has a thickness of 0.02 mm by electrolytic plating and a surface finish of R _MAX 0.8S (JIS standard) ▽▽▽▽) A chrome-plated layer is formed) and an outer ring (wall of the resin flow path is formed of a zirconia layer) (A zirconia layer having a thickness of 0.1 mm formed by thermal spraying) was used, and a foamed sheet was obtained in exactly the same manner as in Test Example 1.

The obtained foamed sheet had a thickness of 1.0 mm and a density of 0.3 g / cc. The foamed sheet was observed for 2 hours after 4 hours from the start of extrusion, and 88 dusts were generated.

Test Example 9 In the die of Test Example 1, the outer ring whose wall constituting the resin flow path was formed of a chromium plating layer was used for the out ring whose wall constituting the resin flow path was a metal surface. Except that the foamed sheet was obtained in the same manner as in Test Example 1.

The obtained foamed sheet was 1.0 mm thick and had a density of 0.3 g / cc. The foamed sheet was observed for 2 hours from 4 hours after the start of extrusion. The foamed sheet was rough in appearance due to melt fracture and had a poor appearance. Was.

Test Example 10 A core whose wall surface constituting the resin flow path is a metal surface (the core body is used as it is), and a wall surface forming the resin flow path has a thickness of 0.1 mm
Using a die consisting of an out ring formed of a zirconia layer of (a zirconia layer having a thickness of 0.1 mm formed by spraying zirconia on an out ring body obtained by processing an iron lump), A foam sheet was obtained in exactly the same manner as in Test Example 1.

The obtained foamed sheet was 1.0 mm thick and had a density of 0.3 g / cc. The foamed sheet was observed for 2 hours after 4 hours from the start of extrusion. It was a rough foamed sheet with bad appearance.

[0045]

As described above, according to the method for producing a polyester resin foam sheet according to the present invention, the core-side wall surface has one of zirconia, alumina and titania having an extremely small coefficient of friction, or any of these. A resin whose outer ring side wall has a coefficient of friction smaller than that of a metal surface obtained by processing a metal lump, and which is formed by plating larger than that of the above zirconia. Through a flow path, a resin melt of a low-viscosity polyester-based resin melted at a temperature higher than the melting point of the polyester-based resin by 10 ° C. or more is passed through the resin flow path at an opening area of 1 cm.
^Since the extruder was extruded at a high speed such that the flow rate per ² became 30 liters / hr or more, an appropriate pressure that did not cause foaming of the entire resin melt was applied, and the flow state of the resin melt was Can be prevented, and even if the temperature of the core becomes high, heat generation such as decomposition of the resin melt into the resin does not occur.
Therefore, the resin melt made of the polyester resin passes through the resin flow path and foams without generating foaming, resin decomposition, and melt fracture in the resin flow path, and as a result, the sheet There is an effect that a polyester-based foam sheet having a beautiful appearance and having no surface roughness and having no adhesion of the eyes to the surface can be produced with high production efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration of a main part including a die of a manufacturing apparatus used when carrying out a manufacturing method of the present invention.

FIG. 2 is a diagram schematically showing an example of the entire configuration of a manufacturing apparatus used when carrying out the manufacturing method of the present invention.

FIG. 3 is a schematic cross-sectional view showing a configuration of a main part including a die of a manufacturing apparatus used for manufacturing a foamed sheet by a conventional extrusion foaming method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Core 1a Core main body 1b Layer which comprises the wall surface of resin flow path which consists of any one of zirconia, alumina, titania, or a mixture of two or more of these 2 Out ring 2a Out ring main body 2b Wall surface of resin flow path 3 Annular gap (resin flow path) 4 Cylindrical foam sheet 4a Foam sheet (product) 5 Cylindrical cooling mandrel 6 Cutter 7 Take-up roll 10,20 Die 30 Single screw extruder 30a Hopper

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-3-142203 (JP, A) JP-A-63-102918 (JP, A) JP-A-3-215016 (JP, A) (58) Survey Field (Int. Cl. ⁷ , DB name) B29C 47/00-47/96

Claims (1)

(57) [Claims] 1. A low pressure of a molten mixture of a polyester resin and a foaming agent melt-mixed in an extruder through an annular gap formed by an out ring and a core of a die attached to a tip of the extruder. Extruded and foamed in the region, the cylindrical resin foam sheet obtained by the foaming,
A method for manufacturing a polyester resin foam sheet along the outer periphery of a cylindrical cooling mandrel, wherein a surface of the core in the annular gap that contacts the molten mixture is selected from the group consisting of zirconia, alumina, and titania. Formed from a mixture of two or more of
The surface of the out ring, which is in contact with the molten mixture, is formed by plating. The molten mixture is brought to a temperature higher than the melting point of the polyester resin by 10 ° C. or more, and the opening area of the annular gap is 1 cm ^2. A method for producing a foamed sheet of a polyester resin, wherein the extruded sheet is extruded at a flow rate of 30 liter / hr or more.