JP2006007511A - Manufacturing method of foamed sheet made of propylene resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a foamed sheet made of a propylene resin having a smooth surface. <P>SOLUTION: A molten foamed sheet made of the propylene resin, which is obtained by melting and kneading the propylene resin and a foaming agent in an extruder and extruding the molten kneaded mixture into the atmosphere from a circular die, is passed through an inner cylindrical part and an outer cylindrical part to be brought into contact with the outer wall surface of the inner cylindrical part and the inner wall surface of the outer cylindrical part to manufacture the foamed sheet made of the propylene resin. A plurality of holes are provided to the inner wall surface of the outer cylindrical part and the space between the molten foamed sheet made of the propylene resin and the outer cylindrical part is depressurized through the holes to bring the molten foamed sheet made of the propylene resin into contact with the inner wall surface of the outer cylindrical part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a propylene-based resin foam sheet.

Foamed sheets made of propylene-based resins are excellent in heat insulation, light weight, heat resistance, and recyclability, and are therefore used in a wide range of fields such as food packaging containers and automobile members. In particular, when a propylene-based resin foam sheet is manufactured using a circular die, a method of manufacturing the melted foam sheet extruded from the die by bringing it into contact with the cylindrical inner cylinder portion and cooling is common. According to this method, the sheet surface in contact with the inner cylinder portion of the obtained foamed sheet is smoothed, but the sheet surface not in contact with the inner cylinder portion is naturally cooled in the atmosphere, so that it contacts with the inner cylinder portion. The smoothness was often inferior to the surface.
As a method for obtaining a foam sheet having a smooth surface, a method is known in which an outer mandrel whose temperature is adjusted by cooling water is applied to the surface of a foam sheet having a surface temperature of 70 ° C. to 160 ° C. (see, for example, Patent Document 1).

JP 2001-328155 A

However, in the above method, since it is difficult to make the outer mandrel and the foamed sheet contact uniformly, the surface is smoother than the foamed sheet obtained without applying the outer mandrel, but the smoothness is still insufficient. Met.
An object of the present invention is to provide a method for producing a propylene-based resin foam sheet having a smooth surface.

  That is, the present invention relates to a molten propylene-based resin foam sheet obtained by melt-kneading a propylene-based resin and a foaming agent with an extruder and then extruding the same from a circular die to atmospheric pressure. Is a method of producing a propylene-based resin foam sheet by contacting the outer wall surface of the inner cylinder part and the inner wall surface of the outer cylinder part through between the parts, the inner wall surface of the outer cylinder part is provided with a plurality of holes, Providing a method for producing a propylene-based resin foam sheet in which the molten propylene-based resin foam sheet is brought into contact with the inner wall surface of the outer cylinder portion by reducing the pressure between the molten propylene-based resin foam sheet and the outer cylinder portion through the holes. To do.

  By the production method of the present invention, a propylene-based resin foam sheet having a smooth surface can be produced.

Hereinafter, the present invention will be described in detail.

As the propylene-based resin, known propylene-based resins such as homopolypropylene, block polypropylene, and random polypropylene can be used. From the viewpoint of foaming properties, it is preferable to include a propylene polymer in which the melt tension at 190 ° C. (MT (190)) and the melt flow rate at 230 ° C. (MFR (230)) satisfy the following formula 1.
MT (190) ≧ 7.52 × MFR (230) ^(−0.576) [Formula 1]

Examples of the propylene polymer satisfying Formula 1 include linear polymers and branched polymers containing a high molecular weight component.
As the linear polymer, for example, a propylene polymer (T) introduced with an ultrahigh molecular weight component disclosed in JP-A-11-228629, that is, a crystalline propylene polymer having an intrinsic viscosity of 5 dl / g or more. Obtained by a polymerization method comprising a step of producing a polymer part (A) and a step of producing a crystalline propylene polymer part (B) having an intrinsic viscosity of less than 3 dl / g, and the intrinsic viscosity is less than 3 dl / g And a propylene polymer (T) in which the proportion of the crystalline propylene polymer portion (A) is 0.05% by weight or more and less than 35% by weight.
Examples of the branched polymer include those obtained by irradiating an ordinary linear polymer with an electron beam as disclosed in JP-A No. 62-121704. PF814, SD632 from Sun Aroma Co., Ltd. Etc.

The melt flow rate at 230 ° C. (MFR (230)) is a value measured in accordance with JIS K7210 at a temperature of 230 ° C. and a load of 2.16 kgf (unit: g / 10 minutes). Melt tension at 190 ° C. (MT (190)) means a sample amount of 5 g, a heating temperature of 190 ° C., a heating time of 5 minutes, an extrusion speed of 5.7 mm / min, a length of 8 mm, using a commercially available melt tension tester. This is the tension when a strand is extruded from an orifice having a diameter of 2 mm and the strand is wound at a winding speed of 100 rpm using a roller having a diameter of 50 mm (unit: g).

The propylene resin preferably contains 10% or more of a propylene polymer satisfying the formula 1 in all propylene resins, and includes other known homopolypropylene, block polypropylene, and random polypropylene that do not satisfy the formula 1. Also good. A propylene-based resin containing a propylene-based polymer that satisfies Formula 1 is less foamed and excellent in foamability. The propylene-based resin may contain an ethylene-based resin and other olefin-based resins to the extent that foamability is not impaired.

The foaming agent used by this invention is not specifically limited, A well-known foaming agent can be used. Examples of physical foaming agents include carbon dioxide gas, nitrogen gas, air, propane, butane, pentane, hexane, dichloroethane, dichlorodifluoromethane, dichloromonofluoromethane, and trichloromonofluoromethane, such as nitrogen gas, carbon dioxide gas, It is preferable to use a safe and environmentally friendly inorganic gas such as air, and it is more preferable to use carbon dioxide gas because of its high solubility in a propylene-based resin. When using carbon dioxide gas, it is preferable to mix with a propylene-based resin in a supercritical state of 7.4 MPa or more and 31 ° C. or more from the viewpoint of diffusion into the resin and solubility.

Examples of chemical blowing agents used in the present invention include sodium bicarbonate, a mixture of sodium bicarbonate and an organic acid such as citric acid, sodium citrate, stearic acid, azodicarbonamide, tolylene diisocyanate, 4,4′diphenylmethane diisocyanate, etc. Isocyanate compounds, azobisbutyronitrile, barium azodicarboxylate, azo such as diazoaminobenzene, trihydrazinotriazine, diazo compounds, benzene sulfonyl hydrazide, P, P'-oxybis (benzenesulfonyl hydrazide), Hydrazine derivatives such as toluene sulfonyl hydrazide, nitroso compounds such as N, N′-dinitroso pentamethylene tetramine, N, N′-dimethyl-N, N′-dinitroso terephthalamide, P-toluene sulfonyl Semicarbazide, can be given other azide compound or a triazole compound of semicarbazide compounds such as 4,4 'oxybisbenzenesulfonyl semicarbazide. In particular, sodium bicarbonate, citric acid, and azodicarbonamide are preferable.

The above physical foaming agent and chemical foaming agent may be used alone or in combination of two or more. When a chemical foaming agent is used, a foaming aid may be used in combination in order to adjust the decomposition temperature and decomposition rate. For example, since the decomposition temperature of azodicarbonamide alone is as high as about 200 ° C., a small amount of zinc oxide, zinc stearate, urea or the like may be added as a foaming aid when processing at a low temperature is desired.

When a physical foaming agent is used, a cell nucleating agent can be added. Bubble nucleating agents include talc, silica, diatomaceous earth, calcium carbonate, magnesium carbonate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium silicate, zeolite, mica, clay, wollastonite, hydrotalcite Examples thereof include polymer beads such as magnesium oxide, zinc oxide, zinc stearate, calcium stearate, PMMA, synthetic aluminosilicate, and the above chemical foaming agents.

The amount of the foaming agent added to the propylene-based resin is appropriately set according to the desired expansion ratio. When carbon dioxide is used as the physical foaming agent, the amount added is generally 0.1 to 4 PHR. For example, 0.3 PHR is used when producing a foam sheet with a foaming ratio of 3 times, and 0 when foaming ratio is 5 times. About 6 PHR.

As the extruder, an extruder used for single-screw or multi-screw ordinary extrusion molding can be used, and a tandem extruder combining a plurality of extruders can also be used. In particular, a twin-screw extruder rotating in the same direction is preferable, and an extruder having a structure in which the amount of extrusion per screw rotation is large and a predetermined extrusion amount can be obtained at a low rotation and the shear heat generation due to screw rotation is small. More preferably, the extruder is capable of adjusting the temperature by circulating a cooling medium in the screw body.

A gear pump is installed between the extruder and the circular die, a metering feeder is installed to supply the raw material, and the system that controls the gear pump inlet pressure constant by feeding back to the rotational speed of the screw or gear pump and the raw material supply amount is also in the extruded foam state It is effective for stabilization.
In addition, it is also effective for stabilizing the foamed state that a static mixer or the like is inserted into the adapter connecting the extruder and the circular die to equalize the resin temperature.

When a physical foaming agent is used, the extruder has a structure that allows the foaming agent to be pressed into the molten resin, but the resin raw material is sufficiently melt-plasticized before the press-fitting position, and after the press-fitting, the resin and the foaming agent are sufficiently injected. It is necessary to be able to mix and homogenize and control the resin temperature suitable for foaming.

As the circular die, a die used for normal extrusion molding can be used, and a structure capable of adjusting the lip opening degree and the die temperature in the circumferential direction is preferable in order to make the thickness distribution in the circumferential direction uniform. In general, the lip diameter is 50 mm to 500 mm, and the lip opening is 0.3 mm to 3 mm.

In the production method of the present invention, the cylindrical molten propylene-based resin foam sheet extruded from the circular die into the atmospheric pressure is passed between the cylindrical inner cylinder part and the outer cylinder part, and the outer wall surface of the inner cylinder part and It is made to contact with the inner wall surface of an outer cylinder part. The outer wall surface of the inner tube portion is a wall surface facing the outer tube portion, and the inner wall surface of the outer tube portion is a wall surface facing the inner tube portion. The molten propylene-based resin foam sheet is cooled by contacting the outer wall surface of the inner cylinder portion and the inner wall surface of the outer cylinder portion, and a propylene-based resin foam sheet is obtained.

The inner cylinder portion is installed so that the outer wall surface thereof is in uniform contact with the inner surface of the molten propylene-based resin foam sheet extruded from the circular die. The outer diameter of the inner cylinder part is usually 1.5 to 5 times the lip diameter of the circular die, and the length of the inner cylinder part in the extrusion direction is usually 300 mm to 1500 mm. It is preferable to use aluminum, stainless steel, or the like having high thermal conductivity as the material for the inner cylinder portion, and it is preferable to make the surface in contact with the sheet a Teflon (registered trademark) treatment to make it slippery. Moreover, it is preferable to circulate cooling water through the inner cylinder portion so that the temperature in the circumferential direction becomes uniform.

The outer cylinder part is uniform with the outer surface of the molten propylene-based resin foam sheet in which the outer wall surface of the inner cylinder part and the inner wall surface of the outer cylinder part face each other and the inner wall surface of the outer cylinder part is extruded from a circular die. Installed in contact. The length of the outer cylinder part in the extrusion direction may be the same as or shorter than the length of the inner cylinder part in the extrusion direction. It is preferable to use aluminum, stainless steel, or the like having high thermal conductivity as the material of the outer tube portion, and it is preferable to make the surface in contact with the sheet teflon-treated to make it slippery. Further, it is preferable to circulate cooling water through the outer cylinder portion so that the circumferential temperature becomes uniform.

The outer cylinder part wall surface (inner wall surface) in contact with the molten propylene-based resin foam sheet is provided with a plurality of holes, and using a vacuum pump, the pressure between the sheet and the outer cylinder part is reduced through these holes, The sheet is brought into uniform contact with the inner wall surface of the outer cylinder. The hole diameter is usually 0.1 mm to 1 mm, and the number of holes is usually 1 to 10 holes / cm ² . The degree of vacuum is usually 0.02 to 0.05 MPa lower than the atmospheric pressure.

The outer cylinder part preferably has a structure capable of adjusting the position in the sheet pushing direction and the distance between the opposing wall surfaces of the outer cylinder part and the inner cylinder part. It is possible to adjust the extrusion conditions and the position of the outer cylinder part in the extrusion direction so that the surface temperature of the molten propylene-based resin foam sheet in contact with the die side opening of the outer cylinder part is 100 ° C. or higher and 160 ° C. or lower. preferable. The sheet surface temperature is more preferably 110 ° C. or higher and 140 ° C. or lower. By bringing a sheet having a surface temperature in the above temperature range into contact with the outer cylinder wall surface, a propylene-based resin foam sheet having extremely excellent surface smoothness can be obtained.

The distance between the opposing wall surfaces of the inner cylinder part and the outer cylinder part is preferably set as follows. First, a propylene-based resin foam sheet is manufactured using only the inner cylinder part without using the outer cylinder part, and the thickness of the resulting foam sheet is defined as t. In the case of manufacturing under the same conditions except that the outer cylinder part is used, the distance between the wall surfaces of the inner cylinder part and the outer cylinder part facing each other is set to be not less than the thickness t of the foam sheet and not more than 1.5 times the foam sheet thickness t. It is preferable to set it, and it is more preferable to set it to 1.3 times or less. If the distance between the opposing wall surfaces of the inner cylinder part and outer cylinder part is too short, the seat surface may become rough due to friction with the inner wall surface of the outer cylinder part. May be difficult to do.

A plurality of holes may be provided on the outer wall surface of the inner cylinder portion in contact with the molten propylene-based resin foamed sheet in the same manner as the outer cylinder portion, and the pressure may be reduced through these holes to bring the sheet into close contact with the inner cylinder portion.

The foamed sheet made of propylene resin obtained in the present invention can be subjected to surface treatment such as corona treatment, ozone treatment or antistatic agent application, which is usually applied to the surface of the foamed sheet.

The foaming ratio and thickness of the foamed sheet obtained in the present invention are not particularly limited, but usually the thickness is 0.5 to 4 mm and the foaming ratio is 2 to 15 times. The foamed sheet obtained in the present invention may be a multilayer foamed sheet formed by ordinary multilayer coextrusion molding.

The foam sheet obtained by the present invention can be used for packaging, boxing, partition plates, food containers, stationery, building materials, automobile interior materials, and the like. In addition, a coating layer may be provided by bonding a sheet or film (thin plate-like material) on one or both sides of the foamed sheet, or applying a solution such as an antistatic agent solution or a gas barrier resin composition solution. In this case, it is preferable to perform surface treatment such as corona treatment or ozone treatment on the surface of the foam sheet.
As the thin plate to be bonded, known ones can be used depending on the application, for example, a thin plate made of metal such as aluminum or iron, thermoplastic resin, paper, synthetic paper, hemp, glass wool, etc. And non-woven fabrics and woven fabrics.

When the foamed sheet obtained in the present invention is used as a food packaging material, it is preferable to paste a propylene-based resin film or a gas barrier resin film having a thickness of 10 to 100 μm on at least one side of the sheet. As the gas barrier resin, known gas barrier resins such as an ethylene / vinyl alcohol copolymer, polyvinylidene chloride, polyvinyl alcohol, and polyamide are used.

Moreover, when using the foamed sheet obtained by this invention as a vehicle interior material, it is preferable to bond and use a nonwoven fabric, a woven fabric, hemp, glass wool etc. at least on one side of this sheet | seat.
When the foam sheet is used as a box partition plate or the like, it is preferable that another foam sheet having a high expansion ratio is bonded to at least one surface in order to protect the contents.

The method for laminating a film or thin plate on the foamed sheet obtained in the present invention is not particularly limited. For example, (1) an adhesive is applied to the surface of the foamed sheet and / or the surface of the thin plate. (2) A method of using a thin plate laminated with an adhesive resin film, heating and melting the adhesive resin film surface and pasting it to the foamed sheet, (3) a foamed sheet with a heater or hot air, etc. Examples of the method include melting and bonding the surface and / or the surface of the thin plate, and (4) a method of extruding and laminating the molten resin between the thin plate and the foamed sheet.

It can also be used as a molded product obtained by molding the foamed sheet obtained by the present invention, a foamed sheet and the like into a desired shape by thermoforming such as vacuum forming.
A known method can be used as the thermoforming method, and examples thereof include vacuum forming and heat ruled line processing.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these examples at all.

(1) Intrinsic Viscosity of Polymer The measurement was performed in 135 ° C. tetralin using an Ubbelohde viscometer. The intrinsic viscosity of the crystalline propylene polymer portion (B) is calculated from the intrinsic viscosity of the crystalline propylene polymer portion (A) and the entire propylene polymer (T) as described in JP-A-11-228629. I asked more.

(2) MFR
According to JIS K7210, measurement was performed at a temperature of 230 ° C. and a load of 2.16 kgf. The unit is g / 10 minutes.

(3) Melt tension (MT)
Using a melt tension tester MT-501D3 manufactured by Toyo Seiki Co., Ltd., a strand was extruded from an orifice having a length of 8 mm and a diameter of 2 mm at a sample amount of 5 g, a heating temperature of 190 ° C., a heating time of 5 minutes, and an extrusion speed of 5.7 mm / min. The tension when the strand was wound at a winding speed of 100 rpm using a roller having a diameter of 50 mm was measured as melt tension (MT) (unit: g).

(4) Foaming ratio According to JIS K7112, the density ρf of the foamed sheet was obtained using a measurement method by an underwater substitution method, and the foaming ratio χ was calculated by the following formula 2 using the resin density ρs (0.90).
χ = ρs / ρf [Formula 2]
ρs: Resin density (g / cm ³ ), ρf: Foam density (g / cm ³ )

(5) Surface roughness The surface precision measuring device SURFCOM200C made by Tokyo Seimitsu Co., Ltd. was used, and the tip of the stylus was made of diamond having a radius of 5 μm. Three measurement sites were taken from the width direction of the sheet, a sample having a width direction of 80 mm × extrusion direction of 40 mm was cut out, and the measurement distance was 50 mm in the width direction. The difference between the maximum and minimum displacement was defined as the surface roughness, and three locations were averaged.

[Reference Example 1] (Production of propylene-based resin PP1)
Propylene polymer powder was produced by the method disclosed in JP-A-11-228629. The propylene polymer powder had a crystalline propylene polymer portion A having an intrinsic viscosity of 7.7 dl / g and a crystalline propylene polymer portion B having an intrinsic viscosity of 1.2 dl / g. The weight ratio of A and B was 11:89, and the intrinsic viscosity of the entire propylene polymer was 1.9 dl / g.
0.1 parts by weight of calcium stearate, 0.05 parts by weight of trade name Irganox 1010 (manufactured by Ciba Geigy Co., Ltd.), trade name of Sumilizer BHT (manufactured by Sumitomo Chemical Co., Ltd.) 0.2 parts by weight was added and mixed, and melt-kneaded at 230 ° C. to obtain pellets (propylene resin PP1) having a melt flow rate MFR of 12 g / 10 minutes. The melt tension MT of the pellet was measured to be 4.7 g, and the right side of [Formula 1] 7.52 × MFR (230) ^(−0.576) was 1.80, which satisfies [Formula 1]. there were.

[Example 1] (Extrusion Foam Test)
A two-layer, three-layer, propylene-based resin multilayer foam sheet in which a foam layer was provided on the intermediate layer and a non-foam layer was provided on both sides thereof was prepared by the method described below.
A 65 mmΦ co-rotating twin screw extruder (L / D = 41.5, L is the effective screw length, D is the screw diameter) with a gear pump at the tip as the foam layer extruder, and the non-foam layer extruder A 60 mmΦ single screw extruder (L / D = 30) was used, and a multilayer circular die with a lip diameter of 230 mmΦ (external lip radius r ₂ = 11.6 cm, inner lip radius r ₁ = 11.5 cm, lip opening) Device with a degree of r ₂ -r ₁ = 0.1 cm) was used.
A cell nucleating agent for a blend of 70 parts by weight of the polypropylene resin PP1 (MFR = 12) obtained in Reference Example 1 and 30 parts by weight of low density polyethylene PE1 (Sumitomo Chemical Co., Ltd., Sumikasen G201). A raw resin obtained by blending 1 PHR blend (Nippon Boehringer Ingelheim Co., Ltd., Hydrocerol CF40E) into a foaming layer extruder hopper through a quantitative feeder, melt kneading, and the position where melting has progressed (L / In D = 20), 2.7 PHR of liquefied carbon dioxide gas was injected at a high pressure using a diaphragm metering pump. After sufficiently melting and kneading the raw material resin and carbon dioxide, the temperature was adjusted to 185 ° C. and introduced into the multilayer die using a gear pump at a discharge rate of 110 kg / h.
On the other hand, a quantitative feeder comprising a blend of 70 parts by weight of polypropylene resin PP2 (manufactured by Sun Aroma Co., Ltd., PF814 (MFR = 3)) and 30 parts by weight of low density polyethylene PE1 (manufactured by Sumitomo Chemical Co., Ltd., Sumikasen G201). Then, the mixture was introduced into a non-foamed layer extruder hopper and melt kneaded, adjusted to 185 ° C., and introduced into a multilayer die at a discharge rate of 55 kg / h.
A cylindrical molten propylene-based resin foam sheet extruded from a multilayer die into the atmospheric pressure has an outer diameter of 700 mmφ (three times the lip diameter) and a length of 1000 mm installed 250 mm away from the die outlet. The inner cylinder part and the outer cylinder part were made to contact between the inner cylinder part outer wall surface and the outer cylinder part inner wall surface. Both the inner cylinder part and the outer cylinder part were made of aluminum, the surface in contact with the sheet was subjected to Teflon treatment, cooling water was circulated inside, and the temperature was uniformly controlled in the circumferential direction.
The outer cylinder portion covered the entire inner cylinder portion in the circumferential direction, and the length of the outer cylinder portion in contact with the sheet in the extrusion direction was 300 mm, and was installed near the center of the inner cylinder portion in the extrusion direction.
Further, holes (diameter 0.5 mm) are provided at a density of 5 holes / cm ² on the sheet contact surface of the outer cylinder portion, and the pressure is reduced by 0.02 MPa from atmospheric pressure through the holes, and the sheet is placed in the outer cylinder portion. Adhered. The thickness of the foamed sheet of Comparative Example 1 obtained by using only the inner cylinder portion as the molten propylene-based resin sheet surface temperature at the outer cylinder portion entrance is 120 ° C., and the gap between the inner cylinder portion and the outer cylinder portion is used. 1.1 times.
A cylindrical propylene resin foam sheet cooled in contact with the wall surfaces of the inner and outer cylinder portions is slit with a cutter from the left and right sides, and the cylinder is cut into a flat plate shape. Each sheet was taken up by a take-up machine equipped with a nip roll, and then taken up by a twin-screw turret electric reversing winder.
The obtained foamed sheet has an expansion ratio of 9.2 times, a thickness of 1.9 mm, a surface roughness of the surface in contact with the inner wall surface of the outer cylinder portion is 142 μm, and a surface roughness of the surface in contact with the outer wall surface of the inner cylinder portion is The sheet had a surface smoothness of 150 μm.

[Comparative Example 1]
The same procedure as in Example 1 was performed except that the outer cylinder portion was not used and only the inner cylinder portion was used for cooling molding. The obtained foamed sheet had a foaming ratio of 8.4 times, a thickness of 1.7 mm, and the surface roughness of the surface in contact with the outer wall surface of the inner cylinder portion was 150 μm. Was 228 μm and was a sheet inferior in surface smoothness.

[Comparative Example 2]
Propylene-based resin foaming in the same manner as in Example 1, except that the distance between the inner wall surface of the outer cylinder part and the outer wall surface of the inner cylinder part was set to 2.7 mm, which is 1.6 times the sheet thickness of Comparative Example 1. Although production of the sheet was attempted, the degree of vacuum could not be maintained, and the obtained foamed sheet was inferior in smoothness equivalent to that of Comparative Example 1.

FIG. 1 is a diagram showing an example of a method for producing a propylene-based resin foam sheet in the present invention.

Explanation of symbols

1: Circular die 2: Molten propylene resin foam sheet 3: Inner cylinder part 4: Outer cylinder part

Claims (1)

A melted propylene resin foam sheet obtained by extruding a propylene resin and a foaming agent into an atmospheric pressure from a circular die after being melt kneaded by an extruder is inserted between the cylindrical inner cylinder part and the outer cylinder part. A method for producing a propylene-based resin foam sheet by contacting with an outer wall surface of a cylindrical portion and an inner wall surface of an outer cylindrical portion, wherein a plurality of holes are provided in the inner wall surface of the outer cylindrical portion, and a molten state is formed through the holes. A method for producing a propylene-based resin foam sheet in which a molten propylene-based resin foam sheet is brought into contact with the inner wall surface of the outer cylinder portion by reducing the pressure between the propylene-based resin foam sheet and the outer cylinder portion.

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