JPH05124125A - Propylene resin foam sheet and manufacture thereof - Google Patents

Abstract

PURPOSE:To extend a foaming suitable temperature range, to control an extrusion foaming temperature easily and to obtain a propylene resin foamed sheet, the whole of which is homogenized and has excellent properties, by forming long-chain branches to a copolymer as the base material resin of the foamed sheet while specifying draw-down properties. CONSTITUTION:The copolymer of propylene and a small quantity of olefin except propylene is used as a base material resin constituting a foamed sheet, and the copolymer has long-chain branches while having draw-down properties of 60m/min or less. The copolymer and foaming agent are melted and kneaded in an extruder and the molten kneaded article is extruded and foamed under low pressure through a die mounted at the front end of the extruder as a method, in which the foamed sheet is obtained. A method, in which a tubular foam is cut open and formed in a sheet shape, is adopted normally for particularly acquiring a sheet-shaped foam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a propylene-based resin foamed sheet and a method for producing the same, and more particularly to a propylene-based resin foamed sheet suitable for secondary forming and a method for producing the same. Among them, it particularly relates to a propylene-based resin foam sheet suitable for deep drawing and a method for producing the same.

[0002]

2. Description of the Related Art As a method for producing a long foam or a sheet foam for molding a container or the like, a thermoplastic resin is melt-kneaded with a foaming agent in an extruder and then subjected to low pressure. The extrusion foaming method of extruding and foaming is widely adopted.

In the extrusion foaming method of an olefinic resin, when a melt-kneaded product of a resin and a foaming agent is extruded from the extruder under a low pressure, the foaming agent in the melt-kneaded product expands to foam. However, when the temperature of the resin is raised, the viscosity drops sharply, and the resin cannot hold the foaming agent and escapes from the resin to become a foam of open cells. Conversely, the resin temperature must be increased to increase the viscosity of the resin. If it is lowered, the crystallization of the resin will proceed, and as a result, the foam will not foam sufficiently and uniformly, and the surface of the foam will become uneven. It is necessary to perform viscoelasticity that can be retained at a temperature that the resin has. The temperature range in which viscoelasticity suitable for foaming is obtained differs depending on the type of resin, and this temperature range is generally called the foaming suitable temperature range.

[0004]

However, the viscoelasticity of the propylene resin, which has a higher degree of crystallinity than that of low density polyethylene and the like, greatly changes due to a slight temperature change, and the foaming suitable temperature range is very narrow. It is extremely difficult to carry out extrusion foaming while maintaining the resin temperature within such a narrow temperature range, and when the extrusion foaming temperature fluctuates and goes out of the foaming suitable temperature range, the foamed part has an open cell structure. However, it was difficult to obtain a foam having good and uniform properties as a whole. Conventionally, in the case of a non-crosslinked propylene-based resin, a relatively good foam can be obtained only when the density is a low expansion ratio of more than 0.2 g / cm ³ or when the density is 0.013 g / cm ^3. It has a high expansion ratio of less than.

The above-mentioned problems are considered to be caused by the high crystallinity of the propylene-based resin, and the density of the propylene-based resin is 0.
The reason why an extruded foam with a low expansion ratio of more than 2 g / cm ³ can be obtained relatively well is that the ratio of the resin is larger than the amount of the foaming agent. It is considered that this is because the temperature can be set to be considerably higher than that. The density is 0.013 g / cm ³
The reason why it is possible to obtain a foam having a high expansion ratio of less than 1 relatively well is as follows.

Generally, the olefin resin being foamed during extrusion foaming is subjected to an external cooling operation using a cooling means, thereby solidifying the cell walls to obtain a good foam. However, since propylene-based resin has a higher degree of crystallinity than low-density polyethylene, the amount of heat generated during crystallization is large. This heat hinders the cooling and thus the solidification of the cell walls, and destroys or deforms the cells of the propylene-based resin in the process of foaming.

Therefore, by foaming the foaming agent in a large amount, the heat of vaporization (expansion heat) of the foaming agent is used to drastically lower the temperature of the propylene resin during foaming, thereby solidifying the cell wall. Promote. Further, a large amount of foaming agent has a function of delaying the crystallization of the resin in the extruder. As a result, the foam can be obtained relatively well. However,
In this case, due to the necessity of blending a large amount of a foaming agent, the resulting foam will necessarily have a high expansion ratio with a density of less than 0.013 g / cm ³ . Also in this case, the temperature range suitable for foaming is only about 0.6 ° C.

In view of the fact that only a propylene resin extruded foam having a high expansion ratio or a low expansion ratio can be obtained, the present inventors use a propylene resin having a specific melt tension to obtain a density of 0. 2 to 0.013 g / cm
We found a method that can easily produce even the propylene-based resin extruded foam of ³ and found that the foamed sheet obtained by this method is suitable for secondary molding, and filed an application first (Patent application Hira 3-86168).

However, in the case of the foamed sheet described in the above-mentioned prior application, this is not a serious problem in obtaining a molded product having a relatively shallow drawing ratio in the secondary molding, but the drawing ratio (the height of the molded product and the upper opening) Part diameter (when the shape of the opening is not circular, the diameter of a circle with the same area as the area of the opening)
Ratio] of more than 0.5, there is a problem that the thickness may be remarkably reduced or holes are partially formed, leaving room for improvement.

The present invention has been made in view of the above points,
It is an object of the present invention to provide an excellent propylene-based resin foam sheet which does not cause the above problems even if it is a deep-drawing product having a drawing ratio of more than 0.5, and a method for producing the same.

[0011]

[Means for Solving the Problems] That is, the propylene-based resin foamed sheet of the present invention is a non-crosslinked propylene-based resin foamed sheet using a copolymer of propylene and a small amount of olefin other than propylene as a base resin. The copolymer, which is the base resin of the foamed sheet, has a long chain branch and has drawdown property (however, the drawdown property means that the molten propylene resin heated to 230 ° C. is a nozzle of the melt indexer (bore diameter 2 0.095 mm, length 8 mm) at a constant speed of 10 mm / min in a cord shape, and then the cord material is passed through a feed roll located above the tension detecting pulley located below the nozzle and wound. The winding speed of the winding roll is gradually increased while being wound by the winding roll to cut the string-like object, and the winding speed of the string-like object at the time of this cutting is referred to. ] Is 60 m / min or less.

In the method for producing a propylene-based resin foamed sheet of the present invention, the above-mentioned specific copolymer consisting of propylene and a small amount of olefin other than propylene and a foaming agent are melt-kneaded in an extruder, and then the tip of the extruder is melted and kneaded. It is characterized in that it is extruded and foamed under a low pressure through a die attached to. In the present invention, the base resin is preferably a propylene / ethylene block copolymer.

The base resin constituting the foamed sheet of the present invention is a copolymer of propylene and a small amount of olefins other than propylene, and the copolymer has long chain branching and a drawdown property of 60 m / Must be less than a minute.

Examples of the small amount of olefin other than propylene which is copolymerized with propylene include ethylene and α-olefins having 4 to 10 carbon atoms, and these can be used alone or in combination of two or more. The α-olefin having 4 to 10 carbon atoms is, for example, 1
-Butene, isobutylene, 1-pentene, 3-methyl-
1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene and the like can be mentioned.

The above-mentioned α-olefin is usually contained in the copolymer in an amount of not more than 20% by weight, preferably not more than 10% by weight, and particularly when the α-olefin is ethylene, not more than 5% by weight. It is preferable that the content is included. The preferable lower limit of the content of these α-olefins in the copolymer is 0.5% by weight in any α-olefin. The copolymer may be a random copolymer or a block copolymer, but a block copolymer is preferable because of the ease of forming long chain branches, and a propylene / ethylene block copolymer is particularly preferable. preferable.

The above-mentioned copolymer, which is the base resin of the foamed sheet of the present invention, must have a long-chain branch in the main chain, unlike a usual propylene-based copolymer. Such a special copolymer is an ordinary crystalline linear propylene-based copolymer (usually having a weight average molecular weight of 100,000 or more), and has atactic content and / or isotactic content, but a crystalline content. A copolymer containing components that are not included (hereinafter, in order to distinguish from the copolymer used in the present invention,
This copolymer is called a "normal copolymer". The term "copolymer" means the copolymer used in the present invention. ), A low temperature decomposition type (decomposition temperature: room temperature to 12
(Around 0 ° C.) is mixed and heated to 120 ° C. or lower, and an atactic or / and non-crystallized isotactic component is bonded to the main chain of a usual copolymer as a branched chain. It can be obtained and is generally considered to have a branched structure with long chain branching predominantly at the ends.

Examples of the low temperature decomposition type peroxide include di (s-butyl) peroxydicarbonate and bis (2-
Ethoxy) peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-n-propylperoxydicarbonate, di-n-butylperoxydicarbonate, diisopropylperoxydicarbonate,
Examples thereof include t-butyl peroxy neodecanoate, t-amyl peroxy neodecanoate and t-butyl peroxypivalate.

The propylene-based copolymer, which is the base resin for the foamed sheet of the present invention, is prepared by stirring the above-mentioned ordinary copolymer in a reaction vessel equipped with a stirrer with an inert gas such as argon in a reaction vessel. And then replace the above peroxide with 1 kg of resin
Usually, 5 to 50 mmol is added, and the mixture is heated to about 120 ° C., preferably about 70 to 105 ° C. while continuing stirring to react (usually 30 to 120 minutes), and then,
It is obtained by stopping the reaction. In stopping the reaction, a method of introducing a reaction terminator such as methyl mercaptan into the reaction vessel, or heating the reaction product at about 130 to 150 ° C. for 20 to 40 minutes is adopted.

The propylene-based copolymer, which is the base resin of the foamed sheet of the present invention, has a drawdown property of 60 m / min or less,
It is preferably 30 m / min or less, particularly preferably 15 m / min or less. This drawdown property means that the molten propylene-based resin heated to 230 ° C. is extruded into a string shape at a constant speed of 10 mm / min from a melt indexer nozzle (caliber 2.095 mm, length 8 mm), and then the string-like material. After passing through a feed roll located above the tension detecting pulley located below the nozzle, and then winding with a winding roll while gradually increasing the winding speed of the winding roll. And the winding speed of the string-like material at the time of this cutting.

The drawdown property can be adjusted by the number and length of the long chain branches. Generally speaking, the greater the number of long chain branches and the longer the branch length, the lower this value tends to be. Therefore, in order to obtain a desired copolymer having a drawdown property, it is necessary to set the reaction conditions in consideration of these things. If there is no long-chain branching, or if there are branches that are too short or too little, or in the case of ordinary copolymers, the drawdown property is 60 m /
It exceeds the minutes. Even when trying to obtain a foamed sheet having a density of about 0.2 to 0.013 g / cm ³ by performing extrusion foaming using such an ordinary copolymer, the obtained foamed sheet has many corrugations and surface irregularities, It has no commercial value.

On the other hand, even if the drawdown property is 60 m / min or less, if it is a propylene homopolymer, a good foamed sheet can be obtained, but a deep-drawing molded product is obtained using the foamed sheet. If it is attempted to obtain a product, the thickness will be remarkably reduced or holes will be partially formed, and a good molded product cannot be obtained.

The copolymer used in the present invention preferably has a half-crystallization time at the crystallization temperature + 15 ° C. of 800 seconds or longer, and particularly preferably 1000 seconds or longer. A crystallization rate measuring device can be used for the measurement of the semi-crystallization time.

In order to measure the semi-crystallization rate, first, the support holding the film-like sample is placed in the air bath of the crystallization rate measuring instrument to completely melt the sample, and then the molten sample is taken together with the support. The sample was immersed in an oil bath maintained at the crystallization temperature of + 15 ° C so as to block the optical path between the light source and the optical sensor, and a constant amount of light was constantly emitted in the optical sensor until the melted sample solidified again. The voltage of the light source is adjusted so that it is detected, and the voltage-time curve as shown in FIG. 1 is obtained. When the voltage when the voltage in this curve has a constant value is V ₀ , the time until the voltage becomes 1/2 V ₀ is the half-crystallization time.

In the present invention, not only the above copolymers can be used alone, but also other resins can be mixed and used in the above copolymers. Examples of the resin to be mixed and used are propylene-based resins other than the above, or high-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-butene copolymer, ethylene-anhydrous. Examples thereof include ethylene-based resins such as maleic acid copolymers, butene-based resins, polyvinyl chloride, vinyl chloride-based resins such as vinyl chloride-vinyl acetate copolymers, and styrene-based resins.

When the other resins are mixed, the mixing amount thereof is limited to 40% by weight of the total weight of the polymer after mixing, and the drawdown property of the mixture should not exceed 60 m / min. There is.

The foamed sheet of the present invention usually has a density of 0.6-
It is obtained by extrusion foaming with a target of 0.018 g / cm ³ and a thickness of 0.1 to 5 mm. As a method for obtaining the foamed sheet of the present invention, a method of melt-kneading a copolymer and a foaming agent in an extruder, and then extruding the melt-kneaded product under low pressure through a die attached to the tip of the extruder to foam is adopted. It In particular, in order to obtain a sheet-like foam, a circular die having an annular lip is used, and a tube-like foam is obtained by extrusion foaming from the lip of this die, and then the tube is cut open to form a sheet. Is usually adopted.

As the foaming agent, an inorganic foaming agent, a volatile foaming agent, a decomposable foaming agent or the like can be used. Carbon dioxide, air, nitrogen, etc. can be used as an inorganic foaming agent.

Examples of the volatile blowing agent include propane, n-butane, i-butane, pentane, hexane and other aliphatic hydrocarbons, cyclobutane, cyclopentane and other cycloaliphatic hydrocarbons, trichlorofluoromethane and dichlorodifluoromethane. , Dichlorotetrafluoroethane, methyl chloride,
Halogenated hydrocarbons such as ethyl chloride and methylene chloride can be used.

As the decomposition type foaming agent, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like can be used. These foaming agents can also be used by appropriately mixing them.

The amount of the foaming agent used varies depending on the kind of the foaming agent, the desired expansion ratio, etc., but the density is, for example, 0.2 to 0.2.
The standard of the amount of foaming agent used to obtain a foam of about 013 g / cm ³ is 0.5 parts volatile foaming agent per 100 parts by weight of resin.
It is about 25 parts by weight (butane conversion). Also the density is 0.0
The standard of the amount of foaming agent used to obtain a foam of more than 9 g / cm ³ is 100 parts by weight of the resin, in the case of an inorganic foaming agent.
It is about 0.1 to 10 parts by weight, and about 0.1 to 5 parts by weight in the case of a decomposition type foaming agent.

In the present invention, a cell regulator may be further added to the melt-kneaded product of the copolymer and the foaming agent. Examples of the bubble control agent include inorganic powders such as talc and silica, acidic salts of polyvalent carboxylic acids, and reaction mixtures of polyvalent carboxylic acids with sodium carbonate or sodium bicarbonate. It is preferable to add about 13 parts by weight or less of the cell regulator to 100 parts by weight of the resin (except when a large amount of the inorganic filler is contained in the resin). Further, if necessary, additives such as a heat stabilizer, an ultraviolet absorber, an antioxidant and a colorant may be added.

In the present invention, 40% by weight of the total weight is previously added to the copolymer or the mixture of the copolymer and another resin.
An inorganic filler may be contained up to the limit. Examples of the inorganic filler include talc, silica, calcium carbonate,
Examples include clay, zeolite, alumina, barium sulfate and the like. The average particle size of these is preferably 1 to 70 μm. When a large amount of such an inorganic substance is contained,
The foamed sheet obtained has improved heat resistance and can reduce the calories burned during incineration.

The method for molding the foamed sheet of the present invention includes vacuum forming, pressure forming, and applications of these, such as free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming and drape forming. , Reverse draw molding, air slip molding,
It is possible to apply plug-assist molding, plug-assist reverse draw molding, etc., or a method combining these.

[0034]

EXAMPLES The present invention will be described in more detail with reference to examples. The physical properties of the resins used in Examples and Comparative Examples are shown in Table 1. In addition, in the examples and comparative examples, the total amount of the foaming agent and the cell regulator is 100 based on the total amount of the copolymer.
It is the weight% when it is defined as the weight%. A melt indexer and a melt tension tester type II manufactured by Toyo Seiki Seisakusho Co., Ltd. were used in combination to measure the drawdown property and melt tension of the resin used, and the half-crystallization time was measured by Kotaki Corporation. Crystallization rate measuring instrument MK-80
Type 1 was used.

Incidentally, in the measurement of drawdown property, 7
Since 8.5 m / min is the measurable upper limit, 78.5 m / min
When the string-like material was not cut in minutes, it was expressed as "78.5 m / min or more". Further, the tension (gf) detected by the pulley immediately before the string-like object was cut was read and used as the melt tension. However, when the string-like material was not cut at the winding speed of 78.5 m / min, the tension detected by the pulley at this speed was taken as the melt tension.

[0036]

[Table 1]

Examples 1 to 7 and Comparative Examples 1 to 3 Resin, foaming agent (isobutane) and foam control agent (monosodium citrate salt in Examples 1, 7 and 3 and talc in others) were used. Blended in a tandem extruder (first extruder: screw diameter 65 mm, L / D = 34, second extruder: screw diameter 90 mm, L / D = 32) in the proportions shown in Table 2, melt-kneaded, and then extruded. 55mm attached to the machine tip
φ (die diameter), gap (lip clear) 0.3-0.5 mm Circular dies are extruded and foamed into a tube shape while the inner surface of the tubular foam is in contact with the cooling mandrel (mandrel diameter 200 mm). Then, the tubular foam was cut open in the extrusion direction to obtain a sheet. The extrusion conditions at this time and the properties of the obtained foamed sheet (one week after the production) are also shown in Table 2.

[0038]

[Table 2]

Then, a deep drawing test was conducted using the foamed sheets obtained in Examples 2 and 5 and Comparative Example 1. Molding test is performed with a heater of 50W each on the upper and lower sides (distance between heaters: 20c
Each sheet was introduced to the approximate center of the heating furnace having m), heated for 8 seconds, and then subjected to plug-assisted vacuum forming, and the formed state of the obtained formed article was observed.

As shown in FIG. 2, the target molded product is a hemisphere having a depth of 45 mm and a diameter of d = 80 mm in a foam sheet 1 having a length: a = 453 mm and a width: b = 300 mm. The storage units 2 are arranged horizontally in four rows, and the storage units 2 are arranged in five rows so that the positions of the storage sections 2 are displaced by half between the upper and lower rows. It is about 0.56.

When the sheet of Example 2 was used, the obtained molded article had a high degree of homogeneity in that the thickness did not become extremely thin or holes were partially formed, and the so-called mold was excellent. Although it was a molded product, the molded product using the sheet of Comparative Example 1 was a defective molded product in which holes were pierced everywhere and the thickness was remarkably thin in the places where no holes were formed.

Then, using the foamed sheets obtained in Example 7 and Comparative Example 3, a deep drawing test was conducted. Molding test is performed with a heater of 50 W each on the top and bottom (distance between heaters: 20 cm)
Each sheet was introduced to the approximate center of the heating furnace having the above, heated for 14 seconds, and then molded in the same manner as above. The molding state of the obtained molded product was observed.

The target molded product has an opening outer diameter of 1
50 mm, height 80 mm, bottom outer diameter 110 mm bowl,
The aperture ratio is about 0.53.

The obtained molded article was a molded article using the sheet of Example 7 and had a high degree of homogeneity in which the thickness did not become extremely thin or holes were partially formed, and moreover, it was excellent in so-called molding. Although it was a molded product, the molded product using the sheet of Comparative Example 3 was a defective molded product in which the elongation was uneven and the portion where the thickness was remarkably thin was observed.

[0045]

As described above, in the method of the present invention, the foaming temperature range is wider than that of the conventional extrusion foaming method using a non-crosslinked propylene resin as a base material, and therefore the extrusion foaming temperature can be easily controlled. By using the non-crosslinked propylene-based resin as the base resin, it is possible to obtain a propylene-based resin foamed sheet having uniform properties and excellent properties as a whole.

Further, the foamed sheet obtained by the method of the present invention has small shrinkage and corrugation, and when a container or the like is molded using this foamed sheet, even a deep-drawing product having a drawing ratio of more than 0.5 is obtained. As a result, an excellent molded product can be obtained without the molded product having a remarkably thin thickness or a hole.

[Brief description of drawings]

FIG. 1 is a voltage-time curve obtained by crystallization rate measurement.

FIG. 2 is a plan view of a molded product molded using the foamed sheets obtained in Example 2 and Comparative Example 1.

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[Procedure amendment]

[Submission date] October 20, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The propylene-based copolymer, which is the base resin for the foamed sheet of the present invention, is prepared by stirring the above-mentioned ordinary copolymer in a reaction vessel equipped with a stirrer with an inert gas such as argon in a reaction vessel. And then replace the above peroxide with resin 1k.
It is usually obtained by adding 5 to 50 millimoles per g and heating to about 120 ° C., preferably about 70 to 105 ° C. while continuing stirring to react (usually for 30 to 120 minutes), and then stopping the reaction. .. In stopping the reaction, a reaction terminator such as methyl mercaptan is introduced into the reaction vessel, or the reaction product is heated at 130 to 150 ° C.
A method of heating for about 20 to 40 minutes or the like is adopted. The
Whether long-chain branch exists in the molecular chain of ropylene copolymer
It can be confirmed by the following method. That is, extension flow
Dynamic measuring device (for example, rheometrics extensional flow measurement
Constant device: Trade name RER-9000), propylene
A measurement sample was prepared from the system copolymer and
Elongational viscosity (poise) at strain rate (sec ^-1 )
Graph the relationship between time and seconds. On this graph
And a long-chain branched propylene-based copolymer
A propylene-based copolymer that does not have a branch has a long-chain branch.
The propylene-based copolymer has an extensional viscosity curve with a slope
It increases with time, while it does not have long chain branching.
In the ropylene-based copolymer, the slope of the extensional viscosity curve changes with time.
It can be distinguished from the fact that it becomes very small. The above
Ometrics extensional flow measuring device (RER-900
0) shows that propylene having a long-chain branch
-Based copolymers and propylene-based copolymers without long-chain branching
Shows the relationship between elongational viscosity and time at body strain rate.
What is the graph of FIG. Curve A in the graph is the long chain
Showing a propylene-based copolymer having a large number, and the curve B is a long chain.
A propylene-based copolymer having no branching is shown. This gra
From F, in the propylene-based copolymer having a long chain branch,
As the slope of the elongational viscosity curve increases with time,
However, in propylene-based copolymers that do not have long chain branching,
Is it clear that the slope of the long-viscosity curve decreases with time?
It The measurement sample and measurement conditions are as follows.
It ・ Measurement sample size and shape: length 30 mm, diameter 5
Cylindrical column of mm ・ Strain rate: 1.0 sec ■ -1 ・ Measurement temperature: melting point of base resin + 20 ° C (However, melting point is based on
Material resin 1 to 5 mg by differential scanning calorimeter at 10 ° C / min
Of the endothermic peak of the DSC curve obtained when the temperature is raised by
Temperature. )

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Added

[Correction content]

FIG. 3 is a graph showing the relationship between elongational viscosity and time at strain rate for a propylene-based copolymer having long chain branches and a propylene-based copolymer having no long chain branches.

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Added

[Correction content]

[Figure 3]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location B29L 7:00 4F (72) Inventor Ken Aoki 690-6 Noguchi, Nikko City, Tochigi Prefecture

Claims (4)

[Claims] 1. A non-crosslinked propylene resin foam sheet comprising a base resin of a copolymer of propylene and a small amount of an olefin other than propylene, wherein the copolymer which is the base resin of the foam sheet is long. A propylene-based resin foamed sheet having chain branching and a drawdown property of 60 m / min or less (however, the drawdown property is 23
10 mm of molten propylene-based resin heated to 0 ° C from the melt indexer nozzle (caliber 2.095 mm, length 8 mm)
Per minute at a constant speed, and then the string-like material is passed through a feed roll located above the tension detecting pulley located below the nozzle and then wound up by a winding roll while being wound up. The winding speed of the roll is gradually increased to cut the string-like material, and the winding speed of the string-like material at the time of this cutting is referred to. ]. 2. The propylene-based resin foam sheet according to claim 1, wherein the base resin is a propylene / ethylene block copolymer. 3. A copolymer composed of propylene and a small amount of olefin other than propylene, having a long chain branching and a drawdown property of 60 m / min or less, and a foaming agent are melt-kneaded in an extruder, and then extruded. A method for producing a propylene-based resin foam sheet, which comprises extruding and foaming under low pressure through a die attached to a machine tip (however, the drawdown property means that the molten propylene-based resin heated to 230 ° C. is used as a melt indexer). Nozzle (caliber 2.095 mm,
Extruded in a string shape from a length of 8 mm) at a constant speed of 10 mm / min,
Then, after passing the string-like object through a feed roll located above the tension detecting pulley located below the nozzle,
While winding with a winding roll, the winding speed of the winding roll is gradually increased to cut the string-like object, and the winding speed of the string-like object at the time of this cutting is referred to. ]. 4. The method for producing a propylene-based resin foam sheet according to claim 3, wherein the copolymer is a propylene / ethylene block copolymer.