JP6673706B2 - Polypropylene resin foam sheet and method for producing the same - Google Patents

Description

  The present invention relates to a foamed sheet containing a polypropylene-based resin as a main component and a method for producing the same.

Polypropylene resin has excellent physical balance and recyclability, and is inexpensive, so it is used in a wide range of industrial fields such as daily necessities, food containers, parts and housings for electric products, interior and exterior materials for automobiles, and building materials. Have been. In applications requiring lightness, heat insulation or shock absorption, a foamed sheet of a polypropylene resin may be used.
As a polypropylene-based resin foamed sheet, a multilayer foamed sheet including a foamed intermediate layer and non-foamed surface layers provided on both sides of the foamed intermediate layer is known (Patent Documents 1 and 2). In the multilayer foamed sheet described in Patent Document 1, by providing polypropylene having a long chain branch as a component having high strength in a molten state on the surface of the non-foamed layer, bubbles formed in the foamed intermediate layer or destruction of bubbles are formed. The effect of preventing the occurrence of unevenness due to the above is exhibited. Therefore, a good appearance with high surface smoothness can be obtained while having a high expansion ratio (light weight). Further, in the multilayer foam sheet described in Patent Document 2, the surface layer is a layer containing a linear polypropylene-based resin having a melt tension and a melt flow rate satisfying specific conditions, thereby increasing the expansion ratio and improving the appearance. I have to.

JP 2001-113653 A JP 2004-291626 A

However, in the conventional polypropylene resin foam sheet, it cannot be said that the high expansion ratio and the good surface appearance can both be sufficiently achieved. In particular, when the polypropylene resin is extruded into a sheet and then cooled by bringing the sheet into close contact with a metal roll by blowing the air, the appearance of the surface on which the air is blown tends to deteriorate.
Accordingly, an object of the present invention is to provide a foamed polypropylene resin sheet having a high expansion ratio and excellent surface appearance. Further, the present invention provides a method for producing a polypropylene resin foam sheet which can easily produce a polypropylene resin foam sheet having a high expansion ratio and excellent surface appearance despite being in close contact with a metal roll by blowing air. The purpose is to provide.

[1] A foamed intermediate layer, and a non-foamed surface layer provided on both sides of the foamed intermediate layer, wherein both the foamed intermediate layer and the surface layer include a polypropylene resin,
The foaming ratio of the thickness of the intermediate layer _{(T 1)} and the thickness of the surface layer and _{(T 2) (T 1 /} T 2) is 3 / 1-10 / 1,
The polypropylene resin constituting the foamed intermediate layer has a melt tension index determined by the following formula (1) of 1.2 or more, and the polypropylene resin forming the surface layer is determined by the following formula (1). A polypropylene resin foam having a melt tension index of 1.8 or more, and a melt tension index of a polypropylene resin constituting the surface layer being equal to or greater than a melt tension index of a polypropylene resin constituting the foamed intermediate layer. Sheet.
log (melt tension index) = log (MT) + 0.85 log (MFR)-0.82 (1)
MT was measured using a melt tension measuring device having a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface, a measurement temperature of 200 ° C., a resin extrusion speed of 15 mm / min, and a take-up speed of 6.5 m /. It is the melt tension (g weight) of the polypropylene resin measured under the conditions of minutes.
MFR is a melt flow rate of a polypropylene resin measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210.
[2] The polypropylene resin contained in the surface layer contains a propylene polymer and an ethylene / α-olefin copolymer, and has a melt flow rate measured at 230 ° C. under a load of 21.18 N according to JIS K7210. Is 2 to 15 g / 10 min, the intrinsic viscosity of the xylene-soluble component in tetrahydronaphthalene at 135 ° C. is 6 to 10 dl / g, and the xylene-insoluble component has a mass average molecular weight _Mw and a number average molecular weight _Mn . The ratio ( _Mw / _Mn ) is 7 or more, and the content ratio of the ethylene / α-olefin copolymer is 20 to 40% by mass;
In the propylene polymer, the total content of ethylene units and α-olefin units is 5.0% by mass or less, and the content ratio of propylene units is 95% by mass or more,
The foamed polypropylene resin sheet according to [1], wherein the ethylene / α-olefin copolymer contains 20 to 40% by mass of ethylene units and 60 to 80% by mass of α-olefin units.
[3] The polypropylene resin according to [2], wherein the polypropylene resin contained in the surface layer is a polymerization mixture obtained by polymerizing an ethylene monomer and an α-olefin monomer in the presence of a propylene polymer. Resin foam sheet.
[4] The polypropylene resin contained in the foamed intermediate layer has a melt flow rate of 2 to 15 g / 10 minutes measured at 230 ° C. under a load of 21.18 N according to JIS K7210, and a mass average molecular weight of a xylene-insoluble component. The foamed polypropylene resin sheet according to any one of [1] to [3], wherein the ratio ( _Mw / _Mn ) of _Mw to the number average molecular weight _Mn is 6 or more.
[5] The polypropylene resin contained in the foamed intermediate layer is at least one of a propylene homopolymer and a propylene random copolymer containing at least one of an ethylene unit and an α-olefin unit at 5.0% by mass or more. The polypropylene resin foam sheet according to any one of [1] to [4].
[6] The foamed polypropylene resin sheet according to any one of [1] to [5], wherein the content ratio of the polypropylene resin in the foamed intermediate layer is 60% by mass or more.
[7] The foamed polypropylene resin sheet according to any one of [1] to [6], which has an expansion ratio of 1.30 or more.

[8] A foamed intermediate layer-forming resin composition containing a polypropylene resin for a foamed intermediate layer and a foaming agent is extruded into a sheet to form a foamed intermediate layer, and a surface containing a polypropylene resin for a surface layer. An extrusion molding step of forming a surface layer by extruding the layer-forming resin composition into a sheet shape, and laminating the surface layer on both sides of the foamed intermediate layer to produce a polypropylene-based resin foam sheet,
A cooling step of cooling the polypropylene-based resin foam sheet by blowing air onto one surface of the polypropylene-based resin foam sheet to bring the other surface of the polypropylene-based resin foam sheet into close contact with a peripheral surface of a metal roll; And
The polypropylene resin for the foamed intermediate layer has a melt tension index determined by the following formula (1) of 1.2 or more, and the polypropylene resin for the surface layer has a melt tension index determined by the following formula (1). A method for producing a foamed polypropylene resin sheet, wherein the melt tension index of the polypropylene resin for the surface layer is 1.8 or more and the melt tension index of the polypropylene resin for the foamed intermediate layer is not less than 1.8.
log (melt tension index) = log (MT) + 0.85 log (MFR)-0.82 (1)
MT was measured using a melt tension measuring device having a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface, a measurement temperature of 200 ° C., a resin extrusion speed of 15 mm / min, and a take-up speed of 6.5 m /. It is the melt tension (g weight) of the polypropylene resin measured under the conditions of minutes.
MFR is a melt flow rate of a polypropylene resin measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210.
[9] The method for producing a foamed polypropylene resin sheet according to [8], wherein foaming is performed at a foaming ratio of 1.30 or more at the time of forming the foamed intermediate layer in the extrusion molding step.
[10] The polypropylene resin for a surface layer contains a propylene polymer and an ethylene / α-olefin copolymer, and has a melt flow rate of 2 measured at 230 ° C. under a load of 21.18 N according to JIS K7210. -15 g / 10 min, the intrinsic viscosity of the xylene-soluble component in tetrahydronaphthalene at 135 ° C. is 6 to 10 dl / g, and the ratio of the mass-average molecular weight _Mw to the number-average molecular weight _Mn of the xylene-insoluble component ( _Mw / _Mn ) is 7 or more, and the content ratio of the ethylene / α-olefin copolymer is 20 to 40% by mass,
In the propylene polymer, the total content of ethylene units and α-olefin units is 5.0% by mass or less, and the content ratio of propylene units is 95% by mass or more,
The method for producing a foamed polypropylene resin sheet according to [8] or [9], wherein the ethylene / α-olefin copolymer contains 20 to 40% by mass of ethylene units and 60 to 80% by mass of α-olefin units.
[11] The method for producing a foamed polypropylene resin sheet according to [10], wherein the polypropylene resin for a surface layer is obtained by polymerizing an ethylene monomer and an α-olefin monomer in the presence of a propylene polymer.
[12] An electron donor selected from (A) magnesium, titanium, halogen, and a succinate compound in the polymerization for obtaining at least one of the polypropylene resin for the foamed intermediate layer and the polypropylene resin for the surface layer. Any one of [8] to [11], using a catalyst containing an external electron donor compound selected from (B) an organoaluminum compound; and (C) a silicon compound; The method for producing a foamed polypropylene-based resin sheet according to item 1.

The polypropylene-based resin foam sheet of the present invention has a high expansion ratio and excellent surface appearance.
According to the method for producing a foamed polypropylene resin sheet of the present invention, a foamed polypropylene resin sheet having a high expansion ratio and an excellent surface appearance can be easily produced despite being adhered to a metal roll by blowing air. .

It is sectional drawing which shows one Embodiment of the polypropylene resin foam sheet of this invention. 4 is a graph showing melt flow rate dependency of melt tension. It is a photograph which shows an example of each stage in evaluation criteria of a surface appearance.

One embodiment of the polypropylene-based resin foam sheet (hereinafter abbreviated as “foam sheet”) of the present invention will be described.
As shown in the embodiment of FIG. 1, the foam sheet 10 of the present embodiment includes a configuration including a foam intermediate layer 11 and surface layers 12 and 13 provided on both surfaces of the foam intermediate layer. That is, as the foamed sheet of the present embodiment, a laminated sheet of two or three layers or three or three layers is exemplified.

Both the foamed intermediate layer 11 and the surface layers 12, 13 contain a polypropylene-based resin. However, the polypropylene resin constituting the surface layers 12 and 13 (polypropylene resin for the surface layer) is different from the polypropylene resin constituting the foamed intermediate layer 11 (the polypropylene resin for the foamed intermediate layer) by the following formula (1). Are equal or large. The larger the melt tension index determined by the formula (1), the higher the melt tension of the resin.
log (melt tension index) = log (MT) + 0.85 log (MFR)-0.82 (1)
In the formula (1), MT is measured using a melt tension measuring device having a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm with a flat upper surface, a measurement temperature of 200 ° C., a resin extrusion speed of 15 mm / min, It is the melt tension (melt tension, unit is g weight) of the polypropylene resin measured under the condition of a take-up speed of 6.5 m / min. Specifically, a polypropylene-based resin is melted at a temperature of 200 ° C. using a capillary rheometer having a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface. The melted polypropylene resin is discharged from the orifice at a resin extrusion speed of 15 mm / min to form a strand. The strand is taken up at a take-up speed of 6.5 m / min using a rotating take-up means, and the tension is measured.
MFR is a melt flow rate of a polypropylene resin measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210.
The technical meaning of Expression (1) will be supplementarily described. FIG. 2 shows the MFR dependence of MT (g weight) measured at 230 ° C. in general-purpose linear homopolypropylene. MT increases with lower MFR, and log (MT) decreases almost linearly with increasing log (MFR). Even for polypropylene having a higher melt tension, if the same type, the same linear relationship is established, and the slope of the straight line is almost constant (0.85 in the equation (1) has a minus sign). Therefore, the relative evaluation of the melt tension independent of the MFR can be made by the value of the Y intercept of the straight line (the value at MFR = 1 (log (MFR) = 0)). Further, in the equation (1), a constant term is defined and standardized so that the melt tension index becomes 1 (log (melt tension index) = 0) in general-purpose linear homopolypropylene.
In the formation of a multilayer foam sheet, a phenomenon called "curning" occurs, and the sheet surface tends to be wavy, and the surface appearance tends to deteriorate. When the polypropylene resin for the surface layer has a smaller melt tension index than the polypropylene resin for the foamed intermediate layer, the effect of preventing the curtain is insufficient, and the surface appearance of the foamed sheet 10 is easily damaged.
The melt tension index of the polypropylene resin for the surface layer is 1.8 or more, and preferably 2.0 or more. Further, the melt tension index of the polypropylene resin for the foamed intermediate layer is 1.2 or more. If the melt tension index of the polypropylene resin for the surface layer and the polypropylene resin for the foamed intermediate layer is less than the lower limit, the surface appearance of the foamed sheet 10 may be impaired or the expansion ratio may not be increased.
From the viewpoint of practicality, the melt tension index of the polypropylene resin for the surface layer and the melt tension index of the polypropylene resin for the foamed intermediate layer are both preferably 10 or less, more preferably 5 or less. If the melt tension index of the polypropylene resin for the surface layer is too large, foaming in the intermediate layer is adversely affected, and a good foamed sheet may not be obtained.

The ratio of the thickness of the foamed intermediate layer 11 and _{(T 1)} thickness of surface layer 12 and 13 _{(T 2) (T 1 /} T 2) is 3 / 1-10 / 1, 5 / 1-8 / 1 is preferred. If the thickness ratio of the surface layers 12 and 13 is too small, the surface appearance tends to be impaired. If the thickness ratio of the surface layers 12 and 13 is too large, the foamed intermediate layer becomes thin, and In some cases, the body cannot exhibit its advantageous properties (light weight, heat insulation, shock absorption).
The two surface layers 12, 13 need not be of the same thickness. However, from the viewpoint of ease of manufacturing the foam sheet 10, the thickness of the one surface layer 12 may be 0.8 to 1.2 times the thickness of the other surface layer 13. preferable.

The expansion ratio of the foam sheet 10 is preferably 1.30 times or more, more preferably 1.35 times or more, and even more preferably 1.40 times or more. When the expansion ratio of the foam sheet 10 is equal to or more than the lower limit, the properties as a foam can be sufficiently exhibited.
On the other hand, from the viewpoint of easy production of the foamed sheet 10, the expansion ratio of the foamed sheet 10 is preferably 5 times or less, more preferably 3 times or less.
The expansion ratio of the foam sheet 10 is determined by the following method.
That is, measuring the density _{D 1} of the foamed sheet 10 in accordance with JIS K7112. The calculated ratio of the density _{D 1 (D 1 / D 0} ) for the density D ₀ of the resin when the foam sheet 10 is not expanded, and its value as expansion ratio.
Although the foam sheet 10 includes the non-foamed surface layers 12 and 13, the foaming ratio is a value obtained including the non-foamed surface layer. In the case where a layer other than the surface layer and the foamed intermediate layer is included, the value is a value including the layer.

The foamed intermediate layer 11 is a layer that is a main component of the foamed sheet 10.
Examples of the polypropylene resin for the foamed intermediate layer include a propylene homopolymer, a propylene random copolymer containing at least one of ethylene units and α-olefin units in an amount of 5.0% by mass or less, and block polypropylene (ethylene copolymer in the presence of a propylene polymer. A polymerization mixture obtained by polymerizing a monomer and an α-olefin monomer). Among these polypropylene resins, a propylene homopolymer or a propylene random copolymer containing at least one of an ethylene unit and an α-olefin unit at 5.0% by mass or less is preferable because rigidity and heat resistance are increased, Propylene homopolymer is more preferred. Examples of the α-olefin include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-dodecene, and the like.
In addition, the foamed intermediate layer 11 may contain other polyolefin-based resin in addition to the polypropylene-based resin. Examples of other polyolefin-based resins include branched low-density polyethylene, linear low-density polyethylene, ethylene / α-olefin copolymer, high-density polyethylene, and branched polypropylene. Among these other polyolefin-based resins, a branched low-density polyethylene is preferable because foamability is high.
The content ratio of the polypropylene resin in the foamed intermediate layer 11 is preferably 60% by mass or more, and more preferably 75% by mass or more, since the heat resistance of the foamed sheet 10 increases. The resin component of the foamed intermediate layer 11 may be composed of only a polypropylene resin.

The polypropylene resin for the foamed intermediate layer preferably has an MFR of 2 to 15 g / 10 g, more preferably 5 to 12 g / 10 min, and even more preferably 3 to 10 g / 10 min. Here, the MFR is a value measured under the conditions of a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210.
If the MFR of the polypropylene resin for the foamed intermediate layer is equal to or higher than the lower limit, the extrusion moldability when producing the foam sheet 10 is increased.

The polypropylene resin for the foamed intermediate layer preferably has a ratio ( _Mw / _Mn ) of the mass average molecular weight _Mw to the number average molecular weight _Mn of the xylene-insoluble component of 6 or more, more preferably 8 or more. preferable. Here, the mass average molecular weight _Mw and the number average molecular weight _Mn of the xylene-insoluble portion of the polypropylene-based resin are values measured using gel permeation chromatography. As a method for collecting xylene-insoluble components, a sample of a polypropylene-based resin is dissolved in o-xylene at 135 ° C., then cooled to 25 ° C., and the cooled solution is filtered using a filter paper, and placed on a filter paper. There is a method of collecting the remaining xylene-insoluble matter.
When the _Mw / _{Mn of the} polypropylene resin for the foamed intermediate layer is at least the lower limit, the foaming ratio of the foamed sheet 10 can be increased.

  In the foamed intermediate layer 11, optional components include, for example, chlorine absorber, heat stabilizer, antioxidant, light stabilizer, ultraviolet absorber, internal lubricant, external lubricant, antiblocking agent, antistatic agent, antifogging agent , Crystal nucleating agents, flame retardants, dispersants, copper damage inhibitors, neutralizers, plasticizers, foaming agents, foam inhibitors, crosslinking agents, peroxides, oil extensions and pigments (organic or inorganic) An agent may be included.

The surface layer 12 is an outermost non-foamed layer.
The polypropylene resin for the surface layer preferably contains a propylene polymer and an ethylene / α-olefin copolymer mainly composed of a rubber component from the viewpoint of improving foamability and surface appearance. Further, a polypropylene-based resin containing a propylene polymer and an ethylene / α-olefin copolymer is a block polypropylene (a polymerization mixture obtained by polymerizing an ethylene monomer and an α-olefin monomer in the presence of a propylene polymer). Is more preferred. The polymerization mixture has different physical properties from a mixture obtained by mechanically mixing a separately obtained propylene polymer and an ethylene / α-olefin copolymer (mechanical mixture). This is presumed to be because the polymerization mixture and the mechanical mixture are different in the dispersion state of the ethylene / α-olefin copolymer in the propylene polymer, but at the molecular level of the ethylene / α-olefin copolymer. At present, there is no known practical means for analyzing the state of dispersion.

Specifically, the polypropylene-based resin comprising the above-mentioned polymerization mixture can be produced by multi-stage polymerization. For example, in a first-stage polymerization reactor, a propylene monomer alone or a mixture of a propylene monomer and a small amount of an α-olefin monomer is polymerized in the presence of a catalyst, and the obtained propylene polymer is subjected to two-stage polymerization. The polypropylene-based resin can be obtained by supplying to the second polymerization reactor and copolymerizing the ethylene monomer and the α-olefin monomer in the second-stage polymerization reactor. In this method, in a second-stage polymerization reactor, an ethylene / α-olefin copolymer is produced in the presence of a propylene polymer, and the produced ethylene / α-olefin copolymer is mixed with the propylene polymer. .
By producing the ethylene / α-olefin copolymer in the presence of the propylene polymer, the productivity is increased, and the dispersibility of the ethylene / α-olefin copolymer in the propylene polymer is increased. The balance of impact resistance is improved.
Further, the multi-stage polymerization is not limited to the above method, the propylene polymer may be polymerized in a plurality of polymerization reactors, or the ethylene / α-olefin copolymer may be polymerized in a plurality of polymerization reactors. .
As a method for obtaining a polypropylene-based resin, a method using a polymerization vessel having a gradient of monomer concentration or polymerization conditions may be mentioned. In such a polymerization vessel, for example, one in which at least two polymerization regions are joined can be used, and the monomer can be polymerized by gas phase polymerization.
Specifically, in the presence of a catalyst, a monomer is supplied and polymerized in a polymerization region composed of a riser, and the monomer is supplied and polymerized in a descender connected to the riser, and the riser is formed. The polymer product is recovered while circulating through the downcomer. The method comprises means for completely or partially preventing the gas mixture present in the riser from entering the downcomer. Also, a gas and / or liquid mixture having a different composition than the gas mixture present in the riser is introduced into the downcomer.
As the polymerization method, for example, a method described in JP-T-2002-520426 can be applied.
At the time of polymerization, the molecular weight of the obtained polymer can be adjusted by adding hydrogen. As the amount of hydrogenation increases, the molecular weight decreases.

  In the polymerization for obtaining the polymerization mixture, it is preferable to use a stereospecific Ziegler-Natta catalyst. More preferably, the catalyst contains (A) a solid catalyst component containing magnesium, titanium, halogen and an electron donor compound; (B) an organoaluminum compound; and (C) an external electron donor compound.

As the titanium compound used for preparing the solid catalyst component (A), a tetravalent compound represented by the general formula: Ti (OR) _g X _4-g (R is a hydrocarbon group, X is a halogen, and 0 ≦ g ≦ 4) Are preferred. Examples of the hydrocarbon group include methyl, ethyl, propyl, and butyl, and examples of the halogen include Cl and Br.
More specific titanium _compounds, TiCl _4, TiBr 4, titanium tetrahalides such as _{TiI 4; Ti (OCH 3)} Cl 3, Ti (OC 2 H 5) Cl 3, Ti (O n -C 4 H _{9) Cl 3, Ti (OC} 2 H 5) Br 3, Ti (O-isoC 4 H 9) trihalide, alkoxy titanium such as _{Br 3; Ti (OCH 3)} 2 Cl 2, Ti (OC 2 H 5) _{2 Cl 2, Ti (O n} -C 4 H 9) 2 Cl 2, Ti (OC 2 H 5) 2 dihalogenated alkoxy titanium such as _{Br 2; Ti (OCH 3)} 3 Cl, Ti (OC 2 H 5) _{3 Cl, Ti (O n -C} 4 H 9) 3 Cl, Ti (OC 2 H 5) 3 monohalogenated trialkoxy titanium such as _{Br; Ti (OCH 3) 4} , Ti (OC 2 H 5 _{4, Ti (O n -C 4} H 9) 4 and the like tetraalkoxytitanium such. One of these titanium compounds may be used alone, or two or more thereof may be used in combination.
Preferred among the above titanium compounds are halogen-containing titanium compounds, particularly titanium tetrahalides, and particularly preferred is titanium tetrachloride (TiCl ₄ ).

As the magnesium compound used for preparing the solid catalyst component (A), a magnesium compound having a magnesium-carbon bond or a magnesium-hydrogen bond, such as dimethylmagnesium, diethylmagnesium, dipropylmagnesium, dibutylmagnesium, diamylmagnesium, dihexylmagnesium, Didecyl magnesium, ethyl magnesium chloride, propyl magnesium chloride, butyl magnesium chloride, hexyl magnesium chloride, amyl magnesium chloride, butyl ethoxy magnesium, ethyl butyl magnesium, butyl magnesium hydride and the like.
These magnesium compounds can be used in the form of a complex compound with, for example, organoaluminum, and may be in a liquid state or a solid state.
Further preferred magnesium compounds include magnesium halides such as magnesium chloride, magnesium bromide, magnesium iodide, and magnesium fluoride; and alkoxy such as methoxy magnesium chloride, ethoxy magnesium chloride, isopropoxy magnesium chloride, butoxy magnesium chloride, and octoxy magnesium chloride. Magnesium halide; allyoxy magnesium halide such as phenoxy magnesium chloride, methylphenoxy magnesium chloride; alkoxy magnesium such as ethoxy magnesium, isopropoxy magnesium, butoxy magnesium, n-octoxy magnesium, 2-ethylhexoxy magnesium; phenoxy magnesium, dimethyl Allyloxymagnesium such as phenoxymagnesium; magnesium laurate , And the like carboxylates of magnesium such as magnesium stearate.
One of these magnesium compounds may be used alone, or two or more thereof may be used in combination.

Examples of the electron donor compound used in the preparation of the solid catalyst component (A) used in the production of the above-described propylene resin composition include alcohols, phenols, ketones, aldehydes, carboxylic acids, esters of organic acids or inorganic acids, ethers, Oxygen-containing electron donors such as acid amides and acid anhydrides, and nitrogen-containing electron donors such as ammonia, amines, nitriles, and isocyanates are known. Is preferred. Dicarboxylic acids are compounds having two carboxyl groups. The following are specific examples of dicarboxylic acid diesters.
Diethyl succinate, dibutyl succinate, diethyl methyl succinate, diethyl diisopropyl succinate, diallyl ethyl succinate, diisobutyl α-methylglutarate, dibutyl methyl malonate, diethyl malonate, diethyl ethyl malonate, isopropyl Diethyl malonate, diethyl butylmalonate, diethyl phenylmalonate, diethyl diethylmalonate, diethyl allylmalonate, diethyldiisobutylmalonate, diethyldinormalbutylmalonate, dimethylmaleate, monooctyl maleate, dioctyl maleate, maleic acid Dibutyl, dibutyl butyl maleate, diethyl butyl maleate, diisopropyl β-methylglutarate, di-2-ethylhexyl fumarate, diethyl itaconate, di itaconate Aliphatic polycarboxylic acid esters such as butyl, dioctyl citraconic acid and dimethyl citraconic acid;
Alicyclic polycarboxylates such as diethyl 1,2-cyclohexanecarboxylate, diisobutyl 1,2-cyclohexanecarboxylate, diethyl tetrahydrophthalate and diethyl nadiclate.

Monoethyl phthalate, dimethyl phthalate, methyl ethyl phthalate, monoisobutyl phthalate, mononormal butyl phthalate, diethyl phthalate, ethyl isobutyl phthalate, ethyl normal butyl phthalate, di-n-propyl phthalate, diisopropyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, Di-n-heptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, dineopentyl phthalate, didecyl phthalate, benzyl butyl phthalate, diphenyl phthalate, diethyl naphthalene dicarboxylate, dibutyl naphthalene dicarboxylate, triethyl trimellitate, trimellitate Aromatic polycarboxylic acid esters such as dibutyl acid.
Heterocyclic polycarboxylic acid esters such as 3,4-furandicarboxylic acid.

  Polyhydric hydroxy compound esters can also be used, and preferred specific examples thereof are 1,2-diacetoxybenzene, 1-methyl-2,3-diacetoxybenzene, 2,3-diacetoxynaphthalene, and ethylene glycol diester. Pivalate, butanediol pivalate and the like can be mentioned. Similarly, an ester of a hydroxy-substituted carboxylic acid can be used as the electron donor compound, and preferred specific examples thereof include benzoylethyl salicylate, acetylisobutyl salicylate, and acetylmethyl salicylate.

Other examples of the polyvalent carboxylic acid diester that can be supported in the solid catalyst component include diethyl adipate, diisobutyl adipate, diisopropyl sebacate, di-n-butyl sebacate, di-n-octyl sebacate, and sebacic acid. Esters of long-chain dicarboxylic acids such as di-2-ethylhexyl can be mentioned.
Dicarboxylic acids also include succinic acid and substituted succinic acids having a substituent such as an alkyl group at the 1- or 2-position of succinic acid. Among the dicarboxylic acid diesters, diesters of succinic acid, substituted succinic acid, phthalic acid, maleic acid, and substituted malonic acid are more preferable, and a succinate (succinate) -based electron donor compound can be suitably used.
Suitable succinate-based compounds are compounds having a succinate structure represented by the following chemical formula (I).
When a polymerization mixture obtained by polymerization using a catalyst containing a succinate-based compound as an electron donor is used, the _Mw / _Mn of the xylene-insoluble component can be easily set in the following range, and the surface appearance can be easily improved. it can. The fact that the xylene-insoluble matter has a large M _w / M _n means that the molecular weight distribution of the propylene polymer and the ethylene / α-olefin copolymer constituting the polypropylene resin is wide. It is considered that when the molecular weight distribution is wide, the melt tension index of each component is improved, and the dispersibility between both components is improved, so that the melt tension index of the polypropylene resin is further improved.

In the formula (I), R ¹ and R ² are the same or different from each other, and may be a linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl, or alkylaryl having 1 to 20 carbon atoms which may contain a hetero atom. Group. Desirable R ¹ and R ² are an alkyl, cycloalkyl, aryl, arylalkyl, and alkylaryl group having 1 to 8 carbon atoms. R ¹ and R ² are particularly preferably compounds selected from primary alkyls, especially branched primary alkyls. Specific examples of suitable R ¹ and R ² include methyl, ethyl, n-propyl, n-butyl, isobutyl, neopentyl and 2-ethylhexyl, with ethyl, isobutyl and neopentyl being particularly preferred.
R ^{3 to} R ⁶ are the same or different from each other, and are hydrogen or a linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl, or alkylaryl group having 1 to 20 carbon atoms which may contain a hetero atom. It is. R ³ and R ⁴ , and R ⁵ and R ⁶ bonded to the same carbon atom may be bonded to each other to form a ring structure. Any two or more of R ^{3 to} R ⁶ bonded to different carbon atoms may be bonded to each other to form a ring structure.

One preferred group of compounds of formula (I) is that wherein R ³ -R ⁵ are hydrogen and R ⁶ has 3-10 carbon atoms, branched alkyl, cycloalkyl, aryl, arylalkyl And a monosubstituted succinate compound of an alkylaryl group.
Specific examples of suitable monosubstituted succinate compounds include diethyl-sec-butylsuccinate, diethyltexylsuccinate, diethylcyclopropylsuccinate, diethylnorbonylsuccinate, diethylperhydrosuccinate, and diethyltrimethylsilyl. Succinate, diethylmethoxysuccinate, diethyl-p-methoxyphenylsuccinate, diethyl-p-chlorophenylsuccinate, diethylphenylsuccinate, diethylcyclohexylsuccinate, diethylbenzylsuccinate, diethylcyclohexylmethyl Succinate, diethyl-t-butyl succinate, diethyl isobutyl succinate, diethyl isopropyl succinate, diethyl neopentyl succinate, diethyl isopentyl succinate Succinate, diethyl (1-trifluoromethylethyl) succinate, diethyl fluorenyl succinate, 1- (ethoxycarbodiisobutylphenyl) succinate, diisobutyl-sec-butyl succinate, diisobutyl texyl succinate, diisobutyl cyclopropyl succinate , Diisobutylnorbonyl succinate, diisobutyl perhydrosuccinate, diisobutyl trimethylsilyl succinate, diisobutyl methoxy succinate, diisobutyl-p-methoxyphenyl succinate, diisobutyl-p-chlorophenyl succinate, diisobutyl cyclohexyls Succinate, diisobutylbenzylsuccinate, diisobutylcyclohexylmethylsuccinate, diisobutyl-t-butylsuccinate Diisobutyl isobutyl succinate, diisobutyl isopropyl succinate, diisobutyl neopentyl succinate, diisobutyl isopentyl succinate, diisobutyl (1-trifluoromethylethyl) succinate, diisobutyl fluorenyl succinate, dineopentyl-sec-butyl Succinate, Dineopentyl Texyl Succinate, Dineopentyl Cyclopropyl Succinate, Dineopentyl Norbonyl Succinate, Dineopentyl Perihydrosuccinate, Dineopentyl Trimethylsilyl Succinate, Dineopentyl Methoxy succinate, Dineopentyl-p-methoxyphenyl succinate, Dineopentyl-p-chlorophenyl succinate, Dineopentylphenyl succinate, Dineo Pentyl cyclohexyl succinate, Dineopentyl benzyl succinate, Dineopentyl cyclohexyl methyl succinate, Dineopentyl-t-butyl succinate, Dineopentyl isobutyl succinate, Dineopentyl isopropyl succinate, Dineo Examples include pentyl neopentyl succinate, dineopentyl isopentyl succinate, dineopentyl (1-trifluoromethylethyl) succinate, and dineopentyl fluorenyl succinate.
One of these compounds may be used alone, or two or more of them may be used in combination.

Other preferred compounds of the formula (I) are those in which at least two of R ^{3 to} R ⁶ are not hydrogen, but are linear or branched alkyl having 1 to 20 carbon atoms which may contain a hetero atom. Examples include disubstituted succinate compounds selected from alkenyl, cycloalkyl, aryl, arylalkyl, or alkylaryl groups. Preferably, the two non-hydrogen groups are attached to the same carbon atom.
Specific examples of suitable disubstituted succinate compounds include diethyl-2,2-dimethylsuccinate, diethyl-2-ethyl-2-methylsuccinate, diethyl-2-benzyl-2-isopropylsuccinate, diethyl -2-cyclohexylmethyl-2-isobutylsuccinate, diethyl-2-cyclopentyl-2-n-propylsuccinate, diethyl-2-cyclopentyl-2-n-butylsuccinate, diethyl-2,2-diisobutyl Succinate, diethyl-2-cyclohexyl-2-ethylsuccinate, diethyl-2-isopropyl-2-methylsuccinate, diethyl-2-tetradecyl-2-ethylsuccinate, diethyl-2-isobutyl-2 -Ethyl succinate, diethyl-2- (1-trifluoromethylethyl -2-methylsuccinate, diethyl-2-isopentyl-2-isobutylsuccinate, diethyl-2-phenyl-2-n-butylsuccinate, diisobutyl-2,2-dimethylsuccinate, diisobutyl-2 -Ethyl-2-methylsuccinate, diisobutyl-2-benzyl-2-isopropylsuccinate, diisobutyl-2-cyclohexylmethyl-2-isobutylsuccinate, diisobutyl-2-cyclopentyl-2-n-propylsuccinate , Diisobutyl-2-cyclopentyl-2-n-butylsuccinate, diisobutyl-2,2-diisobutylsuccinate, diisobutyl-2-cyclohexyl-2-ethylsuccinate, diisobutyl-2-isopropyl-2-methyl Succinate, diisobutyl-2-tet Decyl-2-ethylsuccinate, diisobutyl-2-isobutyl-2-ethylsuccinate, diisobutyl-2- (1-trifluoromethylethyl) -2-methylsuccinate, diisobutyl-2-isopentyl-2- Isobutyl succinate, diisobutyl-2-phenyl-2-n-butyl succinate, diisobutyl-2,2-diisopropyl succinate, diisobutyl-2-phenyl-2-n-propyl succinate, dineopentyl-2, 2-dimethylsuccinate, dineopentyl-2-ethyl-2-methylsuccinate, dineopentyl-2-benzyl-2-isopropylsuccinate, dineopentyl-2-cyclohexylmethyl-2-isobutylsuccinate, dineopentyl-2 -Cyclopentyl-2-n-propyl Succinate, dineopentyl-2-cyclopentyl-2-n-butylsuccinate, dineopentyl-2,2-diisobutylsuccinate, dineopentyl-2-cyclohexyl-2-ethylsuccinate, dineopentyl-2-isopropyl-2-methyl Succinate, dineopentyl-2-tetradecyl-2-ethylsuccinate, dineopentyl-2-isobutyl-2-ethylsuccinate, dineopentyl-2- (1-trifluoromethylethyl) -2-methylsuccinate, Dineopentyl-2,2-diisopropylsuccinate, dineopentyl-2-isopentyl-2-isobutylsuccinate, and dineopentyl-2-phenyl-2-n-butylsuccinate are exemplified.
One of these compounds may be used alone, or two or more of them may be used in combination.

Particularly preferred as the compound represented by the formula (I) is a compound wherein at least two groups different from hydrogen, that is, R ³ and R ⁵ , or R ⁴ and R ⁶ are bonded to different carbon atoms. Are also mentioned.
Specific examples of this compound include diethyl-2,3-bis (trimethylsilyl) succinate, diethyl-2,2-sec-butyl-3-methylsuccinate, and diethyl-2- (3,3,3-trifluoro) Propyl) -3-methylsuccinate, diethyl-2,3-bis (2-ethylbutyl) succinate, diethyl-2,3-diethyl-2-isopropylsuccinate, diethyl-2,3-diisopropyl-2-methyl Succinate, diethyl-2,3-dicyclohexyl-2-methylsuccinate, diethyl-2,3-dibenzylsuccinate, diethyl-2,3-diisopropylsuccinate, diethyl-2,3-bis ( Cyclohexylmethyl) succinate, diethyl-2,3-di-t-butylsuccinate, diethyl-2,3-diethyl Butyl succinate, diethyl-2,3-dineopentyl succinate, diethyl-2,3-diisopentyl succinate, diethyl-2,3- (1-trifluoromethylethyl) succinate, diethyl-2 , 3-tetradecylsuccinate, diethyl-2,3-fluorenylsuccinate, diethyl-2-isopropyl-3-isobutylsuccinate, diethyl-2-tert-butyl-3-isopropylsuccinate, diethyl -2-isopropyl-3-cyclohexylsuccinate, diethyl-2-isopentyl-3-cyclohexylsuccinate, diethyl-2-tetradecyl-3-cyclohexylmethylsuccinate, diethyl-2-cyclohexyl-3-cyclopentylsuccinate Nate, diethyl-2,2,3,3-tetramethyl Succinate, diethyl-2,2,3,3-tetraethylsuccinate, diethyl-2,2,3,3-tetrapropylsuccinate, diethyl-2,3-diethyl-2,3-diisopropylsuccinate, Diisobutyl-2,3-bis (trimethylsilyl) succinate, diisobutyl-2,2-sec-butyl-3-methylsuccinate, diisobutyl-2- (3,3,3-trifluoropropyl) -3-methylsuccinate , Diisobutyl-2,3-bis (2-ethylbutyl) succinate, diisobutyl-2,3-diethyl-2-isopropylsuccinate, diisobutyl-2,3-diisopropyl-2-methylsuccinate, diisobutyl-2, 3-dicyclohexyl-2-methylsuccinate, diisobutyl-2,3-dibenzylsuccinate, Isobutyl-2,3-diisopropylsuccinate, diisobutyl-2,3-bis (cyclohexylmethyl) succinate, diisobutyl-2,3-di-t-butylsuccinate, diisobutyl-2,3-diisobutylsuccinate, Diisobutyl-2,3-dineopentylsuccinate, diisobutyl-2,3-diisopentylsuccinate, diisobutyl-2,3- (1-trifluoromethylethyl) succinate, diisobutyl-2,3-n-propyl Succinate, diisobutyl-2,3-tetradecylsuccinate, diisobutyl-2,3-fluorenylsuccinate, diisobutyl-2-isopropyl-3-isobutylsuccinate, diisobutyl-2-tert-butyl-3 -Isopropyl succinate, diisobutyl-2- Isopropyl-3-cyclohexylsuccinate, diisobutyl-2-isopentyl-3-cyclohexylsuccinate, diisobutyl-2-n-propyl-3- (cyclohexylmethyl) succinate, diisobutyl-2-tetradecyl-3-cyclohexylmethylsuccinate , Diisobutyl-2,2,3,3-tetramethylsuccinate, diisobutyl-2,2,3,3-tetraethylsuccinate, diisobutyl-2,2,3,3-tetrapropylsuccinate, diisobutyl -2,3-diethyl-2,3-diisopropylsuccinate, diisobutyl-2-cyclohexyl-3-cyclopentylsuccinate, dineopentyl-2,3-bis (trimethylsilyl) succinate, dineopentyl-2,2-sec-butyl -3-me Rusuccinate, Dineopentyl-2- (3,3,3-trifluoropropyl) -3-methylsuccinate, Dineopentyl-2,3-bis (2-ethylbutyl) succinate, Dineopentyl-2,3-diethyl-2-isopropyl Succinate, Dineopentyl-2,3-diisopropyl-2-methylsuccinate, Dineopentyl-2,3-dicyclohexyl-2-methylsuccinate, Dineopentyl-2,3-dibenzylsuccinate, Dineopentyl-2, 3-diisopropylsuccinate, dineopentyl-2,3-bis (cyclohexylmethyl) succinate, dineopentyl-2,3-di-t-butylsuccinate, dineopentyl-2,3-diisobutylsuccinate, dineopentyl-2, 3-dineopentylsk , Dineopentyl-2,3-diisopentylsuccinate, dineopentyl-2,3- (1-trifluoromethylethyl) succinate, dineopentyl-2,3-dineopentylsuccinate, dineopentyl-2,3- Diisopentyl succinate, dineopentyl-2,3-tetradecylsuccinate, dineopentyl-2,3-fluorenylsuccinate, dineopentyl-2-isopropyl-3-isobutylsuccinate, dineopentyl-2-tert- Butyl-3-isopropylsuccinate, dineopentyl-2-isopropyl-3-cyclohexylsuccinate, dineopentyl-2-isopentyl-3-cyclohexylsuccinate, dineopentyl-2-tetradecyl-3-cyclohexylmethylsuccinate , Dineopentyl-2-n-propyl-3- (cyclohexylmethyl) succinate, Dineopentyl-2-cyclohexyl-3-cyclopentylsuccinate, Dineopentyl-2,2,3,3-tetraethylsuccinate, Dineopentyl-2,2 , 3,3-tetrapropyl succinate, and dineopentyl-2,3-diethyl-2,3-diisopropyl succinate.
One of these compounds may be used alone, or two or more of them may be used in combination.

Further, as the compound represented by the formula (I), a compound in which at least two or more of R ^{3 to} R ⁶ are bonded to form a ring is also preferable.
As such compounds, compounds described in JP-T-2002-542347, for example, 1- (ethoxycarbonyl) -1- (ethoxyacetyl) -2,6-dimethylcyclohexane, 1- (ethoxycarbonyl)- 1- (ethoxyacetyl) -2,5-dimethylcyclopentane, 1- (ethoxycarbonyl) -1- (ethoxyacetylmethyl) -2-methylcyclohexane, 1- (ethoxycarbonyl) -1- (ethoxy (cyclohexyl) acetyl ) Cyclohexane. Further, cyclic succinate compounds such as diisobutyl 3,6-dimethylcyclohexane-1,2-dicarboxylate disclosed in WO 2009/069483 and WO 2009/057774 can also be suitably used.

When R ^{3 to} R ^{6 in the} compound represented by the formula (I) include a hetero atom, the hetero atom is a group 15 atom such as a nitrogen atom or a phosphorus atom, or a group 16 atom such as an oxygen atom or a sulfur atom. It is preferably a group atom. Examples of the compound in which R ^{3 to} R ⁶ contain a Group 15 atom include the compounds disclosed in JP-A-2005-306910. Examples of the compound in which R ^{3 to} R ⁶ contain a Group 16 atom include the compounds disclosed in JP-A-2004-131537.
Examples of the halogen atom constituting the solid catalyst component (A) include fluorine, chlorine, bromine, iodine and a mixture thereof, and chlorine is particularly preferable.

Examples of the organoaluminum compound (B) include trialkylaluminums such as triethylaluminum and tributylaluminum, trialkenylaluminums such as triisoprenylaluminum, dialkylaluminum alkoxides such as diethylaluminum ethoxide and dibutylaluminum butoxide, and ethylaluminum sesquiethoxy. In addition to alkyl aluminum sesquialkoxides such as butyl aluminum butyl sesquibutoxide, R ⁷ _2.5 Al (OR ⁸ ) _0.5 (R ⁷ and R ⁸ may be different or the same hydrocarbon groups. Partially alkoxylated alkylaluminum, diethylaluminum chloride, dibutylaluminum chloride, diethylaluminum having an average composition represented by: Alkyl aluminum sesquihalogenides such as dialkylaluminum halogenides such as mubromide, ethylaluminum sesquichloride, butylaluminum sesquichloride, ethylaluminum sesquibromide, alkylaluminum dihalogenides such as ethylaluminum dichloride, propylaluminum dichloride and butylaluminum dibromide Partially halogenated alkyl aluminum such as dialkyl aluminum hydride such as alkyl aluminum, diethyl aluminum hydride and dibutyl aluminum hydride, and partially hydrogenated alkyl aluminum such as alkyl aluminum dihydride such as ethyl aluminum dihydride and propyl aluminum dihydride , Ethyl aluminum ethoxy cyclolide, butyl aluminum butoki Chlorides, alkylaluminum, and the like which are partially alkoxylated and halogenated, such as ethylaluminum ethoxy bromide.
As the organoaluminum compound (B), one type may be used alone, or two or more types may be used in combination.

The external electron donor compound (C) includes an organosilicon compound.
Preferred organic silicon compounds include, for example, trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, t-butylmethyldimethoxysilane, t-butylmethyldiethoxysilane, t-amylmethyldiethoxysilane Silane, diphenyldimethoxysilane, phenylmethyldimethoxysilane, diphenyldiethoxysilane, bis-tolyldimethoxysilane, bis-m-tolyldimethoxysilane, bis-p-tolyldimethoxysilane, bis-p-tolyldiethoxysilane, bisethylphenyldimethoxysilane , Dicyclopentyldimethoxysilane, dicyclohexyldimethoxysilane, cyclohexylmethyldimethoxysilane, cyclohexylmethyldiethoxysila , Ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, n-propyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, phenyltrimethoxysilane, γ-chloropropyltrimethoxysilane , Methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, t-butyltriethoxysilane, texyltrimethoxysilane, n-butyltriethoxysilane, iso-butyltriethoxysilane, phenyltriethoxysilane, γ- Aminopropyltriethoxysilane, chlorotriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane Orchid, 2-norbornanetrimethoxysilane, 2-norbornanetriethoxysilane, 2-norbornanemethyldimethoxysilane, ethyl silicate, butyl silicate, trimethylphenoxysilane, methyltriallyloxysilane, vinyltris (β-methoxyethoxysilane ), Vinyltriacetoxysilane, dimethyltetraethoxydisiloxane, and the like.
Among them, ethyltriethoxysilane, n-propyltriethoxysilane, t-butyltriethoxysilane, texyltrimethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, vinyltributoxysilane, diphenyldimethoxysilane, diisopropyldimethoxysilane Silane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, phenylmethyldimethoxysilane, bis p-tolyldimethoxysilane, p-tolylmethyldimethoxysilane, dicyclohexyldimethoxysilane, cyclohexylmethyldimethoxysilane, 2-nonebornanetriethoxysilane, 2 -Norbornanemethyldimethoxysilane, diphenyldiethoxysilane, ethyl silicate are preferred.
One kind of the external electron donor compound (C) may be used alone, or two or more kinds may be used in combination.

  Among the above catalysts, the solid catalyst component (A) is a solid catalyst containing magnesium, titanium, halogen, and an electron donor compound including a phthalate or succinate compound, and the organoaluminum compound (B) is triethylaluminum, tributylaluminum. Preferably, the trialkylaluminum and the external electron donor compound (C) are organosilicon compounds such as dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane and diisopropyldimethoxysilane.

The propylene polymer contained in the polymerization mixture preferably has a total content of ethylene units and α-olefin units of 5.0% by mass or less and a content ratio of propylene units of 95% by mass or more. If the total content of ethylene units and α-olefin units in the propylene polymer exceeds the above upper limit, rigidity tends to decrease.
The propylene polymer may have a propylene unit content of 100% by mass (a content ratio of an ethylene unit and an α-olefin unit is 0% by mass).

The ethylene / α-olefin copolymer preferably contains 20 to 40% by mass of ethylene units and 60 to 80% by mass of α-olefin units, and contains 25 to 35% by mass of ethylene units and 65 to 75% by mass of α-olefin units. Is preferred. If the ethylene unit of the ethylene / α-olefin copolymer is less than the lower limit or exceeds the upper limit, the surface appearance of the foamed sheet 10 tends to be impaired.
Examples of the α-olefin in the ethylene / α-olefin copolymer include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-dodecene, and the like. The α-olefin is preferably propylene from the viewpoint of improving foamability and surface appearance. That is, the ethylene / α-olefin copolymer is preferably an ethylene / propylene copolymer composed of ethylene units and propylene units.

The polypropylene resin for the surface layer has an MFR of preferably 2 to 15 g / 10 min, and more preferably 7 to 12 g / 10 min, since the surface appearance of the foamed sheet 10 becomes better. Here, the MFR is a value measured under the conditions of a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210.
Even if the MFR of the polypropylene resin for the surface layer is less than the lower limit or exceeds the upper limit, the surface appearance of the foamed sheet 10 may be impaired.

  The intrinsic viscosity of the xylene-soluble component in tetrahydronaphthalene at 135 ° C. of the polypropylene resin for the surface layer is preferably 6 to 10 dl / g, more preferably 6 to 8 dl / g. If the intrinsic viscosity of the polypropylene resin for the surface layer is not less than the lower limit, the surface appearance of the foamed sheet 10 can be improved, and if it is less than the upper limit, the polypropylene resin can be easily produced by polymerization.

In the polypropylene resin for the surface layer, the ratio of the mass average molecular weight _Mw to the number average molecular weight _Mn ( _Mw / _Mn ) of the xylene-insoluble component is preferably 7 or more, more preferably 9 or more. .
When the _Mw / _{Mn of the} polypropylene resin for the surface layer is at least the lower limit, the surface appearance of the foamed sheet 10 can be further improved.

The content ratio of the ethylene / α-olefin copolymer in the polypropylene resin for the surface layer is preferably 20 to 40% by mass, and more preferably 25 to 35% by mass. When the content ratio of the ethylene / α-olefin copolymer in the polypropylene resin for the surface layer is equal to or more than the lower limit, the surface appearance of the foamed sheet 10 can be improved, and when the content is equal to or less than the upper limit, rigidity is improved. Can be.
As the polypropylene resin for the surface layer, a polypropylene having a long chain branch can be used (Patent Document 1). However, polypropylene having long-chain branching has a more complicated production facility and process, has higher maintenance cost and is more expensive than linear polypropylene. As a result, it cannot be said that it is widely used in practice and production bases are limited, resulting in restrictions on the procurement of raw materials required for sheet molding. You will have a risk of stability. The linear polypropylene-based resin is preferable in that it not only provides a foamed sheet having excellent surface appearance, but also is a raw material that can be stably supplied at low cost and in large quantities in a wide range of industrial fields.

  The surface layers 12 and 13 also include optional components such as chlorine absorbers, heat stabilizers, antioxidants, light stabilizers, ultraviolet absorbers, internal lubricants, external lubricants, antiblocking agents, antistatic agents, and antifogging agents. Additives such as chemicals, crystal nucleating agents, flame retardants, dispersants, copper damage inhibitors, neutralizers, plasticizers, foam inhibitors, crosslinking agents, peroxides, oil extensions and pigments (organic or inorganic). May be included.

Next, a method for manufacturing the foam sheet of the present embodiment will be described.
The method for manufacturing a foam sheet according to the present embodiment includes an extrusion molding step and a cooling step.

In the extrusion molding step, the foamed intermediate layer resin composition is extruded into a sheet to form a foamed intermediate layer, and the surface layer-forming resin composition is extruded into a sheet to form a surface layer. In this step, the surface layer is laminated on both sides of the foamed intermediate layer to produce a foamed sheet.
In the extrusion molding step in the present embodiment, for example, a three-layer co-extrusion machine including three extruders and a T-die capable of three-layer stacking can be used. Specifically, the resin composition for forming a foamed intermediate layer is melted using one extruder. The resin composition for forming a surface layer is melted using two extruders. Using a T-die, the molten foamed intermediate layer forming resin composition is formed into a sheet to form a foamed intermediate layer, and the molten surface layer forming resin composition is formed into a sheet to form a surface layer. . Further, inside the T die, a surface layer is laminated on both sides of the foamed intermediate layer. The sheet discharged from the T-die becomes a foamed sheet in which surface layers are provided on both sides of the foamed intermediate layer.
The temperature at which the resin composition for forming a foamed intermediate layer and the resin composition for forming a surface layer are melted is preferably from 160 to 350C, more preferably from 170 to 260C.

The resin composition for a foamed intermediate layer contains a polypropylene resin for a foamed intermediate layer and a foaming agent. The polypropylene resin for the foamed intermediate layer is as described above. Further, the resin composition for the foamed intermediate layer may be mixed with the recycled material of the foamed sheet of the present embodiment.
The foaming agent may be a volatile foaming agent or a decomposable foaming agent.
Examples of the volatile blowing agent include aliphatic hydrocarbons such as propane, butane, pentane, isobutane, neopentane, isopentane, hexane, and heptane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; methyl chloride, methylene chloride, Dichlorofluoromethane, chlorotrifluoromethane, dichlorodifluoromethane, chlorodifluoromethane, difluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, monochloropentafluoroethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1 And halogenated hydrocarbons such as 1,1-difluoroethane, 1,2-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane.
Examples of the decomposition type foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium carbonate, sodium bicarbonate, potassium bicarbonate and the like.
Carbon dioxide, nitrogen, water and the like can also be used as other foaming agents.
The above foaming agents may be used as a mixture of two or more.
The content of the foaming agent is preferably from 0.1 to 6.0 parts by mass, more preferably from 0.5 to 2.0 parts by mass, per 100 parts by mass of the polypropylene resin for the foamed intermediate layer. preferable. When the content of the foaming agent is within the above range, a foamed layer having a uniform bubble diameter and uniformly dispersed bubbles can be easily formed.

The resin composition for forming a surface layer contains a polypropylene resin for a surface layer and does not contain a foaming agent. The polypropylene resin for the surface layer is as described above, and has the same or greater melt tension than the polypropylene resin for forming the foamed intermediate layer.
The melt tension index of the polypropylene resin for the surface layer and the melt tension index of the polypropylene resin for the foamed intermediate layer are set to the above specific ranges, and the melt tension index of the polypropylene resin for the surface layer is set to the melting point of the polypropylene resin for the foamed intermediate layer. In order to make the tensile index equal to or larger than the tensile index, it is preferable to include the following polypropylene resin for a surface layer.
That is, a preferable polypropylene resin for a surface layer contains a propylene polymer and an ethylene / α-olefin copolymer, and has a melt flow rate of 2 to 30 measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210. The intrinsic viscosity of the xylene-soluble component in tetrahydronaphthalene at 135 ° C. in tetrahydronaphthalene is 6 to 10 dl / g, and the ratio of the mass average molecular weight _Mw to the number average molecular weight _Mn of the xylene-insoluble component (M _w / _Mn ) is 7 or more, the content ratio of the ethylene / α-olefin copolymer is 20 to 40% by mass, and the propylene polymer has a total content ratio of the ethylene unit and the α-olefin unit of 5.0. % By mass and the content of propylene units is 95% by mass or more, and the ethylene / α-olefin copolymer has an ethylene unit content of 20 to 40%. It is intended to include 60 to 80 wt% amount% and α-olefin units.
Further, the melt tension index of the polypropylene resin for the surface layer and the melt tension index of the polypropylene resin for the foamed intermediate layer are in the above-mentioned specific ranges, and the melt tension index of the polypropylene resin for the surface layer is set to the polypropylene resin for the foamed intermediate layer. In order to make the melt tension index equal to or larger than the above, it is preferable to include the following polypropylene resin for a foamed intermediate layer.
That is, a preferred polypropylene resin for the foamed intermediate layer has a melt flow rate measured at a temperature of 230 ° C. under a load of 21.18 N according to JIS K7210, a mass average molecular weight _{Mw of 2} to 15 g / 10 min, and a xylene-insoluble component. The ratio ( _Mw / _Mn ) to the number average molecular weight _Mn is 6 or more.

The cooling step is a step of cooling the foamed sheet by blowing air on one side of the foamed sheet 10 and bringing the other side of the foamed sheet into close contact with the peripheral surface of the metal roll.
In order to facilitate cooling of the foam sheet 10, the temperature of the metal roll is preferably set to 50 ° C. or less.

In the foamed sheet 10 of the present embodiment, as described above, the melt tension index of the polypropylene resin for the surface layer and the melt tension index of the polypropylene resin for the foamed intermediate layer are within the above specific ranges, and The melt tension index of the resin is not less than the melt tension index of the polypropylene resin for the foamed intermediate layer. In such a foam sheet 10, the surface layers 12, 13 can prevent the formation of unevenness on the surface, and can improve the surface appearance. Further, since the surface appearance is hardly impaired by the surface layers 12 and 13, even if the expansion ratio is increased, an excellent surface appearance can be maintained.
Therefore, the foam sheet 10 of the present embodiment has a high expansion ratio and excellent surface appearance. In particular, the foam sheet 10 having a high expansion ratio and excellent surface appearance can be easily manufactured even when the sheet is brought into close contact with the metal roll by blowing air.

Note that the present invention is not limited to the above embodiment.
For example, the foamed sheet of the present invention may be provided with another layer between the foamed intermediate layer and the surface layer, or may be a laminated sheet of three kinds, five layers, or a laminated sheet of four kinds, seven layers. . An example of another layer includes an adhesive layer.

  The foamed multilayer sheet of the present invention can be easily processed into containers and trays by a known secondary forming method such as vacuum forming, vacuum pressure forming, and hot plate forming. The secondary molded article can be used as a lunch container, a side dish tray, an insulated container, and the like.

Hereinafter, Examples and Comparative Examples are shown, but the present invention is not limited to the following Examples.
In each example, the content ratio of the ethylene unit in the ethylene / α-olefin copolymer (ethylene / propylene copolymer), the intrinsic viscosity of the xylene-soluble portion of the polypropylene resin, and the _Mw / M of the xylene-insoluble portion of the polypropylene resin. _n , the MFR of the polypropylene resin, and the melt tension index of the polypropylene resin were measured as follows.

1) Content ratio of ethylene unit in ethylene / α-olefin copolymer:
The content ratio of the ethylene unit of the ethylene / α-olefin copolymer was determined by measuring a sample dissolved in a mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene using JNM LA-400 ( ¹³ C resonance, manufactured by JEOL Ltd.). The frequency was measured using a ¹³ C-NMR method.
2) Intrinsic viscosity of xylene-soluble component of polypropylene resin:
The xylene-soluble component of the polypropylene resin was obtained by the following method.
2.5 g of a sample is placed in a flask containing 250 ml of o-xylene (solvent) and stirred at 135 ° C. for 30 minutes using a hot plate and a reflux device while purging with nitrogen to completely dissolve the polypropylene resin. Then, the mixture was cooled at 25 ° C. for 1 hour. The resulting solution was filtered using filter paper. 100 ml of the filtrate after filtration was collected, transferred to an aluminum cup or the like, evaporated to dryness at 140 ° C. while purging with nitrogen, and allowed to stand at room temperature for 30 minutes to obtain a xylene-soluble matter.
Using the obtained xylene-soluble component as a sample, intrinsic viscosity was measured in tetrahydronaphthalene at 135 ° C. using a capillary automatic viscosity measurement device (SS-780-H1, manufactured by Shibayama Scientific Instruments Co., Ltd.).
3) _Mw / _Mn of xylene-insoluble content of the polypropylene resin:
The mass average molecular weight _Mw and the number average molecular weight _Mn of the xylene-insoluble portion of the polypropylene resin were measured using gel permeation chromatography (PL-GPC220 manufactured by Polymer Laboratories Co., Ltd.).
As a method for collecting the xylene-insoluble component, acetone is added to the residue (mixture of xylene-insoluble component and solvent) remaining on the filter paper when the xylene-soluble component is filtered as described above, and then filtered. The resulting components were evaporated to dryness in a vacuum drying oven set at 80 ° C. to obtain xylene-insoluble components.
4) MFR:
The MFR of the polypropylene resin was measured under the conditions of a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210.
5) Melt tension index of polypropylene-based resin Using a capillary rheometer (Capillograph 1C manufactured by Toyo Seiki Seisaku-sho, Ltd.) equipped with a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface, and a temperature of 200 ° C. To melt the polypropylene resin. The melted polypropylene resin was discharged from the orifice at a resin extrusion speed of 15 mm / min to form a strand. The strand was pulled using a rotating pulling means at a pulling speed of 6.5 m / min, and the tension (MT, unit: g weight) was measured.
Then, the melt tension index was determined from the equation log (melt tension index) = log (MT) + 0.85 log (MFR)-0.82.

In Examples and Comparative Examples, polypropylene resins shown in Table 1 were used.
In the table, “Suc” in the polymerization catalyst is a succinate catalyst, and “Ph” is a phthalate catalyst.
“HECO” in the type of polypropylene-based resin is block polypropylene (a polymerization mixture of a propylene polymer and an ethylene / α-olefin copolymer mainly composed of a rubber component), and “HOMO” is a propylene homopolymer.
“C2C3” in the type of the ethylene / α-olefin copolymer in the polypropylene-based resin is an ethylene / propylene copolymer.
Hereinafter, a method for producing each polypropylene-based resin will be described.

1) Polypropylene resin for surface layer [A1]
A solid catalyst component was prepared according to the preparation method described in the examples of JP-A-2011-500907. Specifically:
250 mL of TiCl ₄ was introduced at 0 ° C. into a 500 mL four-necked round bottom flask purged with nitrogen. While stirring, 10.0 g of fine spherical MgCl ₂ .1.8C ₂ H ₅ OH (prepared according to the method described in Example 2 of USP-4,399,054, but operating at 3000 rpm instead of 10000 rpm) And 9.1 mmol of diethyl-2,3- (diisopropyl) succinate. The temperature was raised to 100 ° C. and held for 120 minutes. Next, the stirring was stopped, the solid product was allowed to settle, and the supernatant was drawn off. The following procedure was then repeated twice: 250 mL of fresh TiCl ₄ was added, the mixture was allowed to react at 120 ° C. for 60 minutes, and the supernatant was drawn off. The solid was washed six times at 60 ° C. with anhydrous hexane (6 × 100 mL).
The solid catalyst was mixed with triethylaluminum (TEAL) and dicyclopentyldimethoxysilane (DCPMS) in an amount such that the mass ratio of TEAL to the solid catalyst was 18 and the mass ratio of TEAL / DCPMS was 10, and the temperature was 5 at room temperature. Minutes of contact. Preliminary polymerization was performed by holding the obtained catalyst system in liquid propylene in a suspended state at 20 ° C. for 5 minutes.
The obtained prepolymer was introduced into a first-stage polymerization reactor to obtain a propylene homopolymer, and the obtained polymer was purged with unreacted monomers, and then subjected to a second-stage polymerization reaction. The copolymer (ethylene-propylene copolymer) was introduced into the vessel and polymerized. During the polymerization, the temperature and pressure were adjusted, and hydrogen was used as a molecular weight regulator. In the first-stage reactor, the polymerization temperature and the hydrogen concentration were 70 ° C. and 0.90 mol%, respectively, and in the second-stage reactor, the polymerization temperature and the hydrogen concentration were C2 / ( C2 + C3) at 80 ° C., 0.01 mol%, and 0.25 mol ratio, respectively. The residence time distributions of the first and second stages were adjusted so that the amount of the copolymer component was 30% by mass. The obtained polypropylene polymer was mixed with 0.2% by mass of B255 manufactured by BASF as an antioxidant and 0.05% by mass of calcium stearate manufactured by Tannan Chemical Co., Ltd. as a neutralizing agent, and mixed with a Henschel mixer. After stirring and mixing for 1 minute, the mixture was extruded at a cylinder temperature of 230 ° C. with a single screw extruder having a screw diameter of 50 mm (NVC manufactured by Nakatani Machine Co., Ltd.), the strand was cooled in water, cut with a pelletizer, and pelletized polypropylene. A resin composition was obtained.

[A2]
A solid catalyst comprising MgCl ₂ and Ti and diisobutyl phthalate as an internal donor was prepared by the method described in Example 5 of EP 728,769. Next, using the solid catalyst, triethylaluminum (TEAL) as the organoaluminum compound, and dicyclopentyldimethoxysilane (DCPMS) as the external electron donor compound, the weight ratio of TEAL to the solid catalyst was 20, and the weight ratio of TEAL / DCPMS was 20 Was contacted at 12 ° C. for 24 minutes in such an amount as to give 10. Preliminary polymerization was performed by maintaining the obtained catalyst system in liquid propylene in a suspended state at 20 ° C. for 5 minutes. The obtained prepolymer was introduced into a first-stage polymerization reactor of a polymerization apparatus having a two-stage polymerization reactor in series to produce a propylene homopolymer, and ethylene-propylene was produced in the second-stage polymerization reactor. A copolymer was produced. During the polymerization, the temperature and pressure were adjusted, and hydrogen was used as a molecular weight regulator.
In the first-stage reactor, the polymerization temperature and the hydrogen concentration were 70 ° C. and 1.24 mol%, respectively, and in the second-stage reactor, the polymerization temperature and the hydrogen concentration were C2 / ( C2 + C3) at 80 ° C., 1.17 mol%, and 0.25 mol ratio, respectively. The residence time distributions of the first and second stages were adjusted so that the amount of the copolymer component was 30% by mass. Using this polypropylene polymer, a pellet-shaped polypropylene resin composition was obtained in the same manner as in A1.

[A3]
The hydrogen concentration in the first-stage reactor was 0.32 mol%, the hydrogen concentration in the second-stage reactor, C2 / (C2 + C3) was 3.31 mol% and 0.39 mol ratio, respectively. The pellet-like polypropylene resin composition was obtained in the same manner as in A2, except that the residence time distributions of the first and second stages were adjusted so that the amount was 15.5% by mass.

[A4]
The prepolymer used in the production of A1 is introduced into a first-stage polymerization reactor to obtain a propylene homopolymer, and the obtained polymer is introduced into a second-stage polymerization reactor to obtain a copolymer. The union (ethylene / propylene copolymer) was polymerized. During the polymerization, the temperature and pressure were adjusted, and hydrogen was used as a molecular weight regulator. In the first-stage reactor, the polymerization temperature and the hydrogen concentration were 70 ° C. and 0.18 mol%, respectively, and in the second-stage reactor, the polymerization temperature and the hydrogen concentration were C2 / ( C2 + C3) at 80 ° C., 1.33 mol%, and 0.20 mol ratio, respectively. The residence time distributions of the first and second stages were adjusted so that the amount of the copolymer component was 29% by mass. A pellet-shaped polypropylene resin composition was obtained in the same manner as in A1, using the obtained polypropylene polymer.

2) Polypropylene resin for foamed intermediate layer [B1]
After introducing the prepolymer used for the production of A1 into the polymerization reactor, hydrogen and propylene are fed, the polymerization temperature and the hydrogen concentration are respectively set to 75 ° C. and 0.25 mol%, and the pressure is adjusted. A propylene homopolymer was produced. A pellet-shaped polypropylene resin composition was obtained in the same manner as in A1, using the obtained polypropylene polymer.

[B2]
A pellet-shaped polypropylene resin composition was obtained in the same manner as in B1, except that the hydrogen concentration was changed to 0.13 mol%.

[B3]
A solid catalyst in which Ti and diisobutyl phthalate as an internal donor were supported on MgCl ₂ , and a solid catalyst for polymerization was prepared by the method described in Example 1 of EP-A-679991. Next, the solid catalyst, triethylaluminum (TEAL) and cyclohexylmethyldiethoxysilane (CHMMS) were added in such an amount that the mass ratio of TEAL to the solid catalyst was 8, and the mass ratio of TEAL / CHMMS was 6.5. Contact was made at -5 ° C for 5 minutes. Preliminary polymerization was performed by holding the obtained catalyst system in liquid propylene in a suspended state at 20 ° C. for 5 minutes.
After introducing the obtained prepolymer into a polymerization reactor, hydrogen and propylene are fed, the polymerization temperature and the hydrogen concentration are set to 75 ° C. and 0.04 mol%, respectively, and the pressure is adjusted to adjust the propylene single weight. A coalescence was produced. A pellet-shaped polypropylene resin composition was obtained in the same manner as in A1, using the obtained polypropylene polymer.

(Example 1)
A foamed sheet was produced using a multilayer sheet molding machine (manufactured by Thermo Plastics Industry Co., Ltd.) equipped with three extruders having a screw diameter of 25 mm and provided with a T die capable of laminating three layers.
More specifically, using a single extruder, forming a foamed intermediate layer containing a polypropylene-based resin for a foamed intermediate layer composed of a polypropylene-based resin B1 and a chemical foaming agent composition (CellMike MB3064 manufactured by Sankyo Chemical Co., Ltd.) The resin composition for use was melted at 210 ° C. The amount of the chemical foaming agent composition was adjusted within a range of 1 to 3 parts by mass with respect to 100 parts by mass of the polypropylene resin so that the expansion ratio was about 1.5 times.
Further, the polypropylene resin for the surface layer composed of the polypropylene resin A1 was melted at 210 ° C. using two extruders.
A foamed intermediate layer was formed using a multi-layer T-die, a surface layer was formed, a surface layer was laminated on both sides of the foamed intermediate layer, and then the foamed sheet was discharged from the T-die. At that time, the ratio of the layer thickness of the surface layer / foamed intermediate layer / surface layer was 1/5/1.
The foamed sheet was cooled by blowing air on one side of the foamed sheet to bring the other side of the foamed sheet into close contact with the peripheral surface of the metal roll.

(Other Examples and Comparative Examples)
A foamed sheet was obtained in the same manner as in Example 1 except that the polypropylene resin for the foamed intermediate layer, the polypropylene resin for the surface layer, and the layer thickness ratio were changed as shown in Tables 2 and 3.
In the table, LDPE is a branched low-density polyethylene (MFR measured under conditions of 190 ° C., load: 21.18 N, 2.0 g / 10 min according to JIS K7210, Novatec LD400 manufactured by Japan Polyethylene Corporation). It is. In Examples 3 and 5, the dry blend of B1 and LDPE is melt-kneaded in an intermediate layer extruder of a sheet forming machine. In Comparative Example 2 having a single layer, a dry blend of A1 and B1 (A1: B1 = 2: 8 mass ratio) is melt-kneaded in an extruder for an intermediate layer of a sheet forming machine. In Example 6, a dry blend of A1 and B1 (mass ratio of A1: B1 = 6: 4) is melt-kneaded in a surface extruder of a sheet forming machine.

<Evaluation>
With respect to the foam sheet of each example, the expansion ratio and density were measured by the following methods, and the surface appearance and heat resistance were evaluated. Tables 2 and 3 show the measurement results and evaluation results.

[Expansion ratio and density]
Using an electronic densimeter MD-200S manufactured by Alpha Mirage Co., in accordance with JIS K7112, measuring the specific gravity of the foam sheet were the specific gravity and density _{D 1.} The ratio (D ₁ / D ₀ ) of the density D ₁ to the density D ₀ of the resin when the foam sheet 10 was not foamed was determined, and the value was defined as the foaming ratio.

[Surface appearance]
The surface of the foamed sheet was visually observed and evaluated according to the following criteria.
5: Smooth.
4: Almost smooth.
3: A streak pattern is seen.
2: Some unevenness is conspicuous.
1: Unevenness is conspicuous.
FIG. 3 shows an example of the appearance of the sheet surface at each stage.

[Heat-resistant]
The foamed sheet was immersed in hot water at 100 ° C., and the degree of deformation was visually observed and evaluated according to the following criteria.
2: No deformation.
1: Deformed.

In each of the examples, the surface appearance of the foamed sheet was excellent, and the foaming ratio could be increased. This is because the melt tension index of the polypropylene resin for the surface layer and the melt tension index of the polypropylene resin for the foamed intermediate layer are in a specific range, and the melt tension index of the polypropylene resin for the surface layer is the polypropylene type for the foamed intermediate layer. This is because it is not less than the melt tension index of the resin.
Further, the foamed sheets of Examples 1 to 4 and Examples 6 to 7 in which the LDPE content in the foamed intermediate layer is 20% by mass or less (that is, the content of the polypropylene-based resin is 80% by mass or more) also have heat resistance. It was excellent.
The single-layer foamed sheet of Comparative Example 2 composed of a resin in which a polypropylene resin having a large melt tension index and a polypropylene resin having a small melt tension index were mixed had a poor surface appearance.
The foam sheet of Comparative Example 3 in which the layer thickness ratio of the surface layer / foamed intermediate layer / surface layer was 1/15/1, had a poor surface appearance.
The foamed sheet of Comparative Example 4 in which the polypropylene resin for the surface layer had a melt tension index of 1.7 had a poor surface appearance.
The foam sheet of Comparative Example 5, in which the polypropylene resin for the surface layer had a melt tension index of 1.4, had a poor surface appearance, and it was difficult to increase the expansion ratio.
The foam sheet of Comparative Example 6 in which the melt tension index of the polypropylene resin for the surface layer was smaller than the melt tension index of the polypropylene resin for the foamed intermediate layer had poor surface appearance.
The foamed sheet of Comparative Example 7 in which the polypropylene-based resin for a foamed intermediate layer had a melt tension index of 1.0 had a poor surface appearance, and it was difficult to increase the foaming ratio.
The foamed sheet of Comparative Example 8 in which the polypropylene resin constituting the foamed intermediate layer and the surface layer were all of the same kind and the polypropylene resin for the surface layer had a melt tension index of 1.4 had a poor surface appearance.

10 Foamed sheet 11 Foamed intermediate layer 12, 13 Surface layer

Claims (10)

A foamed intermediate layer, comprising a non-foamed surface layer provided on both sides of the foamed intermediate layer, the foamed intermediate layer and the surface layer both contain a polypropylene resin,
The foaming ratio of the thickness of the intermediate layer _{(T 1)} and the thickness of the surface layer and _{(T 2) (T 1 /} T 2) is 3 / 1-10 / 1,
The polypropylene resin constituting the foamed intermediate layer has a melt tension index determined by the following formula (1) of 1.2 or more, and the polypropylene resin forming the surface layer is determined by the following formula (1). melt tension index is not less than 1.8, and melt tension index of the polypropylene resin constituting the surface layer state, and are above the melting tension index of the polypropylene resin constituting the foamed intermediate layer,
The polypropylene-based resin contained in the surface layer contains a propylene polymer and an ethylene / α-olefin copolymer, and has a melt flow rate of 2 to 30 measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210. 15 g / 10 min, xylene-soluble content, 135 ° C. with an intrinsic viscosity of 6~10dl / g in tetrahydronaphthalene, the ratio of the weight-average molecular mass _{M w} to number average molecular weight _{M n} of xylene insolubles (M _w / _Mn ) is 7 or more, and the content ratio of the ethylene / α-olefin copolymer is 20 to 40% by mass,
In the propylene polymer, the total content of ethylene units and α-olefin units is 5.0% by mass or less, and the content ratio of propylene units is 95% by mass or more,
The foamed polypropylene resin sheet, wherein the ethylene / α-olefin copolymer contains 20 to 40% by mass of ethylene units and 60 to 80% by mass of α-olefin units .
log (melt tension index) = log (MT) + 0.85 log (MFR)-0.82 (1)
MT was measured using a melt tension measuring device having a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface, a measurement temperature of 200 ° C., a resin extrusion speed of 15 mm / min, and a take-up speed of 6.5 m /. It is the melt tension (g weight) of the polypropylene resin measured under the conditions of minutes.
MFR is a melt flow rate of a polypropylene resin measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210. The polypropylene resin foam sheet according to claim 1 , wherein the polypropylene resin contained in the surface layer is a polymerization mixture obtained by polymerizing an ethylene monomer and an α-olefin monomer in the presence of a propylene polymer. . According to JIS K7210, the polypropylene resin contained in the foamed intermediate layer has a melt flow rate of 2 to 15 g / 10 minutes measured at a temperature of 230 ° C. and a load of 21.18 N, a mass average molecular weight M _{w of} a xylene-insoluble component, and the ratio of the number average molecular weight _{M n (M w / M n} ) is 6 or more, the polypropylene-based resin foam sheet according to claim 1 or 2. The polypropylene-based resin contained in the foamed intermediate layer is at least one of a propylene homopolymer and a propylene random copolymer containing at least one of an ethylene unit and an α-olefin unit at 5.0% by mass or less. The foamed polypropylene resin sheet according to any one of claims 1 to 3 . The foamed polypropylene resin sheet according to any one of claims 1 to 4 , wherein the content ratio of the polypropylene resin in the foamed intermediate layer is 60% by mass or more. The foamed polypropylene resin sheet according to any one of claims 1 to 5 , wherein an expansion ratio is 1.30 times or more. A resin composition for forming a foamed intermediate layer containing a polypropylene resin for a foamed intermediate layer and a foaming agent is extruded into a sheet to form a foamed intermediate layer, and a surface layer containing a polypropylene-based resin for a surface layer is formed. An extrusion molding step of extruding a resin composition into a sheet to form a surface layer, laminating the surface layer on both sides of the foamed intermediate layer to produce a polypropylene resin foam sheet,
A cooling step of cooling the polypropylene-based resin foam sheet by blowing air onto one surface of the polypropylene-based resin foam sheet to bring the other surface of the polypropylene-based resin foam sheet into close contact with a peripheral surface of a metal roll; And
The polypropylene resin for the foamed intermediate layer has a melt tension index determined by the following formula (1) of 1.2 or more, and the polypropylene resin for the surface layer has a melt tension index determined by the following formula (1). is 1.8 or more, and melt tension index of the polypropylene resin for the surface layer state, and are above the melting tension index of the polypropylene resin for the foamed intermediate layer,
The polypropylene resin for a surface layer contains a propylene polymer and an ethylene / α-olefin copolymer, and has a melt flow rate of 2 to 15 g / m 2 measured at 230 ° C. under a load of 21.18 N according to JIS K7210. 10 minutes, the xylene-soluble content has an intrinsic viscosity in tetrahydronaphthalene at 135 ° C. of 6 to 10 dl / g, and the ratio of the mass average molecular weight M _w to the number average molecular weight M _n (M _w / M _n) is 7 or more, the content ratio of the ethylene · alpha-olefin copolymer is 20 to 40 wt%,
In the propylene polymer, the total content of ethylene units and α-olefin units is 5.0% by mass or less, and the content ratio of propylene units is 95% by mass or more,
The method for producing a foamed polypropylene resin sheet, wherein the ethylene / α-olefin copolymer contains 20 to 40% by mass of ethylene units and 60 to 80% by mass of α-olefin units .
log (melt tension index) = log (MT) + 0.85 log (MFR)-0.82 (1)
MT was measured using a melt tension measuring device having a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface, a measurement temperature of 200 ° C., a resin extrusion speed of 15 mm / min, and a take-up speed of 6.5 m /. It is the melt tension (g weight) of the polypropylene resin measured under the conditions of minutes.
MFR is a melt flow rate of a polypropylene resin measured at a temperature of 230 ° C. and a load of 21.18 N according to JIS K7210. The method for producing a polypropylene resin foam sheet according to claim 7 , wherein foaming is performed at a foaming ratio of 1.30 times or more when the foaming intermediate layer is formed in the extrusion molding step. The method for producing a foamed polypropylene resin sheet according to claim 7 or 8 , wherein the polypropylene resin for the surface layer is obtained by polymerizing an ethylene monomer and an α-olefin monomer in the presence of a propylene polymer. At the time of polymerization to obtain at least one of the polypropylene resin for the foamed intermediate layer and the polypropylene resin for the surface layer,
(A) a solid catalyst containing, as an essential component, an electron donor compound selected from magnesium, titanium, halogen, and a succinate compound;
The method for producing a foamed polypropylene resin sheet according to any one of claims 7 to 9 , wherein a catalyst containing an external electron donor compound selected from (B) an organic aluminum compound; and (C) a silicon compound is used.