JP7059554B2 - Polypropylene-based multilayer foam sheet resin composition for surface layer - Google Patents

Description

The present invention relates to a resin composition for the surface layer of a polypropylene-based multi-layer foamed sheet. Specifically, the present invention can be uniformly laminated when arranged on the surface layer of a multi-layer foamed sheet, and the appearance of the sheet is beautiful and the foaming agent is lost. It relates to a polypropylene resin composition capable of suppressing scattering and forming a good foamed sheet, and further to a multilayer foamed sheet manufactured by using the resin composition, and a molded product obtained by thermoforming the multilayer foamed sheet. ..

From the viewpoint of weight reduction of materials and reduction of environmental load, resin foam sheets have been conventionally used for industrial materials and daily necessities, but in recent years, demand for polyolefin foam sheets is increasing. Polyolefin-based foam sheets are widely used in various applications such as vehicle parts, building materials such as heat insulation and sound insulation, and daily necessities. Among them, they are heavily used as thermoforming materials for manufacturing various food and drink containers and trays. ing.
As a general method for producing a polyolefin-based foamed sheet, a polyolefin-based resin is melted in an extruder, kneaded with a foaming agent, and this foamable melt-kneaded product is extruded into a sheet from a die at the tip of the extruder to be foamed. Extruded foaming is well known (eg, Non-Patent Document 1).
In the polyolefin-based foamed sheet thus obtained, if the surface of the foamed sheet is significantly uneven, the adhesiveness may be difficult even if a film is to be bonded to the surface of the foamed sheet immediately after foam molding or by post-processing. There is a problem that the film peels off (= polyolefin), and even if you try to print directly on the surface of the product, printing may be difficult and the design may deteriorate, and the foamed sheet has high surface smoothness. Is required.
As a method for obtaining a polyolefin-based foamed sheet having high surface smoothness, it is very effective to stack a non-foamed surface layer on a foamed layer, and particularly recently, further improvement of container moldability, rigidity and It is widely used from the viewpoint of improving heat resistance (Patent Document 1).
However, when the extruded foam sheet is made into multiple layers, the balance of the resin viscosity of each layer, the state of the resin confluence at the confluence of each layer, the pressure at the tip of the die when extruding the effervescent melt-kneaded product from the extruder, etc. If a slight change occurs in various points, there arises a problem that the foaming state of the melt-kneaded product in which the foaming agent is kneaded changes significantly, and the surface smoothness is impaired.
In order to solve such problems, when the foam layer and the surface layer are co-extruded and laminated, they are shaped and cooled while being transported by being sandwiched between a pair of endless steel belts controlled in a specific temperature range, and the thickness is cooled. A technique for obtaining a multilayer polyolefin resin foamed sheet having less unevenness and excellent flatness is disclosed (Patent Document 2).
However, in this method, the surface can be smoothed to some extent by forced heating shaping, but if the original layered state of the surface layer is not uniform, the ratio between the foam layer and the surface layer will not be constant and the mechanical properties will vary. There are problems such as high cost due to the need for special endless rolls.
Further, in Patent Document 3, a specific nucleating agent having a crystal nucleating action on a polypropylene-based resin is added to a non-foaming surface layer resin to accelerate crystallization and suppress gas escape from the foaming layer to give an appearance. A technique for obtaining an improved multilayer foam sheet is disclosed. However, in this technique, it is necessary to precisely control the crystallization rate of the surface layer resin, and if the crystallization is too fast, the foaming of the foamed layer is inhibited, and if the crystallization is too slow, the effect cannot be obtained. Further, regarding the stackability of the surface layer resin, it cannot be said that it is sufficient only to specify the MFR.
In Patent Document 4, when a molten polypropylene-based resin (A) containing an effervescent gas and a molten polyolefin-based resin (B) containing a filler are laminated to form a multilayer foamed sheet, the temperature and pressure of each layer are formed. Is disclosed, and a method for obtaining a foamed sheet having excellent stackability is disclosed by specifying and setting the conditions in which they are correlated.
However, this method requires precise control of the temperature and pressure of each layer, and in particular, the resin pressure (P1) at the screw tip of the effervescent gas-containing polypropylene resin (A) is maintained as high as 15 to 30 MPa. There is also a need and there are large equipment restrictions. Further, it is necessary to set a high MFR of the filler-containing molten polyolefin resin (B) used for the surface layer, and there are material restrictions.

Special Fair 7-98349 Gazette Japanese Unexamined Patent Publication No. 2008-260233 Japanese Patent No. 3994730 Japanese Patent No. 5457072

FOAM EXTRUSION (Principle and Practice), S.T. Lee, TECHNOMIC PUBLISHING Co. Inc., 2000.

An object of the present invention is to provide a polypropylene-based resin composition that can be suitably used as a surface layer material of a polypropylene-based multilayer foamed sheet in view of the current state of the prior art and that significantly improves the surface appearance of the obtained multilayer foamed sheet. The present invention is to provide a multilayer foamed sheet using the same, and a molded product thermoformed by using the same.

As a result of diligent research to solve the above problems, the present inventors can obtain a polypropylene-based multilayer foamed sheet having a beautiful surface appearance by using a polypropylene-based resin composition having a specific composition for the surface layer. Based on this finding, the present invention was completed.

That is, the present invention includes the following inventions.
[1] A propylene (co) polymer (X-1) and a propylene-ethylene copolymer (X) which may contain 10% by weight or less of comonomer having the following characteristics (X-i) to (X-iii). A resin composition for the surface layer of a polypropylene-based multilayer foamed sheet containing 10 to 100% by weight of a propylene-based block copolymer (X) and 0 to 90% by weight of a propylene homopolymer (Y) comprising -2).
Characteristics (X-i): The ratio of (X-1) and (X-2) is 50 to 99% by weight for (X-1) and 1 to 50% by weight for (X-2) (provided that it is 1 to 50% by weight). , (X-1) and (X-2) are 100% by weight based on the total amount of the propylene-based block copolymer (X).)
Characteristics (X-ii): The ethylene content in the propylene-ethylene copolymer (X-2) is 11.0 to 60.0% by weight (however, the weight ratio of the ethylene content is the propylene-ethylene copolymer weight. The total amount of the monomers constituting the coalescence (X-2) is 100% by weight).
Characteristics (X-iii): The intrinsic viscosity of the propylene-ethylene copolymer (X-2) in 135 ° C. decalin is 8.0 (dl / g) or more.
[2] The resin composition for the surface layer of a polypropylene-based multilayer foamed sheet according to [1], wherein the propylene-based block copolymer (X) is a multi-stage polymer.
[3] The resin composition for the surface layer of a polypropylene-based multilayer foamed sheet according to [1] or [2], wherein the melt flow rate (MFR) of the propylene-based block copolymer (X) is 1 to 15 g / 10 minutes.
[4] A polypropylene-based multilayer foamed sheet in which the polypropylene-based multilayer foamed sheet surface resin composition according to any one of [1] to [3] is laminated on one or both sides of the foamed layer.
[5] The description according to any one of [1] to [3], which has an MFR of 0.5 times or more and 2.5 times or less with respect to the MFR of the expandable polypropylene resin composition (Z) constituting the foam layer. Polypropylene-based multilayer foamed sheet A polypropylene-based multilayer foamed sheet in which the resin composition for the surface layer is laminated on one side or both sides of the foamed layer.
[6] The foamable polypropylene-based resin composition (Z) constituting the foam layer contains 20% by weight or more of high melt tension polypropylene (Z-1) satisfying the following characteristics (Z-i) to (Z-iii). The polypropylene-based multilayer foamed sheet according to [4] or [5] (however, the weight ratio of the high melt tension polypropylene (Z-1) is the total amount of the polypropylene-based resin constituting the expandable polypropylene-based resin composition (Z)). Is 100% by weight.).
Characteristics (Z-i): The melt tension (MT) measured at 230 ° C. is 3 to 25 g.
Characteristics (Z-ii): The melt flow rate (MFR) is more than 0.9 g / 10 minutes and 15 g / 10 minutes or less.
Characteristic (Z-iii): The strain hardening degree (λmax (0.1)) in the measurement of extensional viscosity at a strain rate of 0.1 s-1 is 6.0 or more.
[7] A polypropylene-based resin foam-molded body obtained by thermoforming the polypropylene-based multilayer foamed sheet according to any one of [4] to [6].

The polypropylene-based multilayer foamed sheet surface layer resin composition of the present invention is very beautiful because it can be uniformly laminated on the surface of the foamable polypropylene resin composition without being pushed away by the foamed layer when the foamable polypropylene resin composition is foamed to form a sheet. It is possible to produce a multilayer foamed sheet having an appearance. As a result, the appearance of the thermoformed body obtained by thermoforming the multilayer foam sheet is also beautiful, and when the printing film is adhered to the surface, the unevenness of the foam layer is less likely to appear on the film surface and the finish is improved. Not only that, direct printing is also possible.
Further, the surface layer formed by the surface layer resin composition suppresses the dissipation of the foaming agent, and the foaming ratio of the foamed layer can be easily improved.
The multi-layer foam sheet thus obtained is excellent in appearance, thermoformability, impact resistance, light weight, rigidity, heat resistance, heat insulation, oil resistance, etc., and thus is used for trays, dishes, cups, etc. It can be suitably used for vehicle interior materials such as food containers, automobile door trims, automobile trunk mats, packaging, stationery, building materials, and the like.

It is a figure explaining the conceptual diagram of CFC-FT-IR.

Hereinafter, embodiments of the present invention will be described in detail, but the description of the constituent elements described below is an example of the embodiments of the present invention, and the present invention is described below as long as the gist thereof is not exceeded. It is not limited to the description.

The polypropylene-based multilayer foamed sheet surface layer resin composition of the present invention (hereinafter, may also be referred to as a surface layer resin composition) has a propylene-based block copolymer (X) of 10 to 100% by weight and a propylene single weight. It is characterized by containing 0 to 90% by weight of the coalesced (Y). (Hereinafter, the propylene-based block copolymer (X) may be referred to as (X) or the component (X).)
Further, the foamable polypropylene-based resin composition (Z: hereinafter may be referred to as a resin composition for a foamed layer) constituting the foamed layer of the polypropylene-based multilayer foamed sheet of the present invention is a high melt tension polypropylene (Z-1). ) Is contained in an amount of 20% by weight or more.
In particular, in the present invention, it is preferable that the propylene-based block copolymer (X) and the high melt tension polypropylene (Z-1) satisfy specific requirements and specific physical properties, as will be described later.
Below, the resin composition for the surface layer, the propylene-based block copolymer (X) and the propylene homopolymer (Y) constituting the surface layer resin composition, and the effervescent polypropylene-based resin composition (Z) constituting the foamed layer. The high melt tensile polypropylene (Z-1) contained in the effervescent polypropylene-based resin composition (Z) and the properties that it is preferable to satisfy will be described in detail for each item.

I. Propylene block copolymer (X)
The polypropylene-based multilayer foamed sheet surface layer resin composition of the present invention contains at least a propylene-based block copolymer (X), and here, the weight ratio of the propylene-based block copolymer (X) in the surface layer resin composition. Is 10 to 100% by weight (however, the weight ratio of the propylene-based block copolymer (X) is 100% by weight based on the total amount of the polypropylene-based resin constituting the surface layer resin composition).
The propylene-based block copolymer (X) contained in the resin composition for the surface layer of the polypropylene-based multilayer foamed sheet of the present invention may contain 10% by weight or less of the comonomer propylene (co) polymer (X-1) and propylene-. It is composed of an ethylene copolymer (X-2). (Hereinafter, the propylene (co) copolymer (X-1) is referred to as a component (X-1) or (X-1), and the propylene-ethylene copolymer (X-2) is referred to as (X-2) or. (X-2) It may be described as a component.)
The term block copolymer used here is different from the so-called (real) block copolymer or graft copolymer in which the components polymerized at each stage are bonded by chemical bonds.
(X-1) and (X-2) may be polymerized independently and used, but can be produced by performing multi-stage polymerization by a sequential polymerization method. Since the components (X-1) and (X-2) produced in each step of the multi-step polymerization are not chemically bonded, generally, the crystallinity, the molecular weight, or the solubility in a solvent is added to each component. It is possible to separate by a method such as crystalline separation, molecular weight separation, or solubility separation by utilizing the difference such as. A polymer produced by such multi-step polymerization is referred to as a multi-step polymer.

1. 1. Method for Producing Propylene Block Copolymer (X) 1-1. Polymerization catalyst Any catalyst for producing the propylene-based block copolymer (X) can be used, but the propylene-ethylene copolymer weight satisfying the following characteristics (Xi) to (X-iii). When the coalescence (X-2) is produced as a constituent component, it is preferable to use a Ziegler-Natta catalyst. When the Ziegler-Natta catalyst is used, the specific method for producing the catalyst is not particularly limited, but the catalyst disclosed in JP-A-2007-254671 can be exemplified as an example.
Specifically, as a typical example of the Ziegler-Natta catalyst suitable for producing the propylene-based block copolymer (X) of the present invention, the following constituents,
(ZN-1) A solid component containing titanium, magnesium, and halogen as essential components,
(ZN-2) Organoaluminium compound,
(ZN-3) electron donor,
A catalyst consisting of a catalyst can be mentioned.

(1) Solid component (ZN-1)
The solid component (ZN-1) which is a constituent component of the Ziegler-Natta catalyst suitable for producing the propylene-based block copolymer (X) used in the present invention includes titanium (ZN-1a), magnesium (ZN-1b), and the like. It contains halogen (ZN-1c) as an essential component, and an electron donor (ZN-1d) can be used as an optional component. Here, "containing as an essential component" indicates that any component may be contained in any form as long as the effect of the present invention is not impaired, in addition to the three components shown. .. It will be described in detail below.
(ZN-1a) Titanium Any titanium compound can be used as a titanium source. As a typical example, the compound disclosed in JP-A-3-234707 can be mentioned. Regarding the valence of titanium, a titanium compound having an arbitrary valence of tetravalent, trivalent, divalent or 0 valent can be used, but it is desirable to use a tetravalent titanium compound.
(ZN-1b) Magnesium Any magnesium compound can be used as a magnesium source. As a typical example, the compound disclosed in JP-A-234707 can be mentioned. Generally, magnesium chloride, diethoxymagnesium, metallic magnesium, and butylmagnesium chloride are often used.
(ZN-1c) Halogen As the halogen, fluorine, chlorine, bromine, iodine, and a mixture thereof can be used. Of these, chlorine is particularly preferable.
(ZN-1d) Electron Donor The solid component (ZN-1) may contain an electron donor as an optional component. As a typical example of the electron donor (ZN-1d), the compound disclosed in JP-A-2004-124090 can be mentioned. In general, organic and inorganic acids and their derivatives (esters, acid anhydrides, acid halides, amides) compounds, ether compounds, ketone compounds, aldehyde compounds, alcohol compounds, amine compounds, It is desirable to use such as.
Among these, phthalic acid ester compounds typified by dibutyl phthalate, dibutyl phthalate, diisobutyl phthalate, diheptyl phthalate, phthalic acid halide compounds typified by phthaloyl dichloride, 2-n- are preferable. Malonic acid ester compounds having one or two substituents at the 2-position such as diethyl butyl-malonate, one or two substituents or 2 at the 2-position such as diethyl 2-n-butyl-diethyl succinate. Succinic acid ester compounds having one or more substituents at the positions and 3-positions, 2-isopropyl-2-isobutyl-1,3-dimethoxypropane and 2-isopropyl-2-isopentyl-1,3-dimethoxypropane. Free of aliphatic polyvalent ether compounds typified by 1,3-dimethoxypropane and aromatics typified by 9,9-bis (methoxymethyl) fluorene having one or two substituents at such 2-positions. Polyvalent ether compounds having a group in the molecule, and the like.

(2) Organoaluminium compound (ZN-2)
As the organoaluminum compound (ZN-2), a compound disclosed in JP-A-2004-124090 can be used. Generally, it is desirable to use a compound represented by the following general formula (1).
R ⁹ cAlXd (OR ¹⁰ ) e ... (1)
(In the general formula (1), R ⁹ represents a hydrocarbon group. X represents a halogen or a hydrogen atom. R ¹⁰ represents a hydrocarbon group or a bridging group by Al. C ≧ 1, 0 ≦ d. ≦ 2, 0 ≦ e ≦ 2, c + d + e = 3)
Specific examples include trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, diethylaluminum chloride, ethylaluminum chloride, diethylaluminum ethoxide, methylalmoxane, and the like.

(3) Electron donor (ZN-3)
As the electron donor (ZN-3), an organosilicon compound having an alkoxy group (ZN-3a) or a compound having at least two ether bonds (ZN-3b) can be exemplified.
(ZN-3a) Organic Silicon Compound with Alkoxy Group Organic Silicon Compound with Alkoxy Group (ZN-3a) which is a constituent component of the Ziegler-Natta catalyst suitable for producing the propylene-based block copolymer (X) according to the present invention. ) Can be a compound or the like disclosed in JP-A-2004-124090. Generally, it is desirable to use a compound represented by the following general formula (2).
R ³ R ⁴ aSi (OR ⁵ ) b ... (2)
(In the general formula (2), R ³ represents a hydrocarbon group or a hetero atom-containing hydrocarbon group. R ⁴ is selected from the group consisting of a hydrogen atom, a halogen atom, a hydrocarbon group and a hetero atom-containing hydrocarbon group. Represents any free group to be used. R ⁵ represents a hydrocarbon group. 0 ≦ a ≦ 2, 1 ≦ b ≦ 3, a + b = 3)
As specific examples, t-Bu (Me) Si (OME) ₂ , t-Bu (Me) Si (OEt) ₂ , t-Bu (Et) Si (OMe) ₂ , t-Bu (n-Pr) Si (OMe) ₂ , c-Hex (Me) Si (OMe) ₂ , c-Hex (Et) Si (OMe) ₂ , c-Pen ₂ Si (OMe) ₂ , i-Pr ₂ Si (OMe) ₂ , i-Bu ₂ Si (OMe) ₂ , i-Pr (i-Bu) Si (OMe) ₂ , n-Pr (Me) Si (OMe) ₂ , t-BuSi (OEt) ₃ , (Et ₂ N) ₂ Si (OMe) ₂ , Et ₂ N-Si (OEt) ₃ , and the like can be mentioned.
(ZN-3b) Compound having at least two ether bonds Examples of the compound having at least two ether bonds (ZN-3b) include the compounds disclosed in JP-A-3-294302 and JP-A-8-333413. Can be used. Generally, it is desirable to use a compound represented by the following general formula (3).
R ⁸ OC (R ⁷ ) ₂ -C (R ⁶ ) ₂ -C (R ⁷ ) ₂ -OR ⁸ ... (3)
(In the general formula (3), R ⁶ and R ⁷ represent any free group selected from the group consisting of a hydrogen atom, a hydrocarbon group and a hetero atom-containing hydrocarbon group. R ⁸ represents a hydrocarbon group or a hetero. Represents an atomic-containing hydrocarbon group.)
As specific examples, 2,2-diisopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2-isobutyl-2-isopropyl-1,3-dimethoxypropane, 2-isopropyl -2-Isopentyl-1,3-dimethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane, 9,9-bis (methoxymethyl) fluorene, and the like can be mentioned.

1-2. Prepolymerization The catalyst exemplified above may be prepolymerized before being used in the main polymerization. By forming a small amount of polymer around the catalyst in advance prior to the polymerization process, the catalyst becomes more uniform and the amount of fine powder generated can be suppressed.
As the monomer in the prepolymerization, the compound disclosed in JP-A-2004-124090 can be used. Specifically, ethylene, propylene, 3-methylbutene-1, 4-methylpentene-1, styrene, divinylbenzene and the like are particularly preferable.
The reaction conditions between the catalyst exemplified above and the above-mentioned monomer are not particularly limited, but are generally preferably within the following range.
On the basis of 1 g of the solid component (ZN-1), the amount of prepolymerization is preferably in the range of 0.001 to 100 g, preferably 0.1 to 50 g, and more preferably 0.5 to 10 g. The reaction temperature during prepolymerization is −150 to 150 ° C., preferably 0 to 100 ° C. Then, it is desirable that the reaction temperature at the time of prepolymerization is lower than the polymerization temperature at the time of main polymerization. The reaction is generally preferably carried out under stirring, and at that time, an inert solvent such as hexane or heptane can also be present.

1-3. Step-growth polymerization Next, the method for producing the propylene-based block copolymer (X) used in the present invention will be described in detail.
The propylene-based block copolymer (X) used in the present invention is preferably a propylene-based block copolymer composed of a propylene (co) polymer (X-1) and a propylene-ethylene copolymer (X-2). Yes, in the production of such a propylene-based block copolymer (X), two polymer components, a propylene (co) polymer (X-1) and a propylene-ethylene copolymer (X-2), are produced. There is a need to. A propylene-ethylene copolymer (X-2) having a relatively high molecular weight and a low viscosity and MFR is neatly dispersed in a propylene (co) polymer (X-1) to form a propylene-based block copolymer (X) originally. From the viewpoint of exhibiting the performance of the above, it is necessary to produce both of the components by sequential polymerization.
Specifically, it is desirable to polymerize the propylene (co) polymer (X-1) in the first step and then polymerize the propylene-ethylene copolymer (X-2) in the second step. Although it is possible to reverse the production order, the propylene-ethylene copolymer (X-2) is contained in the copolymer (X-2) as can be seen from the following characteristics (X-ii). Since the ethylene content of the polymer is in the range of 11.0 to 60.0% by weight and the crystallinity is low, if it is produced in the first step, it may adhere inside the polymerization tank or block the transfer pipe. There is a high possibility of causing manufacturing troubles, which is not very preferable.
When performing step-growth polymerization, either the batch method or the continuous method can be used, but it is generally desirable to use the continuous method from the viewpoint of productivity.
In the case of the batch method, the propylene (co) polymer (X-1) and the propylene-ethylene copolymer (X-2) are individually separated by using a single polymerization reactor by changing the polymerization conditions with time. It is possible to polymerize to. A plurality of polymerization reactors may be connected in parallel and used as long as the effects of the present invention are not impaired.
In the case of the continuous method, it is necessary to polymerize the propylene (co) polymer (X-1) and the propylene-ethylene copolymer (X-2) individually, so that two or more polymerization reactors are connected in series. It is necessary to use equipment. Regarding the polymerization reactor corresponding to the first step of producing the propylene (co) polymer (X-1) and the polymerization reactor corresponding to the second step of producing the propylene-ethylene copolymer (X-2), Although it must be in a series relationship, a plurality of polymerization reactors may be connected in series and / or in parallel for each of the first step and the second step.

1-4. Polymerization process Any polymerization process can be used.
The reaction phase may be a method using a liquid medium or a method using a gas medium. Specific examples include a slurry method, a bulk method, and a gas phase method. It is possible to use supercritical conditions as intermediate conditions between the bulk method and the gas phase method, but since they are substantially the same as the gas phase method, they are included in the gas phase method without any particular distinction. In the case of a multi-tank continuous polymerization process, a vapor phase polymerization reactor may be attached after the bulk method polymerization reactor, but in this case, it will be referred to as the bulk method according to the convention in the art. Further, in the case of the batch method, the first step may be performed by the bulk method and the second step may be performed by the vapor phase method. In this case as well, the bulk method is used. As described above, the reaction phase is not particularly limited, but the slurry method has a problem that the production cost is generally high because many auxiliary equipments are used because an organic solvent such as hexane or heptane is used. Therefore, it is more preferable to use the bulk method or the gas phase method.
In addition, various processes have been proposed for the bulk method and the gas phase method. Although there are differences in the stirring (mixing) method and the heat removal method, the present invention does not particularly limit the process species from this viewpoint.

1-5. General Polymerization Conditions The polymerization temperature can be used without any problem as long as it is in the normally used temperature range. Specifically, a range of 0 ° C. to 200 ° C., preferably 40 ° C. to 100 ° C. can be used.
The polymerization pressure varies depending on the selected process, but can be used without any problem as long as it is in the normally used pressure range. Specifically, a range larger than 0 and up to 200 MPa, preferably 0.1 to 50 MPa can be used. At this time, there is no problem even if an inert gas such as nitrogen is allowed to coexist.
Further, in the second step of producing the propylene-ethylene copolymer (X-2), a polymerization inhibitor such as ethanol or oxygen can be added. When such a polymerization inhibitor is used, not only the amount of polymerization in the second step can be easily controlled, but also the properties of the polymer particles can be improved.
The propylene (co) polymer (X-1) produced in the first stage of the step-growth polymerization is a propylene homopolymer or a propylene random copolymer obtained by copolymerizing a small amount of comonomer within the range not deviating from the gist of the present invention. Is. As the comonomer, α-olefins having up to about 10 carbon atoms excluding 3 such as ethylene, butene, and hexene are usually used.
The content of the comonomer is not particularly limited, but is preferably 10% by weight or less, more preferably 3% by weight or less, and particularly preferably 1% by weight or less. The weight ratio of the content of the comonomer is 100% by weight based on the total amount of the monomers constituting the propylene (co) polymer (X-1). The control of the comonomer content is usually performed by appropriately adjusting the amount ratio of the monomer supplied to the polymerization tank (eg, the amount ratio of ethylene to propylene). The copolymerization characteristics of the catalyst to be used may be investigated in advance, and the supply amount ratio of the monomers may be adjusted so that the gas composition of the polymerization tank becomes a value corresponding to the desired comonomer content.

2. 2. Characteristics of the propylene-based block copolymer (X) As a result of many experimental studies, the present inventors have found that the propylene-based block copolymer (X) contained in the surface resin composition is the following (X-i). It has been found that a good polypropylene-based multilayer foamed sheet can be produced when it has the characteristics of (X-iii). It will be described in detail below.

2-1. Characteristics (X-i): Weight ratio of (X-1) and (X-2) In the present invention, the weight ratio of (X-1) and (X-2) is 50 to 99 for (X-1). By weight%, preferably 55 to 97% by weight, more preferably 60 to 95% by weight. Correspondingly, (X-2) is 1 to 50% by weight, preferably 3 to 45% by weight, and more preferably 5 to 40% by weight.
(However, regarding the weight ratios of (X-1) and (X-2), the total amount of the propylene-based block copolymer (X) is 100% by weight).
By blending this propylene-based block copolymer (X) with the resin composition for the surface layer, a polypropylene-based multilayer foamed sheet having good surface stackability and a good appearance can be obtained.
When the amount of the component (X-2) is not less than the lower limit of the above range, a sufficient force to suppress the foam layer can be sufficiently secured and the layers are uniformly laminated, while when the amount is not more than the upper limit of the above range, the component is crystalline (X-2). The heat resistance and rigidity of the surface layer according to X-1) can be ensured.
The weight ratio of the propylene (co) polymer (X-1) to the propylene-ethylene copolymer (X-2) is the amount produced in the first step of producing the propylene (co) polymer (X-1) and propylene. -Controlled by the production amount in the second step of producing the ethylene copolymer (X-2). For example, in order to increase the amount of the propylene (co) polymer (X-1) and decrease the amount of the propylene-ethylene copolymer (X-2), the second step is performed while maintaining the production amount of the first step. It is only necessary to reduce the production amount of the above, which may shorten the residence time of the second step or lower the polymerization temperature. It can also be controlled by adding a polymerization inhibitor such as ethanol or oxygen, or, if originally added, increasing the amount of the addition. The reverse is also true.

2-2. Characteristics (X-ii): Ethylene content in the propylene-ethylene copolymer (X-2) In the present invention, the ethylene content in the propylene-ethylene copolymer component (X-2) is 11.0 to 60% by weight. (However, the weight ratio of the ethylene content is 100% by weight based on the total amount of the monomers constituting the propylene-ethylene copolymer (X-2)). The preferable range of the ethylene content in the propylene-ethylene copolymer component (X-2) is 15 to 58% by weight, more preferably 20 to 55% by weight.
When the ethylene content in the propylene-ethylene copolymer component (X-2) is at least the lower limit of the above range, the increase in crystallinity is suppressed, the occurrence of solidification is prevented, and as a result, the foam is uniformly spread over the foamed layer. Can be laminated. On the other hand, if it is not more than the upper limit of the above range, it is possible to prevent the component (X-2) from forming a sea-island structure with the component (X-1) and existing as a completely different phase, whereby the surface layer itself can be prevented from existing. It is possible to prevent the occurrence of thickness unevenness and evenly suppress the expansion of the foam layer. That is, the ethylene content in (X-2) is crystalline while maintaining compatibility with (X-1), which is a propylene (co) polymer component having some crystallinity, and propylene homopolymer (Y). It is necessary to have a range that does not have much.

2-3. Characteristics (X-iii): Intrinsic viscosity of propylene-ethylene copolymer (X-2) in 135 ° C. decalin In the present invention, measurement was performed using 135 ° C. decalin of propylene-ethylene copolymer (X-2) as a solvent. The intrinsic viscosity to be obtained needs to be 8.0 dl / g or more, preferably 8.5 dl / g or more, more preferably 9.0 dl / g or more, and most preferably 9.5 dl / g or more. ..
When the intrinsic viscosity is 8.0 dl / g or more, the swelling force of the foamed layer can be suppressed, so that the occurrence of uneven thickness of the surface layer can be prevented, and the bubbles of the foamed layer bite into the surface layer portion to roughen the interface. Therefore, it is possible to prevent the appearance of the multilayer foam sheet from being deteriorated. The upper limit value does not need to be specified in particular, but is preferably 25.0 dl / g or less, more preferably 20.0 dl / g or less, still more preferably 18.0 dl / g or less, most preferably, from the viewpoint of preventing the generation of gel. It is preferably 16.0 dl / g or less.
The intrinsic viscosity here is a value measured using a Ubbelohde type capillary viscometer at a temperature of 135 ° C. and using decalin as a solvent. In order to obtain the intrinsic viscosity of (X-2), the component (X-2) is recovered as a 25 ° C. paraxylene-soluble component, and the intrinsic viscosity of the component is measured. The 25 ° C. para-xylene soluble component is prepared by dissolving 2 g of a sample in 300 ml of p-xylene (containing 0.5 mg / ml BHT) at 130 ° C. to make a solution, and then leaving it at 25 ° C. for 12 hours, and then leaving it at 25 ° C. for 12 hours. The precipitated polymer is filtered off, p-xylene is evaporated from the filtrate, and the components are further dried under reduced pressure at 100 ° C. for 12 hours.
However, if the ethylene content of the component (X-2) is less than 15% by weight, it becomes difficult to sufficiently separate the component (X-2). In such a case, a small amount of the component (X-1) during the sequential polymerization is extracted and the intrinsic viscosity is measured, and further, the intrinsic viscosity of the entire propylene-based block copolymer (X) after the completion of the sequential polymerization is measured. However, it shall be calculated by the following formula.
(X-2) Intrinsic viscosity of component = [(X) Intrinsic viscosity of the whole-{Intrinsic viscosity of (X-1) component × Weight fraction of (X-1) component / 100}] / {(X-2) ) Intrinsic weight fraction / 100}
Here, as a method for determining the ratio of (X-1) and (X-2) in the component (X) and the ethylene content in (X-2), conventionally known IR, NMR, or solubility separation is used. It can be determined by an analysis method that combines the method and the IR method.

In the present invention, the various indexes of the component (X) were mainly determined by the combination method of the cross fractionation method and the FT-IR method described below.
(1) Analytical device to be used (i) Cross sorting device CFC T-100 manufactured by Dia Instruments (abbreviated as CFC)
(Ii) Fourier Transform Infrared Absorption Spectrum Analysis FT-IR, PerkinElmer 1760X
The fixed wavelength infrared spectrophotometer attached as a CFC detector is removed, and an FT-IR is connected instead, and this FT-IR is used as a detector. The transfer line from the outlet of the solution eluted from CFC to FT-IR shall be 1 m long and the temperature shall be maintained at 140 ° C. throughout the measurement. The flow cell attached to the FT-IR has an optical path length of 1 mm and an optical path width of 5 mmφ, and the temperature is maintained at 140 ° C. throughout the measurement.
(Iii) Gel Permeation Chromatography (GPC)
The GPC column in the latter stage of the CFC is used by connecting three AD806MS manufactured by Showa Denko KK in series.
(2) CFC measurement conditions (i) Solvent: Orthodichlorobenzene (ODCB)
(Ii) Sample concentration: 4 mg / mL
(Iii) Injection amount: 0.4 mL
(Iv) Crystallization: The temperature is lowered from 140 ° C to 40 ° C over about 40 minutes.
(V) Sorting method:
The separation temperature at the time of temperature-raising elution separation is 40, 100, and 140 ° C., and the components are separated into three fractions in total. The elution ratio (unit weight%) of the component eluted at 40 ° C. or lower (fraction 1), the component eluted at 40 to 100 ° C. (fraction 2), and the component eluted at 100 to 140 ° C. (fraction 3) is W40, respectively. , W100, W140. W40 + W100 + W140 = 100. Further, each separated fraction is automatically transported to the FT-IR analyzer as it is.
(Vi) Solvent flow rate at elution: 1 mL / min (3) FT-IR measurement conditions After elution of the sample solution from the GPC in the subsequent stage of CFC started, FT-IR measurement was performed under the following conditions, and each fraction 1 described above was performed. GPC-IR data is collected for ~ 3.
A conceptual diagram of CFC-FT-IR is shown in FIG.
(I) Detector: MCT
(Ii) Resolution: 8 cm ^-1
(Iii) Measurement interval: 0.2 minutes (12 seconds)
(Iv) Number of integrations per measurement: 15 times (4) Post-treatment and analysis of measurement results The elution amount and molecular weight distribution of the components eluted at each temperature are chromatograms of the absorbance of 2945 cm ^-1 obtained by FT-IR. Use as a request. The elution amount is standardized so that the total elution amount of each elution component is 100%. The conversion from the holding capacity to the molecular weight is performed using a calibration curve made of standard polystyrene prepared in advance. The specific method is the same as described above.
For the ethylene content distribution (distribution of ethylene content along the molecular weight axis) of each eluted component, the ratio of the absorbance of 2956 cm ^-1 and the absorbance of 2927 cm ^-1 obtained by GPC-IR was used, and polyethylene, polypropylene, and ¹³ C- Using ethylene-propylene-rubber (EPR) whose ethylene content is known by NMR measurement or the like and a mixture thereof, it is converted into ethylene content (% by weight) by a calibration curve prepared in advance. ..
(5) Content of propylene-ethylene copolymer The content of the propylene-ethylene copolymer (X-2) (hereinafter referred to as EP) of the propylene-based block copolymer (X) in the present invention is represented by the following formula (I). It is defined and obtained by the following procedure.
EP content (% by weight) = W40 × A40 / B40 + W100 × A100 / B100 + W140 × A140 / B140 (I)
W40, W100, and W140 are elution ratios (unit weight%) in each of the above-mentioned fractions, and A40, A100, and A140 are average ethylene contents (units) of actual measurements in each fraction corresponding to W40, W100, and W140. By weight%), and B40, B100, and B140 are ethylene contents (unit weight%) of EP contained in each fraction.
How to obtain A40, A100, A140, B40, B100, B140 will be described later.
The meaning of the formula (I) is as follows. The first term on the right side of the equation (I) is a term for calculating the amount of EP contained in fraction 1 (a portion soluble at 40 ° C.). When fraction 1 contains only EP and does not contain propylene polymer (PP), W40 directly contributes to the EP content derived from fraction 1 in the whole, but fraction 1 contains components derived from EP. In addition to this, a small amount of PP-derived components (extremely low molecular weight components and atactic polypropylene) are also contained, so that portion needs to be corrected. Therefore, by multiplying W40 by A40 / B40, the amount derived from the EP component in fraction 1 is calculated. For example, when the average ethylene content (A40) of fraction 1 is 30% by weight and the ethylene content (B40) of EP contained in fraction 1 is 40% by weight, 30/40 = 3/4 of fraction 1 (that is, that is). 75% by weight) is derived from EP, and the remaining 1/4 is derived from PP. As described above, the operation of multiplying A40 / B40 in the first term on the right side means that the contribution of EP is calculated from the weight% (W40) of fraction 1. The same applies to the second and subsequent terms on the right-hand side, and the EP content is the sum of the calculated contributions of EP for each fraction.
(I) As described above, the average ethylene contents corresponding to fractions 1 to 3 obtained by CFC measurement are A40, A100, and A140, respectively (units are all by weight). How to determine the average ethylene content will be described later.
(Ii) Let B40 be the ethylene content corresponding to the peak position in the differential molecular weight distribution curve of fraction 1 (unit is weight%). Fractions 2 and 3 are defined as B100 = B140 = 100 in the present invention because it is considered that the rubber portions are all eluted at 40 ° C. and cannot be defined by the same definition. B40, B100, and B140 are the ethylene contents of EP contained in each fraction, but it is practically impossible to determine this value analytically. The reason is that there is no means to completely separate and separate PP and EP mixed in the fraction. As a result of studies using various model samples, it was found that B40 can well explain the effect of improving the material properties by using the ethylene content corresponding to the peak position of the differential molecular weight distribution curve of fraction 1. .. Further, B100 and B140 have two reasons: they have crystallinity derived from an ethylene chain, and the amount of EP contained in these fractions is relatively smaller than the amount of EP contained in fraction 1. Therefore, it is closer to the actual situation when both are close to 100, and almost no error occurs in the calculation. Therefore, the analysis is performed with B100 = B140 = 100.
(Iii) The EP content is determined according to the following formula.
EP content (% by weight) = W40 × A40 / B40 + W100 × A100 / 100 + W140 × A140 / 100 (II)
That is, W40 × A40 / B40, which is the first term on the right side of the equation (II), indicates the EP content (% by weight) having no crystallinity, and is the sum of the second term and the third term, W100 × A100 /. 100 + W140 × A140 / 100 indicates the EP content (% by weight) having crystallinity.
Here, the average ethylene contents A40, A100, and A140 of each fraction 1 to 3 obtained by B40 and CFC measurement are obtained as follows.
Fraction 1 separated by the difference in crystal distribution is converted into a molecular weight distribution curve by a curve in which the molecular weight distribution is measured by a GPC column constituting a part of a CFC analyzer, and an FT-IR connected behind the GPC column. Obtain the distribution curve of the ethylene content measured correspondingly. The ethylene content corresponding to the peak position of the differential molecular weight distribution curve is B40.
Further, the sum of the product of the weight ratio of each data point and the ethylene content of each data point, which is taken in as data points at the time of measurement, is the average ethylene content A40.
The significance of setting the above three types of sorting temperatures is as follows.
In the CFC analysis of the present invention, 40 ° C. refers only to non-crystalline polymers (eg, most of EP, or extremely low molecular weight and atactic components among propylene polymer (PP) components). It has the significance of being a necessary and sufficient temperature condition for sorting. Further, 100 ° C. is a component that is insoluble at 40 ° C. but soluble at 100 ° C. (for example, a component having crystallinity due to the chain of ethylene and / or propylene in EP, and a component having low crystallinity. The temperature is sufficient to elute only PP). Further, 140 ° C. is a component that is insoluble at 100 ° C. but soluble at 140 ° C. (for example, a component having particularly high crystallinity in PP, and a component having extremely high molecular weight and ethylene crystallinity in EP. ) Is eluted, and the temperature is sufficient to recover the entire amount of the propylene-based block copolymer used for analysis. The EP component contained in W140 is extremely small and can be substantially ignored.
Ethylene content in EP (% by weight) = (W40 x A40 + W100 x A100 + W140 x A140) / [EP] (III)
However, [EP] is the EP content (% by weight) obtained above.
The ethylene content (E) (% by weight) of the non-crystalline portion of EP is approximated by the value of B40 because the elution of the rubber portion is completed at almost 40 ° C. or lower.
However, in the analysis method using the combination of the above-mentioned cross fractionation method and FT-IR, the ethylene content of (X-2) is less than 15 wt%, the crystallinity with (X-1) is not significantly different, and the fractionation is based on temperature. If it cannot be done sufficiently, accurate analysis becomes difficult. In such a case, the component (X-1) is extracted during the step-growth polymerization, its molecular weight (in the case of copolymerizing with a comonomer, the comonomer content is also measured), and further calculated by material balance. , The amount ratio of the components (X-1) and (X-2) is determined, and the comonomer content of the entire component (X) at the end of the step-growth polymerization is measured. It is preferable to determine the copolymer content of the component (X-2) by using. When ethylene is used as the comonomer of (X-1), the ethylene content of (X-2) shall be determined by the following formula.
Ethylene content of (X-2) component = [(X) overall ethylene content-{(X-1) component ethylene content x (X-1) component weight fraction / 100}] / {(X-2) ) Component weight fraction / 100}
For other methods for determining the quantitative ratio of the (X-1) component and the (X-2) component, when producing a product in which the average molecular weights of the (X-1) component and the (X-2) component differ to some extent. After the step-growth polymerization is completed, the entire GPC (X) is measured, the obtained multimodal molecular weight distribution curve is peak-separated using commercially available data analysis software, etc., and the weight ratio is calculated. It is also possible.

2-4. MFR of propylene-based block copolymer (X)
The range of MFR of the propylene-based block copolymer (X) used in the present invention is preferably in the range of 1 to 15 g / 10 minutes. It is more preferably in the range of 1.5 to 14.5 g / 10 minutes, and particularly preferably in the range of 2 to 14 g / 10 minutes.
When it is at least the lower limit of this MFR range, it is possible to prevent the load of the extruder from increasing, secure a stable flow, and further improve the effect of uniformly spreading to the foam layer. On the contrary, when it is not more than the upper limit of this MFR range, it is possible to form a uniform laminate without being pushed away by the foam layer and being biased.
Especially in T-die foaming, if the MFR is too low, the surface layer resin composition is biased toward the center of the foamed sheet in the "width direction" and becomes difficult to turn to the edges (here, the "width direction" is the extrusion direction of the sheet). Of the directions perpendicular to the above direction, which is not the thickness direction), if the MFR is too high, it tends to flow to the end. In either case, the thickness of the surface resin composition becomes non-uniform in the width direction, and as a result, the effect of suppressing the dissipation of the foaming agent also changes, and not only a density difference occurs between the center and the edges of the width of the foamed sheet, but also foaming occurs. There may be a problem that the appearance of the sheet deteriorates.
The measurement of MFR in the present invention is carried out in Method A of JIS K7210: 1999 "Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic plastic", condition M (230 ° C., 2. It is a value measured according to 16 kg load).
Next, a method for controlling the MFR of the propylene-based block copolymer (X) will be described. Regarding the MFR of the propylene-based block copolymer (X), the following relational expression is given between the MFR of the propylene (co) polymer (X-1) and the MFR of the propylene-ethylene copolymer (X-2). (4) holds.
(Hereinafter, the MFR of the propylene-based block copolymer (X) is described as MFR (X), the MFR of the propylene (co) polymer (X-1) is described as MFR (X-1), and propylene-ethylene. The MFR of the copolymer (X-2) may be referred to as MFR (X-2).)
Loge [MFR (X)] = W (X-1) x loge [MFR (X-1)] + W (X-2) x loge [MFR (X-2)] ... (4)
(Here, loge is a logarithm with e as the base. Further, W (X-1) and W (X-2) are propylene (co) polymers in the propylene-based block copolymer (X), respectively. It is the weight fraction of (X-1) and the propylene-ethylene copolymer (X-2), and the relationship of W (X-1) + W (X-2) = 1 is established.)
This relational formula (4) is an empirical formula called the logarithmic addition rule of viscosity, and is used on a daily basis in the art. That is, the weight fractions of the propylene (co) polymer (X-1) and the propylene-ethylene copolymer (X-2), MFR (X), MFR (X-1), and MFR (X-2) are Not independent. Therefore, in order to control MFR (X), three factors of the weight fraction of the propylene-ethylene copolymer (X-2), MFR (X-1) and MFR (X-2) may be controlled. .. For example, in order to increase MFR (X), MFR (X-1) may be increased or MFR (X-2) may be increased. Further, when the MFR (X-2) is lower than the MFR (X-1), the MFR (X) is increased even if the W (X-1) is increased and the W (X-2) is decreased. You can easily understand what you can do. The same applies to the control method in the reverse direction.
Which of these methods is more preferable is that the MFR (X-2) needs to be controlled to a value low to some extent from the above-mentioned regulation of the characteristic (X-iii), and when the MFR (X) is controlled, it is necessary to control the MFR (X-2). It is desirable to use a method of controlling the weight ratio of MFR (X-1) and / or (X-1) and (X-2). Furthermore, since the weight ratio of (X-1) and (X-2) has the above-mentioned limitation of the characteristic (X-i), it is most preferable to use the method of controlling MFR (X-1). ..
The simplest method for controlling MFR (X-1) and MFR (X-2) is to use hydrogen as a chain transfer agent. Specifically, when the concentration of hydrogen, which is a chain transfer agent, is increased, the MFR (X-1) of the propylene (co) polymer (X-1) is increased. The reverse is also true. In order to increase the concentration of hydrogen in the polymerization tank, the supply amount of hydrogen to the polymerization tank may be increased, which is extremely easy for those skilled in the art. The same applies to the control of MFR (X-2).

II. Propylene homopolymer (Y)
The surface resin composition of the present invention is usually used by mixing a propylene-based block copolymer (X) with a propylene homopolymer (Y). Here, the weight ratio of the propylene homopolymer (Y) in the surface layer resin composition is 0 to 90% by weight, preferably 10 to 90% by weight, more preferably 15 to 85% by weight, still more preferably 20 to 20. It is 80% by weight, particularly preferably 50 to 80% by weight (however, the weight ratio of the propylene homopolymer (Y) is 100% by weight based on the total amount of the polypropylene-based resin constituting the surface resin composition). ..
The weight ratio of the propylene homopolymer (Y) is appropriately adjusted and set according to the MFR of the expandable polypropylene-based resin composition (Z) used for the foamed layer, and is set by appropriately adjusting the weight ratio of the propylene-based block as described later. The MFR value of the surface layer resin composition composed of the combined product (X) and the propylene homopolymer (Y) is 0.5 times or more and 2.5 times or less the MFR value of the effervescent polypropylene-based resin composition (Z). It is preferable to set it to be a value.
The propylene-based block copolymer (X) and the propylene homopolymer (Y) can be mixed with a dry blend, a Henschel mixer (trade name), or the like to prepare a resin composition for a surface layer. Further, in terms of enhancing the homogeneity, these may be melt-kneaded using a single-screw extruder, a twin-screw extruder or the like. At this time, it is preferably pelletized for use in extrusion molding.
Further, when the above requirements for the MFR ratio can be satisfied, the propylene-based block copolymer (X) can be used alone as the surface layer resin composition without mixing the propylene homopolymer (Y). ..

III. MFR ratio of foamable polypropylene-based resin composition (Z) and surface layer resin composition The MFR of the surface layer resin composition used in the polypropylene-based multilayer foamed sheet of the present invention is the foamable polypropylene-based resin constituting the foamed layer. It is preferably 0.5 times or more and 2.5 times or less the MFR of the composition (Z). More preferably, it is 0.7 times or more and 2.4 times or less, and particularly preferably 0.9 times or more and 2.3 times or less.
Within the above MFR ratio range, by adjusting the extrusion temperature of the surface layer resin composition, the fluidity with the foamable polypropylene-based resin composition (Z) containing a foaming agent can be easily matched, and a good laminated state can be obtained. It will be easier to achieve.

IV. Effervescent polypropylene resin composition (Z)
The foamable polypropylene-based resin composition (Z) constituting the foamed layer of the polypropylene-based multilayer foamed sheet of the present invention is a high melt tension polypropylene (Z-1) satisfying the following characteristics (Z-i) to (Z-iii). ) Is preferably contained in an amount of 20% by weight or more (however, the weight ratio of the high melt tension polypropylene (Z-1) is 100% by weight based on the total amount of the polypropylene resin constituting the foamable polypropylene resin composition (Z). do.).
Characteristics (Z-i): The melt tension (MT) measured at 230 ° C. is 3 to 25 g.
Characteristics (Z-ii): Melt flow rate (MFR) exceeds 0.9 g / 10 minutes and is 15 g / 10 minutes or less.
Characteristic (Z-iii): The strain hardening degree (λmax (0.1)) in the measurement of elongation viscosity at a strain rate of 0.1 s ^-1 is 6.0 or more.
The high melt tension polypropylene (Z-1) may be a propylene homopolymer, a propylene copolymer, or a mixture thereof. In the case of a propylene copolymer, the comonomer is at least one olefin selected from the group consisting of ethylene and an α-olefin having 4 to 10 carbon atoms, and the content of the comonomer is 3% by weight or less. The weight ratio of the content of the comonomer is 100% by weight based on the total amount of the monomers constituting the high melt tension polypropylene (Z-1).
The details will be described below in order.

1. 1. Characteristics of high melt tension polypropylene (Z-1) 1-1. Characteristics (Z-i): Melt tension (MT)
The melt tension (MT) of the high melt tension polypropylene (Z-1) contained in the foamable polypropylene resin composition (Z) constituting the foam layer of the polypropylene-based multilayer foamed sheet of the present invention is 3 to 25 g. Is preferable. Regarding the lower limit of MT, it is preferable that MT is 3 g or more. Thereby, it is possible to maintain the tension that does not cause foaming during the formation of the foamed cell, suppress the increase in the open cell ratio, keep the cell diameter small, and make the cell size uniform. Regarding the upper limit of MT, it is preferable that MT is 25 g or less, more preferably MT is 20 g or less, and most preferably 15 g or less. Thereby, the ductility at the time of extrusion molding can be improved, the appearance of the sheet, the film, the molded body and the like can be improved, foam rupture due to poor spreading can be prevented, and an increase in the open cell ratio can be suppressed.
Specific methods for controlling MT within the above range include cross-linking with an electron beam or organic peroxide, introduction of long-chain branching by polymerization, and within the range satisfying the characteristics (Z-ii). There is a way to adjust the MFR. If the degree of cross-linking is increased, the number of long-chain branches is increased, or the MFR is decreased, the MT becomes higher. On the other hand, in order to lower the MT, it may be adjusted in the opposite direction.
The melt tension (MT) in the present invention is a value measured under the following conditions.
[MT measurement conditions]
Measuring device: Capillograph 1B manufactured by Toyo Seiki Seisakusho Co., Ltd.
Capillaries: diameter 2.0 mm, length 40 mm
Barrel diameter: 9.55 mm
Barrel temperature: 230 ° C
Piston speed: 20 mm / min Pick-up speed: 4.0 m / min (However, if the MT is too high and the resin breaks, reduce the pick-up speed and measure at the maximum pick-up speed that can be picked up without breaking. )

1-2. Characteristic (Z-ii): MFR
The MFR of the high melt tension polypropylene (Z-1) contained in the foamable polypropylene resin composition (Z) constituting the foam layer of the polypropylene-based multilayer foamed sheet of the present invention exceeds 0.9 g / 10 minutes and is 15 g / g. It is preferably 10 minutes or less.
The MFR in the present invention is the method A, condition M (230 ° C., 2.16 kg load) of JIS K7210: 1999 “Plastic-Test Method for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastics”. It is a value measured according to.
The lower limit of MFR is preferably 1 g / 10 minutes or more, more preferably 1.2 g / 10 minutes or more, and most preferably 1.5 g / 10 minutes or more. Thereby, the ductility at the time of extrusion molding can be improved, the appearance of the sheet, the film, the molded body and the like can be improved, foam rupture due to poor spreading can be prevented, and an increase in the open cell ratio can be suppressed. The upper limit of MFR is preferably 14 g / 10 minutes or less, more preferably 13 g / 10 minutes or less, still more preferably 12 g / 10 minutes or less, and most preferably 10 g / 10 minutes or less. As a result, it is possible to suppress the generation of a portion that is excessively stretched during the formation of the foamed cell, prevent an increase in the open cell ratio due to foam rupture, keep the cell diameter small, and make the cell size uniform.
As a specific method for adjusting the MFR to the above range, a method for changing the amount of hydrogen added during polymerization can be mentioned. Since hydrogen acts as a chain transfer agent in the polymerization of propylene, the MFR can be increased by increasing the amount of hydrogen added, and conversely, the MFR can be decreased by decreasing the amount of hydrogen added. The value of MFR with respect to the hydrogen concentration inside the polymerization tank varies depending on the catalyst used and other polymerization conditions, but the relationship between the hydrogen concentration and MFR is grasped in advance according to the catalyst type and other polymerization conditions, and the desired MFR can be obtained. Adjusting the hydrogen concentration to a value is extremely easy for those skilled in the art.

1-3. Characteristics (Z-iii): Strain hardening degree (λmax) in measuring elongation viscosity
In the measurement of elongation viscosity of high melt tension polypropylene (Z-1) contained in the foamable polypropylene resin composition (Z) constituting the foam layer of the polypropylene-based multilayer foamed sheet of the present invention at a strain rate of 0.1 s- ¹ . The strain hardening degree (λmax (0.1)) is preferably 6.0 or more. It is more preferably 6.0 to 14.5, and even more preferably 7-14. Those having a strain hardening degree (λmax (0.1)) within this range are more preferable because the balance between ductility and cell formation during foaming is particularly good.
As a specific method for controlling the strain hardening degree (λmax (0.1)) within the above range, a method for increasing the entanglement of molecular chains by cross-linking with an electron beam or an organic peroxide or introducing a long chain branch by polymerization. Alternatively, there is a method of adjusting the MFR within a range satisfying the characteristic (Z-ii). Increasing the degree of cross-linking, increasing the number of long-chain branches, or decreasing the MFR increases the strain hardening degree (λmax (0.1)). On the other hand, in order to lower the strain hardening degree (λmax (0.1)), it may be adjusted in the opposite direction.
In the calculation of the strain hardening degree (λmax (0.1)) in the present invention, the value of the elongation viscosity measured under the following conditions is used.
Equipment: Ares manufactured by Rheometrics
Jig: Extensional Viscosity Fixture manufactured by TA Instruments Co., Ltd.
Measurement temperature: 180 ° C
Strain rate: 0.1 / sec
Method for producing test piece: Press molding Sheet of test piece shape: 18 mm × 10 mm, thickness 0.7 mm Next, a method of calculating λmax from the obtained elongation viscosity value will be described.
First, the time t (seconds) is plotted on the horizontal axis and the extensional viscosity η _E (Pa · sec) is plotted on the vertical axis in a log-log graph, and the viscosity immediately before strain curing is approximated by a straight line on the log-log graph. Specifically, first, the slope at each time when the stretch viscosity is plotted against time is obtained, but in that case, considering that the measurement data of the stretch viscosity is discrete, the slope of the adjacent data is obtained. , And use the method of taking the moving average of several points around.
Stretch viscosity becomes a simple increasing function in the region of low strain rate, gradually approaches a constant value, and matches the Truton viscosity after a sufficient time without strain hardening, but is common in the case of strain hardening. From about 1 strain amount (= strain rate x time), the elongation viscosity begins to increase with time. That is, the slope tends to decrease with time in the low strain region, but tends to increase from about 1 strain amount, and there is an inflection point on the curve when the elongation viscosity is plotted against time. .. Therefore, in the range of the strain amount of about 0.1 to 2.5, find the point where the slope of each time obtained above takes the minimum value, draw a tangent line at that point, and draw a straight line with the strain amount of 4.0. Extrapolate until The maximum value (ηmax) of the extensional viscosity η _E until the strain amount becomes 4.0 is obtained, and the viscosity on the approximate straight line up to that time is defined as ηlin. ηmax / ηlin is defined as λmax (0.1).

2. 2. Preparation of Effervescent Polypropylene Resin Composition (Z) 2-1. Method for Preparing Foamable Polypropylene Resin Composition (Z) A known resin composition (Z) for a foaming layer constituting the foamed layer of the polypropylene-based multilayer foamed sheet of the present invention can be used. For example, high melt tension polypropylene (Z-1), polypropylene-based resin (Z-2) which does not satisfy the properties (Z-i) to (Z-iii), if necessary, and any additive described later. A resin composition can be prepared by mixing each predetermined amount of each of the above with a dry blend, a Henschel mixer (trade name), or the like. Further, these may be melt-kneaded by a single-screw extruder, a twin-screw kneader, a kneader or the like.

2-2. Content of High Melt Tension Polypropylene (Z-1) The content of high melt tension polypropylene (Z-1) in the resin composition for foam layer (Z) constituting the foam layer of the polypropylene-based multilayer foamed sheet of the present invention is 20 weight by weight. % Or more is preferable (however, the weight ratio of the high melt tension polypropylene (Z-1) is 100% by weight based on the total amount of the polypropylene-based resin constituting the effervescent polypropylene-based resin composition (Z)).
By setting the content of high melt tension polypropylene (Z-1) to the lower limit of the above range or more, the increase in the open cell ratio of the multilayer foamed sheet can be suppressed, and the drawdown can be reduced during thermoforming. ..

2-3. MFR of effervescent polypropylene resin composition (Z)
The MFR of the resin composition (Z) for a foam layer constituting the foam layer of the polypropylene-based multilayer foam sheet of the present invention is preferably 1 to 20 g / 10 minutes. More preferably, the MFR is 1.5 to 15 g / 10 minutes, and even more preferably 2 to 13 g / 10 minutes. By setting the MFR to be equal to or higher than the lower limit of this range, the ductility can be improved, the appearance of the sheet or film can be improved, and the extrusion amount can be increased to improve the productivity. By setting the MFR to or less than the upper limit of this range, it is possible to suppress an increase in the open cell ratio of the multilayer foam sheet, keep the size of bubbles uniform, and suppress drawdown during thermoforming.
There are several ways to adjust the MFR within the above range. For example, the MFR of the foamed layer resin composition (Z) can be adjusted by adjusting the MFR of the high melt tension polypropylene (Z-1) and the polypropylene-based resin (Z-2). Further, the MFR of the polypropylene resin composition can also be adjusted by changing the blending amounts of (Z-1) and (Z-2). For example, when the MFR of high melt tension polypropylene (Z-1) is higher than the MFR of polypropylene resin (Z-2), increasing the blending amount of high melt tension polypropylene (Z-1) results in a foamable polypropylene resin. The MFR of the composition (Z) is high.

V. Additives Various additives can be added as optional components to the surface layer resin composition and the foamed layer resin composition (Z) of the present invention. Specifically, antioxidants, UV absorbers, light stabilizers, metal deactivating agents, stabilizers, neutralizers, lubricants, antistatic agents, antifogging agents, etc., which are conventionally known as compounding agents for polyolefin resins. Various additives such as nucleating agents, peroxides, fillers, antibacterial fungicides, and fluorescent whitening agents can be added as long as the effects of the present invention are not impaired. The blending amount of these additives is generally 0.0001 to 3% by weight, preferably 0.001 to 1% by weight, based on 100% by weight of the resin composition.
First, the antioxidant will be described.
Oxidation deterioration of polyolefin is a radical chain reaction via a peroxide radical or a hydroperoxide compound generated by the action of oxygen with heat, light, mechanical force, metal ions, etc., and is generally called autoxidation. .. Antioxidants are used to suppress this autoxidation, and depending on where they act in the chain reaction, there are three major types: phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. It is common to be separated.
Phenolic antioxidants are radical scavengers, and since the radicals generated by reacting with peroxide radicals and the like are relatively stable, the radical concentration in the system can be lowered. Generally, a substituted phenol compound, particularly a substituted phenol compound having a bulky substituent at the ortho position is used.
Hereinafter, typical compounds will be exemplified as phenolic antioxidants.
Among monophenol type compounds, 2,6-di-t-butyl-4-methylphenol (commonly known as BHT), tocopherol (vitamin E), n-octadecyl-3- (4'-hydroxy-3', 5') -Di-t-butylphenyl) propionate (trade name: Irganox1076, Sumilyzer BP-76) can be exemplified.
Among bisphenol type compounds, 2,2'-methylenebis (4-methyl-6-t-butylphenol) (trade name: Sumilyzer MDP-S), 1,1-bis (2'-methyl-4'-hydroxy-5) '-T-Butylphenyl) Butan (trade name: Sumilyzer BBM-S, Adecastab AO-40), 3,9-bis [2- {3- (3-t-butyl-4-hydroxy-5-methylphenyl) Propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5,5] undecane (trade name: Sumilyzer GA-80, Adecastab AO-80) can be exemplified.
Among the triphenol type compounds, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane (trade name: Adecastab AO-30), 1,3,5-trimethyl-2 , 4,6-Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (trade name: Irganox1330, Adecastab AO-330), Tris- (3,5-di-t-butyl-4-) Hydroxybenzyl) -isosianurate (trade name: Irganox3114, Adecastab AO-20), 1,3,5-tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate (trade name: smilizer) BP-179, Cyanox1790), Tris- (3,5-di-t-butyl-4-hydroxyphenyl) -isocyanurate (trade name: Cheminox 314) can be exemplified.
As the tetraphenol type compound, tetrakis {methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate} methane (trade name: Irganox1010) can be exemplified.
Phosphorus-based antioxidants have the effect of reducing hydroperoxide compounds and are also called hydroperoxide decomposing agents. Although it has an antioxidant effect alone, when used in combination with the above-mentioned phenolic antioxidant, a synergistic effect is generated and the antioxidant effect is further enhanced. Therefore, both are usually used in combination. This synergistic effect occurs because the phenol-based antioxidant is regenerated by the reduction of the phenoxy radical species generated by the reaction between the phenol-based antioxidant and the radical species involved in autoxidation by the phosphorus-based antioxidant. It is believed that.
Hereinafter, typical compounds will be exemplified as phosphorus-based antioxidants.
Among the phosphite-type compounds, tris (2,4-di-t-butylphenyl) phosphite (trade name: Irgafos168, Sumilyzer P-16, Adecastab 2112), Trisnonylphenyl phosphite (trade name: Sumilyzer TNP, Adecastab) 1178), Tris (mixed, mono-dinonylphenylphosphite) (trade name: Adecastab 329K), tetrakis (2,4-di-t-butylphenyl) -4,4'-biphenylenediphosphonite (commonly known as: P-EPQ), cyclic neopentanetetraylbis (2,6-di-t-butyl-4-methylphenylphosphite) (trade name: Adecastab PEP-36) can be exemplified.
Similar to phosphorus-based antioxidants, sulfur-based antioxidants also have the effect of reducing hydroperoxide compounds and are also called hydroperoxide decomposing agents. Similar to phosphorus-based antioxidants, it is said that this also has a synergistic effect when used in combination with phenol-based antioxidants.
Hereinafter, typical compounds will be exemplified as sulfur-based antioxidants.
Among sulfide-type compounds, dilauryl-3,3'-thio-dipropionate (commonly known as DLTDP), di-myristyl-3,3'-thio-dipropionate (commonly known as DMTDP), disstearyl-3,3'-thio- Dipropionate (commonly known as DSTDP), pentaerythritol-tetrakis- (3-laurylthio-propionate) (trade name: Sumilyzer TP-D, Adecastab AO-412S) can be exemplified.
Next, the ultraviolet absorber and the light stabilizer will be described.
Additives for suppressing photodegradation are ultraviolet absorbers and light stabilizers. When polypropylene is exposed to ultraviolet light, radicals are generated and autoxidation occurs. The ultraviolet absorber has an effect of suppressing the generation of radicals by absorbing ultraviolet rays, and the light stabilizer has an effect of capturing and inactivating radicals generated by ultraviolet rays.
The ultraviolet absorber is a compound having an absorption band in the ultraviolet region, and is known to be triazole-based, benzophenone-based, salicylate-based, cyanoacrylate-based, nickel chelate-based, inorganic fine particle-based, and the like. The most commonly used of these is the triazole system.
Hereinafter, typical compounds as ultraviolet absorbers will be exemplified.
Among triazole-based compounds, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole (trade name: Sumisorb 200, TinuvinP), 2- (2'-hydroxy-5'-t-octylphenyl) benzotriazole (Product names: Sumisorb 340, Tinuvin399), 2- (2'-hydroxy-3', 5'-di-t-butylphenyl) Benzotriazole (Product names: Sumisorb 320, Tinuvin320), 2- (2'-hydroxy) -3', 5'-di-t-amylphenyl) Benzotriazole (trade name: Sumisorb 350, Tinuvin328), 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5- Chlorobenzotriazole (trade name: Sumisorb 300, Tinuvin 326) can be exemplified.
Examples of the benzophenone-based compound include 2-hydroxy-4-methoxybenzophenone (trade name: Sumisorb 110) and 2-hydroxy-4-n-octoxybenzophenone (trade name: Sumisorb 130).
As the salicylate-based compound, 4-t-butylphenyl salicylate (trade name: Seasorb 202) can be exemplified. As the cyanoacrylate compound, ethyl (3,3-diphenyl) cyanoacrylate (trade name: Seasove 501) can be exemplified. As the nickel chelate compound, nickel dibutyldithiocarbamate (trade name: Antigen NBC) can be exemplified. Examples of the inorganic fine particle-based compound include TiO ₂ , ZnO ₂ , and CeO ₂ .
As the light stabilizer, it is common to use a hindered amine-based compound, which is called HALS. HALS has a 2,2,6,6-tetramethylpiperidine skeleton and cannot absorb ultraviolet rays, but suppresses photodegradation by a wide variety of functions. It is said that its three main functions are the capture of radicals, the decomposition of hydroxyperoxide compounds, and the capture of heavy metals that accelerate the decomposition of hydroxyperoxide.
Hereinafter, representative compounds as HALS will be exemplified.
For sebacate-type compounds, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate (trade names: Adecastab LA-77, Tinuvin770), bis (1,2,2,6,6-pentamethyl- 4-Piperidyl) sebacate (trade name: Tinuvin765) can be exemplified.
Among the butane tetracarboxylate type compounds, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) -1,2,3,4-butane tetracarboxylate (trade name: Adecastab LA-57), tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate (trade name: Adecastab LA-52), 1,2,3,4-butanetetra Condensate of carboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and tridecyl alcohol (trade name: Adecastab LA-67), 1,2,3,4-butanetetracarboxylic acid and 1, A condensate of 2,2,6,6-pentamethyl-4-piperidinol and tridecyl alcohol (trade name: Adecastab LA-62) can be exemplified.
In the succinic acid polyester type compound, a condensed polymer of succinic acid and 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine can be exemplified.
For triazine-type compounds, N, N'-bis (3-aminopropyl) ethylenediamine, 2,4-bis {N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino } -6-Chloro-1,3,5-triazine condensate (trade name: Chimassorb 199), poly {6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2 , 4-Diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino} (trade name: Chimassorb 944) ), Poly (6-morpholino-s-triazine-2,4-diyl) {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetra) Methyl-4-piperidyl) imino} (trade name: Chimasorb 3346) can be exemplified.
Some other additives are also exemplified.
Lubricants are additives used to improve moldability and fluidity, and have the effect of reducing the frictional force between polymer molecules and the frictional force between the polymer and the inner wall of the molding machine in a molding machine or extruder. .. Compounds used as lubricants include hydrocarbon compounds such as paraffin and wax, alcohols such as stearyl alcohol and propylene glycol, higher fatty acid esters such as n-butyl stearate, higher fatty acid amides such as oleic acid amide and stearic acid amide, and stearic acid. There are higher fatty acid salts such as calcium phosphate, partial esters of polyhydric alcohols such as stearic acid monoglyceride, and silicon oil.
Among these, specific examples of higher fatty acid amides include lauric acid amides, palmitic acid amides, stearic acid amides, oleic acid amides, erucic acid amides, and behenic acid amides. The fatty acid amide compound may have a substituent on the alkyl chain or N. Examples of fatty acid amide compounds having substituents include hydroxystearic acid amides, N-oleyl palmitate amides, N-stearyl oleic acid amides, N-stearyl erucic acid amides, methylene bisstearic acid amides, ethylene bisstearic acid amides, Can be mentioned.
Stabilizers are additives for polyvinyl chloride (PVC) in the first place, and are used for the purpose of preventing hydrochloric acid (HCl) from desorbing from PVC and deteriorating. Since some compounds among various stabilizers also have a function as a neutralizing agent, they may also be used as an additive for polyolefin.
The neutralizer is a compound used to neutralize the chlorine component derived from the Ziegler catalyst used in the production of polyolefins. As the neutralizing agent, a carboxylate having a neutralizing ability is often used, but an inorganic compound having a ability to capture chloride ions can also be used. Both are compounds used as stabilizers. Basically, when using a metallocene catalyst that does not contain chlorine atoms, it is an additive that is not originally necessary, but since chlorine atoms are a chemical species that easily contaminates, they are used as insurance from the viewpoint of stable production. Is often done.
Hereinafter, typical compounds as neutralizing agents will be illustrated.
Examples of the carboxylate type compound include calcium stearate and zinc stearate. Examples of the inorganic compound include hydrotalcite and inclusions of aluminum hydroxide and lithium carbonate (trade name: Mizukarak).

VI. Extrusion foam molding, multi-layer foam sheet, foam molded product The polypropylene-based multi-layer foam sheet surface layer resin composition of the present invention has excellent stackability on the foam layer and is suitable for various extrusion foam sheet molding. What kind of extrusion foam molding is used is not particularly limited, but typical extrusion foam sheet molding includes T-die (rectangular die) extrusion foam sheet molding and circular die (round die) extrusion foam sheet molding. Can be mentioned.
The extruder used for extrusion foam sheet molding represented by the above may be single-screw or biaxial.
The details will be described below in order.

1. 1. Foaming Agent When performing extrusion foam molding for obtaining a polypropylene-based multilayer foamed sheet using the surface layer resin composition and the foaming layer resin composition (Z) of the present invention, it is necessary to use a foaming agent. At this time, the type of foaming agent is not particularly limited, and known foaming agents used for plastics, rubbers, and the like can be used. Further, any foaming agent used for various foam molding can be used, and examples thereof include a physical foaming agent, a degradable foaming agent (chemical foaming agent), and microcapsules containing a thermal expansion agent.
Specific examples of the physical foaming agent include aliphatic hydrocarbons such as propane, butane, pentane, and hexane, alicyclic hydrocarbons such as cyclopentan and cyclohexane, chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, and dichloro. Difluoromethane, chloromethane, dichloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, trichlorotrifluoroethane, dichlorotetrafluoroethane. , Hydrocarbons such as chloropentafluoroethane and perfluorocyclobutane, inorganic gases such as water, carbon dioxide, and nitrogen, and the like can be exemplified. These compounds may be used alone or in combination of a plurality of compounds.
Among them, aliphatic hydrocarbons such as propane, butane and pentane and carbon dioxide gas are preferable because they are inexpensive and have high solubility in polypropylene-based resins. In particular, when carbon dioxide gas is used, supercritical conditions of 7.4 MPa or more and 31 ° C. or higher are more preferable because they are in a state of excellent diffusion and solubility in the polymer.
When a physical foaming agent is used, a bubble adjusting agent can be used if necessary. Examples of the bubble adjusting agent include inorganic degradable foaming agents such as ammonium carbonate, sodium bicarbonate (sodium hydrogencarbonate), ammonium bicarbonate and ammonium nitrite, and azo compounds such as azodicarboxylic amide, azobisisobutyronitrile and diazoaminobenzene. N, N'-dinitrosopentanmethylenetetramine and nitroso compounds such as N, N'-dimethyl-N, N'-dinitrosoterephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p, p'-oxybisbenzene Organic degradable foaming agents such as sulfonyl semicarbazide, p-toluene sulfonyl semicarbazide, trihydrazinotriazine, barium azodicarboxylate, inorganic powders such as talc and silica (inorganic powder), acidic salts such as polyvalent carboxylic acid, many A reaction mixture of a valent carboxylic acid and sodium carbonate or a sodium bicarbonate can be exemplified. These bubble adjusting agents may be used alone or in combination of two or more.
When using the bubble adjusting agent, the blending amount of the bubble adjusting agent shall be in the range of 0.01 to 5 parts by weight in pure content with respect to 100 parts by weight of the effervescent polypropylene resin composition (Z). Is preferable.
Specific examples of the degradable foaming agent (chemical foaming agent) include a mixture of sodium bicarbonate and an organic acid such as citric acid, an azo foaming agent such as azodicarboxylic amide and barium azodicarboxylate, and N, N'-dinitrosopentamethylene. Nitroso-based foaming agents such as tetramine, N, N'-dimethyl-N, N'-dinitrosoterephthalamide, sulfohydrazide-based foaming agents such as p, p'-oxybisbenzenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, tri Hydrazinotriazine and the like can be mentioned.
The blending amount of the foaming agent is preferably in the range of 0.05 to 6.0 parts by weight, more preferably 0.05 to 3.0 parts by weight, based on 100 parts by weight of the effervescent polypropylene resin composition (Z). Parts, more preferably 0.5 to 2.5 parts by weight, and particularly preferably 1.0 to 2.0 parts by weight.

2. 2. Polypropylene-based multilayer foamed sheet The polypropylene-based multilayer foamed sheet of the present invention was produced by using the surface layer resin composition and the foamed layer resin composition (Z) of the present invention. The thickness of the polypropylene-based multilayer foamed sheet of the present invention is preferably about 0.3 mm to 10 mm. It is more preferably 0.5 mm to 5 mm, still more preferably 0.7 mm to 3 mm.
The polypropylene-based multilayer foamed sheet of the present invention is secondarily processed mainly by thermoforming, and is widely used industrially mainly in various containers and the like. Further, polypropylene-based multilayer foam sheets have the advantage of being lightweight, and are being widely used in various applications.
Here, since the polypropylene-based multilayer foamed sheet contains many bubbles (cells) in the sheet, if the bubbles are rough or uneven, these appear on the sheet surface, deteriorating the surface appearance and commercial value. Will decrease. Further, when thermoforming is performed, it is necessary to heat the mold sufficiently in order to transfer the mold, but in the foamed sheet, bubbles also expand during heating. As a result, if the foam cell is rough, the surface tends to be deteriorated, and if it is uneven, the sheet may be torn during heating.
In order to solve these problems, it is considered necessary to form bubbles having a high closed cell ratio and having a high density and uniform size. However, the resin composition for foam layer (Z) and the surface layer of the present invention are used. These are realized by using a combination of resin compositions. In particular, by multi-layering using the surface layer resin composition of the present invention, specifically, by laminating the surface layer resin composition of the present invention on one side or both sides of the foam layer, the appearance as a foam sheet is very excellent. In addition, a sheet having high thermoforming suitability can be obtained.
In order to obtain the polypropylene-based multilayer foamed sheet of the present invention, specifically, the foamed layer using the foamed layer resin composition (Z) and the surface layer using the surface layer resin composition may be coextruded. At this time, a known coextrusion method using a feed block using a plurality of extruders, a multi-die, or the like can be used.
The surface layer of the polypropylene-based multilayer foamed sheet of the present invention may be provided on any surface of the foamed layer, or may have a structure (sandwich structure) in which the foamed layer is present between the surface layers.
The thickness of the surface layer of the polypropylene-based multilayer foamed sheet is 1 to 50%, more preferably 5 to 20% of the total thickness of the obtained polypropylene-based multilayer foamed sheet so as not to hinder the growth of bubbles in the foamed layer. It is desirable to form it so that it becomes.
The polypropylene-based multilayer foamed sheet provided with the surface layer is excellent in strength, and at least on the outside of the foamed layer, the non-foamed surface layer is provided, so that the surface smoothness and appearance are also excellent. ..
The surface resin composition of the present invention contains high-density polyethylene, low-density polyethylene, linear low-density polyethylene, propylene-α-olefin copolymer, and poly-4-methyl-pentene as long as the effects of the present invention are not impaired. Polyolefins such as -1, olefinic elastomers such as polyethylene-propylene elastomer, or other monomers copolymerizable with these, such as vinyl acetate, vinyl chloride, (meth) acrylic acid, (meth) acrylic acid ester, etc. The copolymer and the mixture of the above can be blended.
Further, when the polypropylene-based multilayer foamed sheet of the present invention is thermoformed and used as a foamed molded product, the rigidity of the molded product is very important. In particular, in order to improve this, for the surface layer used for the surface layer. An inorganic filler can be added to the resin composition. It is desirable that the blending amount of the inorganic filler is 50% by weight or less in 100% by weight of the resin composition for the surface layer. If it is 50% by weight or less, it is possible to prevent the generation of shavings at the outlet of the die and to form the sheet without impairing the appearance of the sheet.
As another means for improving the rigidity of the foamed molded product, between the "surface layer" using the surface layer resin composition of the present invention and the "foaming layer" using the foamed layer resin composition (Z). A non-foaming "intermediate layer" containing an inorganic filler may also be provided.
From the viewpoint that the effect of the surface layer resin composition of the present invention is not impaired, it is preferable to provide an intermediate layer containing an inorganic filler rather than the above-mentioned surface layer resin composition.
The intermediate layer is obtained by coextrusion molding with a foam layer using the foam layer resin composition (Z) and a surface layer using the surface layer resin composition.
When the intermediate layer is provided on the polypropylene-based multilayer foamed sheet of the present invention, the thickness thereof is 1 to 40%, more preferably 5 to 20% of the thickness of the foamed layer so as not to hinder the growth of bubbles in the foamed layer. It is desirable to form it so that it becomes%.
Examples of the thermoplastic resin constituting the intermediate layer include polypropylene, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, propylene-α-olefin copolymer, elastomer such as poly-4-methyl-penten-1, and ethylene-. Olefin elastomers such as propylene elastomers, or other monomers copolymerizable with them, for example, copolymers and mixtures such as vinyl acetate, vinyl chloride, (meth) acrylic acid, (meth) acrylic acid ester, etc. You can choose.
It is desirable that the blending amount of the inorganic filler in the intermediate layer is 50% by weight or less in 100% by weight of the resin composition in the intermediate layer. When it is 50% by weight or less, it becomes easy to suppress shearing heat generation and prevent the temperature from rising, and it is possible to suppress a decrease in the closed cell property of the foamed layer near the interface when laminated on the foamed layer. ..
Examples of the inorganic filler that can be blended in the surface layer and the intermediate layer for improving the rigidity include talcite, calcium carbonate, silica, hydrotalcite, zeolite, aluminum silicate, magnesium silicate and the like.
The bubbles constituting the foam layer of the polypropylene-based multilayer foam sheet of the present invention are preferably small in size, dense, uniform in size, and highly independent. Specifically, the bubble diameter of the foam layer is preferably 500 μm or less, more preferably 400 μm or less, still more preferably 300 μm or less. It is preferable that the foam layer bubble diameter is 500 μm or less because it is possible to prevent the occurrence of appearance defects such as holes in the thermoformed body during thermoforming. The bubble diameter of the foamed layer is a value obtained by using an optical microscope by the method described in Examples.
Further, the independence of bubbles can be judged by the open cell ratio. The open cell ratio is preferably 30% or less, more preferably 20% or less, still more preferably 15% or less. When the open cell ratio is 30% or less, expansion of the foam cell preferably occurs in the foam sheet during thermoforming, and molding can be performed without reducing the thickness of the thermoformed body, which is preferable. Further, it is preferable because it may lead to improvement of the heat insulating performance of the thermoformed body.
The open cell ratio is a value obtained by using an air pycnometer (manufactured by Tokyo Science Co., Ltd.) by the method described in Examples.
Further, the polypropylene-based multilayer foamed sheet of the present invention may be subjected to surface treatment such as corona discharge treatment, flame treatment, plasma treatment or the like on the surface thereof in order to improve printability and coatability.

3. 3. Thermoformed Polypropylene Resin Foam Molded Body of the present invention is a thermoformed polypropylene-based multilayer foamed sheet.
The thermoforming method is not particularly limited, and is not particularly limited, for example, straight molding, reverse draw molding, plug assist molding, plug assist reverse draw molding, drape molding, air slip molding, matched molding, snapback molding, and free drawing. Methods such as molding, plug-and-ridge molding, and ridge molding can be exemplified.

4. Applications The polypropylene-based multilayer foam sheet of the present invention has uniform and fine bubbles and is excellent in appearance, thermoformability, impact resistance, light weight, rigidity, heat resistance, heat insulation, oil resistance, etc. By forming a thermoformed body by thermoforming, it can be suitably used for food containers such as trays, plates and cups, vehicle interior materials such as automobile door trims and automobile trunk mats, packaging, stationery and building materials.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

1. 1. Methods for Measuring Various Physical Properties The characteristics of the polypropylene-based block copolymer (X), the resin composition for the surface layer, the resin composition for the foamed layer (Z), and the high melt tension polypropylene (Z-1) were measured by the following methods.
1-1. Ratio of propylene (co) polymer (X-1) to propylene-ethylene copolymer (X-2) and ethylene content in propylene-ethylene copolymer (X-2) The cross-separation method described in the specification. It was determined by a combination method of FT-IR method and FT-IR method.
1-2. Intrinsic Viscosity of Propylene-Ethylene Copolymer (X-2) 2 g of propylene-based block copolymer (X) was dissolved in 300 mL of p-xylene (including 0.5 mg / mL BHT) at 130 ° C. to prepare a solution. After that, it is left at 25 ° C. for 12 hours. Then, the precipitated polymer is filtered off, p-xylene is evaporated from the filtrate, and the mixture is further dried under reduced pressure at 100 ° C. for 12 hours to recover the xylene-soluble component at 25 ° C. Intrinsic viscosity was measured using this recovered component. The intrinsic viscosity was measured using a Ubbelohde type capillary viscometer at a temperature of 135 ° C. and a decalin solvent.
1-3. Melt flow rate (MFR)
Measurement was performed in accordance with JIS K7210: 1999 method A, condition M (230 ° C., 2.16 kg load). The unit is g / 10 minutes.
1-4. Melt tension (MT)
The measurement was performed under the following conditions using a capillograph manufactured by Toyo Seiki Seisakusho.
・ Capillary: diameter 2.0 mm, length 40 mm
・ Cylinder diameter: 9.55 mm
・ Piston extrusion speed: 20 mm / min ・ Pick-up speed: 4.0 m / min ・ Temperature: 230 ° C
If the MT is extremely high, the resin may break at a pick-up speed of 4.0 m / min. In such a case, the pick-up speed is reduced and the tension at the maximum pick-up speed is MT. And. The unit is grams.
1-5. Strain hardening degree (λmax)
Stretch viscosity was measured using Ares manufactured by Rheometolix, and the strain hardening degree (λmax) was determined from the results. The specific measurement method and calculation method are as described above.

2. 2. Characteristic evaluation of propylene-based multilayer foamed sheet The characteristic evaluation of foamed sheet was carried out by the following method.
2-1. Density A test piece was cut out from the foam sheets obtained in Examples and Comparative Examples, and the weight (g) of the test piece was divided by the volume (cm ³ ) obtained from the external dimensions of the test piece. The density (apparent overall density) was determined by measuring according to JIS K7222.
2-2. Sheet average thickness A test piece is cut out at the full width in the width direction (the width direction means a direction orthogonal to the extrusion direction) of the foamed sheet obtained in the examples and comparative examples, and 40 mm from the center in the width direction to the left and right, etc. The average value was calculated by measuring the thickness of the parts divided by the interval with a thickness gauge.
2-3. Foam layer average bubble diameter A 25 mm square sample was cut out from the foam sheets obtained in Examples and Comparative Examples. The foam layer cross section is magnified and projected using a stereoscopic microscope (manufactured by Nikon Corporation: SMZ-1000-2 type), and the bubble diameter in the extrusion direction cross section and its vertical cross section is determined from the number of bubbles and the bubble diameter in the cross section. Each was calculated, and the average value was taken as the bubble diameter of the foam layer of the foam layer.
2-4. The open cell rate A test piece was cut out from the foam sheets obtained in Examples and Comparative Examples, and measured using an air pycnometer (manufactured by Tokyo Science Co., Ltd.) according to the method described in ASTM D2856.
2-5. Appearance evaluation In the appearance evaluation of the foamed sheet, the polypropylene-based resin foamed sheets obtained in each Example and Comparative Example were evaluated according to the following criteria.
⊚: Smooth with very few thickness spots. There are almost no colored spots on the surface layer (the surface layer thickness is uniform).
The bubble shape is also fine and uniform.
◯: There are few thickness spots. There are few colored spots on the surface layer (the surface layer thickness is relatively uniform).
The bubble shape is uniform.
Δ: There is a thickness spot. There are colored spots on the surface layer (the thickness of the surface layer varies).
X: There are many thickness spots. Severe color spots on the surface layer (large variation in surface thickness)

3. 3. Materials used 3-1. Propylene block copolymer (X)
The propylene block copolymers obtained in Production Examples 1 and 2 below are "X1" and "X2", respectively, and are manufactured by Nippon Polypro Co., Ltd. Product name: Novatec, grade name "BC3BRF", grade name "BC3BHB", The grade name "BC03B" was used as "X3", "X4" and "X5" respectively. The properties are summarized in Table 1.

[Production Example 1: Production of Propylene Block Copolymer (X1)]
1. 1. Production of solid catalyst components A 10 liter autoclave equipped with a stirrer was sufficiently replaced with nitrogen and 2 liters of purified toluene was introduced. To this, at room temperature, 200 g of diethoxymagnesium Mg (OEt) ₂ and 1 liter of titanium tetrachloride were added. The temperature was raised to 90 ° C. and 50 ml of -n-butyl phthalate was introduced. Then, the temperature was raised to 110 ° C. and the reaction was carried out for 3 hours. The reaction product was thoroughly washed with purified toluene.
Then, purified toluene was introduced to adjust the total liquid volume to 2 L. 1 liter of titanium tetrachloride was added at room temperature, the temperature was raised to 110 ° C., and the reaction was carried out for 2 hours. The reaction product was thoroughly washed with purified toluene. Further, using purified n-heptane, toluene was replaced with n-heptane to obtain a slurry of solid catalyst components.
A portion of this slurry was sampled and dried. As a result of analysis, the titanium content of the solid catalyst component was 2.7% by weight, and the magnesium content was 18% by weight. The average particle size of the solid catalyst component was 33 μm.
Next, an autoclave having a capacity of 20 liters equipped with a stirrer was sufficiently replaced with nitrogen, and 100 g of the slurry of the solid catalyst component was introduced as the solid catalyst component. Purified n-heptane was introduced to adjust the concentration of the solid catalyst component to 25 g / liter. 50 mL of silicon tetrachloride SiCl ₄ was added, and the reaction was carried out at 90 ° C. for 1 hour. The reaction product was thoroughly washed with purified n-heptane.
Then, purified n-heptane was introduced to adjust the liquid level to 4 liters. Here, 30 ml of dimethyldivinylsilane, 30 ml of t-butylmethyldimethoxysilane (t-C 4H ₉ ) (CH ₃ ) Si (OCH ₃ ) ₂ , and n-heptane diluted solution of triethylaluminum Et ₃ Al are _{added to Et 3 .} 80 g of Al was added, and the reaction was carried out at 40 ° C. for 2 hours. The reaction product was thoroughly washed with purified n-heptane, and a portion of the obtained slurry was sampled and dried. As a result of analysis, the solid component contained 1.2% by weight of titanium and 8.8% by weight of (tC ₄ H ₉ ) (CH ₃ ) Si (OCH ₃ ) ₂ .
Prepolymerization was carried out by the following procedure using the solid component obtained above.
Purified n-heptane was introduced into the above slurry to adjust the concentration of the solid component to 20 g / liter. After cooling the slurry to 10 ° C., 10 g of an n-heptane diluted solution of triethylaluminum Et ₃ Al was added as Et ₃ Al, and 280 g of propylene was supplied over 4 hours. After the supply of propylene was finished, the reaction was continued for another 30 minutes.
The gas phase was then sufficiently replaced with nitrogen and the reaction product was thoroughly washed with purified n-heptane. The obtained slurry was taken out from the autoclave and vacuum dried to obtain a solid catalyst component (catalyst 1). This solid catalyst component (catalyst 1) contained 2.5 g of polypropylene per 1 g of the solid component. As a result of analysis, in the portion of the solid catalyst component (catalyst 1) excluding polypropylene, titanium was 1.0% by weight, and (t-C ₄ H ₉ ) (CH ₃ ) Si (OCH ₃ ) ₂ was 8.2. It was contained in% by weight.
2. 2. Production of propylene-based block copolymer Polymerization was carried out using a continuous reactor consisting of two fluidized bed reactors with an internal volume of 2000 liters connected together.
First, in the first reactor, the polymerization temperature is 65 ° C., the propylene partial pressure is 1.8 MPa (absolute pressure), and hydrogen as a molecular weight control agent is continuously added so that the molar ratio of hydrogen / propylene is 0.015. At the same time, the above-mentioned catalyst 1 was supplied at 4.0 g / hr of triethylaluminum so that the polymerization rate of the monomer was 16 kg / hr. The powder (crystalline propylene polymer) polymerized in the first reactor is continuously withdrawn at a extraction rate of 16 kg / hr so that the amount of powder retained in the reactor is 40 kg, and is continuously extracted into the second reactor. Transferred (first stage polymerization step).
Next, in the second reactor, propylene and ethylene were continuously supplied so as to have a monomer pressure of 1.5 MPa at a polymerization temperature of 70 ° C. and a molar ratio of ethylene / propylene of 0.29, and further. , Hydrogen as a molecular weight control agent is continuously supplied so that the molar ratio of hydrogen / propylene is 0.0008, and ethyl alcohol is supplied to the first reactor at 1.17 with respect to triethylaluminum. It was supplied so as to be double the molars.
The powder polymerized in the second reactor is continuously extracted into the vessel so that the amount of powder held in the reactor becomes 60 kg, and nitrogen gas containing water is supplied to stop the reaction, and the propylene-based block copolymer weight is used. A coalescence was obtained (second stage polymerization step).
0.2 parts by weight of "IRGASTAB FS 301 FF" (trade name manufactured by BASF), 1,3,5-tris (2) as an antioxidant with respect to 100 parts by weight of the obtained propylene block copolymer powder. , 6-Dimethyl-3-hydroxy-4-t-butylbenzyl) Isocyanurate (manufactured by Songwon, trade name: SONGNOX1790) 0.1 part by weight, 3,9-bis (2,6-di-tert-butyl- 4-Methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] Undecane (manufactured by ADEKA, trade name: ADEKA STAB PEP-36) 0.05 part by weight, as a neutralizing agent 0.03 part by weight of calcium stearate was added, and the mixture was mixed with a super mixer (manufactured by Kawata Corporation) for 5 minutes.
Using the obtained mixture, pellets of the propylene-based block copolymer (X1) were obtained by an underwater cut granulation method under the following equipment and conditions.
-Two-screw extruder (KZW25TW-45MG-NH manufactured by Technobel Co., Ltd.)
・ Caliber 30 mm, L / D = 25 (PMS30-25 manufactured by KG)
・ Screw: Full flight CR2.0, Feed groove depth 4mm + Dalmage ・ Screw rotation speed: 60rpm
-Set temperature: hopper sewage cooling, C1 to C4 220, 200, 200, 200 ° C.
・ Die: Strand die ・ Granulation processing rate: 200kg / hr
・ Cooling water temperature: 43 ° C
-Screen mesh: BMT140ZZ (obtained from Ishikawa Wire Net Co., Ltd., special Aya tatami mat)

[Production Example 2: Production of Propylene Block Copolymer (X2)]
1. 1. Production of solid catalyst component Instead of (t-C ₄ H ₉ ) (CH ₃ ) Si (OCH ₃ ) ₂ in the solid catalyst component production method of Production Example 1, (i-Pr) ₂ Si (OCH ₃ ) ₂ Was used, but the procedure was carried out according to Production Example 1.
2. 2. Production of Propylene-based Block Polymer Using the catalyst prepared above, the molar ratio of hydrogen / propylene in the first-stage polymerization was set to 0 according to the procedure for producing the propylene-based block copolymer (X1) of Production Example 1. The amount of ethyl alcohol input was changed to .016 and the molar ratio of hydrogen / propylene in the second stage polymerization was 0.00015 and the molar ratio of propylene and ethylene was 0.26. Is 1.19 times the molar amount of triethylaluminum supplied to the first reactor to produce a propylene / ethylene block copolymer, and the same granulation as in Production Example 1 is carried out to produce a propylene-based block copolymer. (X2) pellets were obtained.

3-2. Propylene homopolymer (Y)
Product name made by Japan Polypropylene Corporation: Novatec, grade name "MA1B", product name made by the same company: Waymax, grade name "MFX3", grade name "MFX6" as "Y1", "Y2", "Y3" respectively Using.

3-3. High melt tension polypropylene (Z-1)
Product name: Waymax, grade name "EX4000", grade name "MFX6" manufactured by Japan Polypropylene Corporation were used as "Z-1-1" and "Z-1-2", respectively. The characteristics are summarized in Table 2.

4. Production and Evaluation of Propylene-based Multilayer Foam Sheet [Example 1]
High melt tension polypropylene "Z-1-1" as a resin composition (Z) for a foaming layer (trade name: Waymax, grade name "EX4000", MFR = 6.2 g / 10 minutes manufactured by Japan Polypropylene Corporation) 100 0.5 parts by weight and 0.5 parts by weight of a chemical foaming agent (trade name: Hydrocerol CF40E-J, manufactured by Clariant Japan) as a bubble adjusting agent are uniformly stirred and mixed with a ribbon blender, and the obtained mixture is mixed in the middle of the barrel. It was put into a single-screw extruder having a barrel hole for injecting a physical foaming agent. 0.50 parts by weight of liquefied carbon dioxide is injected into 100 parts by weight of the "Z-1-1" with a high-pressure pump while being heated and melted in the previous stage of the extruder to plasticize and decompose the bubble conditioner. After kneading, the polypropylene resin foam-molded material was rapidly cooled in the subsequent stage of the extruder and extruded from a T-die having a width of 1,180 mm and a lip width of 0.4 mm via a feed block.
At this time, as a resin composition for the surface layer, 20 parts by weight of the propylene-based block copolymer "X1" and the propylene homopolymer "Y1" (trade name: Novatec, grade name "MA1B", MFR = 21 manufactured by Nippon Polypro Co., Ltd.) .0 g / 10 minutes) 80 parts by weight, black pigment masterbatch (manufactured by Polycol Kogyo Co., Ltd., "EPE-K-12601") 2 parts by weight are uniformly stirred and mixed with a ribbon blender, and then the obtained mixture is uniaxially extruded. It was put into a machine, heated and melted, and laminated on both sides of the foam layer via a feed block to obtain a multi-layer foam sheet having a two-kind, three-layer structure consisting of a surface layer, a foam layer, and a surface layer. One side of the extruded multilayer foam sheet was first cooled by a roll with a diameter of 110 mm installed near the die, then both sides were cooled by three rolls with a diameter of 110 mm installed after that, and the sheet was picked up at a constant speed by a pinch roll. ..
The operating conditions of each extruder are as follows.
・ Extruder (foam layer)
Caliber: 120 mmφ, L / D = 42, Physical foaming agent injection port: L / D = 20 position Screw rotation speed: 54 rpm
Discharge rate: Approximately 240 kg / h
・ Extruder (surface layer)
Caliber: 90 mmφ, L / D = 32
Screw rotation speed: 36 rpm
Discharge rate: Approximately 70 kg / h
・ Feed block temperature: 160 ℃
・ Die temperature: 160 ℃
・ Cooling roll temperature: 10 ℃
・ Pick-up speed: 11.4m / min
The obtained multi-layer foam sheet has a density of 0.30 g / cm ³ , an average thickness of 1.30 mm, an average cell diameter of the foam layer of 85 μm, and a dense cell structure with an open cell ratio of 9%, and has a good appearance. Met. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Example 2]
As the resin composition for the surface layer, the multilayer foamed sheet was prepared by the same method as in Example 1 except that the ratios of the propylene-based block copolymer "X1" and the propylene homopolymer "Y1" were 30 parts by weight and 70 parts by weight, respectively. Manufactured.
The obtained multi-layer foam sheet has a density of 0.30 g / cm ³ , an average thickness of 1.29 mm, an average cell diameter of the foam layer of 80 μm, and an open cell ratio of 11%, and has a good appearance. Met. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Example 3]
A multilayer foamed sheet was produced by the same method as in Example 1 except that 25 parts by weight of the propylene-based block copolymer "X2" and 75 parts by weight of the propylene homopolymer "Y1" were used as the surface resin composition.
The obtained multi-layer foam sheet has a density of 0.31 g / cm ³ , an average thickness of 1.30 mm, an average cell diameter of the foam layer of 90 μm, and a dense cell structure with an open cell ratio of 10%, and has a good appearance. Met. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Example 4]
A multilayer foamed sheet was produced by the same method as in Example 1 except that 100 parts by weight of the propylene-based block copolymer "X3" was used as the surface resin composition.
The obtained multi-layer foam sheet has a density of 0.30 g / cm ³ , an average thickness of 1.32 mm, an average cell diameter of the foam layer of 75 μm, and a dense cell structure with an open cell ratio of 12%, and has a good appearance. Met. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Example 5]
30 parts by weight of the propylene-based block copolymer "X1" and 70 parts by weight of the propylene homopolymer "Y2" as the surface resin composition, and high melt tension polypropylene "Z-1-" as the foamable polypropylene-based resin composition (Z). Examples except that 50 parts by weight of "1" and 50 parts by weight of the propylene resin "Y1" (here, "Y1" is "Z-2" which does not satisfy the characteristics (Z-i) to (Z-iii)) are used. A multilayer foamed sheet was produced in the same manner as in 1.
The obtained multi-layer foam sheet has a density of 0.29 g / cm ³ , an average thickness of 1.31 mm, an average cell diameter of the foam layer of 80 μm, and a dense cell structure with an open cell ratio of 12%, and has a good appearance. Met. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Comparative Example 1]
A multilayer foamed sheet was produced by the same method as in Example 1 except that 100 parts by weight of the propylene-based block copolymer "X4" was used as the surface resin composition.
The obtained multilayer foamed sheet has a dense cell structure having a density of 0.31 g / cm ³ , an average thickness of 1.29 mm, an average cell diameter of the foamed layer of 80 μm, and an open cell ratio of 17%, but has a surface layer. Some colored spots were confirmed. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Comparative Example 2]
A multilayer foamed sheet was produced by the same method as in Example 1 except that 30 parts by weight of the propylene-based block copolymer "X4" and 70 parts by weight of the propylene homopolymer "Y1" were used as the surface resin composition.
The obtained multilayer foamed sheet had a density of 0.34 g / cm ³ , an average thickness of 1.27 mm, an average foam diameter of the foamed layer of 85 μm, and an open cell ratio of 22%. Coloring spots were confirmed on the surface layer, and the surface layer thickness also varied. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Comparative Example 3]
A multilayer foamed sheet was produced by the same method as in Example 5 except that 100 parts by weight of the propylene-based block copolymer "X5" was used as the surface resin composition.
The obtained multilayer foamed sheet had a density of 0.28 g / cm ³ , an average thickness of 1.25 mm, an average foam diameter of 120 μm, and an open cell ratio of 25%. The colored spots on the surface layer were remarkable, and the variation in the surface layer thickness was also large. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Example 6]
High melt tension polypropylene "Z-1-2" as a resin composition (Z) for a foaming layer (trade name: Waymax, grade name "MFX6", MFR = 2.5 g / 10 minutes manufactured by Japan Polypropylene Corporation) 100 A parts by weight and 0.05 parts by weight of a chemical foaming agent (trade name: Hydrocerol CF40E-J, manufactured by Clariant Japan) as a bubble adjusting agent are uniformly stirred and mixed with a ribbon blender, and the obtained mixture has a screw diameter. It was put into a 65 mm single-screw extruder. The temperature set in front of the cylinder of the extruder is set to 230 ° C, the resin is heated and melted to make it plastic, the bubble regulator is decomposed, 0.95 parts by weight of isobutane is injected and kneaded with a high pressure pump, and then the cylinder of the extruder is used. The polypropylene-based resin foam composition was rapidly cooled at a set temperature of 175 ° C. in the subsequent stage from a circular die (diameter = 100 mmΦ, gap = 0.5 mm) attached to the tip of the extruder at a set temperature of 175 ° C. It was extruded into the atmosphere and foamed.
At this time, as a resin composition for the surface layer, 30 parts by weight of the propylene-based block copolymer "X1" and 70 parts by weight of the propylene homopolymer "Y3", a black pigment masterbatch (manufactured by Polycol Kogyo Co., Ltd., "EPE-K-12601"). ) After uniformly stirring and mixing 2 parts by weight with a ribbon blender, the obtained mixture was put into two single-screw extruders having a diameter of 30 mm. Each cylinder is heated and melted at a set temperature of 190 ° C, and one unit is laminated on the outside of the foam layer and the other unit is laminated on the inside of the foam layer via a multi-layer spiral mandrel, and the tip of the circular die is laminated with the foam layer. It was co-extruded from the above to obtain a multi-layer foam sheet having a two-kind, three-layer structure consisting of an outer surface layer, a foam layer, and an inner surface layer.
The foam extruded from the die was passed through a cooling mandrel having an outer diameter of 200 mm through which water was passed at a water temperature of 10 ° C. to cool the inner surface, and at the same time, air was blown from the air ring attached near the die to cool the outer surface. .. Then, after cutting open with a rotor cutter to form a sheet, the thickness was adjusted at the speed of a take-up roll, and the sheet was taken up by a pinch roll and a take-up roll.
The operating conditions of each extruder are as follows.
・ Extruder (foam layer)
Caliber: 65 mmφ, L / D = 50, Physical foaming agent injection port: L / D = 30 position Screw rotation speed: 60 rpm
Discharge rate: Approximately 40 kg / h
・ Extruder (surface layer)
Caliber: 30 mmφ, L / D = 32
Screw rotation speed: 30 rpm
・ Die temperature: 175 ℃
・ Cooling mandrel temperature: 10 ℃
・ Pick-up speed: 3.0m / min
The obtained multi-layer foam sheet has a density of 0.18 g / cm ³ , an average thickness of 1.80 mm, an average cell diameter of the foam layer of 150 μm, an open cell ratio of 15%, less corrugation, and a good appearance. Met. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

[Comparative Example 4]
A multilayer foamed sheet was produced by the same method as in Example 6 except that 100 parts by weight of the propylene-based block copolymer "X4" was used as the surface resin composition.
The obtained multilayer foamed sheet had a density of 0.20 g / cm ³ , an average thickness of 1.72 mm, an average foam diameter of the foamed layer of 240 μm, and an open cell ratio of 30%. Both the inner and outer surface layers had strong coloring spots and large variations in thickness. In addition, some bubbles were found in the foam layer, and corrugated was also confirmed. Table 3 shows the evaluation results of the obtained multilayer foamed sheet.

By comparing the examples and the comparative examples, it can be seen that by using the surface layer resin composition according to the present invention, a polypropylene-based multilayer foamed sheet having a beautiful appearance can be obtained without impairing the foaming performance. Further, it is clear that the appearance of the thermoformed body obtained by thermoforming the multilayer foam sheet is also excellent.

The polypropylene-based multi-layer foam sheet surface resin composition of the present invention is suitable for obtaining a multi-layer foam sheet having a very beautiful appearance with improved foaming performance while suppressing the dissipation of the foaming agent. The obtained polypropylene-based multilayer foamed sheet is excellent in thermoforming property, impact resistance, light weight, rigidity, heat resistance, heat insulating property, oil resistance, etc., and the appearance of the obtained molded body is also beautiful. A wide range of fields such as trays, plates, cups and other foamed food containers that can be heated by microwave ovens and filled with high-temperature liquids, automobile door trims, automobile interior materials such as automobile trunk mats, building materials, heat insulating materials, packaging, stationery, etc. It can be suitably used for, and its industrial value is extremely high.

Claims (5)

A propylene (co) polymer (X-1) and a propylene-ethylene copolymer (X-2) which may contain 10% by weight or less of comonomer having the following characteristics (X-i) to (X-iii). ) , The melt flow rate (MFR) is 1 to 15 g / 10 minutes, and the propylene-based block copolymer (X) is 10 to 90% by weight, and the propylene homopolymer (Y) is 10 to 90% by weight. A resin composition for the surface layer of a polypropylene-based multilayer foamed sheet containing.
Characteristics (X-i): The ratio of (X-1) and (X-2) is 50 to 99% by weight for (X-1) and 1 to 50% by weight for (X-2) (provided that it is 1 to 50% by weight). , (X-1) and (X-2) are 100% by weight based on the total amount of the propylene-based block copolymer (X).)
Characteristics (X-ii): The ethylene content in the propylene-ethylene copolymer (X-2) is 11.0 to 60.0% by weight (however, the weight ratio of the ethylene content is the propylene-ethylene copolymer weight. The total amount of the monomers constituting the coalescence (X-2) is 100% by weight).
Characteristics (X-iii): The intrinsic viscosity of the propylene-ethylene copolymer (X-2) in 135 ° C. decalin is 8.0 (dl / g) or more. The resin composition for the surface layer of a polypropylene-based multilayer foamed sheet according to claim 1, wherein the propylene-based block copolymer (X) is a multi-stage polymer. The polypropylene -based multilayer foamed sheet surface layer resin composition is a polypropylene-based multilayer foamed sheet laminated on one or both sides of the foamed layer, and the polypropylene-based multilayer foamed sheet surface layer resin composition constitutes the foamed layer. It has an MFR of 0.5 times or more and 2.5 times or less with respect to the MFR of the effervescent polypropylene-based resin composition (Z), and has the following characteristics (Xi) to (X-iii). 10 to 90% by weight of a propylene-based block copolymer (X) composed of a propylene (co) polymer (X-1) and a propylene-ethylene copolymer (X-2) which may contain comonomer of weight% or less. A polypropylene-based multilayer foamed sheet containing 10 to 90% by weight of the propylene homopolymer (Y) .
Characteristics (X-i): The ratio of (X-1) and (X-2) is 50 to 99% by weight for (X-1) and 1 to 50% by weight for (X-2) (provided that it is 1 to 50% by weight). , (X-1) and (X-2) are 100% by weight based on the total amount of the propylene-based block copolymer (X).)
Characteristics (X-ii): The ethylene content in the propylene-ethylene copolymer (X-2) is 11.0 to 60.0% by weight (however, the weight ratio of the ethylene content is the propylene-ethylene copolymer weight. The total amount of the monomers constituting the coalescence (X-2) is 100% by weight).
Characteristics (X-iii): The intrinsic viscosity of the propylene-ethylene copolymer (X-2) in 135 ° C. decalin is 8.0 (dl / g) or more. Claimed that the foamable polypropylene-based resin composition (Z) constituting the foam layer contains 20% by weight or more of high melt tension polypropylene (Z-1) satisfying the following characteristics (Z-i) to (Z-iii). 3. The weight ratio of the polypropylene-based multilayer foamed sheet (however, the high melt tension polypropylene (Z-1)) is 100% by weight based on the total amount of the polypropylene-based resin constituting the expandable polypropylene-based resin composition (Z). ).
Characteristics (Z-i): The melt tension (MT) measured at 230 ° C. is 3 to 25 g.
Characteristics (Z-ii): The melt flow rate (MFR) is more than 0.9 g / 10 minutes and 15 g / 10 minutes or less.
Characteristic (Z-iii): The strain hardening degree (λmax (0.1)) in the measurement of extensional viscosity at a strain rate of 0.1s ^-1 is 6.0 or more. A polypropylene-based resin foam molded product obtained by thermoforming the polypropylene-based multilayer foamed sheet according to claim 3 or 4 .

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