JP2004176047A - Polypropylene-based resin foamed particle and in-mold processed product by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide polypropylene-based resin foamed particles having excellent fusion characteristics between particles, even when molded by using a conventional molding machine in which clamping pressure is low, and therefore capable of obtaining an in-mold processed product having excellent surface appearance and mechanical characteristics, and having a high heat-resistant temperature, and to provide the in-mold processed product. <P>SOLUTION: The polypropylene-based resin foamed particles 1 are each composed of a core layer 11 and a cover layer 12, wherein the core layer 11 comprises a polypropyrene-based polymer [A] and a polypropylene-based polymer [B]. The in-mold processed product is given by using the foamed particles 1. The polypropylene-based polymer [A] satisfies requirements (a) and (b) as follows: (a) having propylene structural units in an amount of 100-85mol.% and other structural units including ethylene and α-olefin units in an amount of 0-15mol.%; and (b) having a ratio of irregularly positioned units caused by 2,1-addition of a propylene monomer unit of 0.5-2.0% and a ratio of irregularly positioned units caused by 1,3-addition of the propylene monomer unit of 0.005-0.4%, and the polypropylene-based polymer [B] satisfies the requirement (a). <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to expanded polypropylene resin particles capable of obtaining an in-mold molded article having excellent fusion properties between foamed particles, surface appearance, and mechanical properties at a low molding temperature, and a mold using the same. Related to molded articles.

  The resin foam particles have a low thermal conductivity based on a closed cell structure. Therefore, it is widely used as a raw material for forming heat insulating materials, cushioning materials, various core materials, and the like. As the thermoplastic resin constituting the resin foam particles, polyethylene, polypropylene, polystyrene and the like are usually used.

  Among the above thermoplastic resins, in-mold molded articles obtained by using resin having crystallinity, that is, expanded resin particles obtained from polyethylene or polypropylene, have higher chemical resistance than molded articles formed by expanded polystyrene resin particles. There is an advantage that heat resistance and heat resistance are excellent.

  However, in the case of a high melting point resin represented by a polypropylene resin, since the melting point is as high as 135 ° C. or more, the pressure for fusing the resin foamed particles together during in-mold molding is 0.2 MPaG (“ G ": meaning of gauge pressure; the same applies to the following).

  Therefore, there is a drawback that the molding cost is increased and the molding cycle is lengthened. In the case of foamed resin particles made of the above-mentioned high-melting point resin, molding cannot be performed using a widely-used in-mold foaming molding machine for expanded polystyrene, so that a high-pressure steam control system is provided and the mold clamping pressure is high. A molding machine is required.

On the other hand, in the case of polyethylene resin, since the melting point is as low as 125 ° C. or less, the water vapor pressure for fusing the resin foam particles may be a low pressure of less than 0.2 MPaG, and the in-mold foam molding for polystyrene is sufficient. It has the advantage that it can be molded with almost no change in specifications.
However, an in-mold molded article of a polyethylene resin has low heat resistance because the base resin has a low melting point, and particularly, a highly foamed in-mold molded article has a small energy absorbing ability.
Therefore, the in-mold molded product of a polyethylene resin can be generally used only in the field of low foaming as compared with the in-mold molded product of another thermoplastic resin.

In order to solve the various problems as described above, the foamed core layer is made of a crystalline thermoplastic resin and the coating layer is made of an ethylene-based polymer and is in a substantially non-foamed state. A resin foam particle having a specific structure has been proposed (see Patent Document 1).
In this case, there is a characteristic that foamed resin particles exhibiting excellent fusion property can be obtained even when the heating steam pressure in the in-mold molding is low, but the mechanical strength of the obtained molded product is not necessarily sufficient, and further improvement is required. Improvement was desired.

JP-A-10-77359 (pages 2 to 4)

  The present invention has been made in view of such conventional problems, and has excellent surface appearance, mechanical properties, and fusion between foamed particles even when molded with a general-purpose molding machine having a low mold clamping pressure, and An object of the present invention is to provide expanded polypropylene resin particles capable of obtaining an in-mold molded article having a high heat resistance temperature, and to provide the in-mold molded article.

The first invention provides a foamed polypropylene resin particle comprising a foamed core layer made of a crystalline thermoplastic resin and a coating layer made of a thermoplastic resin covering the foamed core layer.
The core layer is composed of 5 to 95% by weight of the following propylene polymer [A] and 95 to 5% by weight of the following propylene polymer [B] (provided that the propylene polymer (A) and the propylene polymer (The total amount of [B] is 100% by weight) as the base resin.
Propylene-based polymer [A]: A propylene-based polymer having the following requirements (a) and (b).
(A) 100 to 85 mol% of structural units obtained from propylene, and 0 to 15 mol% of structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms (provided that propylene is obtained from propylene) The total amount of the structural units and the structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is 100 mol%).
(B) the ratio of the position irregular units based on the 2,1-insertion of the propylene monomer units in the total propylene insertion is 0.5 to 2.0%, as measured by 13C-NMR, and the propylene monomer The ratio of the position irregular units based on the 1,3-insertion of the unit is 0.005 to 0.4%.
Propylene-based polymer [B]: A propylene-based polymer having only the requirement (a) among the requirements (a) and (b).

In the expanded polypropylene resin particles of the present invention, the expanded core layer has a base resin made of a polypropylene resin composition comprising the propylene polymer [A] and the propylene polymer [B]. .
Therefore, it is possible to provide expanded polypropylene resin particles having a high mechanical strength of the core layer. Even when molded with a general-purpose molding machine with a low clamping pressure, such polypropylene resin foamed particles have excellent fusion properties between foamed particles, excellent mechanical properties such as compressive strength and tensile strength, and excellent surface appearance. Thus, an in-mold molded article can be obtained.

Next, a second invention is an in-mold molded article having a density of 0.5 to 0.008 g / cm ³ formed by molding foamed polypropylene resin particles in a mold.
The foamed polypropylene resin particles are those obtained by using those of the first invention (invention 8).

The in-mold molded article of the present invention has a density of 0.5 to 0.008 g / cm ³ and is made of the above-mentioned first invention.
Therefore, the in-mold molded article is obtained by heating with steam of about 0.2 MPaG, has excellent mechanical properties such as compressive strength and tensile strength, and has excellent surface appearance such as smoothness and gloss. It will be.
Therefore, the in-mold molded article is suitable, for example, for packaging containers, toys, automobile parts, helmet core materials, cushioning packaging materials, and the like.
In addition, the density of the in-mold molded body means an apparent overall density defined by JIS K7222 (1999).

The expanded polypropylene resin particles of the present invention have a composite structure formed of a core layer and a coating layer.
In the first invention (claim 1), the core layer is a base resin made of a polypropylene resin composition comprising the propylene polymer [A] and the propylene polymer [B].

Here, the base resin means a basic thermoplastic resin component constituting the above-mentioned foamed core layer. The core layer is composed of the base resin and other polymer components to be added as required, or additives such as a foaming agent, a catalyst neutralizing agent, a lubricant, a crystal nucleating agent, and other additives. However, it is desirable that other polymer components and additives be as small as possible within a range not to impair the object of the present invention.
That is, when the total amount of the propylene-based polymer [A] and the propylene-based polymer [B] is 100 parts by weight, the addition amount of the other polymer components is preferably 40 parts by weight or less. More preferably, the amount is 30 parts by weight or less, and even more preferably 15 parts by weight or less. Most preferably, the amount is 5 parts by weight or less.
When the total amount of the propylene-based polymer [A] and the propylene-based polymer [B] is 100 parts by weight, the additive amount of the above-mentioned additive (for the foaming agent, the one that eventually disappears, such as a foaming agent, Is excluded), but is preferably 40 parts by weight or less, depending on the purpose of use of the additive. More preferably, the amount is 30 parts by weight or less, and still more preferably 0.001 to 15 parts by weight.

First, the propylene polymer [A] will be described below.
First, the requirement (a) is that 100 to 85 mol% of the structural unit obtained from propylene and 0 to 15 mol% of the structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms are present. is there.
Here, the total amount of the structural units obtained from propylene and the structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is 100 mol%.
Therefore, as the propylene-based polymer satisfying the requirement (a), there is a polymer composed of propylene homopolymer or a copolymer composed of propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms. .

  Specific examples of the comonomer ethylene and / or an α-olefin having 4 to 20 carbon atoms copolymerized with propylene include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4- Methyl-1-butene and the like can be mentioned.

Further, in the present invention, as the propylene-based polymer [A], other monomers which have been conventionally difficult to polymerize with a Ziegler / Natta catalyst are copolymerized with propylene as long as the object of the present invention is not impaired. Things can be used. In this case, the structural unit obtained from the other monomer is preferably 0.01 to 20 mol%, more preferably 0.05 to 10 mol% in the propylene-based polymer [A].
The polypropylene-based resin composition containing such a propylene-based polymer is used as a base resin for forming a foamed core layer constituting the polypropylene-based resin expanded particles.

  Such other monomers include, for example, cycloolefins such as cyclopentene, norbornene, 1,4,5,8-dimethano-1,2,3,4,4a, 8,8a, 5-octahydronaphthalene, Chain non-conjugated dienes such as methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene, 5-ethylidene-2-norbonene, dicyclopentadiene , 5-vinyl-2-norbornene, norbornadiene and the like, and one or more kinds of aromatic unsaturated compounds such as styrene and divinylbenzene.

  The propylene-based polymer [A] used in the present invention is the above-mentioned requirement (a), that is, a propylene-based (co) polymer resin containing 85 to 100 mol% of a structural unit obtained from propylene in the propylene-based polymer. It is necessary that a structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms (comonomer) is contained in a proportion of 0 to 15 mol%.

  When the proportion of the structural unit of the comonomer exceeds 15 mol%, mechanical properties such as bending strength and tensile strength of the polypropylene resin composition are greatly reduced. Further, even if the polypropylene-based resin expanded particles are produced using the polypropylene-based resin composition as a base resin of the core layer, desired expanded particles cannot be obtained. Furthermore, even if the foamed particles are molded, a desired in-mold molded article excellent in mechanical strength and compression recovery cannot be obtained.

In the propylene-based polymer [A], 98 to 85 mol% of structural units obtained from propylene, and 2 to 15 mol% of structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms. It is preferably present (provided that the total amount of the structural units obtained from propylene and the structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is 100 mol%).
In this case, the structural units obtained from propylene and the structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms are essential components. The expanded particles of the polypropylene-based resin containing such a propylene-based polymer [A] as one component of the core layer can have an effect that the cell diameter becomes extremely uniform. .

In the propylene polymer [A], 100 mol% of the structural unit obtained from propylene, that is, 0 mol% of the structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms. Can be.
In this case, the propylene-based polymer [A] is a so-called propylene homopolymer. The expanded polypropylene resin particles containing such a propylene polymer [A] as one component of the core layer are more excellent in the strength of an in-mold molded product obtained by molding the same. It becomes.

Next, as shown in the requirement (b), the propylene-based polymer [A] has a position based on the 2,1-insertion of the propylene monomer unit in the total propylene insertion as measured by 13C-NMR. The proportion of irregular units is 0.5 to 2.0%, and the proportion of positional irregular units based on 1,3-insertion of propylene monomer units is 0.005 to 0.4%.
This requirement (b) relates to the proportion of the position irregular units in the propylene polymer, and the irregular units have an effect of reducing the crystallinity of the propylene polymer, and the propylene polymer [A ] Is used as the base resin of the core layer for foaming, the effect of enhancing foaming suitability is exhibited.

  If the proportion of the irregular units based on the 2,1-insertion is less than 0.5%, the expanded polypropylene resin particles having a foamed core layer containing the same as a base resin are molded in a mold. Sometimes, there is a problem that the effect of reducing the compression set of the obtained in-mold molded product is poor. On the other hand, if it exceeds 2.0%, the mechanical properties of the polypropylene-based resin composition as a base resin, such as bending strength and tensile strength, are reduced, so that the expanded particles and the in-mold molded product obtained therefrom are reduced. There is a problem that strength is reduced.

  When the ratio of the position irregular units based on the 1,3-insertion is less than 0.005%, the expanded polypropylene resin particles having a foamed core layer containing the same as a base resin are placed in a mold. When molding, there is a problem that the effect of reducing the compression set of the obtained molded article in the mold is inferior. On the other hand, if it exceeds 0.4%, the mechanical properties of the polypropylene-based resin composition as a base resin, such as bending strength and tensile strength, are reduced. There is a problem that the strength of the molded body is reduced.

  In the above requirement (b), the positional irregularity unit based on the 2,1-insertion and the positional irregularity unit based on the 1,3-insertion are both crystals of the propylene-based polymer containing these units in the structure. Has the effect of reducing the properties. More specifically, these regio-irregular units have an action of lowering the melting point and an action of lowering the crystallinity of the propylene-based polymer.

  These two effects are effective when the polypropylene resin composition containing the propylene-based polymer [A] is subjected to foaming as a base resin of the core layer for foaming. The effect of reducing the compression set is shown. The propylene-based polymer [A] having the above-mentioned positionally irregular units has excellent compatibility with the propylene-based polymer [B] described below, and therefore, when both are melt-kneaded, they mix very well. Such a polypropylene-based resin composition has, in addition to the above-mentioned features of the propylene-based polymer [A], an effect that the secondary foamability is good when the core layer is processed into foamed particles and molded in a mold. Play.

  However, if the proportion of the positionally irregular units contained in the propylene-based polymer is too high, the melting point and the crystallinity of the base resin are highly reduced, so that the propylene-based polymer [ A], the foamed resin particles obtained may be subjected to foaming, which may cause a problem that the cell diameter of the core layer constituting the foamed resin particles becomes large. However, there is a problem that the appearance of a molded article obtained from the composition is impaired. Further, as described above, there is a problem that the strength of the in-mold molded article obtained from such expanded particles is reduced.

Here, the fraction of the structural unit obtained from propylene in the propylene-based polymer, the fraction of the structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms, and the fraction of an isotactic triad described below are: This is a value measured using the 13C-NMR method.
The method of measuring the 13C-NMR spectrum is, for example, as follows.
That is, about 350 to 500 mg of a sample was placed in a sample tube for NMR having a diameter of 10 mmφ, and completely dissolved using about 2.0 ml of o-dichlorobenzene as a solvent and about 0.5 ml of deuterated benzene for rock. Thereafter, the measurement was performed at 130 ° C. under the condition of complete proton decoupling.

As the measurement conditions, a flip angle of 65 deg and a pulse interval of 5T1 or more (where T1 is the longest value among the spin lattice relaxation times of the methyl group) were selected. In the propylene-based polymer, the spin lattice relaxation time of the methylene group and the methine group is shorter than that of the methyl group. Therefore, under these measurement conditions, the recovery of the magnetization of all carbons is 99% or more.
In addition, the detection sensitivity of the position irregular unit in the 13C-NMR method is usually about 0.01%, but it can be increased by increasing the number of integrations.

  The chemical shift in the above measurement was determined by setting the peak of the methyl group in the third unit of the five propylene units having 5 head-to-tail bonds and the same direction of methyl branching as 21.8 ppm. The chemical shifts of other carbon peaks were set.

  Using this criterion, the peak based on the methyl group of the second unit in the 3 chains of propylene units represented by PPP [mm] in the following formula [Chemical Formula 1] falls within the range of 21.3 to 22.2 ppm, and The peak based on the methyl group of the second unit in the three chains of propylene units represented by [mr] is in the range of 20.5 to 21.3 ppm, and the second unit in the three chains of propylene units represented by PPP [rr] The peak based on the methyl group of the eye appears in the range of 19.7 to 20.5 ppm.

  Here, PPP [mm], PPP [mr], and PPP [rr] are respectively shown as follows.

  Further, in the present invention, the propylene-based polymer [A] has the following partial structures (Ι) and (ΙΙ) containing regiorandom units based on 2,1-insertion and 1,3-insertion of propylene. Content.

It is considered that such a partial structure is caused by positional irregularities that occur during the polymerization of a propylene-based polymer, for example, when a polymerization reaction is performed using a metallocene-based catalyst.
That is, the propylene monomer usually reacts in a manner in which the methylene side is bonded to the metal component in the catalyst, that is, a so-called “1,2-insertion”. , 3-insertion ". “2,1-insertion” is a reaction type in which the addition direction is opposite to “1,2-insertion”, and forms a structural unit represented by the above partial structure (Ι) in a polymer chain.

  The term "1,3-insertion" means that the propylene monomer is incorporated into the polymer chain by C-1 and C-3, and as a result, a linear structural unit, that is, the above partial structure ( ΙΙ).

  The propylene-based polymer [A] in which the proportion of each of the above-mentioned positionally irregular units falls within the range of the present invention can be obtained by selecting an appropriate catalyst. Specifically, for example, it can be obtained using a metallocene-based polymerization catalyst having a hydroazulenyl group as a ligand. Here, the metallocene-based polymerization catalyst is composed of a transition metal compound component having a metallocene structure and a promoter component. Although the proportion of each regio-irregular unit differs depending on the chemical structure of the metal complex component of the catalyst used for the polymerization, generally, the higher the polymerization temperature, the larger the tendency. In the present invention, the polymerization temperature is preferably from 0 to 80 ° C. in order to keep the proportion of each position irregular unit in the propylene-based polymer [A] within the above specific range.

The metal complex component can be used as it is as a catalyst component, but it can be used as a solid catalyst in which the above metal complex component is supported on an inorganic or organic fine-grained carrier that is a granular or fine solid. May be used.
When the metal complex component is supported on the fine particle carrier, the amount of the metal complex component supported is preferably 0.001 to 10 mmol, more preferably 0.001 to 5 mmol per 1 g of the carrier.

Among the above metallocene catalysts having a hydroazulenyl group as a ligand, catalysts using titanium, zirconium, and hafnium as metal atoms are preferable. Among them, complexes having zirconium are preferable because of high polymerization activity. .
Among the above metallocene catalysts, zirconium dichloride type complexes are preferably used, and among them, it is particularly preferable to use a crosslinked type complex.
Specifically, methylenebis {1,1 ′-(2-methyl-4-phenyldihydroazulenyl)} zirconium dichloride, methylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazulenyl)} zirconium dichloride , Methylenebis {1,1 '-(4-phenyldihydroazulenyl)} zirconium dichloride, methylenebis {1,1'-(4-naphthyldihydroazulenyl)} zirconium dichloride, ethylenebis {1,1 '-(2- Methyl-4-phenyldihydroazulenyl) zirconium dichloride, ethylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazulenyl)} zirconium dichloride, ethylenebis {1,1 ′-(4-phenyldihydro (Azulenyl) zirconium dichloride, ethylenebis 1,1, '-(4 Naphthyldihydroazulenyl) {zirconium dichloride, isopropylidenebis} 1,1 ′-(2-methyl-4-phenyldihydroazulenyl)} zirconium dichloride, isopropylidenebis {1,1 ′-(2-ethyl-4- Phenyldihydroazulenyl)｝ zirconium dichloride, isopropylidenebis ｛1,1 ′-(4-phenyldihydroazulenyl)｝ zirconium dichloride, isopropylidenebis ｛1,1 ′-(4-naphthyldihydroazulenyl)｝ zirconium dichloride , Dimethylsilylenebis {1,1 '-(2-methyl-4-phenyldihydroazulenyl)} zirconium dichloride, dimethylsilylenebis {1,1'-(2-ethyl-4-phenyldihydroazulenyl)} zirconium dichloride , Dimethylsilylene bis {1,1 ′-(4-phenyldihydroazulenyl)} zirconium dichloride, dimethylsilylenebis {1,1 ′-(4-naphthyldihydroazulenyl)} zirconium dichloride, diphenylsilylenebis {1,1 ′-(2 -Methyl-4-phenyldihydroazulenyl) {zirconium dichloride, diphenylsilylenebis} 1,1 ′-(2-ethyl-4-phenyldihydroazulenyl)} zirconium dichloride, diphenylsilylenebis {1,1 ′-(4 -Phenyldihydroazulenyl) zirconium dichloride, diphenylsilylene bis {1,1 '-(4-naphthyldihydroazulenyl)} zirconium dichloride, and the like.
Among them, dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyldihydroazulenyl)} zirconium dichloride and dimethylsilylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazulene) are particularly preferable. (Nyl)｝ It is preferable to use zirconium dichloride. In this case, the proportion of each of the above-mentioned positional irregular units can be easily controlled within the range of the present invention, and the requirement (d) described later is satisfied (the isotactic triad fraction is 97%). The above-mentioned) propylene-based polymer can be obtained.

  Examples of the co-catalyst component include aluminoxanes such as methylaluminoxane, isobutylaluminoxane and methylisobutylaluminoxane; Lewis acids such as triphenylborane, tris (pentafluorophenyl) borane and magnesium chloride; and dimethylaniliniumtetrakis (pentafluorophenyl). And ionic compounds such as borate. It is also possible to use these cocatalyst components in combination with other organoaluminum compounds, for example, trialkylaluminums such as trimethylaluminum, triethylaluminum, and triisobutylaluminum.

  The mm fraction (isotactic triad fraction) in the entire polymer chain of the propylene-based polymer according to the present invention is expressed by the following [Equation 1]. By the way, in the partial structure (ΙΙ), as a result of 1,3-insertion, one methyl group derived from a propylene monomer has disappeared.

In this formula, ΣΙCH ₃ indicates the area of all methyl groups (all peaks at 19 to 22 ppm of chemical shift). A <1>, A <2>, A <3>, A <4>, A <5>, A <6>, A <7>, A <8>, and A <9> are The peak areas at 42.3 ppm, 35.9 ppm, 38.6 ppm, 30.6 ppm, 36.0 ppm, 31.5 ppm, 31.0 ppm, 37.2 ppm, and 27.4 ppm, and the partial structures (Ι) and (ΙΙ) ) Indicates the abundance ratio of carbon.
Further, the ratio of 2,1-inserted propylene and the ratio of 1,3-inserted propylene relative to the total propylene insertion were calculated by the following equations.

Next, the propylene polymer [A] is the melting point of the polymer Tm [° C.], also the water vapor permeability in the case of forming the polymer into a film and ^{Y [g / m 2 / 24hr} ] In this case, it is preferable that Tm and Y satisfy the following relational expression (1).
(−0.20) Tm + 35 ≦ Y ≦ (−0.33) Tm + 60 Equation (1)

  The water vapor permeability can be measured according to JIS K7129 (1992), “Test Method for Water Vapor Permeability of Plastic Films and Sheets”. In this measurement, an infrared sensor method is employed as a test method, and a test temperature of 40 ± 0.5 ° C. and a relative humidity (90 ± 2)% RH are employed as test conditions.

The propylene-based polymer [A] in the range of the above formula (1) shows a moderate water vapor permeability. The moderate water vapor permeability promotes the penetration of the saturated steam used for molding into the core layer during molding in the mold, thereby increasing the secondary foaming property of the foamed particles, Production of an in-mold molded article having no or few voids becomes easy.
In addition, as a method for producing expanded polypropylene resin particles, a method is described in which resin particles comprising a composite, which will be described later, are impregnated with a foaming agent while being dispersed in water, and then released from high temperature and high pressure to low pressure to form expanded particles. In this case, appropriate water vapor permeability makes it easy for water and a foaming agent to penetrate into the resin particles (base resin for forming the core layer). As a result, the dispersion of water and the foaming agent in the resin particles becomes uniform, so that the cell diameter of the core layer of the obtained foamed particles can be made uniform, and the expansion ratio can be improved.
The water vapor permeability (Y) is expressed in relation to the melting point (Tm) of the propylene-based polymer because the foaming temperature during the production of foamed particles and the saturated steam temperature during in-mold molding are generally This is based on the fact that the higher the melting point (Tm) of the propylene polymer as the base resin, the higher the melting point (Tm), and the lower the melting point (Tm), the lower the melting point (Tm).

  When the water vapor permeability (Y) is less than [(−0.20) · Tm + 35], the permeability of the water vapor and the foaming agent to the base resin constituting the core layer becomes poor. If it exceeds [(−0.33) · Tm + 60], the permeability of the water vapor to the base resin becomes too good. The dispersion of the agent tends to be non-uniform, and the uniformity of the cell diameter of the core layer of the obtained expanded particles may be reduced. In particular, when the water vapor permeability (Y) exceeds [(−0.33) · Tm + 60], coarse bubbles may be mixed in the core layer of the obtained expanded particles.

  A propylene-based polymer having a melting point (Tm) and a water vapor permeability (Y) satisfying the relationship of the formula (1) can be obtained by selecting an appropriate catalyst in producing the polymer. Specifically, among the above-mentioned metallocene-based catalysts, it can be suitably obtained by using bridged bis {1,1 '-(4-hydroazulenyl)} zirconium dichloride as a metal complex component. Preferred examples of such a metal complex component are as described above.

In the present invention, the melting point (Tm) of the propylene-based polymer [A] is generally from 125 ° C to 165 ° C, preferably from 130 ° C to 160 ° C, more preferably from 133 ° C to 158 ° C. 141 ° C to 158 ° C is more preferred.
The melting point (Tm), the melting point of the propylene-based polymer [B] described later, and the melting point of the thermoplastic resin forming the coating layer are all described in “Constant heat treatment” described in JIS K7121 (1987). After that, measure the melting temperature ”(The heating rate and the cooling rate in the conditioning of the test piece are both 10 ° C / min.), And the heat flux DSC device is used. A DSC curve is drawn at 10 ° C., and the apex of the melting peak on the obtained DSC curve is adopted. If multiple peaks are observed, the peak with the highest melting peak is used based on the baseline on the high-temperature side. If there are multiple peaks with the highest melting peak, their arithmetic mean values are used. Is adopted. The melting point of the coating layer described later is also measured by this method. With respect to the coating layer, "having substantially no melting point" refers to a case where no clear melting peak is exhibited when measured by the above method. If the sample does not show a clear melting peak, the maximum temperature for heating in the conditioning of the test piece by heat flux DSC is up to 220 ° C.

Next, the propylene-based polymer [B] in the first invention will be described.
The propylene-based polymer [B] is a propylene-based polymer having only the requirement (a) among the requirements (a) and (b). That is, in the propylene-based polymer [B], 100 to 85 mol% of structural units obtained from propylene and 0 to 15 mol% of structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms are present. That is, the requirement (a) is satisfied, but the requirement (b) is not satisfied. The propylene-based polymer [B] usually does not satisfy the above formula (1). Such a propylene-based polymer [B] can be obtained using, for example, a Ziegler / Natta catalyst or the like.
The requirement (a) is the same as the requirement [a] for the propylene-based polymer [A].

  The polypropylene-based polymer having a foamed core layer obtained by using the polypropylene-based resin composition obtained by mixing the propylene-based polymer [B] with the propylene-based polymer [A] as a base resin. Resin expanded particles are more excellent in secondary expandability in in-mold molding than foamed particles having a foamed core layer obtained by using the propylene-based polymer [A] alone. Is characterized by having an excellent surface appearance.

The reason for this is not necessarily clear, but is presumed to be due to the following mechanism.
That is, the propylene-based polymer [A] generally has a narrow molecular weight distribution, while the propylene-based polymer [B] generally has a wide molecular weight distribution. Therefore, the polypropylene-based resin composition obtained by mixing the propylene-based polymer [B] with the propylene-based polymer [A] has a wide molecular weight distribution.

Also, the process of expanding the resin particles to produce the expanded particles can be regarded as a process of stretching the resin portion, and thus can be considered as a process of orienting the resin. When the degree of this orientation is high, the oriented portion is considered to act in a direction to suppress secondary foaming when the foamed particles are heated. Conversely, the lower the degree of orientation, the higher the secondary foamability in in-mold molding.
In general, when the molecular weight distribution is broad, the degree of orientation is lower than when the molecular weight distribution is narrow. From this, the expanded polypropylene resin particles obtained by using the polypropylene resin composition obtained by mixing the propylene polymer [B] with the propylene polymer [A], It is estimated that the secondary foaming power is higher than the foamed resin particles obtained by using the polymer [A] alone.

  Further, the polypropylene resin having a foamed core layer obtained by using the polypropylene resin composition obtained by mixing the propylene polymer [A] and the propylene polymer [B] as a base resin. The foamed particles can be molded at a lower temperature than the foamed particles having a foamed core layer obtained by using the propylene-based polymer [B] alone, and furthermore, the mechanical properties of the obtained molded body For example, it has a feature of being excellent in compressive strength and bending strength.

The mixing ratio of the propylene-based polymer [A] and the propylene-based polymer [B] is 5 to 95% by weight of the propylene-based polymer [A] and 95 to 95% by weight of the propylene-based polymer [B]. It is necessary to be in the range of 5% by weight (however, the total amount of the propylene-based polymer [A] and the propylene-based polymer [B] is 100% by weight).
When the blending ratio of the propylene-based polymer [A] is less than 5% by weight, since the propylene-based polymer [B] is a main component, the bubble diameter in the core layer constituting the obtained expanded particles is reduced. It tends to be small, and its mechanical properties may be insufficient. In addition, high-temperature steam may be required for in-mold molding of such expanded particles.
On the other hand, if the blending ratio of the propylene-based polymer [A] exceeds 95% by weight, the obtained foamed polypropylene-based resin particles may have insufficient secondary expandability.

  The mixing ratio of the propylene polymer [A] and the propylene polymer [B] is preferably 10 to 80% by weight of the propylene polymer [A] and the propylene polymer [B]. 90 to 20% by weight (however, the total amount of the propylene-based polymer [A] and the propylene-based polymer [B] is 100% by weight), and more preferably the propylene-based polymer [A] is 20 to 20% by weight. The propylene-based polymer [B] is preferably 80 to 20% by weight relative to 80% by weight (however, the total amount of the propylene-based polymer [A] and the propylene-based polymer [B] is 100% by weight).

  Next, the coating layer is made of a thermoplastic resin and covers the core layer. The coating layer is preferably in a non-foamed state. If the coating layer is in a foamed state, the fusion property between the foamed particles may be deteriorated during the in-mold molding of the polypropylene resin foamed particles.

Further, it is preferable that the coating layer is made of an olefin polymer having a melting point lower than that of each of the propylene polymers [A] and [B] forming the core layer, or having substantially no melting point. (Claim 2).
In this case, there is an effect that an in-mold molded body can be obtained at a lower temperature. Here, the olefin-based polymer is a homopolymer of olefin, a copolymer of olefins, a copolymer of olefin with another comonomer other than olefin (the structural unit obtained from the olefin in the copolymer is 50 units). Mol% or more of a copolymer), a mixture of two or more of them, or a mixture of one or more of these with another (co) polymer (a mixture in which the structural unit derived from an olefin in the mixture is 50 mol% or more) ).

  Examples of the olefin polymer having a lower melting point than the propylene polymers [A] and [B] include high-pressure low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, vinyl acetate, Examples include a copolymer of ethylene with an unsaturated carboxylic acid, an unsaturated carboxylic acid ester, and the like, and a copolymer of propylene with ethylene and α-olefins.

  Examples of the olefin polymer having substantially no melting point include rubber such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-acrylic rubber, chlorinated polyethylene rubber, and chlorosulfonated polyethylene rubber. Elastomers. These rubbers and elastomers can be used alone or in combination of two or more.

In the present invention, the propylene polymer [A] preferably further has the following requirement (d) (claim 3).
(D) The isotactic triad fraction in the propylene unit chain portion composed of head-to-tail bonds, as measured by 13C-NMR, is 97% or more.

  That is, in addition to the requirements (a) and (b) described above, the propylene polymer [A], which is a constituent component of the polypropylene resin composition, further includes a propylene unit chain having a head-to-tail bond. Isotactic triad fraction measured by 13 C-NMR (nuclear magnetic resonance method) (that is, among three arbitrary chains of propylene units in the polymer chain, each propylene unit is bonded head-to-tail, and Of propylene units having the same methyl branch direction (the ratio of three chains) is 97% or more.

The isotactic triad fraction is hereinafter referred to as the mm fraction as appropriate. When the mm fraction is 97% or more, the mechanical properties of the polypropylene resin composition become higher. Therefore, the mechanical properties of a molded article made of foamed particles having a core layer obtained by using this as a base resin can be made higher.
In addition, more preferably, the mm fraction is 98% or more.

Next, the propylene-based polymer [A] preferably further has the following requirement (e) (claim 4).
(E) The melt flow rate is 0.5 to 100 g / 10 minutes.

  In this case, the polypropylene resin composition can be produced while maintaining industrially useful production efficiency. Furthermore, an in-mold molded article made of expanded particles obtained by using this as a base resin can have the effect of having excellent mechanical properties.

  If the melt flow rate (MFR) is less than 0.5 g / 10 minutes, the production efficiency of the polypropylene-based resin composition, especially the productivity when performing the melt-kneading described below, may be reduced. When the MFR exceeds 100 g / 10 minutes, the compression of a molded article obtained by further molding foamed particles having a core layer using the obtained polypropylene resin composition as a base resin of the core layer is performed. Mechanical properties such as strength and tensile strength may be reduced. In addition, Preferably, it is 1.0 to 50 g / 10 minutes, Furthermore, it is 1.0 to 30 g / 10 minutes. The above MFR means a melt mass flow rate measured according to the conditions described in Table 3 of JIS K6921-2 (1997).

Next, the polypropylene resin composition of the core layer preferably exhibits a substantially single melting peak as measured by a differential scanning calorimeter (claim 5).
"A melting point measured by a differential scanning calorimeter shows a substantially single melting peak" means that when the melting point of the polypropylene resin composition is measured by the same method as the method for measuring the melting point (Tm), 1 In addition to the case where two melting peaks are observed, even when multiple melting peaks are observed, the temperature difference between the apexes of adjacent melting peaks (the apex of the hot side melting peak-the low temperature side) The temperature difference is preferably within 5 ° C, more preferably within 3 ° C.

However, in this case, the temperature difference is the difference between the tops of the respective melting peaks (high-temperature side) obtained when the melting points of the propylene-based polymer [A] and the propylene-based polymer [B] are measured independently. (The peak of the melting peak−the peak of the low-temperature melting peak).
The smaller the temperature difference between the vertexes of the adjacent melting peaks, the higher the level of the propylene-based polymer [A] and the higher the propylene-based polymer [B] are. This shows that the composition has high uniformity. As a result, foamed particles having a foamed core layer obtained by using such a polypropylene-based resin composition as a base resin have excellent secondary foamability during in-mold molding.
In the present invention, the melting point of the propylene polymer [B] may be the same as the melting point of the propylene polymer [A] used, but the melting points of both polymers are 2 ° C. or more. It is preferably separated, more preferably 3 ° C or more, more preferably 5 to 30 ° C.

Next, the coating layer may be formed by blending 1 to 100 parts by weight of the propylene-based polymer [A] and / or the propylene-based polymer [B] with respect to 100 parts by weight of the olefin-based polymer. Preferred (claim 6).
In this case, the adhesion between the core layer and the coating layer is improved, and as a result, the fusion between the expanded particles in the in-mold molded article obtained using the expanded polypropylene resin particles becomes strong, As a result, the strength and the like of the molded article in the mold are improved.
When the total amount of the propylene-based polymer [A] and the propylene-based polymer [B] is less than 1 part by weight, the above-described effect of improving the degree of fusion between the foamed particles can be sufficiently obtained. May not be possible. On the other hand, if it exceeds 100 parts by weight, the steam pressure (forming steam pressure) required for fusing the foamed particles to obtain a molded product may be increased. The amount is more preferably 2 to 50 parts by weight, and further preferably 3 to 10 parts by weight.

Next, the expanded polypropylene resin particles are preferably foamed using a blowing agent satisfying the following requirement (f).
(F) When the critical temperature of the foaming agent is Tc [° C.], Tc satisfies the following expression (2).
-90 ° C ≦ Tc ≦ 400 ° C Equation (2)

  In this case, the cell diameter of the core layer constituting the expanded polypropylene resin particles tends to be more uniform, and as a result, the mechanical properties of the in-mold expanded molded article obtained using the expanded particles are increased. The characteristics are good.

When Tc is lower than -90 ° C, the nonuniformity of the cell diameter of the core layer constituting the expanded polypropylene resin particles may be remarkable. The reason for this is not necessarily clear, but is presumed to be due to the rapid progress of foaming.
On the other hand, when the temperature exceeds 400 ° C., it may be extremely difficult to obtain high magnification, for example, expanded polypropylene resin particles having a bulk density of 0.1 g / cm ³ or less.

  Specific examples of the foaming agent are as follows. The critical temperature (° C) is also described after the substance name. Chains of methane (-82), ethane (32), propane (97), butane (152), isobutane (135), pentane (197), hexane (235), cyclopentane (239), cyclohexane (280), etc. And halogenated hydrocarbons such as dichlorodifluoromethane (112) and trichloromonofluoromethane (198), and inorganic gases such as carbon dioxide (31).

Further, among the foaming agents satisfying the above formula (2), when the following formula (3) is further satisfied, there is an advantage that special equipment and apparatus are not required particularly for handling these foaming agents. There is.
0 ° C ≦ Tc ≦ 300 ° C Equation (3)

Further, when the following formula (4) is satisfied, in addition to the industrial utility described in the preceding section, there is an effect that the bubble diameter of the core layer becomes extremely uniform.
30 ° C ≦ Tc ≦ 200 ° C Equation (4)
The above-mentioned foaming agents may be used alone or in combination with a plurality of foaming agents.

  Further, as the foaming agent, a so-called inorganic gas such as nitrogen, oxygen, air, carbon dioxide, and water is used as the foaming agent as a whole or as a main component (50 mol% or more of the entire foaming agent, preferably 70 mol% or more, more preferably Is 90 mol% or more.) When used, the energy absorption of the final in-mold foam molded article can be increased. Among these inorganic gases, nitrogen, air, and carbon dioxide are particularly preferable in consideration of the stability of the apparent density of the expanded particles, the environmental load, the cost, and the like.

  Next, in the expanded polypropylene resin particles of the present invention, as described above, the base resin of the polypropylene resin composition comprising the propylene polymer [A] and the propylene polymer [B] is used. Other polymer components and additives can be mixed as long as the effects of the invention are not impaired.

  Examples of the other polymer components include ethylene resins such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene which is a copolymer of ethylene and α-olefin (having 4 or more carbon atoms); polybutene resin; Ethylene-propylene rubber; Ethylene-propylene-diene rubber; hydrogenated block obtained by saturating at least a part of the ethylene-based double bond of styrene-diene block copolymer or styrene-diene block copolymer by hydrogenation Styrene-based thermoplastic elastomers such as copolymers; and graft-modified products of these resins, elastomers or rubbers with acrylic acid-based monomers. In the present invention, these resins, elastomers, rubbers or modified products thereof can be used alone or in combination of two or more.

As the above additives, various additives such as a foam nucleating agent, a coloring agent, an antistatic agent, a lubricant and the like can be added. These are usually added together at the time of melt kneading described later and contained in the resin particles.
Examples of the foam nucleating agent include inorganic compounds such as talc, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, zinc borate, and aluminum hydroxide, as well as carbon, phosphoric acid nucleating agents, and phenolic nucleating agents. And organic nucleating agents such as amine nucleating agents. The amount of these various additives varies depending on the purpose of the addition, but is not more than 15 parts by weight, preferably not more than 8 parts by weight, more preferably not more than 5 parts by weight based on 100 parts by weight of the base resin of the present invention. preferable.

  In the present invention, when mixing the propylene-based polymer [A] and the propylene-based polymer [B], and when mixing the other components with the base resin, solid mixing may be performed. However, in general, melt kneading is used. That is, using a kneader such as a roll, a screw, a Banbury mixer, a kneader, a blender, or a mill, the above-mentioned propylene-based polymers or the above-mentioned base resin and other components are kneaded at a desired temperature. After kneading, it is formed into resin particles having a size suitable for the production of expanded particles.

The raw material of the expanded polypropylene resin particles of the present invention is usually resin particles composed of a composite including a non-expanded core layer and a non-expanded coating layer.
As a specific method for producing such resin particles, for example, the following methods can be used.
For example, a sheath-core type composite die described in JP-B-41-16125, JP-A-43-23858, JP-A-44-29522, and JP-A-60-185816 is used.

In this case, two extruders are used. One extruder melts and kneads the thermoplastic resin forming the core layer, and the other extruder melts and kneads the resin constituting the coating layer. A sheath-core type composite comprising a layer and a coating layer is discharged in a string shape.
Thereafter, a cutting machine equipped with a take-off machine is used to cut the resin into a prescribed weight or size to obtain resin particles composed of a columnar pellet-like composite composed of a substantially non-foamed core layer and a coating layer. it can. The thinner the coating layer is, the harder it is for the coating layer to foam when the resin particles made of the composite are expanded, and if the resin layer is too thin, it becomes difficult to sufficiently coat the resin particles. Therefore, the thickness of the coating layer is preferably 0.5 to 60 micrometers before being manufactured into foamed particles, and is preferably 0.5 to 50 micrometers after manufacturing the foamed particles.

  In general, if the weight of one resin particle made of the above composite is 0.1 to 20 mg, there is no problem in the production of foamed particles. If the weight of one resin particle is in the range of 0.2 to 10 mg and the variation in the weight between the particles is small, the production of the expanded particles becomes easy, and the density variation of the obtained expanded particles also becomes small. The filling property of the foamed particles into a molding die or the like is improved.

  As a method of obtaining expanded particles, a method of impregnating a resin particle made of the above-mentioned composite with a volatile blowing agent and then heating and expanding the resin particles, specifically, for example, Japanese Patent Publication Nos. 49-2183 and 56-1344. The methods described in Japanese Unexamined Patent Publications, West German Patent Publication Nos. 1285722 and 2107683 can be used.

  When impregnating the resin particles comprising the composite with a foaming agent and then performing foaming by heating, put the resin particles together with the volatile foaming agent in a closed and openable pressure vessel, and heat the resin particles to a temperature higher than the softening temperature of the base resin. The resin particles are impregnated with a volatile blowing agent. After that, the contents in the closed container are released from the closed container to a low-pressure atmosphere, and then the drying process is performed. Thereby, foamed particles are obtained.

  The expanded core layer of the expanded polypropylene resin particles of the present invention has a DSC curve determined by differential scanning calorimetry (provided that 2 to 4 mg of expanded particles are measured at a heating rate of 10 ° C./min by a differential scanning calorimeter). In a DSC curve obtained when the temperature is raised from 20 ° C. to 200 ° C.), it is preferable to show a higher endothermic peak in addition to the endothermic peak inherent to the base resin.

  The foamed core layer in which the DSC curve shows an endothermic peak specific to the base resin and an endothermic peak at a higher temperature than the endothermic peak may be produced by a method described in, for example, JP-A-2002-200635. It can be obtained by controlling the conditions for foaming the resin particles, specifically, the temperature, pressure, time, etc., until the resin particles are released into a low-pressure atmosphere.

In the method of producing foamed particles by discharging the contents in the closed container from the closed container to a low-pressure atmosphere, if the decomposable foaming agent is kneaded in the resin particles in advance, the foaming agent is contained in the pressure container. The above-mentioned expanded particles can be obtained without blending.
As the decomposable foaming agent, any one that decomposes at the foaming temperature of the resin particles to generate gas can be used. Specific examples include sodium bicarbonate, ammonium carbonate, azide compounds, azo compounds and the like.

  Further, at the time of heating and foaming, it is preferable to use water, alcohol, or the like as a dispersion medium for the resin particles. In addition, aluminum oxide, tribasic calcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, amsunite, mica, clay, and other poorly water-soluble inorganic substances, polyvinylpyrrolidone, and polyvinyl alcohol so that the resin particles are uniformly dispersed in the dispersion medium. It is preferable to use a water-soluble polymer-based protective colloid agent such as methyl cellulose and anionic surfactants such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate alone or as a mixture of two or more.

Further, a dispersion enhancer that enhances the dispersing power of the dispersant (prevents fusion of the resin particles in the container even when the amount of the dispersant is reduced) may be added to the dispersion medium. In particular, when producing low-expanded foamed particles having an apparent density of 100 g / L or more, it is preferable to use a dispersion enhancer.
As such a dispersion enhancer, an inorganic substance which can be dissolved in at least 1 mg or more in 100 cc of water at 40 ° C. and in which at least one of the anion and cation of the compound is divalent or trivalent, is used. be able to. Examples of such an inorganic substance include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, and iron nitrate.

  When releasing resin particles into a low-pressure atmosphere, in order to facilitate the release, the same inorganic gas or volatile foaming agent as described above is introduced into the closed container from outside to keep the pressure in the closed container constant. It is preferable to hold.

  The expanded polypropylene resin particles obtained by the above-described method are aged under atmospheric pressure, and after increasing the internal pressure of the cells as necessary, are heated with steam or hot air to form expanded particles having a higher expansion ratio. It can be a particle.

  Next, the expanded polypropylene resin particles of the present invention are molded using dies under various conditions. For example, after filling foamed polypropylene resin particles into a cavity composed of a pair of cavities and depressions under atmospheric pressure or reduced pressure, the cavities are compressed so as to reduce the volume of the cavities by 5 to 70%. A compression molding method in which a heat medium is introduced into the cavity and the polypropylene resin foam particles are heated and fused is exemplified (for example, Japanese Patent Publication No. 46-38359).

  In addition, the foaming particles are treated with one or more kinds of volatile foaming agents or inorganic gas in advance and are impregnated into the core layer to increase the secondary foaming power of the foamed particles, and then maintain the secondary foaming power. Pressure aging molding method in which foamed particles are filled into a cavity consisting of a pair of irregularities under atmospheric pressure or reduced pressure, and a heating medium is introduced into the mold cavity to heat and fuse the foamed particles. (For example, Japanese Patent Publication No. 51-22951).

  Also, after filling the foamed particles pressurized above the atmospheric pressure into the mold cavity pressurized by the compressed gas or more, the heating medium such as steam is introduced into the mold cavity to remove the foamed particles. There is also a compression filling molding method in which heat fusion is performed (for example, Japanese Patent Publication No. 4-46217).

  Furthermore, the foamed particles are filled into a cavity composed of a pair of dies under atmospheric pressure or reduced pressure by using foamed particles having a high secondary foaming power obtained under special conditions. There is also a normal pressure filling molding method in which a heating medium such as steam is introduced into the inside and the foamed particles are heated and fused (for example, Japanese Patent Publication No. 6-49795). It can also be formed by a combination of the above methods (for example, see Japanese Patent Publication No. Hei 6-22919).

  Further, a film can be laminated on the in-mold molded body obtained by molding as described above, if necessary. The film to be laminated is not particularly limited. For example, polystyrene resin films such as OPS (biaxially oriented polystyrene sheet), heat-resistant OPS and HIPS, and polypropylene such as CPP (unoriented polypropylene film) and OPP (biaxially oriented polypropylene film) A resin film, a polyethylene resin film, a polyester resin film, or the like is used.

  The thickness of the film to be laminated is not limited, but usually a film of 15 μm to 150 μm is used. These films may be printed as needed. When lamination is performed, it may be performed simultaneously with the heat fusion molding (in-mold molding) of the expanded particles. Further, lamination may be performed on the in-mold formed body once formed. In addition, lamination can also be performed using a hot-melt adhesive as needed.

Next, in the in-mold molded product of the second invention, the density of the in-mold molded product is 0.008 to 0.5 g / cm ³ . If the density of the in-mold molded body is more than 0.5 g / cm ³ , favorable characteristics of the foam such as light weight, shock absorption, and heat insulation cannot be sufficiently exhibited, and the low foaming ratio results in a disadvantage in cost. May be caused.
On the other hand, if the density is less than 0.008 g / cm ³ , the closed cell ratio tends to be small, and mechanical properties such as bending strength and compressive strength may be insufficient.
The in-mold molded product of the present invention is suitable for, for example, packaging containers, toys, automobile parts, helmet core materials, cushioning packaging materials, and the like.

  Next, embodiments of the present invention will be described.

[Production of propylene-based polymer]
First, propylene polymers [A] and [B] for producing a foamed core layer were synthesized by the methods shown in Production Examples 1 to 8 below.

Production Example 1
(I) Synthesis of [dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyl-4-hydroazulenyl)} zirconium dichloride] The following reactions were all carried out in an inert gas atmosphere. A dried and purified solvent was used.

(A) Synthesis of racemic-meso mixture 2.22 g of 2-methylazulene synthesized according to the method described in JP-A-62-207232 was dissolved in 30 mL of hexane, and 15.6 mL of a cyclohexane-diethyl ether solution of phenyllithium (15.6 mL). 1.0 eq) at 0 ° C. in small portions.
The solution was stirred at room temperature for 1 hour, cooled to -78 ° C, and 30 mL of tetrahydrofuran was added.

  Next, after adding 0.95 mL of dimethyldichlorosilane, the temperature was raised to room temperature, and the mixture was further heated at 50 ° C. for 90 minutes. Thereafter, a saturated aqueous solution of ammonium chloride was added, the organic layer was separated, dried over sodium sulfate, and the solvent was distilled off under reduced pressure.

The resulting crude product was purified by silica gel column chromatography (hexane-: dichloromethane = 5: 1) to give bis {1,1 '-(2-methyl-4-phenyl-1,4-dihydroazulenyl). 1.) 1.48 g of dimethylsilane were obtained.
786 mg of bis {1,1 ′-(2-methyl-4-phenyl-1,4-dihydroazulenyl) dimethylsilane obtained above is dissolved in 15 mL of diethyl ether, and n-butyllithium hexane is added at −78 ° C. 1.98 mL of a solution (1.68 mol / L) was added dropwise, and the temperature was gradually raised to room temperature, followed by stirring at room temperature for 12 hours. The solid obtained by evaporating the solvent under reduced pressure was washed with hexane and dried under reduced pressure.

Further, 20 mL of a toluene-diethyl ether mixed solvent (40: 1) was added, 325 mg of zirconium tetrachloride was added at -60 ° C, and the mixture was gradually heated and stirred at room temperature for 15 minutes.
The obtained solution is concentrated under reduced pressure, and hexane is added to cause reprecipitation, whereby dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyl-4-hydroazulenyl)} zirconium dichloride is obtained. / Meso mixture 150 mg was obtained.

(B) Separation of a racemic body 887 mg of a racemic / meso mixture obtained by repeating the above reaction was placed in a glass container, dissolved in 30 mL of dichloromethane, and irradiated with light from a high-pressure mercury lamp for 30 minutes. Thereafter, dichloromethane was distilled off under reduced pressure to obtain a yellow solid.
To this solid, 7 mL of toluene was added, stirred, and allowed to stand, whereby a yellow solid was separated as a precipitate. The supernatant was removed, and the solid was dried under reduced pressure to give 437 mg of a racemate comprising dimethylsilylenebis {1,1 '-(2-methyl-4-phenyl-4-hydroazulenyl)} zirconium dichloride.

(Ii) Synthesis of catalyst (a) Treatment of catalyst carrier 135 mL of demineralized water and 16 g of magnesium sulfate were placed in a glass container, and stirred to form a solution. 22.2 g of montmorillonite ("Kunipia-F" manufactured by Kunimine Industries) was added to this solution, and then the temperature was raised and the temperature was maintained at 80 ° C for 1 hour.
Then, after adding 300 mL of demineralized water, the solid content was separated by filtration. After adding 46 mL of demineralized water, 23.4 g of sulfuric acid, and 29.2 g of magnesium sulfate to the solid content, the mixture was heated, treated with heating under reflux for 2 hours, added with 200 mL of demineralized water, and filtered.
Further, an operation of adding 400 mL of deionized water and filtering was performed twice. Thereafter, the solid was dried at 100 ° C. to obtain a chemically treated montmorillonite as a catalyst carrier.

(B) Preparation of catalyst component After sufficiently replacing the inside of a 1-liter stirred autoclave with propylene, 230 mL of dehydrated heptane was introduced, and the system temperature was maintained at 40 ° C.
Here, 10 g of the chemically treated montmorillonite as a catalyst carrier prepared above was suspended in 200 mL of toluene and added.

  Furthermore, racemic (0.15 mmol) of dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyl-4-hydroazulenyl)} zirconium dichloride and triisobutylaluminum (3 mmol) prepared in separate containers. Was mixed in toluene (20 mL in total) and added to the autoclave.

  Thereafter, propylene was introduced at a rate of 10 g / hr for 120 minutes, and thereafter the polymerization reaction was continued for 120 minutes. Thereafter, the solvent was distilled off and dried under a nitrogen atmosphere to obtain a solid catalyst component. This catalyst component contained 1.9 g of polymer per 1 g of solid component.

(Iii) Polymerization of propylene (production of propylene-based polymer [A], propylene homopolymerization)
After sufficiently replacing the inside of a stirred autoclave having an internal volume of 200 L with propylene, 45 kg of sufficiently dehydrated liquefied propylene was introduced. To this, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum and hydrogen (3NL) were introduced, and the inside of the autoclave was heated to 70 ° C.
Thereafter, the solid catalyst component (1.7 g) was press-injected with argon to start polymerization, and a polymerization reaction was performed for 3 hours.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the remaining gas components were purged to obtain 14.1 kg of a polymer.
This polymer has 100 mol% of structural units obtained from propylene, that is, it is a propylene homopolymer. This satisfies the requirement (a).

This polymer has an MFR (melt flow rate) of 10 g / 10 min, an isotactic triad fraction of 99.7%, and a melting point (Tm) of 146 ° C., and satisfies the above requirements (d) and (e). Meets Furthermore, the ratio of the position irregular units based on the 2,1-insertion is 1.32%, and the ratio of the position irregular units based on the 1,3-insertion is 0.08%, which satisfies the requirement (b). I have.
Hereinafter, the obtained polypropylene-based polymer is referred to as “polymer 1”.

(Iv) Measurement of Water Vapor Permeability The polymer 1 obtained above was formed into a film having a thickness of 25 μm, and the water vapor permeability Y was measured according to the method described in JIS K7129 (the same applies to the following production examples). was ^{.5 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of the polymer 1 is 146 ° C. as described above, from the above formula (1), Y should be within the range of 5.8 ≦ Y ≦ 11.8. Was.

Production Example 2 (Production of propylene-based polymer [A], propylene homopolymerization)
After sufficiently replacing the inside of a stirred autoclave having an internal volume of 200 L with propylene, 45 kg of sufficiently dehydrated liquefied propylene was introduced. To this, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum and hydrogen (3 NL) were introduced, and the inside of the autoclave was heated to 40 ° C.
Thereafter, the solid catalyst component (3.0 g) was injected with argon to start polymerization, and a polymerization reaction was performed for 3 hours.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the remaining gas components were purged to obtain 4.4 kg of a polymer.
This polymer has 100 mol% of structural units obtained from propylene, that is, it is a propylene homopolymer. This satisfies the requirement (a).

Further, this polymer has MFR = 2, an isotactic triad fraction of 99.8%, and a melting point (Tm) of 152 ° C., and satisfies the requirements (d) and (e). Further, the ratio of the position irregular units based on the 2,1-insertion is 0.89%, and the ratio of the position irregular units based on the 1,3-insertion is 0.005%, which satisfies the requirement (b). I have.
Hereinafter, the obtained polymer is referred to as “polymer 2”.

As for the polymer 2, as in the polymer 1 was examined the water vapor transmission rate Y when molded into a film was ^{9.5 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of the polymer 2 is 152 ° C. as described above, from the above formula (1), Y should be within the range of 4.6 ≦ Y ≦ 9.8, but is within the range. Was.

Production Example 3 (Production of propylene polymer [A], propylene / ethylene copolymerization)
After sufficiently replacing the inside of a 200 L stirred autoclave with propylene, 60 L of purified n-heptane was introduced, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum was added, and the inside of the autoclave was heated to 70 ° C. Warmed up. Thereafter, the solid catalyst component (9.0 g) was added, and a mixed gas of propylene and ethylene (propylene: ethylene = 97.5: 2.5; weight ratio) was introduced so that the pressure became 0.7 MPa. To initiate polymerization, and a polymerization reaction was carried out under these conditions for 3 hours.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the remaining gas components were purged to obtain 9.3 kg of a polymer.
This polymer contains 97.0 mol% of structural units obtained from propylene and 3.0 mol% of structural units obtained from ethylene. This satisfies the requirement (a).

This polymer had MFR = 14, ethylene content = 2.0 wt%, isotactic triad fraction of 99.2%, and melting point (Tm) of 141 ° C., satisfying the above requirements (d) and (e). Meets Further, the ratio of the position irregular units based on the 2,1-insertion is 1.06%, and the ratio of the position irregular units based on the 1,3-insertion is 0.16%, which satisfies the requirement (b). I have.
Hereinafter, the obtained polymer is referred to as “polymer 3”.

Further, the polymer 3, in the same manner as in the polymer 1 and polymer 2, was examined water vapor transmission rate Y after molding into a film was ^{12.0 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of the polymer 3 is 141 ° C. as described above, from the above formula (1), Y should be within the range of 6.8 ≦ Y ≦ 13.5, but should be within the range. Was.

Production Example 4 (Production of propylene-based polymer [A], propylene / 1-butene copolymerization)
After sufficiently replacing the inside of a 200 L stirred autoclave with propylene, 60 L of purified n-heptane was introduced, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum was added, and the inside of the autoclave was heated to 70 ° C. Warmed up. Thereafter, the solid catalyst component (9.0 g) was added, and a mixed gas of propylene and 1-butene (propylene: 1-butene = 90: 10) was introduced so that the pressure became 0.6 MPa, to start polymerization. Then, a polymerization reaction was carried out under these conditions for 3 hours.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the remaining gas components were purged to obtain 8.6 kg of a polymer.
This polymer contains 95.4 mol% of a structural unit obtained from propylene and 4.6 mol% of a structural unit obtained from 1-butene. This satisfies the requirement (a).

  This polymer had MFR = 6,1-butene content = 6.0 wt%, a melting point (Tm) of 142 ° C., an isotactic triad fraction of 99.3%, and the above requirements (d) and (e). ). Furthermore, the ratio of the position irregular units based on the 2,1-insertion is 1.23%, and the ratio of the position irregular units based on the 1,3-insertion is 0.09%, which satisfies the requirement (b). I have. The polymer obtained here is referred to as “Polymer 4”.

Polymer 4 was formed into a film in the same manner as in the polymer 1 to 3, were examined water vapor transmission rate Y, it was ^{11.5 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of the polymer 4 is 142 ° C. as described above, from the above formula (1), Y should be within the range of 6.6 ≦ Y ≦ 13.1. Was.

Production Example 5 (Production of propylene polymer [B], propylene homopolymerization)
After sufficiently replacing the inside of a 200 L stirred autoclave with propylene, 60 L of purified n-heptane was introduced, and 11.5 g of diethylaluminum chloride (45 g) and a titanium trichloride catalyst manufactured by Marubeni Solvay Co., Ltd. were placed in a propylene atmosphere. Introduced. Further, while maintaining the hydrogen concentration in the gas phase at 7.0% by volume, propylene was introduced into the autoclave at an internal temperature of 60 ° C. at a rate of 9 kg / hr for 4 hours.

After stopping the introduction of propylene, the reaction was further continued for 1 hour, the reaction was stopped by adding 100 mL of butanol to the reaction system, and the remaining gas components were purged to obtain 26 kg of a polymer. The polymer obtained here is referred to as “Polymer 5”.
This polymer 5 has 100 mol% of structural units obtained from propylene, that is, it is a propylene homopolymer. This satisfies the requirement (a).

This polymer 5 had an MFR of 7, a melting point (Tm) of 165 ° C., an isotactic triad fraction of 97.6%, a proportion of positional irregular units based on 2,1-insertion of 0%, and 1,3-. The proportion of irregularly positioned units due to insertion was 0%.
That is, this one does not satisfy the requirement (b).

For Polymer 5, in the same manner as in the above polymers 1 to 4, were examined water vapor transmission rate Y after molding into a film was ^{7.8 (g / m 2 / 24hr} ).
Since the melting point Tm of the polymer 5 is 165 ° C. as described above, from the above formula (1), Y should be within the range of 2.0 ≦ Y ≦ 5.6, but should be within the range. Absent.

Production Example 6 (Production of propylene-based polymer [B], propylene / ethylene copolymerization)
After sufficiently replacing the inside of a 200 L stirred autoclave with propylene, 60 L of purified n-heptane was introduced, and diethyl aluminum chloride (40 g) and 7.5 g of Marubeni Solvay's titanium trichloride catalyst were placed in a propylene atmosphere. Introduced. Further, while maintaining the hydrogen concentration in the gas phase at 7.0% by volume, a mixed gas of propylene and ethylene (propylene: ethylene = 97.5: 2.5; weight ratio) was applied at an internal temperature of the autoclave of 60 ° C. The pressure was introduced so as to be 0.7 MPa.

After stopping the introduction of the mixed gas, the reaction was further continued for 1 hour, the reaction was stopped by adding 100 mL of butanol to the reaction system, and the residual gas component was purged to obtain 32 kg of a polymer. This polymer is referred to as “polymer 6”.
In the polymer 6, 96.1% by mole of a structural unit obtained from propylene and 3.9% by mole of a structural unit obtained from ethylene exist. This satisfies the requirement (a).

This polymer 6 had MFR = 12, melting point (Tm) of 146 ° C., an isotactic triad fraction of 96.0%, and a proportion of positional irregular units based on 2,1-insertion of 0%, 1,3. -The proportion of irregularly positioned units due to insertion was 0%.
That is, the polymer 6 does not satisfy the requirement (b).

Further, the polymer 6, in the same manner as in the above polymers 1 to 5, were examined water vapor transmission rate Y after molding into a film was ^{15.0 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of the polymer 6 is 146 ° C., from the above formula (1), Y should be within the range of 5.8 ≦ Y ≦ 11.8, but does not fall within the range.

Production Example 7 (Production of propylene polymer [B], propylene homopolymerization)
The method was carried out by applying the method described in [Production of base resin 1] in the examples of JP-A-6-240041.
That is, after thoroughly replacing the inside of a 200 L stirred autoclave with propylene, 60 L of purified n-heptane was introduced, and 120 g of methylalumoxane (average degree of oligomer 16) manufactured by Tosoh Akzo Co., Ltd. was used. Rac-Dimethylsilylenebis (2-methylindenyl) zirconium dichloride (150 mg) synthesized by the method described in Japanese Patent No. 268307 was introduced in a propylene atmosphere. Further, while maintaining the hydrogen concentration in the gas phase at 0.5% by volume, propylene was introduced into the autoclave at an internal temperature of 40 ° C. at a rate of 7 kg / hr for 3 hours.

After stopping the introduction of propylene, the reaction was further continued for 1 hour, the reaction was stopped by adding 100 mL of butanol to the reaction system, and the residual gas component was purged to obtain 9.4 kg of a polymer. This polymer is referred to as “polymer 7”.
This polymer 7 had an MFR = 9, a melting point (Tm) of 150 ° C., an isotactic triad fraction of 94.4%, a proportion of positional irregular units based on 2,1-insertion of 0.25%, and 1,1. 3- The proportion of regio-irregular units due to insertion was below the detection limit, ie less than 0.005%. That is, this one does not satisfy the requirement (b).
In Table 2, which will be described later, the ratio of the position irregular units based on the 1,3 insertion of the polymer 7 is shown as 0%.

Also, for the polymer 7, in the same manner as in the above polymers 1 to 6, were examined water vapor transmission rate Y after molding into a film was ^{4.8 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of this polymer 7 is 150 ° C., Y should be within the range of 5.0 ≦ Y ≦ 10.5 from the above formula (1), but it was outside the range.

Production Example 8 (Production of propylene-based polymer [B], propylene homopolymerization)
After sufficiently replacing the inside of a 200 L stirred autoclave with propylene, 60 L of purified n-heptane was introduced, and 120 g of methylalumoxane (average degree of oligomer: 16) manufactured by Tosoh Akzo Co., Ltd. was used. H. Yamazaki et al., "Chemistry Letters", Japan, 1989, Vol. 18, p. 1853], rac-dimethylsilylenebis (3-methylcyclopentadienyl) zirconium dichloride (100 mg) was introduced under a propylene atmosphere. Further, while maintaining the hydrogen concentration in the gas phase at 0.5% by volume, propylene was introduced into the autoclave at an internal temperature of 40 ° C. at a rate of 7 kg / hr for 3 hours.

After stopping the introduction of propylene, the reaction was further continued for 1 hour, the reaction was stopped by adding 100 mL of butanol to the reaction system, and the residual gas component was purged to obtain 5.6 kg of a polymer. This polymer is referred to as "polymer 8".
This polymer 8 has an MFR = 20, a melting point of 141 ° C., an isotactic triad fraction of 91.5%, a proportion of regiorandom units based on 2,1-insertion of 2.1%, and 1,3-insertion. Was 0.45%.
That is, this one does not satisfy the requirement (b).

Also, for the polymer 8, in the same manner as in the above polymers 1 to 7, were examined water vapor transmission rate Y after molding into a film was ^{13.8 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of this polymer 8 is 141 ° C., from the above formula (1), Y should be within the range of 6.8 ≦ Y ≦ 13.5, but was out of the range.
Tables 1 and 2 show the results of Production Examples 1 to 8 described above.

As can be seen from Table 1, Polymer 1 to Polymer 4 satisfy the above requirements (a) and (b) and correspond to the propylene-based polymer [A]. Polymers 1 to 4 also satisfy the above requirements (d) and (e).
On the other hand, Table 2 shows that Polymer 5 to Polymer 8 satisfy the above requirement (a) but do not satisfy the above requirement (b). That is, the polymers 5 to 8 correspond to the propylene-based polymer [B].

  Next, using the various propylene-based polymers (polymers 1 to 8) obtained in Production Examples 1 to 8, a polypropylene-based resin composition and expanded polypropylene-based resin particles were produced. An example in which an in-mold molded body was manufactured using the method will be described.

Example 1
Using a single-screw extruder having an inner diameter of 65 mm, the polymer 1 (propylene polymer [A]) obtained in Production Example 1 and the polymer 5 (propylene polymer [B]) obtained in Production Example 5 were mixed with 90: 10 (weight ratio), and an antioxidant (0.05% by weight of Yoshinox BHT manufactured by Yoshitomi Pharmaceutical Co., Ltd. and 0.10% by weight of Irganox 1010 manufactured by Ciba Geigy) was added to the mixture. And kneaded. On the other hand, linear low density polyethylene (LLDPE) having a density of 0.920 g / cm ³ and a melting point of 121 ° C. was kneaded using a single screw extruder having an inner diameter of 30 mmφ.

  Next, from a die having a die orifice with a diameter of 1.5 mm, the above-mentioned kneaded product of Polymer 1 and Polymer 5 was used as a core layer and a linear low-density polyethylene was used as a coating layer and extruded into a strand.

  Further, the strand was cooled by passing through a water tank, and cut into pieces each having a weight of 1.0 mg to obtain fine pellets as resin particles. Observation of the resin particles with a phase contrast microscope revealed that the coating layer having a thickness of 30 microns covered the core layer.

  When the DSC measurement was performed on the polypropylene resin composition forming the resin particles thus obtained in the same manner as the measurement of the melting point Tm, the portion derived from the propylene polymer showed one endothermic peak, Its peak temperature (melting point) was 153 ° C.

  Next, in order to make the resin particles into foamed particles, 1000 g of the fine pellets were put into an autoclave having an internal volume of 5 liters together with 2500 g of water, 36 g of tribasic calcium phosphate and 0.8 g of sodium dodecylbenzenesulfonate. Was added, and the temperature was raised to 140 ° C. for 60 minutes, and then maintained at this temperature for 30 minutes.

Thereafter, the valve at the bottom of the autoclave was opened and the content was discharged to the atmosphere while foaming nitrogen was externally applied in order to maintain the pressure in the autoclave at a gauge pressure of 2.3 MPa.
After drying the expanded polypropylene resin particles obtained by the above operations, the bulk density was measured and found to be 45 g / L. The foamed particles of the expanded polypropylene resin particles had an average diameter of 270 μm and were very uniform.

  The average cell diameter of the expanded polypropylene resin particles is determined by a micrograph (or this cross section) obtained by observing a cross section of the expanded particle cut through a substantially central portion of a randomly selected expanded particle with a microscope. Is projected on a screen), 50 bubbles are randomly selected, their diameter (maximum length) is measured, and the average value is shown.

Next, an in-mold molded article is prepared using the expanded polypropylene resin particles as follows.
First, the foamed polypropylene resin particles obtained as described above were filled with a hopper using a compressed air while being sequentially compressed into a molding die made of aluminum. Thereafter, the mixture was heated and molded in a chamber of a mold through steam having a gauge pressure of 0.16 MPa (indicated as “molding vapor pressure” in the table below) to obtain an in-mold molded body.

This molded article in the mold has a density of 60 kg / m ³ (0.060 g / cm ³ ), a length of 300 mm, a width of 300 mm, a thickness of 50 mm, a mold dimensional shrinkage of 1.6%, a small surface gap, and no irregularities. The molded product had an excellent surface appearance. In addition, the molded body was broken at the center of the molded body, and the fusion degree of the cross section was measured to be 90%.

  The degree of fusion is determined by dividing the molded body in the mold, visually measuring the number of particle breaks and the number of interparticle breaks in the cross section, and expressing the ratio of the number of particle breaks to the total number of both. did.

  Further, a test piece having a length of 50 mm, a width of 50 mm and a thickness of 25 mm was prepared from another molded body molded under the same molding conditions, and the specimen temperature was 23 ° C. and the compression speed was 10 mm / min in accordance with JIS K7220 (1999). When a compression test was carried out under the conditions, the stress at the time of 50% compression (same as at the time of 50% strain) was 0.73 MPa. Further, the compression set was measured by the method described in JIS K6767 (1976) using test pieces of the same size and found to be 11%.

Further, using a test piece prepared in the same procedure as the test piece used for the above-mentioned determination of the degree of fusion, the dimensional shrinkage upon heating at 110 ° C. was measured in accordance with JIS K6767 (1976). (Heat resistance test).
：: dimensional shrinkage is less than 3%.
Δ: The dimensional shrinkage is 3% or more and 6% or less.
×: The dimensional shrinkage exceeds 6%.
The results are shown in Table 3 below.

Examples 2 to 10 and Comparative Examples 1 to 6
As the base resin for forming the core layer, “Polymer 1” to “Polymer 8” described in Tables 1 and 2 are blended in the respective compositions shown in Tables 3 to 6, and the resin for forming the coating layer is formed. Are used as in Example 1 except that the amount of isobutane used as a foaming agent and the foaming temperature are set to the conditions described in Tables 3 to 6. Resin expanded particles and in-mold molded articles were produced.
The results are as shown in Tables 3 to 6. In addition, the evaluation criteria of the molded article appearance in Tables 3 to 6 are as follows.
○ A molded product with small surface gaps and excellent surface appearance without irregularities.
Δ: A molded article with a slightly inferior surface appearance in which gaps on the surface are slightly recognized or surface irregularities are slightly recognized.
× A molded article having a poor surface appearance with many gaps on the surface or many irregularities on the surface.

  Further, the melting point of the composition in the core layer shown in Tables 3 to 6 was determined by measuring the propylene when the DSC measurement was performed on the polypropylene resin composition forming the resin particles by the same method as the measurement of the melting point Tm. It shows the temperature at the top of the melting peak derived from the polymer. In the case where there is only one peak of the melting peak, only the temperature of that peak is shown. However, when there are multiple peaks of the melting peak, the temperature of each peak is shown.

As is known from Tables 3 to 6, Comparative Examples 1 to 4 used the propylene homopolymer obtained in Production Examples 1, 5, 7, and 8 alone (propylene polymer) as a raw material for the core layer. [A] alone or a propylene-based polymer [B] alone) was used, but the appearance of the molded article was inferior (Comparative Examples 1 to 3) or the heat resistance was inferior (Comparative Examples 1, 3, and 4) ).
In Comparative Examples 5 and 6, the propylene homopolymers obtained in Production Examples 7 and 8 (however, those which do not satisfy the requirement (b)) were used as the raw materials of the core layer. Although a mixture using a homopolymer was used, the appearance of the molded article was inferior, and the compression set of the molded article was large relative to the compressive strength (stress at 50% compression).
On the other hand, in Examples 1 to 10 according to the present invention, the bubbles of the expanded polypropylene resin particles were very uniform, and the in-mold molded product using the same was heated at a low molding vapor pressure. It shows that the degree of fusion is high and the surface appearance is also excellent. Also, the mechanical properties were high in compressive strength (stress at 50% compression) and small in compression set.

Incidentally, Production Example 1 and Production Example 2 show examples in which propylene homopolymers were produced using the same metallocene-based polymerization catalyst, but the properties of the obtained propylene homopolymers were different (see Table 1). The reason for this is based on the difference in polymerization temperature. That is, in Production Example 1 having a higher polymerization temperature, the proportion of each position irregular unit in the propylene homopolymer obtained is higher.
Production Examples 5 and 6 show examples in which no regioregular units were formed in the obtained propylene-based polymer by using a Ziegler / Natta catalyst different from the metallocene-based polymerization catalyst ( See Table 2).

Production Example 7 shows an example in which a propylene homopolymer is produced using a metallocene-based polymerization catalyst different from that of Production Example 1. However, under the conditions described in the known literature, the proportion of each position irregular unit is reduced. It can be seen that the value falls below the range of the requirement (b) (see Table 2). In Production Example 7, the polymerization temperature was 40 ° C., but when the polymerization temperature was increased to, for example, 70 ° C. or higher, the propylene homopolymer obtained had a position irregular unit within the range of the present invention. However, the [mm] fraction is expected to be lower than that of the propylene homopolymer of Production Example 7.
Production Example 8 shows an example in which a propylene homopolymer was produced using a metallocene polymerization catalyst different from Production Examples 1 and 7, and the metal complex component of the metallocene polymerization catalyst used was not suitable. Therefore, the ratio of each position irregular unit exceeded the range of the requirement (b) (see Table 2).

FIG. 2 is a perspective view of the expanded polypropylene resin particles according to Example 1.

Explanation of reference numerals

1. . . Foamed polypropylene resin particles 11. . . Core layer 12. . . Coating layer

Claims (8)

In a foamed polypropylene resin particle comprising a foamed core layer made of a crystalline thermoplastic resin and a coating layer made of a thermoplastic resin covering the core layer,
The core layer is composed of 5 to 95% by weight of the following propylene polymer [A] and 95 to 5% by weight of the following propylene polymer [B] (provided that the propylene polymer [A] and the propylene polymer (B is 100% by weight in total) as the base resin.
Propylene-based polymer [A]: A propylene-based polymer having the following requirements (a) and (b).
(A) 100 to 85 mol% of structural units obtained from propylene, and 0 to 15 mol% of structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms (provided that propylene is obtained from propylene) The total amount of the structural units and the structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is 100 mol%).
(B) the ratio of the position irregular units based on the 2,1-insertion of the propylene monomer units in the total propylene insertion is 0.5 to 2.0% as measured by 13C-NMR, and the propylene monomer units The ratio of the position irregular units based on the 1,3-insertion is 0.005 to 0.4%.
Propylene-based polymer [B]: A propylene-based polymer having only the requirement (a) among the requirements (a) and (b).   2. The method according to claim 1, wherein the coating layer is formed of an olefin polymer having a melting point lower than that of any of the propylene polymers [A] and [B] forming the core layer, or having substantially no melting point. Foamed polypropylene resin particles, characterized in that: 3. The expanded polypropylene resin particles according to claim 1, wherein the propylene polymer [A] further has the following requirement (d). 4.
(D) The isotactic triad fraction of 97% or more of the propylene unit chain portion composed of head-to-tail bonds measured by 13C-NMR. 4. The expanded polypropylene resin particles according to claim 1, wherein the propylene-based polymer [A] further has the following requirement (e). 5.
(E) The melt flow rate is 0.5 to 100 g / 10 minutes.   The expanded polypropylene resin particles according to any one of claims 1 to 4, wherein the polypropylene resin composition of the core layer exhibits a substantially single melting peak as measured by a differential scanning calorimeter. .   The coating layer according to any one of claims 1 to 5, wherein the coating layer contains the propylene-based polymer [A] and / or the propylene-based polymer [B] in an amount of 1 to 100 parts by weight of the olefin-based polymer. A foamed polypropylene resin particle, which is obtained by blending 100 parts by weight. The foamed polypropylene resin particles according to any one of claims 1 to 6, wherein the foamed polypropylene resin particles are foamed using a foaming agent satisfying the following requirement (f).
(F) When the critical temperature of the foaming agent is Tc [° C.], Tc is given by the following formula (2).
-90 ° C ≦ Tc ≦ 400 ° C Equation (2)
To be satisfied. An in-mold molded article obtained by molding foamed polypropylene resin particles in a mold and having a density of 0.5 to 0.008 g / cm ³ .
The molded article in a mold, characterized in that the foamed polypropylene resin particles are formed by using the one according to any one of claims 1 to 7.

Images