JP2005139350A - Polypropylene resin expandable particle and in-mold molded product obtained using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene resin expandable particle which gives an in-mold molded product exhibiting excellent external appearances and excellent fusion between expandable particles and having a high heat-resistant temperature even when subjected to in-mold molding using a general-purpose molding machine having a low clamping pressure, and the in-mold molded product. <P>SOLUTION: The polypropylene resin expandable particle is composed of a core layer in an expanded state and a covering layer covering the same and the base resin forming the core layer is comprised of a propylene polymer satisfying the following requirements (a)-(c). (a) The propylene polymer contains 98-85 mol% of a structural unit obtained from propylene and 2-15 mol% of a structural unit obtained from ethylene and/or 4-20C α-olefins. (b) The ratio of position irregular units based on 2,1-insertion of propylene monomer units is 0.5-2.0% and the ratio of position irregular units based on 1,3-insertion is 0.005-0.4% in the whole propylene insertion. (c) The melting point Tm is lower than 141°C. The in-mold molded product of the propylene expandable particles is also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a polypropylene resin foam that exhibits excellent fusion properties, can lower the molding temperature for obtaining an in-mold molded product, and can produce an in-mold molded product with excellent surface appearance and the like. The present invention relates to a particle and an in-mold molded body using the same.

  The resin foam particles can take any shape and have a low thermal conductivity based on a closed cell structure. For this reason, it is widely used as an in-mold forming raw material such as a heat insulating material, a buffer material, and a core material. And as a thermoplastic resin which comprises said resin expanded particle, polyethylene, a polypropylene, a polystyrene etc. are normally used.

  Among the thermoplastic resins described above, in-mold molded products obtained by using crystalline resin, that is, resin expanded particles obtained from polyethylene or polypropylene, are more resistant to chemicals than molded products made of polystyrene resin expanded particles. There is an advantage that the heat resistance and heat resistance are excellent.

  However, in the case of a high melting point resin typified by a polypropylene resin, since the melting point is generally as high as 140 ° C. or higher, the pressure for fusing the resin foam particles during in-mold molding is 0.25 MPaG. High-pressure water vapor exceeding “G”: gauge pressure;

  For this reason, there is a disadvantage that the molding cost in the mold becomes high and the molding cycle becomes long. In addition, in the case of resin foam particles made of the above-mentioned high melting point resin, since it cannot be molded by a widely used in-mold foam molding machine for expanded polystyrene, a control system for high-pressure steam is provided and the mold clamping pressure is high. An in-mold 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 vapor pressure for fusing the resin foam particles may be a low pressure of less than 0.2 MPaG, and in-mold foam molding for polystyrene. The machine has the advantage that it can be molded almost without changing the specifications.
However, polyethylene resin foam molded articles have low heat resistance because the base resin has a low melting point, and particularly high foam foam molded articles (in-mold molded articles) have low energy absorption performance. Therefore, the foamed molded body of polyethylene resin is generally usable only in the field of low foaming compared with the foamed molded body of other thermoplastic resins.

In order to solve the various problems as described above, it is composed of a foamed core layer made of a crystalline thermoplastic resin and a coating layer made of an ethylene polymer and substantially non-foamed. Resin foam particles having a specific structure have been proposed (see Patent Document 1).
In this case, there is a feature that resin foam particles exhibiting excellent fusing property can be obtained even when the heating steam pressure in the mold is relatively low, but from the viewpoint of energy reduction, molding can be performed at a lower heating steam pressure. A polypropylene resin expanded particle has been desired. In addition, the in-mold molded product obtained by in-mold molding of the obtained resin foam particles with low heating steam pressure is still insufficient in terms of surface appearance, fusion between foam particles, heat resistance temperature, etc. Further improvements were desired.

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

  The present invention is a polypropylene-based resin foam that can provide an in-mold molded body having excellent surface appearance, fusion between foamed particles and high heat-resistant temperature even when molded in a general-purpose molding machine with a low mold clamping pressure. The present invention intends to provide particles and molded bodies in the mold.

1st invention is a polypropylene resin expanded particle comprised from the core layer of the foaming state which uses a propylene-type polymer as base resin, and the coating layer which consists of a thermoplastic resin which coat | covers this,
The propylene-based polymer forming the core layer is a polypropylene-based resin expanded particle having the following requirements (a) to (c) (Claim 1).
(A) The structural unit obtained from propylene is 98 to 85 mol%, and the structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is present (provided that it is obtained from propylene). The total amount of structural units and structural units obtained from ethylene and / or α-olefin having 4 to 20 carbon atoms is 100 mol%).
(B) The proportion of position irregular units based on 2,1-insertion of propylene monomer units in all propylene insertions measured by 13C-NMR is 0.5 to 2.0%, and 1 of propylene monomer units , 3- The percentage of irregular units based on insertion is 0.005 to 0.4%.
(C) When the melting point is Tm [° C.], Tm is the following formula (1)
Tm <141 [° C.] Formula (1)
To be satisfied.

The expanded polypropylene resin particles of the present invention are composed of a foamed core layer having a propylene polymer having the above requirements (a) to (c) as a base resin, and a thermoplastic resin layer covering the expanded core layer. Has been.
Therefore, even if molding is performed in a mold using a general-purpose molding machine having a low mold clamping pressure, an in-mold molded body having excellent surface appearance and fusion between foamed particles and having a high heat resistance temperature can be obtained.

Next, the second invention is an in-mold molded product having a density of 0.5 to 0.008 g / cm ³ formed by molding polypropylene-based resin expanded particles in a molding die, and the above polypropylene-based resin. The foamed particles are in an in-mold molded product using the above-mentioned first invention (Claim 5).

The in-mold molded product of the second invention uses the above-mentioned polypropylene resin foamed particles of the first invention, and has a specific density of 0.5 to 0.008 g / cm ^3. It is in.
For this reason, the molded body in the mold is excellent in surface appearance such as smoothness and gloss, and is excellent in the fusion property between the expanded particles and the compression recovery property. Further, the in-mold molded body has a high heat resistance temperature.

When the density of the in-mold molded product is greater than 0.5 g / cm ³ , the preferred properties of the foam such as lightness, shock absorption, and heat insulating properties are not fully exhibited, and the low foaming ratio causes an increase in cost. May cause disadvantages.
On the other hand, when the density is smaller 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 remarkably lowered.
Therefore, the in-mold molded body is suitable for packaging containers, toys, automobile parts, helmet core materials, buffer packaging materials, and the like.
The density of the in-mold molded product means the apparent overall density defined by JIS K7222 (1999).

In the present invention, the polypropylene resin expanded particles have a composite structure formed of a foamed core layer using a propylene polymer (polypropylene resin) as a base resin and a coating layer made of a thermoplastic resin. .
Here, the base resin means a basic resin component constituting the core layer. The core layer is composed of the base resin and other polymer components added as necessary, or additives such as a catalyst neutralizing agent, a lubricant, a crystal nucleating agent, and other resin additives. However, it is desirable that other polymer components and additives be as small as possible within the range not impairing the object of the present invention.

That is, when the propylene polymer is 100 parts by weight, the amount of other polymer components added is preferably 40 parts by weight or less. More preferably, it is 30 parts by weight or less, and more preferably 15 parts by weight or less. Most preferably, it is 5 parts by weight or less.
In addition, when the propylene polymer is 100 parts by weight, the amount of the additive (except for the foaming agent that does not eventually dissipate) depends on the intended use of the additive. Part by weight or less is preferred. More preferably, it is 30 parts by weight or less, and more preferably 0.001 to 15 parts by weight.

In the present invention, the propylene polymer forming the core layer satisfies the requirements (a) to (c). First, the requirement (a) will be described.
The requirement (a) is that the structural unit obtained from propylene is 98 to 85 mol%, and the structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is present in 2 to 15 mol%. That is, the propylene polymer satisfying the above requirement (a) is a copolymer of propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms.

  Specific examples of the ethylene comonomer copolymerized with propylene and / or the α-olefin having 4 to 20 carbon atoms include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4- Examples thereof include methyl-1-butene.

Further, in the present invention, as the above-mentioned propylene-based polymer, a copolymer obtained by copolymerizing propylene with another monomer that has been difficult to polymerize in the conventional Ziegler / Natta catalyst within the range not impairing the object of the present invention. can do. 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 polymer.
Examples of such other monomers include cyclic olefins such as cyclopentene, norbornene, 1,4,5,8-dimethano-1,2,3,4,4a, 8,8a, 5-octahydronaphthalene, 5 Examples thereof include non-conjugated dienes such as methyl-1,4-hexadiene and 7-methyl-1,6-octadiene and aromatic unsaturated compounds such as styrene and divinylbenzene.

  In the present invention, the propylene polymer is a propylene copolymer resin containing 85 mol% to 98 mol% of a structural unit obtained from propylene in the propylene polymer, and is composed of ethylene and / or carbon. It is necessary that the structural unit (comonomer structural unit) obtained from the α-olefin of several 4 to 20 is contained in a proportion of 2 to 15 mol%.

  When the proportion of the comonomer structural unit exceeds 15 mol%, the mechanical properties such as bending strength and tensile strength of the propylene-based polymer forming the core layer are greatly reduced, and the expanded particles have a desired effect. And the desired in-mold molded product obtained therefrom cannot be obtained. Further, when the proportion of the structural unit of the comonomer is less than 2 mol%, it becomes difficult to make the melting point (Tm) of the propylene polymer less than 141 ° C., and the polypropylene resin foamed particles have a low clamping pressure. When the molding is performed in a mold by a general-purpose molding machine, the core layer does not sufficiently expand, and there is a concern that the incidence of molded articles with a poor appearance is increased.

Next, as shown in the requirement (b), the propylene-based polymer has a proportion of position irregular units based on 2,1-insertion of propylene monomer units in all propylene insertions measured by 13C-NMR of 0. 0.5 to 2.0%, and the proportion of position 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 of the propylene polymer, and these irregular units have the effect of lowering the crystallinity of the propylene polymer, and the propylene polymer is the core. The effect which raises the foaming aptitude of the polypropylene-type resin expanded particle used as the base resin of a layer is shown. An in-mold molded product obtained by in-mold molding of foamed particles using the propylene polymer having the proportion of the position irregular unit in the range of the requirement (b) as a base resin for the core layer is There is a feature that permanent set becomes small.

  If the proportion of regioregular units based on 2,1-insertion is less than 0.5% or the proportion of regioregular units based on 1,3-insertion is less than 0.005%, propylene When polypropylene-based resin expanded particles having a base polymer as a core layer base resin are molded in the mold, there is a problem that the effect of reducing the compression set of the molded mold in the mold is inferior. On the other hand, when the ratio of the position irregular unit based on the 2,1-insertion exceeds 2.0% or the ratio of the position irregular unit based on the 1,3-insertion exceeds 0.4%, Since the mechanical properties of the propylene-based polymer as the base resin, such as bending strength and tensile strength, are lowered, there is a problem that the strength of the expanded particles and the in-mold molded product obtained therefrom is lowered.

  The regioregular unit based on 2,1-insertion and the regioregular unit based on 1,3-insertion in the above requirement (b) are both propylene-based polymer crystals containing these units in their structures. Has the effect of reducing the properties. More specifically, these regioregular units have an action to lower the melting point and an action to lower the crystallinity of the propylene polymer.

  These two actions show the effect of improving the foamability when such a propylene-based polymer is subjected to foaming, and the effect of reducing the compression set of the obtained foam. Accordingly, the polypropylene resin foamed particles using the propylene polymer having the position irregular unit as the base resin for the core layer can be suitably used for foaming, and obtained by molding the foamed particles in a mold. The in-mold molded product obtained has a small compression set.

  However, if the ratio of the position irregular units contained in the propylene polymer is too high, the melting point and crystallinity of the propylene polymer are high. When subjected to foaming as a resin, there may be a problem that the bubble diameter in the resulting foamed particles becomes coarse. In such a case, the appearance of the molded product obtained from such foamed particles is impaired. There is a problem of being. Further, as described above, there is a problem that the strength of the in-mold molded body obtained from the expanded particles is lowered.

Here, the fraction of structural units obtained from propylene in the propylene-based polymer, the fraction of structural units obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms, and an isotactic triad described later. The fraction is a value measured using a 13C-NMR method.
The measuring method of 13C-NMR spectrum is, for example, as follows.
That is, a sample of about 350 to 500 mg was placed in an NMR sample tube 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 locking. Thereafter, measurement was performed at 130 ° C. under the condition of complete proton decoupling.

As measurement conditions, a flip angle of 65 deg and a pulse interval of 5T1 or more (where T1 is the longest value of the spin lattice relaxation time of the methyl group) were selected. In the propylene polymer, since the spin lattice relaxation time of the methylene group and methine group is shorter than that of the methyl group, the recovery of the magnetization of all the carbons is 99% or more under these measurement conditions.
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.

  In addition, the chemical shift in the above measurement was set with 21.8 ppm as the peak of the 3rd unit methyl group in the 5 units of propylene units that are head-to-tail bonded and have the same methyl branching direction. The chemical shifts of other carbon peaks were set as

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

  Furthermore, the propylene polymer of the present invention specifies partial structures (Ι) and (ΙΙ) of the following formula [Chemical Formula 2] containing regioregular units based on 2,1-insertion and 1,3-insertion of propylene. It is contained in an amount.

Such a partial structure is considered to be caused by positional irregularities generated during the polymerization of the propylene polymer, for example, when a polymerization reaction is performed using a metallocene catalyst.
That is, the propylene monomer usually reacts by a method in which the methylene side is bonded to a metal component in the catalyst, that is, so-called “1,2-insertion”, but rarely “2,1-insertion” or “1” , 3-insertion ". “2,1-insertion” is a reaction mode in which the addition direction is opposite to “1,2-insertion”, and forms a structural unit represented by the above partial structure (構造) in the polymer chain.

  Further, “1,3-insertion” means that propylene monomers C-1 and C-3 are incorporated into a polymer chain, and as a result, a linear structural unit, that is, the above partial structure ( Ii).

  The propylene-based polymer in which the proportion of each position irregular unit is in a specific range can be obtained by selecting an appropriate catalyst. Specifically, it can be obtained using, for example, a metallocene polymerization catalyst having a hydroazurenyl group as a ligand. Here, the metallocene polymerization catalyst comprises a transition metal compound component having a metallocene structure and a promoter component. The proportion of each position irregular unit varies depending on the chemical structure of the metal complex component of the catalyst used in the polymerization, but generally the higher the polymerization temperature, the higher the tendency. In the present invention, the polymerization temperature is preferably 0 to 80 ° C. in order to make the proportion of each position irregular unit of the propylene polymer in a specific range.

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

Among the metallocene catalysts having the hydroazurenyl group as a ligand, a catalyst using titanium, zirconium, or hafnium as a metal atom is preferable, and a complex having zirconium is particularly preferable because of high polymerization activity.
Among the metallocene-based catalysts, zirconium dichloride type complexes are preferably used, and among these, cross-linked complexes are particularly preferable. Specifically, methylenebis {1,1 ′-(2-methyl-4-phenyldihydroazulenyl)} zirconium dichloride, methylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazulenyl)} zirconium dichloride. , Methylenebis {1,1 ′-(4-phenyldihydroazurenyl)} zirconium dichloride, methylenebis {1,1 ′-(4-naphthyldihydroazurenyl)} zirconium dichloride, ethylenebis {1,1 ′-(2- Methyl-4-phenyldihydroazurenyl)} zirconium dichloride, ethylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazurenyl)} zirconium dichloride, ethylenebis {1,1 ′-(4-phenyldihydro) Azulenyl)} zirconium dichloride, ethylenebis {1,1 ′-(4 Naphthyldihydroazulenyl)} zirconium dichloride, isopropylidenebis {1,1 ′-(2-methyl-4-phenyldihydroazurenyl)} zirconium dichloride, isopropylidenebis {1,1 ′-(2-ethyl-4-) Phenyldihydroazurenyl)} zirconium dichloride, isopropylidenebis {1,1 ′-(4-phenyldihydroazulenyl)} zirconium dichloride, isopropylidenebis {1,1 ′-(4-naphthyldihydroazurenyl)} zirconium dichloride , Dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyldihydroazurenyl)} zirconium dichloride, dimethylsilylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazurenyl)} zirconium dichloride , Dimethylsilylenebis {1,1 ′-(4-Phenyldihydroazurenyl)} zirconium dichloride, dimethylsilylenebis {1,1 ′-(4-naphthyldihydroazulenyl)} zirconium dichloride, diphenylsilylenebis {1,1 ′-(2 -Methyl-4-phenyldihydroazurenyl)} zirconium dichloride, diphenylsilylenebis {1,1 ′-(2-ethyl-4-phenyldihydroazurenyl)} zirconium dichloride, diphenylsilylenebis {1,1 ′-(4 -Phenyldihydroazurenyl)} zirconium dichloride, diphenylsilylenebis {1,1 ′-(4-naphthyldihydroazurenyl)} zirconium dichloride, and the like.

  Among these, in particular, dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyldihydroazulenyl)} zirconium dichloride, and dimethylsilylenebis {1,1 ′-(2-ethyl-4-phenyldihydro). Azulenyl)} zirconium dichloride is preferably used. In this case, the ratio of each position irregular unit can be easily controlled within the scope of the present invention, and the later-described requirement (d) is satisfied (the isotactic triad fraction is 97%). The propylene-based polymer can be easily obtained.

  The promoter component includes aluminoxanes such as methylaluminoxane, isobutylaluminoxane, methylisobutylaluminoxane, Lewis acid such as triphenylborane, tris (pentafluorophenyl) borane, magnesium chloride, dimethylanilinium tetrakis (pentafluorophenyl). ) An ionic compound such as borate can be exemplified. These promoter components can also be used in the presence of other organoaluminum compounds such as trialkylaluminum such as trimethylaluminum, triethylaluminum and triisobutylaluminum.

  The mm fraction (isotactic triad fraction) in the entire polymer chain of the propylene 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, only one methyl group derived from the propylene monomer has disappeared.

In this formula, ΣΙCH ₃ represents the area of all methyl groups (all peaks at 19-22 ppm of chemical shift). A <1>, A <2>, A <3>, A <4>, A <5>, A <6>, A <7>, A <8> and A <9> are respectively 42.3 ppm, 35.9 ppm, 38.6 ppm, 30.6 ppm, 36.0 ppm, 31.5 ppm, 31.0 ppm, 37.2 ppm, 27.4 ppm peak area, part in the above formula [Chemical Formula 2] The abundance ratio of carbon shown in the structures (Ι) and (ΙΙ) is shown.
The ratio of 2,1-inserted propylene and the ratio of 1,3-inserted propylene with respect to the total propylene insertion were calculated by the following equations.

Further, in the present invention, the propylene polymer, 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 (2).
(−0.20) · Tm + 35 ≦ Y ≦ (−0.33) · Tm + 60 ·· Equation (2)

  The water vapor permeability can be measured by JIS K7129 (1992) “Test method for water vapor permeability of plastic films and sheets”. In this measurement, an infrared sensor method is adopted as a test method, and a test temperature of 40 ± 0.5 ° C. and a relative humidity (90 ± 2)% RH are adopted as test conditions.

The propylene-based polymer within the range of the above formula (2) exhibits moderate water vapor permeability. The appropriate water vapor permeability facilitates the penetration of saturated steam used for molding into the foamed particles (in the core layer) during molding, thereby increasing the secondary foamability of the foamed particles. It becomes easy to produce an in-mold molded product with no or little space between them.
Also, as a method for producing polypropylene resin expanded particles, a method in which resin particles are dispersed in water and impregnated with a foaming agent and then discharged from high temperature and pressure to low pressure to form expanded particles. In this case, the proper water vapor permeability facilitates the penetration of water and the foaming agent into the resin particles. As a result, the water and the foaming agent are uniformly dispersed in the resin particles, the cell diameter 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. Generally, the foaming temperature at the time of production of foamed particles and the saturated steam temperature at the time of in-mold molding are used. 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).

  When the water vapor permeability (Y) is lower than [(−0.20) · Tm + 35], the permeability of the water vapor or the foaming agent to the base resin constituting the core layer becomes inferior. If it exceeds (−0.33) · Tm + 60], the permeability of water vapor to the base resin will be too good, and in any case, the dispersion of water and foaming agent in the resin particles during the process of producing foamed particles Tends to be non-uniform, and the uniformity of the bubble diameter of the resulting expanded particles may be reduced. Further, there is a possibility that the compression strength of the in-mold molded product obtained by molding the foamed particles in-mold may be reduced, or the strain recovery property 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 foamed particles.

  A propylene polymer in which the melting point (Tm) and the water vapor permeability (Y) satisfy the relationship of the above formula (2) can be obtained by selecting an appropriate catalyst in producing the polymer. . Specifically, for example, among the above metallocene catalysts, it can be suitably obtained by using bridged bis {1,1 '-(4-hydroazurenyl)} zirconium dichloride as a metal complex component. Preferred examples of such metal complex components are as described above.

Next, the requirement (c) is that the melting point Tm [° C.] of the propylene polymer satisfies the following formula (1).
Tm <141 [° C.] Formula (1)

  When the melting point Tm satisfies the above formula (1), that is, when the melting point Tm is less than 141 ° C., the propylene-based polymer is extremely excellent in processability at a low temperature. For this reason, even if the polypropylene resin foam particles having a foam core layer using the propylene polymer as a base resin are molded in a mold with a general-purpose molding machine with a low clamping pressure, the secondary foamability of the foam particles is improved. As a result, it is possible to obtain an in-mold molded article having a good appearance with little or no void between the expanded particles. An in-mold molded product obtained from expanded particles having the above propylene polymer having a melting point Tm of less than 141 ° C. as the base resin for the core layer is also excellent in flexibility and strain recovery.

  When the melting point Tm is 141 ° C. or higher, a higher molding vapor pressure is required to produce an in-mold molded article having a better appearance as compared with a melting point Tm of less than 141 ° C. When the melting point Tm is 141 ° C. or higher, mechanical properties such as bending strength and tensile strength of the polypropylene polymer are too high as compared with the melting point Tm of less than 141 ° C. Therefore, the in-mold molded product obtained by using the expanded particles using this as the base resin is poor in flexibility. In the present invention, the melting point (Tm) of the propylene polymer is less than 141 ° C., preferably 115 ° C. or more and less than 141 ° C., more preferably 120 ° C. to 140 ° C., and 122 ° C. to 138 ° C. Is even more preferable.

  The melting point (Tm) and the melting point of the thermoplastic resin forming the coating layer to be described later are both described in JIS K7121 (1987) "When melting temperature is measured after performing a certain heat treatment" (The heating rate and cooling rate in adjusting the condition of the test piece are both 10 ° C./min), and using a heat flux DSC apparatus, draw a DSC curve at a heating rate of 10 ° C./min. The peak of the melting peak on the obtained DSC curve is adopted as the melting point (Tm). If multiple melting points are observed, the one with the highest peak of the melting peak is adopted based on the baseline on the high temperature side, and if there are multiple peaks with the highest melting peak, the arithmetic average value thereof is used. Is adopted. Further, the melting point of the coating layer described later was also measured by this method. With respect to the coating layer, “substantially no melting point” means a case where no clear melting peak is shown when measured by the above method. In the case of a sample that does not show a clear melting peak, the maximum heating temperature in the conditioning of the test piece by heat flux DSC is up to 220 ° C.

  In general, the melting point (Tm) of the propylene-based polymer can be lowered as the proportion of the structural units obtained from the comonomer increases and as the proportion of the irregular units increases.

Next, in the present invention, the thermoplastic resin forming the coating layer is a polyolefin polymer (olefin homopolymer, olefin copolymer containing 50 mol% or more of olefin structural units, or two or more of these). Or a polystyrene-based polymer (a styrene homopolymer or a styrene copolymer containing 50 mol% or more of styrene structural units or a mixture of two or more thereof). In this case, it is possible to obtain an effect that the mechanical properties of the in-mold molded product obtained by molding the polypropylene resin expanded particles in the mold are excellent. The polyolefin polymer is particularly preferably an ethylene or propylene homopolymer or copolymer.
Moreover, it is preferable that the said coating layer is a non-foaming state or a substantially non-foaming state. In this case, when the polypropylene-based resin expanded particles are molded in the mold, an in-mold molded body having excellent fusion between the expanded particles can be obtained.

  In addition, the polypropylene resin expanded particles according to the present invention are used as a material for filling a molding die, foaming and heat-sealing to obtain an in-mold molded product.

  Next, the coating layer is preferably made of an olefin polymer having a melting point lower than or substantially not showing the melting point of the propylene polymer forming the core layer. In this case, the above-mentioned polypropylene resin expanded particles can obtain the desired in-mold molded product even if the in-mold molding is performed with a lower heating water vapor pressure.

  Examples of the olefin polymer having a melting point lower than that of the propylene polymer for the core layer include high pressure method low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, vinyl acetate, unsaturated carboxylic acid. Examples thereof include copolymers of acid, unsaturated carboxylic acid ester and the like with ethylene, and copolymers of propylene with ethylene and α-olefins.

  Examples of the olefin polymer having substantially no melting point include rubbers such as ethylene / propylene rubber, ethylene / propylene / diene rubber, ethylene / acrylic rubber, chlorinated polyethylene rubber, and chlorosulfonated polyethylene rubber. An elastomer is mentioned. These rubbers and elastomers can be used alone or as two or more compositions.

Next, the propylene polymer forming the core layer preferably further has the following requirement (d) (Claim 3).
(D) The isotactic triad fraction measured by 13C-NMR of the propylene unit chain part composed of a head-to-tail bond is 97% or more.

  That is, as the propylene polymer serving as the base resin of the core layer, in addition to the requirements (a) to (c) described above, 13C-NMR ( Isotactic triad fraction measured by nuclear magnetic resonance (that is, each propylene unit is linked head-to-tail out of three arbitrary propylene units in the polymer chain, and the methyl branching in the propylene unit is Those having a propylene unit 3 chain ratio in the same direction) of 97% or more are used.

  The isotactic triad fraction is hereinafter referred to as mm fraction. When the mm fraction is 97% or more, the mechanical properties of the propylene polymer are higher. Therefore, the polypropylene resin foamed particles using the propylene polymer as a base resin for the core layer can be obtained by molding the foamed particles in a mold, thereby obtaining an in-mold molded article having further excellent mechanical properties. It will be a thing. More preferably, the mm fraction is 98% or more.

Next, the propylene polymer forming the core layer 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 foamed particles can be produced while maintaining industrially useful production efficiency, and the mechanical properties of the in-mold molded body made of the foamed particles can be improved.

  When the melt flow rate (MFR) is less than 0.5 g / 10 min, the production efficiency of the polypropylene resin foamed particles, particularly the productivity in the melt-kneading process described later, may be reduced. If the MFR exceeds 100 g / 10 min, the mechanical properties such as compressive strength and tensile strength of the in-mold molded product obtained by molding the polypropylene resin expanded particles in the mold may be lowered. . Preferably, the propylene-based polymer has an MFR of 1.0 to 50 g / 10 minutes, more preferably 1.0 to 30 g / 10 minutes. The MFR means a melt mass flow rate measured according to the conditions described in Table 3 of JIS K6921-2 (1997).

  In addition, as described above, with respect to the propylene-based polymer as the base resin that forms the core layer of the polypropylene-based resin expanded particles, as long as it does not impair the effects of the present invention, other polymer components and additives are added. Agents can be mixed.

Examples of the other polymer components include high-density polyethylene, low-density polyethylene, and ethylene-based resins such as linear low-density polyethylene that is a copolymer of ethylene and α-olefin (4 or more carbon atoms); polybutene resin; Ethylene-propylene rubber; ethylene-propylene-diene rubber; hydrogenated block formed by saturating at least part of ethylene double bonds of styrene-diene block copolymer or styrene-diene block copolymer by hydrogenation Examples thereof include styrene-based thermoplastic elastomers such as copolymers; 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 said additive, various additives, such as a foam nucleating agent, a coloring agent, an antistatic agent, and a lubricant, can be added. These are usually added together during the melt kneading described later and contained in the resin particles.
The above foaming nucleating agents include inorganic compounds such as talc, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, zinc borate, carbon, phosphate nucleating agent, phenolic nucleating agent. And organic nucleating agents such as amine nucleating agents. The addition amount of these various additives varies depending on the purpose of addition, but is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, still more preferably 15 parts by weight or less, based on 100 parts by weight of the propylene polymer. 8 parts by weight or less is even more preferable, and 5 parts by weight or less is most preferable.

  The mixing of the other components with the propylene polymer as the base resin of the core layer can be performed by liquid mixing or solid mixing, but generally melt kneading is used. That is, for example, by using various kneaders such as rolls, screws, Banbury mixers, kneaders, blenders, mills, etc., the base resin and other components are kneaded at a desired temperature, and after kneading, production of expanded particles Molded into resin particles of a size suitable for

The raw material of the polypropylene-based foamed resin particles is usually resin particles made of a composite composed of a non-foamed core layer and a non-foamed coating layer.
For example, the following methods are used as specific methods for producing resin particles made of such a composite.
For example, a sheath-core type composite die described in Japanese Patent Publication Nos. 41-16125, 43-23858, 44-29522, and JP-A-60-185816 is used.

In this case, two extruders are used, one of the extruders melts and kneads the thermoplastic resin for forming the core layer, and the other extruder melts and kneads the resin constituting the coating layer. Then, a sheath-core type composite composed of a non-foamed core layer and a non-foamed coating layer is extruded into a string shape.
Thereafter, a method of obtaining resin particles in the form of columnar pellets comprising a core layer and a coating layer that are not substantially foamed by cutting to a specified weight or size with a cutting machine equipped with a take-up machine is preferable. When the coating layer is thinner, foaming is less likely to occur when the composite resin particles are foamed, and when the coating layer is too thin, sufficient coating becomes difficult. Therefore, the thickness of the coating layer is preferably 0.5 to 60 micrometers before being produced into expanded particles, and preferably 0.5 to 50 micrometers after being produced.

  In general, when the weight of one resin particle is 0.1 to 20 mg, there is no problem in the production of foamed particles obtained by heating and foaming the resin 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 further small, the production of the expanded particles is facilitated, and the variation in the density of the obtained expanded particles is also reduced. Fillability of the expanded particles in the mold or the like is improved.

  As a method for obtaining expanded particles from the resin particles, a method in which the resin particles produced as described above are impregnated with a volatile foaming agent and then heated and foamed, specifically, for example, Japanese Patent Publication No. 49-2183. The methods described in JP-A No. 56-1344, West German Patent No. 1285722 and No. 2107683 can be used.

  Examples of the volatile foaming agent include aliphatic hydrocarbons such as butane, pentane, hexane, and heptane, halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoromethane, tetrachlorodifluoroethane, and dichloromethane, Or 2 or more types can be mixed and used. Also, inorganic gases such as nitrogen, air and carbon dioxide can be used.

When resin particles consisting of a core layer and a coating layer are impregnated with a foaming agent and then heated and foamed, the resin particles are placed in a pressure vessel that can be sealed and opened together with the volatile foaming agent, and the softening temperature of the core layer in the base resin By heating as described above, the resin particles are impregnated with the volatile foaming agent.
After that, the contents in the sealed container are discharged from the sealed container to a low-pressure atmosphere and then dried. Thereby, a polypropylene resin expanded particle is obtained.

  The core layer of the polypropylene resin foam particles is a DSC curve obtained by differential scanning calorimetry (however, 2 to 4 mg of foam particles are measured at a normal temperature (20 ° C. to 45 ° C. at a heating rate of 10 ° C./min with a differential scanning calorimeter). It is preferable to have two or more endothermic peaks in the DSC curve obtained when the temperature is raised from 220 to 220 ° C. This is manifested by the component derived from the base resin forming a portion showing an endothermic peak unique to the resin and a portion showing an endothermic peak at a higher temperature.

  The foamed core layer in which two or more endothermic peaks appear in the DSC curve can be produced by, for example, a method described in JP-A-2002-200355 and the like when foaming the resin particles. It can be obtained by controlling the conditions, specifically the temperature, pressure, time, etc. when discharging into a low-pressure atmosphere.

In the method for producing foamed particles by releasing the contents in the sealed container into a low-pressure atmosphere from the sealed container, a decomposable foaming agent is kneaded in advance into the resin particles comprising the core layer and the coating layer. Therefore, the foamed particles can be obtained without blending a foaming agent in the pressure vessel.
As the above decomposable foaming agent, any gas can be used as long as it decomposes at the foaming temperature of the resin particles to generate gas. Specifically, sodium bicarbonate, ammonium carbonate, an azide compound, an azo compound, etc. are mentioned, for example.

  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. Furthermore, in order to uniformly disperse the resin particles in the dispersion medium, poorly water-soluble inorganic substances such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide and kaolin, and highly water-soluble substances such as polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose. It is preferable to use an anionic surfactant such as molecular protective colloid agent, sodium dodecylbenzenesulfonate, sodium alkanesulfonate, or a mixture of two or more.

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

Next, the in-mold molded product of the present invention can be produced by various in-mold molding methods using the polypropylene resin expanded particles of the present invention.
For example, after filling polypropylene resin foam particles into a cavity consisting of a pair of concave and convex molds under atmospheric pressure or reduced pressure, the mold cavity volume is compressed so as to decrease by 5 to 70%, and then steam or the like is used. There is a compression molding method in which the heat transfer medium is introduced into the cavity and the polypropylene resin expanded particles are heated and fused (for example, Japanese Patent Publication No. 46-38359).

  Also, the secondary foaming power of the foamed particles is increased by pre-treating the resin foamed particles with one or more volatile foaming agents or inorganic gases and impregnating them in the core layer. Pressurized aging in which foamed particles are filled into a cavity consisting of a pair of concave and convex molds under atmospheric pressure or reduced pressure while holding, and then a heat medium is introduced into the mold cavity to heat-fuse resin foam particles There is also a molding method (for example, Japanese Patent Publication No. 51-22951).

  In addition, after filling the mold cavity pressurized above the atmospheric pressure with compressed gas with resin foam particles pressurized above the pressure, a heating medium such as steam is introduced into the mold cavity to expand the foam particles. There is also a compression filling molding method in which the material is heat-sealed (for example, Japanese Patent Publication No. 4-46217).

  Furthermore, the foamed particles are filled into a cavity formed by a pair of concave and convex molds under atmospheric pressure or reduced pressure using resin foam particles with high secondary foaming power obtained under special conditions, and then mold cavities There is also an atmospheric pressure filling molding method in which a heat medium such as steam is introduced into the tee and the foamed particles are heated and fused (for example, Japanese Patent Publication No. 6-49795). Moreover, it can also shape | mold by the combination of said method (for example, refer to Japanese Patent Publication No. 6-22919).

  In addition, a film or a sheet (hereinafter referred to as a film or the like) can be laminated on the in-mold molded body obtained by molding as described above, if necessary. There are no particular restrictions on the film to be laminated. For example, OPS (biaxially stretched polystyrene sheet), polystyrene resin film such as high heat resistant OPS, HIPS, etc., CPP (unstretched polypropylene film), OPP (biaxially stretched polypropylene film) Polypropylene resin film, etc., or polyethylene resin film, polyester resin film, etc. are used.

  Moreover, although there is no restriction | limiting in the thickness of the film etc. to laminate, Usually, a film of 15 micrometers-4000 micrometers is used. These films may be printed as necessary. In addition, when laminating, it may be performed simultaneously with heat fusion molding (in-mold molding) of foamed particles. Moreover, you may laminate to the molded object once shape | molded. If necessary, lamination can be performed using a hot-melt adhesive.

Next, examples of the present invention will be described.
In this example, a polypropylene resin foamed particle composed of a foamed core layer made of a propylene polymer as a base resin and a coating layer made of a thermoplastic resin covering the core layer, and this in-mold An in-mold molded product is produced by molding. The expanded polypropylene resin particles have the above requirements (a) to (c).
Further, in this example, in order to clarify the excellent characteristics of the present invention, a comparative polypropylene resin foamed particle and an in-mold molded product obtained by molding the same are molded. Hereinafter, this example will be described in detail.

[Manufacture of base resin 1]
First, a propylene polymer as a base resin for forming a core layer was synthesized by the method shown in the following Production Examples 1 to 7.

Production Example 1
(I) Synthesis of [dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyl-4-hydroazurenyl)} zirconium dichloride] The following reactions are 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 cyclohexane-diethyl ether solution of phenyllithium ( 1.0 equivalent) was added in small portions at 0 ° C.
The solution was stirred at room temperature for 1 hour, cooled to -78 ° C, and 30 mL of tetrahydrofuran was added.

  Subsequently, after adding 0.95 mL of dimethyldichlorosilane, it heated up to room temperature, and also heated at 50 degreeC 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 obtained crude product was purified by silica gel column chromatography (hexane: dichloromethane = 5: 1) to give bis {1,1 ′-(2-methyl-4-phenyl-1,4-dihydroazurenyl). ) 1.48 g of dimethylsilane was obtained.
786 mg of the bis {1,1 ′-(2-methyl-4-phenyl-1,4-dihydroazurenyl) dimethylsilane obtained above was dissolved in 15 mL of diethyl ether, and hexane of n-butyllithium was added at −78 ° C. 1.98 mL of the solution (1.68 mol / L) was added dropwise, the temperature was gradually raised to room temperature, and then the mixture was stirred at room temperature for 12 hours. The solid obtained by distilling off the solvent under reduced pressure was washed with hexane and dried under reduced pressure.

Furthermore, 20 mL of a toluene-diethyl ether mixed solvent (40: 1) was added, 325 mg of zirconium tetrachloride was added at −60 ° C., the temperature was gradually raised, and the mixture was stirred at room temperature for 15 minutes.
The resulting solution was concentrated under reduced pressure, and reprecipitated by adding hexane, whereby racemic dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyl-4-hydroazurenyl)} zirconium dichloride was prepared. A 150 mg / meso mixture was obtained.

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

(Ii) Catalyst synthesis (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 obtain a solution. After adding 22.2 g of montmorillonite (“Kunipia-F” manufactured by Kunimine Kogyo Co., Ltd.) to this solution, the temperature was raised and kept at 80 ° C. for 1 hour.
Next, 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 this solid content, the temperature was raised and the mixture was heated and refluxed for 2 hours, and then 200 mL of demineralized water was added and filtered.
Further, 400 mL of demineralized water was added and filtration was performed twice. Thereafter, the solid was dried at 100 ° C. to obtain chemically treated montmorillonite as a catalyst support.

(B) Preparation of catalyst component After the inside of a stirring autoclave having an internal volume of 1 liter was sufficiently substituted 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 prepared as described above as a catalyst support was suspended in 200 mL of toluene and added.

  Furthermore, the racemic form (0.15 mmol) of dimethylsilylenebis {1,1 ′-(2-methyl-4-phenyl-4-hydroazurenyl)} zirconium dichloride prepared in a separate container in (b) of (i) above. ) And triisobutylaluminum (3 mmol) in toluene (20 mL in total) were added to the autoclave.

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

(Iii) Polymerization of propylene After the inside of a stirred autoclave having an internal volume of 200 L is sufficiently substituted with propylene, 60 L of purified n-heptane is introduced, and 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum is added, and the autoclave is added. The inside was heated to 70 ° C. Thereafter, the solid catalyst component (6.0 g) was added, and a mixed gas of propylene and ethylene (propylene: ethylene = 96.5: 3.5; weight ratio) was introduced so that the pressure became 0.7 MPa. Then, the polymerization was started, and the polymerization reaction was carried out for 3 hours under these conditions.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the remaining gas component was purged to obtain 8.8 kg of a polymer as a propylene polymer for the core layer.
This polymer has MFR = 8 g / 10 min, isotactic triad fraction of 99.2%, melting point Tm of 125 ° C., structural unit obtained from propylene, 95.3 mol%, structure obtained from ethylene The unit is 4.7 mol%, the ratio of position irregular units based on 2,1-insertion is 0.95%, the ratio of position irregular units based on 1,3-insertion is 0.11%, and the above requirements (A), (b), (c), and (d) are satisfied.
Hereinafter, the polypropylene polymer (propylene / ethylene random copolymer) obtained here is referred to as “polymer 1”.

(Iv) Measurement of water vapor permeability The polymer 1 obtained above was molded into a film having a thickness of 25 microns, and the water vapor permeability Y was measured according to the method described in JIS K7129 (the same is true for the following production examples). was ^{.8 (g / m 2 / 24hr} ).
Since this polymer 1 has a melting point Tm of 125 ° C., Y should be within the range of 10.0 ≦ Y ≦ 18.8 from the above formula (2), but was within that range.

Production Example 2
After thoroughly replacing the inside of the stirred autoclave with an internal volume of 200 L with propylene, introduce 60 L of purified n-heptane, add 500 mL (0.12 mol) of hexane solution of triisobutylaluminum, and raise the inside of the autoclave to 70 ° C. Warm up. Thereafter, the solid catalyst component (9.0 g) was added, and a mixed gas of propylene and ethylene (propylene: ethylene = 97.0: 3.0; weight ratio) was introduced so that the pressure became 0.7 MPa. Then, the polymerization was started, and the polymerization reaction was carried out for 3 hours under these conditions.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the remaining gas component was purged, thereby obtaining 10.4 kg of a polymer as a propylene-based polymer for the core layer.
This polymer has MFR = 10 g / 10 min, isotactic triad fraction of 99.1%, melting point Tm of 135 ° C., structural unit obtained from propylene, 97.1 mol%, structural unit obtained from ethylene Is 2.9 mol%, the ratio of position irregular units based on 2,1-insertion is 1.02%, the ratio of position irregular units based on 1,3-insertion is 0.13%, a), (b), (c), and (d) are satisfied.
Hereinafter, the polypropylene polymer (propylene / ethylene random copolymer) obtained here 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 ^{13.5 (g / m 2 / 24hr} ).
Since this polymer 2 has a melting point Tm of 135 ° C., Y should be within the range of 8.0 ≦ Y ≦ 15.5 from the above formula (2), but was within that range.

Production Example 3
After thoroughly replacing the inside of the stirred autoclave with an internal volume of 200 L with propylene, introduce 60 L of purified n-heptane, add 500 mL (0.12 mol) of hexane solution of triisobutylaluminum, and raise the inside of the autoclave to 70 ° C. Warm 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. Then, the polymerization was started, and the polymerization reaction was carried out for 3 hours under these conditions.

Thereafter, 100 mL of ethanol was injected into the reaction system to stop the reaction, and the residual gas component was purged to obtain 9.3 kg of polymer. This polymer has MFR = 8 g / 10 min, 97.6 mol% of structural units obtained from propylene, 2.4 mol% of structural units obtained from ethylene, and 99.2% of isotactic triad fraction. The melting point Tm was 141 ° C., the ratio of position irregular units based on 2,1-insertion was 1.06%, and the ratio of position irregular units based on 1,3-insertion was 0.17%.
That is, this polymer satisfies the requirements (a) and (b) but does not satisfy the requirement (c).
Hereinafter, the propylene polymer (propylene / ethylene random copolymer) obtained here is referred to as “polymer 3”.

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

Production Example 4
After thoroughly replacing the inside of the stirred autoclave with an internal volume of 200 L with propylene, 60 L of purified n-heptane was introduced, and 7.5 g of diethylaluminum chloride (40 g) and a titanium trichloride catalyst manufactured by Marubeni Solvay Co. 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 = 96.5: 3.5; weight ratio) at an autoclave temperature of 65 ° C. It introduced so that a pressure might be set to 0.7 Mpa.

After stopping the introduction of the mixed gas, the reaction was continued for an additional hour, 100 mL of butanol was added to the reaction system to stop the reaction, and the residual gas component was purged to obtain 33 kg of polymer.
This polymer has MFR = 12 g / 10 min, structural unit obtained from propylene 96.0 mol%, structural unit obtained from ethylene 4.0 mol%, melting point Tm 141 ° C., isotactic triad content The rate was 96.5%, the ratio of position irregular units based on 2,1-insertion was 0%, and the ratio of position irregular units based on 1,3-insertion was 0%.
That is, this polymer satisfies the requirement (a) but does not satisfy the requirements (b) and (c).
Hereinafter, the polypropylene polymer (propylene / ethylene random copolymer) obtained here is referred to as “polymer 4”.

Further, for the above polymer 4, in the same manner as in the polymer 1 was examined the water vapor transmission rate Y when molded into a film was ^{15.2 (g / m 2 / 24hr} ).
In addition, since the melting point Tm of the polymer 4 is 141 ° C., Y should be within the range of 6.8 ≦ Y ≦ 13.5 from the above formula (2), but not within the range. It was.

Production Example 5
After thoroughly replacing the inside of the stirred autoclave with an internal volume of 200 L with propylene, 60 L of purified n-heptane was introduced, and 7.5 g of diethylaluminum chloride (40 g) and a titanium trichloride catalyst manufactured by Marubeni Solvay Co. 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 = 95.5: 4.5; weight ratio) at an autoclave temperature of 65 ° C. It introduced so that a pressure might be set to 0.7 Mpa.

After stopping the introduction of the mixed gas, the reaction was continued for another hour, 100 mL of butanol was added to the reaction system to stop the reaction, and the remaining gas components were purged to obtain 35 kg of polymer.
This polymer has MFR = 14 g / 10 min, structural unit obtained from propylene is 94.6 mol%, structural unit obtained from ethylene is 5.4 mol%, melting point Tm is 135 ° C., isotactic triad content. The rate was 96.5%, the ratio of position irregular units based on 2,1-insertion was 0%, and the ratio of position irregular units based on 1,3-insertion was 0%.
That is, this polymer satisfies the requirements (a) and (c) but does not satisfy the requirement (b).
Hereinafter, the polypropylene polymer (propylene / ethylene random copolymer) obtained here is referred to as “polymer 5”.

Further, for the above polymer 5, as in the polymer 1 was examined the water vapor transmission rate Y when molded into a film was ^{18.9 (g / m 2 / 24hr} ).
Since the melting point Tm of the polymer 5 is 135 ° C., Y should be within the range of 8.0 ≦ Y ≦ 15.5 from the above formula (2), but is not within the range. It was.

Production Example 6
This was carried out by applying the catalyst system described in [Production of base resin 1] in the examples of JP-A-6-240041. That is, after the inside of a stirring autoclave having an internal volume of 200 L is sufficiently substituted with propylene, 60 L of purified n-heptane is introduced, and 120 g of methylalumoxane (average oligomer degree 16) manufactured by Tosoh Akzo Co., Ltd. is disclosed. Rac-dimethylsilylenebis (2-methylindenyl) zirconium dichloride (150 mg) synthesized by the method described in Japanese Patent No. 268307 was introduced under a propylene atmosphere. Furthermore, while maintaining the hydrogen concentration in the gas phase at 0.5% by volume, a mixed gas of propylene and ethylene (propylene: ethylene = 98.0: 2.0; weight ratio) at an autoclave internal temperature of 40 ° C. The polymerization was started by introducing the pressure so as to be 0.7 MPa, and the polymerization reaction was carried out for 2 hours under these conditions.

Thereafter, 100 mL of butanol was added to the reaction system to stop the reaction, and the residual gas component was purged to obtain 7.3 kg of a polymer (propylene / ethylene random copolymer). This polymer is referred to as “Polymer 6”.
This polymer 6 has an MFR = 10 g / 10 min, a structural unit obtained from propylene of 97.1 mol%, a structural unit obtained from ethylene of 2.9 mol%, a melting point Tm of 140 ° C., and isotactic tri The add fraction is 94.8%, the ratio of irregular position units based on 2,1-insertion is 0.26%, and the ratio of position irregular units based on 1,3-insertion is below the detection limit, that is, 0.005. %. In Table 1 to be described later, the ratio of the position irregular units based on 1,3-insertion of the polymer 6 was expressed as 0%.
That is, this polymer 6 satisfies the requirement (a) and the requirement (c), but does not satisfy the requirement (b).

Further, for the above polymer 6, in the same manner as in the polymer 1 was examined the water vapor transmission rate Y when molded into a film was ^{6.6 (g / m 2 / 24hr} ).
Since this polymer 6 has a melting point Tm of 140 ° C., Y should be within the range of 7.0 ≦ Y ≦ 13.8 from the above formula (2), but not within that range. there were.

Production Example 7
After sufficiently replacing the interior of the stirred autoclave with an internal volume of 200 L with propylene, 60 L of purified n-heptane was introduced, and 120 g of methylalumoxane (average oligomer degree 16) manufactured by Tosoh Akzo Co., Ltd., a known method [H. H. Yamazaki et.al, “Chemistry Letters”, Japan, 1989, Vol. 18, p. Rac-dimethylsilylene bis (3-methylcyclopentadienyl) zirconium dichloride (100 mg) synthesized in 1853] was introduced in a propylene atmosphere. Furthermore, while maintaining the hydrogen concentration in the gas phase at 0.5% by volume, a mixed gas of propylene and ethylene (propylene: ethylene = 98.5: 1.5; weight ratio) at an autoclave internal temperature of 40 ° C. The polymerization was started by introducing the pressure so as to be 0.7 MPa, and the polymerization reaction was carried out for 3 hours under these conditions.

Thereafter, 100 mL of butanol was added to the reaction system to stop the reaction, and the residual gas component was purged to obtain 6.4 kg of a polymer (propylene / ethylene random copolymer). This polymer is referred to as “Polymer 7”.
This polymer 7 has an MFR of 19 g / 10 min, a structural unit obtained from propylene of 98.0 mol%, a structural unit obtained from ethylene of 2.0 mol%, a melting point of 137 ° C., and an isotactic triad. The fraction was 92.0%, the ratio of position irregular units based on 2,1-insertion was 2.05%, and the ratio of position irregular units based on 1,3-insertion was 0.45%.
That is, this satisfies the requirement (a) and the requirement (c) but does not satisfy the requirement (b).

As for the polymer 7, in the same manner as in the polymer 1 was examined the water vapor transmission rate Y when molded into a film was ^{15.4 (g / m 2 / 24hr} ).
Since the base resin has a melting point Tm of 137 ° C., Y should be within the range of 7.6 ≦ Y ≦ 14.8 from the above formula (2), but not within the range. Met.

  The results of the above Production Examples 1 to 7 are shown in Table 1.

As is also known from Table 1, the polymer 1 and the polymer 2 satisfy the requirements (a) to (c). The polymer 1 and the polymer 2 also satisfy the requirements (d) and (e).
On the other hand, the polymer 3 satisfies the requirements (a) and (b) but does not satisfy the requirement (c).
The polymer 4 satisfies the requirement (a) but does not satisfy the requirements (b) and (c).
Furthermore, although the said polymers 5-7 satisfy | fill the said requirements (a) and (c), they do not satisfy the said requirements (b).

Next, Examples in which polypropylene resin expanded particles are produced using the propylene polymers (Polymer 1 to Polymer 7) obtained in Production Examples 1 to 7 will be described.
In each of the following examples, each physical property was obtained as follows.

  <Melting point> 20 to 3 to 5 mg of a sample composed of the propylene-based polymer obtained in the above Production Examples 1 to 7 or the resin of the coating layer described in Tables 2 to 4 described later by a heat flux differential scanning calorimeter (DSC). DSC curve obtained by increasing the temperature from 10 ° C to 220 ° C at a rate of 10 ° C / min, then decreasing to 20 ° C at a rate of 10 ° C / min, and further increasing the temperature to 220 ° C at a rate of 10 ° C / min. From the above, the melting point was measured as described above.

  <Heat-resistant temperature> According to JIS K6767 (1976), the heating dimensional change rate at each temperature was measured in increments of 5 ° C from 80 ° C to 115 ° C, and the upper limit temperature at which the dimensional shrinkage rate was 3% or less was defined as the heat-resistant temperature. .

Example 1
Using an internal diameter 65 mmφ single screw extruder, the propylene polymer obtained in Production Example 1 was added with an antioxidant (trade name “Yoshinox BHT” 0.05 wt%, manufactured by Yoshitomi Pharmaceutical Co., Ltd.), and product name “Irganox 1010” manufactured by Ciba Geigy. “0.10 wt%) was added and kneaded.

Next, from the die having a die orifice with a diameter of 1.5 mm, the above propylene polymer is used as a non-foamed core layer, a linear low density polyethylene having a density of 0.907 g / cm ³ and a melting point of 100 ° C. 2 to 4 were labeled as “LLDPE1”) and extruded as a non-foamed coating layer in the form of a strand.

  Further, this strand was cooled through a water tank, and cut so that the weight of one strand became 1.0 mg to obtain fine pellets as resin particles. When the resin particles (resin particles made of a composite) are observed with a phase contrast microscope, a coating layer made of linear low density polyethylene having a thickness of 30 microns covers a non-foamed core layer made of a propylene polymer. Had a structure.

  Next, in order to make the resin particles (composite particles) into expanded particles, 1000 g of the fine pellets (resin particles made of the composite) are 2500 g of water, 200 g of tribasic calcium phosphate (however, 10% aqueous dispersion), The mixture was placed in an autoclave having an internal volume of 5 liters together with 30.0 g of sodium dodecylbenzenesulfonate (2% aqueous solution), 200 g of isobutane was further added, the temperature was raised to 110 ° C. over 60 minutes, and the temperature was maintained for 30 minutes.

Thereafter, in order to keep the pressure in the autoclave at 2.3 MPa, the valve at the bottom of the autoclave was opened while the compressed nitrogen gas was added from the outside, and the contents were released to the atmosphere.
When the bulk density of the expanded polypropylene resin particles obtained by the above operation was measured after drying, it was 18 g / L. Further, the bubbles of the expanded particles had an average diameter of 320 μm and were very uniform.

  The average bubble diameter (average bubble diameter) of the polypropylene resin foamed particles is a microscope obtained by observing a cross section of the foamed particles cut through almost the center of the randomly selected foamed particles with a microscope. In the photograph or the cross-section projected on the screen, the diameter (maximum length) of each bubble was measured for 50 random bubbles and the average value was shown.

Next, an in-mold molded body is produced as follows using the polypropylene resin expanded particles.
That is, first, the polypropylene resin expanded particles obtained above were filled while being compressed sequentially into a mold made of aluminum using compressed air using a hopper. Thereafter, the mold chamber was heat-formed through steam having a gauge pressure of 0.06 MPa (indicated as “molding vapor pressure” in Tables 2 to 4 below) to obtain an in-mold molded body.

This in-mold molded body has a density of 30 kg / m ³ , a length of 300 mm, a width of 300 mm, a thickness of 50 mm, a mold size shrinkage of 2.0%, a small surface gap, and an excellent surface appearance with no irregularities. there were. Moreover, it fractured | ruptured from the center part of the in-mold molded object, and it was 90% when the fusion degree of the cross section was measured.

  The degree of fusion is determined by cleaving a test piece prepared from an in-mold molded body, visually measuring the number of particle breaks and the number of interparticle breaks in the cross section, Expressed as a percentage.

Further, the appearance of the molded body in the mold (molded body appearance) was visually judged according to the following criteria.
○: The surface of the molded body in the mold is smooth and there is no gap between particles. △: The surface of the molded body in the mold is smooth, but the gap between particles is conspicuous. ×: The surface of the molded body in the mold is smooth. Chips and gaps between particles are conspicuous

In addition, a test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was prepared from another in-mold molded body molded under the same molding conditions, and a compression test was performed at a compression rate of 10 mm / min in accordance with JIS K7220 (1999). As a result, the stress at 50% compression was 0.23 MPa. Furthermore, when the compression set was measured by the method described in JIS K6767 (1976) using a test piece of the same size, it was 8%.
The results are shown in Table 2 below.

(Examples 2-4) and (Comparative Examples 1-6)
Example 1 except that those described in Production Examples 1 to 7 above were used as the base resin for forming the core layer, and those described in Tables 2 to 4 below were used as the resin for forming the coating layer. It implemented similarly and those results were shown in Table 2-Table 4. The following abbreviations shown in Tables 2 to 4 have the following meanings.
LLDPE1 A linear low density polyethylene resin having a density of 0.907 g / cm ³ and a melting point of 100 ° C.
LLDPE2 A linear low density polyethylene resin having a density of 0.920 g / cm ³ and a melting point of 121 ° C.
HIPS high impact polystyrene resin.

(Comparative Example 7) Production of polyethylene resin expanded particles (however, no coating layer)
In this example, polyethylene-based resin expanded particles having no coating layer were prepared, and an in-mold molded product was prepared using the expanded particles.
That is, first, the linear low density polyethylene “LLDPE2” used for the coating layer of Example 2 was kneaded using a single screw extruder having an inner diameter of 30 mmφ, and cut so that the weight of one piece became 1.0 mg. Thus, fine pellets as resin particles were obtained.

  Next, 1000 g of the above-mentioned fine pellets were put in an autoclave having an internal volume of 5 liters together with 3000 g of water, 200 g of tribasic calcium phosphate (however, 10% aqueous dispersion) and 25.0 g of sodium dodecylbenzenesulfonate (2% aqueous solution). After adding 150 g of isobutane and raising the temperature to 113 ° C. over 60 minutes, this temperature was maintained for 30 minutes.

Thereafter, in order to keep the pressure in the autoclave at 2.3 MPa, the valve at the bottom of the autoclave was opened while the compressed nitrogen gas was added from the outside, and the contents were released to the atmosphere.
The polyethylene resin expanded particles obtained by the above operation were dried, and the bulk density was measured and found to be 27 g / L.

  Next, using this expanded particle, an in-mold molded product was produced in the same manner as in Example 1. Further, this in-mold molded body was evaluated in the same manner as in Example 1. The results are shown in Table 4.

  As is known from Table 3, when the propylene polymer (Polymer 3) obtained from Production Example 3 was used as the base resin for the core layer (Comparative Examples 1 and 2), the obtained polypropylene resin Since the melting point of the propylene polymer, which is the base resin for the core layer, is as high as 141 ° C., the expanded particles have an in-mold molded product with an excellent appearance at a very low molding vapor pressure (very low molding temperature). Couldn't get. Moreover, in Comparative Example 2, although an example of in-mold molding with a low molding vapor pressure of the same level as in Examples 1 to 4 is shown, since the melting point of the base resin of the core layer is high, the secondary foamability is inferior, This resulted in an in-mold molded product with many gaps between the expanded particles, resulting in a large compression set.

  Further, as is known from Tables 3 and 4, when the propylene-based polymer (Polymers 4 to 7) obtained in the above Production Examples 4 to 7 was used for the base resin of the core layer (Comparative Examples 3, 4, 5, 6), since these polymers 4 to 7 do not satisfy the requirement (b), the obtained polypropylene resin foamed particles were inferior in secondary foamability. Further, the in-mold molded product molded using the polypropylene resin foamed particles has a heating steam pressure (molded) required for molding as compared with the case where the polypropylene resin foamed particles obtained in Examples 1 to 4 are used. Although the vapor pressure was high, the surface appearance of the molded product thus obtained was still poor and the compression set was large.

  On the other hand, as is known from Table 2, in Examples 1 to 4 according to the present invention, a propylene polymer satisfying the above requirements (a) to (c) was used as the base resin for the core layer. In any case, when the in-mold molding is performed using the obtained polypropylene resin expanded particles, an in-mold molded body having a high degree of fusion even at a low heating steam pressure and having an excellent surface appearance can be obtained. I was able to. The mechanical properties were also very flexible and the compression set was very small. Moreover, it can be known from the stress at the time of 50% compression in Table 2 that the molded bodies in Examples 1 to 4 are excellent in flexibility.

  Further, as is known from Table 4, in Comparative Example 7, which shows an example of linear low density polyethylene resin expanded particles without a coating layer, the melting point of the used linear low density polyethylene resin was 121 ° C. However, when compared with Examples 1 and 2 in which a resin having substantially the same melting point as this was used as the base resin for the core layer, the molded articles in Examples 1 and 2 had higher heat resistance than Comparative Example 7. I understand that it is expensive.

Claims (5)

In expanded polypropylene resin particles composed of a core layer in a foamed state using a propylene polymer as a base resin and a coating layer made of a thermoplastic resin covering the core layer,
The propylene-based polymer forming the core layer has the following requirements (a) to (c): Polypropylene-based resin expanded particles,
(A) The structural unit obtained from propylene is 98 to 85 mol%, and the structural unit obtained from ethylene and / or an α-olefin having 4 to 20 carbon atoms is present (provided that it is obtained from propylene). The total amount of structural units and structural units obtained from ethylene and / or α-olefin having 4 to 20 carbon atoms is 100 mol%).
(B) The proportion of position irregular units based on 2,1-insertion of propylene monomer units in all propylene insertions measured by 13C-NMR is 0.5 to 2.0%, and 1 of propylene monomer units , 3- The percentage of irregular units based on insertion is 0.005 to 0.4%.
(C) When the melting point is Tm [° C.], Tm is the following formula (1)
Tm <141 [° C.] Formula (1)
To be satisfied.   2. The polypropylene resin according to claim 1, wherein the coating layer is made of an olefin polymer having a melting point lower than or substantially not showing the melting point of the propylene polymer forming the core layer. Expanded particles. 3. The expanded polypropylene resin particle according to claim 1, wherein the propylene polymer forming the core layer further has the following requirement (d).
(D) The isotactic triad fraction measured by 13C-NMR of the propylene unit chain part composed of a head-to-tail bond is 97% or more. The polypropylene resin expanded particle according to any one of claims 1 to 3, wherein the propylene polymer forming the core layer further has the following requirement (e).
(E) The melt flow rate is 0.5 to 100 g / 10 minutes. An in-mold molded product having a density of 0.5 to 0.008 g / cm ³ formed by molding polypropylene resin expanded particles in a mold,
And the said polypropylene-type resin expanded particle uses the thing in any one of the said Claims 1-4, The molded object in the mold characterized by the above-mentioned.