JP5190426B2 - Polyethylene for hollow foam molding - Google Patents

Description

  The present invention relates to polyethylene for hollow foam molding, more specifically, high foamability, moldability, mechanical strength, surface appearance and excellent durability, heat insulation, sound absorption, rigidity is improved, The present invention relates to a foamed hollow molding polyethylene suitable for lightweight containers.

Polyethylene is widely used to produce foamed hollow molded articles. The polyethylene used for this purpose is required not only to obtain uniform high foamability but also to have high mechanical strength and rigidity, and to have excellent durability.
Furthermore, in the foamed hollow molded product, not only the above-mentioned characteristics, but also a container with good design and appearance and a highly lightweight product may be required.

  For example, in foamed hollow molded containers, those using polypropylene (PP) can be cited and used in some applications. However, when polypropylene is used, there is room for improvement in terms of molding efficiency and cost, and a more preferable material is required. Further, containers hollow-molded with LDPE are also used for some applications, but there are problems such as heat-resistant deformation due to high temperature filling of contents.

  Under these circumstances, there is a need for a foamed hollow molding polyethylene material that has high foamability, moldability, mechanical strength, surface appearance, and excellent durability, and that is suitable for lightweight containers. It has been. Further, the lightweight container is required to have a high buckling strength, and an even more excellent foamed hollow molding material is desired.

As a method for producing a foamed hollow molded body, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 08-072127), a method for producing a foamed blow molded product in which a thermoplastic resin containing a foaming agent is melted and extruded and blow molded. In the present invention, a method for producing a foamed blow-molded product is proposed, wherein the foaming agent comprises two or more kinds of foaming agents whose decomposition components are mainly nitrogen gas and whose decomposition temperatures are different from each other. Yes.
However, even if such a method is adopted, depending on the type of molding resin, a foamed hollow molded article having good performance is not necessarily obtained. It is not easy to obtain a well-balanced foamed hollow molding material having all of foamability, moldability, mechanical strength, durability, and the like, and a material with further excellent performance is required.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2001-277340) discloses a blow molded container having a foam layer, wherein the resin composition of the foam layer is a high density polyethylene resin having a resin density of 0.93 g / cm ³ or more. And a foam blow molded container comprising a mixture of a low density polyethylene resin having a resin density of less than 0.93 g / cm ^{3, wherein} the blending ratio of the low density polyethylene resin is 5 to 15 parts by weight relative to the total weight, A foamed blow molded container has been proposed in which the resin is foamed to increase the wall thickness, the resin extrusion amount is reduced to reduce the weight, and both the weight reduction of the container and the maintenance of load resistance are achieved.
However, when a low density polyethylene resin is used, moldability is improved, but rigidity and mechanical strength are lowered.

In Patent Document 3 (Japanese Patent Laid-Open No. 2001-278916), the melt tension (MT) is 1.0 (g) or more, and the crystallization temperature (DS: ° C.) and MT are DS ≧ −1. 3 (MT) +110, the shear rate when the shear stress is 0.4 × 10 ⁶ (dyne / cm ² ) (R ₁ : 1 / second) and the shear stress is 2.4 × 10 ⁶ (dyne). / Cm ² ), a highly foamable polyethylene resin having a product of 20 or more in shear rate (R ₂ : 1 / second) is disclosed, and the polyethylene resin is molded to an expansion ratio of 10 times or more by an inert gas. Foamed molded article having a uniform cell diameter and suitable for the production of a high-foamed body having uniformly dispersed cells, and a high-foamed molded article having a constant quality and good appearance Is disclosed.
However, the polyethylene resin of Patent Document 3 uses one kind of a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, and has a high foaming ratio in extrusion foaming, whereas a foamed parison. There is no specific disclosure about a material suitable for foam hollow molding in which blow molding pressure is applied to the material, and a person skilled in the art finds a material suitable for foam hollow molding with a high expansion ratio based on the description of the document. It ’s difficult.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2002-003663) discloses a polyethylene resin composition comprising a polyethylene resin (A) and a crosslinked polyethylene (B) and satisfying the following characteristics (a) to (g). A polyethylene-based resin composition that is disclosed and excellent in moldability and a polyethylene-based container obtained by thermoforming or blow-molding the same are proposed.
(A) the insoluble component is 0.1 to 20% by weight, (b) the MFR is 0.05 to 10 g / 10 min, and (c) the flow activation energy obtained in the range of 160 to 220 ° C. is 35 kJ / mol. Hereinafter, (d) melt tension is 50 mN or more, (e) (melt tension)> 110-100xlog (MFR), (f) nonlinear parameter as an index of strain-hardening property of elongational viscosity is 3 or more, (g) 190 ° C. The melt tension after extrusion is 50% or more of the melt tension before extrusion.
However, the polyethylene-based resin composition of Patent Document 4 can improve the balance between drawdown resistance and melt dripping resistance in simple extrusion such as thermoforming and blow molding, and applies blowing pressure to the foamed parison. There is no specific disclosure about a material suitable for foaming hollow molding for hollow molding, and it is difficult for those skilled in the art to find a material suitable for foaming hollow molding with a high expansion ratio based on the description in the document.

In Patent Document 5 (Japanese Patent Application Laid-Open No. 2004-249680), a foamable molten resin composition obtained by melting and kneading a polyethylene resin and a physical foaming agent is extruded from a die to a low pressure region to form a foam layer. A foamed molded product is described in which a cylindrical molded product having a foamed layer is sandwiched between molds.
Here, the apparent density of the foamed molded product foamed layer is 0.03 to 0.4 g / cm ³ , and at least one melting peak by differential scanning calorimetry of the foamed molded product foamed layer exists at 125 ° C. or higher. The calorific value of the melting peak at 125 ° C. or higher by scanning calorimetry is 50 to 95% with respect to the total ratio, the melt flow rate of the foamed molded product foamed layer is 0.2 to 25 g / 10 min, and the melt tension is 1. A foamed molded article characterized by being 5 cN or more is disclosed. This is a polyethylene resin foam molding that has excellent lightness, mechanical strength, heat insulation, heat resistance, soundproofing, vibration proofing, chemical resistance, recyclability, and better low-temperature impact resistance than conventional products. It is said to be a body.

However, foam molded article of Patent Document 5, (A) Density 0.94 g / cm ³ greater, 0.97 g / cm ³ or less, a polyethylene resin 40-85 wt melt flow rate 0.1 to 20 g / 10 min (B) 15 to 60% by weight of a polyethylene resin having a density of 0.89 to 0.94 g / cm ³ , a melt flow rate of 0.2 to 20 g / 10 minutes, and a melt tension of 2.0 cN or more (provided that the resin ( A) and (B) total is 100% by weight), and a physical foaming agent is used, whereas a foaming parison is used without using a physical foaming agent. There is no specific disclosure about a material suitable for foam hollow molding in which blow molding pressure is applied to the material, and a person skilled in the art finds a material suitable for foam hollow molding with a high expansion ratio based on the description of the document. It ’s difficult.

Further, in Patent Document 6 (Japanese Patent Laid-Open No. 2006-305793), a foamed molten resin obtained by melting and kneading a polyolefin resin and a foaming agent in an extruder is extruded from an annular die to form a polyolefin resin foam layer. A method of producing a foamed hollow molded article having an average thickness of 0.5 to 5 mm by forming a foamed parison having a softened state, sandwiching the foamed parison in a split mold that can be opened and closed, and blowing a gas into the foamed parison. Has been.
Here, a foamed parison obtained by using an annular die having a lip diameter of 0.20 to 0.50 times the maximum width of the foamed hollow molded body is used. The pressure is expanded by blowing a pressurized gas inside the foamed parison so that the maximum width is 0.70 to 1.50 times, and the internal maximum pressure of the foamed parison is within the range of 0.01 to 0.20 MPa (G). A method for producing a hollow foam molded article is disclosed in which a mold is blown and molded by blowing a pressurized gas higher than the maximum pressure into the foamed parison, and the uneven thickness of the thin molded article is disclosed. It is said that a high-quality foamed hollow molded article having a uniform thickness that is thin and has very little uneven thickness can be obtained.

However, for the production of the foamed hollow molded article of Patent Document 6, the polyolefin resin has a density of 0.93 to 0.97 g / cm ³ , a melt flow rate of 0.1 to 20 g / 10 minutes, and a melt tension of 1. Polyethylene resin containing at least 50% by weight of high density polyethylene resin or polypropylene resin is preferred from the viewpoint of mechanical properties such as heat resistance and strength, although polyethylene resin of 0 cN or more is used. What kind of material is suitable for light-weight containers with high foamability, moldability, mechanical strength, surface appearance, and excellent foam durability, and also has excellent buckling strength. Since there is no specific disclosure, it is difficult for those skilled in the art to find a material suitable for foaming hollow molding with a high expansion ratio based on the description in the document.

Japanese Patent Application Laid-Open No. 08-072127 JP 2001-277340 A JP 2001-278916 A JP 2002-003663 A JP 2004-249680 A JP 2006-305793 A

  An object of the present invention is to provide a foamed hollow molding polyethylene suitable for a lightweight container having good moldability, mechanical strength, excellent durability, and particularly high buckling strength, in view of the problems of the above prior art. There is.

  As a result of intensive studies to solve the above problems, the present inventors have found that polyethylene having a specific density, MFR, molecular weight distribution, melt tension, crystallization temperature, in particular, having a specific density, MFR, molecular weight By using polyethylene obtained by mixing two types of polyethylene having different distributions and melt tensions, it was found that a foamed hollow molded article that can solve these problems can be produced, and the present invention has been completed.

That is, according to the first aspect of the present invention consists of a polyethylene (A) 10 to 95 wt% of polyethylene (B) 5 to 90 wt%, satisfies the following properties (a) ~ (d) foam Hollow molding polyethylene ,
The polyethylene (A) has a density of 0.935 to 0.970 g / cm ³ , a melt flow rate (MFR) of 0.1 to 55 g / 10 min at a temperature of 190 ° C. and a load of 2.16 kg, and an Mw / Mn of 3 0.5-30, melt tension (MT) is 4.0-15 cN, and polyethylene (B) has a density of 0.935-0.970 g / cm ³ , a temperature of 190 ° C. and a load of 2.16 Kg. The rate (MFR) is 0.02 to 1.0 g / 10 min, the Mw / Mn is 6.5 to 30, the melt tension (MT) is 10 to 30 cN, and the melt tension of the polyethylene (B) is polyethylene (A The foamed hollow molding polyethylene is provided.
Physical property (a): Density is 0.935 to 0.970 g / cm ³ .
Physical property (b): Melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg is 0.05 to 0.20 g / 10 min.
Physical property (c): The ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined by gel permeation chromatography (GPC) is 4.0-30.
Physical property (d): Melt tension is 6.0-25 cN.

According to the second invention of the present invention, in the first invention, the polyethylene (A) is a polyethylene produced by using a Ziegler-based catalyst or a chromium-based catalyst. Polyethylene is provided.

Further, according to a third invention of the present invention, there is provided a foamed hollow molding polyethylene according to the first or second invention, wherein the polyethylene (B) is a polyethylene produced by a chromium catalyst. The

According to the present invention, the foamed hollow molding polyethylene has a specific density, MFR, molecular weight distribution, and melt tension. Therefore, a blowing agent is added to the polyethylene and blown blown at the time of hollow molding at a specific pressure and time. Thus, a uniform and high-density foamed hollow molded product can be obtained. In particular, when a foamed hollow molding polyethylene having specific properties obtained by mixing two or more kinds of polyethylene having specific physical properties is used, a higher performance foamed hollow molded product can be obtained.
The molded foam-molded container is a container that is more rigid and difficult to deform than an unfoamed container of the same weight, and the molded container also has performance such as sound absorption and heat insulation. is there.
In foamed hollow molding, in comparison with foaming in injection molding and extrusion sheet molding, the foamable parison extruded from the die core is crushed by the mold in the process of blowing with a blow pin, and the air bubbles inside the parison are exposed to the outside. Previously, it was difficult to obtain a fine and high-density foam product due to escape, but the present invention makes it easy to perform foam molding, and the molded product is superior in terms of quality and cost. Therefore, the industrial utility is very high.

  The present invention relates to polyethylene for foamed hollow molding. Hereinafter, the configuration of the foamed hollow molding polyethylene of the present invention, the foamed hollow molded product, the molding method thereof, and the like will be described in detail.

1. Polyethylene for hollow foam molding The polyethylene for hollow hollow molding of the present invention is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms using a Ziegler catalyst, a chromium catalyst, a metallocene catalyst, a so-called post metallocene catalyst, or the like. Is obtained. A copolymer of ethylene and an α-olefin having 4 to 6 carbon atoms is preferable, and a copolymer of ethylene and 1-butene is more preferable.
The foamed hollow molding polyethylene of the present invention can be produced by a production process such as a gas phase polymerization method, a solution polymerization method, or a slurry polymerization method. Among the polymerization conditions of the ethylene polymer, the polymerization temperature can be selected from the range of 0 to 300 ° C. The polymerization pressure can be selected from the range of atmospheric pressure to about 100 kg / cm ² .

The foamed hollow molding polyethylene of the present invention may be made of a kind of polyethylene, but the MFR, the molecular weight distribution, and the melt tension are different from 10 to 95% by weight polyethylene (B) 5 to 5%. It is preferably composed of 90% by weight. Polyethylene (A) and polyethylene (B) may be polymerized separately or may be continuously polymerized by multistage polymerization. Preferred is 15 to 90% by weight of polyethylene (A), 10 to 80% by weight of polyethylene (B), more preferred is 20 to 85% by weight of polyethylene (A), 15 to 80% by weight of polyethylene (B). It consists of
When the composition ratio of the polyethylene (A) and the polyethylene (B) is out of the above range, problems such as drawdown in basic foam hollow molding and occurrence of melt fracture at high speed molding are likely to occur. Furthermore, it becomes difficult to obtain a uniform foamed molded article with respect to foaming performance, and the performance of the foamed hollow molded article is impaired. In particular, when the polyethylene (B) is less than 5% by weight, the foaming performance is deteriorated, and when it exceeds 90% by weight, the resin pressure is increased and it becomes difficult to control the resin temperature, making it difficult to obtain a stable foamable product. Problems such as generation and rough skin of the parison occur.

The foamed hollow molding polyethylene of the present invention has the following physical properties.
Physical properties of foamed hollow molding polyethylene (a): Density is 0.935 to 0.970 g / cm ³ . When the density is less than 0.935 g / cm ³ , the rigidity of the molded container is small, and it is difficult to maintain the strength of the thin product. On the other hand, a product having a density exceeding 0.970 g / cm ³ is difficult to manufacture. Here, the density is a value measured according to JIS K6922-1, 2: 1997. The density can be increased or decreased depending on the amount of α-olefin copolymerized with ethylene, and can be adjusted by changing the composition ratio of polyethylene (A) and polyethylene (B) described later.

Physical property (b) of foamed hollow molding polyethylene: MFR is 0.05 to 0.80 g / 10 min at a temperature of 190 ° C. and a load of 2.16 kg. When the MFR is less than 0.05 g / 10 min, the resin pressure and the resin temperature increase, and the moldability tends to decrease. On the other hand, if the MFR exceeds 0.80 g / 10 min, drawdown and foaming performance deteriorate. Here, MFR is a value measured according to JIS K6922-2: 1997 “Plastics—Polyethylene (PE) molding and extrusion materials—Part 2: How to make test pieces and properties”. .
MFR can be adjusted by changing the composition ratio of polyethylene (A) and polyethylene (B), which will be described later, by adjusting the ethylene polymerization temperature, the use of a chain transfer agent, or the like.

Physical property (c) of polyethylene for foam hollow molding: Mw / Mn is a ratio of weight average molecular weight (Mw) and number average molecular weight (Mn) determined by GPC, and is 4.0 to 30, preferably 5.0. -30, more preferably 6.0-25. If Mw / Mn is less than 4.0, melt fracture tends to occur, and the resin pressure tends to increase and the resin temperature tends to increase. When Mw / Mn exceeds 30, the pinch-off strength and the weld strength tend to decrease. Mw / Mn is measured by GPC by the method described later.
Mw / Mn by GPC measurement can be adjusted by the polymerization temperature and the residence time in the polymerization reactor, and can be adjusted by the temperature, pressure, shear rate, etc. of the finish extruder. Preferably, it can be increased or decreased by adjusting the composition ratio of the high molecular weight component and the low molecular weight component, polymer components having different molecular weights are produced by changing the polymerization temperature and the amount of chain transfer agent during the polymerization reaction, As a result, the molecular weight distribution of the entire polymer can be changed.

  Physical property (d) of foamed hollow molding polyethylene: Melt tension (MT) is 6.0 to 25 cN, preferably 7.0 to 23 cN, and more preferably 8.0 to 20 cN. For melt tension (MT), Capillograph 1-B manufactured by Toyo Seiki Seisakusho Ltd. was used, and the molten resin extruded at 190 ° C. and the piston speed of 10 m / min was withdrawn by 4 m / min with a capillary having a capillary diameter of 2 mm and a capillary length of 8 mm. It is determined by measuring the melt tension when it is drawn to the filament at a speed. When the melt tension is less than 6.0 cN, the foamability tends to decrease, and when it exceeds 25 cN, the resin pressure and the resin temperature tend to increase. The melt tension can be increased by introducing long chain branching into the polyethylene chain or broadening the molecular weight distribution.

2. Polyethylene (A)
The density of the polyethylene (A) is 0.935 to 0.970 g / cm ³ , preferably 0.940 to 0.965 g / cm ³ , more preferably 0.952 to 0.960 g / cm ³ . When the density is less than 0.935 g / cm ³ , the rigidity of the molded container is small, and it is difficult to maintain the strength of the thin product. On the other hand, if the density exceeds 0.970 g / cm ³ , it is difficult to produce. Here, the density is a value measured according to JIS K6922-1, 2: 1997. A desired density can be obtained by changing the density depending on the kind and amount of the comonomer copolymerized with ethylene.

The melt flow rate (MFR) of the polyethylene (A) is 0.1 to 55 g / 10 minutes, preferably 0.15 to 40 g / 10 minutes, more preferably 0.2 to 0.2 at a temperature of 190 ° C. and a load of 2.16 kg. 30 g / 10 minutes. When the MFR is less than 0.1 g / 10 min, the melt tension becomes low and the foam molding performance cannot be sufficiently exhibited. On the other hand, if the MFR exceeds 55 g / 10 min, the draw-down property at the time of hollow molding is large and the hollow molding is basically difficult. Here, MFR is a value measured according to JIS K6922-2: 1997 “Plastics—Polyethylene (PE) molding and extrusion materials—Part 2: How to make test pieces and properties”. .
MFR can be adjusted by ethylene polymerization temperature, use of a chain transfer agent, etc., and a desired thing can be obtained. That is, by increasing the polymerization temperature of ethylene and α-olefin, the molecular weight can be decreased, and as a result, the MFR can be increased. Conversely, by decreasing the polymerization temperature, the molecular weight can be increased, and as a result, the MFR can be decreased. Can do. In addition, the molecular weight can be lowered by increasing the amount of hydrogen coexisting in the copolymerization reaction of ethylene and α-olefin (chain transfer agent amount), resulting in an increase in MFR, and the amount of hydrogen coexisting (chain transfer). The molecular weight can be increased by decreasing the (drug amount), and as a result, the MFR can be reduced.

Mw / Mn of polyethylene (A) is the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined by gel permeation chromatography (GPC), preferably 3.5-30. More preferably, it is 4.0-20. If Mw / Mn is less than 3.5, melt fracture is likely to occur during high-speed extrusion, and the melt tension is low, and a fine foamed hollow molded product cannot be obtained. There is a tendency for the strength and weld strength to decrease.
Mw / Mn by GPC measurement can be adjusted by the polymerization temperature, the residence time in the polymerization reactor, the number of polymerization reactors, and the like, and can be adjusted by the temperature, pressure, shear rate, etc. of the finishing extruder. Preferably, it can be increased or decreased by adjusting the composition ratio of the high molecular weight component and the low molecular weight component, and polymer components having different molecular weights are produced by changing the polymerization temperature or the amount of the chain transfer agent during the polymerization reaction. As a result, the molecular weight distribution of the entire polymer can be changed. It is also possible to increase or decrease the molecular weight distribution by carrying out polymerization in different stages under different polymerization conditions.

The measurement conditions and measurement method of GPC, and the molecular weight calculation method are as follows.
(I) Measurement conditions GPC measurement is performed under the following conditions using a 150C model manufactured by Waters, and the weight average molecular weight (Mw) is obtained.
Column: 1 Shodex HT-G manufactured by Showa Denko KK and 2 HT-806Ms of the same Solvent: 1,2,4-trichlorobenzene Temperature: 140 ° C.
Flow rate: 1.0 ml / min Injection volume: 300 μl
(Ii) Sample preparation About 3 mg of a sample and 3.0 ml of a solvent are weighed into a commercially available 4 ml screw top vial, and shaken at a temperature of 150 ° C for 2 hours using a SSC-9300 type stirrer manufactured by Senshu Kagaku.
(Iii) Calculation of molecular weight The molecular weight is obtained by loading GPC chromatographic data into a computer at a frequency of 1 point / second and performing data processing as described in Chapter 4 of “Size Exclusion Chromatography” by Sadao Mori and Kyoritsu Publishing Co., Ltd. Calculate the Mw value.
(Iv) Column calibration Column calibration was performed by using monodisperse polystyrene (S-7300, S-3900, S-1950, S-1460, S-1010, S-565, S-152, S-66 manufactured by Showa Denko KK 0.0, S-28.5, S-5.05), n-eicosane and 0.2 mg / l each solution of n-tetracontane, a series of monodisperse polystyrene measurements were taken and their elution peaks A curve obtained by fitting the logarithm of time and molecular weight with a quartic polynomial is used as a calibration curve.
In addition, the molecular weight (MPS) of polystyrene is converted into the molecular weight (MPE) of polyethylene using the following formula.
MPE = 0.468 × MPS

  The melt tension (MT) of polyethylene (A) is 4.0 to 15 cN, preferably 5.0 to 13, and more preferably 8.0 to 12. When using the Capillograph 1-B manufactured by Toyo Seiki Seisakusho, the molten resin extruded at 190 ° C. with a piston speed of 10 m / min is drawn into a filament at a take-up speed of 4 m / min with a capillary having a capillary diameter of 2 mm and a capillary length of 8 mm. It is calculated | required by measuring melt tension of this. When the melt tension is less than 4.0 cN, the foamability tends to decrease, and when it exceeds 15 cN, the resin pressure and the resin temperature tend to increase. The melt tension can be increased by introducing long chain branching into the polyethylene chain or broadening the molecular weight distribution.

The polyethylene (A) is preferably a copolymer obtained by copolymerizing ethylene and an α-olefin having 4 to 8 carbon atoms using a Ziegler catalyst or a chromium catalyst, and more preferably ethylene and 1-butene. It is a copolymer.
Polyethylene (A) can be produced by a production process such as a gas phase polymerization method, a solution polymerization method, or a slurry polymerization method. Among the polymerization conditions for the ethylene polymer, the polymerization temperature can be selected from the range of 0 to 300 ° C. The polymerization pressure can be selected from the range of atmospheric pressure to about 100 kg / cm ² .

3. Polyethylene (B)
The polyethylene (B) has a density of 0.935 to 0.970 g / cm ³ , preferably 0.938 to 0.960 g / cm ³ , more preferably 0.940 to 0.958 g / cm ³ . When the density is less than 0.935 g / cm ³ , the rigidity of the molded container is small, and it is difficult to maintain the strength of the thin product. On the other hand, if the density exceeds 0.970 g / cm ³ , it is difficult to produce. Here, the density is a value measured according to JIS K6922-1, 2: 1997.

  The MFR of polyethylene (B) is 0.02 to 1.0 g / 10 min, preferably 0.03 to 0.8 g / 10 min, more preferably 0.05 to 0 at a temperature of 190 ° C. and a load of 2.16 kg. .6 g / 10 min. When the MFR is less than 0.02 g / 10 min, the dispersibility is deteriorated and a gelled product is easily obtained. On the other hand, when the MFR exceeds 1.0 g / 10 min, the melt tension is lowered and good foaming performance cannot be exhibited. Here, MFR is a value measured according to JIS K6922-2: 1997 “Plastics—Polyethylene (PE) molding and extrusion materials—Part 2: How to make test pieces and properties”. .

In the polyethylene (B), the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) determined by GPC is preferably 6.5 to 30, more preferably 8.0. 25. When Mw / Mn is less than 6.5, melt fracture tends to occur during high-speed extrusion, and when it exceeds 30, pinch-off strength and weld strength tend to decrease. Mw / Mn is measured by GPC in the same manner as described above.
Mw / Mn by GPC measurement can be adjusted by the polymerization temperature and the residence time in the polymerization reactor, and can be adjusted by the temperature, pressure, shear rate, etc. of the finish extruder. Preferably, it can be increased or decreased by adjusting the composition ratio of the high molecular weight component and the low molecular weight component, polymer components having different molecular weights are produced by changing the polymerization temperature and the amount of chain transfer agent during the polymerization reaction, As a result, the molecular weight distribution of the entire polymer can be changed.

The melt tension (MT) of polyethylene (B) is 10 to 30 cN, preferably 12 to 28 cN, and more preferably 15 to 25 cN. When a Capillograph 1-B manufactured by Toyo Seiki Seisakusho was used and extruded with a capillary having a capillary diameter of 2 mm and a capillary length of 8 mm at 190 ° C. and a piston speed of 10 m / min. It is calculated | required by measuring melt tension of this. When the melt tension is less than 10 cN, the foamability tends to decrease, and when it exceeds 30 cN, the resin pressure and the resin temperature tend to increase. The melt tension can be increased by introducing long chain branching into the polyethylene chain or widening the molecular weight distribution.
The melt tension (MT) of the polyethylene (B) is preferably larger than the melt tension (MT) of the polyethylene (A). When the melt tension (MT) of polyethylene (B) is the same as or smaller than the melt tension (MT) of polyethylene (A), there is a problem that it is difficult to obtain a product having a fine closed-cell foam.

The polyethylene (B) is preferably a copolymer obtained by copolymerizing ethylene and an α-olefin having 4 to 8 carbon atoms using a chromium catalyst, and more preferably a copolymer of ethylene and 1-butene. is there. Compared to Ziegler catalyst-produced polyethylene, chromium catalyst-produced polyethylene has high melt tension and is suitable for foam molding, and also has a high crystallization temperature and a high crystallization speed. In the foaming process in the mold at the time of molding, the surface and inner surface layers solidify quickly, and there is little escape of bubbles in the parison due to being pressed by the blow pressure, and it is easy to obtain a container that is fine and highly foamed and has good moldability It has characteristics.
Polyethylene (B) can be produced by a production process such as a gas phase polymerization method, a solution polymerization method, or a slurry polymerization method. Among the polymerization conditions for the ethylene polymer, the polymerization temperature can be selected from the range of 0 to 300 ° C. The polymerization pressure can be selected from the range of atmospheric pressure to about 100 kg / cm ² .

  As described above, the foamed hollow molding polyethylene composition of the present invention has a ratio (Mw / Mn) of weight average molecular weight (Mw) and number average molecular weight (Mn) determined by GPC of 4.0 to 30, It is preferable that it is 5.0-30. When Mw / Mn is less than 4.0, the foaming performance at the time of hollow molding tends to be lowered, and when it exceeds 30, pinch-off strength and weld strength tend to be lowered. Mw / Mn is measured by GPC in the same manner as described above.

As described above, the present invention is a foamed hollow molding polyethylene composition having a specific density, MFR, molecular weight distribution, and melt tension, and particularly polyethylene (A) and polyethylene (B) having different MFR, molecular weight distribution, and melt tension. ) Is blended at a specific ratio, the foamed state and weld state during foam blow molding, the surface state of the molded product, and the moldability are good, and many of these required properties are balanced at excellent levels. Can be achieved well.
On the other hand, in the case of conventional polyethylene, even if one kind of polyethylene is used or two kinds of polyethylene are selected, the selection is not preferable. Since it is not easy to obtain, the technical advantage of the present invention is clear.

4). Optional component In addition, the foamed hollow molding polyethylene of the present invention includes other olefin polymers and rubbers, as well as antioxidants, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, anti-static agents, in accordance with conventional methods. Clouding agent, anti-blocking agent, processing aid, color pigment, pearl pigment, glittering material, polarizing pearl pigment, crosslinking agent, foaming agent, neutralizing agent, heat stabilizer, crystal nucleating agent, inorganic or organic filler, flame retardant A known additive such as can be blended. Regarding blending of color pigments, etc., a necessary amount may be added to the base resin to form a compound, or a master batch with a high concentration added may be post-blended. The crystal nucleating agent may be added during molding in a master batch.

  Specifically, as an additive, for example, an antioxidant (phenolic, phosphorus, sulfur), a lubricant, an antistatic agent, a light stabilizer, an ultraviolet absorber, etc. is selected, and one or two or more kinds are appropriately used in combination. can do. As the filler, calcium carbonate, talc, metal powder (aluminum, copper, iron, lead, etc.), silica, diatomaceous earth, alumina, gypsum, mica, clay, asbestos, graphite, carbon black, titanium oxide, etc. can be used. . In any case, the foamed hollow molding polyethylene of the present invention can be blended with various additives as necessary, and kneaded with a kneading extruder, Banbury mixer, or the like to obtain a molding material.

5. Molding method In the foamed hollow molding polyethylene of the present invention, a physical foaming agent and / or a chemical foaming agent is used as the foaming agent to be added to form the foamed layer of the foamed parison, preferably a chemical foaming agent is used. Is done.
Examples of the physical foaming agent include aliphatic hydrocarbons such as propane, n-butane, i-butane, cyclobutane, n-pentane, i-pentane, cyclopentane, n-hexane, i-hexane, cyclohexane, and methyl chloride. Halogenated hydrocarbons such as ethyl chloride, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, alcohols such as methanol and ethanol, ethers such as dimethyl ether, diethyl ether and methyl ethyl ether, dioxide Examples thereof include carbon, nitrogen, argon, and water. Examples of the chemical foaming agent include sodium hydrogen carbonate and azodicarbonamide. These foaming agents can be used alone or mixed with other foaming agents. In the present invention, among these foaming agents, sodium hydrogen carbonate or a mixture of sodium hydrogen carbonate and azodicarbonamide is preferable from the viewpoint of expansion ratio.

  The amount of the foaming agent used is appropriately determined in consideration of the desired apparent density (foaming ratio). Generally, the physical foaming agent is in a proportion of 0.01 to 1.2 mol with respect to 1 kg of polyethylene. 0.2 to 0.6 g of chemical foaming agent is used.

  In addition, a bubble regulator such as talc is added to the polyethylene. The cell regulator is generally used in the form of a masterbatch with a base resin mainly composed of polyethylene. The amount of the air bubble regulator used is usually 0.05 to 10 parts by weight with respect to 100 parts by weight of polyethylene.

  Furthermore, if necessary, various additives and the like are blended and pelletized by mechanical melt mixing with a pelletizer or homogenizer according to a conventional method, and then molded by various molding machines to obtain a desired molded product. it can. Various molding methods can be employed, and foamed hollow molding is preferable, and foamed multistage blow molding is particularly preferably used. The conditions for foamed hollow molding are not particularly limited, but conventionally known conditions can be employed using a conventionally known hollow molding apparatus.

  The foamed hollow molding polyethylene of the present invention has a parison temperature of 150 to 230 ° C., a mold temperature of 20 ° C., a low pressure blow pressure of 0.01 to 0.29 MPa after extrusion of the parison for 1 to 15 seconds, and then a high pressure blow pressure of 0.30. -0.60 MPa is molded in 5 to 30 seconds. Preferably, blow is performed for 1 to 10 seconds at a low pressure blow pressure of 0.05 to 0.20 MPa after the parison extrusion, and then the high pressure blow pressure is set to 0.40 to 0.55 MPa and molding is performed for 10 to 15 seconds. If it is out of the above range, the foamed bubbles in the parison are not enlarged, and a highly foamed molded product cannot be obtained.

6). Molded product The foamed hollow molding polyethylene of the present invention can be used for producing containers such as cosmetics, detergents, foods and beverages by foaming hollow molding, but is not limited thereto, and can be used for various product applications. is there.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist. The measurement methods and materials used in the examples are as follows.

1. Measuring method (1) Density The density was measured according to JIS K6922-1 and 2: 1997.
(2) Melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg
Measured according to JIS K6922-2: 1997.
(3) GPC measurement conditions and measurement method, and molecular weight calculation method (i) Measurement conditions GPC measurement was carried out under the following conditions using a 150C model manufactured by Waters, and the weight average molecular weight (Mw) was determined.
Column: 1 Shodex HT-G manufactured by Showa Denko KK and 2 HT-806Ms of the same Solvent: 1,2,4-trichlorobenzene Temperature: 140 ° C.
Flow rate: 1.0 ml / min Injection volume: 300 μl
(Ii) Sample preparation Approximately 3 mg of a sample and 3.0 ml of a solvent were weighed into a commercially available 4 ml screw top vial, and shaken at a temperature of 150 ° C for 2 hours using a SSC-9300 type stirrer manufactured by Senshu Kagaku.
(Iii) Calculation of molecular weight GPC chromatographic data is loaded into a computer at a frequency of 1 point / second, processed according to the description in Chapter 4 of “Size Exclusion Chromatography” published by Sadao Mori and Kyoritsu Publishing Co. Was calculated.
(Iv) Column calibration Column calibration was performed by using monodisperse polystyrene (S-7300, S-3900, S-1950, S-1460, S-1010, S-565, S-152, S-66 manufactured by Showa Denko KK 0.0, S-28.5, S-5.05), n-eicosane and 0.2 mg / l each solution of n-tetracontane, a series of monodisperse polystyrene measurements were taken and their elution peaks A curve obtained by fitting a logarithmic relationship between time and molecular weight with a quartic polynomial was used as a calibration curve.
In addition, the molecular weight (MPS) of polystyrene was converted into the molecular weight (MPE) of polyethylene using the following formula.
MPE = 0.468 × MPS

(4) Melt Tension Using a Capillograph 1-B manufactured by Toyo Seiki Seisakusho, molten resin extruded at 190 ° C. and a piston speed of 10 m / min with a capillary having a capillary diameter of 2 mm and a capillary length of 8 mm at a take-up speed of 4 m / min. The melt tension when taken up by the filament was measured.
(5) Flexural modulus Measured according to JIS K-6922-2 by press molding.
(6) Crystallization temperature Using DCS7 manufactured by Parking Elma, 10 mmg of sample resin was placed in an aluminum pan, heated to 210 ° C, held for 5 minutes, and then cooled to 40 ° C at a rate of 10 ° C / min. .
(7) Molding state and comprehensive evaluation The molding results were evaluated by visual observation of the foamed state, the welded state, the surface state, and the moldability. The foamed state was evaluated as “◯” when uniformly foamed, “Δ” when there was a non-uniform portion, and “X” when it was non-uniform. In addition, the weld state was evaluated as “Good”, “Slightly thin” as Δ, and “Thin” as ×. In addition, the surface condition was evaluated as “Good”, “Slightly uneven” as “B”, and “Poor” as “B”. Furthermore, the moldability (container shape retention) was evaluated as “good”, “not partially molded” as Δ, and poor (including puncture) as “poor”.
In addition, as a comprehensive evaluation, “Good” indicates that all are good, “Δ” indicates almost good, and “Poor” indicates that one is poor or slightly inferior.

2. Resin used As polyethylene (A) and polyethylene (B), physical properties A-1 to A-7 and B-1 to B-4 shown in Table 1 were used.

(Examples 1-14)
Polyethylene (A) and polyethylene (B) having physical properties shown in Table 1 were mixed to prepare foamed hollow molding polyethylene of the present invention.
Next, using an electric blow molding machine having a screw diameter of 70 mmφ, a die diameter of 17 mmφ (straight), and a core diameter (divergent) of 16 mmφ, a resin and a foaming agent shown in Table 2 using a mold of a 250 ml flat shape bottle The parison was melt-kneaded at a measured resin temperature of 210 ° C. or 160 ° C. by master batch blending, and the extruded parison was blow-molded under the conditions shown in Table 3. The mold size of the flat bottle is as follows: body length: 110 mm, maximum body width 70 mm, minimum body width 48 mm, average body thickness 1.1 mm, cylindrical mouth length 22 mm The maximum diameter of the cylindrical mouth portion was 26 mm, and the inner diameter of the cylindrical mouth portion was 19 mm.
At the time of molding, various evaluations were performed after molding, and the results are shown in Table 3.
Example 13 is a reference example.

(Comparative Examples 1 to 13)
Polyethylene (A) and polyethylene (B) having physical properties shown in Table 1 were used alone or mixed to prepare a comparative foamed hollow molding polyethylene. Next, in the same manner as in Examples, the resin and foaming agent master batch shown in Table 2 were melt-kneaded at an actually measured resin temperature of 210 ° C. or 160 ° C., and the extruded parison was blow-molded under the conditions shown in Table 3.
Various evaluations were performed during molding and after molding, and the results are shown in Table 3.

3. Evaluation As is apparent from Table 3 showing the molding conditions and molding results of Examples and Comparative Examples, in Examples 1 to 14, the foamed hollow molding of the present invention consisting of specific polyethylene (A) and polyethylene (B) is used. Since polyethylene is used, the container formed by adding the foaming agent MB has good foamed state, welded state, surface state, and moldability.
On the other hand, in Comparative Examples 1 to 13, any one of polyethylene (A) and polyethylene (B) is used alone, or a mixed foamed hollow molding polyethylene is used, and the physical properties deviate from the present invention. At least any one of the weld state, the surface state, and the moldability was not good, and a good molded product could not be obtained. From this, it is clear that the polyethylene for foamed hollow molding of the present invention has excellent characteristics for foaming hollow molding of containers.

  The polyethylene for foamed hollow molding of the present invention has high foamability, good moldability, mechanical strength, good surface appearance, and excellent durability, and has improved heat insulation, sound absorption, rigidity, cosmetics, detergents, It is suitable for manufacturing lightweight containers such as food and beverages, and has high industrial applicability.

Claims (3)

A foamed hollow molding polyethylene comprising 10 to 95% by weight of polyethylene (A) and 5 to 90% by weight of polyethylene (B ) and satisfying the following physical properties (a) to (d),
The polyethylene (A) has a density of 0.935 to 0.970 g / cm ³ , a melt flow rate (MFR) of 0.1 to 55 g / 10 min at a temperature of 190 ° C. and a load of 2.16 kg, and an Mw / Mn of 3 0.5-30, melt tension (MT) is 4.0-15 cN, and polyethylene (B) has a density of 0.935-0.970 g / cm ³ , a temperature of 190 ° C. and a load of 2.16 Kg. The rate (MFR) is 0.02 to 1.0 g / 10 min, the Mw / Mn is 6.5 to 30, the melt tension (MT) is 10 to 30 cN, and the melt tension of the polyethylene (B) is polyethylene (A And a foamed hollow molding polyethylene characterized by being larger than .
Physical property (a): Density is 0.935 to 0.970 g / cm ³ .
Physical property (b): Melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg is 0.05 to 0.20 g / 10 min.
Physical property (c): The ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined by gel permeation chromatography (GPC) is 4.0-30.
Physical property (d): Melt tension (MT) is 6.0 to 25 cN.   2. The foamed hollow molding polyethylene according to claim 1, wherein the polyethylene (A) is a polyethylene produced using a Ziegler catalyst or a chromium catalyst. The polyethylene for foaming hollow molding according to claim 1 or 2 , wherein the polyethylene (B) is a polyethylene produced by a chromium-based catalyst.