Ethylene-based polymer

Abstract

To provide an ethylene-based polymer capable of forming a hollow molded body with less surface roughness.SOLUTION: An ethylene-based polymer has a density of 910 to 940 kg / m3, a melt flow rate of 0.1 to 10 g / 10 min measured under the conditions of a temperature of 190°C and a load of 21.18 N, a die swell ratio of 1.20 to 1.40 measured under the condition of a temperature of 190°C, and a relaxation time of 0.5 to 10 seconds measured under the condition of a temperature of 170°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to ethylene-based polymers. [Background technology]

[0002] Ethylene-based polymers are processed into hollow molded articles such as hollow containers by blow molding (for example, Patent Document 1). The hollow molded articles are used as various industrial materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-203983 A Summary of the Invention [Problem to be solved by the invention]

[0004] In particular, in the case of a hollow molded article for use in applications where it is likely to be visible to humans or in applications where it will come into contact with the skin, it is desirable that the surface roughness of the hollow molded article formed during blow molding of an ethylene-based polymer be as small as possible from the viewpoints of the appearance and feel of the hollow molded article.

[0005] The present disclosure relates to an ethylene-based polymer capable of forming a hollow molded article having a minimal surface roughness. [Means for solving the problem]

[0006] The present disclosure includes the following. [1] 910~940kg / m 3 and the density of Melt strength of 0.1 to 10g / 10min measured at 190℃ and 21.18N load. and A die swell ratio of 1.20 to 1.40 measured at a temperature of 190°C; An ethylene-based polymer having a relaxation time of 0.5 to 10 seconds measured at a temperature of 170°C. [2] The ethylene polymer according to [1], which has a molecular weight distribution of 3.0 to 4.0. [3] The ethylene-based polymer according to [1] or [2], wherein the ethylene-based polymer is obtained by a high-pressure radical polymerization method. [4] The ethylene polymer according to any one of [1] to [3], which is for blow molding. [5] The ethylene polymer according to any one of [1] to [4], which is for blow-fill-seal molding. Effect of the Invention

[0007] An ethylene-based polymer capable of forming a hollow molded article having a less rough surface can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention is not limited to the following examples.

[0009] An example of an ethylene polymer is 910 to 940 kg / m 3 It has a density of 0.1 to 10 g / 10 min measured under conditions of a temperature of 190°C and a load of 21.18 N, a die swell ratio of 1.20 to 1.40 measured under conditions of a temperature of 190°C, and a relaxation time of 0.5 to 10 seconds measured under conditions of a temperature of 170°C.

[0010] The ethylene-based polymer is a homopolymer of ethylene (i.e., an ethylene polymer) or a copolymer containing a monomer unit based on ethylene. The copolymer may be, for example, an ethylene-α-olefin copolymer. From the viewpoint of improving moldability, the ethylene-based polymer may be a homopolymer of ethylene.

[0011] The number of carbon atoms of the α-olefin in the ethylene-α-olefin copolymer may be 3 to 20, 3 to 14, or 3 to 8. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4-methyl-1-pentene, and 4-methyl-1-hexene. The α-olefin may be used alone or in combination of two or more kinds.

[0012] The content of monomer units based on ethylene (ethylene units) in the copolymer containing monomer units based on ethylene may be 50 mass% or more, 70 mass% or more, 75 mass% or more, or 79 mass% or more, and may be 99.5 mass% or less, 95 mass% or less, 92 mass% or less, or 89 mass% or less, relative to the total mass of the copolymer containing monomer units based on ethylene.

[0013] The content of monomer units based on an α-olefin in the copolymer containing monomer units based on ethylene may be 0.5 mass% or more, 5 mass% or more, 8 mass% or more, or 11 mass% or more, and may be 50 mass% or less, 30 mass% or less, 25 mass% or less, or 21 mass% or less, relative to the total mass of the copolymer containing monomer units based on ethylene.

[0014] The ethylene-based polymer may have monomer units based on other monomers in addition to monomer units based on ethylene and α-olefins. Examples of the other monomers include conjugated dienes (e.g., butadiene and isoprene), non-conjugated dienes (e.g., 1,4-pentadiene), acrylic acid, acrylic acid esters (e.g., methyl acrylate and ethyl acrylate), methacrylic acid, methacrylic acid esters (e.g., methyl methacrylate and ethyl methacrylate), and vinyl acetate.

[0015] Examples of ethylene-based polymers include ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-octene copolymers, ethylene-1-butene-1-hexene copolymers, ethylene-1-butene-4-methyl-1-pentene copolymers, and ethylene-1-butene-1-octene copolymers.

[0016] The density of ethylene polymers is 910 to 940 kg / m 3 The density of the ethylene polymer is set to 915 kg / m from the viewpoint of increasing the rigidity of the molded body and reducing deformation of the molded body due to load. 3 or more than 920kg / m 3 The density of the ethylene polymer may be 935 kg / m or more from the viewpoint of improving the transparency of the molded article and increasing the impact strength of the molded article. 3 or less than 925kg / m 3 The density of the polyethylene resin means a value measured according to the method specified in Method A of JIS K7112-1980.

[0017] The melt flow rate (MFR) of the ethylene polymer is 0.1 to 10 g / 10 min. The MFR of the ethylene polymer may be 0.2 g / 10 min or more, or 0.5 g / 10 min or more, from the viewpoint of improving moldability, improving molding stability, and reducing the load during extrusion. The MFR of the ethylene polymer may be 6.0 g / 10 min or less, 5.5 g / 10 min or less, 2.0 g / 10 min or less, or 1.0 g / 10 min or less, from the viewpoint of improving the mechanical strength of the molded product. The MFR of the ethylene polymer means a value measured by Method A under the conditions of a load of 21.18 N and a temperature of 190° C. in the method specified in JIS K7210-1995.

[0018] The die swell ratio (SR) of the ethylene polymer is 1.20 to 1.40. From the viewpoint of improving moldability, the SR of the ethylene polymer may be 1.25 or more, 1.30 or more, or 1.35 or more. From the viewpoint of the appearance of the obtained molded product, the SR of the ethylene polymer may be 1.37 or less. The SR of the ethylene polymer means a value obtained by dividing the diameter of the strand at a position about 5 mm from the upstream end of the extrusion of the strand extruded under the same conditions as those for measuring the melt flow rate by the orifice diameter. Specifically, the SR of the ethylene polymer can be calculated by the method described in the Examples below.

[0019] The relaxation time of the ethylene polymer is 0.5 to 10 seconds. From the viewpoint of improving moldability, the relaxation time of the ethylene polymer may be 0.5 seconds or more, 4 seconds or more, 5 seconds or more, or 6 seconds or more. From the viewpoint of the appearance of the obtained molded product, the relaxation time of the ethylene polymer may be 9.0 seconds or less, 7.5 seconds or less, or 7.0 seconds or less. The relaxation time of the ethylene polymer means a value calculated by fitting a complex viscosity-angular frequency curve obtained by frequency dispersion measurement using a strain-controlled rotational viscometer under the conditions of a temperature of 170°C, a strain of 5%, and an angular frequency of 100 to 0.1 rad / s (measurement at 10 logarithmically equal intervals per digit) with the following formula (1). Specifically, the relaxation time of the ethylene polymer can be calculated by the method described in the Examples below.

[0020]

number

[0021] In formula (1), η * where (Pa·sec) is the complex viscosity, η0 (Pa·sec) is the zero shear viscosity, ω (rad / sec) is the angular frequency, τ (sec) is the relaxation time, and n (unitless) is the non-Newtonian exponent.

[0022] The molecular weight distribution Mw / Mn (MWD) of the ethylene polymer may be 3.0 to 4.0. The MWD of the ethylene polymer may be 3.3 or more, or 3.5 or more, from the viewpoint of improving moldability and reducing the load during extrusion. The MWD of the ethylene polymer may be 3.9 or less, from the viewpoint of improving the mechanical strength of the molded product. The MWD of the ethylene polymer means a value calculated from the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by a gel permeation chromatography (GPC) method. Specifically, the MWD of the ethylene polymer can be calculated by the method described in the examples below.

[0023] The ethylene-based polymer may be produced by a high-pressure radical polymerization method. In the high-pressure radical polymerization method, for example, a tubular reactor is used to radically polymerize ethylene in the presence of a radical generator and a chain transfer agent by appropriately setting the temperature and pressure. The density, MFR, SR, relaxation time, and MWD of the resulting ethylene-based polymer can be adjusted by adjusting the type and amount of the radical generator and the chain transfer agent, the temperature, and the pressure. The density of the ethylene-based polymer can be adjusted mainly based on the temperature and pressure. The MFR of the ethylene-based polymer can be adjusted mainly based on the type and amount of the chain transfer agent. The SR of the ethylene-based polymer can be adjusted mainly based on the temperature and pressure. The relaxation time of the ethylene-based polymer can be adjusted mainly based on the temperature and pressure. The MWD of the ethylene-based polymer can be adjusted mainly based on the temperature and pressure.

[0024] Examples of the radical generator include t-butylperoxyisopropyl carbonate, t-butylperoxypivalate, and t-butylperoxy-2-ethylhexanate. The radical generator may be used alone or in combination of two or more. The radical generator may be supplied to the reaction system as a solution using n-heptane as a solvent.

[0025] Examples of chain transfer agents include propane, ethane, and propylene.

[0026] The ethylene-based polymer may be for blow molding or for blow-fill-seal molding. By blow molding or blow-fill-seal molding using the ethylene-based polymer, a hollow molded article having a less rough surface can be easily formed.

[0027] The blow molding may be, for example, direct blow molding. Direct blow molding includes, for example, extruding an ethylene-based polymer from a die of an extrusion blow molding machine to form a tubular parison, sandwiching the parison between a mold having a cavity of a shape corresponding to the hollow molded body, and then blowing pressurized gas into the parison. The parison is shaped into a shape that conforms to the mold cavity by the pressure of the pressurized gas, and is cooled. Thereafter, the mold is opened to eject the hollow molded body.

[0028] The blow-fill-seal molding includes, for example, molding an ethylene-based polymer by the above-mentioned direct blow molding to form a hollow molded body having a mouth in a mold, and then filling the hollow molded body with a liquid product in the same mold and then sealing the mouth.

[0029] The molding stability index of the hollow molded article of the ethylene-based polymer may be 3 or less, 1.5 or less, or 0.5 or less. The molding stability index of the hollow molded article of the ethylene-based polymer means a value calculated from the weights of three arbitrary hollow molded articles produced by the same method by measuring the weights of these three articles using the following formula (2). The smaller the molding stability index, the higher the molding stability. Forming stability index = (maximum weight - minimum weight) / average weight x 100 (2)

[0030] The hollow molded body may be a hollow container. The hollow container usually has a mouth for putting in and taking out the contents. The mouth may form an opening, in which case a removable lid may be attached to the mouth. Alternatively, the hollow container may be a sealed container having a sealed mouth. When the hollow container is formed by blow-fill-seal molding, a liquid-sealed container can be formed that includes the hollow container and a liquid product contained in the hollow container.

[0031] The hollow container is not particularly limited in its use, but is particularly useful as a food container or a medical container. The food container may be, for example, a container for storing liquid products such as mayonnaise, ketchup, sauce, dressing, honey, jam, soft drinks, popsicles, etc. The medical container may be a container for storing liquid products such as blood components, physiological saline, electrolytes, dextran preparations, mannitol preparations, sugar preparations, amino acid preparations, fat emulsions, eye drops, and liquid foods. EXAMPLES

[0032] The present invention will be described in detail below with reference to examples. However, the present invention is limited to the following examples. Not limited to this.

[0033] 1. Ethylene polymers Using a tubular reactor, ethylene polymers of Samples 1 to 5 were produced by high-pressure radical polymerization while appropriately adjusting the pressure, temperature, and the types and amounts of the radical generator and chain transfer agent. An ethylene / 1-butene copolymer of Sample 6 was produced by high pressure ionic polymerization using a tank type reactor.

[0034] 2. Evaluation of ethylene polymers Melt Flow Rate (MFR) In the method specified in JIS K7210-1995, the MFR (g / 10 min) of the ethylene polymer was measured under conditions of a load of 21.18 N and a temperature of 190° C. by Method A.

[0035] Die swell ratio (SR) Under the same conditions as in the measurement of the melt flow rate, a strand extruded from the orifice with a length of about 15 to 20 mm was cooled in air to obtain a solid strand. Next, the diameter D (unit: mm) of the strand was measured at a position about 5 mm from the upstream tip of the extrusion of the strand. The value (D / D0) obtained by dividing the diameter D by the orifice diameter of 2.095 mm (D0) was taken as SR.

[0036] Molecular weight distribution Mw / Mn(MWD) The weight average molecular weight Mw and number average molecular weight Mn of the ethylene polymer were measured in terms of standard polystyrene using gel permeation chromatography (GPC) under the following conditions (1) to (8). The value obtained by dividing the obtained Mw by the obtained Mn (Mw / Mn) was taken as the MWD of the ethylene polymer. The baseline on the chromatogram was a straight line connecting the points of a stable horizontal region with a retention time sufficiently shorter than the appearance of the elution peak of the ethylene polymer and the points of a stable horizontal region with a retention time sufficiently longer than the observation of the solvent elution peak. (1) Apparatus: Waters 150C, manufactured by Waters (2) Separation column: TOSOH TSKgelGMH6-HT (3) Measurement temperature: 140℃ (4) Carrier: o-dichlorobenzene (5)Flow rate: 1.0mL / min (6) Injection volume: 500μL (7) Detector: Differential refraction (8) Molecular weight standard: standard polystyrene

[0037] density The density of the ethylene polymer was measured according to the method specified in Method A of JIS K7112-1980.

[0038] Relaxation time A test piece of the ethylene polymer for measurement was prepared using a heat press. More specifically, the ethylene polymer was preheated at 150° C. for 5 minutes, pressurized at 5 MPa at 150° C. for 5 minutes, and then cooled at 25° C. for 5 minutes to obtain a test piece for measurement having a thickness of about 1 mm and a diameter of about 25 mm. The obtained test piece was subjected to frequency dispersion measurement using a strain-controlled rotational viscometer ARES-G2 (manufactured by TA Instruments) to calculate the relaxation time. More specifically, a parallel plate was attached to the device, and the jig part including the parallel plate was preheated at a temperature of 170°C for about 30 minutes. The test piece was attached to the preheated jig and left to stand for about 5 minutes. Then, the gap of the parallel plate was adjusted to about 1 mm, and the test piece was left to stand for about 5 minutes. Then, the frequency dispersion measurement was performed under the conditions of a temperature of 170°C, a strain of 5%, and an angular frequency of 100 to 0.1 rad / s (10 points measured at equal logarithmic intervals per digit). The obtained complex viscosity-angular frequency curve was fitted with the above formula (1) to calculate the relaxation time (seconds). The fitting was performed so that d in the following formula (3) was minimized.

[0039]

number

[0040] In formula (3), η exp * (ω) (Pa·sec) is the measured complex viscosity, η calc * (ω) (Pa sec) is the complex viscosity η in the above equation (1) after fitting. * It is.

[0041] 3. Evaluation of blow moldability A 500 ml hollow container for mayonnaise with a 250 μm deep relief for designing was produced from an ethylene-based polymer by direct blow molding using a Tahara MSE-55E / 54M-A(E1) hollow molding machine. More specifically, an elliptical die with a major axis of 14.95 mm and a minor axis of 14.80 mm and a circular core with an outer diameter of 14.30 mm were used, and an ethylene-based polymer was extruded to form a cylindrical hot parison by adjusting the opening between the die and the core under the conditions of a crosshead temperature of 155° C. and a die temperature of 155° C. The hot parison was immediately sandwiched between a mold at 20° C. having a cavity shaped to correspond to the above mayonnaise container, and compressed air was blown into the hot parison to obtain a hollow container.

[0042] Formability The appearance of the hollow container was visually observed, and the moldability was evaluated according to the following evaluation criteria. A hollow container that satisfies the "good appearance" criteria is a hollow container with almost no visible roughness on the surface, or a hollow container with no visible roughness on the surface. 1: Appearance is good 2: Slightly rough surface 3: The surface is very rough. 4: Unable to mold

[0043] Molding stability The weights of three randomly selected hollow containers were measured, and the molding stability index was calculated from these three weights using the above formula (2).

[0044] [Table 1]

[0045] The evaluation results are shown in Table 1. 910-940kg / m 3It was confirmed that the ethylene polymers of Examples 1 to 3, each having a density of 0.1 to 10 g / 10 min measured under conditions of a temperature of 190° C. and a load of 21.18 N, a die swell ratio of 1.20 to 1.40 measured under conditions of a temperature of 190° C., and a relaxation time of 0.5 to 10 seconds measured under conditions of a temperature of 170° C., exhibit good moldability.

Claims

1. 910-940kg / m ３ and the density of A melt flow rate of 0.1 to 10 g / 10 min measured under conditions of a temperature of 190° C. and a load of 21.18 N; A die swell ratio of 1.20 to 1.40 measured at a temperature of 190° C.; The ethylene polymer has a relaxation time of 0.5 to 10 seconds measured at a temperature of 170°C.

2. The ethylene polymer according to claim 1, having a molecular weight distribution of 3.0 to 4.

0.

3. The ethylene-based polymer according to claim 1 or 2, which is an ethylene-based polymer obtained by a high-pressure radical polymerization method.

4. The ethylene polymer according to claim 1 or 2, which is for blow molding.

5. The ethylene polymer according to claim 1 or 2, which is for blow-fill-seal molding.

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