Pyrolysis polyethylene wax and method for producing the same

Abstract

To provide a polyethylene wax exhibiting high fluidity during melt-kneading and high reactivity with a resin containing a polar group such as a hydroxyl group.SOLUTION: A polyethylene wax satisfies the following conditions (1)-(3). (1) The number average molecular weight measured by gel permeation chromatography (GPC) is 500 or more and 8,000 or less. (2) The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), measured by GPC, is 1.0 or more and less than 3.5. (3) The number of intramolecular double bonds per molecule is 0.4 or more and less than 2.0, and the ratio of the number of intramolecular double bonds per molecule to the number of terminal double bonds is 1.0 or more and less than 10.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to pyrolyzed polyethylene wax and a method for producing the same.

Background Art

[0002] Low molecular weight polymers with a molecular weight of 10,000 or less exhibit physical and chemical properties different from those of general polymers with a molecular weight of tens of thousands to hundreds of thousands. Among them, polyolefin waxes such as low molecular weight polyethylene and low molecular weight polypropylene are widely used as viscosity regulators for polyolefins, which account for a large part of the plastics produced, molding processing aids for polyvinyl chloride and engineering plastics, additives for inks or paints, pigment dispersants, additives for hot melt adhesives, and the like. The synthesis methods of polyethylene wax include a polymerization method and a pyrolysis method. As the polymerization method, polyethylene wax synthesized by a high-pressure polymerization production method (for example, see Patent Document 1) and an ultra-low molecular weight ethylene polymer synthesized by a solution polymerization method (for example, see Patent Document 2) are disclosed. As the pyrolysis method, pyrolyzed low molecular weight polyolefin (for example, see Patent Document 3) is disclosed. Thus, polyethylene wax produced by various synthesis methods can be adjusted to a higher molecular weight than natural wax, and thus has excellent mechanical strength and heat resistance, and can be utilized in applications where these physical properties are required. In particular, the pyrolysis method is useful from the viewpoint of environmental consideration because it can contribute to the resource circulation of used polyethylene.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the pyrolyzed polyethylene wax has a broader molecular weight distribution compared to the polymerized polyethylene wax, it has been a problem that its heat resistance and mechanical properties are inferior. Furthermore, since the terminal double bonds generated by the pyrolysis of polyethylene are chemically unstable, there have been problems such as inducing radical reactions during high-temperature processing in the atmosphere.

[0005] Therefore, an object of the present invention is to provide a pyrolyzed polyethylene wax having a narrower molecular weight distribution and lower reactivity than conventional ones, and a method for producing the same.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that a specific pyrolyzed polyethylene wax has a narrow molecular weight distribution and fewer terminal double bonds compared to chemically stable internal double bonds, and have completed the present invention.

[0007] That is, each aspect of the present invention is as follows [1] to [4]. [1] A polyethylene wax satisfying (1) to (3). (1) The number average molecular weight measured by gel permeation chromatography (GPC) is 500 or more and 8,000 or less. (2) The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by GPC is 1.0 or more and less than 3.5 (3) The number of internal double bonds per molecule is 0.4 or more and less than 2.0, and the ratio of the number of internal double bonds per molecule to the number of terminal double bonds is 1.0 or more and less than 10. [2] A method for producing the polyethylene wax according to [1], wherein a polyethylene resin having a ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by GPC of 1.0 or more and less than 6.0 is pyrolyzed. [3] The method for producing polyethylene wax according to [2], wherein the polyethylene resin is polyethylene synthesized by polymerization using a metallocene catalyst. [4] The method for producing polyethylene wax according to [2] or [3], wherein the polyethylene resin is waste polyethylene.

Advantages of the Invention

[0008] According to the present invention, a polyethylene wax useful as an ink and paint additive, a pigment dispersant, a hot melt adhesive, a molding aid for plastics and rubbers, particularly a molding aid and a mold release agent for engineering plastics that require molding at high temperatures can be provided, and its industrial value is extremely high.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described in detail.

[0010] The polyethylene wax according to one embodiment of the present invention has a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) of 500 or more and 8,000 or less. When the number average molecular weight (Mn) is less than 500, there is a lot of smoke generation during high-temperature processing and stickiness of the molded body, and the blocking resistance and toughness are inferior. On the other hand, when it exceeds 8,000, the fluidity as a molding aid for plastics is inferior.

[0011] The polyethylene wax has a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (molecular weight distribution: Mw / Mn) measured by GPC of 1.0 or more and less than 3.5, preferably 1.0 or more and less than 3.3, more preferably 1.0 or more and less than 3.0. When the molecular weight distribution is 3.5 or more, uneven dispersion may occur when used as a molding aid or additive for plastics.

[0012] The polyethylene wax has the number of internal double bonds per molecule of 0.4 or more and less than 2.0, and the ratio of the number of internal double bonds per molecule to the number of terminal double bonds is 1.0 or more and less than 10. By satisfying these conditions simultaneously, the polyethylene wax is chemically stable during high-temperature forming processing, but due to the presence of internal double bonds, it becomes a polyethylene wax that is easy to modify.

[0013] Here, the molecular weight per molecule is the number-average molecular weight measured by GPC, the number of internal double bonds per molecule is the sum of the number of transvinylene and trisubstituted olefins determined by nuclear magnetic resonance spectroscopy ( 1 1H-NMR), and the number of terminal double bonds is the sum of the number of terminal vinyl and vinylidene.

[0014] Specific examples of more detailed measurement methods for gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (1H-NMR) are shown in the Examples section below.

[0015] Next, the method for producing the above polyethylene wax will be described.

[0016] The polyethylene wax of the present invention is obtained by thermally decomposing a polyethylene resin in which the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) measured by GPC is 1.0 or more and less than 6.0, preferably 1.0 or more and less than 4.5.

[0017] When the Mw / Mn of the polyethylene resin is 6.0 or more, the Mw / Mn of the obtained polyethylene wax may be 3.5 or more.

[0018] Furthermore, the polyethylene resin is preferably polyethylene synthesized by polymerization using a metallocene catalyst.

[0019] The polyethylene-based resin may be the polyethylene-based resin alone or a composition containing the polyethylene-based resin and further other components. When the polyethylene-based resin is a composition, it can be used in any state, whether the components are in a state of being dissolved in each other or in a state of being physically mixed in a solid state such as pellets or scraps. When the polyethylene-based resin is a composition, it is preferably contained in an amount of 80% by weight or more, more preferably 95% by weight or more, and particularly preferably 99% by weight or more of the polyethylene-based resin. If the polyethylene-based resin is less than 80% by weight, the resulting low-molecular-weight polyethylene may turn yellow or become colored, and it may be extremely difficult to remove components other than polyethylene, or the quality of the product may be significantly reduced. Examples of the polyethylene resin constituting the polyethylene-based resin include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, etc., and any one or more of these may be used. When the polyethylene-based resin is a composition, in addition to the polyethylene resin, polypropylene and polystyrene can be included.

[0020] The polyethylene resin can be used as it is with the antioxidant added during the production of the raw material polyethylene resin or during the molding into products such as films. Furthermore, when performing a thermal decomposition reaction, an antioxidant can be added for the purpose of preventing oxidative degradation, and the thermal decomposition reaction can also be carried out. There are no particular restrictions on the antioxidant to be added. For example, phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol, 2-t-butyl-4-methylphenol, n-octadecyl 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, and tetrakis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionitrileoxymethyl]methane can be mentioned. The addition amount or content is preferably 0.005 to 0.5 parts by weight, more preferably 0.01 to 0.1 parts by weight, per 100 parts by weight of the raw material polyethylene. Adding 0.005 parts by weight or more of the antioxidant may improve the hue or odor of the thermally decomposed wax. If the antioxidant is less than 0.005 parts by weight, the effect as an antioxidant cannot be found, and if the antioxidant is 0.5 parts by weight or less, less coke and bad odor are generated during thermal decomposition.

[0021] The shape of the polyethylene resin is not limited to pellets, powders, etc., and may be molded products such as films, sheets, bottles, and their crushed materials, or even waste polyethylene referred to as used products, off-spec products, waste products, etc.

[0022] The conditions for pyrolyzing the polyethylene resin are not particularly limited. However, heating is carried out at 350 to 500 °C for 2 minutes to 5 hours in an inert gas atmosphere, and volatile pyrolysis products having a boiling point temperature below the pyrolysis temperature are removed by nitrogen substitution or exhaust suction, and after cooling, methods such as purification are included. In the cooling step, the pyrolysis products are cooled in the form of powder, thin film, strand, drop form, etc., so that even polyethylene and pyrolysis products with low heat conduction efficiency can be rapidly cooled to a temperature below the pyrolysis temperature, and pyrolysis due to the residual heat in the pyrolysis product molecules does not proceed. The pyrolysis reaction includes, for example, a method in which raw material polyethylene is put into a reaction vessel, replaced with nitrogen, and then heated to the pyrolysis temperature while supplying nitrogen gas to the reaction vessel at a constant flow rate and held. There are no particular restrictions on the reaction vessel either, but any commonly used one may be used, such as a hot plate type heater, an electric furnace, a tubular electric furnace, a quartz mantle heater, a gas furnace, a gas heating kiln, an electric heating kiln and other kiln type reaction furnaces, a single-screw or twin-screw type extruder, a stainless steel autoclave with a stirrer, a quartz flask, a fluidized bed type reaction furnace, a fixed bed type reaction furnace, a tubular reaction furnace, a microwave type heating furnace, etc. Among them, a hot plate type heater, an electric furnace, a screw type extruder, and a kiln type reaction furnace can be mentioned because it is easy to remove volatile components.

[0023] The polyethylene wax may contain various additives to form a polyethylene wax composition within a range that does not inhibit the effects of the present invention. Examples of the additives include one or more selected from the group consisting of antioxidants, slip agents, flame retardants, antiblocking agents, antistatic agents, ultraviolet absorbers, colorants, mold release agents, and compatibilizers. These additives may be contained in the polyethylene that is the raw material of the polyethylene wax of the present invention, or may be added after the purification of the polyethylene wax.

[0024] The polyethylene wax can be used in any form such as pellets, powder, flakes, etc. after passing through a purification process. The methods of purification and molding are not particularly limited and ordinary methods may be used.

[0025] Polyethylene wax can be used as a raw material for modified polyethylene wax. The modification is not particularly limited, and examples thereof include maleic anhydride modification, epoxy modification, silane modification, and oxidation. In particular, maleic anhydride modification is preferably used because maleic anhydride can react with the internal double bond of polyethylene wax without a radical initiator such as an organic peroxide.

Examples

[0026] Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited thereto. (1) GPC measurement Apparatus: HLC-8321GPC / HT (detector: RI method) (manufactured by Tosoh Corporation) Column: One column of (i) below and three columns of (ii) are used in series (i) TSKgel® guardColumuH (HR) (30) HT (7.5 mm I.D.) × 7.5 Cm) (manufactured by Tosoh Corporation) × 1 piece (ii) TSKgel® GMH (HR)-H (20) HT (7.5 mm I.D.) × 30 Cm) (manufactured by Tosoh Corporation) × 3 pieces Eluent: 1,2,4-trichlorobenzene (containing 0.05 wt% BHT) (Purchased from Fujifilm Wako Pure Chemical Corporation) Flow rate: 1.0 mL / min Injection volume: 0.3 mL Column temperature: 140 °C System temperature: 40 °C Sample concentration: 1 mg / mL Calibration curve: A fifth-order approximation curve using standard polystyrene manufactured by Tosoh Corporation. However, the molecular weight was converted to a PE-equivalent molecular weight using the Q factor. (2) 1 1H-NMR measurement Apparatus: ECZ 400 (manufactured by JEOL Ltd.) Solvent: ortho-dichlorobenzene-d4 Temperature: 120 °C Integration count: 128 times ~Calculation of double bond number~ The number of internal double bonds and terminal double bonds per molecule was determined from the following equation using the number average molecular weight (Mn) of GPC and 1 the signal intensity of the 1H-NMR spectrum.

[0027] Number of internal double bonds (per Mn) = (Iva + Ivb) × (Mn / 14000) Number of terminal double bonds (per Mn) = (Ivc + Ivd) × (Mn / 14000) Here, Iva, Ivb, Ivc, and Ivd are the integrated intensities of trans vinylene (internal double bond), trisubstituted olefin (internal double bond), terminal vinyl (terminal double bond), and vinylidene (terminal double bond) per molecule, respectively, and are the amounts represented by the following equations.

[0028] Iva = (I5.5~5.3) / 2 Ivb = (I5.3~5.1) Ivc = (I5.1~4.85) / 2 Ivd = (I4.85~4.6) / 2 I represents the integrated intensity, and the subscript numerical value of I indicates the chemical shift range.

[0029] For example, I5.5~5.3 represents the integrated intensity of the proton signal detected between 5.5 ppm and 5.3 ppm.

[0030] The integrated intensity is the value when the integrated intensity of the signal derived from the main chain methylene proton detected between 1.8 ppm and 1.0 ppm is set to 2000. The chemical shift is set with the proton signal of 1,2-dichlorobenzene at 6.95 ppm, and the chemical shifts of the signals from other protons are based on this. [Example 1] 10 g of linear low density polyethylene (L-LDPE) (Nipolon (registered trademark) Z HF213K manufactured by Tosoh Corporation; number average molecular weight 42,300 g / mol, Mw / Mn = 2.1) obtained by a polymerization reaction using a metallocene catalyst as the raw material polyethylene was placed in a stainless steel autoclave and purged with nitrogen. Next, while supplying nitrogen gas at a constant flow rate of 50 mL / min to the autoclave, the temperature was raised from room temperature at 50 °C / min and held at 450 °C for 6 minutes. Then, heating and holding were stopped, and nitrogen gas was supplied at 100 mL / min to cool the system. After sufficient cooling and solidification, the polyethylene wax recovered was taken out of the autoclave, and GPC and NMR were measured. The evaluation results are shown in Table 1. [Example 2] Polyethylene wax was obtained in the same manner as in Example 1 except that ultra-high molecular weight polyethylene (UHMWPE) (number average molecular weight 623,000 g / mol, Mw / Mn = 4.4) obtained by the following polymerization reaction using a metallocene catalyst as the raw material polyethylene was used. Then, GPC and NMR were measured using the obtained polyethylene wax. The evaluation results are shown in Table 1. [Preparation of Modified Clay] 300 mL of industrial alcohol (Ekinen F-3 (trade name) manufactured by Nippon Alcohol Sales Co., Ltd.) and 300 mL of distilled water were placed in a 1 L flask, 15.0 g of concentrated hydrochloric acid and 42.4 g (120 mmol) of dimethyl behenylamine (Lipomin DM22D (trade name) manufactured by Lion Specialty Chemicals Co., Ltd.) were added, and the mixture was heated to 45 °C to disperse 100 g of synthetic hectorite (Laponite RD (trade name) manufactured by BYK Additives Limited). Then, the temperature was raised to 60 °C and stirred for 1 hour while maintaining the temperature. After filtering this slurry, it was washed twice with 600 mL of water at 60 °C and dried in a dryer at 85 °C for 12 hours to obtain 125 g of organically modified clay. This organically modified clay was pulverized with a jet mill to have a median diameter of 10 μm. [Preparation of Polymerization Catalyst] After purging a 300 mL flask equipped with a thermometer and a reflux tube with nitrogen, 25.0 g of the organically modified clay obtained in (1) and 108 mL of hexane were placed therein. Then, 0.715 g (1 mmol) of diphenylmethylene(cyclopentadienyl)(2 - diethylamino - 9 - fluorenyl)hafnium dichloride and 142 mL of 20% triisobutylaluminum were added, and the mixture was stirred at 60 °C for 3 hours. After cooling to 45 °C, the supernatant was removed, washed twice with 200 mL of hexane, and then 200 mL of hexane was added to obtain a catalyst suspension (solid weight fraction: 12.0 wt%). [Polymerization] 1.2 L of hexane, 1.0 mL of 20% triisobutylaluminum, and 358 mg (equivalent to 43 mg of solid content) of the catalyst suspension obtained in [Preparation of Polymerization Catalyst] were added to a 2 L autoclave. After heating to 70 °C, an ethylene / hydrogen mixed gas was continuously supplied so that the partial pressure became 0.80 MPa (hydrogen concentration in the ethylene / hydrogen mixed gas: 340 ppm). After 108 minutes, the pressure was released, and the slurry was filtered and dried to obtain 155 g of a polymer (activity: 3,600 g / g catalyst). [Comparative Example 1] A polyethylene wax was obtained in the same manner as in Example 1, except that a linear low - density polyethylene (specific L - LDPE) (Nipolon (registered trademark) Z ZF260 manufactured by Tosoh Corporation; number - average molecular weight 17,000 g / mol, Mw / Mn = 5.3) obtained by a polymerization reaction using a Ziegler catalyst was used as the raw material polyethylene. Then, GPC and NMR were measured using the obtained polyethylene wax. The evaluation results are shown in Table 1. [Comparative Example 2] A polyethylene wax was obtained in the same manner as in Example 1, except that a ultra - high - molecular - weight polyethylene (specific UHMWPE) (Millions 240M manufactured by Mitsui Chemicals, Inc.; number - average molecular weight 242,000 g / mol, Mw / Mn = 8.3) obtained by a polymerization reaction using a Ziegler catalyst was used as the raw material polyethylene. Then, GPC and NMR were measured using the obtained polyethylene wax. The evaluation results are shown in Table 1. [Comparative Example 3] A polyethylene wax was obtained in the same manner as in Example 1, except that low-density polyethylene (specific LDPE) (Tosoh Corporation's Petrothene (registered trademark) 202K; number-average molecular weight 15,000 g / mol, Mw / Mn = 8.1) obtained by a polymerization reaction using the high-pressure method was used as the raw material polyethylene. Then, GPC and NMR were measured using the obtained polyethylene wax. The evaluation results are shown in Table 1. [Comparative Examples 4 and 5] GPC and NMR were measured using the following commercially available polyethylene waxes. The evaluation results are shown in Table 1.

[0031] Hiwax 400P manufactured by Mitsui Chemicals, Inc.: Polymerization type Sun wax (registered trademark) 171-P manufactured by Sanyo Chemical Industries, Ltd.: Thermal decomposition type

[0032]

Table 1

Industrial Applicability

[0033] The present invention provides a polyethylene wax having high fluidity when melt-kneaded, high stability during high-temperature processing, and excellent reactivity in modification treatment, and is particularly useful as a molding processing aid for plastics and rubbers, an additive for inks or paints, a raw material for modified polyethylene waxes, and the like.

Claims

1. A polyethylene wax satisfying the following (1) to (3). (1) The number average molecular weight measured by gel permeation chromatography (GPC) is 500 or more and 8,000 or less. (2) The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by GPC is 1.0 or more and less than 3.5 (3) The number of internal double bonds per molecule is 0.4 or more and less than 2.0, and the ratio of the number of internal double bonds per molecule to the number of terminal double bonds is 1.0 or more and less than 10.

2. A method for producing the polyethylene wax according to Claim 1, wherein a polyethylene resin having a ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by GPC of 1.0 or more and less than 6.0 is pyrolyzed.

3. The method for producing a polyethylene wax according to Claim 2, wherein the polyethylene resin is polyethylene synthesized by polymerization using a metallocene catalyst.

4. The method for producing a polyethylene wax according to Claim 2, wherein the polyethylene resin is used polyethylene.

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