Oxidized polyethylene wax and method for producing the same

Abstract

To provide an oxidized polyethylene wax that has high fluidity when melt-kneaded and high reactivity with resins containing polar groups such as hydroxyl groups.SOLUTION: An oxidized polyethylene wax satisfies the following conditions (1) to (4): (1) the number average molecular weight (Mn) measured by the GPC method is 500 or more and 8,000 or less; (2) the number of double bonds per molecule is 0.4 or more and 2.0 or less; (3) the acid value is 0.1 mgKOH / g or more and 2.0 mgKOH / g or less; and (4) 0.80<(X)<0.99, where (X)=(number average molecular weight) / (661.26×ln(melt viscosity at 140°C [mPa s])-1944.4).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an oxidized polyethylene wax and a method for producing the same. [Background technology]

[0002] Low-molecular-weight polymers (molecular weights below 10,000) exhibit physical and chemical properties distinct from those of typical polymers with molecular weights in the tens of thousands to hundreds of thousands. Polyolefin waxes, such as low-molecular-weight polyethylene and low-molecular-weight polypropylene, are used in a wide range of applications, including not only polyolefins, which account for the majority of plastics produced, but also pigment dispersants, molding processing aids, ink and paint additives, and hot-melt adhesive additives. Furthermore, oxidized polyolefin waxes, obtained by oxidizing polyolefin waxes, are highly compatible with polar group-containing components such as hydroxyl groups. Therefore, they are useful not only as compatibilizers in polymer alloys composed of polyolefins and synthetic resins such as polyvinyl alcohol, polyester, polyamide, and polycarbonate, but also as dispersants for compounding cellulose-based powders such as wood flour and paper powder, and glass fiber with polyolefin resins.

[0003] Known methods for synthesizing oxidized polyolefin wax include a method of oxidizing a polymerized polyolefin wax in a molten state (see, for example, Patent Documents 1 to 4), a method of oxidizing a thermally decomposed polyolefin wax (see, for example, Patent Documents 5 and 6), and a method of producing an oxidized polyolefin wax by oxidizing a polyolefin in a solid state and then decomposing it (see, for example, Patent Document 7). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2000-509417 [Patent Document 2] Special Publication No. 2004-501246 [Patent Document 3] Patent No. 3813554 [Patent Document 4] Patent No. 4799716 [Patent Document 5] Special Publication No. 43-9367 [Patent Document 6] Special Publication No. 47-49313 [Patent Document 7] Patent No. 5410991 Summary of the Invention [Problem to be solved by the invention]

[0005] In the methods proposed in Patent Documents 1 to 6, oxidized wax is synthesized by oxidizing wax, but the oxidation requires pressurized conditions, long reaction times, or the use of harmful oxidizing agents such as ozone. The method proposed in Patent Document 7 requires controlling the particle size of the polyethylene resin to uniformly oxidize the polyethylene, which increases production costs. Furthermore, the resulting oxidized polyethylene wax has a high acid value and a high melt viscosity relative to its molecular weight, so reducing the molecular weight to adjust the melt viscosity can lower the melting point. Furthermore, no mention is made of environmental considerations such as the use of plant-derived ethylene or waste plastics.

[0006] Therefore, an object of the present invention is to provide a slightly oxidized wax that can be obtained simply and efficiently from waste plastics, particularly preferably discarded polyethylene resins.More specifically, an object of the present invention is to provide an oxidized wax that is useful not only as a wax for use as a molding aid for plastics and rubber, a lubricant, a mold release agent, an ink and paint additive, a pigment dispersant, and a hot melt adhesive, but also as a compatibilizer for polymer alloys and a dispersant for fillers, etc. [Means for solving the problem]

[0007] As a result of intensive research aimed at solving the above problems, the present inventors have found that a specific oxidized polyethylene wax has high fluidity and reactivity with polar group-containing components, and is low in cost, and have thus completed the present invention.

[0008] That is, the embodiments of the present invention are [1] to [7] shown below. [1] Oxidized polyethylene wax that satisfies the following (1) to (4): (1) The number average molecular weight (Mn) measured by the GPC method is 500 or more and 8,000 or less. (2) The number of double bonds per molecule is 0.4 or more and 2.0 or less. (3) Acid value is 0.1 mg KOH / g or more and 2.0 mg KOH / g or less. (4)(X) = (number average molecular weight) / (661.26 × ln(melt viscosity at 140°C [mPa·s]) - 1944.4), and the relationship 0.80 < (X) < 0.99 holds. [2] A method for producing the oxidized polyethylene wax according to [1], which comprises thermally decomposing a polyethylene resin that satisfies the following (5) to (7): (5) The number average molecular weight (Mn) measured by the GPC method is 5,000 or more and 100,000 or less. (6) The number of double bonds per molecule is 2.0 or less. (7) Acid value is 0.1 mg KOH / g or more and 4.0 mg KOH / g or less. [3] The method for producing an oxidized polyethylene wax according to [2], wherein the polyethylene resin is waste polyethylene. [4] The oxidized polyethylene wax and its manufacturing method according to [3], wherein the waste polyethylene is used polyethylene generated in extrusion lamination molding. [5] The method for producing the oxidized polyethylene wax according to [2], wherein polyethylene is thermally decomposed in an extruder. [6] The method for producing an oxidized polyethylene wax according to [5], wherein the extruder is a twin-screw extruder. [7] A method for producing an oxidized polyethylene wax according to [5] or [6], wherein polyethylene is thermally decomposed in an extruder under conditions of a cylinder temperature of 330 to 480°C in the thermal decomposition region of the extruder and a tip temperature of 100 to 300°C for extruding the wax after thermal decomposition. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an oxidized polyethylene wax which is useful not only as a polyethylene wax for applications such as a molding aid for plastics and rubber, a lubricant, a mold release agent, an ink and paint additive, a pigment dispersant, and a hot melt adhesive, but also as a compatibilizer for polymer alloys and a dispersant for fillers, etc., and which is of extremely high industrial value. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below.

[0011] The oxidized polyethylene wax according to one embodiment of the present invention has a number-average molecular weight (Mn) of 500 to 8,000 as measured by gel permeation chromatography (GPC). If the number-average molecular weight (Mn) is less than 500, the wax will emit smoke during high-temperature processing, the molded product will be sticky, and the blocking resistance and toughness will be poor. On the other hand, if the number-average molecular weight (Mn) is more than 8,000, the wax will have poor fluidity as a molding processing aid for plastics.

[0012] The oxidized polyethylene wax has a number of double bonds per molecule of 0.4 to 2.0. By simultaneously satisfying these requirements, the oxidized polyethylene wax has appropriate hardness and excellent moldability.

[0013] Here, the molecular weight per molecule is the number average molecular weight measured by GPC, and the number of double bonds is the number average molecular weight measured by nuclear magnetic resonance spectroscopy ( 1 The number of trans vinylenes, trisubstituted olefins, and terminal double bonds determined by H-NMR is the sum of the number of terminal vinyls and vinylidenes.

[0014] Gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy ( 1 More detailed examples of the measurement method using H-NMR will be given in the Examples section below.

[0015] The acid value of the oxidized polyethylene wax is 0.1 mgKOH / g or more and 2.0 mgKOH / g or less. If it is less than 0.1 mgKOH / g, the reactivity when mixed with a polar group-containing component as a compatibilizer for polymer alloys and a filler dispersant is poor, and the function as an internal lubricant during molding of engineering plastics is poor. Conversely, if it exceeds 2.0 mgKOH / g, the melt viscosity relative to the molecular weight becomes high, and if the molecular weight is reduced to lower the viscosity, the melting point may be significantly reduced.

[0016] For the oxidized polyethylene wax, (X) = (number average molecular weight) / (661.26 × ln(melt viscosity at 140°C [mPa·s]) - 1944.4), where 0.80 < (X) < 0.99 holds. The above formula (X) is an approximation created by plotting the melt viscosity and number average molecular weight (Mn) of commercially available non-oxidized polyethylene waxes. Here, commercially available non-oxidized polyethylene wax refers to the non-oxidized polyethylene waxes in the "Hiwax" series manufactured by Mitsui Chemicals, Inc. and the "Sunwax" series manufactured by Sanyo Chemical Industries, Ltd. For non-oxidized polyethylene wax, (X) = 1 ± 0.1. However, since oxidized polyethylene wax contains polar groups such as carboxyl groups, aldehyde groups, ketone groups, and hydroxyl groups, it has stronger intermolecular forces than non-oxidized polyethylene wax, resulting in a higher melt viscosity, and therefore (X) < 1. If (X) exceeds 0.99, the reactivity will be poor when mixed with polar group-containing components as a compatibilizer for polymer alloys and a filler dispersant, and the function as an internal lubricant during molding of engineering plastics will be poor. If (X) is 0.80 or less, the melt viscosity will be high relative to the molecular weight, and if the molecular weight is reduced to lower the viscosity, the melting point may drop significantly.

[0017] The oxidized polyethylene wax can be produced by, but is not particularly limited to, thermal decomposition of a polyethylene resin.

[0018] Examples of polyethylene resins include polyethylenes such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high-molecular-weight polyethylene, ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as EVA), and saponified EVA. Among these polyethylene resins, polyethylene resins primarily composed of low-density polyethylene resin are preferred because they can be used in a wide range of applications, such as molding processing aids, compatibilizers for polymer alloys, and filler dispersants, and are easily converted to low molecular weight by thermal decomposition. The content of the low-density polyethylene resin is preferably 70% by weight or more, and more preferably 80% by weight or more, because this results in an oxidized polyethylene wax of stable quality.

[0019] The polyethylene resin preferably has a number average molecular weight (Mn) measured by GPC of 5,000 to 100,000. If the number average molecular weight (Mn) is less than 5,000, the resin will emit a lot of smoke during thermal decomposition. On the other hand, if the number average molecular weight (Mn) is more than 100,000, the resin will have poor fluidity during melting, resulting in reduced stirring efficiency.

[0020] The polyethylene resin preferably has a double bond number per molecule of 2.0 or less. If the number exceeds 2.0, the color number of the oxidized wax deteriorates.

[0021] The acid value of the waste polyethylene is preferably 0.1 mgKOH / g or more and 4.0 mgKOH / g or less. If it is less than 0.1 mgKOH / g, the resulting oxidized polyethylene wax will have poor reactivity when mixed with a polar group-containing component as a compatibilizer for polymer alloys and a filler dispersant, and will also have poor function as an internal lubricant during molding of engineering plastics. Conversely, if it exceeds 4.0 mgKOH / g, thermal decomposition will proceed rapidly, causing problems such as the generation of coke, odor, and coloration.

[0022] The polyethylene resin can be made from waste polyethylene, such as off-specification polyethylene or used polyethylene. Used polyethylene generated during extrusion lamination molding is particularly difficult to reuse as recycled polyethylene due to its history of processing under high-temperature conditions, which can cause oxidative degradation and molecular chain recombination reactions. However, it is preferred because it does not require an oxidizing agent and can be safely used to produce oxidized polyethylene wax under an inert gas atmosphere. The used polyethylene generated during extrusion lamination molding is preferably extruded at an extruder cylinder temperature in the range of 250 to 360°C, more preferably 270 to 350°C, and particularly preferably 280 to 340°C.

[0023] The form of the polyethylene resin is not limited to pellets, powder, etc., but may also be a film, sheet, bottle, fiber, pipe, injection molded product, or other molded product, or crushed product thereof.

[0024] Examples of the extruder include a single-screw extruder, a multi-screw extruder having two or more screws, and a tandem extruder having two or more extruders connected together. Among these extruders, a twin-screw extruder is preferred because it can produce an oxidized polyethylene wax with stable quality and has excellent stability in torque and discharge rate during extrusion.

[0025] The extruder is preferably equipped with a vacuum vent port to efficiently discharge pyrolyzed low-molecular-weight gas components outside the extruder. Furthermore, the ratio (L / D) of the screw length (L) to the screw diameter (D) is preferably 30 or more, particularly 40 or more, so that the pyrolysis of polyethylene can be efficiently carried out and an oxidized polyethylene wax of stable quality can be obtained.

[0026] In the method for producing an oxidized polyethylene wax using an extruder, a polyethylene resin is fed into the extruder, and the temperature should be adjusted appropriately depending on the desired molecular weight of the oxidized polyethylene wax. The cylinder temperature in the thermal decomposition region can be in the range of 330 to 480°C, more preferably 350 to 460°C, and particularly preferably 380 to 450°C. Furthermore, the thermal decomposition time in the thermal decomposition region, i.e., the residence time of the polyethylene resin in the extruder, can be in the range of 0.5 to 30 minutes, more preferably 1 to 20 minutes, and particularly preferably 1.5 to 15 minutes. Furthermore, the tip temperature of the extruder when extruding the wax after thermal decomposition can be in the range of 100 to 300°C or less, more preferably 130 to 280°C, and particularly preferably 140 to 250°C, since this facilitates more precise control of the molecular weight. In addition, since this reduces the odor of the resulting pyrolysis wax and makes it easier to control the molecular weight, it is preferable to replace the atmosphere inside the extruder during pyrolysis with an inert gas such as hydrogen, helium, argon, nitrogen, or carbon dioxide, and nitrogen gas is particularly preferable. The pyrolyzed wax extruded from the extruder can be molded into a desired shape by methods such as hot cutting, mist cutting, or underwater cutting.

[0027] The oxidized polyethylene wax can be used in any form such as pellets, powder, flakes, granules, grains, paste, etc. The oxidized polyethylene wax can also be used in a wide range of applications, including as a dispersant for fillers, pigments, etc., a molding aid for plastics and rubber such as a mold release agent, lubricant, or plasticizer, an additive for inks, paints, coating agents, polishes, sealants, natural waxes, or hot-melt adhesives, cosmetics, facial cleansers, paper quality improvers, civil engineering additives such as road markings and asphalt modifiers, and compatibilizers for polymer alloys. [Example]

[0028] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these. (1) GPC measurement Apparatus: HLC (registered trademark)-8321GPC / HT (detector: RI method) (manufactured by Tosoh Corporation) Columns: One column of (i) and three columns of (ii) below are used in series. (i) TSKgel® guardColumuH(HR)(30)HT (7.5mm I.D.) x 7.5cm) (Tosoh Corporation) x 1 (ii) TSKgel® GMH(HR)-H(20)HT (7.5mm I.D.) x 30cm) (Tosoh Corporation) x 3 Eluent: 1,2,4-trichlorobenzene (containing 0.05 wt% BHT) (Purchased from Fujifilm Wako Pure Chemical Industries, Ltd.) Flow rate: 1.0mL / min Injection volume: 0.3mL Column temperature: 140℃ System temperature: 40°C Sample concentration: 1 mg / mL Calibration curve: quintic approximation curve using standard polystyrene manufactured by Tosoh Corporation. However, the molecular weight was converted to PE equivalent molecular weight using the Q factor. (2) Evaluation of wax fluidity The melt viscosity was measured at a measurement temperature of 140°C using a viscometer (manufactured by Brookfield, trade name DV2T). (3) Acid value measurement Measurement was carried out in accordance with JIS K 2501 under the following conditions.

[0029] Equipment: 50 mL burette (minimum graduation 0.1 mL), Erlenmeyer flask Reagents: toluene, methanol, dimethylformamide, pure water, phenolphthalein indicator, N / 20KOH-n-propanol / toluene solution (F=0.9758) Melting conditions: 165℃×30min Reaction conditions: room temperature x 30 min Sample amount: approx. 1g (4) 1 H-NMR measurement Equipment: ECZ 400 (manufactured by JEOL Ltd.) Solvent: orthodichlorobenzene-d4 Temperature: 120℃ Number of times accumulated: 128 ~Calculating the number of double bonds~ The number of double bonds per molecule is calculated by the GPC number average molecular weight (Mn) and 1 The signal intensity of the H-NMR spectrum was used to calculate the value from the following equation.

[0030] Number of double bonds (pieces / Mn)=(Iva+Ivb+Ivc+Ivd)×(Mn / 14000) Here, Iva, Ivb, Ivc, and Ivd are the integrated intensities of transvinylene (intramolecular double bond), trisubstituted olefin (intramolecular double bond), terminal vinyl (terminal double bond), and vinylidene (terminal double bond), respectively, and are quantities expressed by the following formula.

[0031] Iva=(I5.5~5.3) / 2 Ivb=(I5.3~5.1) Ivc=(I5.1~4.85) / 2 Ivd=(I4.85~4.6) / 2 I denotes the integrated intensity, and the subscripts of I indicate the range of chemical shifts.

[0032] For example, I5.5-5.3 indicates the integrated intensity of the proton signal detected between 5.5 ppm and 5.3 ppm.

[0033] The integrated intensity was determined by setting the integrated intensity of the signal derived from the main chain methylene protons detected between 1.8 ppm and 1.0 ppm to 2000. The chemical shift was set to the proton signal of 1,2-dichlorobenzene at 6.95 ppm, and the chemical shifts of the signals derived from other protons were based on this.

[0034] [Example 1] The extruder used was a co-rotating intermeshing twin-screw extruder with a screw diameter of 11 mm and a screw length L to screw diameter D ratio (L / D) of 40. The extruder had a total of eight temperature zones, with each zone corresponding to L / D = 5. Zones 1 to 8 were designated from the base of the screw to the die outlet, with zones 1 to 3 designated as plasticization zones, zones 4 to 7 designated as thermal decomposition zones, and zone 8 designated as a cooling zone. The raw material was used as waste polyethylene (A-1) (number average molecular weight 15,000) generated during resin switching in extrusion lamination molding of low-density polyethylene (Petrothene (registered trademark) 205 manufactured by Tosoh Corporation). The polyethylene was pulverized to an average particle size of 10 mm or less in a pulverizer, reduced in volume, and fed into the main feeder of the extruder at a feed rate of 150 g / hr together with a constant flow rate of nitrogen gas. The extruder was then melt-kneaded and thermally decomposed under conditions where the cylinder temperature in the thermal decomposition zone of the extruder was 450 °C and the cooling zone was heated to 200 °C. The molten mixture was then extruded onto a steel plate placed under a nitrogen atmosphere, cooled, and pulverized to obtain a powdered oxidized polyethylene wax. The obtained oxidized polyethylene wax was then subjected to GPC, melt viscosity, acid value, and NMR measurements. It took 3 minutes to obtain the oxidized polyethylene wax, and the yield was 96%. The results of the measurements and evaluations are shown in Table 1.

[0035] [Example 2] An oxidized polyethylene wax was obtained in the same manner as in Example 1, except that the feeding rate was set to 75 g / hr. The obtained oxidized polyethylene wax was subjected to GPC, melt viscosity, acid value, and NMR measurements. The evaluation results are shown in Table 1.

[0036] [Comparative Example 1] A polyethylene wax was obtained in the same manner as in Example 1, except that a low-density polyethylene (Petrothene (registered trademark) 205 manufactured by Tosoh Corporation) was used as a raw material. The obtained polyethylene wax was subjected to GPC, melt viscosity, acid value, and NMR measurements. The evaluation results are shown in Table 1.

[0037] Comparative Example 2 GPC, melt viscosity, acid value, and NMR measurements were carried out using a commercially available oxidized polyethylene wax (Hiwax 4052E manufactured by Mitsui Chemicals, Inc.). The evaluation results are shown in Table 1.

[0038] [Table 1] [Industrial Applicability]

[0039] The present invention provides a method for simply and efficiently pyrolyzing waste plastics and recycling them into oxidized polyethylene wax, which is useful as a molding aid for plastics and rubber, a lubricant, a mold release agent, an ink and paint additive, a pigment dispersant, a hot melt adhesive, a compatibilizer for polyolefins and polar polymers, etc.

Claims

1. An oxidized polyethylene wax that satisfies the following (1) to (4): (1) The number average molecular weight (Mn) measured by GPC is 500 or more and 8,000 or less. (2) The number of double bonds per molecule is 0.4 or more and 2.0 or less. (3) The acid value is 0.1 mg KOH / g or more and 2.0 mg KOH / g or less. (4) (X) = (number average molecular weight) / (661.26 × ln (melt viscosity at 140°C [mPa·s]) - 1944.4), and 0.80 < (X) < 0.99 holds.

2. The method for producing the oxidized polyethylene wax according to claim 1, which comprises thermally decomposing a polyethylene resin that satisfies the following (5) to (7): (5) The number average molecular weight (Mn) measured by GPC is 5,000 or more and 100,000 or less. (6) The number of double bonds per molecule is 2.0 or less. (7) The acid value is 0.1 mg KOH / g or more and 4.0 mg KOH / g or less.

3. The method for producing an oxidized polyethylene wax according to claim 2, wherein the polyethylene resin is waste polyethylene.

4. 4. The method for producing oxidized polyethylene wax according to claim 3, wherein the waste polyethylene is used polyethylene generated in the manufacturing process of extrusion lamination molding.

5. The method for producing the oxidized polyethylene wax according to claim 2, wherein the polyethylene resin is thermally decomposed in an extruder.

6. The method for producing an oxidized polyethylene wax according to claim 5, wherein the extruder is a twin-screw extruder.

7. The method for producing the oxidized polyethylene wax according to claim 5, wherein the polyethylene resin is thermally decomposed in an extruder under conditions of a cylinder temperature of 330 to 480°C in a thermal decomposition region of the extruder and a tip temperature of 100 to 300°C of the extruder that extrudes the oxidized polyethylene wax after thermal decomposition.

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