Polyethylene composition for coating molding

Abstract

The invention provides a coating and molding method. The coat gel molding method according to embodiments disclosed herein includes a loading step, a heating step, a cooling step, and a removal step. The coat gel molding process comprises using a particulate polyethylene composition comprising a polyethylene polymer, a polyalkylene glycol having a weight average molecular weight greater than 2000 at a concentration of 0.01 to 1 wt%, based on the weight of the polyethylene polymer. The gelling molding methods disclosed herein can result in suitable densification with reduced PIAT.

Description

Polyethylene compositions for coating and molding Technical Field

[0001] This application relates to the field of polyethylene compositions that can be used for rotational molding. Background Technology

[0002] Rotational molding, or "coating molding," is a common method for manufacturing molded polymer articles, such as large items like water tanks, kayaks, and sports equipment. Generally, the coating molding method involves at least four steps. In the loading step, a granulated polyethylene composition is loaded into a mold in the desired shape of the finished product, and the mold is closed. In the heating step, the mold is heated to and maintained at the molding temperature of the granulated polyethylene composition while being continuously rotated in two perpendicular directions, ensuring uniform contact of the polymer with all the inner surfaces of the mold. In this step, the polymer in the mold melts, fuses, and adheres to the mold surface. In the cooling step, the mold is cooled to solidify the polymer. In the removal step, the mold is opened, and the molded article is recovered.

[0003] Polyethylene polymers are commonly used in coating molding processes. These polyethylene polymers can include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), but LLDPE is currently the primary PE used in coating molding. Polyethylene polymers are typically ground into powder before use to accelerate melting and provide a more uniform distribution in the mold.

[0004] For several purposes, such as providing antioxidant properties, UV resistance, color and opacity, crack resistance and toughness, additives are often added to polyethylene powder. Common additives are referred to as "densifying agents".

[0005] Compared to the absence of densifying agents, densifying agents enhance the ability of polyethylene powder particles to coalesce into solidified masses more quickly and / or at lower temperatures. During the heating step, as the polymer melts and fuses, air between the polymer particles is trapped in bubbles. These bubbles indicate that the polymer is not fully consolidated, which typically results in molded articles with poor physical properties, such as low impact resistance. Most bubbles can be released by continuing the heating step for a longer period up to a higher temperature to allow the polymer to fully coalesce, but prolonged heating at high temperatures is inefficient and can degrade the polymer. Densifying agents reduce the time and temperature required for complete consolidation, thereby improving efficiency and protecting the polymer from degradation while providing robust molded articles. Examples of commonly used densifying agents include long-chain hydrocarbon waxes.

[0006] A common measurement used to determine the heating process is the peak internal air temperature (PIAT). A thermometer in the mold measures the rise and fall of the air temperature inside the mold during the heating and cooling processes and records the highest temperature reached.

[0007] The aim is to identify densifying agents for polyethylene coating molding polymers that can achieve appropriate densification under reduced PIAT conditions. Summary of the Invention

[0008] A first aspect of the present invention is a coating molding method, the coating molding method comprising the following steps:

[0009] a) Loading the granular polyethylene composition into a mold and closing the mold (“loading step”);

[0010] b) Heating the mold to the melting temperature of the polyethylene composition while rotating the mold on at least two axes to form a coating of the polyethylene composition adhering to the inner surface of the mold (“heating step”).

[0011] c) Cooling the mold to solidify the polyethylene composition adhered to the inner surface of the mold (“cooling step”); and

[0012] d) Release the molded article from the mold (“removal step”),

[0013] The granular polyethylene composition is characterized by comprising (1) a polyethylene polymer and (2) a polyalkylene glycol with a weight average molecular weight greater than 2000 Da, at a concentration of 0.01% to 1% by weight based on the polyethylene polymer.

[0014] A second aspect of the present invention is a molded article manufactured by the method of the present invention.

[0015] A third aspect of the invention is a molded article containing a polyethylene composition comprising (1) a polyethylene polymer and (2) a polyalkylene glycol having a weight average molecular weight greater than 2000 Da at a concentration of 0.01% to 1% by weight based on the polyethylene polymer.

[0016] Polyalkylene glycols in polyethylene compositions act as densifying agents for the polyethylene polymer, thereby reducing the PIAT required to achieve proper consolidation of the polyethylene composition during the heating step. Attached Figure Description

[0017] Figure 1 shows a micrograph of the mold side surface of a molded article made using the polyethylene composition of the present invention and a comparative polyethylene composition. Detailed Implementation

[0018] The coating molding method of the present invention uses a granular polyethylene composition comprising a polyethylene polymer and a polyalkylene glycol.

[0019] Polyethylene polymers are widely known and commercially available. Polyethylene primarily contains repeating units derived from ethylene, as shown in Formula 1:

[0020]

[0021] In some implementations, the polyethylene polymer is a homopolymer that consists essentially of repeating units derived from ethylene.

[0022] In some embodiments, the polyethylene polymer is a copolymer wherein at least 70% by weight of the repeating units are derived from ethylene monomers and at least 0.5% by weight of the repeating units are derived from one or more comonomers. Examples of suitable comonomers may include α-olefins. Suitable α-olefins may include α-olefins containing 3 to 20 carbon atoms (C3-C20). For example, α-olefins may be C4-C20 α-olefins, C4-C12 α-olefins, C3-C10 α-olefins, C3-C8 α-olefins, C4-C8 α-olefins, or C6-C8 α-olefins. In some embodiments, the α-olefin is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, and 1-decene. In other embodiments, the α-olefin is selected from the group consisting of propylene, 1-butene, 1-hexene, and 1-octene. In another embodiment, the α-olefin is selected from the group consisting of 1-hexene and 1-octene. For example, repeating units derived from the comonomer may conform to formula 2:

[0023]

[0024] R is an alkyl or substituted alkyl group containing 1 to 18 carbon atoms. In some embodiments, R contains 1 to 8 carbon atoms, 2 to 6 carbon atoms, or 3 to 6 carbon atoms.

[0025] Polyethylene polymers are generally classified into the following groups:

[0026] • High-density polyethylene (HDPE), which, as disclosed herein, has a density of 0.93 g / cm³. 3 Up to 0.98 g / cm 3 The density;

[0027] • Low-density polyethylene (LDPE), which, as disclosed herein, has a density of 0.90 g / cm³. 3 Up to 0.93 g / cm 3The density; and

[0028] • Linear low-density polyethylene (LLDPE), which, as disclosed herein, has a density of 0.90 g / cm³. 3 Up to 0.94 g / cm 3 The density.

[0029] In some embodiments, the polyethylene polymer in the polyethylene composition is an HDPE polymer. HDPE polymers typically have low levels of comonomers. In some embodiments, the HDPE polymer contains at least 94% by weight, or at least 96% by weight, or at least 98% by weight, or substantially 100% by weight of repeating units derived from ethylene monomers.

[0030] In some embodiments, the polyethylene polymer in the polyethylene composition is an LLDPE polymer. LLDPE polymers typically contain higher levels of comonomers than HDPE polymers. In some embodiments, ethylene-derived repeating units comprise at least 80% by weight, or at least 90% by weight, or at least 92% by weight of the LLDPE polymer. In some embodiments, ethylene-derived repeating units comprise at most 98% by weight, or at most 96% by weight, or at most 94% by weight, or at most 93% by weight of the LLDPE polymer. In some embodiments, α-olefin-derived repeating units comprise at most 20% by weight, or at most 18% by weight, or at most 15% by weight, or at most 12% by weight, or at most 10% by weight, or at most 8% by weight of the LLDPE polymer. In some embodiments, α-olefin-derived repeating units comprise at least 2% by weight, or at least 4% by weight, or at least 6% by weight, or at least 7% by weight of the LLDPE polymer.

[0031] The comonomer content is sometimes expressed as short-chain branches per 1000 carbon atoms, wherein the short-chain branches are residues of the comonomer and contain no more than 18 carbon atoms, no more than 10 carbon atoms, or no more than 6 carbon atoms. In some embodiments, the LLDPE polymer has at least 2, at least 5, at least 7, or at least 9 short-chain branches per 1000 carbon atoms. In some embodiments, the LLDPE polymer has at most 20, at most 18, at most 15, at most 13, or at most 11 short-chain branches per 1000 carbon atoms.

[0032] In some embodiments, the polyethylene polymer may also contain long-chain branches. These long-chain branches contain at least 20 carbon atoms. LDPE polymers typically contain a higher level of long-chain branching than HDPE and LLDPE polymers. In some embodiments, the polyethylene polymer contains at least 3 long-chain branches per 1000 carbon atoms. In some embodiments, the polyethylene polymer contains no more than 3, 2, or 1 long-chain branches per 1000 carbon atoms. In some embodiments, the polyethylene polymer is substantially linear, except for short-chain branches (essentially 0 long-chain branches per 1000 carbon atoms) generated by the comonomer.

[0033] Polyethylene polymers are typically characterized based on density and melt index. In some embodiments, the polyethylene polymer used in this invention has a density of at least 0.90 g / cm³ or at least 0.910 g / cm³. 3 Or at least 0.920 g / cm 3 Or at least 0.925 g / cm 3 Or at least 0.930 g / cm 3 Or at least 0.932 g / cm 3 Or at least 0.935 g / cm 3 The density. In some embodiments, the polyethylene polymer used in this invention has a density of at most 0.98 g / cm³ or at most 0.97 g / cm³. 3 Or at most 0.96 g / cm 3 Or at most 0.95g / cm 3 Or at most 0.947 g / cm³ 3 The density.

[0034] In some embodiments, the melt index (I2) of the polyethylene polymer is at least 0.1 dg / min, or at least 0.3 dg / min, or at least 0.5 dg / min, or at least 1 dg / min, or at least 2 dg / min, or at least 3 dg / min. In some embodiments, the melt index (I2) of the polyethylene polymer ranges from at most 30 dg / min, or at most 20 dg / min, or at most 15 dg / min, or at most 10 dg / min, or at most 7 dg / min, or at most 5 dg / min. In some embodiments, the melt index (I2) of the polyethylene polymer is from 1 dg / min to 20 dg / min, or from 2 dg / min to 10 dg / min.

[0035] In some embodiments, the polyethylene composition has a tensile stress yield of at least 14 MPa, at least 16 MPa, at least 17 MPa, at least 18 MPa, or at least 19 MPa (for compression-molded samples). In some embodiments, the polyethylene composition has a tensile stress yield of no more than 30 MPa.

[0036] In some embodiments, the polyethylene composition has a tensile strain at break of at least 300%, at least 400%, at least 500%, or at least 550% (of a compression-molded sample). In some embodiments, the tensile strain at break is at most 1000%, at most 800%, at most 700%, or at most 600%.

[0037] In some embodiments, the polyethylene composition has a flexural modulus (1% secant) of at least 500 MPa, at least 600 MPa, at least 650 MPa, at least 700 MPa, or at least 720 MPa. In some embodiments, the flexural modulus (1% secant) is at most 1000 MPa, at most 900 MPa, at most 850 MPa, or at most 800 MPa.

[0038] In some embodiments, the polyethylene composition has environmental stress cracking resistance (ESCR) that reaches 50% failure (F50) within at least 50 hours, 55 hours, 60 hours, 65 hours, or 70 hours, according to the test method.

[0039] The ESCR, flexural modulus, and tensile properties are measured according to the test methods described below.

[0040] In some embodiments, the polyethylene composition contains a single polyethylene polymer. In some embodiments, the polyethylene composition contains a blend of two or more polyethylene polymers. In some embodiments, the polyethylene polymer and polyalkylene glycol are the only polymers in the polyethylene composition, and in some embodiments, the polyethylene composition contains another polymer in addition to the polyethylene polymer and polyalkylene glycol. In some embodiments, based on the total weight of the polyethylene composition (excluding pigments and fillers), the polyethylene polymer accounts for at least 50% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight, or at least 92% by weight, or at least 94% by weight of the polyethylene composition (excluding pigments and fillers).

[0041] Suitable polyethylene polymers are commercially available from many manufacturers, including DOWLEX from The Dow Chemical Company. ™ AFFINITY ™ ELITE ™ ENGAGE ™ ATTANE ™ and DOW ™ HDPE is a brand of polyethylene polymers sold under the name HDPE.

[0042] Other polyethylene polymers can be prepared by known methods, such as solution, slurry, and / or gas-phase polymerization of ethylene monomers and optional comonomers in the presence of Ziegler-Natta catalysts, chromium catalysts, metallocene catalysts, or other single-point catalysts.

[0043] In some embodiments, a Ziegler-Natta catalyst system is used to prepare polyethylene polymers. An exemplary Ziegler-Natta catalyst system is a granular catalyst composition containing (1) a titanium-containing main catalyst, such as titanium tetrachloride and / or titanium trichloride, and (2) an aluminum-containing co-catalyst, such as triethylaluminum (TEA). In many cases, the titanium-containing main catalyst is deposited on a support, such as magnesium chloride. Suitable Ziegler-Natta catalysts and methods of their preparation and use are described in numerous publications, such as the following patent publications: US 6,982,237 B2, US 7,507,780 B2, US 8,012,903 B2, US 8,497,330 B2, and WO2019 / 112929. Suitable Ziegler-Natta catalyst systems are also commercially available.

[0044] In some implementations, a chromium catalyst is used to prepare the polyethylene polymer. An exemplary chromium catalyst contains chromium oxide supported on silica gel.

[0045] In some embodiments, metallocene catalysts or other single-site catalysts are used to prepare polyethylene polymers. Metallocene catalysts contain metal atoms and ions, such as titanium, zirconium, or hafnium, coordinated to one or more cyclopentadienyl rings, which may be substituted or are part of a larger organic structure. Other single-site catalysts contain metal atoms and ions coordinated to other organic ligands, particularly polydentate ligands containing two or more amine or hydroxyl sites available for coordination.

[0046] The granular polyethylene composition used in the coating molding method of the present invention also contains polyalkylene glycols with a weight average molecular weight greater than 2000 Da, which act as densification aids.

[0047] Polyalkylene glycols contain repeating units that satisfy formula 3:

[0048]

[0049] Where R 1 and R 2 Each of them is a hydrogen or alkyl group.

[0050] In some implementation schemes, R 1 and R 2Each of them independently contains no more than 6 carbon atoms, no more than 4 carbon atoms, no more than 2 carbon atoms, or no more than 1 carbon atom. In some embodiments, R 1 and R 2 Each contains, on average, no more than 8 carbon atoms, no more than 6 carbon atoms, no more than 4 carbon atoms, no more than 2 carbon atoms, no more than 1 carbon atom, no more than 0.5 carbon atoms, or no more than 0.25 carbon atoms. In some embodiments, R 1 and R 2 The repeating units are all hydrogen in at least 80% or at least 90% or substantially 100%. In some embodiments, the polyalkylene glycol contains ethyleneoxy[-CH2-CH2-O-] units, propyleneoxy[-CH2(CH3)-CH2--O-] units, or both types of units, or is substantially composed of them.

[0051] In some embodiments, the polyalkylene glycol is polyethylene glycol. In some embodiments, the polyalkylene glycol is a polyethylene glycol / polypropylene glycol copolymer.

[0052] In some embodiments, the polyalkylene glycol has a weight-average molecular weight of at least 2100 Da, at least 2200 Da, at least 2400 Da, at least 2600 Da, at least 2800 Da, at least 3000 Da, at least 3200 Da, at least 3350 Da, at least 3500 Da, at least 4000 Da, at least 4500 Da, or at least 5000 Da. In some embodiments, the polyalkylene glycol has a weight-average molecular weight of at most 30,000 Da, at most 20,000 Da, at most 15,000 Da, at most 12,000 Da, or at most 10,000 Da.

[0053] In some embodiments, the polyalkylene glycol contains an average of at least 48, at least 50, at least 60, at least 65, or at least 70 repeating alkylene units. In some embodiments, the polyalkylene glycol contains an average of at most 500, at most 400, at most 300, at most 250, at most 220, or at most 200 repeating alkylene units.

[0054] In some embodiments, the polyalkylene glycol has a melt temperature of at least 30°C, at least 35°C, at least 40°C, at least 45°C, at least 48°C, or at least 50°C. In some embodiments, the polyalkylene glycol has a melt temperature of at most 100°C, at most 90°C, at most 80°C, or at most 70°C.

[0055] In some embodiments, the polyalkylene glycol has a hydroxyl value of less than 70 mg KOH / gm, or not more than 50 mg KOH / gm, or not more than 40 mg KOH / gm. In some embodiments, the polyalkylene glycol has a hydroxyl value of at least 5 mg KOH / gm, or at least 8 mg KOH / gm, or at least 10 mg KOH / gm, or at least 12 mg KOH / gm.

[0056] In some embodiments, the polyalkylene glycol has a viscosity of at least 20 cSt, at least 40 cSt, at least 60 cSt, or at least 80 cSt at 100°C. In some embodiments, the polyalkylene glycol has a viscosity of at most 2000 cSt, at most 1200 cSt, at most 1000 cSt, or at most 900 cSt at 100°C.

[0057] Suitable polyalkylene glycols can be CARBOWAX ™ Available commercially from the trademark. Other preparations can be made by known methods, such as polymerization of the corresponding epoxide monomer in the presence of an acid or base initiator. See, for example, U.S. Patent Publication US2007 / 0179199 A1 and “Introduction of Polyethylene Glycol (PEG)”, provided by BOC Sciences https: / / peg.bocsci.com / resources / technical-information / introduction-of-polyethylene-glycol-peg.

[0058] A certain concentration of polyalkylene glycol in the granulated polyethylene composition is suitable as a densifying agent for the polyethylene polymer. In some embodiments, the granulated polyethylene composition contains at least 0.01 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.4 wt%, at least 0.5 wt%, at least 0.6 wt%, at least 0.7 wt%, or at least 0.75 wt% of polyalkylene glycol based on the weight of the polyethylene polymer. In some embodiments, the granulated polyethylene composition contains at most 1 wt%, at most 0.8 wt%, at most 0.6 wt%, at most 0.4 wt%, at most 0.3 wt%, at most 0.2 wt%, or at most 0.1 wt% of polyalkylene glycol based on the weight of the polyethylene polymer. Exemplary concentrations of polyalkylene glycols include 0.01% to 1% by weight of polyethylene polymer, or 0.02% to 0.8% by weight of polyethylene polymer, or 0.04% to 0.6% by weight of polyethylene polymer, or 0.06% to 0.3% by weight of polyethylene polymer, or 0.07% to 0.2% by weight of polyethylene polymer, or 0.75% to 0.1% by weight of polyethylene polymer.

[0059] The compositions of the present invention may optionally further comprise additives suitable for molding polyethylene. Additives for polyethylene polymers are well known and commercially available. These additives are described in numerous publications, such as the booklet published by Plastics Design Library in 2015: Tolinski, “Additives for Polyolefins. Getting the Most out of Polypropylene, Polyethylene and TPO (Second Edition)”. Examples of commonly used additives include antioxidants, light stabilizers, deacidifiers, processing aids (such as lubricants, rheology controllers, release agents, anti-blocking additives, and slip agents), antistatic additives, flame retardants, pigments, and fillers. The preferred selection of additives will depend on the polyethylene polymer and the intended use of the final product.

[0060] Antioxidants are generally classified into primary antioxidants (free radical scavengers) and secondary antioxidants (hydroperoxide scavengers).

[0061] Examples of commonly used primary antioxidants include: hindered phenols, such as pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenol)propionate), which is commercially available under the name Irganox 1010, or octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, which is commercially available under the name Irganox 1076; hindered amines, such as polyamines commercially available under the names Chimassorb 944 or Chimassorb 2020; vitamin E, natural or synthetic; and lactones.

[0062] Examples of commonly used auxiliary antioxidants include: phosphites, such as tris(2,4-di-tert-butylphenyl) phosphite (which may be named IRGAFOS). ™ 168 commercially available) or tri(nonylphenyl) phosphite; and thioesters, such as distearate thiodipropionate.

[0063] Light stabilizers typically work by blocking light (especially ultraviolet light) or absorbing destructive light and emitting energy in a less destructive form. Examples of commonly used light stabilizers include: carbon black; pigments such as titanium dioxide; benzophenones such as 2-hydroxy-4-n-octyloxybenzophenone, commercially available as Chimassorb 81 and Cyasorb UV-531; benzotriazoles such as 2-(5-chloro-2H-benzotriazole-2-yl)-6-(1,1-dimethylethyl)-4-methylphenol, commercially available as Tinuvin 326; and cyanoacrylates such as 1,3-bis-((2'-cyano-3',3'-diphenylacryloyl)oxy)-2,2-bis-(((2'-cyano-3',3'-diphenylacryloyl)oxy)methyl)propane, commercially available as Uvinul 3030 is commercially available; and phenyl or aryl esters, such as benzoic acid, 3,5-(1,1-dimethylethyl)-phenyl ester, 2,4-bis(1,1-dimethylethyl)-phenyl ester, which are commercially available as Tinuvin 120.

[0064] Some of the aforementioned primary antioxidants can be used in combination with light stabilizers to scavenge free radicals that can be generated when light stabilizers absorb light. Hindered amine stabilizers can be used for this purpose.

[0065] Examples of acid removers include hydrotalcite (such as those commercially available under the name DHT-4A), metal stearates (such as calcium stearate and zinc stearate), and zinc oxide.

[0066] Examples of processing aids include: lubricants—some lubricants are metal salts of fatty acids, such as metal stearates like calcium stearate and zinc stearate; some lubricants are fatty amides, esters, acids, or alcohols, such as glyceryl monostearate, erucamide, oleamide, and ethylene bis(stearamide); and some lubricants are polymers, such as silicones, fluoropolymers, and polyolefin plastomers or oligomers; rheology control agents, such as 3M Dynamar. ™ Products; Mold Release Agents - Mold release agents reduce the adhesion of polyolefin polymers to molds, and examples of mold release agents include fatty acids or esters, such as glyceryl monostearate; amides, such as erucamide and oleamide; hydrocarbon microcrystalline waxes; and partially oxidized polyethylene; Slip Agents - Slip agents reduce friction between polyolefin polymers and processing equipment, and examples of slip agents include fatty acid amides, such as erucamide, oleamide, stearamide, ethylene bis-stearamide, and stearoyl stearamide; Antiblocking Agents - Antiblocking agents prevent the layers of polyolefin polymers from adhering to each other, and examples of antiblocking agents include inorganic materials that roughen the surface of the film, such as diatomaceous earth, silica, or talc, and fatty acid amides, such as betaine, erucamide, or stearamide.

[0067] Examples of antistatic additives include: nonionic compounds such as glycerides, such as glyceryl monostearate, diethanolamide laurate (commercially available as Chemstat LD-100), and ethoxylated amines (commercially available as Chemstat 122); dissipative polymers such as polyether block amides and ethylene ionomers; conductive fillers such as carbon black, graphene, graphite, metal particles, and coated inorganic particles; and conductive fibers such as metal fibers or carbon fibers.

[0068] Examples of flame retardants include: brominated or chlorinated compounds, such as decabromodiphenyl ether (commercially available as FR1210), tetrabromobisphenol A bis(2,3-dibromopropyl) ether (commercially available as FR-720), and chlorinated paraffin (commercially available as Chlororez 700), as well as phosphate flame retardants, which typically contain an acid source (such as ammonium polyphosphate (commercially available as Exolit AP-570)), a crosslinking agent (such as pentaerythritol), and a foaming agent (such as melamine).

[0069] Examples of pigments include: white colorants such as titanium dioxide, zinc sulfide, and barium sulfate; black colorants such as carbon black, copper chromate, and limonite; colored pigments such as azo dyes for various colors, iron oxide or quinacridone for red, cadmium sulfide for yellow, chromium(III) oxide for green, or cobalt aluminate for blue; metallic flakes to give a metallic appearance; and mica flakes to add a pearlescent or speckled appearance.

[0070] Examples of commonly used fillers include calcium carbonate, talc, mica, wollastonite, silica, and glass spheres. Many common fillers have an average particle size of 1 micrometer to 100 micrometers or 2 micrometers to 50 micrometers.

[0071] Many potential additives can be used for more than one purpose. For example, calcium stearate can be used as both a lubricant and an acid remover in polyolefins, and hindered amine antioxidants are also frequently used in light stabilizer packages. Fatty amides can be used as lubricants, slip agents, and anti-blocking additives.

[0072] In some embodiments, the concentration of the additive (excluding pigments and fillers) is at most 5% by weight, or at most 4% by weight, or at most 3% by weight, or at most 2% by weight, or at most 1% by weight, or at most 0.5% by weight of the polyethylene polymer. In some embodiments, the concentration of the additive (excluding pigments and fillers) is substantially 0% by weight, or at least 0.01% by weight, or at least 0.2% by weight, or at least 0.3% by weight, or at least 0.4% by weight, or at least 0.5% by weight of the polyethylene polymer.

[0073] Pigments and fillers can be used at higher concentrations. In some embodiments, the concentration of pigments and fillers is up to 70% by weight, up to 60% by weight, up to 50% by weight, up to 40% by weight, up to 30% by weight, or up to 20% by weight of the polyethylene polymer. In some embodiments, the concentration of pigments and fillers is substantially 0% by weight, or at least 0.5% by weight, or at least 1% by weight, or at least 3% by weight, or at least 5% by weight, or at least 1% by weight of the polyethylene polymer.

[0074] Polyethylene compositions used in coating molding are typically in powder form. It is known to grind or pulverize granules of polyethylene polymer to prepare powders of the desired size, and equipment for this purpose is commercially available with the instruction manual. See, for example, McDaid, “The Grinding of Polyethylene Powders for Use in Rotational Molding (Thesis)”, published by Queen's University Belfast (1998), and more. https: / / pure.qub.ac.uk / en / studentTheses / the-grinding-of-polyethylene-powders-for-use- in-rotational-mouldi The optimal powder size can vary depending on the equipment and process used for grinding and coating molding. In some cases, the median particle size is no more than 28 mesh (600 microns), 35 mesh (500 microns), or 45 mesh (350 microns). In other cases, the median particle size is at least 140 mesh (100 microns), at least 100 mesh (150 microns), at least 60 mesh (250 microns), or at least 50 mesh (300 microns).

[0075] In some embodiments, the components of the granular polyethylene composition may be individually ground and physically blended to prepare the composition used in this invention.

[0076] In some embodiments, the components of the polyethylene composition can be melt-blended and co-extruded to form pellets, wires, or other molded articles for storage and transport. When powder is required, the pellets or other molded articles can be ground to form powder. Equipment for melt blending and co-extrusion is commercially available, and methods for melt blending and co-extrusion are well known. In general, the components of the polyethylene composition are subjected to heating and shearing in an extruder, blender, kneader, or similar equipment until they melt and become homogeneously blended together. Extruders are commonly used blending equipment, and extrusion is a common blending technique. In some embodiments, the melt temperature during blending is at least 180°C, at least 185°C, or at least 190°C. In some embodiments, the melt temperature during blending is at most 210°C, at most 205°C, or at most 200°C. Pellet can be prepared by extruding, cooling, and shredding the melt-blended polyethylene composition. Suitable pelleting equipment is commercially available and comes with instructions for use. In some embodiments, the resulting pellets may have a diameter of 1 mm to 5 mm and a length of 1 mm to 10 mm.

[0077] In some embodiments, the masterbatch can be formed by melt blending a high concentration of polyalkylene glycol and optional other additives with a polyethylene polymer. The method for melt blending and extruding the masterbatch is similar to the method for melt blending and extruding granules as described above, except that the concentration of polyalkylene glycol and / or other additives in the masterbatch is higher. In some embodiments, the concentration of polyalkylene glycol in the masterbatch is at least 1% by weight, at least 3% by weight, or at least 5% by weight, based on the weight of polyethylene. In some embodiments, the concentration of polyalkylene glycol in the masterbatch is at most 20% by weight, at most 15% by weight, or at most 10% by weight, based on the weight of polyethylene. Other embodiments of the masterbatch can be readily melt blended with further polyethylene polymers to form compositions suitable for coating molding.

[0078] Using a granular polyethylene composition containing a polyalkylene glycol polymer in a rotational molding method, the method comprising the following steps:

[0079] a) Load the granular polyethylene composition into a mold and close the mold (“loading step”);

[0080] b) Heating the mold to the temperature at which the polymer melts while rotating the mold on at least two axes to form a coating of the polyethylene composition adhering to the inner surface of the mold (“heating step”).

[0081] c) Cooling the mold to solidify the polyethylene composition adhered to the inner surface of the mold (“cooling step”); and

[0082] d) Release the molded article from the mold (“removal step”).

[0083] Suitable rotary molding equipment and operating instructions for its use are known and commercially available.

[0084] Rotational molding produces hollow articles. Therefore, the amount of polyethylene composition loaded into the mold during the loading step may be less than the amount required to completely fill the mold. In some embodiments, the amount of polyethylene composition loaded into the mold is sufficient to produce a molded article with an average wall thickness of at least 1.0 mm, at least 1.5 mm, at least 2.0 mm, or at least 3.0 mm. In some embodiments, the amount of polyethylene composition loaded into the mold is sufficient to produce a molded article with an average wall thickness of at most 50 mm, at least 40 mm, at most 30 mm, or at most 25 mm.

[0085] Closed molds typically contain vents to allow air to escape during the heating step. The vents usually protrude to the center of the mold so that the molten and powdery polyethylene composition does not escape from the vents as the mold rotates.

[0086] In some embodiments, the peak internal air temperature (PIAT) achieved during the heating and cooling steps is at least 160°C, at least 165°C, at least 170°C, or at least 180°C. In some embodiments, the peak internal air temperature (PIAT) achieved during the heating and cooling steps is at most 250°C, at most 240°C, at most 230°C, at most 220°C, at most 210°C, at most 200°C, or at most 190°C.

[0087] The heated mold rotates on at least two axes, allowing the polyethylene composition to contact all internal surfaces of the mold. In some embodiments, the axes of rotation are substantially perpendicular to each other. In some embodiments, the rotation speed is at least 1 rpm, at least 3 rpm, or at least 5 rpm. In some embodiments, the rotation speed is at most 40 rpm, at most 30 rpm, or at most 20 rpm. The two axes do not necessarily rotate at the same speed. Depending on the shape of the mold, it may be desirable to rotate the longer axis at a faster or slower speed than the shorter axis.

[0088] The duration of the heating step varies depending on the equipment and the article being manufactured. In most embodiments, it is desirable to maintain the heating step until the polyethylene composition coalesces to form the molded article. In some embodiments, a time of 5 to 40 minutes is used.

[0089] Following the heating step, the mold is cooled in a cooling step. Cooling can be accelerated by blowing cold air onto the mold or spraying cooling water onto the mold, or both. In most embodiments, the cooling step continues until the molded article has cured sufficiently to maintain its shape outside the mold. In some embodiments, the mold is cooled to a temperature below the Vicat softening temperature of the polyethylene composition. In some embodiments, the mold is cooled to a temperature of up to 110°C, up to 100°C, up to 90°C, or up to 80°C.

[0090] When the mold reaches the required temperature, open the mold and recycle the molded product in the removal step.

[0091] The resulting molded article contains the polymer composition of the present invention.

[0092] Densification of molded parts can be directly observed under a microscope by examining the mold side of the part and noting the number and size of visible bubbles on the surface. Fewer and smaller bubbles indicate a denser molded part.

[0093] Alternatively, densification can be indirectly determined by the physical properties of the molded article, such as impact strength. In some embodiments, when the ARM impact strength is prepared and tested according to the test method, a 5-inch × 5-inch × 0.125-inch coated molded sample can achieve an average failure energy of at least 55 ft-lbs, at least 57 ft-lbs, or at least 58 ft-lbs.

[0094] In some implementations, when ARM impact strength is prepared and tested according to the test method, a 5-inch × 5-inch × 0.125-inch coated molded sample can achieve an average failure energy of at least 50 ft-lbs, at least 55 ft-lbs, at least 60 ft-lbs, at least 62 ft-lbs, at least 65 ft-lbs, or at least 70 ft-lbs when molded with PIAT at a temperature of at most 200°C, at most 190°C, at most 180°C, or at most 170°C.

[0095] In some embodiments, the coating molding method includes a polyethylene composition comprising: at least 90% by weight of an HDPE or LLDPE polyethylene polymer (excluding pigments and fillers); 0.05% to 0.5% by weight of a polyalkylene glycol substantially composed of ethylene oxide repeating units or propylene oxide repeating units or both, based on the weight of the polyethylene polymer; and 0% to 5% by weight of an additive selected from the group consisting of antioxidants, light stabilizers, deacidifiers, processing aids (such as lubricants, rheology controllers, release agents, anti-blocking additives and slip agents), antistatic additives and flame retardants, based on the weight of the polyethylene polymer.

[0096] Test methods

[0097] The parameters described in this application can be measured using the following measurement methods:

[0098]

[0099] Molecular weight and long-chain branching frequency Number-average molecular weight (M) is measured using gel permeation chromatography (GPC) (also known as size exclusion chromatography (SEC)). n ) and weight-average molecular weight (M w This technique utilizes an instrument comprising a column filled with porous beads, an elution solvent, and a detector to separate polymer molecules of different sizes. Molecular weight measurement via SEC is well known in the art and is discussed in more detail below: e.g., Slade, PE editor, Polymer Molecular Weights Part II, Marcel Dekker, Inc., NY, (1975) 287-368; Rodriguez, F., Principles of Polymer Systems, 3rd Edition, Hemisphere Pub. Corp., NY, (1989) 155-160; U.S. Patent 4,540,753; and Verstrate et al., Macromolecules, Vol. 21, (1988) 3360; T. Sun et al., Macromolecules, Vol. 34, (2001) 6812-6820; and U.S. Patent 9,670,345B2 (columns 20-21). The measurement of long chain branching is described in Pathraweeisariyakul et al., “Methods of Long Chain Branching Detection in PE by Triple-Detector Gel Permeation Chromatography”, J. APPL.POLYM. SCI. 2015, DOI: 10.1002 / APP.42222.

[0100] Example

[0101] The materials listed in Table 1 are used in these embodiments:

[0102]

[0103] In addition to the above, linear low-density polyethylene (LLDPE) is prepared via a solution process of ethylene and 1-hexene using a Ziegler-Natta catalyst, and has a density of 0.939 g / cm³. 3 The density and melt index are 3.8 g / 10 min. Essentially according to US Patent 4,612,300, the Ziegler-Natta catalyst premix is ​​prepared by sequentially adding anhydrous magnesium chloride in ISOPAR E, a solution of EtAlCl2 in heptane, and a solution of Ti(O-iPr)4 in heptane to a certain volume of ISOPAR E to obtain a composition having a magnesium concentration of 0.20 M and a Mg / Al / Ti ratio of 40 / 12.5 / 3. The catalyst premix is ​​contacted with a diluted Et3Al solution at an Al to Ti molar ratio of 4.0 during and before entering the polymerization reactor to obtain an active catalyst.

[0104] Sample preparation

[0105] Masterbatch containing LLDPE resin and the aforementioned densifying agents was prepared by continuous compounding using a Thermo Scientific Rheomex PTW 16 OS electrically temperature-controlled 16mm twin-screw extruder driven by a RheoDRive 7 OS. The components shown in Table 2 were co-extruded. The screw was configured for three mixing stages suitable for polymer compounding with an L / D ratio of 40:1. Samples were compounded at 300 rpm at 20% feeder output, yielding 2.7 lbs / hr. Each sample was fed through the extruder and then through a single-hole 2mm diameter die at a 45-degree angle into a cooling water bath. The resulting filament was fed into a VariCut pellet mill.

[0106]

[0107] To prepare co-extruded granule formulations with the contents shown in Table 3, the masterbatch was co-extruded with additional LLDPE using the following method. The LLDPE resin and masterbatch were weighed into 55-gallon drums with lids and liners. The drums were sealed and blended on a drum mixer for 30 minutes. Samples of the co-extruded blends were produced on a co-extrusion line with the following characteristics:

[0108]

[0109] The filament was extruded into a 6ft cooling water bath, dried with Huestis Air Block, and pelleted using a Conair 304 filament pelletizer. The shredded pellets were stored overnight in open 50lb paper bags and then sealed.

[0110] Pure LLDPE (CE1) and co-extruded granule formulations: IE2, IE3, IE4, and CE5 were milled in the grinding chamber at approximately 65°C using a PKA-18 laboratory mill manufactured by Powder King. The powder exiting the grinding chamber passed through a grading section with a 35-mesh sieve. Material that did not pass through the mesh was recycled to the blade chamber for further size reduction. IE4 and CE5 each contained 150 ppmw of commercial UV absorber.

[0111]

[0112] Each sample was coated and molded into a 12in × 12in × 12in cube using a Rotoline Lab 0.50 rotary molding machine equipped with an aluminum mold. Each box used a sample size of 2.9 lbs, resulting in a wall thickness of approximately 0.125in (3.17 mm). The furnace temperature during the heating phase was set to 288°C (550°F). The main shaft rotation was set to 6 rpm, and the secondary shaft rotation was set to 1.5 rpm. The reverse arm rotation was performed every 3 minutes.

[0113] Monitor the temperature inside the mold using a thermocouple at the center of the mold. Record the peak internal air temperature (PIAT) for each cube. (PIAT is the peak temperature measured inside the mold during the heating and cooling steps.) For each sample, prepare cubes with PIAT values ​​of 170°C, 180°C, 190°C, 200°C, 210°C, and 220°C. Cool each part to 90°C and then remove it from the mold.

[0114] A total of 16 specimens (5in × 5in plates) were obtained from each coated molded cube (4 on each side, excluding the top and bottom).

[0115] The mold side surface of each sample was observed under an 8x microscope using reflected light. The observations showed that, for similar PIAT, especially at lower PIAT, the polyethylene compositions of the present invention generally achieved excellent densification (fewer and / or smaller bubbles). Figure 1 compares IE4 with CE1 and CE2 at 170°C and 200°C.

[0116] The arm impact strength of each specimen was tested according to the test method. The average results of the arm impact strength tests for each group of four specimens are shown in Table 4. The results are presented as mean failure energy (MFE) in ft-lbs.

[0117]

[0118] Test results show that the composition of the present invention achieves high impact strength under low PIAT conditions, thus requiring a shorter heating time.

Claims

1. A coating molding method, the coating molding method comprising the following steps: a) Loading the granular polyethylene composition into a mold and closing the mold ("loading step"); b) Heating the mold to the melting temperature of the polyethylene composition while rotating the mold on at least two axes to form a coating of the polyethylene composition adhering to the inner surface of the mold ("Heating Step"); c) Cooling the mold to solidify the polyethylene composition adhering to the inner surface of the mold ("Cooling Step"); and d) Releasing the molded article from the mold ("Removal Step"), characterized in that the granular polyethylene composition comprises (1) a polyethylene polymer, and (2) a polyalkylene glycol with a weight average molecular weight greater than 2000 Da at a concentration of 0.01% to 1% by weight based on the polyethylene polymer.

2. The coating molding method according to claim 1, wherein the polyethylene polymer has a content of 0.93 g / cm³. 3 Up to 0.98 g / cm 3 High-density polyethylene polymers with a density and melt index (I2) ranging from 1 dg / min to 20 dg / min.

3. The coating molding method according to claim 1, wherein the polyethylene polymer has a content of 0.90 g / cm³. 3 Up to 0.94 g / cm 3 Linear low-density polyethylene polymers with a density and melt index (I2) ranging from 1 dg / min to 20 dg / min.

4. The coating molding method according to any of the preceding claims, wherein the polyalkylene glycol is substantially composed of ethylene oxide repeating units or propylene oxide repeating units or both.

5. The coating molding method according to any of the preceding claims, wherein the polyalkylene glycol in the polyethylene composition has a weight-average molecular weight of at least 2600 Da.

6. The coating molding method according to any of the preceding claims, wherein the polyalkylene glycol in the polyethylene composition has a melting temperature of 40°C to 90°C.

7. The coating molding method according to any of the preceding claims, wherein the concentration of polyalkylene glycol is from 0.05% to 0.5% by weight based on the weight of the polyethylene polymer.

8. The coating molding method according to any of the preceding claims, wherein the polyethylene composition is in powder form with a median particle size of 28 to 140 mesh.

9. The coating molding method according to any of the preceding claims, wherein the mold is heated to a peak internal air temperature of 170°C to 250°C.

10. The coating molding method according to any of the preceding claims, wherein the mold is heated to a peak internal air temperature of up to 250°C.

11. The coating molding method according to any of the preceding claims, wherein the polyethylene composition comprises: a) at least 90% by weight of HDPE or LLDPE polyethylene polymer (excluding pigments and fillers); b) 0.05% by weight to 0.5% by weight of a polyalkylene glycol substantially composed of ethylene oxy repeating units or propylene oxy repeating units or both, based on the weight of the polyethylene polymer; and c) 0% by weight to 5% by weight of an additive selected from the group consisting of antioxidants, light stabilizers, deacidifiers, processing aids such as lubricants, rheology control agents, release agents, anti-blocking additives and slip agents, antistatic additives and flame retardants, based on the weight of the polyethylene polymer.

12. The coating molding method according to claim 11, wherein the mold is heated to a peak internal air temperature of 180°C to 250°C.

13. The coating molding method according to claim 12, wherein the mold is heated to a peak internal air temperature not exceeding 250°C.

14. A molded article, said molded article being manufactured by the coating molding method according to any one of claims 1 to 13.

15. The molded article according to claim 14, wherein the average wall thickness is from 2 mm to 40 mm.

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