LDPE compositions, process for their preparation and articles

Abstract

By using high concentration silica masterbatches containing as few additives as possible, and preferably using a combination of a satellite extruder and a main extruder, the present invention achieves an LDPE composition with a simpler composition. The LDPE composition of the present invention does not have special requirements for the conditions for the preparation of an LDPE article, and the LDPE article (in particular an LDPE film) prepared therefrom has satisfactory properties, in particular good optical properties (e.g. haze).

Description

Technical Field

[0001] This invention relates to LDPE compositions, methods for their preparation, and articles prepared therefrom. Background Technology

[0002] Polyethylene is a thermoplastic resin obtained by homopolymerization of ethylene monomers. Polyethylene is odorless, non-toxic, has a waxy feel, excellent low-temperature resistance, good chemical stability, and is resistant to most acids and alkalis. It is insoluble in common solvents at room temperature, has low water absorption, and excellent electrical insulation properties. Polyethylene can be processed and molded using general thermoplastic molding methods.

[0003] Homopolymerization of ethylene is typically a free radical polymerization process, and its products are often described as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), and metallocene polyethylene (mPE).

[0004] The classification of polyethylene according to density is known to those skilled in the art. For reference, the densities of fully amorphous and fully crystalline polyethylene are 0.880 and 1.000 g / cm³, respectively. 3 .

[0005] Generally, when high pressure (e.g., 82-276 MPa) is used in ethylene polymerization, the density of the resulting polymer is 0.915-0.940 g / cm³. 3 It is classified as LDPE. The reaction is usually carried out at a temperature of 132-332°C, resulting in the formation of a large number of branched structures. Therefore, LDPE has a structure of random long chains with a large number of randomly distributed branched branches. The length of the branched branches is not uniform, but rather has a certain distribution, mainly consisting of 2, 3, or 4 carbon atoms. LDPE is usually a transparent, slightly whitish, elastic solid.

[0006] Various types of polyethylene, especially LDPE, can be prepared by methods known to those skilled in the art. However, more commonly, polyethylene is commercially available. For example, LDPE can be the LDPE series products from Dow Chemical (USA), mPE can be the Affinity series products from Dow Chemical (USA), and HDPE can be the Rigidex series products from Ineos.

[0007] Polyethylene used in the manufacture of polyethylene products is typically used in the form of compositions containing additives. Anti-blocking agents are among the most common additives. Polyethylene products (especially polyethylene films) are prone to sticking, meaning the contact layers of the polyethylene plastic adhere to each other, making it difficult to separate the layers. In practical applications, the inconvenience caused by sticking includes difficulty in opening packaging bags, resulting in wasted manpower and time. Furthermore, the adhesion causes significant friction between the contact layers of the plastic film, making the film easily torn during unfolding. To reduce or even eliminate sticking in plastic films, especially polyethylene films, anti-blocking agents are added to the polyethylene.

[0008] Inorganic antiblocking agents commonly used in plastic film products include diatomaceous earth, talc, calcium carbonate, silica, and glass microspheres. Different materials often require different antiblocking agents. For example, for packaging materials, talc and calcium carbonate significantly affect the film's optical properties, impacting haze; diatomaceous earth, with its high hardness, easily scratches the film surface, limiting its application. The antiblocking effects of different materials also vary.

[0009] On the other hand, organic antiblocking agents include silicone polymers or polymers of methacrylates. These cross-linked polymer particles with specific structures, after being mixed with polymeric resins, form protrusions of a certain height on the surface of the film obtained through directional stretching, thereby achieving an antiblocking effect. Organic antiblocking agents have good optical properties, have almost no impact on the transparency of the film, and also have a slip-enhancing function, resulting in a low coefficient of friction, preventing scratches on the film surface, and producing a high gloss. However, organic antiblocking agents are generally much more expensive than inorganic antiblocking agents.

[0010] For LDPE products, silica particles are an important anti-blocking agent. To avoid affecting the optical properties of the final product, fine silica particles are required for finishing areas. However, fine silica particles are easily dispersed in the air during use, potentially causing dust explosions and posing industrial safety risks due to their potential for inhalation.

[0011] In addition, silica particles themselves have the disadvantages of being prone to agglomeration and having poor dispersibility. However, silica particles can only exert their anti-blocking effect after being well dispersed. Good dispersion of silica particles can also effectively reduce their dosage, help maintain film transparency, and benefit the appearance quality of the film.

[0012] Therefore, silica particles are usually processed into masterbatch before use.

[0013] Adding additives to a base polymer via masterbatch is a common method in polymer processing. To achieve uniform dispersion with small amounts of additives and / or avoid using the additives directly, the additives are often first prepared into a masterbatch, for example, granules, with a suitable dispersion carrier. The concentration of the additives in the masterbatch is significantly higher than that in the finished product. The masterbatch is then mixed with the polymer used to prepare the finished product, which is subsequently processed. Adding additives to a base polymer via masterbatch facilitates uniform dispersion of the additives, ensures consistent product quality, and reduces operating time and costs, improves production efficiency, and ensures safe production because it eliminates the need for separate additive addition during production.

[0014] Additives that are frequently added through masterbatch (hereinafter referred to as masterbatch additives) include fillers, colorants, flame retardants, stabilizers and other functional additives, such as antiblocking agents, opening slip agents, whitening and brightening agents, etc.

[0015] Masterbatch is often produced by melting and mixing the material to be made into the final product with the desired masterbatch additives using an extruder, and then granulating it.

[0016] There is a large body of literature in the existing technology concerning silica masterbatch.

[0017] CN103849033A discloses a polyethylene anti-blocking and slip-forming masterbatch and its preparation method. The masterbatch comprises 40-75% polyethylene, 10-20% anti-blocking agent (e.g., fumed silica with a particle size of 2-4 micrometers), and 10-30% slip-forming agent (e.g., oleamide and erucamide). The masterbatch is prepared using a twin-screw extruder, exhibiting good anti-blocking and slip-forming effects, high concentration, good impact resistance, toughness, and processability. It can be widely used in the production of polyethylene films or blown film products and is convenient and easy to use.

[0018] CN102765190A discloses a method for producing a biaxially oriented, multilayer co-extruded polyolefin heat-shrinkable film. The heat-shrinkable film is obtained by biaxially stretching three layers of co-extruded thick sheets. The upper and lower surfaces of the three layers contain ternary copolymer polypropylene and a high-sphericity synthetic silica microsphere masterbatch with an effective silica content of 5% by mass as an anti-blocking agent. These synthetic silica microspheres provide excellent anti-sticking and isolation effects on the film surface, effectively preventing adhesion between film layers and scratches during the stretching process. The silica masterbatch used in this invention contains only 5% silica.

[0019] CN103374194A discloses a fumed-phase nano-silica masterbatch for plastic modification. In this method, nano-sized fumed-phase silica undergoes surface hydrophobication treatment with octamethylcyclotetrasiloxane, followed by melt plasticization and kneading with maleic anhydride-grafted polyethylene in a twin-screw extruder. Finally, the mixture is granulated to obtain the silica masterbatch, wherein the amount of silica is approximately 40-60% by mass of the total components. Using this silica masterbatch achieves better dispersion in plastic modification applications, while also being convenient and environmentally friendly. This application clearly teaches that the silanol groups on the surface of nano-sized fumed-phase silica particles give the particle surface strong hydrophilicity, making it difficult to wet and disperse in organic phases. The surface hydrophobication treatment reduces the number of silanol groups, eliminating the problems caused by silanol groups.

[0020] CN118165407A discloses a directly sprayable polypropylene composite material with high light transmittance and a good balance of rigidity and toughness. It comprises an ionic polymer, such as a sodium or zinc ion copolymer of ethylene-methacrylic acid, ethylene-acrylic acid, or butadiene-acrylonitrile-acrylic acid, an antioxidant, and polypropylene, wherein the silica masterbatch contains 30-50% by weight of silica, a coupling agent (e.g., silanes and titanates), a lubricant (e.g., calcium stearate, magnesium stearate, and zinc stearate), and polypropylene as the matrix. The silica masterbatch is prepared using a single-screw extruder. The addition of the silica masterbatch can significantly improve the rigidity and light diffusion effect of the polypropylene material without affecting its light transmittance. This application teaches that the ratio of coupling agent to silica is related to the light transmittance and mechanical properties of the product.

[0021] CN118562229A discloses a high-transmittance, low-density, high-performance glass fiber reinforced polypropylene composite material for direct injection molding of exterior finishes. The material comprises glass fiber masterbatch, silica masterbatch, toughening agent, colorant, other additives, and polypropylene as a matrix. The silica masterbatch contains 30-50% by weight of silica, a lubricant, and polypropylene as the matrix. The silica is silica micropowder or fumed silica with a particle size of less than or equal to 10 micrometers. The silica masterbatch is prepared using a twin-screw extruder. By adding a high concentration of silica masterbatch, the warpage of the glass fiber reinforced polypropylene material can be improved without affecting the light transmittance of the polypropylene material. This application explicitly states that, due to its low bulk density, silica is difficult to disperse when its content exceeds 5% under conventional production processes. Adding a small amount of tap water and wetting the silica surface under high-speed mixing increases the bulk density of the silica, making it easier to produce a high-concentration silica masterbatch. The lubricant in the silica masterbatch of this application is essential.

[0022] It is evident that silica masterbatch has been used in existing technologies, but it may have low silica concentration, strict requirements on the size or shape of silica particles, or need to be used in conjunction with other specific masterbatch additives (such as slip agents, surface modifiers, coupling agents, and lubricants), or require special treatment in the preparation method.

[0023] However, the above conditions are clearly unfavorable for the use of silica masterbatch. In particular, the use of certain other masterbatch additives is both unavoidable and detrimental to the use of silica masterbatch in the preparation of LDPE products (especially LDPE films), because in the preparation of LDPE products (especially LDPE films), high-concentration silica masterbatch containing as few other masterbatch additives as possible is preferred.

[0024] On the one hand, considering both the economic efficiency of raw materials used in preparing the final product and the simplicity and ease of preparation of the raw material composition, minimizing the types and amounts of additives in the raw material composition, or even eliminating the use of specific additives altogether, is preferable. Furthermore, for food applications, minimizing the types and amounts of additives is becoming a requirement for regulators, market supervisors, and end-users. Clearly, since all masterbatch additives will ultimately be incorporated into the finished product, this means that the masterbatch should contain as few other masterbatch additives as possible.

[0025] On the other hand, using high-concentration silica masterbatch will reduce the amount of masterbatch added to the raw material composition used to prepare LDPE products, enabling very high productivity even with relatively small satellite extruders operating at lower RPMs, thereby reducing capital costs. Furthermore, this will reduce equipment wear, masterbatch quantity, and on-site masterbatch unloading, thus lowering operating costs and minimizing industrial hygiene risks associated with additives.

[0026] Therefore, it is beneficial to use high-concentration silica masterbatches containing as few other masterbatch additives as possible for the preparation and use of polyethylene products (especially LDPE products). In other words, only the additives necessary for the raw material composition used in the preparation of the product should be used in the high-concentration silica masterbatch. Summary of the Invention

[0027] The inventors of this invention have surprisingly discovered that LDPE products (especially LDPE films) can be readily prepared using LDPE compositions that meet the following conditions: The LDPE composition comprises a first LDPE, an optional additive selected from a first antioxidant, a colorant, a filler and a flame retardant or a combination thereof, a second LDPE, silica particles, a second antioxidant, or a combination thereof; The silica particles are introduced into the composition from a silica masterbatch that meets the following conditions: 1) The silica masterbatch is composed of a second LDPE, silica particles, and a second antioxidant, wherein the silica particles in the silica masterbatch contain 30-60% by weight, preferably 40-50% by weight. 2) The D50 of the silica particles is 1-10 micrometers, preferably 3-6 micrometers, and is preferably obtained by crushing diatomaceous earth.

[0028] The LDPE composition of the present invention does not have special requirements for the conditions for preparing LDPE articles, and the LDPE articles (especially LDPE films) prepared therefrom have satisfactory properties.

[0029] The technical solution and its effects of the present invention are unexpected, because they are completely opposite to the preconditions for using silica masterbatch taught in the prior art (low silica concentration, strict limitation on the size or shape of silica particles, simultaneous use with other specific masterbatch additives, or special treatment in the preparation method).

[0030] A first aspect of the present invention relates to an LDPE composition comprising a first LDPE, an optional additive selected from a first antioxidant, a colorant, a filler and a flame retardant or a combination thereof, a second LDPE, silica particles, a second antioxidant, or a combination thereof.

[0031] In the LDPE composition of the present invention, the first LDPE may be the same as or different from the second LDPE.

[0032] In the LDPE composition of the present invention, the first antioxidant and the second antioxidant may be the same or different, and are preferably selected independently from aromatic amine antioxidants and hindered phenolic antioxidants, more preferably from 2,6-di-tert-butyl-4-methylphenol (BHT) and octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate.

[0033] Preferably, the density of the first LDPE is 0.922-0.924 g / cc, and the melt index is 1.8-2.2 g / 10min.

[0034] Preferably, the silica particles have a D50 of 1-10 micrometers, more preferably 3-6 micrometers, and are preferably obtained by pulverizing diatomaceous earth.

[0035] A second aspect of the invention relates to a method for preparing the LDPE composition of the invention, comprising the step of adding the silica particles in the form of a silica masterbatch to a first LDPE, the silica masterbatch being composed of a second LDPE, silica particles, and a second antioxidant, wherein the silica particles are present in the silica masterbatch at a content of 30-60% by weight, preferably 40-50% by weight.

[0036] Preferably, the silica masterbatch is in granular form.

[0037] Preferably, the silica masterbatch is PE8000M purchased from Beijing-based Beihua High-Tech New Technology Co., Ltd., or Antiblock MB purchased from Kunshan Hezhen Ruixin Composite Materials Co., Ltd., Kunshan, China.

[0038] A third aspect of the invention relates to an LDPE article formed from the LDPE composition of the invention.

[0039] Preferably, the method includes the following steps: (i) The silica masterbatch is mixed with the first LDPE using a satellite extruder, and the resulting mixture is fed to the main extruder; (ii) Using the main extruder described above, the mixture obtained from step (i), the further first LDPE, and optional additives are mixed; and (iii) Prepare LDPE articles from the mixture obtained from step (ii).

[0040] Preferably, step (iii) includes molding the mixture obtained from step (ii) into LDPE particles and then into an LDPE film. Detailed Implementation

[0041] This invention relates to LDPE compositions, methods for their preparation, and articles prepared therefrom.

[0042] In this article, "first LDPE" refers to LDPE used as the matrix of the LDPE composition.

[0043] In this document, "additive" refers to additives that are added directly to the LDPE composition. Those skilled in the art will recognize that adding additives to the LDPE composition in the form of a masterbatch is not considered as adding them directly to the LDPE composition.

[0044] In this article, "second LDPE" refers to LDPE used as a matrix for silica masterbatch.

[0045] In this document, "secondary antioxidant" refers to an antioxidant directly added to the silica masterbatch. Those skilled in the art will recognize that antioxidants directly added to the LDPE composition are not considered secondary antioxidants.

[0046] Unless otherwise stated, all contents in this application are by weight, so all percentages are weight percentages.

[0047] In this document, the term "about" used to modify numerical values ​​means that the value should take into account experimental errors and variations that can be expected by those skilled in the art. In particular, "about" can refer to a value that is added to or subtracted from the modified value by 20%, preferably 10%, and more preferably 5%.

[0048] The first aspect of the present invention relates to LDPE compositions for preparing LDPE articles (particularly LDPE films).

[0049] The LDPE composition of the present invention comprises a first LDPE, an optional additive selected from a first antioxidant, a colorant, a filler and a flame retardant or a combination thereof, a second LDPE, silica particles, a second antioxidant, or a combination thereof.

[0050] The LDPE composition of the present invention comprises a first LDPE as the matrix of the composition.

[0051] The choice of the first LDPE (and consequently the choice of its properties) depends on the LDPE product to be prepared and the preparation process used. For example, in this invention, a first LDPE with a density of 0.922-0.924 g / cc and a melt index of 1.8-2.2 g / 10 min can be used.

[0052] In one particular embodiment of the invention, the first LDPE may be purchased from ExxonMobil Chemicals in Texas, USA, under the trade names LD 100AC, LD 160AT, and LD104BR.

[0053] The LDPE composition of the present invention further comprises optional additives selected from a first antioxidant, colorant, filler, flame retardant and combinations thereof.

[0054] The first antioxidant in the LDPE composition of the present invention may be selected from antioxidants commonly used in the preparation of LDPE compositions and LDPE articles, such as aromatic amine antioxidants and / or hindered phenolic antioxidants, such as 2,6-di-tert-butyl-4-methylphenol (BHT) and / or octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate. This first antioxidant may be the same as or different from the second antioxidant. For example, the first antioxidant may be available under the trade name Irganox 1076 from BASF SE in Ludwigshafen, Germany.

[0055] The amount of the first antioxidant can be determined by those skilled in the art according to actual needs.

[0056] The LDPE compositions of the present invention may contain colorants commonly used in polyethylene materials. Depending on their solubility in solvents and the dyeing medium, the colorants may be classified as pigments (which are often further classified as inorganic and organic pigments) and dyes, but it is precisely because of the uncertainty of this classification standard that it is sometimes unclear whether a particular colorant is classified as a pigment or a dye.

[0057] Examples of the colorant may include: Inorganic pigments, such as metal oxides, sulfides, metal salts, carbon black, and effect pigments, specifically, such as chrome yellow, chrome green, molybdenum chrome red, cadmium yellow, cadmium red, zinc sulfide, cerium red, cerium orange, ultramarine blue, ultramarine violet, titanium dioxide, iron oxide yellow, iron oxide red, iron oxide brown, iron oxide black, titanium yellow, titanium violet, cobalt blue, cobalt green, manganese violet, bismuth yellow, flake aluminum powder, copper powder, pearlescent pigments, phosphorescent pigments, carbon black, etc. Organic pigments, such as azo pigments, phthalocyanine pigments, and heterocyclic and fused-ring ketone pigments, specifically, such as Pigment Yellow 168, Pigment Red 53:1, Pigment Red 170, Pigment Red 48:2, Pigment Yellow 17, Pigment Yellow 128, Pigment Yellow 214, Pigment Red 15, Pigment Violet 15, Pigment Violet 23, Pigment Yellow 109, Pigment Yellow 139, Pigment Orange 43, Pigment Orange 71, Pigment Red 177, Pigment Red 138, Pigment Yellow 150, etc. Solvent dyes, such as azo dyes, anthraquinone dyes, triarylmethane dyes, methylene dyes, methylimine dyes, phthalocyanine dyes, acid / basic dye complexes, heterocyclic dyes, etc., specifically, such as Solvent Red 195, Solvent Orange 116, Solvent Yellow 21, Solvent Red 225, Solvent Red 111, Solvent Orange 86, Solvent Violet 59, Solvent Yellow 163, Solvent Yellow 93, Solvent Yellow 133, Solvent Yellow 179, Solvent Orange 80, Solvent Orange 107, Solvent Violet 49, Solvent Brown 53, Solvent Blue 67, Solvent Orange 60, Solvent Red 135, Solvent Red 179, Pigment Yellow 192, Solvent Yellow 114, Solvent Yellow 33, Solvent Yellow 157, Solvent Green 5, Solvent Yellow 160:1, Solvent Yellow 145, Vat Red 41, Pigment Red 181, Solvent Red 52, Solvent Orange 63, etc.

[0058] The colorant can be added in the form of color powder, color masterbatch, color paste, or color oil. Therefore, the colorant can further include a carrier and / or additives used in combination therewith to improve the application method and / or effect of the colorant. For example, the color masterbatch may contain a carrier, preferably LDPE, more preferably a first LDPE, as its matrix, and / or a dispersant, such as polyethylene wax and stearate.

[0059] The amount of colorant used can be determined by those skilled in the art according to actual needs.

[0060] The LDPE compositions of the present invention may contain fillers commonly used in polyethylene materials, including incremental fillers designed to reduce costs and reinforcing fillers designed to improve the physicochemical properties (e.g., mechanical properties) of LDPE articles.

[0061] Examples of the fillers may include barium sulfate, calcium carbonate, carbon black, calcium sulfate whiskers, diatomaceous earth, glass fiber, glass spheres, hollow silicate, kaolin, mica, talc, wollastonite, silicon dioxide, magnesium hydroxide, hydrotalcite, red mud, ferromagnetic powder, nickel fiber, wood flour, zirconium silicate, starch, fly ash, marble, aluminum, lignin, sand, etc., and combinations thereof.

[0062] Those skilled in the art will recognize that the filler may further include additives used in combination with it to improve the performance of the filler. For example, aminosilane-modified kaolin may be used, calcium carbonate may be treated with phosphate esters to promote adhesion to the LDPE matrix material and improve the mechanical properties of the material, and low molecular weight polyethylene wax may be used as a dispersant for carbon black.

[0063] The amount of filler used can be determined by those skilled in the art according to actual needs.

[0064] The LDPE composition of the present invention may contain flame retardants commonly used in polyethylene materials.

[0065] Examples of the flame retardant may include: Halogenated flame retardants, such as brominated flame retardants (e.g., decabromodiphenyl ether, bis(tetrabromophthalimide) ethane, hexabromobenzene), and chlorinated flame retardants (e.g., chlorinated paraffin, bis(hexachlorocyclopentadiene)cyclooctane), and combinations thereof, optionally used in combination with antimony trioxide; Phosphorus-containing flame retardants, such as alkylamine acid phosphates, red phosphorus, polyaryl phosphates and ammonium polyphosphates obtained by transesterification of triphenyl phosphates with polyols (such as bisphenol A or hydroquinone), and combinations thereof. Inorganic filler flame retardants, such as aluminum hydroxide and magnesium hydroxide; and Intumescent flame retardants, such as Exolit IFR from Hoechst Celanese, Spinflam MF from Montedison, Chargard CN-329 from Great Lake, Amgard EDAP from Albright & Wilson, and melamine salt of dipentaerythritol triphosphate.

[0066] Those skilled in the art will recognize that different flame retardants can be used in combination, and better results may be obtained.

[0067] The amount of flame retardant used can be determined by those skilled in the art according to actual needs.

[0068] The LDPE composition of the present invention contains silica particles as an anti-blocking agent.

[0069] In the prior art, requirements are often placed on the particle size, shape, and / or surface modification of silica particles used as anti-blocking agents in high-concentration silica masterbatches. In contrast, any silica anti-blocking agent commonly used in LDPE products can be used in this invention.

[0070] In a preferred embodiment of the present invention, the silica particles used as an anti-blocking agent have a D50 of 1-10 micrometers, preferably 3-6 micrometers.

[0071] In this invention, silica particles are added to the first LDPE in the form of silica masterbatch. Preferably, a silica masterbatch consisting of a second LDPE, silica particles, and a second antioxidant is used, wherein the silica particles in the silica masterbatch contain 30-60% by weight, preferably 40-50% by weight.

[0072] The silica particles in the silica masterbatch of this invention can be natural or synthetic. Synthetic silica particles can be obtained by gas-phase or precipitation methods known to those skilled in the art. However, natural silica particles, such as those obtained by pulverizing diatomaceous earth, are preferred. These silica particles can be purchased, for example, under the trade name Minbloc M4000 from the Sibelco Group in Antwerp, Belgium.

[0073] The second LDPE in the silica masterbatch of the present invention may be the same as or different from the first LDPE. Choosing a second LDPE that is different from the first LDPE means that a silica masterbatch can be used in a variety of LDPE compositions, thereby providing a wider range of applications for the silica masterbatch. Conversely, choosing a second LDPE that is the same as the first LDPE means that the LDPE composition contains only one type of LDPE, thereby obtaining a simpler LDPE composition and the resulting LDPE articles.

[0074] When the second LDPE differs from the first LDPE, the second LDPE may be selected from LDPEs commonly used in LDPE masterbatches. For example, the second LDPE may be purchased under the trade name LD 101BA from ExxonMobilChemicals in Texas, USA.

[0075] The second antioxidant in the silica masterbatch of the present invention may be the same as or different from the first antioxidant. When the second LDPE is different from the first LDPE, the second LDPE may be selected from antioxidants commonly used in the preparation of masterbatches, such as aromatic amine antioxidants and / or hindered phenolic antioxidants, such as 2,6-di-tert-butyl-4-methylphenol (BHT) and / or octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate. This second antioxidant may be purchased, for example, under the trade name Irganox 1076 from BASF SE in Ludwigshafen, Germany. The content of the second antioxidant in the silica masterbatch can be determined by those skilled in the art according to actual needs.

[0076] To avoid introducing new substances into the LDPE composition, it is preferable to use a silica masterbatch in which the silica particles are not surface-treated during preparation, thus preventing the introduction of new substances into the silica masterbatch. For example, it is preferable to use a silica masterbatch in which the silica particles are not surface-treated for hydrophobicity and / or coupling agents, since such surface treatments inevitably introduce new substances.

[0077] The silica masterbatch of the present invention can be in any form suitable for addition to LDPE compositions, such as particles having a suitable average particle size (e.g., 1-10 mm, particularly 3-7 mm).

[0078] In one embodiment of the present invention, the silica masterbatch can be commercially available, for example, it can be purchased under the trade name PE8000M from Beijing-based Beihua High-Tech New Technology Co., Ltd., or under the trade name Antiblock MB from Kunshan Hezhen Ruixin Composite Materials Co., Ltd., Kunshan, China.

[0079] The LDPE composition of the present invention can be prepared by uniformly mixing a first LDPE, optional additives, and silica masterbatch. The mixing method and conditions used can be determined by those skilled in the art according to actual needs.

[0080] The LDPE articles of the present invention can be final products in the form of plastic molded products, such as films, tubes, sheets, and granules, preferably LDPE films, such as transparent LDPE films. The LDPE articles of the present invention can be prepared from the LDPE compositions of the present invention using plastic molding methods common in the art, preferably under conditions common in the art.

[0081] Those skilled in the art will recognize that the preparation of the LDPE composition and LDPE article of the present invention can be carried out in a continuous series of steps.

[0082] For example, silica masterbatch and first LDPE can be first added to a satellite extruder and mixed to obtain a mixture in the form of LDPE melt. This mixture, along with further first LDPE and optional additives, is then added to a main extruder and mixed to obtain a mixture in the form of LDPE melt, i.e., the LDPE composition of the present invention. The LDPE composition exiting the main extruder in the form of LDPE melt can be directly molded into LDPE articles.

[0083] Those skilled in the art will recognize that the preparation of the LDPE composition and the LDPE article of the present invention can also be carried out as separate steps. For example, the LDPE composition of the present invention can first be molded into an LDPE intermediate product, such as LDPE granules, and then the LDPE article of the present invention can be further prepared from the LDPE intermediate product.

[0084] For example, in a preferred embodiment of the invention, silica masterbatch and a portion of first LDPE are metered into and mixed in a satellite extruder to obtain a mixture of LDPE melts. This mixture is then fed into the main extruder in a region with no or low back pressure, where it is mixed with the remaining first LDPE and optional additives from the main extruder hopper and extruded through a die to obtain the LDPE composition of the invention in LDPE melt form. The resulting LDPE melt form LDPE composition is then fed directly into a blow molding apparatus including a blow molding die, cooling, traction molding, and winding devices to obtain the LDPE article of the invention as an LDPE film.

[0085] Those skilled in the art will recognize that the LDPE composition of the present invention in the form of LDPE melt described above can also be cooled and granulated to obtain LDPE particles as an intermediate product, and then the particles can be used to prepare the LDPE article of the present invention as the final product.

[0086] The proportion of the first LDPE introduced into the satellite extruder in the total first LDPE can be determined by those skilled in the art according to actual needs.

[0087] The structural materials of the satellite extruder, particularly the screw and barrel, must be able to withstand the abrasiveness of the silica masterbatch, especially in the feeding and melting zones. Wear resistance of the feed screw and barrel requires the use of specific materials or coatings. The barrel can be a bimetallic type with a wear-resistant coating. Any non-"hard surface" (e.g., the feed section) must be chrome-plated. The above structure and design are standard practice for those skilled in the art.

[0088] The main extruder is an extruder commonly used to prepare LDPE products, especially an extruder with an annular die, such as a blow molding extruder, or a cast film extruder that casts molten polymer onto cooling rollers to form a film.

[0089] The operation of satellite extruders and main extruders can include conventional techniques used for molding LDPE products. For example, the material can be degassed before being fed into the extruder barrel.

[0090] By using a high-concentration silica masterbatch containing as few additives as possible, and preferably using a combination of satellite extruders and main extruders, the present invention obtains LDPE compositions with simpler compositions.

[0091] The LDPE composition of the present invention does not have special requirements for the conditions for preparing LDPE articles, and the LDPE articles (especially LDPE films) prepared therefrom have satisfactory properties, especially good optical properties (e.g., haze).

[0092] In the preparation of the LDPE articles of the present invention, the use of high-concentration silica masterbatch when adding it to the first LDPE allows for the use of smaller satellite extruders operating at lower RPMs while still achieving high productivity. Using smaller satellite extruders reduces capital costs and also decreases equipment wear and masterbatch consumption, thereby reducing operating costs. The combined use of satellite extruders and main extruders ensures uniform mixing of materials, particularly the high-concentration silica masterbatch and the first LDPE.

[0093] Example

[0094] The technical solution of the present invention will be explained below with reference to comparative examples and embodiments. Those skilled in the art should understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques and conditions described in the literature in this field, or in accordance with the techniques and conditions conventionally used in this field, or in accordance with the instructions in the product manual.

[0095] LD 100AC, LD 160AT and LD104BR, purchased from ExxonMobil Chemicals in Texas, USA, were used as the first LDPE.

[0096] PE8000M, purchased from Beijing Chemical High-Tech New Technology Co., Ltd., and Antiblock MB, purchased from Kunshan Hezhen Ruixin Composite Materials Co., Ltd., were used as silica masterbatch 1, silica masterbatch 2, and silica masterbatch 3. The silica particles contained in both masterbatches were Minbloc M4000 from Sibelco Group in Antwerp, Belgium, which is pulverized diatomaceous earth with a D50 of 5 microns. The composition of silica masterbatch 1, silica masterbatch 2, and silica masterbatch 3 is shown in Table 1.

[0097] Table 1. Composition of silica masterbatch as raw material

[0098] Using a twin-screw extruder and a single-screw extruder as the satellite extruder and main extruder respectively, LDPE melt strips were prepared according to the formulation in Table 2. The LDPE melt strips extruded from the main extruder die were granulated underwater to obtain LDPE particles 1, LDPE particles 2, and LDPE particles 3 with a particle size of approximately 3.8 mm.

[0099] Table 2. Composition of LDPE particles

[0100] Using a blow molding apparatus from OCS Optical Control Systems GmbH in North Rhine-Westphalia, Germany, which includes a blow molding extruder, blow molding die, cooling, traction molding, and winding system, LDPE films 1, LDPE films 2, and LDPE films 3, respectively, are prepared as the final products from LDPE granules 1, LDPE granules 2, and LDPE granules 3.

[0101] The thickness and haze of the final product were measured using the thickness measurement module and haze measurement module built into the blow molding machine. The results are shown in the table below.

[0102] Table 3. Properties of LDPE film as the final product

[0103] The haze of the LDPE film, as the final product, meets the requirements of conventional products.

Claims

1. An LDPE composition comprising a first LDPE, an optional additive selected from a first antioxidant, a colorant, a filler and a flame retardant or combinations thereof, a second LDPE, silica particles, a second antioxidant, or a combination thereof.

2. The LDPE composition of claim 1, wherein the first LDPE is the same as or different from the second LDPE.

3. The LDPE composition of claim 1 or 2, wherein the first antioxidant and the second antioxidant are the same or different, and are preferably independently selected from aromatic amine antioxidants and hindered phenolic antioxidants, more preferably selected from 2,6-di-tert-butyl-4-methylphenol (BHT) and octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate.

4. The LDPE composition of any one of claims 1-3, wherein the first LDPE has a density of 0.922-0.924 g / cc and a melt index of 1.8-2.2 g / 10 min.

5. The method of any one of claims 1-4, wherein the silica particles have a D50 of 1-10 micrometers, preferably 3-6 micrometers, and are preferably obtained by pulverizing diatomaceous earth.

6. A method for preparing the LDPE composition of any one of claims 1-5, comprising the step of adding the silica particles to a first LDPE in the form of a silica masterbatch, the silica masterbatch being composed of a second LDPE, silica particles, and a second antioxidant, wherein the silica particles are present in the silica masterbatch at a content of 30-60% by weight, preferably 40-50% by weight.

7. The method of claim 6, wherein the silica masterbatch is in particulate form.

8. The method of claim 6 or 7, wherein the silica masterbatch is PE8000M purchased from Beijing Beihua High-Tech New Technology Co., Ltd., China, or Antiblock MB purchased from Kunshan Hezhen Ruixin Composite Materials Co., Ltd., Kunshan, China.

9. An LDPE article, which is formed from the LDPE composition of any one of claims 1-5.

10. A method for preparing the LDPE article of claim 9, the method comprising the following steps: (i) The silica masterbatch is mixed with the first LDPE using a satellite extruder, and the resulting mixture is fed to the main extruder; (ii) Using the main extruder described above, the mixture obtained from step (i), the further first LDPE, and optional additives are mixed; as well as (iii) Prepare LDPE articles from the mixture obtained from step (ii).

11. The method of claim 10, wherein step (iii) comprises molding the mixture obtained from step (ii) into LDPE particles and then into an LDPE film.

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