High gloss polyethylene composition and method for its preparation

Abstract

The application discloses a high-gloss polyethylene composition and a preparation method thereof, and belongs to the technical field of polyethylene compositions. The prior art improves glossiness through color master batches and nucleating agents, but the current production party has not found the problem of "glossiness retention", that is, the improved glossiness by the method cannot meet the glossiness retention requirement of polyethylene resin for hollow products. The application comprises, by weight, polyethylene base resin 100 parts, antioxidant 0.06-0.12 parts, zinc stearate 0.02-0.1 parts, nucleating agent 0.01-0.3 parts, polyethylene glycol 0.01-1 parts and boron nitride 0.02-0.05 parts. Not only the glossiness is significantly improved, but also the technical effect of longer glossiness retention time is obtained, so that the glossiness can not decrease in a relatively long time, and the raw materials are cheap and easy to obtain, and the preparation method is low in requirement.

Description

Technical Field

[0001] A high-gloss polyethylene composition and its preparation method are disclosed, belonging to the technical field of polyethylene compositions. Background Technology

[0002] Polyethylene resin has wide applications in various plastic products, especially in hollow products, with HDPE hollow resin showing particularly rapid development. In existing technologies, adding 6-8% white masterbatch to polyethylene improves the gloss of blown films, maintaining a gloss level of around 80%. Alternatively, adding 0.08% and 0.1% nucleating agents to LLDPE resin increases the gloss of blown films to approximately 88%. The polyethylene density used in these existing technologies for blown films is 0.920 g / cm³. 3 The melt flow rate (190℃, 2.16Kg) is around 2~4g / 10min, and resins with this characteristic have a high gloss.

[0003] However, in practical applications, polyethylene often involves densities of 0.950~0.960 g / cm³. 3 When the melt flow rate is 20-35 g / 10 min (measured at 190℃ and 21.6 kg), the resin exhibits poor gloss, significantly lower than that of polyethylene resin used for blown films. Existing technologies have slightly improved gloss through color masterbatches and nucleating agents, but manufacturers have not yet encountered a problem with "gloss retention." That is, the gloss improved by this method does not meet the gloss retention requirements for polyethylene resin used in hollow products; it easily degrades and decays within a short time at a high initial gloss level, failing to achieve reliable high gloss. Furthermore, methods that add brighteners, CaSO4, and other additives to impart high gloss to the material may result in additive leaching that contaminates the packaged product. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a high-gloss polyethylene composition and its preparation method that has high gloss and high gloss retention under high MFR and high density requirements, and does not precipitate modified components to contaminate the packaging.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a high-gloss polyethylene composition, characterized in that: by weight, it comprises: 100 parts of polyethylene base resin, 0.06~0.12 parts of antioxidant, 0.02~0.1 parts of zinc stearate, 0.01~0.3 parts of nucleating agent, 0.01~1 parts of polyethylene glycol, and 0.02~0.05 parts of boron nitride.

[0006] The above technical solution is based on the inventor's discovery that polyethylene glycol (PEG) is inexpensive and can act as a lubricant for polyethylene, making the polyethylene molecular chains more flexible and forming more perfect crystals, resulting in high gloss in the product. However, in actual experiments, PEG did not play this role. The inventor speculated that PEG, being a plate-like crystal, might be unevenly dispersed in the polyethylene matrix, causing defects in the crystals during resin crystallization, resulting in poor gloss. Therefore, to solve this problem, boron nitride, which has good hot-melt plasticizing effect, was added to the polyethylene resin containing PEG, antioxidants, nucleating agents, and zinc stearate. Under this scheme, the gloss of the initial polyethylene composition obtained by blending, melt plasticizing, extrusion, and granulation was significantly improved, and the gloss retention effect after 15 days was even better, with a smaller decrease, thus achieving a good gloss retention effect.

[0007] Further preferably, the nucleating agent is Milliken nucleating agent HPN20E. The nucleating agent can increase the crystallinity of the resin, refine the grains, and improve gloss. The preferred nucleating agent, when combined with other components, has an even greater effect on improving initial gloss.

[0008] Preferably, the antioxidant is a mixture of hindered phenolic antioxidants of polyphenols and phosphite antioxidants in any proportion.

[0009] More preferably, the weight ratio of the hindered phenolic antioxidant to the phosphite antioxidant is 1:0.5~2.

[0010] Preferably, the mass percentage of the polyethylene base resin crystals with a lamellar thickness of less than 9.6 nm is 4.0~7.0%; the mass percentage of the crystals with a lamellar thickness of 11~12.1 nm is 12~17%; and the mass percentage of the crystals with a lamellar thickness of 18.0~19.3 nm is 75~85%.

[0011] Thicker lamellae correspond to molecules with low branching content and regular, long methylene sequences; thinner lamellae correspond to molecules with high branching content and irregular chain structures.

[0012] Preferably, the polyethylene base resin has a comonomer molar content of 0.15~0.19% as measured by NMR, a branch number of 0.7~0.9 per 1000C, a total terminal methyl group of 1.4~2.0 per 1000C, and a main chain terminal methyl group of 0.5~1.4 per 1000C.

[0013] Further preferably, X-ray diffraction analysis of the 2mm sheet obtained by compression molding of the polyethylene base resin showed that the 110-facet grain size was 18-26 nm, preferably 20-26 nm, more preferably 24-26 nm; the 200-facet grain size was 15-21 nm, preferably 15-19.8 nm, more preferably 15-17.3 nm; and the peak height ratio of the 200-facet to the 110-facet was 0.15-0.25, preferably 0.15-0.23, more preferably 0.15-0.20, and more preferably 0.15-0.18. When the crystallinity of the obtained small hollow polyethylene resin is the same, the resin with a smaller peak height ratio of the 200-facet to the 110-facet has better gloss, with the maximum gloss value at a 60-degree angle reaching 99% in the experiment. This study shows that the degree of crystallinity and grain morphology of the product affect its initial gloss.

[0014] The comonomer content and branching degree determine the number of tie molecules in the resin. Higher comonomer content and greater branching degree result in more short branches attached to the tie molecules, increasing pull-out resistance. A higher branching number improves resistance to environmental stress cracking and impact strength, but excessive branching leads to poor weather resistance and low gloss in the finished product. This is because the presence of branches makes it difficult for the main chain to fold into crystals. Branches partially folded into the crystals can also introduce defects. Branches not incorporated into the crystals are significantly affected by post-processing molding techniques, and these branches have a substantial impact on gloss. Resins with low comonomer content and low branching degree have high density. High-density resins have high crystallinity. Theoretically, crystals can improve the gloss of materials. However, the large crystal size formed by the fast crystal formation speed actually reduces the gloss. This is because, for the same degree of crystallinity, large crystals are not as uniformly dispersed in the material as small crystals. Therefore, only small, uniformly distributed, and stable crystals can enable products to achieve high gloss and gloss retention in the presence of polyethylene glycol lubricant and boron nitride flux.

[0015] Preferably, the density of the polyethylene base resin is 0.950~.960 g / cm³. 3 At 190℃ and 21.6Kg, the melt mass flow rate was 20~35g / 10min.

[0016] Under the above technical solution, gloss modification of polyethylene resin with high-density melt mass flow rate was achieved.

[0017] Preferably, the comonomer of the polyethylene base resin is butene.

[0018] More preferably, the polyethylene base resin, as measured by GPC, has a weight-average molecular weight of 160,000 to 180,000, a number-average molecular weight of 17,000 to 18,000, a Mw / Mn ratio of 9 to 10, a crystallinity of 70 to 80%, a melting temperature of 130 to 134°C, a heat distortion temperature of 89 to 100°C, and a Vicat softening point of 131 to 132°C.

[0019] Preferably, the polyethylene glycol content is 0.3 to 0.7 parts.

[0020] Excessive polyethylene glycol content is not conducive to crystal formation and structural stability, while excessively low content may result in insignificant modification effects and poor synergistic effect with boron nitride.

[0021] Preferably, the boron nitride is hexagonal boron nitride with a powder purity greater than or equal to 99%, a particle size of 0.03~0.1μm, a plate-like crystal structure, and an aspect ratio of 13:1.

[0022] A method for preparing the above-described high-gloss polyethylene composition, characterized by comprising the following steps:

[0023] 1) The polyethylene base resin is divided into two parts, each part being 0.3 to 0.7 times the weight of the polyethylene base resin. One part is mixed with an antioxidant of the corresponding weight ratio, along with all of the zinc stearate and nucleating agent, and then melted, plasticized, extruded, and granulated. The other part is mixed with the remaining antioxidant, along with ground polyethylene glycol and boron nitride, and then melted, plasticized, extruded, and granulated.

[0024] 2) Mix the two polyethylene compositions evenly, then melt, plasticize, extrude and granulate to obtain a high-gloss polyethylene composition.

[0025] Nucleating agents are beneficial for refining grains and increasing crystallinity, thereby improving the gloss of the material. However, the gloss decreases after a period of time because the crystals are not perfect due to internal stress. Therefore, stable crystals are essential for maintaining gloss. The preparation method described above contributes to maintaining crystal stability.

[0026] Polyethylene glycol, being a flaky crystal, has poor dispersibility in resin. By grinding it into powder and adding boron nitride, which can enhance the hot-melt effect, polyethylene glycol can be well dispersed in the resin, reducing molecular chain entanglement. The resin crystals with smooth molecular chains have less internal stress, resulting in perfect and stable crystallization, which can improve the gloss retention of the material.

[0027] Compared with the prior art, the beneficial effects of this invention are: by utilizing the synergistic effect of polyethylene glycol and boron nitride, in the presence of antioxidants, nucleating agents and zinc stearate, not only is the gloss significantly improved, but also the gloss retention time is longer, so that the gloss does not decrease for a longer period of time. Moreover, the raw materials are cheap and readily available, and the preparation method and requirements are low, enabling high-density polyethylene resin with high melt flow rate to also have high gloss and retention.

[0028] Furthermore, the polyethylene resin of this invention, while maintaining the high MFR and high density required for the production of small hollow products, controls the structure of the polyethylene resin, such as: the number of methyl groups at the branch ends, the number of methyl groups at the main chain ends, the weight-average molecular weight, the number-average molecular weight, and the Mw / Mn ratio. The polyethylene resin of this invention has a maximum gloss of 100% at a 60-degree angle, which is higher than that of ordinary polyethylene (gloss of 70-80%). Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments, of which embodiment 4 is the preferred embodiment.

[0030] Examples and Comparative Examples

[0031] A high-gloss polyethylene composition, wherein the parameters of the polyethylene base resin used in each embodiment and comparative example are shown in Table 1 below, and the polyethylene base resin used in Example 5 is the same as the polyethylene base resin used in Example 1.

[0032] Table 1. Parameters of Polyethylene Base Resin

[0033] .

[0034] The components of the polyethylene compositions in each embodiment and comparative example are shown in Table 2 below. Antioxidant A is a hindered phenolic antioxidant of polyphenols, antioxidant B is a phosphite antioxidant, and the nucleating agent is Milliken nucleating agent HPN20E. The following components are expressed in parts by weight.

[0035] Table 2. Formulations of Examples and Comparative Examples

[0036] .

[0037] A method for preparing a high-gloss polyethylene composition, except for Example 5, the high-gloss polyethylene compositions of Examples 1-4 and Comparative Examples 1-4 above are prepared using the following method:

[0038] 1) According to the formula in Table 2 above, 100 parts of polyethylene base resin are divided into two equal parts, each part being 50 parts by weight.

[0039] 2) Add antioxidant A (half the amount), antioxidant B (half the amount), zinc stearate, and nucleating agent to one part, mix in a high-speed mixer for 5-10 minutes until uniform, add the uniformly mixed material to a twin-screw extruder, melt, plasticize, extrude, and granulate.

[0040] 3) Grind polyethylene glycol into 60-mesh powder using a water-cooled grinding mill;

[0041] 4) Add antioxidant A (half the amount), antioxidant B (half the amount), and the polyethylene glycol powder obtained in step 3) to another 50 parts by weight of polyethylene base resin. Mix in a high-speed mixer for 2-3 minutes, then add boron nitride and mix in a low-speed mixer for 5-10 minutes. Add the uniformly mixed material to a twin-screw extruder for melting, plasticizing, extrusion, and granulation. The temperature of the twin-screw extruder is 180℃~210℃. The twin-screw extruder has six temperature control zones, with the set temperature increasing sequentially from 180℃ to 210℃ from the first to the sixth temperature control zone. The die head temperature is set at 200℃.

[0042] 5) Mix the granules obtained in steps 2) and 4) in a low-speed mixer for 3-5 minutes until uniform, then melt, plasticize, extrude and granulate in a single-screw extruder to obtain the high-gloss polyethylene compositions of Examples 1-4 and Comparative Examples 1-4, respectively.

[0043] The high-gloss polyethylene composition of Example 5 is prepared by adding the raw materials used in the invention into a high-low mixing process for 3-5 minutes, then melting, plasticizing, extruding, and granulating the mixture in a twin-screw extruder at a temperature of 180°C to 210°C.

[0044] Performance testing

[0045] The high-gloss polyethylene compositions obtained in the examples and comparative examples were subjected to performance tests. The test methods used in each example and comparative example are as follows:

[0046] Density: Tested according to GB / T 1033.2-2010; using method D, tested after boiling for 30 minutes.

[0047] Tensile strength: Tested according to GB / T 1040.2-2006;

[0048] Melt mass flow rate: Tested according to GB / T3682-2000, with a weight of 21.6 kg and a temperature of 190℃;

[0049] Notched impact strength of simply supported beams: tested according to GB / T 1043.1-2008;

[0050] Bending performance: Tested according to GB / T 9341-2008;

[0051] ESCR: Tested according to GB / T 1842-2008, using condition B;

[0052] Branch type and number: Nuclear magnetic resonance (NMR) spectroscopy was used for testing. The experiment involved placing 75 mg of sample into a 5 mm sample tube, adding 0.5 mL of deuterated o-dichlorobenzene solvent, and maintaining the sample tube in a 140°C constant temperature bath for 3–4 hours to ensure uniform dispersion. The prepared sample tube was then placed in the NMR spectrometer and stabilized at 125°C for 30 minutes before scanning (pulse angle 90°, pulse interval 5 s, spectral width 220 ppm, combined pulse decoupling). After scanning, the spectrum was processed, and peaks in the 5–50 ppm range were accurately integrated (calibrated to 30 ppm using the isolated -CH2- peak in the polymer).

[0053] Molecular weight and its distribution were determined by gel permeation chromatography (GPC) with two columns in series. The solvent and mobile phase were both 1,2,4-trichlorobenzene (containing 0.1% by mass of the antioxidant 2,6-dibutyl-p-cresol). The column temperature was 150℃, the dissolution time was 4 h, and the flow rate was 1.0 ml / min. Narrow-distribution polystyrene standards were used for general standardization.

[0054] Melting temperature, enthalpy of melting and crystallinity: tested according to GB / T 19466.3-2004, with a heating rate of 10℃ / min.

[0055] Sample preparation: Compression molding was performed according to GB / T 2546.2-2003, with a compression temperature of 180℃, a compression pressure of 5MPa, a preheating time of 5min, a holding time of 5min, and a cooling time of 30min.

[0056] Gloss: Tested according to GB / T 8807-1988, at a test angle of 60°.

[0057] X-ray diffraction: A tube voltage of 40 kV and a tube current of 40 mA were used, with a Cu target, a two-dimensional detector, a scanning range of 2θ of 10°-40°, a scattering slit IS of 0.5°, a receiving slit RS1 of 20 mm, and a receiving slit RS2 of 20 mm.

[0058] The test results are shown in Table 3 below.

[0059] Table 3 Performance Test Results

[0060] .

[0061] The high-gloss polyethylene compositions prepared in Examples 4 and 5 were press-molded into 2 mm sheets, and the changes in crystal structure were analyzed by X-ray diffraction. The test results are shown in Table 4 below.

[0062] Table 4 Crystal structure test results

[0063] .

[0064] In Example 4, the peak positions 2θ of the 110 and 200 planes of the sheet are larger than those in Example 5. 2θ is inversely proportional to the interplanar spacing. The interplanar spacing of Example 4 is smaller than that of Example 5, meaning the crystal formed in Example 4 is more dense and complete. After a period of time, the crystal does not change, thus maintaining its gloss without decreasing. The peak heights of the 200 and 110 plane diffraction peaks in Example 4 are greater than those in Example 5. Higher diffraction peaks mean that the material reflects more light, resulting in higher gloss. This indicates that the crystal structure of the material prepared using the method of this invention has changed, giving the material higher gloss and better gloss retention.

[0065] Meanwhile, the melting and crystallization properties of the high-yellow polyethylene compositions of Examples 4 and 5 were analyzed by DSC method, and the test results are shown in Table 5 below.

[0066] Table 5. Melting and crystallization properties.

[0067] .

[0068] Tc(on) - Tc represents the crystallization rate of the system; the smaller the difference, the greater the crystallization rate. Tmend - Tmon reflects the melting range of the system; the melting range characterizes the degree of crystallization perfection, and the smaller the melting range, the more perfect the crystallization. Compared with Example 5, Example 4 has a larger crystallization rate, resulting in faster processing and molding speed; more perfect crystallization results in better gloss retention; and narrower grain size distribution results in better gloss.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A high-gloss polyethylene composition, characterized in that: The product comprises, by weight: 100 parts polyethylene base resin, 0.06-0.12 parts antioxidant, 0.02-0.1 parts zinc stearate, 0.01-0.3 parts nucleating agent, 0.01-1 parts polyethylene glycol, and 0.02-0.05 parts boron nitride; The polyethylene base resin has a crystal mass percentage of 4.0-7.0% with a lamellar thickness of less than 9.6 nm; a crystal mass percentage of 12-17% with a lamellar thickness of 11-12.1 nm; and a crystal mass percentage of 75-85% with a lamellar thickness of 18.0-19.3 nm. The polyethylene base resin, as measured by NMR, has a comonomer molar content of 0.15~0.19%, a branch number of 0.7~0.9 per 1000°C, a total terminal methyl group of 1.4~2.0 per 1000°C, and a main chain terminal methyl group of 0.5~1.4 per 1000°C.

2. The high-gloss polyethylene composition according to claim 1, characterized in that: The antioxidant is a mixture of hindered phenolic antioxidants of polyphenols and phosphite antioxidants in any proportion.

3. The high-gloss polyethylene composition according to claim 2, characterized in that: The weight ratio of the hindered phenolic antioxidant to the phosphite antioxidant is 1:0.5~2.

4. The high-gloss polyethylene composition according to claim 1, characterized in that: The density of the polyethylene base resin is 0.950~.960 g / cm³. 3 At 190℃ and 21.6Kg, the melt mass flow rate was 20~35g / 10min.

5. The high-gloss polyethylene composition according to claim 1, characterized in that: The comonomer of the polyethylene base resin is butene.

6. The high-gloss polyethylene composition according to claim 1, characterized in that: The polyethylene glycol content is 0.3 to 0.7 parts.

7. The high-gloss polyethylene composition according to claim 1, characterized in that: The boron nitride is hexagonal boron nitride with a powder purity greater than or equal to 99%, a particle size of 0.03~0.1μm, a plate-like crystal structure, and an aspect ratio of 13:

1.

8. A method for preparing the high-gloss polyethylene composition according to any one of claims 1 to 7, characterized in that: Includes the following steps: 1) The polyethylene base resin is divided into two parts, each part being 0.3 to 0.7 times the weight of the polyethylene base resin. One part is mixed with an antioxidant of the corresponding weight ratio, along with all of the zinc stearate and nucleating agent, and then melted, plasticized, extruded, and granulated. The other part is mixed with the remaining antioxidant, along with ground polyethylene glycol and boron nitride, and then melted, plasticized, extruded, and granulated. 2) Mix the two polyethylene compositions evenly, then melt, plasticize, extrude and granulate to obtain a high-gloss polyethylene composition.