Injection molding method of ultra-high molecular weight polyethylene

Abstract

The invention discloses an injection molding method of ultra-high molecular weight polyethylene, which comprises the following steps: step 1, mixing ultra-high molecular weight polyethylene resin and polyethylene wax to form a composition; step 2, adding the composition into an injection molding machine for high-temperature melting to form a melt, injecting the melt and filling a mold with the melt; and 3, cooling the mold, and opening the mold after the melt is cured to obtain the ultra-high molecular weight polyethylene product. By adopting the technical scheme, the low-molecular-weight polyethylene wax can greatly improve the fluidity of the ultra-high-molecular-weight polyethylene, so that the injection molding of the ultra-high-molecular-weight polyethylene composition is smoother, and the polyethylene wax can participate in crystallization of the ultra-high-molecular-weight polyethylene in the cooling process; the mechanical property of the ultra-high molecular weight polyethylene can be well maintained.

Description

Technical Field

[0001] The present application relates to the field of polymer technology, and more specifically, to an injection molding method for ultra-high molecular weight polyethylene. Background Art

[0002] Ultra-high molecular weight polyethylene has incomparable comprehensive properties of wear resistance, impact resistance, self-lubrication, corrosion resistance, low temperature resistance, sanitation and non-toxicity, non-stickiness, non-absorption, low density, etc. compared with ordinary polyethylene and other engineering plastics. Therefore, it is recognized as an engineering plastic with extremely excellent comprehensive properties. At present, ultra-high molecular weight polyethylene has been widely used in textile, papermaking, food, chemical industry, agriculture, mining, construction, medical treatment, sports, military and other fields.

[0003] "Excellent performance, difficult processing" is the characteristic of ultra-high molecular weight polyethylene. Ultra-high molecular weight polyethylene is a rubber-like high-viscosity elastic body in the melt state, with a melt viscosity of up to 10 8 Pa•s, the melt flow index is almost zero, so the critical shear rate of ultra-high molecular weight polyethylene is very low, and it is easy to produce defects such as melt fracture. It is difficult to use conventional polymer processing methods to form ultra-high molecular weight polyethylene products, which greatly limits its application. Therefore, it is particularly important to develop ultra-high molecular weight polyethylene molding and processing technology.

[0004] Chinese patent CN1191230A reports that ultra-high molecular weight polyethylene products with high flow properties are prepared by adding liquid crystal polymers and other additives to ultra-high molecular weight polyethylene. However, compared with ultra-high molecular weight polyethylene, liquid crystal polymers are expensive, which greatly limits their application in the market.

[0005] Chinese patent CN1244626C reports that a certain amount of polypropylene and other additives are added to ultra-high molecular weight polyethylene, and melt blended and granulated at high temperature to prepare an ultra-high molecular weight polyethylene product that can be used for injection molding and extrusion molding. This method uses the fluidity of polypropylene to reduce the high viscosity of ultra-high molecular weight polyethylene during processing, but polypropylene and ultra-high molecular weight polyethylene have poor compatibility, so the mechanical properties of the product are greatly reduced.

[0006] Chinese patent CN106317547A reports that a certain amount of high-density polyethylene, long-chain branched polyethylene and other additives are added to ultra-high molecular weight polyethylene, and melt blended and granulated at high temperature to obtain an ultra-high molecular weight polyethylene that can be used for molding, extrusion and injection molding. This method uses the high fluidity of high-density polyethylene to reduce the high viscosity of ultra-high molecular weight polyethylene during processing, but the addition of too many additives reduces the mechanical properties of the ultra-high molecular weight polyethylene polymer and the preparation cost is also high.

[0007] It is difficult for the existing technology to meet the market requirements for ultra-high molecular weight polyethylene injection molding in terms of performance and cost. With the continuous expansion of applications, the market demand for ultra-high molecular weight polyethylene products of various special shapes continues to increase, and thus the demand for ultra-high molecular weight polyethylene injection molding technology with excellent mechanical properties and low cost continues to increase. Therefore, the current status of this field is that it is necessary to provide an ultra-high molecular weight polyethylene injection molding technology to meet the market demand. Summary of the invention

[0008] In order to further effectively improve the processability of ultra-high molecular weight polyethylene and the mechanical properties of ultra-high molecular weight polyethylene products, the present application provides an injection molding method for ultra-high molecular weight polyethylene.

[0009] The present application provides an injection molding method for ultra-high molecular weight polyethylene, comprising the following steps: Step 1: mixing an ultra-high molecular weight polyethylene resin and a polyethylene wax to form a composition; Step 2: adding the composition into an injection molding machine for high temperature melting to form a melt, and injecting the melt to fill the mold; Step 3: Cool the mold, and after the melt solidifies, open the mold to obtain the ultra-high molecular weight polyethylene product.

[0010] By adopting the above technical scheme, low molecular weight polyethylene wax can be used as a flow modifier to greatly improve the fluidity of ultra-high molecular weight polyethylene, making the injection molding of the ultra-high molecular weight polyethylene composition smoother. In addition, during the cooling process, the polyethylene wax can participate in the crystallization of the ultra-high molecular weight polyethylene, and can well maintain the mechanical properties of the ultra-high molecular weight polyethylene.

[0011] Preferably, the content of the ultra-high molecular weight polyethylene resin in the composition of step 1 is 91 to 99 wt %, and the content of the polyethylene wax is 1 to 9 wt %.

[0012] Preferably, the content of the ultra high molecular weight polyethylene resin in the composition is 95 to 98 wt %.

[0013] By adopting the above technical solution, the content of ultra-high molecular weight polyethylene resin is 91-99wt%, especially between 95-98wt%. At this time, the fluidity of the melt is better, the injection molding process is smoother, and the mechanical properties of the injection molded products are also excellent.

[0014] Preferably, the polyethylene wax is a linear polyethylene wax with a weight average molecular weight of 2.0×10 3 ~7.0×10 3 g / mol.

[0015] Preferably, in step 2, the temperature of the feeding section of the injection molding machine is 90-140°C, the temperature of the compression section is 160-250°C, the temperature of the homogenization section is 160-250°C, the temperature of the melt passing through the nozzle is 160-250°C, the screw speed is 5-80rpm, the injection pressure is 10-300MPa, the holding pressure is 5-50MPa, the holding time is 60-180s, and the mold temperature is 30-100°C.

[0016] By adopting the above technical solution, if the temperature is too low, the ultra-high molecular weight polyethylene resin will not be melted enough and will not have sufficient fluidity; if the temperature is too high, the ultra-high molecular weight polyethylene will be severely degraded, which will greatly affect the mechanical properties of the product.

[0017] Preferably, the temperatures of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 170-200°C.

[0018] By adopting the above technical scheme, the folded chain lamellae of the ultra-high molecular weight polyethylene resin can be fully melted within this temperature range, but some straight chain crystals can be retained, so the fluidity of the ultra-high molecular weight polyethylene composition can be guaranteed, and the retained straight chain crystals can act as nucleating agents during the cooling process to induce polyethylene wax to crystallize on its surface, thereby well maintaining the mechanical properties of the ultra-high molecular weight polyethylene product.

[0019] Preferably, the injection pressure is 40 to 120 MPa.

[0020] By adopting the above technical solution, the injection pressure is high, the orientation degree of ultra-high molecular weight polyethylene is high, and the tensile properties of the product are good. Within this injection pressure range, the injection molding is good and there is no porosity. At the same time, the melt will not be unable to completely fill the mold due to too low injection pressure, and there will be no overflow due to too high injection pressure.

[0021] Preferably, the holding pressure of the injection molding machine is 10-28 MPa, and the holding time is 90-180 s.

[0022] By adopting the above technical solution, under the pressure-maintaining condition, the relaxation movement of the oriented polymer chains can be slowed down, the oriented structure generated during the processing can be preserved in the polymer product, and the obtained product has good tensile properties.

[0023] Preferably, the mold temperature is 50 to 70°C.

[0024] Preferably, in step 3, the cooling rate of the melt in the mold is 10-20° C. / min.

[0025] By adopting the above technical scheme, the mold temperature is too low and the cooling speed is too fast, and the ultra-high molecular weight polyethylene and polyethylene wax are not sufficiently crystallized in the mold, which not only affects the tensile properties of the ultra-high molecular weight polyethylene products, but also affects the dimensional stability during use; if the mold temperature is too high and the cooling speed is too slow, the internal temperature of the product is too high and the crystallization is too slow, resulting in warping of the product after demolding and cooling, and greatly affecting the injection molding efficiency.

[0026] In summary, this application has the following beneficial effects: 1. The present invention selects polyethylene wax and ultra-high molecular weight polyethylene resin for mixing, which can not only greatly improve the fluidity of ultra-high molecular weight polyethylene, but also maintain the mechanical properties of ultra-high molecular weight polyethylene products after cooling; 2. The temperature of the compression section, homogenization section and melt passing through the nozzle of the injection molding machine is controlled at 170-200°C, which can fully melt the folded chain lamellae of the ultra-high molecular weight polyethylene resin and retain some straight chain crystals, ultimately improving the mechanical properties of ultra-high molecular weight polyethylene products; 3. The injection pressure is controlled at 40-120Mpa, which is beneficial to improve the orientation of ultra-high molecular weight polyethylene and ensure the integrity of the product, while also avoiding overflow; 4. The mold temperature is 50-70℃ and the cooling rate is controlled at 10-20℃ / min. This can not only prevent the product from warping after demolding and cooling, but also help the ultra-high molecular weight polyethylene and polyethylene wax to crystallize better and maintain the mechanical properties and dimensional stability of ultra-high molecular weight polyethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a two-dimensional wide-angle X-ray diffraction (WAXD) pattern of the ultra-high molecular weight polyethylene product in Example 1 of the present application; Figure 2 It is a two-dimensional wide-angle X-ray diffraction (WAXD) diagram of the ultra-high molecular weight polyethylene product in Comparative Example 7 of the present application; Figure 3 is a differential scanning calorimetry (DSC) diagram of the ultra-high molecular weight polyethylene product in Example 1 of the present application; Figure 4 This is a differential scanning calorimetry (DSC) diagram of the ultra-high molecular weight polyethylene product in Comparative Example 7 of the present application. DETAILED DESCRIPTION

[0028] The present application is further described in detail below in conjunction with the accompanying drawings, embodiments and comparative examples. Example 1

[0029] An injection molding method for ultra-high molecular weight polyethylene comprises the following steps: Step 1: The viscosity average molecular weight is 5.23×106 g / mol ultra-high molecular weight polyethylene resin and a weight average molecular weight of 4.51×10 3 g / mol of linear polyethylene wax are uniformly mixed to form a composition; Step 2: adding the composition into an injection molding machine for high temperature melting to form a melt, and injecting the melt to fill the mold; Step 3: Cool the mold, and after the melt solidifies, open the mold to obtain the ultra-high molecular weight polyethylene product.

[0030] Among them, the content of ultra-high molecular weight polyethylene resin in the composition is 95wt%, and the content of linear polyethylene wax is 5wt%; the temperature of the feeding section of the injection molding machine is 115°C, the temperature of the compression section is 185°C, the temperature of the homogenization section is 185°C, the temperature of the melt passing through the nozzle is 185°C, the screw speed is 40r / min, the injection pressure is 80MPa, the holding pressure is 28MPa, the holding time is 120s, the mold temperature is 60°C, and the cooling rate of the melt in the mold is 15°C / min. Example 2

[0031] An injection molding method for ultra-high molecular weight polyethylene comprises the following steps: Step 1: The viscosity average molecular weight is 5.23×10 6 g / mol ultra-high molecular weight polyethylene resin and a weight average molecular weight of 2.0×10 3 g / mol of linear polyethylene wax are uniformly mixed to form a composition; Step 2: adding the composition into an injection molding machine for high temperature melting to form a melt, and injecting the melt to fill the mold; Step 3: Cool the mold, and after the melt solidifies, open the mold to obtain the ultra-high molecular weight polyethylene product.

[0032] Among them, the content of ultra-high molecular weight polyethylene resin in the composition is 99wt%, and the content of straight-chain polyethylene wax is 1wt%; the temperature of the feeding section of the injection molding machine is 140°C, the temperature of the compression section is 250°C, the temperature of the homogenizing section is 250°C, the temperature of the melt passing through the nozzle is 250°C, the screw speed is 80r / min, the injection pressure is 300MPa, the holding pressure is 50MPa, the holding time is 60s, the mold temperature is 100°C, and the cooling rate of the melt in the mold is 5°C / min. Example 3

[0033] An injection molding method for ultra-high molecular weight polyethylene comprises the following steps: Step 1: The viscosity average molecular weight is 5.23×10 6 g / mol ultra-high molecular weight polyethylene resin and a weight average molecular weight of 7.0×10 3g / mol of linear polyethylene wax are uniformly mixed to form a composition; Step 2: adding the composition into an injection molding machine for high temperature melting to form a melt, and injecting the melt to fill the mold; Step 3: Cool the mold, and after the melt solidifies, open the mold to obtain the ultra-high molecular weight polyethylene product.

[0034] Among them, the content of ultra-high molecular weight polyethylene resin in the composition is 91wt%, and the content of linear polyethylene wax is 9wt%; the temperature of the feeding section of the injection molding machine is 90°C, the temperature of the compression section is 160°C, the temperature of the homogenizing section is 160°C, the temperature of the melt passing through the nozzle is 160°C, the screw speed is 5r / min, the injection pressure is 10MPa, the holding pressure is 5MPa, the holding time is 180s, the mold temperature is 30°C, and the cooling rate of the melt in the mold is 30°C / min.

[0035] Comparative Example 1: The only difference between this comparative example and Example 1 is that the comparative example does not contain linear polyethylene wax.

[0036] Comparative Example 2: The difference between this comparative example and Example 1 is that the 4 g / mol and a branching degree of 2 / 10 4 High-density polyethylene replaces linear polyethylene wax.

[0037] Comparative Example 3: The only difference between this comparative example and Example 2 is that the comparative example does not contain linear polyethylene wax.

[0038] Comparative Example 4: The difference between this comparative example and Example 2 is that the 4 g / mol and a branching degree of 2 / 10 4 High-density polyethylene replaces linear polyethylene wax.

[0039] Comparative Example 5: The only difference between this comparative example and Example 3 is that the comparative example does not contain linear polyethylene wax.

[0040] Comparative Example 6: The difference between this comparative example and Example 3 is that the 4 g / mol and a branching degree of 2 / 10 4 High-density polyethylene replaces linear polyethylene wax.

[0041] The tensile mechanical properties, impact mechanical properties, thermal properties and crystallization properties of the ultra-high molecular weight polyethylene products of Examples 1 to 3 and Comparative Examples 1 to 6 were tested. The specific testing methods are as follows:

[0042] Thermal performance test Weigh 5 to 10 mg of the ultra-high molecular weight polyethylene product and place it in a standard aluminum crucible. Protect it with a dry nitrogen flow and use a differential scanning calorimeter (DSC) to test the thermal properties of the ultra-high molecular weight polyethylene product. Heat and scan from 25 °C to 200 °C at a heating rate of 10 °C / min, and record the thermal performance curve of the product.

[0043] Crystallinity test The crystallinity of the ultra-high molecular weight polyethylene products was tested by wide angle X-ray diffraction (WAXD) device, with an X-ray wavelength of 0.124nm. The two-dimensional WAXD results were collected by Pilatus 900K detector with a resolution of 172×172μm 2 , the distance from the detector to the sample is 210 mm. The WAXD data obtained were processed by FIT2D software. The two-dimensional WAXD image was integrated in one dimension to obtain the intensity distribution curve in the 2θ direction. Then the curve was fitted by peak separation, the ratio of amorphous area to crystalline area was calculated, and then the crystallinity was calculated. The calculation formula is as follows: Xc=Ac / (Ac+Aa), where Ac and Aa represent the area under the crystalline peak and amorphous peak of the I(2θ)~2θ curve, respectively.

[0044] Tensile mechanical properties test: A milling machine was used to cut each sample into a size of 70*15*2 mm. A universal mechanical testing machine was used to carry out tensile mechanical properties tests on ultra-high molecular weight polyethylene products at room temperature. The products were stretched at a speed of 50 mm / min and their mechanical properties were characterized. All operations were carried out in accordance with GB / T1040.1-2018 standard. At least five samples were used for each product to obtain the average value and standard deviation.

[0045] Impact mechanical properties test: The size of each sample cut by a milling machine is 80*10*4 mm. In view of the excellent impact performance of ultra-high molecular weight polyethylene products, it is extremely difficult to use conventional national standard notched samples for impact testing. Therefore, the unidirectional notch depth of the sample is determined to be 8.5 mm, and other conditions are still in accordance with the GB / T1043-2008 standard to perform notched impact strength tests on injection molded samples. In order to accurately calculate the impact strength, the width and thickness of the cross section of each sample must be measured and recorded before and after the impact. Five samples are selected for each group of samples for testing, and the average value is calculated. The impact strength is calculated according to the following process:

[0046] In the formula, A k represents the energy absorbed by the notched sample, in J; b represents the sample width, in mm; d kRepresents the remaining thickness of the sample at the notch, in mm.

[0047] According to the above detection method, the test results of Examples 1 to 3 and Comparative Examples 1 to 6 were obtained, as shown in Table 1 below: Table 1

[0048] Test items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Melting point (℃) 142.5 142.8 142.1 / / / / / / Crystallinity (%) 51.8 48.6 50.9 / / / / / / Tensile strength at break (MPa) 68.4±1.3 63.3±1.6 62.5±1.4 / / / / / / <![CDATA[Impact strength (kJ / m 2 ).]]> 418.8±16.4 416.6±17.0 384.5±17.1 / / / / / / Is the injection molding successful? yes yes yes no no no no no no

[0049] By comparing the test results of Examples 1 to 3 with Comparative Examples 1 to 6, it can be seen that mixing polyethylene wax with ultra-high molecular weight polyethylene resin is conducive to smooth injection molding of ultra-high molecular weight polyethylene. Example 4

[0050] The only difference between this embodiment and embodiment 1 is that the content of ultra-high molecular weight polyethylene resin in the composition is 98 wt % and the content of linear polyethylene wax is 2 wt %. Example 5

[0051] The only difference between this embodiment and embodiment 1 is that the content of ultra-high molecular weight polyethylene resin in the composition is 99 wt % and the content of linear polyethylene wax is 1 wt %. Example 6

[0052] The only difference between this embodiment and embodiment 1 is that the content of the ultra-high molecular weight polyethylene resin in the composition is 91 wt %, and the content of the linear polyethylene wax is 9 wt %.

[0053] The ultra-high molecular weight polyethylene products of Examples 4 to 6 were tested according to the testing method of Table 1. The test results are shown in Table 2 below. Table 2

[0054] Test items Example 4 Example 5 Example 6 Melting point (℃) 142.4 142.3 142.1 Crystallinity (%) 48.1 47.3 51.4 Tensile strength at break (MPa) 62.8±1.5 61.1±1.7 60.6±1.9 <![CDATA[Impact strength (kJ / m 2 )]]> 497.6±16.8 403.5±16.9 388.4±17.0 Is the injection molding successful? yes yes yes

[0055] By comparing the test results of Example 1 and Examples 4 to 6, it can be seen that when the content of ultra-high molecular weight polyethylene resin is 95-98wt%, the fluidity of the melt is better, the injection molding process is smoother, and the molding effect and mechanical properties of the final product are better. Example 7

[0056] The only difference between this embodiment and embodiment 1 is that the linear polyethylene wax is replaced by branched polyethylene wax, and the branching degree of the branched polyethylene wax is 70 / 1000C.

[0057] The ultra-high molecular weight polyethylene product of Example 7 was tested according to the testing method in Table 1 above. The test results are shown in Table 3 below. Table 3

[0058] Test items Example 7 Melting point (℃) 142.6 Crystallinity (%) 48.3 Tensile strength at break (MPa) 47.1±1.8 <![CDATA[Impact strength (KJ / m 2 )]]> 294.4±25.3 Is the injection molding successful? yes

[0059] By comparing the test results of Example 1 and Example 7, it can be seen that the use of straight-chain polyethylene wax is more conducive to improving the mechanical properties of the final ultra-high molecular weight polyethylene product. Example 8

[0060] The only difference between this embodiment and embodiment 1 is that the temperature of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 170°C. Example 9

[0061] The only difference between this embodiment and embodiment 1 is that the temperature of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 200°C. Example 10

[0062] The only difference between this embodiment and embodiment 1 is that the temperature of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 160°C. Embodiment 11

[0063] The only difference between this embodiment and embodiment 1 is that the temperature of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 250°C.

[0064] Comparative Example 7 The only difference between this comparative example and Example 1 is that the temperature of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 270°C.

[0065] Comparative Example 8 The only difference between this comparative example and Example 1 is that the temperature of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 140°C.

[0066] The ultra-high molecular weight polyethylene products of Examples 8 to 11 and Comparative Examples 7 and 8 were tested according to the testing method of Table 1. The specific test results are shown in Table 4 below. Table 4

[0067] Test items Example 8 Example 9 Example 10 Embodiment 11 Comparative Example 7 Comparative Example 8 Melting point (℃) 143.1 141.6 143.8 139.4 135.1 / Crystallinity (%) 52.6 50.6 53.4 48.9 40.3 / Tensile strength at break (MPa) 70.6±1.4 65.3±1.4 66.2±1.8 61.1±1.8 20.1±3.4 / <![CDATA[Impact strength (KJ / m 2 ).]]> 394.2±16.9 442.3±15.6 266.3±26.9 382.1±28.9 94.5±38.1 / Is the injection molding successful? yes yes yes yes yes no

[0068] Combined with the comparison of the test results of Example 1, Example 8 to Example 11 and Comparative Example 7 and Comparative Example 8, and Figure 1 , Figure 2 and Figure 3 , Figure 4 It can be seen from the display that when the temperature of the compression section, homogenization section and melt passing through the nozzle of the injection molding machine is controlled within the temperature range of 160-250°C, especially high-temperature melting within the temperature range of 170-200°C, it is not only easier to process the melt, but also beneficial to improving the mechanical properties of the final ultra-high molecular weight polyethylene product. Example 12

[0069] The only difference between this embodiment and embodiment 1 is that the injection pressure is 40 MPa. Example 13

[0070] The only difference between this embodiment and embodiment 1 is that the injection pressure is 120 MPa. Embodiment 14

[0071] The only difference between this embodiment and embodiment 1 is that the injection pressure is 10 MPa. Embodiment 15

[0072] The only difference between this embodiment and embodiment 1 is that the injection pressure is 300 MPa.

[0073] Comparative Example 9 The only difference between this comparative example and Example 1 is that the injection pressure is 8 MPa.

[0074] Comparative Example 10 The only difference between this comparative example and Example 1 is that the injection pressure is 310 MPa.

[0075] The ultra-high molecular weight polyethylene products of Examples 12 to 15 and Comparative Examples 9 to 10 were tested according to the testing method in Table 1. The specific test results are shown in Table 5 below. Table 5

[0076] Test items Example 12 Example 13 Embodiment 14 Embodiment 15 Comparative Example 9 Comparative Example 10 Melting point (℃) 142.3 142.6 141.7 143.1 / / Crystallinity (%) 51.4 51.9 50.6 53.4 / / Tensile strength at break (MPa) 66.6±1.5 68.9±1.5 62.3±1.9 70.4±3.9 / / <![CDATA[Impact strength (KJ / m 2 ).]]> 409.9±16.7 424.3±17.6 376.5±21.3 401.3±38.8 / / Is the injection molding successful? yes yes yes yes no no

[0077] By comparing the test results of Example 1, Example 12 to Example 15 and Comparative Example 9 and Comparative Example 10, it can be seen that when the injection pressure is 10-300 MPa, especially 40-120 MPa, it is beneficial to ensure the integrity of the final product, and it is also beneficial to avoid overflow, which is beneficial to improving the mechanical properties of the final ultra-high molecular weight polyethylene product. Example 16

[0078] The only difference between this embodiment and embodiment 1 is that the holding pressure is 10 MPa and the holding time is 150 s. Embodiment 17

[0079] The only difference between this embodiment and embodiment 1 is that the holding pressure is 5 MPa and the holding time is 180 s. Embodiment 18

[0080] The only difference between this embodiment and embodiment 1 is that the holding pressure is 50 MPa and the holding time is 60 s.

[0081] The ultra-high molecular weight polyethylene products of Examples 16 to 18 were tested according to the testing method of Table 1. The specific test results are shown in Table 6 below. Table 6

[0082] Test items Example 16 Embodiment 17 Embodiment 18 Melting point (℃) 142.4 142.3 142.4 Crystallinity (%) 51.6 51.3 51.7 Tensile strength at break (MPa) 68.1±1.3 66.7±1.4 67.2±1.4 <![CDATA[Impact strength (KJ / m 2 ).]]> 415.1±16.2 409.2±16.8 410.7±16.7 Is the injection molding successful? yes yes yes

[0083] By comparing the test results of Example 1 and Example 16 to Example 18, it can be seen that when the holding pressure is 5 to 50 MPa, especially 10 to 28 MPa, and the holding time is controlled at 120 to 150 s, the relaxation movement of the oriented polymer chains can be slowed down, and the oriented structure generated during the processing can be preserved in the ultra-high molecular weight polyethylene product, and the tensile properties of the obtained product are better. Embodiment 19

[0084] The only difference between this embodiment and embodiment 1 is that the mold temperature is 30° C. and the cooling rate is 30° C. / min. Embodiment 20

[0085] The only difference between this embodiment and embodiment 1 is that the mold temperature is 50° C. and the cooling rate is 20° C. / min. Embodiment 21

[0086] The only difference between this embodiment and embodiment 1 is that the mold temperature is 70° C. and the cooling rate is 10° C. / min. Embodiment 22

[0087] The only difference between this embodiment and embodiment 1 is that the mold temperature is 100° C. and the cooling rate is 5° C. / min. Comparative Example 11

[0088] The only difference between this comparative example and Example 1 is that the mold temperature is 20° C. and the cooling rate is 35° C. / min. Comparative Example 12

[0089] The only difference between this comparative example and Example 1 is that the mold temperature is 110° C. and the cooling rate is 3° C. / min.

[0090] The ultra-high molecular weight polyethylene products of Examples 19 to 22 and Comparative Examples 11 to 12 were tested according to the testing method of Table 1. The specific test results are shown in Table 7 below. Table 7

[0091] Test items Embodiment 19 Embodiment 20 Embodiment 21 Embodiment 22 Comparative Example 11 Comparative Example 12 Melting point (℃) 142.3 142.4 142.8 143.2 138.5 / Crystallinity (%) 51.1 51.5 52.9 53.3 42.4 / Tensile strength at break (MPa) 64.8±1.4 66.3±1.3 68.8±1.4 69.2±1.8 25.1±3.6 / <![CDATA[Impact strength (KJ / m 2 )]]> 391.2±16.9 406.2±16.5 404.2±16.6 346.2±31.2 264.1±40.8 / Is the injection molding successful? yes yes yes yes yes Warping

[0092] By comparing the test results of Example 1, Example 19 to Example 22, and Comparative Example 11 and Comparative Example 12, it can be seen that the mold temperature is controlled at 30-80°C, especially 50-70°C, and the cooling rate of the product is 5-30°C / min, especially 10-20°C / min, which can prevent the product from warping and ensure the integrity of the product, and at the same time improve the mechanical properties of the product.

[0093] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. An injection molding method for ultra-high molecular weight polyethylene, characterized in that: The following steps are included: Step 1: mixing an ultra-high molecular weight polyethylene resin and a polyethylene wax to form a composition; Step 2: adding the composition into an injection molding machine for high temperature melting to form a melt, and injecting the melt to fill the mold; Step 3: Cool the mold, and after the melt solidifies, open the mold to obtain the ultra-high molecular weight polyethylene product.

2. The method for injection molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The content of the ultra-high molecular weight polyethylene resin in the composition of step 1 is 91-99 wt %, and the content of the polyethylene wax is 1-9 wt %.

3. The method for injection molding of ultra-high molecular weight polyethylene according to claim 2, characterized in that: The content of ultra-high molecular weight polyethylene resin in the composition is 95-98wt%.

4. The method for injection molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The polyethylene wax is a linear polyethylene wax with a weight average molecular weight of 2.0×10 3 ~7.0×10 3 g / mol.

5. The method for injection molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: In step 2, the temperature of the feeding section of the injection molding machine is 90-140°C, the temperature of the compression section is 160-250°C, the temperature of the homogenization section is 160-250°C, the temperature of the melt through the nozzle is 160-250°C, the screw speed is 5-80rpm, the injection pressure is 10-300MPa, the holding pressure is 5-50MPa, the holding time is 60-180s, and the mold temperature is 30-100°C.

6. The method for injection molding of ultra-high molecular weight polyethylene according to claim 5, characterized in that: The temperatures of the compression section, the homogenization section and the melt passing through the nozzle of the injection molding machine are all 170-200°C.

7. The method for injection molding of ultra-high molecular weight polyethylene according to claim 5, characterized in that: The injection pressure is 40~120MPa.

8. The method for injection molding of ultra-high molecular weight polyethylene according to claim 5, characterized in that: The holding pressure of the injection molding machine is 10~28MPa.

9. The method for injection molding of ultra-high molecular weight polyethylene according to claim 5, characterized in that: The mold temperature is 50-70°C.

10. The method for injection molding of ultra-high molecular weight polyethylene according to claim 9, characterized in that: In step 3, the cooling rate of the melt in the mold is 10-20°C / min.

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