A method for producing an ultrahigh molecular weight polyethylene film

Abstract

The present application relates to the field of high polymer material, and particularly relates to a preparation method of ultra-high molecular weight polyethylene film, which has the following steps: after ultra-high molecular weight polyethylene resin and solvent are configured into a uniform suspension, the suspension is sent into a double screw extruder to obtain a high temperature melt, the melt is passed through a metering pump and a slit die, and is cooled and shaped by a polished cold roller to obtain a gel film, then the solvent in the film is removed by extraction, the film after extraction is dried by hot air, and finally the film is synchronously or stepwise bidirectionally hot stretched to obtain the ultra-high molecular weight polyethylene film. The present application adopts a new wet process route of dissolving folded chain lamellae and retaining straight chain lamellae in the preparation process of the ultra-high molecular weight polyethylene solution, and makes the straight chain crystals be kept in the preparation process of the ultra-high molecular weight polyethylene film, so that the resin content in the solution in the preparation of the ultra-high molecular weight polyethylene film is greatly improved, and the production efficiency is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of an ultrahigh molecular weight polyethylene film. TECHNICAL BACKGROUND

[0002] Ultrahigh molecular weight polyethylene is a linear structure thermoplastic plastic, which has the characteristics of non-toxicity, excellent corrosion resistance, good chemical stability, electrical insulation, etc. At present, the application field of the ultrahigh molecular weight polyethylene film is very wide. In the new energy field, it can be used as a lithium ion battery separator. In the marine engineering field, it can be used as a surface anticorrosion, anti-rust, anti-adhesion veneer and cladding material. In the electronic industry field, it can be used as a surface veneer treatment material of precision machine parts and a wear-resistant patch at the bottom of a mouse. In the food field, it can be used as a packaging material of food and medicine.

[0003] The existing ultrahigh molecular weight polyethylene film is usually prepared by using a wet extrusion process. The wet extrusion process is that ultrahigh molecular weight polyethylene is mixed with a suitable solvent, then a gel film is obtained after extrusion casting, the gel film is synchronously or stepwise bidirectional heat stretched, the solvent in the gel film is extracted and dried, and finally the finished film is obtained. The ultrahigh molecular weight polyethylene film obtained by such a process is usually a porous film, which is mainly used for lithium ion battery separators.

[0004] If an ultrahigh molecular weight polyethylene non-porous film with excellent mechanical properties for other fields is prepared, the gel film needs to be extracted and dried first, and then synchronously or stepwise bidirectional heat stretched. However, because the resin has an ultrahigh molecular weight, the viscosity is very large when all the resin raw materials are completely dissolved, and the conditions for preparing a uniform solution are harsh, so it is difficult to obtain a high-concentration uniform solution. Moreover, because the required dissolution temperature of the resin is very high, the molecular weight of the ultrahigh molecular weight polyethylene is greatly reduced, which affects the mechanical properties of the final film.

[0005] Through the analysis and research on the ultra-high molecular weight polyethylene resin, it is found that the ultra-high molecular weight polyethylene resin contains both ordinary folded chain lamellae and straight chain crystals, the melting points of the two kinds of crystals have a large difference, and because the order size of the straight chain crystal is larger than that of the folded chain lamellae, the straight chain crystal is much more difficult to dissolve than the folded chain lamellae. Therefore, if the temperature is accurately controlled during the preparation of the ultra-high molecular weight polyethylene solution to realize the dissolution of only the folded chain lamellae with low melting point in the ultra-high molecular weight polyethylene at low temperature and keep the straight chain crystals in the resin from being dissolved, the high rigidity of the straight chain crystals can be utilized to form the characteristics of the liquid crystal solution, the viscosity of the ultra-high molecular weight polyethylene solution can be greatly reduced, the flowability can be improved, and the molecular weight reduction caused by high processing temperature can be reduced. Moreover, the straight chain crystals reserved during the dissolution process can be used as a high-efficiency nucleating agent for the crystallization of the ultra-high molecular weight polyethylene, and the formation of the straight chain crystals and the folded chain lamellae during the synchronous or stepwise bidirectional hot stretching process can be induced, so that the tensile strength and wear resistance of the final film can be greatly improved, thereby forming a unique preparation process of the ultra-high molecular weight polyethylene film.

[0006] The information disclosed in the background section is only for the purpose of helping to understand the background of the present application and should not be understood as acknowledging or in any way implying that this information forms the prior art known to those skilled in the art. SUMMARY

[0007] The purpose of the present application is to provide a preparation method of an ultra-high molecular weight polyethylene film with high production efficiency and good mechanical properties.

[0008] The present application dissolves the folded chain lamellae in the ultra-high molecular weight polyethylene by accurate temperature control, reserves the straight chain crystals, extrudes and casts to prepare a gel film, and then extracts the gel film through an extraction tank and performs hot air drying. The straight chain crystals reserved in the above process will further induce the formation of straight chain crystals and folded chain lamellae during the synchronous or stepwise bidirectional hot stretching process, thereby a preparation process of an ultra-high molecular weight polyethylene film with high production efficiency and excellent mechanical properties is invented.

[0009] In order to achieve the above-mentioned purposes of the present application, the following technical solutions are adopted:

[0010] A preparation method of an ultra-high molecular weight polyethylene film, the specific steps of which are as follows:

[0011] The UHMWPE resin and solvent are mixed in a certain ratio to form a uniform suspension, which is then fed into a twin-screw extruder to obtain a high-temperature melt, and then the melt is cooled and shaped by a metering pump, a slit die and a polished cold roller to obtain a gel film, the gel film is immersed in an extraction tank with ultrasonic waves to extract and remove the solvent in the film, and then the extracted film is dried by hot air to remove the extractant, and then the dried film is synchronously or stepwise bidirectionally stretched to obtain a final UHMWPE film,

[0012] The weight average molecular weight of the UHMWPE is 1×10 6 ~ 8×10 6 g / mol;

[0013] The solvent is one or more of decalin, tetralin, paraffin oil, kerosene, white oil;

[0014] The mass ratio of the UHMWPE to the solvent is 0.08-0.60;

[0015] The temperature of the feeding section of the twin-screw extruder is 80-130℃, the temperature of the compression section is 130-180℃, the temperature of the homogenization section is 130-180℃, and the temperature of the die is 130-180℃, and the rotation speed of the twin-screw extruder is 30-400r / min;

[0016] The temperature of the polished cold roller is 10-30℃;

[0017] The extractant is one or more of gasoline, n-hexane, heptane, dimethylbenzene, dichloromethane, trichloromethane, carbon tetrachloride and dichloroethane, and the extraction temperature is 20-60℃;

[0018] The drying temperature is 30-60℃;

[0019] The temperature of the hot stretching is 100-150℃, the longitudinal stretching ratio is 5-12 times, and the transverse stretching ratio is 2-6 times.

[0020] The weight average molecular weight of the UHMWPE is preferably 2×10 6 ~ 6×10 6 g / mol. Increasing the molecular weight of the UHMWPE is conducive to forming more perfect crystals, thereby improving the mechanical properties and wear resistance of the UHMWPE film. However, too high a molecular weight will reduce the partial dissolution effect and efficiency of the resin. Therefore, the above range is preferred to improve the mechanical properties of the film while giving greater consideration to the efficiency of the process.

[0021] The solvent is preferably one of decalin, white oil. The above-mentioned solvent has a better dissolving effect on the ultra-high molecular weight polyethylene, and is more advantageous to the dissolving process of dissolving and folding the chain lamella and retaining the stretched chain crystal, and thus is preferred.

[0022] The mass ratio of the ultra-high molecular weight polyethylene to the solvent is preferably 0.18-0.40. The method of partially dissolving the ultra-high molecular weight polyethylene resin reduces the concentration of the actually dissolved solution, and the high rigidity of the retained stretched chain crystal makes the solution have the characteristics of a liquid crystal solution, so that the viscosity of the ultra-high molecular weight polyethylene solution can be greatly reduced. However, too low resin content will result in too low entanglement degree in the prepared gel film, thereby affecting the mechanical properties, and too high resin content will affect the partial dissolving effect. Therefore, the above-mentioned range is preferred in order to balance the dissolving effect of the ultra-high molecular weight polyethylene resin and the mechanical properties of the film.

[0023] The preparation process of the ultra-high molecular weight polyethylene film can further contain an additive. The type of the additive is not particularly limited, and can be exemplified by an antibacterial agent, a flame retardant, a colorant, an antistatic agent, a lubricant, a radiation stabilizer, and the like. The additive contained in the ultra-high molecular weight polyethylene film is one or more of the above-mentioned additive types, and the addition amount is not particularly limited, and is usually 0.01w%-0.3w% of the ultra-high molecular weight polyethylene. Within this range, the additive can play its due role, and will not affect the structure and mechanical properties of the product. The additive does not contain an antioxidant and a heat stabilizer, because the dissolving temperature used in the method of dissolving the ultra-high molecular weight polyethylene resin which retains the stretched chain crystal in the dissolving process of the present application is not high.

[0024] As preferred, the extruder used in the dissolving process of the present application is a twin-screw extruder, which can be exemplified by a parallel counter-rotating twin-screw extruder, a parallel co-rotating twin-screw extruder, a conical twin-screw extruder, and the like. The parallel co-rotating twin-screw extruder is preferred, because it has a good mixing effect and no calendering effect caused by separation force, and thus is preferred.

[0025] As preferred, the internal flow channel of the slit die is in the shape of a clothes hanger, and the thickness of the gel film is more uniform when the material flows through the clothes hanger-shaped flow channel, and thus is preferred.

[0026] As preferred, the compression section temperature, the homogenization section temperature, and the die temperature of the extruder are 140-160°C. Too high temperature will cause most of the stretched chain crystals in the original resin to be dissolved, and too low temperature will cause the lamella to be retained, thereby affecting the dissolving effect and resulting in uneven extruded gel film. Therefore, the above-mentioned range is preferred.

[0027] The temperature of the synchronous or stepwise biaxial hot stretching is preferably 115-135℃. If the temperature of the synchronous or stepwise biaxial hot stretching is low, the effect of melt recrystallization is weak, and the pores caused by extraction and drying cannot be completely eliminated. If the temperature of the synchronous or stepwise biaxial hot stretching is high, the ultra-high molecular weight polyethylene film is prone to disentanglement, which causes instability in the hot stretching process and instability in the film quality.

[0028] The stepwise hot stretching process preferably comprises longitudinal hot stretching first and then transverse hot stretching.

[0029] The longitudinal stretching ratio in the synchronous or stepwise hot stretching process is preferably 7-10 times. If the longitudinal hot stretching ratio is low, the pores in the film after extraction cannot be completely eliminated, and the number of extended chain crystals formed in the stretching process is not enough to greatly improve the mechanical properties of the final film. If the longitudinal hot stretching ratio is too high, the film transverse stretching is affected.

[0030] The transverse stretching ratio in the synchronous or stepwise hot stretching process is preferably 3-5 times. If the transverse hot stretching ratio is low, the film transverse mechanical properties are poor. If the transverse hot stretching ratio is high, the film is prone to rupture in the transverse stretching process.

[0031] Compared with the prior art, the present application has the beneficial effects that: the present application adopts a new wet process route of dissolving and folding chain lamellae in the preparation process of the ultra-high molecular weight polyethylene solution to retain extended chain lamellae, and the extended chain crystals are maintained in the preparation process of the ultra-high molecular weight polyethylene film, which greatly improves the resin content in the solution in the preparation of the ultra-high molecular weight polyethylene film and greatly improves the production efficiency. The retained extended chain crystals provide nucleation points, which can induce the formation of more extended chain crystals and folded chain lamellae in the synchronous or stepwise biaxial hot stretching process after extraction and drying, thereby greatly improving the tensile strength and wear resistance and other mechanical properties of the final film. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Differential scanning calorimetry (DSC) curves of the ultra-high molecular weight polyethylene films prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2;

[0033] Figure 2 Scanning electron microscopy (SEM) images of the ultra-high molecular weight polyethylene films prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2. DETAILED DESCRIPTION

[0034] The technical solutions of the present application are further described and explained below through specific examples, but the present application is not limited to the examples. If not otherwise specified, the raw materials used in the examples of the present application are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0035] Example 1

[0036] A 40 kg of ultra-high molecular weight polyethylene resin with a weight average molecular weight of 5.89 x 10 6 g / mol, 100 kg of paraffin oil and 40 g of antibacterial agent were configured into a uniform suspension, and then added to a parallel co-rotating twin-screw extruder for dissolution, followed by a metering pump and a hanger-shaped slit die, and then cooled and shaped by a polished cold roller to obtain an ultra-high molecular weight polyethylene gel film. The gel film was immersed in a dichloromethane bath with ultrasonic extraction, dried by hot air, and then subjected to stepwise bidirectional heat stretching in the longitudinal direction and then in the transverse direction to obtain the final ultra-high molecular weight polyethylene film. The feeding section temperature of the twin-screw extruder was 130°C, the compression section temperature was 160°C, the homogenization section temperature was 160°C, the die temperature was 160°C, the rotation speed of the twin-screw extruder was 300 r / min, the polished cold roller temperature was 10°C, the extraction temperature was 30°C, the drying temperature was 50°C, the heat stretching temperature was 120°C, the longitudinal stretching ratio was 10 times, and the transverse stretching ratio was 5 times.

[0037] Example 2

[0038] A 30 kg of ultra-high molecular weight polyethylene resin with a weight average molecular weight of 5.89 x 10 6 g / mol, 100 kg of paraffin oil and 40 g of antibacterial agent were configured into a uniform suspension, and then added to a parallel co-rotating twin-screw extruder for dissolution, followed by a metering pump and a hanger-shaped slit die, and then cooled and shaped by a polished cold roller to obtain an ultra-high molecular weight polyethylene gel film. The gel film was immersed in a dichloromethane bath with ultrasonic extraction, dried by hot air, and then subjected to stepwise bidirectional heat stretching in the longitudinal direction and then in the transverse direction to obtain the final ultra-high molecular weight polyethylene film. The feeding section temperature of the twin-screw extruder was 130°C, the compression section temperature was 160°C, the homogenization section temperature was 160°C, the die temperature was 160°C, the rotation speed of the twin-screw extruder was 300 r / min, the polished cold roller temperature was 10°C, the extraction temperature was 30°C, the drying temperature was 50°C, the heat stretching temperature was 120°C, the longitudinal stretching ratio was 10 times, and the transverse stretching ratio was 5 times.

[0039] Example 3

[0040] A 25 kg of ultra-high molecular weight polyethylene resin with a weight average molecular weight of 4 x 10 6A uniform suspension was prepared by mixing g / mol of ultra-high molecular weight polyethylene resin, 100 kg of white oil, and 30 g of antistatic agent. This suspension was then added to a parallel co-rotating twin-screw extruder for dissolution. After passing through a metering pump and a coat hanger-shaped slit die, the mixture was cooled and shaped using polishing cold rollers to obtain an ultra-high molecular weight polyethylene gel film. The gel film was then extracted by immersing it in an ultrasonic carbon tetrachloride bath, followed by hot air drying and simultaneous biaxial hot stretching to obtain the final ultra-high molecular weight polyethylene film. The twin-screw extruder's temperature was set as follows: feeding section temperature 110℃, compression section temperature 140℃, homogenization section temperature 140℃, die temperature 140℃, extruder speed 100 r / min, polishing cold roller temperature 20℃, extraction temperature 35℃, drying temperature 40℃, hot stretching temperature 130℃, longitudinal stretching ratio 8 times, and transverse stretching ratio 5 times.

[0041] Example 4:

[0042] A 20kg weight-average molecular weight of 3×10 6 A uniform suspension was prepared by mixing g / mol of ultra-high molecular weight polyethylene resin, 100 kg of paraffin oil, and 10 g of lubricant. This suspension was then added to a conical twin-screw extruder for dissolution. After passing through a metering pump and a coat hanger-shaped slit die, the mixture was cooled and shaped using polishing cold rollers to obtain an ultra-high molecular weight polyethylene gel film. The gel film was then extracted by immersing it in an ultrasonic gasoline bath, followed by hot air drying and stepwise biaxial hot stretching (first longitudinally, then transversely) to obtain the final ultra-high molecular weight polyethylene film. The twin-screw extruder's temperature was set as follows: feeding section temperature 100℃, compression section temperature 135℃, homogenization section temperature 135℃, die temperature 135℃, extruder speed 300 r / min, polishing cold roller temperature 20℃, extraction temperature 40℃, drying temperature 50℃, hot stretching temperature 135℃, longitudinal stretching ratio 8 times, and transverse stretching ratio 4 times.

[0043] Comparative Example 1:

[0044] 25kg with a weight-average molecular weight of 4×10 6A uniform suspension was prepared by mixing g / mol of ultra-high molecular weight polyethylene resin, 100 kg of white oil, and 30 g of antistatic agent. This suspension was then added to a parallel co-rotating twin-screw extruder for dissolution. After passing through a metering pump and a coat hanger-shaped slit die, the mixture was cooled and shaped using polishing cold rollers to obtain an ultra-high molecular weight polyethylene gel film. The gel film was then extracted by immersing it in an ultrasonic carbon tetrachloride bath, followed by hot air drying and simultaneous biaxial hot stretching to obtain the final ultra-high molecular weight polyethylene film. The twin-screw extruder's temperature was set as follows: feeding section temperature 110℃, compression section temperature 240℃, homogenization section temperature 240℃, die temperature 240℃, extruder speed 100 r / min, polishing cold roller temperature 20℃, extraction temperature 35℃, drying temperature 40℃, hot stretching temperature 130℃, longitudinal stretching ratio 8 times, and transverse stretching ratio 5 times.

[0045] Comparative Example 2:

[0046] A 20kg weight-average molecular weight of 3×10 6 A uniform suspension was prepared by mixing g / mol of ultra-high molecular weight polyethylene resin, 100 kg of paraffin oil, and 10 g of lubricant. This suspension was then added to a conical twin-screw extruder for dissolution. After passing through a metering pump and a coat hanger-shaped slit die, the mixture was cooled and shaped using polishing cold rollers to obtain an ultra-high molecular weight polyethylene gel film. The gel film was then extracted by immersing it in an ultrasonic gasoline bath, followed by hot air drying and stepwise biaxial hot stretching (first longitudinally, then transversely) to obtain the final ultra-high molecular weight polyethylene film. The twin-screw extruder's temperature was set as follows: feeding section temperature 100℃, compression section temperature 135℃, homogenization section temperature 135℃, die temperature 135℃, extruder speed 300 r / min, polishing cold roller temperature 20℃, extraction temperature 40℃, drying temperature 50℃, hot stretching temperature 135℃, longitudinal stretching ratio 4 times, and transverse stretching ratio 1.8 times.

[0047] from Figure 1 As can be seen, the melting points of the ultra-high molecular weight polyethylene films of Examples 1, 2, 3, and 4 are relatively higher than those of Comparative Examples 1 and 2, indicating that the crystal thickness of ultra-high molecular weight polyethylene in the products of Examples 1, 2, 3, and 4 is greater. Therefore, it can be analyzed that the products of Examples 1, 2, 3, and 4 may have more extended chain crystals and cross-linked crystals formed compared to Comparative Examples 1 and 2.

[0048] Table 1 shows the tensile properties, abrasion resistance, and thermodynamic data of the ultra-high molecular weight polyethylene film products prepared in Examples 1, 2, 3, and 4, and Comparative Examples 1 and 2. From the mechanical properties in Table 1, the longitudinal tensile strength of Examples 1, 2, 3, and 4 is 75.9-199.9% higher than that of Comparative Examples 1 and 2, and the transverse tensile strength is 79.0-277.0% higher, indicating that the tensile properties of Examples 1, 2, 3, and 4 are significantly better than those of Comparative Examples 1 and 2. The coefficient of friction of Examples 1, 2, 3, and 4 is 47.1-63.2% lower than that of Comparative Examples 1 and 2, indicating that the abrasion resistance of Examples 1, 2, 3, and 4 is significantly better than that of Comparative Examples 1 and 2. From the thermodynamic properties in Table 1, the crystallinity of Examples 1, 2, 3, and 4 is 20.7-48.5% higher than that of Comparative Examples 1 and 2. Therefore, it can be concluded that the products of Examples 1, 2, 3, and 4 have more crystal formation than those of Comparative Examples 1 and 2, thus improving their mechanical properties.

[0049] from Figure 2 As can be seen, the ultra-high molecular weight polyethylene film products of Examples 1, 2, 3, and 4 have significantly more extended chain crystals and cross-crystals, while no obvious extended chain crystals and cross-crystals are present in Comparative Examples 1 and 2.

[0050] By comparing Example 3 with Comparative Example 1, except for the difference in the dissolution temperature in the twin-screw extruder, all other conditions were the same. However, the longitudinal tensile strength of the film of Example 3 was increased by 77.7% and the transverse tensile strength was increased by 104.7% compared with Comparative Example 1, while the coefficient of friction was reduced by 57.9%. This shows that by selecting a suitable dissolution temperature and effectively retaining the extended chain crystals during the dissolution process, the performance of ultra-high molecular weight polyethylene film products can be greatly improved.

[0051] By comparing Example 4 with Comparative Example 2, except for the difference in the stretching ratio during the hot stretching process, all other conditions were the same. However, the film performance of Example 4 was significantly improved compared with Comparative Example 2, indicating that selecting a suitable longitudinal and transverse stretching ratio can effectively promote the formation of straight-chain crystals and cascade crystals, thereby improving the mechanical properties of the film.

[0052] The above results demonstrate that by retaining most of the extended chain crystals in the ultra-high molecular weight polyethylene gel film, the embodiment can induce the formation of more extended chain crystals and cross-crystals, thereby preparing a high-strength, high-wear-resistant ultra-high molecular weight polyethylene film.

[0053] Table 1

[0054]

Claims

1. A preparation method of ultra-high molecular weight polyethylene film, comprising the following steps: mixing ultra-high molecular weight polyethylene resin with solvent in a certain proportion to form a uniform suspension, feeding the suspension into a double-screw extruder to obtain a high-temperature melt, passing the melt through a metering pump and a slit die, and cooling and shaping the melt by a polished cold roller to obtain a gel film, immersing the gel film in an extraction tank with ultrasonic waves to extract and remove the solvent in the film, drying the extracted film by hot air to remove the extractant, and performing synchronous or stepwise bidirectional heat stretching on the dried film to obtain a final ultra-high molecular weight polyethylene film. The feeding section temperature of the double-screw extruder is 80-130℃, the compression section temperature is 140-160℃, the homogenization section temperature is 140-160℃, and the die temperature is 140-160℃, and the rotation speed of the double-screw extruder is 30-400r / min. The weight average molecular weight of the ultra-high molecular weight polyethylene is 1×10 6 ~ 8×10 6 g / mol; the solvent is one or more of decaline, tetralin, paraffin oil, kerosene, white oil; the mass ratio of the ultra-high molecular weight polyethylene to the solvent is 0.08~0.60; The temperature of the polished cold roller is 10-30℃, the extractant is one or more of gasoline, n-hexane, heptane, dimethylbenzene, dichloromethane, trichloromethane, carbon tetrachloride and dichloroethane, the extraction temperature is 20-60℃, and the drying temperature is 30-60℃. The heat stretching temperature is 115-135℃, the longitudinal stretching ratio is 7-10 times, and the transverse stretching ratio is 3-5 times.

3. The preparation method of ultra-high molecular weight polyethylene film according to claim 1, wherein the mass ratio of ultra-high molecular weight polyethylene to solvent is 0.18-0.

40.

2. The method of claim 1, wherein the ultra-high molecular weight polyethylene has a weight average molecular weight of 2 x 10 6 ~ 6 x 10 6 g / mol. ​

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