Conductive foamed polypropylene bead, preparation method thereof and molded part

Abstract

The invention relates to the technical field of high polymer materials, in particular to a conductive foamed polypropylene bead, a preparation method thereof and a molded part, and the preparation method comprises the following steps: preparing polypropylene particles from a polypropylene raw material; modifying the polypropylene particles by using a conductive inorganic substance with positive charges at 140-150 DEG C to obtain conductive polypropylene particles; and carrying out foaming treatment on the conductive polypropylene particles through a supercritical carbon dioxide kettle pressure foaming process to obtain the conductive foamed polypropylene beads. The surfaces of the polypropylene particles are coated with the conductive inorganic matter with positive charges, the polypropylene microspheres are endowed with conductive performance under the condition that conductive carbon black does not need to be added, the color of the conductive foamed polypropylene beads can be determined according to the types and the use amount of the used conductive inorganic matter, and conductive EPP materials with different colors can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a conductive foamed polypropylene bead and a preparation method and a molded product thereof. Background Art

[0002] Expanded polypropylene material, referred to as EPP, is a new type of foam material that takes into account both strength and environmental protection after lightweight modification of polypropylene material through foaming technology. Its unique closed bubble structure enables polypropylene foam material to have certain resilience and processing performance, especially polypropylene foam beads produced by supercritical autoclave foaming technology. Its unique bead-like appearance enables it to have very good fluidity in the downstream molding process. Various special-shaped parts with structural strength can be obtained through mold design. Compared with general XPP, XPE, and foamed polyurethane, EPP material has its unique properties, making its application market in industrial design more and more extensive, and the market is gradually expanding.

[0003] With the gradual development of the market, the functional requirements of EPP products are also gradually increasing, such as flame retardant, aging resistance, antistatic, conductive materials and other functions. In particular, conductive materials have great application prospects in the fields of electronic packaging, electromagnetic shielding, wave absorption, etc. According to the surface resistance of the material, conductive materials can be simply divided into high conductive materials (surface resistance <10 4 Ω) and semi-conductive materials (surface resistance between 10 4 Ω-10 9 Ω), highly conductive materials are often used in the field of electromagnetic shielding, which can effectively reduce the scattering of electromagnetic waves in space and achieve the effect of radar "stealth". Semi-conductive materials are often used in the equipment packaging industry. By utilizing their low surface resistance, they can quickly disperse the charges generated on the surface of the product and prevent the irreversible damage to the surface of the product caused by concentrated discharge of electrons.

[0004] Traditional conductive foamed polypropylene beads often produce the required pathway for conductivity through the stacking of conductive carbon black in the system, thereby achieving the conductive effect. The conductive properties exhibited by the beads vary to a certain extent through different stacking ratios of conductive carbon black. Although the conductive properties of traditional conductive foamed polypropylene beads are relatively stable, their product color can only be a single black due to the introduction of conductive carbon black, which limits the application of conductive foamed polypropylene materials to a certain extent. Summary of the invention

[0005] In order to solve the problem that the conductive foamed polypropylene beads in the prior art are of a single black color, the present invention provides a method for preparing conductive foamed polypropylene beads. The preparation method obtains conductive foamed polypropylene beads by introducing a conductive inorganic substance to modify the surface of EPP, so that the color of the conductive foamed polypropylene beads can be changed according to the type of the conductive inorganic substance, thereby solving the problem that the conductive foamed polypropylene beads in the prior art are of a single black color.

[0006] The technical solution adopted by the present invention to solve its technical problem is: A method for preparing conductive foamed polypropylene beads comprises the following steps: S1: preparing polypropylene particles using polypropylene raw materials; S2: modifying the polypropylene particles with a positively charged conductive inorganic substance at 140-150° C. to obtain conductive polypropylene particles; S3: foaming the conductive polypropylene particles through a supercritical carbon dioxide autoclave pressure foaming process to obtain conductive foamed polypropylene beads.

[0007] Optionally, the conductive inorganic substance is selected from at least one of graphite, carbon nanotubes, nano silver powder and tin dioxide.

[0008] Optionally, the added amount of the conductive inorganic substance is 0.5%-1% of the mass of the polypropylene particles.

[0009] Optionally, the polypropylene microparticles in step S2 are negatively charged.

[0010] Optionally, step S1 comprises: blending the polypropylene raw material, nucleating agent, stabilizer, lubricant and masterbatch through a single screw extruder, and performing wire drawing and granulation to obtain polypropylene particles.

[0011] Optionally, the polypropylene raw material is random copolymer polypropylene with a melt index of 6-10 g / 10 min.

[0012] Optionally, the polypropylene raw material is obtained by compounding polypropylene A and polypropylene B; the melting point of the polypropylene A is 140-150°C; the melting point of the polypropylene B is 125-135°C.

[0013] Optionally, the mass ratio of the polypropylene A to the polypropylene B is 100:(15-25).

[0014] Optionally, the nucleating agent in step S1 is zinc borate.

[0015] Optionally, the stabilizer in step S1 includes an antioxidant and a light stabilizer.

[0016] Optionally, the lubricant in step S1 includes erucamide and polyethylene wax.

[0017] Optionally, the masterbatch in step S1 is titanium dioxide or carbon black.

[0018] Optionally, the processing temperature of step S1 is 180°C-220°C.

[0019] Another object of the present invention is to provide conductive foamed polypropylene beads, which are prepared by the method for preparing conductive foamed polypropylene beads as described above.

[0020] Another object of the present invention is to provide a molded article prepared from the conductive foamed polypropylene beads as described above.

[0021] The beneficial effects of the present invention are: The preparation method of the conductive foamed polypropylene beads provided by the present invention provides conductive performance to the polypropylene microspheres without adding conductive carbon black by coating the conductive inorganic substance with positive charge on the surface of the polypropylene microspheres, and the color of the conductive foamed polypropylene beads can be determined according to the type and amount of the conductive inorganic substance used, so that conductive EPP materials of different colors can be obtained, thereby helping to enrich the color of the conductive foamed polypropylene beads, solving the problem that the color of the conductive foamed polypropylene beads is single black, and greatly expanding the application field and future development prospects of the EPP market. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0023] Figure 1 It is a schematic structural diagram of the vibration coating device for surface modification of EPP particles in the present invention; Figure 2 It is a simplified structural diagram of the EPP particle surface modification vibration coating device in the present invention.

[0024] In the figure: 1-stirring unit; 11-stirring tank; 12-heating jacket; 2-vibration mixing unit; 21-vibration box; 22-vibration motor; 3-transmission unit. DETAILED DESCRIPTION

[0025] The present invention is now further described in detail. The embodiments described below are exemplary and intended to be used to explain the present invention, but cannot be understood as limiting the present invention. All other embodiments obtained by ordinary technicians in this field without creative work based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0026] In order to solve the problem that the conductive foamed polypropylene beads in the prior art are single black in color, the present invention provides a method for preparing the conductive foamed polypropylene beads, which comprises the following steps: S1: preparing polypropylene particles using polypropylene raw materials; S2: modifying the polypropylene particles with a positively charged conductive inorganic substance at 140-150° C. to obtain conductive polypropylene particles; S3: The conductive polypropylene particles are foamed by a supercritical carbon dioxide autoclave pressure foaming process to obtain conductive foamed polypropylene beads; specifically, the present invention preferably sets the foaming temperature in this step to 145-150°C, the foaming back pressure to 2.0-3.0 MPa, and the density of the obtained conductive foamed polypropylene beads is 40-60 g / L.

[0027] The preparation method of the conductive foamed polypropylene beads provided by the present invention comprises the following steps: through the modification in step S2, a conductive inorganic substance with a positive charge, preferably a conductive inorganic powder with a positive charge, is coated on the surface of polypropylene particles, so that the polypropylene microspheres are endowed with conductive properties without adding conductive carbon black, and the color of the conductive foamed polypropylene beads can be determined according to the type and amount of the conductive inorganic substance used, so that conductive EPP materials of different colors can be obtained, thereby helping to enrich the color of the conductive foamed polypropylene beads, solving the problem that the color of the conductive foamed polypropylene beads is a single black color, and greatly expanding the application field and future development prospects of the EPP market.

[0028] In addition, in the prior art, conductivity is introduced by conductive carbon black, and the conductive carbon black content required for conductivity is relatively high, often above 20%, which undoubtedly creates certain obstacles to the processing difficulty and use cost of the product. The preparation method of the conductive foamed polypropylene beads provided by the present invention greatly reduces the cost of EPP conductive materials and also reduces its processing difficulty to a certain extent.

[0029] Specifically, the present invention preferably selects at least one of the conductive inorganic substance from graphite, carbon nanotubes, nano silver powder, and tin dioxide, and preferably the conductive inorganic substance is a powder, that is, the conductive inorganic substance is selected from at least one of graphite powder, carbon nanotube powder, nano silver powder, and tin dioxide powder. During use, the corresponding conductive inorganic substance can be selected according to the demand for color to enrich the color of the product.

[0030] Conductive inorganic substances need to carry a certain amount of positive charge. This is done by using an electrostatic generator and inserting electrodes to stir and contact the conductive inorganic powder. The inner walls of containers such as mixing barrels that hold the conductive inorganic powder need to be insulated (to prevent discharge and generate a lot of heat). By adjusting the strength of the electric field of the electrostatic generator, the amount of positive charge on the conductive inorganic powder can be controlled to obtain the best adsorption effect.

[0031] The method of making the conductive inorganic substance positively charged can be selected from the corresponding existing technology, and the present invention does not specifically limit this method.

[0032] To ensure the conductive performance, the preferred amount of the conductive inorganic substance added in step S2 of the present invention is 0.5%-1% of the mass of the polypropylene particles.

[0033] To ensure the conductivity, the polypropylene particles in step S2 are preferably negatively charged in the present invention so that the positively charged conductive inorganic substances can be better coated on the outside of the negatively charged polypropylene particles.

[0034] The method of making the polypropylene particles negatively charged can be selected from existing technologies, such as rubbing the polypropylene particles with a nylon object so that the rubbed polypropylene particles are negatively charged.

[0035] In order to facilitate the modification of the polypropylene particles by the conductive inorganic substance with positive charge, the present invention preferably performs the above step S2 by Figure 1 , Figure 2 The EPP particle surface modification vibration coating device shown is implemented; the EPP particle surface modification vibration coating device includes a connected stirring unit 1, a vibration mixing unit 2 and a transmission unit 3; wherein the stirring unit 1 is used to heat and activate the conductive inorganic matter to make the conductive inorganic matter positively charged; the stirring unit 1 includes a stirring tank 11, a heating jacket 12 arranged on the outside of the stirring tank 11, an electrostatic generator connected to the stirring tank 11 (not shown in the figure), and a stirring device (not shown in the figure) arranged in the stirring tank 11; specifically, the present invention preferably connects the electrostatic generator to the stirring tank 11 by inserting an electrode into the conductive inorganic powder in the stirring tank 11, and the inner wall of the stirring tank 11 is insulated.

[0036] The vibration mixing unit 2 is used to make the polypropylene particles negatively charged, and mix the positively charged conductive inorganic matter with the negatively charged polypropylene particles, so that the positively charged conductive inorganic matter covers the negatively charged polypropylene particles; the vibration mixing unit 2 includes a vibration box 21 and a vibration motor 22 connected to the vibration box 21; a nylon vibration screen is arranged in the vibration box 21, so that the polypropylene particles generate negative charges by contacting with the nylon lining; at the same time, the discharge port of the stirring tank 11 is connected to the box body of the vibration box 21, so as to facilitate the transportation of the positively charged conductive inorganic matter into the vibration box 21 to contact with the negatively charged polypropylene particles.

[0037] The conveying unit 3 is connected to the vibration box 21 and is used to convey the polypropylene particles coated with the conductive inorganic substance to the next process.

[0038] During the operation of the vibration coating device, the corresponding conductive inorganic substance is added to the stirring tank 11, heated to 140-150°C under stirring conditions, and then sprayed evenly and proportionally (the spraying ratio is 0.5%-1% of the weight of the polypropylene particles) on the EPP particles at the feed port of the vibration box 21 below through the lower discharge port, and then sprinkled on the conveying unit 3 at the back through the vibration and transmission of the vibration screen (the vibration screen is kept at 120°C during the period), and the conveying unit 3 can be a cooling conveyor belt. After the excess powder is screened out through the micro-pore belt (0.1-0.3mm) on the conveyor belt, the remaining conductive polypropylene particles are sprinkled in the packaging bag at the back for use; the surface modification of the EPP particles is carried out by vibration. The dynamic coating device, the electrode of the high-voltage electrostatic generator is inserted into the conductive inorganic powder in the stirring tank 11, and the inserted electrode is used to stir and contact the conductive inorganic powder, so that the inorganic conductive powder inside is positively charged. The vibrating screen below is lined with nylon material, which will cause the polypropylene particles to be negatively charged when it rubs with the polypropylene particles. When the negatively charged polypropylene particles and the positively charged inorganic conductive powder above are mixed, the coating stability of the product can be better improved; after the polypropylene particles are evenly coated with the inorganic conductive powder, the temperature of the powder can cause a certain amount of softening and melting on the surface of the polypropylene particles, so that the inorganic conductive powder enters the surface of the particle cortex, so that it can better play a coating role.

[0039] The preferred step S1 of the present invention comprises: blending the polypropylene raw material, the nucleating agent, the stabilizer, the lubricant and the masterbatch through a single screw extruder, and drawing and granulating to obtain polypropylene particles.

[0040] Specifically, the polypropylene raw material in the preferred step S1 of the present invention is a random copolymer polypropylene with a melt index of 6-10 g / 10 min; and further preferably, the polypropylene raw material is obtained by compounding polypropylene A and polypropylene B; wherein the melting point of polypropylene A is 140-150° C.; the melting point of polypropylene B is 125-135° C.; and preferably, the mass ratio of polypropylene A to polypropylene B is 100:(15-25), and preferably, in step S1, the amount of the polypropylene raw material used is 115-125 parts by weight.

[0041] In the preferred step S1 of the present invention, the nucleating agent is zinc borate, preferably with a particle size of 0.5-10 μm, and the added amount is 0.1-0.2 parts by weight.

[0042] In the present invention, the stabilizer in step S1 preferably includes an antioxidant and a light stabilizer, and specifically preferably, based on weight parts, the stabilizer in step S1 includes 0.05-0.1 parts of antioxidant 1010 and 0.05-0.1 parts of light stabilizer 622SF.

[0043] In the preferred embodiment of the present invention, the lubricant in step S1 includes erucamide and polyethylene wax, and specifically preferably, based on weight parts, the lubricant in step S1 includes 0.1-0.5 parts of erucamide and 2-5 parts of polyethylene wax.

[0044] In the preferred step S1 of the present invention, the masterbatch is titanium dioxide or carbon black. Specifically, preferably, based on weight, the white masterbatch is 0.2-0.5 parts of titanium dioxide, and the black masterbatch is 0.1-0.2 parts of carbon black.

[0045] In the preferred embodiment of the present invention, the processing temperature in step S1 is 180° C.-220° C., the granulation length is 1.8-3.0 mm, and the granulation weight is 1-2 mg.

[0046] Another object of the present invention is to provide conductive foamed polypropylene beads, which are prepared by the method for preparing conductive foamed polypropylene beads as described above.

[0047] The conductive foamed polypropylene beads provided by the present invention are obtained by coating a conductive inorganic substance with a positive charge, preferably a conductive inorganic substance powder with a positive charge, on the surface of polypropylene particles, thereby giving the polypropylene microspheres conductive properties without adding conductive carbon black. The color of the conductive foamed polypropylene beads can be determined according to the type and amount of the conductive inorganic substance used, and conductive EPP materials of different colors can be obtained, thereby helping to enrich the color of the conductive foamed polypropylene beads, solving the problem that the conductive foamed polypropylene beads are single black in color, and greatly expanding the application field and future development prospects of the EPP market.

[0048] Another object of the present invention is to provide a molded part, which is prepared from the conductive foamed polypropylene beads as described above; preferably, in this step, the prepared conductive EPP foamed beads are pre-pressed and then molded by EPP steam molding equipment, and the desired EPP conductive molded part is obtained by molding under a certain steam pressure.

[0049] Specifically, in the process of preparing the molded parts of the present invention, the pre-pressing pressure is 0.2-0.35 MPa, the time is 6-10 hours, the molding steam pressure is 0.25-0.35 MPa, and the parts are dried at 80° C. for 6-8 hours and then packaged for use.

[0050] The molded article provided by the present invention adopts conductive foamed polypropylene beads. In the preparation process, a conductive inorganic substance with a positive charge, preferably a conductive inorganic powder with a positive charge, is coated on the surface of polypropylene particles, so that the polypropylene microspheres are endowed with conductive properties without adding conductive carbon black. The color of the conductive foamed polypropylene beads can be determined according to the type and amount of the conductive inorganic substance used, and conductive EPP materials of different colors can be obtained, which helps to enrich the color of the conductive foamed polypropylene beads, solves the problem that the color of the conductive foamed polypropylene beads is a single black color, and greatly expands the application field and future development prospects of the EPP market.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0052] Unless otherwise specified, the molded articles in the embodiments and comparative examples of the present invention are prepared according to the following method: S1: Preparation of polypropylene particles: according to the formula, a certain amount of polypropylene raw material, a nucleating agent, a stabilizer, a lubricant and a masterbatch are blended through a single screw extruder, and granulated into polypropylene particles of a certain length and weight, and dried for standby use to obtain polypropylene particles; the processing temperature in this step is 200°C; S2: Preparation of conductive EPP particles: The required conductive inorganic substance is dispersed and heated to 145°C through the upper stirring tank 11 through the EPP particle surface modification vibration coating device, and then sprayed evenly and proportionally (the spraying ratio is 0.8% of the weight of the polypropylene particles) on the EPP particles in the lower vibration box 21 through the lower discharge port. Through the vibration and transmission of the vibrating screen (the vibrating screen is kept at 120°C during this period), the EPP particles coated with the conductive inorganic substance fall on the cooling conveyor belt at the back, and the excess powder is screened out through the micro-pore belt (0.1-0.3mm) on the conveyor belt, and the remaining conductive polypropylene particles fall into the packing bag at the back for use; The stirring tank 11 is connected to a high-voltage electrostatic generator. The electrodes of the electrostatic generator are inserted into the conductive inorganic powder in the stirring tank 11, so that the inorganic conductive powder inside is positively charged. The inner lining of the vibrating screen below is made of nylon. When it rubs against the polypropylene particles, the polypropylene particles will be negatively charged, thereby obtaining conductive polypropylene particles. S3: Preparation of conductive foamed polypropylene beads: Conductive polypropylene particles are foamed by supercritical carbon dioxide autoclave pressure foaming process, the foaming temperature is set at 145-150° C., and the foaming back pressure is set at 2.0-3.0 MPa to obtain conductive foamed polypropylene beads; S4: Molding of conductive EPP foam beads: The prepared conductive foamed polypropylene beads are pre-pressed and then molded by EPP steam molding equipment. Under a certain steam pressure, the required EPP conductive molded parts are obtained by compression molding. The pre-pressing pressure is 0.2-0.35MPa, the time is 6-10h, and the molding steam pressure is 0.25-0.35MPa. The parts are dried at 80℃ for 6-8h and then packaged for use.

[0053] The raw materials, process parameters and product properties in Examples 1 to 7 are shown in Table 1: Table 1 Each comparative example of the present invention is compared with Example 1.

[0054] The difference between Comparative Example 1 and Example 1 is that in step S2, the stirring tank 11 and the vibrating screen are both at room temperature and are not heated.

[0055] The raw materials, process parameters and product properties in Comparative Examples 1 to 3 are shown in Table 2: Table 2 The performance testing method in the present invention is as follows: Surface resistance of the product: Tested in accordance with SIS SS IEC 93-1983 solid insulating material volume resistivity and surface resistivity test method; 10% compression strength: Tested in accordance with GB / T 8813-2020 Determination of compression properties of rigid foam plastics; Tensile strength: Tested in accordance with GBT 6344-1996 Determination of tensile strength and elongation at break of flexible foam polymer materials; Shrinkage rate: The test formula is as follows: Shrinkage rate α = (molding mold size - finalized product size) / molding mold size * 100.

[0056] It can be seen from the data in Table 1 that the molded parts in the embodiments of the present invention have excellent electrical conductivity, controllable surface color, and good mechanical properties.

[0057] As can be seen from the data in Table 2, in step S2 of Comparative Example 1, the stirring tank 11 and the vibrating screen are both at room temperature and not heated. Because there is no heating system, the inorganic powder adsorption capacity is limited by electrostatic adsorption, and it is easy to fall off during the foaming process, resulting in poor surface resistance of the product and no surface resistance of the molded parts. In Comparative Example 2, only polypropylene A is used as the polypropylene raw material. Because the melting point of the base material is too high, the energy consumption of product molding is high, and the molding obtains a low product fusion degree. The molded parts not only have high energy consumption, but also unstable surface resistance. In Comparative Example 3, only polypropylene B is used as the polypropylene raw material. Because the melting point of the base material is low, the thermal stability of molding is poor, the comprehensive performance of the molded parts is average, soft, and the product shrinkage rate is also large.

[0058] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing conductive foamed polypropylene beads, characterized in that: The steps include: S1: preparing polypropylene particles using polypropylene raw materials; S2: modifying the polypropylene particles with a positively charged conductive inorganic substance at 140-150° C. to obtain conductive polypropylene particles; S3: foaming the conductive polypropylene particles through a supercritical carbon dioxide autoclave pressure foaming process to obtain conductive foamed polypropylene beads.

2. The method for preparing conductive foamed polypropylene beads according to claim 1, characterized in that: The conductive inorganic substance is selected from at least one of graphite, carbon nanotubes, nano silver powder and tin dioxide.

3. The method for preparing conductive foamed polypropylene beads according to claim 1, characterized in that: The added amount of the conductive inorganic substance is 0.5%-1% of the mass of the polypropylene particles.

4. The method for preparing conductive foamed polypropylene beads according to claim 1, characterized in that: The polypropylene particles in step S2 are negatively charged.

5. The method for preparing the conductive foamed polypropylene beads according to any one of claims 1 to 4, characterized in that: Step S1 includes: blending the polypropylene raw material, nucleating agent, stabilizer, lubricant and masterbatch through a single screw extruder, and granulating by drawing to obtain polypropylene particles.

6. The method for preparing conductive foamed polypropylene beads according to claim 5, characterized in that: The polypropylene raw material is random copolymer polypropylene, and the melt index is 6-10g / 10min.

7. The method for preparing conductive foamed polypropylene beads according to claim 6, characterized in that: The polypropylene raw material is obtained by compounding polypropylene A and polypropylene B; the melting point of the polypropylene A is 140-150°C; the melting point of the polypropylene B is 125-135°C.

8. The method for preparing conductive foamed polypropylene beads according to claim 7, characterized in that: The mass ratio of the polypropylene A to the polypropylene B is 100:(15-25).

9. The method for preparing conductive foamed polypropylene beads according to claim 6, characterized in that: The nucleating agent in step S1 is zinc borate.

10. The method for preparing conductive foamed polypropylene beads according to claim 6, characterized in that: The stabilizer in step S1 includes an antioxidant and a light stabilizer.

11. The method for preparing conductive foamed polypropylene beads according to claim 6, characterized in that: The lubricant in step S1 includes erucamide and polyethylene wax.

12. The method for preparing conductive foamed polypropylene beads according to claim 6, characterized in that: The masterbatch in step S1 is titanium dioxide or carbon black.

13. The method for preparing conductive foamed polypropylene beads according to claim 5, characterized in that: The processing temperature of step S1 is 180°C-220°C.

14. A conductive foamed polypropylene bead, characterized in that: The conductive foamed polypropylene beads are prepared by the method for preparing the conductive foamed polypropylene beads according to any one of claims 1 to 13.

15. A molded article, characterized in that: Prepared from the conductive foamed polypropylene beads as described in claim 14.

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