A pearlescent board for a mobile phone back cover and its preparation method

Abstract

The present invention discloses a pearlescent board for a mobile phone back cover and a preparation method thereof. After mixing pearlescent pigments with ethanol and a silane coupling agent, the pH is adjusted and then stirred. The pearlescent pigments after solid-liquid separation and drying are added to a mixed solvent of acetone and water. After adjusting the pH, azobisisobutyronitrile and methyl methacrylate monomers are added for reaction to obtain modified pearlescent pigments; then, using a screw extruder, PMMA, a flame retardant, a compatibilizer, the modified pearlescent pigments and a dispersant are extruded and cooled to form pellets to obtain pearlescent masterbatch; then, by means of a double-layer extrusion method, PMMA and the pearlescent masterbatch are mixed and then co-extruded, calendered and heat-treated and shaped with PC to obtain the pearlescent board. By modifying the pearlescent pigments, the present invention provides good dispersibility and stability in PMMA, and then the prepared pearlescent masterbatch is added to PMMA and co-extruded with PC by a double-layer co-extrusion process to obtain the pearlescent board, which can avoid the appearance of orange peel phenomenon on the surface of the pearlescent board.

Description

Technical Field

[0001] The present invention is a pearlescent plate for a mobile phone back cover and a preparation method thereof, and specifically relates to a PC / PMMA composite mobile phone cover plate prepared by using pearlescent pigment and a preparation method thereof, and belongs to the technical field of polymer materials. Background Art

[0002] With the official arrival of the 5G era, the mobile phone industry has ushered in a new round of changes. Since 5G signals transmit faster, this brings at least two changes to the structure of mobile phones: first, with the addition of 5G signals, mobile phones have more radio frequency functions and larger volumes, requiring new internal component designs; second, 5G places higher requirements on the signal transmission capabilities of mobile phone shells. In order to meet the market's demand for functionality and aesthetics, the materials of mobile phone covers have quietly changed. Metal covers are gradually being phased out; in the increasingly competitive mass mobile phone market, 3D glass and ceramics are relatively too expensive; composite sheet mobile phone covers have become a new research hotspot. PC / PMMA composite board is a new mobile phone backplane material bred under the background of 5G. PMMA has good hardness and wear resistance and is generally used for the exterior, while PC has good toughness, so as the inner layer, this not only ensures the product's scratch resistance but also ensures that it has sufficient toughness and overall impact strength. Therefore, PC / PMMA composite board mobile phone covers have become a new favorite.

[0003] However, although the PC / PMMA composite board mobile phone cover can meet various performance indicators, the appearance of the mobile phone back cover largely determines the user experience. The existing mobile phone back panels are mostly flat patterns with single colors, poor three-dimensional layering, and poor aesthetics. In order to increase differentiation and improve the appearance of the mobile phone back cover, the mobile phone back cover material is usually made into a color effect. The popular colored back covers on the market are mostly achieved by inkjet.

[0004] For example, the invention patent with publication number CN111196891A discloses a method for manufacturing a mobile phone back panel with a dazzling effect. This method mixes diethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, isophorone, butyrolactone, and a surfactant, and then puts them into a metal complex dye solution, stirs at 450-600rpm for 15-20min, heats to 40-50℃ and stirs until completely dissolved, and matures for 1.5-2h to obtain aurora dazzling inkjet ink for mobile phone back panels, and then the prepared aurora dazzling inkjet ink is filtered and filled by a multi-stage filtration method to obtain a mobile phone back panel with a dazzling effect. However, this preparation method has a high process difficulty, low production efficiency, and a relatively rigid color display effect, which makes it difficult to meet the ever-increasing needs of consumers.

[0005] In recent years, the preparation of mobile phone back cover materials with a colorful effect by the one-step forming method has attracted more and more attention. Among them, especially the addition of pearlescent pigments can achieve a colorful effect. Common pearlescent pigments are based on mica flakes, and a thin layer composed of transparent or relatively transparent titanium dioxide and iron oxide with a high refractive index is coated on the smooth mica surface. When light irradiates on the mica sheet, the mica sheet is like a transparent small mirror, part of the light is reflected out, and part of the light is transmitted through in a refraction manner. The light that passes through is refracted to the next interface, and there is a second partial reflection and partial transmission, and so on. The light reflected on the two reflection surfaces will interact with each other, thus forming a pearlescent phenomenon with interference characteristics. For example, the invention patent with the publication number CN112852098 A discloses that 65-85% by weight of ABS resin, 5-25% by weight of PMMA resin, 0.1-0.6% by weight of antioxidant, 4-7% by weight of lubricant, 0.5-3.5% by weight of metal powder, 1.6-3% by weight of pearlescent pigment and 0.2-0.8% by weight of white oil are mixed and directly used for injection molding to obtain an injection-molded product with a pearlescent effect.

[0006] However, since the surface of the pearlescent pigment is coated with a thin layer composed of titanium dioxide and iron oxide, it is easy to agglomerate and settle in the organic resin, and its dispersibility and stability are very poor. The surface of the processed products often shows surface orange peel, weld lines, and poor shear breaking and weak scintillation effect of the pearlescent particles, which directly affects the performance and further popularization and application of the excellent properties of the pearlescent pigment. Summary of the Invention

[0007] The present invention aims to solve a series of problems existing in the preparation of PC / PMMA composite mobile phone covers with existing pearlescent pigments, and proposes a pearlescent plate for mobile phone back covers and its preparation method. By modifying the pearlescent powder (pearlescent pigment), the dispersibility and stability in PMMA resin are provided, and then the modified pearlescent powder, PMMA resin and other additives are extruded and granulated under low shear to prepare a pearlescent masterbatch. Finally, the PMMA material added with the pearlescent masterbatch and PC resin are used to prepare a pearlescent composite plate by a double-layer co-extrusion technology, which not only has a pearlescent effect with obvious scintillation effect, but also can avoid the appearance of orange peel and weld lines on the surface.

[0008] The present invention is realized by the following technical solutions: A preparation method of a pearlescent plate for mobile phone back covers, comprising the following steps:

[0009] S1. After mixing the pearlescent pigment with ethanol and a silane coupling agent, adjust the pH to 3-5, stir, add the solid-liquid separated and dried pearlescent pigment into a mixed solvent of acetone and water, adjust the pH to 8-9, then add azobisisobutyronitrile and methyl methacrylate monomer, and after reaction, filter, wash and dry to obtain the modified pearlescent pigment;

[0010] S2. Using a screw extruder, feed PMMA resin, a flame retardant, and a compatibilizer into the screw extruder through the main feed port, and feed the modified pearlescent pigment and a dispersant into the screw extruder through the side feed port. After extrusion and cooling pelletization, a pearlescent masterbatch is obtained.

[0011] S3. Using an extruder, feed PC resin into the main extruder, and feed PMMA resin and the pearlescent masterbatch into the auxiliary extruder. After extrusion, calendering, and heat treatment for shaping, a pearlescent PMMA / PC composite board is obtained.

[0012] In step S1, by weight, add 100 parts of pearlescent pigment with a particle size of 20 - 100 μm to 200 - 500 parts of ethanol, and then add 10 - 30 parts of a silane coupling agent.

[0013] In step S1, by weight percentage, add 100 parts of dried pearlescent pigment to 200 - 500 parts of a mixed solvent, adjust the pH to 8 - 9, and then add 5 - 20 parts of azobisisobutyronitrile and 10 - 35 parts of methyl methacrylate monomer.

[0014] In step S1, in the mixed solvent, the volume ratio of acetone to water is 0.5 - 3:1.

[0015] In step S2, by weight, the PMMA resin fed into the screw extruder is 100 parts, the flame retardant is 5 - 10 parts, the compatibilizer is 1 - 5 parts, the modified pearlescent pigment is 6 - 8 parts, and the dispersant is 0.8 - 2 parts.

[0016] In step S2, control the rotation speed of the screw extruder to be 10 - 50 rpm, the temperature to be 200 - 300 °C, and the residence time to be 3 - 4 min.

[0017] In step S3, by weight, the PC resin fed into the main extruder is 680 - 900 parts, the PMMA resin fed into the auxiliary extruder is 100 parts, and the pearlescent masterbatch is 1 - 5 parts.

[0018] In step S3, in the main extruder, control the temperature to be 200 - 300 °C and the extrusion speed to be 80 rpm; in the auxiliary extruder, control the temperature to be 200 - 280 °C and the extrusion speed to be 28 rpm.

[0019] In step S3, the extrusion temperature is 250 - 270 °C.

[0020] A pearlescent board is prepared by the above method.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) In the presence of the polymerization initiator azobisisobutyronitrile, the pearlescent pigment treated with a silane coupling agent is modified using methyl methacrylate monomer, so that the modified pearlescent pigment has PMMA segments. When preparing the pearlescent masterbatch, it can be fully fused with the PMMA resin, and then rapidly dispersed to form a very stable dispersion system. Compared with the prior art in which the pearlescent pigment and the resin are simply physically mixed, the modified pearlescent pigment in the present invention will not agglomerate and settle with the migration flow during processing or over time, avoiding the generation of orange peel phenomenon and weld lines on the surface of the product.

[0023] (2) The pearlescent masterbatch of the present invention is prepared by extrusion and granulation using a screw extruder under low shear. During extrusion, by adding the pearlescent pigment at the side feeding port, it is beneficial to reduce the residence time of the pearlescent pigment in the extruder. On the one hand, it can inhibit the phenomenon of the pearlescent pigment turning black during extrusion, and on the other hand, it avoids the shear fragmentation phenomenon caused by too long and too high shear, improving the size stability of the pearlescent powder to improve the dispersion effect of the subsequent pearlescent masterbatch in the resin and enhance the pearlescent and colorful effect of the product.

[0024] (3) By adding the self-made pearlescent masterbatch to the resin system in the present invention, due to the excellent dispersion and stability of the pearlescent masterbatch, a composite sheet for a differentiated mobile phone back cover with a pearlescent effect can be prepared directly by using the double-layer coextrusion technology.

[0025] (4) In the present invention, a gorgeous effect can be imparted to the composite board during the extrusion process, that is, the forming process. Compared with the inkjet technology in the prior art, the post-treatment processes such as inkjet or coating are omitted, shortening the production cycle and reducing the production cost.

[0026] In summary, the present invention provides a pearlescent board for a mobile phone back cover with high appearance performance and a preparation method thereof. By modifying the pearlescent pigment to improve the dispersibility and stability of the pearlescent masterbatch, it is beneficial to prepare a pearlescent PC / PMMA composite board in the double-layer coextrusion process. The preparation process is simple, the product has no orange peel phenomenon and weld lines on the surface, and the product quality and production efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an enlarged schematic view of the PMMA surface of the product in Example 1.

[0028] Figure 2 It is a contour measurement diagram of the PMMA surface of the product in Example 1.

[0029] Figure 3 It is an enlarged schematic view of the PMMA surface of the product in Comparative Example 1.

[0030] Figure 4 It is a contour measurement diagram of the PMMA surface of the product in Comparative Example 1. Detailed implementation mode

[0031] The invention purpose, technical solution and beneficial effects of the present invention will be further described in detail below.

[0032] It should be noted that the following detailed description is exemplary and is intended to provide further description of the claimed present invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0033] The present invention is a pearlescent board for a mobile phone back cover, specifically related to a pearlescent PMMA / PC composite board. The advantages of this pearlescent board compared with the existing pearlescent boards are as follows: First, a self-made modified pearlescent pigment is used, which can be fused with PMMA resin to prepare a pearlescent masterbatch with excellent dispersibility and stability, and can be directly added to PMMA for use. Second, the preparation process is simple. By adding the aforementioned pearlescent masterbatch to PMMA, the PMMA / PC composite board can be directly prepared by a double-layer coextrusion technique without an inkjet or coating process, which can shorten the production time and improve production efficiency. Third, the appearance effect of the product is excellent. Due to the special structure of the modified pearlescent pigment, the pearlescent particles have good dispersion effect and are not damaged during the shearing and extrusion processes. Therefore, there is no orange peel phenomenon or weld line on the surface.

[0034] The preparation method adopted by the present invention is as follows:

[0035] Step 1, prepare the modified pearlescent pigment:

[0036] By weight, add 100 parts of pearlescent pigment with a particle size of 20 - 100 μm to 200 - 500 parts of ethanol, then add 10 - 30 parts of silane coupling agent (KH570), dropwise add a certain amount of acetic acid solution to adjust the pH to 3 - 5, carry out constant temperature stirring, after cooling, separate the solid and liquid, and then dry in a vacuum drying oven to obtain the treated pearlescent pigment.

[0037] By weight percentage, add 100 parts of the above-treated pearlescent pigment to 200 - 500 parts of a mixed solvent with a volume ratio of acetone:water = 0.5 - 3:1, adjust the pH to 8 - 9, then add 5 - 20 parts of azobisisobutyronitrile and 10 - 35 parts of methyl methacrylate monomer, stir and react for 2 - 4 h, and then obtain the modified pearlescent pigment through precipitation filtration, washing, and drying.

[0038] Step 2, prepare the pearlescent masterbatch:

[0039] Using a screw extruder, by weight, 100 parts of PMMA resin, 5 - 10 parts of flame retardant, and 1 - 5 parts of compatibilizer are fed into the screw extruder through the main feed port. 6 - 8 parts of the above - modified pearlescent pigment and 0.8 - 2 parts of dispersant are fed into the screw extruder through the side feed port. Control the rotation speed of the screw extruder to be 10 - 50 rpm, the temperature to be 200 - 300 °C, and the residence time to be 3 - 4 min. Then extrude, cool, and pelletize to obtain the pearlescent masterbatch.

[0040] Step three, double - layer co - extrusion to prepare pearlescent PMMA / PC composite board:

[0041] Using a co - extrusion machine, by weight, 680 - 900 parts of PC resin are fed into the main extruder. Control the temperatures of each section in the main extruder to be: feeding section 220 - 250 °C, compression section 280 - 300 °C, and melting section 250 - 280 °C, and the extrusion speed to be 80 rpm. 100 parts of PMMA resin and 1 - 5 parts of the above - mentioned pearlescent masterbatch are fed into the auxiliary extruder. Control the temperatures of each section in the auxiliary extruder to be: feeding section 200 - 230 °C, compression section 250 - 280 °C, and melting section 230 - 250 °C, and the extrusion speed to be 28 rpm;

[0042] After the above control, the molten fluids of PMMA and PC are extruded at the T - die orifice. The die extrusion temperature is 250 - 270 °C. The melt flowing out of the T - die passes through three - roll calendering and heat - treatment shaping to obtain the pearlescent PMMA / PC composite board, where PC is 70 - 90% and the thickness is 300 - 500 μm, and PMMA is 30 - 10% and the thickness is 100 - 200 μm.

[0043] Furthermore, in the above step two, the flame retardant is a halogen - free flame retardant, preferably one or several of organophosphorus - based flame retardants and silicon - based flame retardants. Among them, the phosphorus - containing flame retardants can be known ones, preferably aryl phosphate compounds and phosphazene compounds. Specifically, they can be bisphenol A bisphosphate, hydroquinone bisphosphate, resorcinol bisphosphate, triphenol trisphosphate, bisphenol A bis(dimethylphenyl phosphate), bisphenol A bis(diphenyl phosphate), phenylenebis(diphenyl phosphate), phenylenebis(dimethylphenyl phosphate), tris(2,3 - dibromopropyl) phosphate, tris(2,2 - dibromomethyl - 3 - bromopropyl) phosphate, triphenyl phosphate, resorcinol phosphate, bisphenol A bis(diphenyl) phosphate, bisphenol A bis(dimethyl) phosphate, tris(monochloropropyl) phosphate, etc.; As an example, the organosilicon - based flame retardants can be: hexamethyldisiloxane, octamethylcyclotetrasiloxane, dimethylsiloxane, dimethoxydimethylsilane, diethoxydimethylsilane, ethoxymethyltrimethylsilane, diethoxydiphenylsilane, triethoxyphenylsilane, dimethylphenylsilane, pentamethyldisilane, dimethylethylsilane, poly(dimethylsiloxane) oligomers, etc.

[0044] In the above step 2, the compatibilizer is one or more of MBS (terpolymer of methyl methacrylate, butadiene and styrene) and SMA (copolymer of styrene and maleic anhydride monomers).

[0045] In the above step 2, the dispersant is a mixture obtained by mixing microcrystalline wax and butyl stearate in a mass ratio of 1:1.

[0046] The following takes several typical embodiments to illustrate the specific implementation manners of the present invention. Of course, the protection scope of the present invention is not limited to the following embodiments.

[0047] Example 1:

[0048] Add 1 kg of pearlescent pigment with a particle size of 100 μm to 2 L of ethanol, then add 0.1 kg of KH570, dropwise add a certain amount of acetic acid solution to adjust the pH to 3, carry out constant temperature (28 °C) stirring, separate the solid and liquid after cooling, and then dry in a vacuum drying oven (≤0.1 MPa, 200 ± 5 °C) to obtain the treated pearlescent pigment.

[0049] Take 800 g of the above-treated pearlescent pigment and add it to 1.6 L of a mixed solvent (35% acetone, 65% water), adjust the pH to 9, then add 40 g of azobisisobutyronitrile and 80 g of methyl methacrylate monomer, stir and react for 4 h, and then obtain the modified pearlescent pigment through precipitation filtration, washing, and drying.

[0050] Using a screw extruder, feed 10 kg of PMMA resin, 1 kg of resorcinol bisphosphate, and 0.5 kg of MBS into the screw extruder from the main feed port. Feed a mixture of 0.6 kg of the above-mentioned modified pearlescent pigment, 60 g of microcrystalline wax, and 60 g of butyl stearate into the screw extruder from the side feed port. Control the rotation speed of the screw extruder to be 50 rpm, the temperature to be 200 °C, and the residence time to be 3 min, and then extrude, cool, and pelletize to obtain the pearlescent masterbatch.

[0051] Using a co-extrusion extruder, feed 90 kg of PC resin into the main extruder, and control the temperatures of each section in the main extruder to be 240 °C (feeding section), 280 °C (compression section), and 265 °C (melting section) in sequence, and the extrusion speed to be 80 rpm. Feed 10 kg of PMMA resin and 450 g of the above-mentioned pearlescent masterbatch into the auxiliary extruder, and control the temperatures of each section in the auxiliary extruder to be 230 °C (feeding section), 260 °C (compression section), and 250 °C (melting section) in sequence, and the extrusion speed to be 28 rpm.

[0052] After the above control, the molten fluids of PMMA and PC are extruded at the T-die. The die extrusion temperature is 250 °C. The melt flowing out of the T-die is subjected to three-roll calendering and heat treatment for shaping, and then the pearlescent PMMA / PC composite sheet is obtained. Among them, PC is 89.6%, the thickness is about 493 μm, PMMA is 10.4%, and the thickness is about 57 μm.

[0053] Example 2:

[0054] The difference between this example and Example 1 is only in the process of preparing the pearlescent masterbatch, which is as follows:

[0055] Add 1 kg of pearlescent pigment with a particle size of 20 μm to 4 L of ethanol, then add 0.12 kg of KH570, dropwise add a certain amount of acetic acid solution to adjust the pH to 5, carry out constant temperature (28 °C) stirring, separate the solid and liquid after cooling, and then dry in a vacuum drying oven (≤0.1 MPa, 200 ± 5 °C) to obtain the treated pearlescent pigment.

[0056] Take 800 g of the above-treated pearlescent pigment and add it to 4 L of a mixed solvent (75% acetone, 25% water), adjust the pH to 8, then add 160 g of azobisisobutyronitrile and 280 g of methyl methacrylate monomer, stir and react for 3 h, and then obtain the modified pearlescent pigment through precipitation filtration, washing, and drying.

[0057] Using a screw extruder, 10 kg of PMMA resin, 0.5 kg of dimethyl silicone oil, and 0.1 kg of SMA are fed into the screw extruder through the main feed port. A mixture of 0.8 kg of the above-mentioned modified pearlescent pigment, 0.1 kg of microcrystalline wax, and 0.1 kg of butyl stearate is fed into the screw extruder through the side feed port. Control the rotation speed of the screw extruder to be 40 rpm, the temperature to be 200 °C, and the residence time to be 4 min, and then extrude, cool, and pelletize to obtain the pearlescent masterbatch.

[0058] Example 3:

[0059] The difference between this example and Example 1 is only in the process of preparing the pearlescent masterbatch, which is as follows:

[0060] Add 2 kg of pearlescent pigment with a particle size of 50 μm to 6 L of ethanol, then add 0.4 kg of KH570, dropwise add a certain amount of acetic acid solution to adjust the pH to 5, carry out constant temperature (28 °C) stirring, separate the solid and liquid after cooling, and then dry in a vacuum drying oven (≤0.1 MPa, 200 ± 5 °C) to obtain the treated pearlescent pigment.

[0061] Take 1.5 kg of the above-mentioned treated pearlescent pigment and add it to 4 L of a mixed solvent (50% acetone, 50% water). Adjust the pH to 9, then add 120 g of azobisisobutyronitrile and 150 g of methyl methacrylate monomer. After stirring and reacting for 4 h, precipitate, filter, wash, and dry to obtain the modified pearlescent pigment.

[0062] Using a screw extruder, feed 10 kg of PMMA resin, 0.5 kg of hexamethyldisiloxane, and 0.25 kg of MBS into the screw extruder through the main feed port. Feed a mixture of 0.8 g of the above-mentioned modified pearlescent pigment, 0.4 kg of microcrystalline wax, and 0.4 kg of butyl stearate into the screw extruder through the side feed port. Control the rotation speed of the screw extruder to be 10 rpm, the temperature to be 300 °C, and the residence time to be 3 min. Extrude, cool, and pelletize to obtain the pearlescent masterbatch.

[0063] Example 4:

[0064] The difference between this example and Example 1 is only in the process of co-extruding to prepare the pearlescent PMMA / PC composite sheet, which is as follows:

[0065] Using a co-extrusion machine, feed 80 kg of PC resin into the main extruder. Control the temperatures of each section in the main extruder to be 250 °C (feeding section), 300 °C (compression section), and 275 °C (melting section) in sequence, and the extrusion speed to be 80 rpm. Feed 10 kg of PMMA resin and 350 g of the above-mentioned pearlescent masterbatch into the auxiliary extruder. Control the temperatures of each section in the auxiliary extruder to be 230 °C (feeding section), 280 °C (compression section), and 250 °C (melting section) in sequence, and the extrusion speed to be 28 rpm.

[0066] After the above control, the molten fluids of PMMA and PC are extruded at the T-shaped die orifice. The die extrusion temperature is 270 °C. The melt flowing out of the T-shaped die passes through three-roll calendering and heat treatment for shaping to obtain the pearlescent PMMA / PC composite sheet, where PC is 88.5%, the thickness is about 487 μm, PMMA is 11.5%, and the thickness is about 63 μm.

[0067] Comparative Example 1:

[0068] This comparative example is a process of using unmodified pearlescent pigment to prepare a pearlescent masterbatch and then preparing a pearlescent PMMA / PC composite sheet by double-layer co-extrusion. Among them, the process of preparing the pearlescent masterbatch and double-layer co-extrusion both refer to Example 1.

[0069] Respectively take the pearlescent PMMA / PC composite sheets prepared in Example 1 and Comparative Example 1 above and observe them using a KEYENCE VK-X3000 Series laser microscopy device to observe the surface condition of the PMMA in the sheets. See Figure 1 to Figure 4 as shown.

[0070] It can be seen from Figure 1 and Figure 2 that in the pearlescent PMMA / PC composite sheet of Example 1, the surface of PMMA is smooth and no orange peel phenomenon appears; it can be seen from Figure 3 and Figure 4 that the PMMA surface of the pearlescent PMMA / PC composite sheet of Comparative Example 1 has obvious pits, that is, it shows the surface orange peel phenomenon.

[0071] The above are only the preferred embodiments of the present invention, and do not impose any formal limitations on the present invention. Any simple modifications and equivalent changes made to the above embodiments based on the technical essence of the present invention all fall within the protection scope of the present invention.

Claims

1. A preparation method of a pearlescent board for a mobile phone back cover, characterized in that: It includes the following steps: S1. After mixing pearlescent pigment with ethanol and silane coupling agent, adjust the pH to 3 - 5, stir, add the pearlescent pigment after solid-liquid separation and drying into the mixed solvent of acetone and water, adjust the pH to 8 - 9, then add azodiisobutyronitrile and methyl methacrylate monomer. After reaction, filter, wash and dry to obtain the modified pearlescent pigment; S2. Using a screw extruder, feed PMMA resin, flame retardant and compatibilizer into the screw extruder from the main feed port, and feed the modified pearlescent pigment and dispersant into the screw extruder from the side feed port. Extrude, cool and pelletize to obtain the pearlescent masterbatch; S3. Using an extruder, feed PC resin into the main extruder, and feed PMMA resin and the pearlescent masterbatch into the auxiliary extruder. After extrusion, calendering and heat treatment for shaping, the pearlescent PMMA / PC composite board is obtained.

2. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, wherein: In the step S1, by weight, add 100 parts of pearlescent pigment with a particle size of 20 - 100 μm into 200 - 500 parts of ethanol, and then add 10 - 30 parts of silane coupling agent.

3. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, characterized in that: In the step S1, by weight percentage, add 100 parts of dried pearlescent pigment into 200 - 500 parts of mixed solvent, adjust the pH to 8 - 9, then add 5 - 20 parts of azodiisobutyronitrile and 10 - 35 parts of methyl methacrylate monomer.

4. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, wherein: In the step S1, in the mixed solvent, the volume ratio of acetone to water is 0.5 - 3∶1.

5. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, characterized in that: In the step S2, by weight, the PMMA resin fed into the screw extruder is 100 parts, the flame retardant is 5 - 10 parts, the compatibilizer is 1 - 5 parts, the modified pearlescent pigment is 6 - 8 parts, and the dispersant is 0.8 - 2 parts.

6. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, characterized in that: In the step S2, control the rotation speed of the screw extruder to be 10 - 50 rpm, the temperature to be 200 - 300 °C, and the residence time to be 3 - 4 min.

7. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, characterized in that: In the step S3, by weight, the PC resin fed into the main extruder is 680 - 900 parts, the PMMA resin fed into the auxiliary extruder is 100 parts, and the pearlescent masterbatch is 1 - 5 parts.

8. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, characterized in that: In the step S3, in the main extruder, control the temperature at 200 - 300 °C and the extrusion speed at 80 rpm; in the auxiliary extruder, control the temperature at 200 - 280 °C and the extrusion speed at 28 rpm.

9. The preparation method of a pearlescent board for a mobile phone back cover according to claim 1, characterized in that: In the step S3, the extrusion temperature is 250 - 270 °C.

10. A pearlescent board, characterized in that: Prepared by the method described in any one of claims 1 - 9.

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