A low-shrinkage styrene thermoplastic elastomer and preparation method thereof

Abstract

The present invention discloses a low-shrinkage styrene-based thermoplastic elastomer and a preparation method, and belongs to the technical field of thermoplastic elastomers. A low-shrinkage styrene-based thermoplastic elastomer comprises the following raw materials: 20-30 parts of styrene-butadiene block copolymer, 10-20 parts of polystyrene resin, 30-40 parts of softening process oil, 30-60 parts of modified nano-calcium carbonate, 1-2 parts of lubricating dispersant, and 1-2 parts of antioxidant. Its preparation method comprises the following steps: styrene-butadiene block copolymer and softening process oil are all put into a high-speed blender in sequence; then polystyrene resin, modified nano-calcium carbonate, lubricant, antioxidant, are put into a high-speed blender together to obtain a premix semi-finished product; the premix semi-finished product is added to an extruder, and the premix is ​​melted, extruded, and granulated by the extruder to obtain a finished product. The low-shrinkage styrene-based thermoplastic elastomer prepared by the present invention has excellent flame retardant properties.

Description

Technical Field

[0001] The invention belongs to the technical field of thermoplastic elastomers, and particularly relates to a low-shrinkage styrene-based thermoplastic elastomer and a preparation method thereof. Background Art

[0002] Thermoplastic elastomers are polymer materials that exhibit a highly elastic rubber state at room temperature but can be plasticized and molded at high temperatures. They are known as "third-generation rubbers." The English abbreviation TPE: Thermoplastics Elasticer. Depending on their composition and structure, they can generally be divided into the following categories: styrene-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, etc. Styrene-based thermoplastic elastomers mainly refer to thermoplastic elastomers prepared with SBS and SEBS as raw materials. SEBS is a thermoplastic rubber synthesized by block copolymerization of styrene and butadiene. The SEBS structure contains rigid styrene chains that are in a glassy state at room temperature, giving the material a fixed shape and ensuring its performance; the material structure contains flexible butadiene chains that are in a highly elastic state at room temperature, giving the material a comfortable soft touch and elasticity.

[0003] Currently, styrene-based thermoplastic elastomers (TPEs) are widely used in automotive interior trims. However, most TPEs are rarely used in applications where high dimensional precision is required. To adapt TPEs for these applications, a styrene-based TPE with low shrinkage is needed.

[0004] Patent publication number CN108250653B discloses a thermoplastic elastomer composition and molded products made therefrom. The patented thermoplastic elastomer composition comprises: a styrene block copolymer, oil, a polyolefin resin, a polystyrene resin, and an inorganic filler. The shrinkage rate of the thermoplastic elastomer is reduced through a reasonable ratio. However, the styrene thermoplastic elastomer prepared by this patent and the prior art still has the disadvantage of poor flame retardancy, which limits the application scope of styrene thermoplastic elastomers. Summary of the Invention

[0005] In order to solve the problem that the styrene-based thermoplastic elastomers prepared by the prior art still have poor flame retardant properties, which limits the application range of styrene-based thermoplastic elastomers, the purpose of the present invention is to provide a low-shrinkage styrene-based thermoplastic elastomer and a preparation method.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a low-shrinkage styrene-based thermoplastic elastomer, comprising the following raw materials in parts by weight: 20-30 parts of styrene-butadiene block copolymer, 10-20 parts of polystyrene resin, 30-40 parts of softening operating oil, 30-60 parts of modified nano-calcium carbonate, 1-2 parts of lubricating dispersant, and 1-2 parts of antioxidant.

[0008] The modified nano calcium carbonate is nano calcium carbonate grafted with hyperbranched polysilane, and the hyperbranched polysilane is obtained by hydrolysis and condensation of styrylethyltrimethoxysilane, borate-based siloxane and nitrogen-phosphorus-based siloxane.

[0009] Furthermore, the styrene-butadiene block copolymer is one or more of a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, and a styrene-ethylene-propylene-styrene block copolymer.

[0010] Furthermore, the polystyrene resin is one or more of general-grade polystyrene and high-impact polystyrene.

[0011] Furthermore, the softening process oil has a flash point greater than 200°C and a kinematic viscosity greater than 50 mm at 40°C. 2 / s of one or more of paraffin oil, cycloparaffin oil, aromatic oil, and straight-chain paraffin oil.

[0012] Furthermore, the lubricating dispersant is one or more of erucamide, oleamide, zinc stearate, magnesium stearate, silicone, and polyethylene wax.

[0013] Furthermore, the antioxidant is one or more of the hindered phenol antioxidant Irganox 1010, the phosphite antioxidant IRGAFOS168, and the amine antioxidant A.

[0014] Furthermore, the preparation method of modified nano calcium carbonate is:

[0015] Add nano-calcium carbonate, acetic acid aqueous solution and tetrahydrofuran into a flask, control the temperature at 70-75°C, add hyperbranched monomer, keep warm and react for 24 hours, wash with distilled water, and vacuum dry at 50-55°C for 72 hours to obtain modified nano-calcium carbonate.

[0016] The mass ratio of nano-calcium carbonate, acetic acid aqueous solution, tetrahydrofuran and hyperbranched monomer is 0.2:1:(6-10):2, the mass fraction of acetic acid aqueous solution is 66.7%, and the hyperbranched monomer is composed of styrylethyltrimethoxysilane, borate-based siloxane and nitrogen-phosphorus-based siloxane in a mass ratio of 1:0.2-0.4:0.6-0.8.

[0017] As an inorganic filler, nano-calcium carbonate can effectively fill the gaps between the molecular chains of styrene-based thermoplastic elastomers, increasing the volume fraction of the polymer matrix. This filling effect can restrict the free movement of polymer molecular chains during processing and curing, thereby reducing the overall shrinkage caused by molecular chain shrinkage.

[0018] Nano calcium carbonate surface presents as strong polarity, is incompatible with polymeric materials usually, and this can't form effective interfacial layer between nano calcium carbonate and polymer, makes nano calcium carbonate dispersibility not good, is unfavorable for nano calcium carbonate to play its effect.In the above-mentioned reaction, the methoxyl group hydrolysis in the hyperbranched monomer generates silanol, then passes through hydrogen bond with the hydroxyl on the nano calcium carbonate surface, last dehydration condensation, the silanol dehydration condensation that the remaining hydroxyl generates with the hyperbranched monomer hydrolysis again on the silanol, repeats dehydration condensation reaction, finally forms hyperbranched structure, has obtained modified nano calcium carbonate.Hyperbranched structure has formed one deck " protective coat" on the nano calcium carbonate surface, and this protective coat has certain steric hindrance effect.Steric hindrance effect can stop direct contact and reunion between the nano calcium carbonate particle, thereby improved its dispersibility, and the shrinkage percentage of styrene-based thermoplastic elastomer is reduced. Hyperbranched polysilane can also reduce the surface free energy of nano-calcium carbonate. The reduction of surface free energy helps to disperse and stabilize nano-calcium carbonate in the organic phase, improves its compatibility and interfacial bonding with organic materials, and further reduces the shrinkage of styrene-based thermoplastic elastomers.

[0019] Further, the preparation method of borate siloxane is:

[0020] Add trans-1-propen-1-ylboronic acid and 3-mercaptopropyltrimethoxysilane to tetrahydrofuran, mix well, then add benzoin dimethyl ether, stir for 1-2 hours, irradiate with ultraviolet light for 30-40 minutes at room temperature, remove the solvent by reduced pressure distillation after the reaction, precipitate in n-hexane three times, and vacuum dry at 30-40°C to constant weight to obtain borate-based siloxane.

[0021] The dosage ratio of trans-1-propen-1-ylboronic acid, 3-mercaptopropyltrimethoxysilane, tetrahydrofuran, and benzoin dimethyl ether is 0.84 g: 1.96 g: 14 mL: 0.05-0.08 g; the power of the ultraviolet lamp is 20 W, and the wavelength is 365 nm.

[0022] In the above reaction step, under the action of the initiator benzoin dimethyl ether, the double bond of trans-1-propen-1-ylboronic acid and the mercapto group in 3-mercaptopropyltrimethoxysilane undergo a mercapto-ene click reaction to obtain borate-based siloxane.

[0023] Furthermore, the preparation method of nitrogen-phosphorus siloxane is:

[0024] After the Schlenk flask was closed and nitrogen exchanged three times, it was protected with nitrogen and placed in a -40°C cryostat. γ-Aminopropyltriethoxysilane, triethylamine, and toluene were sequentially added to the Schlenk flask. After stirring for 10 minutes, diphenylphosphine chloride was slowly added dropwise within 30 minutes. Stirring was continued for 15 minutes before removal from the cryostat and stirring at room temperature for 2.5 hours. A fritted funnel was filled with diatomaceous earth, and the generated triethylamine hydrochloride was removed by suction filtration. The Schlenk flask and triethylamine hydrochloride were washed sequentially with toluene and n-hexane. The filtrates were combined and the solvent was removed by rotary evaporation to obtain the nitrogen-phosphorus-based siloxane.

[0025] The volume ratio of γ-aminopropyltriethoxysilane, triethylamine, toluene and diphenylphosphine chloride is 3.5:4.6:60:5.6.

[0026] In the above reaction steps, the amino group of γ-aminopropyltriethoxysilane undergoes a substitution reaction with the chlorine in diphenylphosphine chloride to obtain nitrogen-phosphine siloxane, and triethylamine serves as an acid-binding agent in the reaction.

[0027] In a second aspect, the present invention provides a method for preparing a low-shrinkage styrene-based thermoplastic elastomer, comprising the following steps:

[0028] (1) putting the styrene-butadiene block copolymer and softening process oil into a high-speed mixer in sequence, stirring at a speed of 300-500 r / min for 5-40 minutes, and letting it stand for 24 hours for standby use; then putting the polystyrene resin, modified nano calcium carbonate, lubricant, and antioxidant into the high-speed mixer together, stirring at 100-300 r / min for 3-8 minutes to obtain a premix semi-finished product;

[0029] (2) Adding the semi-finished premix into an extruder, and melt-extruding and granulating the premix to obtain a low shrinkage styrene-based thermoplastic elastomer.

[0030] Furthermore, in step (2), the extruder is a co-rotating twin-screw extruder, the feed speed is 200-300 r / min, the screw speed is 300-500 r / min, and the screw aspect ratio is 52.

[0031] Furthermore, in step (2), the temperature of the first section of melt extrusion does not exceed 170°C, and the temperature of the remaining sections is 190-250°C.

[0032] Beneficial effects of the present invention:

[0033] 1, the present invention added modified nano calcium carbonate when preparing styrene thermoplastic elastomer, nano calcium carbonate carries out surface modification by hyperbranched polysilane, and hyperbranched polysilane is obtained by styrylethyltrimethoxysilane, borate-based siloxane and nitrogen-phosphorus-based siloxane hydrolysis condensation.Styrylethyltrimethoxysilane can make the modified nano calcium carbonate surface contain styrene-based ethyl structure, and the structure of this structure and polystyrene and styrene-butadiene block copolymer has certain similarity, thereby improved the compatibility of modified nano calcium carbonate and matrix, and then improved the mechanical property of styrene thermoplastic elastomer, reduced the shrinkage percentage of styrene thermoplastic elastomer.Contain nitrogen, phosphorus, silicon, boron, sulphur multiple flame retardant element in borate-based siloxane and nitrogen-phosphorus-based siloxane, can improve the flame retardant property of styrene thermoplastic elastomer jointly by synergistic effect between these flame retardant elements. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] Preparation Example 1

[0036] The preparation method of the borate-based siloxane of this preparation example is:

[0037] 0.84 g of trans-1-propen-1-ylboronic acid and 1.96 g of 3-mercaptopropyltrimethoxysilane were added to 14 mL of tetrahydrofuran, mixed evenly, and then 0.05 g of benzoin dimethyl ether was added. The mixture was stirred for 1 hour and irradiated with an ultraviolet lamp at room temperature for 30 minutes. The power of the ultraviolet lamp was 20 W and the wavelength was 365 nm. After the reaction, the solvent was distilled off under reduced pressure, and the mixture was precipitated in n-hexane three times. The mixture was vacuum dried at 30° C. to constant weight to obtain borate-based siloxane.

[0038] Preparation Example 2

[0039] The preparation method of the borate-based siloxane of this preparation example is:

[0040] 0.84 g of trans-1-propen-1-ylboronic acid and 1.96 g of 3-mercaptopropyltrimethoxysilane were added to 14 mL of tetrahydrofuran, mixed evenly, and then 0.08 g of benzoin dimethyl ether was added. The mixture was stirred for 2 h and irradiated with an ultraviolet lamp at room temperature for 40 min. The power of the ultraviolet lamp was 20 W and the wavelength was 365 nm. After the reaction, the solvent was removed by distillation under reduced pressure, and the mixture was precipitated in n-hexane three times. The mixture was vacuum dried at 40° C. to constant weight to obtain borate-based siloxane.

[0041] Preparation Example 3

[0042] The preparation method of the nitrogen-phosphorus-based siloxane in this preparation example is:

[0043] After the Schlenk flask was closed and nitrogen exchanged three times, it was protected with nitrogen and placed in a -40°C cryostat. 3.5 mL of γ-aminopropyltriethoxysilane, 4.6 mL of triethylamine, and 60 mL of toluene were sequentially added to the Schlenk flask. After stirring for 10 minutes, 5.6 mL of diphenylphosphine chloride was slowly added dropwise over 30 minutes. Stirring was continued for 15 minutes before removal from the cryostat and stirring at room temperature for 2.5 hours. A fritted funnel was filled with diatomaceous earth, and the generated triethylamine hydrochloride was removed by suction filtration. The Schlenk flask and triethylamine hydrochloride were washed sequentially with toluene and n-hexane. The filtrates were combined and the solvent was removed by rotary evaporation to obtain the nitrogen-phosphorus-based siloxane.

[0044] Preparation Example 4

[0045] The preparation method of the modified nano calcium carbonate of this preparation example is:

[0046] 0.2g of nano-calcium carbonate, 1g of a 66.7% acetic acid aqueous solution, and 6g of tetrahydrofuran were added to a flask, the temperature was controlled at 70°C, 2g of a hyperbranched monomer was added, and the mixture was kept warm for 24 hours. The mixture was then washed with distilled water and dried under vacuum at 50°C for 72 hours to obtain modified nano-calcium carbonate. The hyperbranched monomer consisted of styrylethyltrimethoxysilane, the borate-based siloxane prepared in Preparation Example 1, and the nitrogen-phosphorus-based siloxane prepared in Preparation Example 3, in a mass ratio of 1:0.2:0.8.

[0047] Preparation Example 5

[0048] The preparation method of the modified nano calcium carbonate of this preparation example is:

[0049] 0.2g of nano-calcium carbonate, 1g of a 66.7% acetic acid aqueous solution, and 8g of tetrahydrofuran were added to a flask, the temperature was controlled at 72°C, 2g of a hyperbranched monomer was added, and the mixture was kept warm for 24 hours. The mixture was then washed with distilled water and dried under vacuum at 52°C for 72 hours to obtain modified nano-calcium carbonate. The hyperbranched monomer consisted of styrylethyltrimethoxysilane, the borate-based siloxane prepared in Preparation Example 2, and the nitrogen-phosphorus-based siloxane prepared in Preparation Example 3, in a mass ratio of 1:0.3:0.7.

[0050] Preparation Example 6

[0051] The preparation method of the modified nano calcium carbonate of this preparation example is:

[0052] 0.2g of nano-calcium carbonate, 1g of a 66.7% acetic acid aqueous solution, and 10g of tetrahydrofuran were added to a flask, the temperature was controlled at 75°C, 2g of a hyperbranched monomer was added, and the mixture was kept warm for 24 hours. The mixture was then washed with distilled water and dried under vacuum at 55°C for 72 hours to obtain modified nano-calcium carbonate. The hyperbranched monomer consisted of styrylethyltrimethoxysilane, the borate-based siloxane prepared in Preparation Example 2, and the nitrogen-phosphorus-based siloxane prepared in Preparation Example 3, in a mass ratio of 1:0.4:0.6.

[0053] Comparative Example 1

[0054] Compared with Preparation Example 4, the only difference is:

[0055] The hyperbranched monomer consists of styrylethyltrimethoxysilane and nitrogen-phosphorus siloxane in a mass ratio of 1:1.

[0056] Comparative Example 2

[0057] Compared with Preparation Example 4, the only difference is:

[0058] The hyperbranched monomer consists of styrylethyltrimethoxysilane and borate-based siloxane in a mass ratio of 1:1.

[0059] Comparative Example 3

[0060] Compared with Preparation Example 4, the only difference is:

[0061] The hyperbranched monomer is styrylethyltrimethoxysilane.

[0062] Comparative Example 4

[0063] Compared with Preparation Example 4, the only difference is:

[0064] Use nano calcium carbonate directly.

[0065] Example 1

[0066] This embodiment provides a low-shrinkage styrene-based thermoplastic elastomer, comprising the following raw materials in parts by weight: 20 parts of styrene-butadiene block copolymer, 10 parts of polystyrene resin, 30 parts of softening operating oil, 30 parts of modified nano-calcium carbonate prepared in Preparation Example 4, 1 part of lubricating dispersant, and 1 part of antioxidant.

[0067] The styrene-butadiene block copolymer is a styrene-ethylene-propylene-styrene block copolymer with a styrene content of 31%, the polystyrene resin is a general-purpose polystyrene resin, and the softening operating oil has a flash point greater than 200°C and a kinematic viscosity greater than 50 mm at 40°C. 2 / s paraffin oil, the lubricant is a mixture of 30% erucamide and 70% zinc stearate, and the antioxidant is Irganox 1010.

[0068] The preparation method of the low shrinkage styrene-based thermoplastic elastomer is as follows:

[0069] (1) putting the styrene-butadiene block copolymer and the softening process oil into a high-speed stirrer in sequence, stirring at a speed of 400 r / min for 25 minutes, and letting it stand for 24 hours for standby use; then putting the polystyrene resin, modified nano calcium carbonate, lubricant, and antioxidant into the high-speed stirrer together, stirring at a speed of 200 r / min for 6 minutes to obtain a premix semi-finished product;

[0070] (2) The semi-finished premix was fed into a co-rotating twin-screw extruder at a feed speed of 250 r / min, a screw speed of 400 r / min, and a screw aspect ratio of 52. The processing temperatures of the plasticizing and melting zones and the melt conveying zones were controlled. A vacuum pump was used to evacuate the tail section of the extruder. The premix was melt-extruded and granulated to obtain the finished product. The temperature of the first section of the melt extrusion was set at 170°C, and the remaining sections were set at 190°C / 190°C / 200°C / 200°C / 210°C / 210°C / 210°C / 200°C / 190°C / 190°C / 190°C.

[0071] Example 2

[0072] Compared with Example 1, the only difference is:

[0073] 22.5 parts of styrene-butadiene block copolymer, 12.5 parts of polystyrene resin, 32.5 parts of softening process oil, 37.5 parts of modified nano-calcium carbonate prepared in Preparation Example 5, 1.25 parts of lubricating dispersant, and 1.25 parts of antioxidant.

[0074] Example 3

[0075] Compared with Example 1, the only difference is:

[0076] 25 parts of styrene-butadiene block copolymer, 15 parts of polystyrene resin, 35 parts of softening process oil, 45 parts of modified nano-calcium carbonate prepared in Preparation Example 6, 1.5 parts of lubricating dispersant, and 1.5 parts of antioxidant.

[0077] Example 4

[0078] Compared with Example 1, the only difference is:

[0079] 27.5 parts of styrene-butadiene block copolymer, 17.5 parts of polystyrene resin, 37.5 parts of softening process oil, 52.5 parts of modified nano-calcium carbonate prepared in Preparation Example 6, 1.75 parts of lubricating dispersant, and 1.75 parts of antioxidant.

[0080] Example 5

[0081] Compared with Example 1, the only difference is:

[0082] 30 parts of styrene-butadiene block copolymer, 20 parts of polystyrene resin, 40 parts of softening process oil, 60 parts of modified nano calcium carbonate prepared in Preparation Example 6, 2 parts of lubricating dispersant, and 2 parts of antioxidant.

[0083] Comparative Example 1

[0084] Compared with Example 1, the only difference is:

[0085] The modified nano-calcium carbonate prepared in Preparation Example 4 was replaced by the product in Control Example 1.

[0086] Comparative Example 2

[0087] Compared with Example 1, the only difference is:

[0088] The modified nano-calcium carbonate prepared in Preparation Example 4 was replaced by the product in Control Example 2.

[0089] Comparative Example 3

[0090] Compared with Example 1, the only difference is:

[0091] The modified nano-calcium carbonate prepared in Preparation Example 4 was replaced by the product in Control Example 3.

[0092] Comparative Example 4

[0093] Compared with Example 1, the only difference is:

[0094] The modified nano-calcium carbonate prepared in Preparation Example 4 was replaced by the product in Control Example 4.

[0095] The performance tests of the styrene-based thermoplastic elastomers prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were conducted. The test items are as follows, and the results are shown in Table 1:

[0096] 1. Shrinkage: The test standard is ASTM D955-2008.

[0097] 2. Tensile strength: The test standard is ISO 37-1, and the tensile test rate is 500mm / min;

[0098] 3. Elongation at break: The test standard is ISO 37-1.

[0099] 4. Flame retardant performance: Test the oxygen index of the sample according to GB / T 2406.2-2009.

[0100] Table 1

[0101]

[0102]

[0103] As can be seen from Table 1, the comprehensive properties of the styrene-based thermoplastic elastomers prepared in Examples 1 to 5 are superior to those of Comparative Examples 1 and 4. Comparative Examples 1 and 2 contain only nitrogen-phosphorus-based siloxane and borate-based siloxane, which cannot synergistically provide flame retardancy, resulting in reduced flame retardancy. Comparative Example 3, which does not contain any flame retardant elements, further deteriorates in flame retardancy. The nano-calcium carbonate in Comparative Example 4, which has not undergone hyperbranching treatment, has poor dispersion properties and ultimately the worst overall properties.

[0104] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0105] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A low shrinkage styrene-based thermoplastic elastomer, characterized in that: The invention comprises the following raw materials in parts by weight: 20-30 parts of styrene-ethylene-propylene-styrene block copolymer, 10-20 parts of polystyrene resin, 30-40 parts of softening process oil, 30-60 parts of modified nano calcium carbonate, 1-2 parts of lubricating dispersant, and 1-2 parts of antioxidant; The modified nano-calcium carbonate is nano-calcium carbonate grafted with hyperbranched polysilane, which is obtained by hydrolysis and condensation of styrylethyltrimethoxysilane, borate-based siloxane and nitrogen-phosphorus-based siloxane. The preparation method of borate-based siloxane is: Add trans-1-propen-1-ylboronic acid and 3-mercaptopropyltrimethoxysilane to tetrahydrofuran, mix well, then add benzoin dimethyl ether, stir for 1-2 hours, irradiate with ultraviolet light for 30-40 minutes at room temperature, and after the reaction is completed, distill under reduced pressure, precipitate, and dry to constant weight to obtain borate-based siloxane; The ratio of trans-1-propen-1-ylboronic acid, 3-mercaptopropyltrimethoxysilane, tetrahydrofuran, and benzoin dimethyl ether is 0.84 g: 1.96 g: 14 mL: 0.05-0.08 g; the power of the ultraviolet lamp is 20 W, and the wavelength is 365 nm; The preparation method of nitrogen-phosphorus siloxane is as follows: After the Schlenk flask was closed and nitrogen was exchanged three times, it was protected with nitrogen and placed in a -40°C cryostat. γ-Aminopropyltriethoxysilane, triethylamine, and toluene were injected into the Schlenk flask in sequence. After stirring for 10 minutes, diphenylphosphine chloride was slowly added dropwise. The solution was added dropwise within 30 minutes. After stirring for 15 minutes, the flask was removed from the cryostat and stirred at room temperature for 2.5 hours. A fritted funnel was filled with diatomaceous earth, filtered, washed, and the filtrates were combined and rotary evaporated to obtain nitrogen-phosphorus-based siloxane. The volume ratio of γ-aminopropyltriethoxysilane, triethylamine, toluene and diphenylphosphine chloride is 3.5:4.6:60:5.

6.

2. The low shrinkage styrene-based thermoplastic elastomer according to claim 1, characterized in that: The polystyrene resin is one or more of general-purpose polystyrene and high-impact polystyrene.

3. The low shrinkage styrene-based thermoplastic elastomer according to claim 1, characterized in that: Softening operating oil has a flash point greater than 200°C and a kinematic viscosity greater than 50 mm at 40°C 2 / s of one or more of paraffin oil, cycloparaffin oil, aromatic oil, and straight-chain paraffin oil.

4. The low shrinkage styrene-based thermoplastic elastomer according to claim 1, characterized in that: The antioxidant is one or more of hindered phenol antioxidant Irganox 1010, phosphite antioxidant IRGAFOS 168, and amine antioxidant A.

5. The low shrinkage styrene-based thermoplastic elastomer according to claim 1, characterized in that: The preparation method of modified nano calcium carbonate is: Add nano-calcium carbonate, acetic acid aqueous solution and tetrahydrofuran into a flask, control the temperature at 70-75°C, add a hyperbranched monomer, keep the temperature for reaction for 24 hours, wash with distilled water, and vacuum dry at 50-55°C for 72 hours to obtain modified nano-calcium carbonate; Among them, the mass ratio of nano-calcium carbonate, acetic acid aqueous solution, tetrahydrofuran, and hyperbranched monomer is 0.2:1:(6-10):2, the mass fraction of acetic acid aqueous solution is 66.7%, and the hyperbranched monomer is composed of styrylethyltrimethoxysilane, borate-based siloxane and nitrogen-phosphorus-based siloxane in a mass ratio of 1:0.2-0.4:0.6-0.

8.

6. The method for preparing a low shrinkage styrene-based thermoplastic elastomer according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Put the styrene-ethylene-propylene-styrene block copolymer and softening process oil into a high-speed mixer in sequence, stir at a speed of 300-500 r / min for 5-40 minutes, and let it stand for 24 hours for use; then put the polystyrene resin, modified nano calcium carbonate, lubricant, and antioxidant into the high-speed mixer together, stir at 100-300 r / min for 3-8 minutes to obtain a premix semi-finished product; (2) The semi-finished premix is ​​added to an extruder, melt-extruded and granulated to obtain a low-shrinkage styrene-based thermoplastic elastomer.

7. The method for preparing a low shrinkage styrene-based thermoplastic elastomer according to claim 6, characterized in that: In step (2), the extruder is a co-rotating twin-screw extruder with a feed speed of 200-300 r / min, a screw speed of 300-500 r / min, and a screw aspect ratio of 52; the temperature of the first section of melt extrusion does not exceed 170°C, and the temperature of the remaining sections is 190-250°C.

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