A gradient polymerization double-crosslinking low-temperature-resistant environment-friendly styrene-butadiene latex, a preparation method and application thereof

Abstract

This invention discloses a gradient-polymerized, double-crosslinked, low-temperature resistant, and environmentally friendly styrene-butadiene latex, its preparation method, and its applications, belonging to the field of polymer materials technology. The styrene-butadiene latex is prepared from raw materials comprising the following parts by weight: 40-60 parts styrene, 30-50 parts butadiene, 10-20 parts butyl acrylate, 15-25 parts thiol crosslinking agent, 0.5-2 parts metal ion crosslinking agent, and 4-10 parts bio-based plasticizer. The styrene-butadiene latex is obtained through a gradient polymerization process, including: firstly, polymerizing styrene and butadiene at 50±2℃ to form a rigid backbone network; then, heating to 75±3℃ to introduce butyl acrylate, forming a rigid-flexible block molecular structure, and constructing a double-crosslinked network using a thiol crosslinking agent and a metal ion crosslinking agent. The styrene-butadiene latex produced by this invention has a peel strength of 25~32.7N / cm, a pull-out force of ≥86.3N, is resistant to cracking at -20℃ without cracking, has a VOC emission of ≤10g / L, an elastic recovery rate of >92%, and a performance retention rate of >89% after aging. It is suitable for the manufacture of high-end environmentally friendly carpet backing adhesives.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex, its preparation method, and its application. Background Technology

[0002] As a crucial medium for architectural space decoration and functionality, carpets have seen global annual consumption exceeding 12 billion square meters. Commercial carpets, in particular, must withstand high-frequency foot traffic and the movement of machinery, placing stringent demands on the durability of their adhesive backing. According to a 2023 industry survey, the replacement cycle for carpets in high-end hotels and hospitals has shortened from 5 years to 2.8 years, primarily due to adhesive peeling leading to edge curling. This results in over $6 billion in maintenance costs annually and increases the risk of slips, trips, and other safety accidents. The market urgently needs a carpet latex that combines high adhesive strength, good low-temperature toughness, and environmental compliance to meet the stringent VOC emission limits imposed by green building certifications on indoor materials.

[0003] While styrene-butadiene rubber (SBR) currently dominates the market for adhesive backing, its molecular structure has inherent defects. Styrene segments tend to form rigid microdomains at low temperatures, causing the adhesive layer to crack below 5°C. Simultaneously, linear butadiene chains lack resilience under dynamic loads, resulting in a significant decrease in adhesive strength after prolonged rolling. Plasticizers added to improve flexibility are prone to migration, polluting the environment and causing the adhesive layer to gradually harden. Existing improvement technologies, such as copolymer modification, nanocomposites, or the use of bio-based plasticizers, while improving certain properties, often sacrifice other key indicators, making it difficult to simultaneously achieve high strength and toughness, low-temperature performance, and environmental requirements. Summary of the Invention

[0004] To overcome the aforementioned technical problems in existing technologies, this invention provides a gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex, its preparation method, and its applications. Through molecular structure design and innovative crosslinking mechanisms, this invention significantly overcomes the technical defects of traditional styrene-butadiene latex, such as low-temperature embrittlement, poor resilience, and excessive VOC emissions. The styrene-butadiene latex prepared by this invention achieves a peel strength of 25~32.7 N / cm under the same testing conditions, which is 37~80% higher than that of traditional latex (18.2 N / cm), and its VOC emissions are ≤10 g / L, only 12.5% ​​of the national standard limit. To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0005] In one aspect, this invention provides a gradient-polymerized, double-crosslinked, low-temperature resistant, environmentally friendly styrene-butadiene latex, prepared from raw materials comprising the following parts by weight:

[0006] Styrene 40-60 parts, butadiene 30-50 parts, butyl acrylate 10-20 parts, thiol crosslinking agent 15-25 parts, metal ion crosslinking agent 0.5-2 parts, bio-based plasticizer 4-10 parts;

[0007] The styrene-butadiene latex is prepared by a gradient polymerization process, which includes: firstly, polymerizing styrene and butadiene at 50±2℃ to form a rigid backbone network; then, heating to 75±3℃ to introduce butyl acrylate to form a rigid-flexible block molecular structure, and constructing a double crosslinking network using a thiol crosslinking agent and a metal ion crosslinking agent.

[0008] As a further embodiment of the present invention: the metal ion crosslinking agent is at least one of zinc acetate, zinc chloride, or zinc sulfate;

[0009] And / or, the bio-based plasticizer is a mixture of epoxidized soybean oil and citrate, wherein the mass ratio of epoxidized soybean oil to citrate is (0~5):(0~1), and the two are not both 0 at the same time.

[0010] As a further aspect of the present invention, the raw materials of the styrene-butadiene latex also include 2 parts of nano-silica.

[0011] As a further embodiment of the present invention, the citrate ester is selected from at least one of tributyl citrate, acetylated tributyl citrate, or triethyl citrate.

[0012] As a further embodiment of the present invention, the mass ratio of the thiol crosslinking agent to the metal ion crosslinking agent is 15~20:1.

[0013] As a further embodiment of the present invention, the thiol crosslinking agent is selected from at least one of dodecyl thiol, isooctyl mercaptoacetate, octadecyl 3-mercaptopropionate, and pentaerythritol tetramercaptoacetate.

[0014] As a further embodiment of the present invention: the solid content of the styrene-butadiene latex is 48~55%, the peel strength is ≥25N / cm, and the VOC emission is ≤10 g / L;

[0015] And / or, when the styrene-butadiene latex is applied to carpet backing, the pull-out force is ≥80 N.

[0016] In another aspect, the present invention provides a method for preparing a gradient-polymerized, double-crosslinked, low-temperature resistant, environmentally friendly styrene-butadiene latex, comprising the following steps:

[0017] (1) Styrene, butadiene and a portion of thiol crosslinking agent were polymerized at 50±2℃ under nitrogen protection for 1 to 1.5 hours.

[0018] (2) Heat to 75±3℃, add butyl acrylate and the remaining thiol crosslinking agent dropwise, and react for 2-3 hours until the conversion rate is >98%;

[0019] (3) Cool down to 70°C, add metal ion crosslinking agent and bio-based plasticizer, and perform curing treatment at 60-75°C to obtain the styrene-butadiene latex.

[0020] As a further aspect of the present invention: the portion of the thiol crosslinking agent mentioned in step (1) is 45-55% of the total mass of the thiol crosslinking agent;

[0021] And / or, in step (2), the heating process is carried out at a rate of 1~3 °C / min;

[0022] And / or, in step (2), the dropping rate of butyl acrylate and the remaining thiol crosslinking agent is 4~6 mL / min;

[0023] And / or, in step (2), when adding butyl acrylate and the remaining thiol crosslinking agent, the operation of adding nano-silica is also included;

[0024] And / or, the aging process described in step (3) is carried out at a temperature of 70°C for 30 to 40 minutes;

[0025] And / or, after step (3), a post-processing step is also included: centrifuging the matured product to remove unreacted monomers and adjusting the pH to 7.0 ± 0.5.

[0026] In a third aspect, the present invention provides the application of the above-mentioned gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex, or the styrene-butadiene latex prepared by the above-mentioned gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex preparation method, in carpet backing adhesive.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) This invention employs a gradient polymerization process of 50℃→75℃ to optimize the monomer sequence distribution of styrene-butadiene-butyl acrylate, forming a "rigid-flexible block" molecular structure, which improves the low-temperature crack resistance by 300%. At the same time, a double cross-linking network of thiol covalent bonds and zinc ion coordination bonds is constructed. By adjusting the mass ratio of the two to 15~20:1, a synergistic cross-linking effect is achieved, resulting in a clustering force exceeding 80N. In addition, a bio-based plasticizing system composed of epoxidized soybean oil and citrate ester (3~5:1) is used to inhibit the migration of plasticizing molecules by utilizing ester group hydrogen bonds. Under the condition of not using phthalate additives, VOC emissions are reduced to below 10g / L, achieving a combination of high strength, low-temperature resistance and environmental protection performance.

[0029] (2) In terms of mechanical properties, the double cross-linked network of the styrene-butadiene latex of this invention results in a pull-out force of 86.3 ~ 94.2 N (ASTM D1335), which is 38 ~ 51% higher than that of traditional latex, and the peel strength retention rate after aging is >89%. In terms of environmental adaptability, it shows no cracks after freezing at -20℃ for 24 hours (ISO 2921:2019), and the elastic recovery rate is 92.1 ~ 95.3%, solving the problem of low-temperature embrittlement. In terms of environmental protection, the bio-based plasticizing system reduces VOC emissions to as low as 4.3 ~ 9.1 g / L, with a migration rate of <0.12%, and has passed the EU REACH Annex XVII certification. It is particularly noteworthy that this latex is fully compatible with existing coating equipment in terms of processing parameters such as viscosity (1200±200 mPa·s) and solid content (50±2%), and can be mass-produced without modifying the production line. Pilot testing has shown that the qualification rate of 10-ton-level products reaches 98.5%. Detailed Implementation

[0030] The present invention is further illustrated below by way of examples, but these examples do not limit the invention to the scope of the embodiments described. Experimental methods in the following examples, unless otherwise specified, were performed according to conventional methods and conditions, or as selected in the product instructions. Furthermore, all reagents and raw materials used in this invention are commercially available.

[0031] The preparation method of the present invention specifically includes the following steps:

[0032] (1) Styrene, butadiene and some thiol crosslinking agent are put into a reactor equipped with an anchor stirrer (speed 200±10rpm), nitrogen is purged three times to replace the air, and the temperature is raised to 50±2℃. The reaction is kept at this temperature for 1~1.5 hours. At this time, the viscosity of the system rises to 800~1200mPa·s.

[0033] (2) Heat the mixture of butyl acrylate and the remaining thiol crosslinking agent at a rate of 1~3℃ / min to 75±3℃, and add it dropwise at a rate of 4~6mL / min. Continue the reaction at this temperature for 2~3 hours, and take samples every 30 minutes to detect the solid content (target value 48~55%). Stop the reaction when the conversion rate is >98%.

[0034] (3) Cool the system to 70°C, add metal ion crosslinking agent and bio-based plasticizer, and stir at 500 rpm at 60-75°C for 30-40 minutes to mature.

[0035] (4) Remove unreacted monomers by centrifugation (centrifugal force 3000g, time 15min), adjust pH to 7.0±0.5, and filter to obtain the finished styrene-butadiene latex.

[0036] This method achieves ordered assembly of molecular chains through gradient temperature control, avoiding the phase separation defects of traditional one-step polymerization, and the staged addition of dual crosslinking agents ensures network uniformity.

[0037] Example 1

[0038] A method for preparing a gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex, using the following raw material components: 50 parts styrene, 40 parts butadiene, 15 parts butyl acrylate, 20 parts dodecyl mercaptan (added in two batches), 1 part zinc acetate, 4 parts epoxidized soybean oil, and 1 part tributyl citrate. The preparation method includes the following steps:

[0039] (1) Styrene, butadiene and 10 parts of thiol were added to the reactor, and after nitrogen purging, the temperature was raised to 50±2℃ and stirred at 200rpm for 1 hour.

[0040] (2) Then, the temperature was increased to 75°C at 2°C / min, and the mixture of butyl acrylate and the remaining 10 parts of thiol was added dropwise at a uniform rate (5 mL / min). The reaction was maintained at this temperature for 2.5 hours until the conversion rate was >98%.

[0041] (3) Cool down to 70°C and add zinc acetate, epoxidized soybean oil and tributyl citrate. Cook at 70°C and 500 rpm for 30 minutes. After centrifugation (3000g, 15min), adjust the pH to 7.0 and filter to obtain the emulsion.

[0042] Example 2

[0043] A method for preparing a gradient-polymerized, double-crosslinked, low-temperature resistant, environmentally friendly styrene-butadiene latex, using the following raw material components: 45 parts styrene, 35 parts butadiene, 20 parts butyl acrylate, 15 parts isooctyl mercaptoacetate, 0.8 parts zinc sulfate, 6 parts epoxidized soybean oil, and 2 parts tributyl citrate. The preparation method includes the following steps:

[0044] (1) Styrene, butadiene and 12 parts of thiol were added to the reactor, and after nitrogen purging, the temperature was raised to 50±2℃ and stirred at 200 rpm for 1.2 hours.

[0045] (2) Then, the temperature was increased to 75°C at 2°C / min, and the mixture of butyl acrylate and the remaining 3 parts of thiol was added dropwise at a uniform rate (5 mL / min). The reaction was maintained at this temperature for 3 hours until the conversion rate was >98%.

[0046] (3) Cool down to 70°C and add zinc sulfate, epoxidized soybean oil and tributyl citrate. Cook at 60°C and 500 rpm for 40 minutes. After centrifugation (3000g, 15min), adjust the pH to 7.0 and filter to obtain the emulsion.

[0047] Example 3

[0048] A method for preparing a gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex, using the following raw material components: 60 parts styrene, 30 parts butadiene, 10 parts butyl acrylate, 25 parts octadecyl 3-mercaptopropionate, 2 parts zinc acetate, 3 parts epoxidized soybean oil, 1 part tributyl citrate, and 2 parts nano-silica (reinforcing phase). The preparation method includes the following steps:

[0049] (1) Styrene, butadiene and 8 parts of mercaptan were added to the reactor, and after nitrogen purging, the temperature was raised to 50±2℃ and stirred at 200rpm for 1.5 hours.

[0050] (2) Then, the temperature was increased to 75°C at 2°C / min, and the mixture of butyl acrylate and the remaining 7 parts of thiol solution and nano silica was added dropwise at a uniform rate (5 mL / min). The reaction was kept at this temperature for 2 hours until the conversion rate was >98%.

[0051] (3) Cool down to 70°C and add zinc acetate, epoxidized soybean oil and tributyl citrate. Cook at 75°C and 500 rpm for 35 minutes. After centrifugation (3000g, 15min), adjust the pH to 7.0 and filter to obtain the emulsion.

[0052] Example 4

[0053] A method for preparing a gradient-polymerized, double-crosslinked, low-temperature resistant, environmentally friendly styrene-butadiene latex, using the following raw material components: 55 parts styrene, 45 parts butadiene, 18 parts butyl acrylate, 22 parts pentaerythritol tetramercaptoacetate, 1.5 parts zinc chloride, and 5 parts tributyl citrate (completely replacing epoxidized soybean oil). The preparation method includes the following steps:

[0054] (1) Styrene, butadiene and 11 parts of thiol were added to the reactor, and after nitrogen purging, the temperature was raised to 50±2℃ and stirred at 200 rpm for 1 hour.

[0055] (2) Then, the temperature was increased to 75°C at 2°C / min, and the mixture of butyl acrylate and the remaining 11 parts of thiol was added dropwise at a uniform rate (5 mL / min). The reaction was maintained at this temperature for 3 hours until the conversion rate was >98%.

[0056] (3) Cool down to 70°C, add zinc chloride and tributyl citrate, and mature at 70°C and 500 rpm for 30 minutes; centrifuge (3000g, 15min), adjust pH to 7.5, and filter to obtain emulsion.

[0057] This application also provides the following comparative examples:

[0058] Comparative Example 1

[0059] Commercially available product: LANXESS XPS-4150 styrene-butadiene latex from Germany.

[0060] Comparative Example 2

[0061] Commercially available product: Dow ES-N210 nanocomposite latex from the USA, containing 5% montmorillonite.

[0062] Comparative Example 3

[0063] Commercially available product: S-2035 physical blending plasticized latex from Soken Chemicals, Japan, with 20% DOP plasticizer added.

[0064] Comparative Example 4

[0065] The difference between Comparative Example 1 and the Example is that the polymerization stage uses a constant 60°C heat preservation process and does not use a gradient temperature increase from 50°C to 75°C. The other monomer composition, double crosslinking network construction, bio-based plasticizing system and post-treatment conditions are completely consistent with the Example.

[0066] Comparative Example 5

[0067] The difference between Comparative Example 2 and the Example is that only thiol covalent crosslinking was introduced, and no zinc ion coordination crosslinking component was added. The remaining gradient polymerization process, bio-based plasticizing system and test conditions are completely consistent with the Example.

[0068] Comparative Example 6

[0069] The difference between Comparative Example 3 and the Example is that dioctyl phthalate (DOP) was used as a plasticizer to replace the bio-based plasticizer system of epoxidized soybean oil and citrate (3~5:1). The remaining gradient polymerization process, double crosslinking network construction and post-treatment conditions were completely consistent with those of the Example.

[0070] Effect Example

[0071] The application performance of the products prepared in the embodiments and comparative examples of this application was tested according to the following standards or methods:

[0072] I. Solid content

[0073] Standard number: GB / T 8298-2017

[0074] Methods: 1. Instruments: Analytical balance (0.1 mg), forced-air drying oven, weighing bottle, desiccator

[0075] 2. Constant weight: Dry the weighing bottle at 105℃ until it reaches a constant weight (m0).

[0076] 3. Weighing: Take approximately 2g of latex and weigh it accurately (m1).

[0077] 4. Drying:

[0078] - Natural latex: Bake at 70℃ / 105℃ until constant weight

[0079] - Synthetic latex: Dry at 105℃ (normal pressure) or under reduced pressure.

[0080] - Constant weight standard: The difference between two consecutive weighings ≤ 0.5 mg

[0081] II. Peel Strength

[0082] Standard number: ISO 8510-2:2006 (equivalent to national standard GB / T 2791)

[0083] Method: Apply 25mm wide tape to a stainless steel plate and peel it off at a speed of 300mm / min at 180°. Take the average value of 5 tests (unit: N / cm).

[0084] III. Pulling force

[0085] Standard number: ASTM D1335-17 (Carpet tufting strength)

[0086] Method: A 10×10cm carpet sample was clamped in a universal tensile testing machine and the tufts were pulled vertically until they detached at a speed of 100mm / min. The peak force (unit: N) was recorded.

[0087] IV. Low-temperature crack resistance

[0088] Standard number: ISO 2921:2019 (Polymer low-temperature embrittlement test)

[0089] Method: The sample was frozen at -20℃±1℃ for 24 hours, and the surface cracks were observed with a 5x magnifying glass and classified as "no cracks / micro-cracks / complete cracking".

[0090] V. VOC emissions

[0091] Standard number: GB 18583 (Determination of volatile organic compounds in coatings)

[0092] Method: Place 1g of sample in a sealed container at 40℃ for 24h, and analyze the total volatile organic compounds (unit: g / L) by GC-MS.

[0093] VI. Migration Rate

[0094] Standard number: ISO 177:2016 (Determination of plasticizer migration in plastics)

[0095] Method: The adhesive film was tightly bonded to the polypropylene board and placed in an oven at 70℃±2℃ for 168 hours. The percentage of mass loss was then calculated.

[0096] VII. Elastic recovery rate

[0097] Standard number: ISO 4662 (Test for elastic recovery of rubber)

[0098] Method: The sample was compressed to 50% and held for 30 seconds. After unloading, the deformation recovery rate (unit: %) was measured 60 seconds later.

[0099] 8. Aging performance retention rate

[0100] Standard number: ISO 188:2011 (Hot air aging of rubber)

[0101] Method: Aging in an oven at 70℃±1℃ for 168h, and comparing the peel strength ratio before and after aging (unit: %).

[0102] 9. Viscosity

[0103] Standard number: GB / T 2794-2013

[0104] Method: - The sample was kept at a constant temperature of 25℃±1℃

[0105] - Select the appropriate rotor and speed (e.g., use rotor No. 2 / 3, 60rpm for NDJ-5S model).

[0106] - Immerse the rotor in latex up to the graduation mark, and record the reading after it stabilizes.

[0107] - Perform 2-3 parallel tests and take the average value.

[0108] The samples from Examples 1-4 and Comparative Examples 1-6 were tested, and the test results are shown in Tables 1 and 2.

[0109] Table 1

[0110]

[0111] Table 2

[0112]

[0113] As shown in Table 1, Examples 1-4 are superior to the comparative examples in all aspects, indicating better performance in practical applications. Specifically, Example 2, after additional testing, showed no cracks even after being frozen at -25°C for 24 hours, making it particularly suitable for carpets in extremely cold regions. Example 3 yielded a latex peel strength of 32.7 N / cm and a pull-out force of 94.2 N, suitable for high-intensity applications such as airports and shopping malls. Example 4's product has a VOC content of only 4.3 g / L, a migration rate of 0.08% (ISO 177:2016), and has passed the EU EC1907 / 2006 environmental certification, maintaining 90.4% of its performance after aging.

[0114] Specifically, the peel strength of Comparative Example 1 was only 18.2 N / cm, 36.1% lower than that of Example 1 (28.5 N / cm); the pull-out strength was 62.4 N, 27.7% lower than that of Example 1 (86.3 N); and the adhesive layer completely cracked after freezing at -20°C for 24 hours, while Example 1 showed no cracks. This difference is attributed to the lack of a gradient polymerization structure and a double cross-linked network in the Comparative Example, where disordered aggregation of styrene led to increased low-temperature brittleness.

[0115] Comparative Example 2 exhibited a pull-out force of 75.3 N at room temperature, but developed network cracks during testing at -20°C (Example 2 showed no cracks). More seriously, its viscosity reached 3200 mPa·s (25°C), exceeding the limit of carpet spraying equipment (<1500 mPa·s), while the viscosity of Example 2 was only 1250 mPa·s. After dynamic load testing (5000 wheelchair rolls), the pull-out force retention rate was only 68.5%, while the pull-out force retention rate of Example 2 was 92.7%. Comparative Example 2 was significantly lower than Example 2, demonstrating that physical fillers cannot replace flexible molecular chain design.

[0116] Comparative Example 3 exhibited a peel strength of 21.5 N / cm (compared to 32.7 N / cm in Example 3) and VOC emissions of 52.7 g / L (compared to only 9.1 g / L in Example 3). After accelerated aging (70°C × 168 h), performance degradation was observed: the peel strength of the comparative example decreased to 14.1 N / cm (a 34.4% decrease), while Example 3 maintained 29.8 N / cm (an 8.9% decrease). This demonstrates that the migration of phthalic plasticizers leads to adhesive layer hardening, while the double cross-linked network of Example 3 effectively inhibits degradation.

[0117] Comparative Example 4 had a VOC of 38.5 g / L, but its migration rate was still 1.2% (compared to 0.08% in Example 4); microcracks appeared at -5°C (compared to no cracks in Example 4 at -20°C); more significantly, its pull-out force was only 69.8 N, 25.3% lower than the 93.4 N in Example 4. These results verify the key role of the synergistic effect of citrate ester / zinc ion on low-temperature performance.

[0118] Comparative Example 5 exhibited a peel strength of 20.5 N / cm and a pull-out force of 70.8 N, significantly lower than that of the Examples (28.4~32.7 N / cm, 86.3~94.2 N). It also showed "network cracking" at -20℃ (unlike the Examples, which showed "no cracking"). Its elastic recovery rate of 83.7% and aging retention rate of 73.1% were also lower than those of the Examples (92.1%~95.3%, 88.7%~91.1%). This indicates that single thiol crosslinking cannot simultaneously achieve high strength and high resilience; the synergistic effect of dual crosslinking networks is key to improving overall performance.

[0119] Comparative Example 6 exhibited a peel strength of 23.9 N / cm and a pull-out force of 76.2 N, lower than that of Examples (28.4~32.7 N / cm, 86.3~94.2 N). Its VOC content of 8.2 g / L was similar to some values ​​in Examples (4.3~9.1 g / L), but its migration rate was as high as 0.13% (Examples 0.07%~0.12%), and its aging retention rate was 79.0%, lower than that of Examples (88.7%~91.1%). This demonstrates that traditional DOP plasticizers have high migration rates and poor long-term stability, while the bio-based plasticizing system of epoxidized soybean oil and citrate esters effectively inhibits migration through ester group hydrogen bonding, achieving a balance between environmental friendliness and aging resistance.

[0120] It should be noted that, among the embodiments of the present invention, Embodiment 4 exhibits the best performance in terms of environmental protection and has excellent overall performance.

[0121] Finally, it should be noted that in this invention, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0122] Although this disclosure has been described above through specific embodiments, it should be understood that those skilled in the art can devise various modifications, improvements, or equivalents to this disclosure within the spirit and scope of the appended solutions. Such modifications, improvements, or equivalents should also be considered to be included within the scope of protection claimed in this disclosure.

Claims

1. A gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex, characterized in that, It is prepared from raw materials comprising the following parts by weight: Styrene 40-60 parts, butadiene 30-50 parts, butyl acrylate 10-20 parts, thiol crosslinking agent 15-25 parts, metal ion crosslinking agent 0.5-2 parts, bio-based plasticizer 4-10 parts; The styrene-butadiene latex is prepared by a gradient polymerization process, which includes: firstly, polymerizing styrene and butadiene at 50±2℃ to form a rigid backbone network; then, heating to 75±3℃ to introduce butyl acrylate to form a rigid-flexible block molecular structure, and constructing a double crosslinking network using a thiol crosslinking agent and a metal ion crosslinking agent.

2. The gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 1, characterized in that, The metal ion crosslinking agent is at least one of zinc acetate, zinc chloride, or zinc sulfate; And / or, the bio-based plasticizer is a mixture of epoxidized soybean oil and citrate, wherein the mass ratio of epoxidized soybean oil to citrate is (0~5):(0~1), and the two are not both 0 at the same time.

3. The gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 1, characterized in that, The raw materials of the styrene-butadiene latex also include 2 parts of nano-silica.

4. The gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 2, characterized in that, The citrate ester is selected from at least one of tributyl citrate, acetylated tributyl citrate, or triethyl citrate.

5. The gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 1, characterized in that, The mass ratio of the thiol crosslinking agent to the metal ion crosslinking agent is 15~20:

1.

6. The gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 1, characterized in that, The thiol crosslinking agent is selected from at least one of dodecyl thiol, isooctyl mercaptoacetate, octadecyl 3-mercaptopropionate, and pentaerythritol tetramercaptoacetate.

7. The gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 1, characterized in that, The styrene-butadiene latex has a solid content of 48-55%, a peel strength of ≥25 N / cm, and a VOC emission of ≤10 g / L; And / or, when the styrene-butadiene latex is applied to carpet backing, the pull-out force is ≥80 N.

8. A method for preparing a gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex as described in claims 1-7, characterized in that, Includes the following steps: (1) Styrene, butadiene and a portion of thiol crosslinking agent were polymerized at 50±2℃ under nitrogen protection for 1 to 1.5 hours. (2) Heat to 75±3℃, add butyl acrylate and the remaining thiol crosslinking agent dropwise, and react for 2-3 hours until the conversion rate is >98%; (3) Cool down to 70°C, add metal ion crosslinking agent and bio-based plasticizer, and perform curing treatment at 60-75°C to obtain the styrene-butadiene latex.

9. The method for preparing gradient polymerization double crosslinked low-temperature resistant environmentally friendly styrene-butadiene latex according to claim 8, characterized in that, The portion of the thiol crosslinking agent mentioned in step (1) constitutes 45-55% of the total mass of the thiol crosslinking agent; And / or, in step (2), the heating process is carried out at a rate of 1~3 °C / min; And / or, in step (2), the dropping rate of butyl acrylate and the remaining thiol crosslinking agent is 4~6 mL / min; And / or, in step (2), when adding butyl acrylate and the remaining thiol crosslinking agent, the operation of adding nano-silica is also included; And / or, the aging process described in step (3) is carried out at a temperature of 70°C for 30 to 40 minutes; And / or, after step (3), a post-processing step is also included: centrifuging the matured product to remove unreacted monomers and adjusting the pH to 7.0 ± 0.

5.

10. The application of the styrene-butadiene latex prepared by the gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to any one of claims 1 to 7, or the styrene-butadiene latex prepared by the gradient polymerization double crosslinking low-temperature resistant environmentally friendly styrene-butadiene latex according to claims 8 to 9, in carpet backing adhesive.

Images