Neoprene latex suitable for dip process and its preparation method

Abstract

The application discloses a neoprene latex suitable for an impregnation process and a preparation method thereof, and belongs to the technical field of neoprene latex synthesis. The water phase of the neoprene latex comprises 90-110 parts of pure water, 3-6 parts of disulfated rosin, 0.1-0.3 parts of a sodium beta-naphthalene sulfonate formaldehyde condensate, 1.5-2 parts of potassium hydroxide and 0.2-0.6 parts of sodium sulfite. The oil phase comprises neopentadiene monomers and a non-sulfur regulator. The water-oil ratio of the water phase and the oil phase is 0.73-0.78. The neoprene latex is prepared through emulsification and polymerization. The application discards a traditional sulfur regulator and a linear surfactant system, adopts a non-sulfur molecular weight regulator and a specific rosin emulsifier compound system, combines a segmented temperature control polymerization process, realizes the improvement of polymer structure, latex stability and impregnation performance, and prepares high-performance neoprene latex suitable for the impregnation process.

Description

Technical Field

[0001] This invention belongs to the field of chloroprene latex synthesis technology, specifically a chloroprene latex suitable for impregnation process and its preparation method. Background Technology

[0002] Neoprene latex, with its excellent oil resistance, acid and alkali resistance, aging resistance, mechanical strength, and film-forming properties, is a core raw material for dip-molding processes and is widely used in medical gloves, industrial protective sleeves, sealing films, and labor protection products. Dip-molding places stringent requirements on latex performance, demanding not only good emulsification and chemical stability, but also ensuring adequate wet gel strength, defect-free continuous dip-molding, smooth demolding without mold contamination, and that the finished product possesses good weather resistance, low-temperature flexibility, and color stability. Currently, existing neoprene latex manufacturing technologies for dip-molding generally suffer from the following technical limitations: 1. Traditional processes often use sulfur as a molecular weight regulator, introducing sulfur-sulfur bonds into the polymer molecular chain. These bonds are easily broken and degraded under ultraviolet light, ozone, and heat-oxygen environments, resulting in rapid aging of impregnated products, severe decline in tensile properties, and easy cracking and embrittlement. They cannot meet the stringent requirements for outdoor use and long-term storage.

[0003] 2. Conventional emulsification systems use non-rosin surfactants such as linear alkyl sulfonates and OP series. These surfactants are prone to desorb from the surface of rubber particles during the impregnation and gelation process, and remain free in the adhesive solution, adhering to the mold surface and forming stubborn stains. This not only affects the appearance of the product, but also leads to fewer consecutive impregnation times and more film defects (such as pinholes, cracks, and uneven thickness), significantly reducing the yield of production products.

[0004] 3. Traditional polymerization processes often involve one-time initiator feeding and single temperature control, making it difficult to accurately regulate polymer gel content and molecular weight distribution. Excessive gel content can lead to excessive latex viscosity and poor flowability, while insufficient wet gel strength makes it unsuitable for automated impregnation production lines. In addition, delayed degassing after termination results in excessive residual monomers and strong latex odor, limiting its application in medical and food contact fields.

[0005] 4. Conventional polymerization processes do not segmentally control the regularity of molecular chains, making the products prone to hardening and cracking at low temperatures, thus failing to meet the requirements of low-temperature operation. Furthermore, the emulsion system is not properly matched, resulting in poor latex stability and easy flocculation when exposed to electrolytes, which cannot meet the needs of long-term continuous production.

[0006] In response to the common challenges faced by the industry, the development of a chloroprene latex with excellent weather resistance, low mold contamination, stable film formation during impregnation, and balanced performance has become an urgent need in the field of impregnated products. Summary of the Invention

[0007] This invention abandons the traditional sulfur-modified and linear surfactant system, and adopts a compound system of non-sulfur molecular weight regulator and specific rosin emulsifier. Combined with segmented temperature-controlled polymerization, continuous drop-addition of initiator, and precise control of termination degassing time, it achieves comprehensive optimization of polymer structure, latex stability, and impregnation performance, solves the core pain points of existing technologies, and prepares high-performance chloroprene latex suitable for impregnation processes.

[0008] This invention is achieved through the following technical solution: A chloroprene latex suitable for impregnation processes comprises the following raw materials in parts by weight: The aqueous phase includes 90-110 parts of pure water, 3-6 parts of disproportionated rosin, 0.1-0.3 parts of sodium β-naphthalenesulfonate formaldehyde condensate, 1.5-2 parts of potassium hydroxide, and 0.2-0.6 parts of sodium sulfite; The oil phase includes chloroprene monomer and non-sulfur regulators; the water-to-oil ratio of the aqueous phase and the oil phase is 0.73~0.78.

[0009] Furthermore, hydrogenated rosin is used instead of disproportionated rosin in equal parts by weight.

[0010] Furthermore, the non-sulfur modifier is n-dodecyl mercaptan or modifier butyl. The molecular weight modifier does not use sulfur; the use of non-sulfur modifiers is key to improving the weather resistance of impregnated products because the polymer does not contain sulfur-sulfur bonds, significantly enhancing the weather resistance of the products.

[0011] Furthermore, when using dodecyl mercaptan, the conversion rate of chloroprene is controlled at 65-75%, and the mercaptan content in chloroprene is 0.05%-0.06%. When using regulator D, the conversion rate of chloroprene is controlled at 80-90%.

[0012] A method for preparing chloroprene latex suitable for impregnation processes includes the following steps: Step 1, Oil phase preparation: Heat the chloroprene monomer and add a non-sulfur regulator, stirring to dissolve; Step 2, Aqueous Phase Preparation: Prepare rosin potassium soap by reacting disproportionated rosin or hydrogenated rosin with potassium hydroxide in water; dissolve sodium β-naphthalenesulfonate formaldehyde condensate and mix it with rosin potassium soap; add sodium sulfite before emulsification and stir to dissolve; The reducing agent (sodium sulfite) in the aqueous phase must be added 5-10 minutes before emulsification. Adding it too early will reduce its effective content in order to ensure the effective content of the reducing agent. Excess sodium sulfite can be used as a bleaching agent, which will significantly improve the color of the impregnated products and give them outstanding resistance to yellowing during drying and vulcanization. It can be more widely used in the manufacture of light-colored and brightly colored products.

[0013] Step 3, Emulsification: Mix and emulsify the aqueous phase and oil phase to form an emulsion; Step 4, Polymerization: The emulsion is subjected to an initiation polymerization reaction in a polymerization reactor.

[0014] In this process, disproportionated rosin (hydrogenated rosin) can be directly added to the oil phase (chloroprene monomer phase), where it reacts with potassium hydroxide in the aqueous phase during emulsification to form soap salts, thus creating a stable emulsion. Alternatively, disproportionated rosin (hydrogenated rosin) potassium soap can be prepared first and then added to the aqueous phase, while only dodecyl mercaptan or the regulator butyl is added to the oil phase (chloroprene monomer phase).

[0015] Furthermore, in step one, the chloroprene monomer is heated to 16~18℃.

[0016] Furthermore, the emulsification temperature of the aqueous and oil phases is 40±2℃.

[0017] Furthermore, during the polymerization process, a 1% potassium persulfate-silver salt initiator aqueous solution is continuously added dropwise to the reactor to initiate the polymerization reaction.

[0018] Furthermore, the polymerization reaction temperature is 38~45℃.

[0019] Furthermore, when the chloroprene conversion rate is less than 55%, the polymerization temperature is 40±2℃; when the conversion rate is greater than 55%, the reaction temperature is 43~45℃. By controlling the polymerization temperature, the regularity of the polymer molecular chain can be controlled, resulting in a polymer with good low-temperature flexibility.

[0020] The resulting chloroprene rubber is a mixture of sol and gel, with the gel content controlled at 70-85% to obtain better wet gel strength, which is beneficial for subsequent impregnation processing.

[0021] The formulation principle of the chloroprene latex preparation formula of the present invention is as follows: 1. A formulation technology for producing chloroprene latex for impregnation applications via free radical emulsion polymerization. The emulsion formulation contains potassium soap of disproportionated rosin (hydrogenated rosin) and sodium β-naphthalenesulfonate formaldehyde condensate, but no other surfactants. The oil phase uses dodecyl mercaptan or butyl as a molecular weight regulator, without using sulfur as a molecular weight regulator. Combined with conversion rate control, a chloroprene polymer with moderate gel content is obtained. The extremely low non-rubber components in the formulation ensure low mold contamination in the finished product. In particular, the stability of the impregnation film is achieved by controlling the total amount of surfactants in the non-rosin components.

[0022] 2. Process technology for producing chloroprene latex for impregnation applications via free radical emulsion polymerization. The initiation system employs an oxidation-reduction-activator system. The reducing agent is added to the aqueous phase in a single step, while the initiator and activator are mixed into a solution and continuously added dropwise. The time from reaction termination to degassing completion is strictly controlled within 4 hours.

[0023] The beneficial effects of this invention compared to the prior art are as follows: 1. Significant improvement in weather resistance: This invention completely eliminates sulfur regulators and adopts a non-sulfur regulation system. The polymer molecular chain has no sulfur-sulfur bonds. The tensile strength retention rate after ultraviolet aging reaches 83%, there is no obvious cracking after ozone aging, and the elongation rate change rate after thermo-oxidative aging is only 80%. The product's aging resistance life is increased by more than 30%, making it suitable for outdoor and long-term storage scenarios.

[0024] 2. Zero mold contamination, doubled continuous impregnation efficiency: This invention uses a compound emulsification system of disproportionated rosin (hydrogenated rosin) potassium soap and sodium β-naphthalenesulfonate formaldehyde condensate, which has no linear surfactants and the emulsifier is not easy to desorb from the rubber particles, thus completely solving the mold contamination problem; the number of continuous impregnations is increased to more than 20 times, with no defects such as pinholes and cracks, and the production yield is increased to more than 98%.

[0025] 3. Precise and controllable process, excellent product consistency: This invention establishes a three-dimensional precise control system for regulator dosage, conversion rate, and polymerization temperature. Segmented temperature control ensures molecular chain regularity, and the gel content is stably controlled at 70~85%, with a wet gel strength of 0.4MPa, making it suitable for automated impregnation production lines. It can be rapidly degassed within 4 hours, with residual monomer ≤0.05% and extremely low latex odor, making it suitable for medical and food contact applications.

[0026] 4. Comprehensive optimization of stability and strong adaptability: The latex has excellent mechanical stability and does not flocculate or gel; it has outstanding chemical stability, is resistant to strong alkalis and organic solvents, does not easily coagulate when exposed to electrolytes, has excellent stability, and can be stored for a long time and produced continuously; it has excellent low-temperature flexibility, and the products do not harden or crack at low temperatures.

[0027] 5. Pure product color and expanded application scenarios: Sodium sulfite has both reduction initiation and bleaching functions. The products do not yellow during the drying and vulcanization process. It can produce light-colored and bright-colored impregnated products, breaking the limitation of traditional latex that can only produce dark-colored products, and expanding the application fields of medical, high-end labor protection and other fields. Detailed Implementation

[0028] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solution of the present invention will be described in detail below with reference to embodiments, but the scope of protection is not limited thereto.

[0029] Example 1 (Disproportionated Rosin System) This embodiment proposes a chloroprene latex suitable for impregnation processes, including its formulation and preparation method: 1. Formula proportions (parts by weight) Aqueous phase: 100 parts deionized water, 4 parts disproportionated rosin, 0.2 parts sodium β-naphthalenesulfonate formaldehyde condensate, 1.67 parts potassium hydroxide, and 0.5 parts sodium sulfite; Oil phase: Chloroprene monomer, n-dodecyl mercaptan 0.055% (relative to monomer), water-oil ratio 0.75; 2. Preparation steps Step 1, Oil phase preparation: Accurately weigh the chloroprene monomer, heat the chloroprene monomer to 17°C, add 0.055% n-dodecyl mercaptan, stir to dissolve for 10 min and set aside.

[0030] Step 2, Aqueous phase preparation: Heat 80 parts of pure water to 88℃, add disproportionated rosin and potassium hydroxide and react for 1 hour to obtain disproportionated rosin potassium soap; dissolve β-naphthalenesulfonate sodium formaldehyde condensate in 20 parts of pure water, mix with disproportionated rosin potassium soap, add water to 100 parts, and adjust the temperature to 56℃; add sodium sulfite 8 minutes before emulsification and stir to dissolve.

[0031] To ensure the effective content of the reducing agent, adding it too early will reduce its effective content. Excess sodium sulfite can be used as a bleaching agent, which will significantly improve the color of the impregnated products and give them outstanding resistance to yellowing during drying and vulcanization, making them more widely applicable in the manufacture of light-colored and brightly colored products.

[0032] Step 3, Emulsification: First, the water phase is introduced through the secondary emulsification pump at a pressure of 0.9 MPa. After the emulsification pump is working normally, the oil phase is added with a water-to-oil ratio of 1:1.3. Emulsify until the emulsion is uniform and free of particles.

[0033] Step 4, Polymerization: The water-oil phase formed by the emulsification pump enters the polymerization reactor as a homogeneous emulsion. A 1% potassium persulfate-silver salt initiator aqueous solution is continuously added dropwise to initiate the polymerization reaction. When the conversion rate is <55%, the temperature is controlled at 40℃. When the conversion rate is >55%, the temperature is raised to 44℃. During the process, stirring and a -20℃ refrigerant are used to remove the heat of reaction. When the conversion rate reaches 69%, the terminator and antioxidant are added.

[0034] Step 5, Degassing: 3.5 hours after termination, complete steam flash degassing, and test the residual monomer ≤0.04% and the total solids content 51%.

[0035] 3. Performance test results Appearance: White emulsion, viscosity 25 mPa·s, surface tension 42 mN / m, pH=12, density 1.2 g / cm³ 2 ; Wet gel strength: 0.4 MPa, no defects after 21 consecutive impregnations; Weather resistance: 83% of the tensile strength was retained after UV aging, and no cracking was observed after ozone aging (Level 1). Mold contamination: No obvious stains, easy to clean Example 2 (Hydrogenated Rosin System) This embodiment proposes a chloroprene latex suitable for impregnation processes, including its formulation and preparation method: 1. Formula proportions (parts by weight) Aqueous phase: 100 parts deionized water, 4 parts hydrogenated rosin, 0.2 parts sodium β-naphthalenesulfonate formaldehyde condensate, 1.67 parts potassium hydroxide, 0.5 parts sodium sulfite. Oil phase: Chloroprene monomer, regulator D, water-oil ratio 0.76; 2. Preparation steps Referring to Example 1, the oil phase uses regulator D to control the conversion rate of chloroprene to 85%; hydrogenated rosin is used instead of disproportionated rosin in the aqueous phase preparation; the remaining process parameters are the same, and the degassing time is 3.8h.

[0036] 3. Performance test results Appearance: White emulsion, viscosity 28 mPa·s, surface tension 41 mN / m, wet gel strength 0.4 MPa; no defects after 22 consecutive impregnations, excellent resistance to yellowing, and the product is white in color.

[0037] Comparative Example 1 (Traditional Sulfur Adjustment System) The formula was modified by adding 0.1 parts of sulfur as a regulator, and the rest of the formula and process were the same as in Example 1. Test results: the tensile strength retention rate after ultraviolet aging was 75%, the ozone aging was level 2, the change rate of elongation at break after thermo-oxidative aging was 70%, defects appeared after 15 consecutive immersions, and the mold was easily contaminated. See Table 1 for details.

[0038] Comparative Example 2 (Traditional Sulfur Adjustment System) The formula was modified by adding 0.3 parts sulfur as a regulator, and the rest of the formula and process were the same as in Example 1. Test results: the tensile strength retention rate after ultraviolet aging was 70%, the ozone aging level was greater than 2, the change rate of elongation at break after thermo-oxidative aging was 60%, defects appeared after 15 consecutive immersions, and the mold was easily contaminated. See Table 1 for details.

[0039] Comparative Example 3 (containing a linear surfactant system) The formulation added 0.3 parts OP-20 and 0.2 parts sodium dodecyl sulfate to replace part of the rosin emulsifier, and the rest of the process was the same as in Example 1; the test results showed that the wet gel strength was 0.25 MPa, defects appeared after 15 consecutive impregnations, the mold was severely contaminated, and the chemical stability was poor. See Table 2 for details.

[0040] Comparative Example 4 (containing a linear surfactant system) The formulation added 0.3 parts OP-20 and 0.2 parts sodium dodecyl sulfate to replace part of the rosin emulsifier, and the rest of the process was the same as in Example 1; the test results showed that the wet gel strength was 0.25 MPa, defects appeared after 15 consecutive impregnations, the mold was severely contaminated, and the chemical stability was poor. See Table 2 for details.

[0041] Comparative Example 5 (containing a linear surfactant system) The formula was modified by adding 0.1 parts OP-20 and 0.1 parts sodium dodecyl sulfate to replace part of the rosin emulsifier, and the rest of the process was the same as in Example 1. Test results: wet gel strength was 0.3 MPa, defects appeared after 10 consecutive impregnations, the mold was severely contaminated, and the chemical stability was poor. See Table 2 for details.

[0042] Comparative Example 6 (Degassing Overtime Process) Degassing was completed 6 hours after termination, and the remaining processes were the same as in Example 1; Test results: residual monomer 0.12%, strong latex odor, decreased mechanical stability, and a small amount of flocculation.

[0043] ; Note: Test conditions for tensile strength retention rate after UV aging: GB / T16422.3, UV-B band, 60℃; Ozone aging cracking level test conditions: GB / T7662, 50pphm 40℃ 50% static elongation for 72 hours; Test conditions for change rate of elongation at break after thermo-oxidative aging: GB / T3512; 70℃*72 hours.

[0044] ; Note: Test conditions for the mechanical stability of latex: Mechanical stability tester GB-2955; Test conditions for wet gel strength: No. 3 cutter GB-528; Latex chemical stability test method: Take 30ml of sample and add the corresponding type and amount of chemical reagent.

[0045] Controlling the structure type of surfactant is a key factor in obtaining these properties. Surfactants should not be linear structures because during impregnation, due to electrolyte gelation, linear surfactants are more likely to be released from the surface of rubber particles and enter the latex, causing changes in the quantity and type of free surfactants in the latex, and making impregnation defects more likely.

[0046] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0047] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this invention.

Claims

1. A chloroprene latex suitable for impregnation processes, characterized in that, Including the following parts by weight of raw materials: The aqueous phase includes 90-110 parts of pure water, 3-6 parts of disproportionated rosin, 0.1-0.3 parts of sodium β-naphthalenesulfonate formaldehyde condensate, 1.5-2 parts of potassium hydroxide, and 0.2-0.6 parts of sodium sulfite; The oil phase includes chloroprene monomer and non-sulfur regulators; the water-to-oil ratio of the aqueous phase and the oil phase is 0.73~0.

78.

2. The chloroprene latex suitable for impregnation process according to claim 1, characterized in that, Hydrogenated rosin was used in place of disproportionated rosin in equal parts by weight.

3. A chloroprene latex suitable for impregnation process according to claim 1, characterized in that, The non-sulfur regulator is n-dodecyl mercaptan or regulator butyl.

4. A chloroprene latex suitable for impregnation process according to claim 3, characterized in that, When using n-dodecyl mercaptan, the conversion rate of chloroprene is controlled at 65-75%, and the mercaptan content in chloroprene is 0.05%-0.06%. When using regulator D, the conversion rate of chloroprene is controlled at 80-90%.

5. A method for preparing chloroprene latex suitable for impregnation processes according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1, Oil phase preparation: Heat the chloroprene monomer and add a non-sulfur regulator, stirring to dissolve; Step 2, Aqueous Phase Preparation: Prepare rosin potassium soap by reacting disproportionated rosin or hydrogenated rosin with potassium hydroxide in water; dissolve sodium β-naphthalenesulfonate formaldehyde condensate and mix it with rosin potassium soap; add sodium sulfite before emulsification and stir to dissolve; Step 3, Emulsification: Mix and emulsify the aqueous phase and oil phase to form an emulsion; Step 4, Polymerization: The emulsion is subjected to an initiation polymerization reaction in a polymerization reactor.

6. The method for preparing chloroprene latex suitable for impregnation process according to claim 5, characterized in that, In step one, the chloroprene monomer is heated to 16~18℃.

7. The method for preparing chloroprene latex suitable for impregnation process according to claim 5, characterized in that, The emulsification temperature of the aqueous and oil phases is 40±2℃.

8. The method for preparing chloroprene latex suitable for impregnation process according to claim 5, characterized in that, During the polymerization process, a 1% potassium persulfate-silver salt initiator aqueous solution is continuously added dropwise to the reactor to initiate the polymerization reaction.

9. The method for preparing chloroprene latex suitable for impregnation process according to claim 5, characterized in that, The polymerization reaction temperature is 38~45℃.

10. A method for preparing chloroprene latex suitable for impregnation process according to claim 9, characterized in that, When the conversion rate of chloroprene is less than 55%, the polymerization reaction temperature is 40±2℃; when the conversion rate is greater than 55%, the reaction temperature is 43~45℃.