High-toughness carboxylic butadiene-acrylonitrile latex and preparation method thereof
By adding microcrystalline cellulose dispersion and antibacterial montmorillonite to carboxyl nitrile latex, the problems of general strength and insufficient antibacterial properties of existing carboxyl nitrile latex films are solved, and a film with high strength and excellent antibacterial properties is achieved.
Patent Information
- Application Number
- CN202510905923.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-02
- Publication Date
- 2025-09-16
AI Technical Summary
The film strength of existing carboxyl nitrile latex is average and its antibacterial property is insufficient, which limits its wide application.
By adding microcrystalline cellulose dispersion and antibacterial montmorillonite to carboxylated nitrile latex, the latex's quality and performance are improved. Microcrystalline cellulose forms hydrogen bonds with the carboxyl groups in the latex through its surface hydroxyl groups, enhancing the film's strength. The antibacterial montmorillonite, loaded with quaternary ammonium salts and silver particles between its layers, enhances its antibacterial properties.
The mechanical properties and antibacterial properties of carboxylated nitrile latex are significantly improved, and the resulting film has excellent strength and antibacterial effect.
Smart Images
Figure CN120647836A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of carboxyl nitrile latex, in particular to a high-strength and tough carboxyl nitrile latex and a preparation method thereof. Background Art
[0002] Nitrile latex is a copolymer made by emulsion polymerization of butadiene and acrylonitrile. It is a dispersion of latex particles in an aqueous solution. The inclusion of highly polar cyano groups in its molecular chain structure gives the product excellent resistance to oil, abrasion, solvents, flexure, and static electricity.
[0003] In order to further improve the mechanical strength and reactivity of acrylonitrile butadiene latex, methacrylic acid is usually introduced to modify the acrylonitrile butadiene latex, and butadiene, acrylonitrile, and methacrylic acid are subjected to ternary emulsion copolymerization to ultimately produce carboxyl acrylonitrile butadiene latex. However, when such carboxyl acrylonitrile butadiene latex is cured to form a film, the resulting film still suffers from general strength and poor antibacterial properties, limiting its widespread application. Based on this, a high-toughness carboxyl acrylonitrile butadiene latex and a preparation method thereof are proposed. Summary of the Invention
[0004] In response to the shortcomings of the existing technology, the present invention provides a high-strength and tough carboxyl nitrile latex and a preparation method thereof. By adding microcrystalline cellulose dispersion and antibacterial montmorillonite to the latex, the quality of the latex is greatly improved, and the resulting film has excellent mechanical properties and antibacterial properties.
[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a high-strength and tough carboxyl nitrile latex, comprising the following raw materials in parts by weight: 70-80 parts of butadiene, 20-30 parts of acrylonitrile, 1-3 parts of methacrylic acid, 5-8 parts of emulsifier, 1.5-2 parts of initiator, 1-2 parts of molecular weight regulator, 1-1.5 parts of microcrystalline cellulose dispersion, 0.5-1 part of antibacterial montmorillonite, and 80-100 parts of deionized water.
[0006] Preferably, the emulsifier is selected from sodium lauryl sulfate and fatty alcohol polyoxyethylene ether; the initiator is selected from sodium persulfate and potassium persulfate; and the molecular weight regulator is selected from n-dodecyl mercaptan and tert-dodecyl mercaptan.
[0007] Preferably, the preparation method of the microcrystalline cellulose dispersion is as follows: S1-1, uniformly stirring sodium hydroxide, urea, thiourea and deionized water to obtain a mixed solution; S1-2, pre-cooling the mixed solution, then adding microcrystalline cellulose and ultrasonically dispersing it, and then freezing it; S1-3, after the freezing is completed, the mixture is thawed and stirred to obtain a microcrystalline cellulose dispersion.
[0008] Preferably, in step S1-1, the mass ratio of sodium hydroxide, urea, thiourea and deionized water is (7-8): (6-8): (5-6): (110-120).
[0009] Preferably, in step S1-2, the pre-cooling treatment is pre-cooling at -10°C for 30-35 minutes; and the freezing treatment is freezing at -10°C for 18-20 hours.
[0010] Preferably, the preparation method of the antibacterial montmorillonite is as follows: S2-1, stirring montmorillonite and deionized water at 75-85° C. for 30-50 minutes to obtain a slurry; S2-2, adding octadecyltrimethylammonium bromide, sodium laurylsulfonate and silver nitrate solution to the slurry, stirring and reacting for 2-3 hours, then irradiating with ultraviolet light, and continuing to stir and react for 40-60 minutes to obtain an antibacterial slurry; S2-3. After the antibacterial slurry is cooled to room temperature, it is filtered, dried and ground to obtain antibacterial montmorillonite.
[0011] Preferably, the material-liquid ratio of the montmorillonite to deionized water is 1:(15-20) g / mL.
[0012] Preferably, in step S2-1 and step S2-2, the mass ratio of the montmorillonite, octadecyltrimethylammonium bromide and sodium dodecylsulfonate is 4:1:1.
[0013] Preferably, in step S2-1 and step S2-2, the material-liquid ratio of the montmorillonite to the silver nitrate solution is 1:3; and the concentration of the silver nitrate solution is 0.1 mol / L.
[0014] The present invention also provides a method for preparing a high-toughness carboxyl nitrile latex, comprising the following steps: (1) After vacuuming the polymerization kettle, deionized water, butadiene and emulsifier are added, and after stirring evenly, acrylonitrile, methacrylic acid, initiator and molecular weight regulator are added. The reaction is carried out at 85-90°C for 5-7 hours, and after cooling to room temperature, a carboxylated butadiene nitrile emulsion is obtained; (2) Add microcrystalline cellulose dispersion and antibacterial montmorillonite to the carboxyl nitrile latex and continue stirring for 3-5 hours to obtain high-strength and tough carboxyl nitrile latex.
[0015] The present invention provides a high-strength and tough carboxyl nitrile latex and a preparation method thereof, which has the following beneficial effects compared with the prior art: The present invention significantly improves the quality of latex by adding microcrystalline cellulose dispersion and antibacterial montmorillonite to latex, and the generated film has excellent mechanical properties and antibacterial properties. Specifically, a large number of hydroxyl groups exist on the surface of the microcrystalline cellulose, which can form strong hydrogen bonds with carboxyl groups in the latex. The dissolved microcrystalline cellulose can be further evenly dispersed in the latex, reducing agglomeration and playing a good reinforcing role, thereby improving the strength of the film. At the same time, montmorillonite is used as a carrier, and quaternary ammonium salts and silver particles are loaded on the interlayer spacing and surface of the montmorillonite, so that the antibacterial property of the latex is significantly improved.
[0016] The present invention uses sodium hydroxide, urea, thiourea and deionized water as a composite solvent to dissolve microcrystalline cellulose. Under low temperature conditions, sodium hydroxide dissolves and destroys hydrogen bonds within and between microcrystalline cellulose molecules to form sodium cellulose. Urea and thiourea do not directly react with the microcrystalline cellulose, but instead act with sodium hydroxide to encapsulate the microcrystalline cellulose, sodium hydroxide and sodium cellulose generated by the reaction of the two, thereby avoiding agglomeration of the microcrystalline cellulose. The microcrystalline cellulose is further dissolved by reducing its size, which is conducive to uniform dispersion of the microcrystalline cellulose dispersion in the latex, thereby enhancing the mechanical properties of the film.
[0017] The present invention utilizes octadecyltrimethylammonium bromide and sodium dodecylsulfonate to modify the interlayer spacing of montmorillonite so that a portion of quaternary ammonium salt is loaded between the layers. At the same time, ultraviolet light is used to reduce silver nitrate so that sufficient silver particles are loaded between the layers and on the surface of the montmorillonite. The prepared antibacterial montmorillonite is added to latex to improve the antibacterial property of the latex. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 These are SEM images of the microcrystalline cellulose dispersions in Example 6 of the present invention and Comparative Example 3. DETAILED DESCRIPTION
[0019] The following examples illustrate the implementation methods of the present application in detail, so that the implementation process of how the present application applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.
[0020] Example 1 The preparation method of microcrystalline cellulose dispersion is as follows: S1-1, uniformly stirring sodium hydroxide, urea, thiourea and deionized water to obtain a mixed solution; wherein the mass ratio of sodium hydroxide, urea, thiourea and deionized water is 8:6:5:110; S1-2, pre-cooling the mixture at -10°C for 35 min, then adding microcrystalline cellulose and ultrasonically dispersing it, followed by freezing at -10°C for 18 h; S1-3, after the freezing is completed, the mixture is thawed and stirred to obtain a microcrystalline cellulose dispersion.
[0021] Example 2 The preparation method of microcrystalline cellulose dispersion is as follows: S1-1, uniformly stirring sodium hydroxide, urea, thiourea and deionized water to obtain a mixed solution; wherein the mass ratio of sodium hydroxide, urea, thiourea and deionized water is 7:8:6:120; S1-2, pre-cooling the mixture at -10°C for 30 min, then adding microcrystalline cellulose and ultrasonically dispersing it, followed by freezing at -10°C for 20 h; S1-3, after the freezing is completed, the mixture is thawed and stirred to obtain a microcrystalline cellulose dispersion.
[0022] Example 3 The preparation method of antibacterial montmorillonite is as follows: S2-1. Stir montmorillonite and deionized water at a solid-liquid ratio of 1:20 g / mL at 75°C for 50 min to obtain a slurry; S2-2. Add octadecyltrimethylammonium bromide, sodium dodecylsulfonate, and 0.1 mol / L silver nitrate solution to the slurry, stir and react for 3 hours, then irradiate with ultraviolet light, and continue stirring and reacting for 60 minutes to obtain an antibacterial slurry; wherein the mass ratio of montmorillonite, octadecyltrimethylammonium bromide, and sodium dodecylsulfonate is 4:1:1; and the material-liquid ratio of montmorillonite to silver nitrate solution is 1:3; S2-3. After the antibacterial slurry is cooled to room temperature, it is filtered, dried and ground to obtain antibacterial montmorillonite.
[0023] Example 4 The preparation method of antibacterial montmorillonite is as follows: S2-1. Stir montmorillonite and deionized water at a solid-liquid ratio of 1:15 g / mL at 85°C for 30 min to obtain a slurry; S2-2. Add octadecyltrimethylammonium bromide, sodium dodecylsulfonate, and 0.1 mol / L silver nitrate solution to the slurry, stir and react for 2 hours, then irradiate with ultraviolet light, and continue stirring and reacting for 40 minutes to obtain an antibacterial slurry; wherein the mass ratio of montmorillonite, octadecyltrimethylammonium bromide, and sodium dodecylsulfonate is 4:1:1; and the material-liquid ratio of montmorillonite to silver nitrate solution is 1:3; S2-3. After the antibacterial slurry is cooled to room temperature, it is filtered, dried and ground to obtain antibacterial montmorillonite.
[0024] Example 5 A high-strength and tough carboxyl nitrile latex comprises the following raw materials in parts by weight: 80 parts of butadiene, 20 parts of acrylonitrile, 3 parts of methacrylic acid, 5 parts of an emulsifier (sodium lauryl sulfate), 2 parts of an initiator (sodium persulfate), 1 part of a molecular weight regulator (n-dodecyl mercaptan), 1.5 parts of a microcrystalline cellulose dispersion, 0.5 parts of antibacterial montmorillonite, and 100 parts of deionized water.
[0025] The preparation method of the high-toughness carboxyl nitrile latex comprises the following steps: (1) After vacuuming the polymerization kettle, deionized water, butadiene and emulsifier were added, and after stirring evenly, acrylonitrile, methacrylic acid, initiator and molecular weight regulator were added. The reaction was carried out at 85°C for 7 hours, and after cooling to room temperature, a carboxylated butadiene nitrile emulsion was obtained. (2) Microcrystalline cellulose dispersion and antibacterial montmorillonite were added to the carboxyl nitrile latex and stirred for 3 h to obtain high-strength and tough carboxyl nitrile latex.
[0026] In this example, the microcrystalline cellulose dispersion obtained in Example 1 and the antibacterial montmorillonite obtained in Example 3 were used.
[0027] Example 6 A high-strength and tough carboxyl nitrile latex comprises the following raw materials in parts by weight: 75 parts of butadiene, 25 parts of acrylonitrile, 2 parts of methacrylic acid, 6 parts of an emulsifier (sodium lauryl sulfate), 2 parts of an initiator (sodium persulfate and potassium persulfate), 1.5 parts of a molecular weight regulator (tert-dodecyl mercaptan), 1.2 parts of a microcrystalline cellulose dispersion, 0.7 parts of antibacterial montmorillonite, and 92 parts of deionized water.
[0028] The preparation method of the high-toughness carboxyl nitrile latex comprises the following steps: (1) After vacuuming the polymerization kettle, deionized water, butadiene and emulsifier were added, and after stirring evenly, acrylonitrile, methacrylic acid, initiator and molecular weight regulator were added. The reaction was carried out at 85°C for 6 hours, and after cooling to room temperature, a carboxylated butadiene nitrile emulsion was obtained. (2) Microcrystalline cellulose dispersion and antibacterial montmorillonite were added to the carboxylated nitrile latex and stirred for 4 h to obtain a high-strength and tough carboxylated nitrile latex.
[0029] In this example, the microcrystalline cellulose dispersion obtained in Example 2 and the antibacterial montmorillonite obtained in Example 4 were used.
[0030] Example 7 A high-strength and tough carboxyl nitrile latex comprises the following raw materials in parts by weight: 70 parts of butadiene, 30 parts of acrylonitrile, 1 part of methacrylic acid, 8 parts of an emulsifier (fatty alcohol polyoxyethylene ether), 1.5 parts of an initiator (potassium persulfate), 2 parts of a molecular weight regulator (n-dodecyl mercaptan), 1 part of a microcrystalline cellulose dispersion, 1 part of antibacterial montmorillonite, and 80 parts of deionized water.
[0031] The preparation method of the high-toughness carboxyl nitrile latex comprises the following steps: (1) After vacuuming the polymerization kettle, deionized water, butadiene and emulsifier were added, and after stirring evenly, acrylonitrile, methacrylic acid, initiator and molecular weight regulator were added. The mixture was reacted at 90°C for 5 hours, and then cooled to room temperature to obtain a carboxylated butadiene nitrile emulsion. (2) Microcrystalline cellulose dispersion and antibacterial montmorillonite were added to the carboxylated nitrile latex and stirred for 5 h to obtain high-strength and tough carboxylated nitrile latex.
[0032] In this example, the microcrystalline cellulose dispersion obtained in Example 1 and the antibacterial montmorillonite obtained in Example 4 were used.
[0033] Comparative Example 1 A high-strength and tough carboxyl nitrile latex comprises the following raw materials in parts by weight: 75 parts of butadiene, 25 parts of acrylonitrile, 2 parts of methacrylic acid, 6 parts of an emulsifier (sodium lauryl sulfate), 2 parts of an initiator (sodium persulfate and potassium persulfate), 1.5 parts of a molecular weight regulator (tert-dodecyl mercaptan), 0.7 parts of antibacterial montmorillonite, and 92 parts of deionized water.
[0034] The preparation method of the above-mentioned high-toughness carboxyl nitrile latex is as follows: Example 6.
[0035] In this comparative example, the antibacterial montmorillonite obtained in Example 4 was used.
[0036] Comparative Example 2 A high-strength and tough carboxyl nitrile latex comprises the following raw materials in parts by weight: 75 parts of butadiene, 25 parts of acrylonitrile, 2 parts of methacrylic acid, 6 parts of an emulsifier (sodium lauryl sulfate), 2 parts of an initiator (sodium persulfate and potassium persulfate), 1.5 parts of a molecular weight regulator (tert-dodecyl mercaptan), 1.2 parts of a microcrystalline cellulose dispersion, and 92 parts of deionized water.
[0037] The preparation method of the above-mentioned high-strength and tough carboxyl nitrile latex is described in Example 6.
[0038] In this comparative example, the microcrystalline cellulose dispersion obtained in Example 2 was used.
[0039] Comparative Example 3 A high-strength and tough carboxyl nitrile latex and a preparation method thereof are basically the same as those in Example 6, except that the preparation method of the microcrystalline cellulose dispersion is different.
[0040] The preparation method of the microcrystalline cellulose dispersion in this comparative example is: S1-1, uniformly stirring sodium hydroxide and deionized water to obtain a mixed solution; wherein the mass ratio of sodium hydroxide to deionized water is 7:120; S1-2, pre-cooling the mixture at -10°C for 30 min, then adding microcrystalline cellulose and ultrasonically dispersing it, followed by freezing at -10°C for 20 h; S1-3, after the freezing is completed, the mixture is thawed and stirred to obtain a microcrystalline cellulose dispersion.
[0041] Comparative Example 4 A high-strength and tough carboxyl nitrile latex and a preparation method thereof are basically the same as those in Example 6, except that the preparation method of the antibacterial montmorillonite is different.
[0042] In this comparative example, the preparation method of antibacterial montmorillonite is: S2-1. Stir montmorillonite and deionized water at a solid-liquid ratio of 1:15 g / mL at 85°C for 30 min to obtain a slurry; S2-2, adding 0.1 mol / L silver nitrate solution to the slurry, stirring and reacting for 2 hours, then irradiating with ultraviolet light, and continuing to stir and react for 40 minutes to obtain an antibacterial slurry; wherein the material-liquid ratio of montmorillonite to silver nitrate solution is 1:3; S2-3. After the antibacterial slurry is cooled to room temperature, it is filtered, dried and ground to obtain antibacterial montmorillonite.
[0043] Quality Inspection The high-strength and tough carboxylated nitrile latex of Examples 5-7 and Comparative Examples 1-4 was used as a base latex. To 100 parts of the base latex, 1 part potassium hydroxide, 1.5 parts sulfur, 2 parts zinc oxide, 0.5 parts zinc diethyldithiocarbamate, and 0.5 parts sodium dodecylbenzenesulfonate were added and thoroughly mixed to produce a mixed latex. A mold was immersed in a coagulant solution for 10 seconds, removed and dried, and then immersed in the mixed latex for 60 seconds. After removal and drying, the mold was vulcanized at 115°C for 30 minutes, cooled to room temperature, and demolded to produce a film.
[0044] 1. Mechanical Properties Test: The film was cut into dumbbell-shaped standard specimens according to GB / T528-2009 and tested at a tensile rate of 500 mm / min. The specific test results are shown in Table 1.
[0045] Table 1 Mechanical properties
[0046] Combined with Table 1 and Figure 1 : (1) Compared with Example 6, the mechanical properties of the film in Comparative Example 1 were significantly reduced because no microcrystalline cellulose dispersion was used; the mechanical properties of the film in Comparative Example 2 were also reduced because no antibacterial montmorillonite was used. This indicates that the combined use of microcrystalline cellulose dispersion and antibacterial montmorillonite can improve the quality of latex film formation.
[0047] (2) Compared with Example 6, the microcrystalline cellulose in Comparative Example 3 was dissolved only by sodium hydroxide, and the dissolution effect was relatively general, resulting in the inability to evenly distribute it in the latex, and the resulting agglomerates would affect the quality of the film. Figure 1 As can be seen on the left, the rod-like structure of microcrystalline cellulose disappears and dispersed particles are formed; Figure 1 As can be seen on the right, the rod-like structures in the microcrystalline cellulose swell and aggregate together.
[0048] 3. Antibacterial Performance Testing: Testing was conducted in accordance with GB / T 31402-2023. Staphylococcus aureus and Escherichia coli were used as test bacteria. An inoculum was prepared and then inoculated onto the film. The inoculated film was incubated at 35°C and humidity greater than 90% for 24 hours. The number of viable bacteria was measured and the antibacterial rate was calculated. Similarly, the film was aged at 70°C for 72 hours and then tested for antibacterial rate using the aforementioned test method. The specific test results are shown in Table 2.
[0049] Table 2 Antibacterial properties
[0050] As shown in Table 2: Compared with Example 6, antibacterial montmorillonite was not used in Comparative Example 2, and its antibacterial performance deviated; in Comparative Example 4, montmorillonite was not jointly modified with octadecyltrimethylammonium bromide and sodium dodecylsulfonate, resulting in the lack of quaternary ammonium salt between montmorillonite layers. At the same time, the smaller interlayer spacing also reduced the silver loading capacity of montmorillonite, resulting in a significant decrease in the antibacterial performance of the film after aging treatment.
[0051] 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 high-toughness carboxyl nitrile latex, characterized in that: The invention comprises the following raw materials in parts by weight: 70-80 parts of butadiene, 20-30 parts of acrylonitrile, 1-3 parts of methacrylic acid, 5-8 parts of emulsifier, 1.5-2 parts of initiator, 1-2 parts of molecular weight regulator, 1-1.5 parts of microcrystalline cellulose dispersion, 0.5-1 part of antibacterial montmorillonite and 80-100 parts of deionized water.
2. The high-toughness carboxyl nitrile latex according to claim 1, characterized in that The emulsifier is selected from sodium lauryl sulfate and fatty alcohol polyoxyethylene ether; the initiator is selected from sodium persulfate and potassium persulfate; and the molecular weight regulator is selected from n-dodecyl mercaptan and tert-dodecyl mercaptan.
3. The high-toughness carboxyl nitrile latex according to claim 1, characterized in that The preparation method of the microcrystalline cellulose dispersion is as follows: S1-1, uniformly stirring sodium hydroxide, urea, thiourea and deionized water to obtain a mixed solution; S1-2, pre-cooling the mixed solution, then adding microcrystalline cellulose and ultrasonically dispersing it, and then freezing it; S1-3, after the freezing is completed, the mixture is thawed and stirred to obtain a microcrystalline cellulose dispersion.
4. The high-toughness carboxyl nitrile latex according to claim 3, characterized in that In step S1-1, the mass ratio of sodium hydroxide, urea, thiourea and deionized water is (7-8): (6-8): (5-6): (110-120).
5. The high-toughness carboxyl nitrile latex according to claim 3, characterized in that In step S1-2, the pre-cooling treatment is pre-cooling at -10°C for 30-35 minutes; the freezing treatment is freezing at -10°C for 18-20 hours.
6. The high-toughness carboxyl nitrile latex according to claim 1, characterized in that The preparation method of the antibacterial montmorillonite is as follows: S2-1, stirring montmorillonite and deionized water at 75-85° C. for 30-50 minutes to obtain a slurry; S2-2, adding octadecyltrimethylammonium bromide, sodium laurylsulfonate and silver nitrate solution to the slurry, stirring and reacting for 2-3 hours, then irradiating with ultraviolet light, and continuing to stir and react for 40-60 minutes to obtain an antibacterial slurry; S2-3. After the antibacterial slurry is cooled to room temperature, it is filtered, dried and ground to obtain antibacterial montmorillonite.
7. The high-toughness carboxyl nitrile latex according to claim 6, characterized in that In step S2-1, the material-liquid ratio of the montmorillonite to deionized water is 1:(15-20) g / mL.
8. The high-toughness carboxyl nitrile latex according to claim 6, characterized in that In step S2-1 and step S2-2, the mass ratio of the montmorillonite, octadecyltrimethylammonium bromide and sodium dodecylsulfonate is 4:1:
1.
9. The high-toughness carboxyl nitrile latex according to claim 6, characterized in that In step S2-1 and step S2-2, the material-liquid ratio of the montmorillonite to the silver nitrate solution is 1:3; and the concentration of the silver nitrate solution is 0.1 mol / L.
10. The method for preparing the high-toughness carboxyl nitrile latex according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) After vacuuming the polymerization kettle, deionized water, butadiene and emulsifier are added, and after stirring evenly, acrylonitrile, methacrylic acid, initiator and molecular weight regulator are added. The reaction is carried out at 85-90°C for 5-7 hours, and after cooling to room temperature, a carboxylated butadiene nitrile emulsion is obtained; (2) Add microcrystalline cellulose dispersion and antibacterial montmorillonite to the carboxyl nitrile latex and continue stirring for 3-5 hours to obtain high-strength and tough carboxyl nitrile latex.