Method for concentrating natural rubber latex and method for producing concentrated natural rubber latex

Abstract

To provide a method for simultaneously concentrating and deproteinizing a natural rubber latex.SOLUTION: The present invention provides a method for concentrating natural rubber latex and a method for producing carbon dioxide-concentrated natural rubber, comprising adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex, introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into the natural rubber latex, allowing the natural rubber latex to stand to cause phase separation into a cream phase and a serum phase, and recovering the cream phase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for concentrating natural rubber latex and a method for producing concentrated natural rubber latex. [Background technology]

[0002] Natural rubber is characterized by its high elongation, high elasticity, high tensile strength, high tear strength, and excellent film strength. Therefore, natural rubber is widely used in household products such as gloves, medical devices such as surgical gloves and various catheters, nursing aids, and contraceptive devices. It has been reported that medical devices made of natural rubber, such as surgical gloves and catheters, can sometimes cause immediate-type (Type I) allergies, including respiratory distress and anaphylactic-like symptoms (angioedema, urticaria, cyanosis, etc.). Natural rubber latex contains many non-rubber components, including proteins, carbohydrates, phospholipids, ash, and enzymes. It is believed that allergen proteins, which are the causative agents of allergies, act as antigens to induce immediate-type allergies. Proteins are physically or chemically adsorbed to the natural rubber in natural rubber latex. If these proteins can be separated and suspended in the serum phase, they can be removed from the natural rubber latex by subsequent solid-liquid separation, allowing the natural rubber latex to be concentrated.

[0003] Generally, natural rubber latex is concentrated to approximately 30% to 60% of its volume at the time of extraction before use. Methods for concentrating natural rubber latex include centrifugation, thermal evaporation, electrodecantation, and dialysis, with continuous centrifugation being the most commonly used. This separates the cream phase (dry rubber content (DRC) 60% by weight) containing the desired natural rubber components from the serum phase (DRC 3-8% by weight). While these concentration methods can remove non-rubber components such as proteins to some extent, they require a large amount of energy and considerable equipment.

[0004] Patent Document 1 discloses a method for producing protein-free natural rubber latex, which comprises adding a urea compound, a surfactant, and a polar organic solvent to natural rubber latex, and then denaturing and removing the proteins in the latex. This method is characterized in that the protein content in the solid rubber obtained by drying the natural rubber latex is at a level of 0.001% or less in terms of nitrogen content as measured by the RRIM test method.

[0005] Patent Document 2 discloses a method for concentrating rubber latex, which is characterized by bringing rubber latex into contact with carbonic acid.

[0006] In the method described in Patent Document 1, after adding a polar organic solvent and a urea compound, which is a protein denaturant, to natural rubber latex to perform a protein denaturation treatment, it was necessary to separate the rubber component and the protein by a powerful means such as centrifugation to remove the protein. On the other hand, in the method described in Patent Document 2, when adding carbonated water or blowing carbon dioxide gas into natural rubber latex, it takes several hours to about one day or more to separate the rubber latex. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2011 / 027739 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-255907 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for simultaneously concentrating and deproteinizing natural rubber latex. [Means for solving the problem]

[0009] In one aspect of the present invention, a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent are added to natural rubber latex, introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into natural rubber latex; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex is characterized by:

[0010] In one embodiment, the solid content of the natural rubber contained in the natural rubber latex is 100%, and the solid content of the natural rubber is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 -4 It is preferred to add 100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

[0011] In one embodiment, it is preferable to further add a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex.

[0012] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable.

[0013] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to redisperse the natural rubber latex; a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable to repeat this process two or more times. In this case, the gas containing at least 0.1 to 100% by volume of carbon dioxide is preferably the exhaust gas.

[0014] In a second aspect of the present invention, a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent are added to natural rubber latex, introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into natural rubber latex; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The present invention relates to a method for producing concentrated natural rubber latex.

[0015] In the second embodiment, the solid mass of the natural rubber contained in the natural rubber latex is 100, and the solid mass of the natural rubber contained in the natural rubber latex is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 -4 It is preferred to add 100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

[0016] In the second embodiment, it is preferable to further add a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex.

[0017] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable.

[0018] A surfactant and ammonia are added to the recovered cream phase to redisperse the natural rubber latex, a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable to repeat this process two or more times.

[0019] In addition, the gas containing at least 0.1 to 100% by volume of carbon dioxide is preferably exhaust gas.

[0020] A third aspect of the present invention is a method for producing a rubber latex by adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex is characterized by:

[0021] In the third embodiment, the solid mass of the natural rubber contained in the natural rubber latex is 100, and the solid mass of the natural rubber is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 -4 It is preferred to add 100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

[0022] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable.

[0023] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to redisperse the natural rubber latex; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable to repeat this process two or more times.

[0024] A fourth aspect of the present invention is a method for producing a rubber latex by adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The present invention relates to a method for producing concentrated natural rubber latex.

[0025] In the fourth and third embodiments, the natural rubber latex contains 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 phr of a natural rubber latex. -4 It is preferred to add 100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

[0026] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable.

[0027] a surfactant and ammonia or a salt thereof are added to the recovered cream phase to redisperse the natural rubber latex; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. It is preferable to repeat this process two or more times. [Effects of the Invention]

[0028] The method for concentrating natural rubber of the present invention enables phase separation of deproteinized natural rubber latex in a simple manner. The separated cream phase containing the natural rubber component remains in a stable colloidal state, so that phase separation can be reinitiated by removing the separated aqueous phase and adding fresh water, allowing the natural rubber latex to be washed. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a process diagram illustrating an example of the procedure for the method for concentrating natural rubber latex of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The embodiments of the present invention will be described in more detail below, but the present invention is not limited to the following embodiments.

[0031] One embodiment of the present invention is a method for producing a rubber latex composition comprising adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into natural rubber latex; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex is characterized by:

[0032] In one embodiment, the natural rubber latex used as a raw material may be natural rubber latex (field latex) extracted from rubber trees (Hevea brasiliensis) without being subjected to a concentration process, or fresh natural rubber latex extracted from rubber trees within three months. Fresh natural rubber latex means latex that has not been subjected to an anticorrosion treatment. Fresh natural rubber latex extracted from rubber trees within 14 days, preferably within 7 days, and more preferably within 3 days can be used. The gel content in the natural rubber latex is 40% or less, preferably 10% or less.

[0033] In one embodiment, a surfactant is preferably added as a stabilizer for natural rubber particles. In particular, when the pH of the raw material natural rubber latex is adjusted to a neutral range to perform a protein removal treatment, the addition of a surfactant is desirable to prevent the rubber component from coagulating.

[0034] Surfactants that can be used in the present invention are listed below. The surfactants exemplified below can be used alone or in combination of two or more.

[0035] (anionic surfactant) Examples of anionic surfactants include carboxylic acid, sulfonic acid, sulfate, and phosphate. Examples of carboxylic acid anionic surfactants include fatty acid salts having 6 to 30 carbon atoms, polycarboxylic acid salts, rosin acid salts, dimer acid salts, polymer acid salts, and tall oil fatty acid salts. Among these, carboxylic acid salts having 10 to 20 carbon atoms are preferred. If the carbon number of the carboxylic acid anionic surfactant is less than 6, the dispersing and emulsifying action of proteins and impurities may be insufficient, and if the carbon number exceeds 30, the surfactant may be difficult to disperse in water.

[0036] Examples of sulfonic acid-based anionic surfactants include alkylbenzene sulfonates, alkyl sulfonates, alkylnaphthalene sulfonates, naphthalene sulfonates, diphenyl ether sulfonates, etc. Examples of sulfate ester-based surfactants include alkyl sulfate esters, polyoxyalkylene alkyl sulfate esters, polyoxyalkylene alkyl phenyl ether sulfates, tristyrenated phenol sulfate esters, polyoxyalkylenedistyrenated phenol sulfate esters, etc.

[0037] Examples of phosphate ester-based anionic surfactants include alkyl phosphate ester salts, polyoxyalkylene phosphate ester salts, etc. Examples of salts of these compounds include metal salts (such as Na, K, Ca, Mg, and Zn), ammonium salts, and amine salts (such as triethanolamine salts).

[0038] (nonionic surfactant) Examples of nonionic surfactants include polyoxyalkylene ethers, polyoxyalkylene esters, polyhydric alcohol fatty acid esters, sugar fatty acid esters, and alkyl polyglycosides. Examples of polyoxyalkylene ether nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene alkylphenyl ethers, polyoxyalkylene polyol alkyl ethers, polyoxyalkylene styrenated phenol ethers, polyoxyalkylene distyrenated phenol ethers, and polyoxyalkylene tristyrenated phenol ethers. Examples of the polyols include polyhydric alcohols having 2 to 12 carbon atoms, such as propylene glycol, glycerin, sorbitol, sucrose, pentaerythritol, and sorbitan.

[0039] Examples of polyoxyalkylene ester-based nonionic surfactants include polyoxyalkylene fatty acid esters. Examples of polyhydric alcohol fatty acid ester-based nonionic surfactants include fatty acid esters of polyhydric alcohols having 2 to 12 carbon atoms or fatty acid esters of polyoxyalkylene polyhydric alcohols. More specific examples include sorbitol fatty acid esters, sorbitan fatty acid esters, fatty acid monoglycerides, fatty acid diglycerides, and polyglycerin fatty acid esters. Polyalkylene oxide adducts of these (e.g., polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene glycerin fatty acid esters, etc.) can also be used. Examples of sugar fatty acid ester-based nonionic surfactants include fatty acid esters of sucrose, glucose, maltose, fructose, and polysaccharides, and polyalkylene oxide adducts of these can also be used.

[0040] Examples of alkyl polyglycoside-based nonionic surfactants include alkyl glucosides, alkyl polyglucosides, polyoxyalkylene alkyl glucosides, polyoxyalkylene alkyl polyglucosides, and the like, as well as fatty acid esters thereof. Polyalkylene oxide adducts of these can also be used. Examples of the alkyl groups in these nonionic surfactants include alkyl groups having 4 to 30 carbon atoms. Examples of polyoxyalkylene groups include those having alkylene groups having 2 to 4 carbon atoms, such as those having an added mole number of ethylene oxide of about 1 to 50. Examples of fatty acids include linear or branched, saturated or unsaturated fatty acids having 4 to 30 carbon atoms.

[0041] (cationic surfactant) Examples of cationic surfactants include alkylamine salts, alkylamine derivatives, and their quaternized derivatives, as well as imidazolinium salts. Examples of alkylamine salt cationic surfactants include salts of primary amines, secondary amines, and tertiary amines. Alkylamine derivative cationic surfactants have at least one of an ester group, an ether group, and an amide group in the molecule, and examples thereof include polyoxyalkylene (AO) alkylamines and their salts, alkylesteramines (including AO adducts) and their salts, alkyletheramines (including AO adducts) and their salts, alkylamidoamines (including AO adducts) and their salts, alkylesteramidoamines (including AO adducts) and their salts, and alkyletheramidoamines (including AO adducts) and their salts.

[0042] Examples of the salts include hydrochlorides, phosphates, acetates, alkyl sulfates, alkylbenzenesulfonic acids, alkylnaphthalenesulfonic acids, fatty acids, organic acids, alkyl phosphates, alkyl ether carboxylic acids, alkylamide ether carboxylic acids, anionic oligomers, and anionic polymers. Specific examples of acetates among alkylamine derivative cationic surfactants include coconut amine acetate and stearyl amine acetate. The alkyl groups in the alkylamine salt and alkylamine derivative cationic surfactants are not particularly limited, but examples include those having a carbon number of 8 to 22 and that are linear, branched, or Guerbet-like.

[0043] Examples of the quaternized alkylamine salt and alkylamine derivative cationic surfactants include those obtained by quaternizing the alkylamine salts and alkylamine derivatives with, for example, methyl chloride, methyl bromide, dimethyl sulfate, diethyl sulfate, etc. Specific examples include alkyltrimethylammonium halides such as lauryltrimethylammonium halide, cetyltrimethylammonium halide, and stearyltrimethylammonium halide; dialkyldimethylammonium halides such as distearyldimethylammonium halide; trialkylmethylammonium halides; dialkylbenzylmethylammonium halides; and alkylbenzyldimethylammonium halides.

[0044] Examples of imidazolinium salt-type cationic surfactants include 2-heptadecenyl-hydroxylethylimidazoline, etc. Among the surfactants exemplified above, those that exhibit stable surface activity particularly in the pH range of 6.5 to 8.5 include polyoxyethylene nonylphenyl ether, which is a nonionic surfactant, and polyoxyethylene alkylphenyl ether sodium sulfate, which is an anionic surfactant. .

[0045] The surfactant is preferably added in an amount of 0.01-5 phr, and more preferably 0.02-3 phr, based on 100% solids mass of natural rubber contained in the natural rubber latex, where phr refers to the parts by mass of various additives per 100% mass of rubber (part 100 rubber).

[0046] In one embodiment, urea or a urea derivative is added to denature proteins adsorbed at the omega-terminus of natural rubber, wherein the urea derivative has the following formula:

[0047] (chemical 1) RNHCONH2(1) (wherein R represents H or an alkyl group having 1 to 5 carbon atoms), and examples thereof include urea, methyl urea, ethyl urea, n-propyl urea, i-propyl urea, n-butyl urea, i-butyl urea, and n-pentyl urea. Preferred urea derivatives include urea, methyl urea, and ethyl urea. In one embodiment, the urea derivative includes a urea double salt, and examples thereof include HNO.CO(NH).HPO.CO(NH), HCO.2CO(NH), Ca(NO).4CO(NH), CaSO.4CO(NH), Mg(NO).CO(NH).2H0, and CaSO.(5-6)CO(NH).2H0.

[0048] The amount of urea or a urea derivative added is preferably 0.01 to 5 phr, and more preferably 0.02 to 3 phr, based on 100% by mass of the solid content of the natural rubber contained in the natural rubber latex.

[0049] In one embodiment, the hydroxide salt is a salt having an anion, hydroxide ion, and is added to decompose lipids adsorbed to the α-terminus of natural rubber. Examples of the hydroxide salt include calcium hydroxide, magnesium hydroxide, sodium hydroxide, manganese hydroxide, iron hydroxide, copper hydroxide, and aluminum hydroxide.

[0050] Ammonia is an inorganic compound with the molecular formula NH3, and its salts, also known as ammonium salts, are formed by the reaction of ammonia with an acid or an acidic oxide. Examples of ammonia salts that can be used include ammonium chloride, ammonium sulfate, and quaternary ammonium salts such as benzalkonium chloride. Ammonia may be added as a preservative to prevent solidification and corrosion of natural rubber latex. When ammonia is added as a preservative to natural rubber latex, its concentration can be 0.29% or more, 0.6% or more, 1% or more, etc.

[0051] It is preferable to add any one compound selected from the group consisting of hydroxide salts, ammonia, and salts of ammonia to natural rubber latex, but two or more compounds can also be used in combination. The compound selected from the group consisting of hydroxide salts, ammonia, and salts thereof is added in an amount of 100% by mass, based on the solid content of the natural rubber contained in the natural rubber latex. -4 -100 phr, preferably 10 -2 -50 phr is preferably added.

[0052] In one embodiment, the polar organic solvent optionally added is preferably one that is miscible with water. It is believed that the polar organic solvent has the effect of removing lipids adsorbed to the α-end of natural rubber molecules. Preferred polar organic solvents include, for example, lower aliphatic alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-pentanol, and 3-pentanol; ketones having 3 to 4 carbon atoms, such as acetone and methyl ethyl ketone; carboxylic acids having 1 to 5 carbon atoms, such as acetic acid and propionic acid; and esters of the above carboxylic acids having 1 to 5 carbon atoms, such as ethyl acetate (lower alkyl esters having 1 to 5 carbon atoms are preferred). These polar organic solvents can be used alone or in combination.

[0053] The blending ratio of the polar organic solvent to the natural rubber latex can be 0.001-30 phr, particularly 0.01-10 phr, and preferably 0.05-1 phr, based on 100% solids mass of natural rubber contained in the natural rubber latex. If the blending ratio of the polar organic solvent is less than 0.001 phr relative to the rubber content, the efficiency of the denaturation treatment of allergenic proteins cannot be sufficiently improved. On the other hand, if the blending ratio of the polar organic solvent is more than 30 phr relative to the rubber content, problems such as coagulation of the rubber content during the protein denaturation treatment process occur.

[0054] In one embodiment, the carbon dioxide-containing gas introduced into the natural rubber latex may contain 0.1 to 100% by volume of carbon dioxide based on the carbon dioxide-containing gas, and may be, for example, carbon dioxide gas supplied from a carbon dioxide cylinder or exhaust gas containing carbon dioxide. Exhaust gas refers to, for example, gas emitted from an internal combustion engine and gas emitted from various factories, cleaning facilities, etc., and is mostly composed of carbon dioxide and water vapor.

[0055] A creaming agent can be added before or after introducing the gas containing carbon dioxide into the natural rubber latex. The creaming agent is an agent that promotes separation of the cream phase and serum phase of the natural rubber latex. The creaming agent can be selected from sulfates, carbonates, hydroxyethyl cellulose, and mixtures thereof.

[0056] A surfactant and ammonia or its salt, preferably in the form of an aqueous solution, are added to the recovered cream phase to re-disperse the natural rubber latex, and a gas containing at least 0.1-100% by volume of carbon dioxide is again introduced into the natural rubber latex. The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is then recovered. These procedures can be repeated two or more times. By performing these procedures, the concentration of natural rubber increases, allowing for the production of protein-free natural rubber with a higher purity.

[0057] Next, the procedure of one embodiment of the method for concentrating natural rubber latex will be specifically described with reference to FIG.

[0058] Commercially available natural rubber latex or high-ammonia natural rubber latex is used as the raw material latex. It is preferable to dilute the raw material natural rubber latex with water so that the concentration of natural rubber in the latex is approximately 30% by weight. A surfactant is first added to the natural rubber latex, followed by urea or a urea derivative. When natural rubber latex without ammonia is used as the raw material latex, ammonia or an ammonia salt can be added, and a polar solvent is added as needed. The natural rubber latex is then stirred and mixed at a temperature between room temperature and approximately 50°C to denature the proteins and lipids adsorbed to the natural rubber molecules. The modified natural rubber latex is then appropriately diluted as needed, and an aqueous solution of ammonia or its salt is added as needed. A gas containing carbon dioxide is then introduced into the natural rubber latex for one to several hours, the introduction of the gas containing carbon dioxide is stopped, and the natural rubber latex is allowed to stand for approximately one day. During the standing, the natural rubber latex separates into an upper phase, which is a cream phase (concentrated natural rubber latex), and a lower phase, which is a serum phase, and the serum phase is removed to recover the cream phase, thereby obtaining concentrated natural rubber latex.

[0059] In a second embodiment of the present invention, a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent are added to natural rubber latex, introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into natural rubber latex; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The present invention relates to a method for producing concentrated natural rubber latex.

[0060] The second embodiment is a method for obtaining concentrated natural rubber latex by carrying out the method for concentrating natural rubber latex of the first embodiment. In the second embodiment, natural rubber latex concentrated to a DRC (dry rubber content) of at least about 60% by mass can be obtained from raw natural rubber latex having a DRC (dry rubber content) of about 10% to 40% by mass. According to the second embodiment, proteins and lipids can be removed from natural rubber while simultaneously concentrating its concentration, making it possible to obtain concentrated protein-free natural rubber latex by a relatively simple method. To produce concentrated natural rubber latex, there is no need to perform operations such as centrifugation or thermal evaporation, which require large-scale equipment and consume a lot of energy.

[0061] A third embodiment of the present invention is a method for producing a natural rubber latex by adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex is characterized by:

[0062] A third embodiment is a method of adding a creaming agent directly to natural rubber latex without carrying out a step of introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into the natural rubber latex in the first embodiment. The creaming agent is an agent that promotes separation of the cream phase and serum phase of the natural rubber latex, and can be selected from sulfates, carbonates, hydroxyethyl cellulose, and mixtures thereof.

[0063] A surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex, and a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof is added again to the natural rubber latex. The natural rubber latex is allowed to stand to again cause phase separation into a cream phase and a serum phase, and the cream phase is recovered. These procedures can be repeated two or more times. By performing these procedures, the concentration of natural rubber increases, allowing for the production of protein-free natural rubber with a higher purity.

[0064] The fourth embodiment is a method for obtaining concentrated natural rubber latex by carrying out the method for concentrating natural rubber latex of the third embodiment. In the fourth embodiment, natural rubber latex concentrated to a DRC (dry rubber content) of at least about 60% by mass can be obtained from raw natural rubber latex having a DRC (dry rubber content) of about 10% to 40% by mass. According to the fourth embodiment, proteins and lipids can be removed from natural rubber while simultaneously concentrating its concentration, making it possible to obtain concentrated protein-free natural rubber latex by a relatively simple method. To produce concentrated natural rubber latex, there is no need to perform operations such as centrifugation or thermal evaporation, which require large-scale equipment and consume a lot of energy. [Example]

[0065] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following examples.

[0066] <Concentration of natural rubber latex> [Example 1] A commercially available high-ammonia natural rubber latex was used as the raw latex, which was diluted with water to a rubber concentration of 30% by weight. 3.3 parts by weight of an anionic surfactant (sodium dodecyl sulfate, hereafter referred to as "SDS") was added to 100 parts by weight of the rubber content of this latex. Next, 0.3 parts by weight of urea as a protein denaturant was added to this natural rubber latex, and the mixture was denatured by stirring at room temperature for 60 minutes.

[0067] The modified latex was diluted with water so that the rubber concentration was 6% by weight, and 67 parts by weight of 28% aqueous ammonia was added.

[0068] Carbon dioxide was introduced into this natural rubber latex for 3 hours. The introduction of carbon dioxide was stopped and the mixture was allowed to stand for 24 hours to perform creaming. The natural rubber latex separated into a cream phase (upper phase) and a serum phase (lower phase), and the cream phase was recovered.

[0069] The resulting cream phase was redispersed in a 0.1% SDS aqueous solution to a rubber concentration of 6% by weight. 67 parts by weight of 28% aqueous ammonia was added to the redispersed natural rubber latex. Carbon dioxide was introduced into this natural rubber latex for 3 hours, and after stopping the introduction of carbon dioxide, the mixture was allowed to stand for 24 hours, and a second creaming was then performed.

[0070] The resulting cream phase was redispersed in a 0.1% SDS aqueous solution and creamed a third time in the same manner as the second creaming, to obtain a reduced protein natural rubber latex.

[0071] [Example 2] A reduced protein natural rubber latex was obtained in the same manner as in Example 1, except that 133 parts by weight of a 5% aqueous sodium hydroxide solution was added to 100 parts by weight of the rubber content of the natural rubber latex that had completed the modification treatment, the natural rubber latex was diluted with water so that the rubber content concentration was 6% by weight, and the mixture was stirred for 20 hours. [Example 3] A reduced protein natural rubber latex was obtained in the same manner as in Example 1, except that 67 parts by weight of a 50% aqueous sodium hydroxide solution was added to 100 parts by weight of the rubber content of the natural rubber latex that had completed the modification treatment, the natural rubber latex was diluted with water so that the rubber content concentration was 6% by weight, and the mixture was stirred for 12 hours. [Example 4] In Example 2, 6.7 parts by weight of a 50% aqueous sodium hydroxide solution was added to 100 parts by weight of the rubber content of the natural rubber latex that had undergone the modification treatment, and the natural rubber latex was diluted with water so that the rubber content concentration was 6% by weight, followed by stirring for 18 hours. In the same manner as in Example 1, a reduced protein natural rubber latex was obtained. [Example 5] A reduced protein natural rubber latex was obtained in the same manner as in Example 2, except that 8.3 parts by weight of acetone was added to 100 parts by weight of the rubber content of the natural rubber latex that had completed the modification treatment, and the mixture was stirred for 4 hours, and then 133 parts by weight of a 5% aqueous sodium hydroxide solution was added, followed by stirring for a further 14 hours, and then 133 parts by weight of 28% aqueous ammonia was added. [Example 6] A reduced protein natural rubber latex was obtained in the same manner as in Example 2, except that 8.3 parts by weight of ethanol was added to 100 parts by weight of the rubber content of the natural rubber latex that had completed the modification treatment, and the mixture was stirred for 4 hours.

[0072] [Example 7] The high ammonia natural rubber latex was diluted with water to a rubber concentration of 30% by weight. 3.3 parts by weight of SDS and 6.7 parts by weight of sodium hydroxide were added to 100 parts by weight of the rubber content of this latex, and the mixture was stirred for 24 hours. 0.3 parts by weight of urea was then added and the mixture was stirred for another hour to carry out a modification treatment.

[0073] The modified latex was diluted with water to a rubber concentration of 6% by weight, and 50 parts by weight of sodium carbonate was added and allowed to stand for 22 hours to perform creaming. The natural rubber latex separated into a cream phase (upper phase) and a serum phase (lower phase), and the cream phase was recovered.

[0074] The obtained cream phase was redispersed in a 0.1% SDS aqueous solution so that the rubber concentration was 6% by weight. 50 parts by weight of sodium carbonate was added to the redispersed natural rubber latex, and the mixture was allowed to stand to perform a second creaming.

[0075] The same procedure as the second creaming was repeated for a total of four creamings to obtain a reduced protein natural rubber latex.

[0076] [Example 8] A reduced protein natural rubber latex was obtained in the same manner as in Example 7, except that 6.7 parts by weight of hydroxyethyl cellulose (HEC) was used instead of sodium carbonate.

[0077] [Comparative Example 1] The same procedure as in Example 1 was carried out except that 28% aqueous ammonia was not added.

[0078] Comparative Example 2 The same procedure as in Example 1 was carried out except that SDS and urea were not added.

[0079] Comparative Example 3 The same procedure as in Example 1 was carried out except that urea was not added.

[0080] The nitrogen content of natural rubber latex was measured as an index representing the amount of protein contained in natural rubber. Each natural rubber latex obtained in the above Examples and Comparative Examples was cast onto a petri dish and dried to prepare a solid natural rubber film, which was used as a sample for nitrogen content measurement.

[0081] As a control sample, the high ammonia natural rubber latex used as the raw material in Example 1 was cast onto a petri dish to prepare a solid natural rubber film.

[0082] The nitrogen content (N%) of each sample in the Examples and Comparative Examples was measured according to the RRIM test method (see Rubber Research Institute of Malaysia (1973), 'SMR Bulletin No. 7') using the following procedure.

[0083] [RRIM test method (Kjeldahl method)] A catalyst consisting of copper sulfate, potassium sulfate, and selenium was added to a solid natural rubber film, and sulfuric acid was added. The film was then heated for approximately one hour to convert the nitrogen to ammonia. An aqueous solution of sodium hydroxide was then added to make the film alkaline, and the liberated ammonia was steam distilled and collected in an ammonium borate solution. The nitrogen content was determined by titrating this ammonia-collected solution with a standard sulfuric acid solution.

[0084] The RRIM test method is also known as the Kjeldahl method, and is a standard method for quantifying nitrogen in proteins, amino acids, etc.

[0085] [Table 1]

[0086] According to Table 1, when carbon dioxide is introduced into natural rubber latex to which ammonia has been added and the mixture is allowed to stand, a serum phase is formed at a rate of 60% to 91%, a cream phase is clearly separated, and the natural rubber latex is concentrated.

[0087] In Example 1, by repeating creaming three times, the nitrogen content was significantly reduced from 0.270% in the raw high-ammonia natural rubber to 0.057%. Furthermore, as shown in Examples 2 to 4, the addition of sodium hydroxide significantly reduced the nitrogen content of the low-protein natural rubber obtained, particularly after the first creaming. Similarly, in Examples 5 and 6, in which polar organic solvents such as acetone or ethanol were added, the nitrogen content was reduced compared to Example 1.

[0088] As shown in Examples 7 and 8, when a polymer such as sodium carbonate or hydroxyethyl cellulose is used as a creaming agent, repeated creaming reduces the nitrogen content to 0.002%, resulting in the preparation of protein-free natural rubber that is substantially free of protein. These results demonstrate that by combining protein denaturation treatment with creaming, it is possible to simultaneously concentrate natural rubber latex and remove proteins. Therefore, the present invention is of great practical value in the production of protein-free natural rubber.

Claims

1. adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into natural rubber latex; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. A method for concentrating natural rubber latex, comprising:

2. The solid mass of natural rubber contained in the natural rubber latex is taken as 100, and the solid mass of the natural rubber latex is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 －４ 2. The method for concentrating natural rubber latex according to claim 1, wherein 100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof is added.

3. 2. The method for concentrating natural rubber latex according to claim 1, further comprising adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof.

4. 3. The method for concentrating natural rubber latex according to claim 2, further comprising adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof.

5. a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex according to any one of claims 1 to 4.

6. a surfactant and ammonia or a salt thereof are added to the recovered cream phase to redisperse the natural rubber latex; a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex according to claim 5, wherein the above steps are repeated two or more times.

7. 6. The method for concentrating natural rubber latex according to claim 5, wherein the gas containing at least 0.1 to 100% by volume of carbon dioxide is exhaust gas.

8. 7. The method for concentrating natural rubber latex according to claim 6, wherein the gas containing at least 0.1 to 100% by volume of carbon dioxide is exhaust gas.

9. adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; introducing a gas containing at least 0.1 to 100% by volume of carbon dioxide into natural rubber latex; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. A method for producing concentrated natural rubber latex.

10. The solid mass of natural rubber contained in the natural rubber latex is taken as 100, and the solid mass of the natural rubber latex is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 －４ 10 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

11. 10. The method of claim 9, further comprising adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof.

12. 11. The method of claim 10, further comprising adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof.

13. A surfactant and ammonia are added to the recovered cream phase to redisperse the natural rubber latex, a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. The method according to any one of claims 9 to 12.

14. A surfactant and ammonia are added to the recovered cream phase to redisperse the natural rubber latex, a gas containing at least 0.1 to 100% by volume of carbon dioxide is again introduced into the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. The method according to claim 13, wherein the above steps are repeated two or more times.

15. The method according to claim 13, wherein the gas containing at least 0.1 to 100% by volume of carbon dioxide is exhaust gas.

16. The method according to claim 14, wherein the gas containing at least 0.1 to 100% by volume of carbon dioxide is exhaust gas.

17. adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. A method for concentrating natural rubber latex, comprising:

18. The solid mass of natural rubber contained in the natural rubber latex is taken as 100, and the solid mass of the natural rubber latex is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 －４ 18. The method for concentrating natural rubber latex according to claim 17, wherein 100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof is added.

19. a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered.

19. The method for concentrating natural rubber latex according to claim 17 or 18.

20. a surfactant and ammonia or a salt thereof are added to the recovered cream phase to redisperse the natural rubber latex; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof to the natural rubber latex; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. The method for concentrating natural rubber latex according to claim 19, wherein the above steps are repeated two or more times.

21. adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof, and optionally a polar organic solvent to natural rubber latex; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is allowed to stand to separate into a cream phase and a serum phase, and the cream phase is recovered. A method for producing concentrated natural rubber latex.

22. The solid mass of natural rubber contained in the natural rubber latex is taken as 100, and the solid mass of the natural rubber latex is 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 －４ and -100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

23. a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered.

23. The method for producing natural rubber latex according to claim 21 or 22.

24. a surfactant and ammonia or a salt thereof are added to the recovered cream phase to redisperse the natural rubber latex; adding to the natural rubber latex a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof; The natural rubber latex is left to stand, and again separated into a cream phase and a serum phase, and the cream phase is recovered. The method for producing natural rubber latex according to claim 23, wherein the above steps are repeated two or more times.

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