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

Abstract

The purpose of the present invention is to provide a method for simultaneously performing concentration and deproteinization of natural rubber latex.　The present invention relates to: a method for concentrating natural rubber latex, the method being characterized by adding a surfactant, urea or a urea derivative, a compound that is 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 0.1-100% by volume of carbon dioxide into the natural rubber latex, leaving the natural rubber latex to stand still so as to separate the natural rubber latex into a cream phase and a serum phase, and recovering the cream phase; and a method for producing a concentrated natural rubber.

Description

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

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

[0002] Natural rubber is characterized by its high elongation, high elasticity, high tensile strength and 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 equipment, contraceptives, and other products. 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, such as proteins, carbohydrates, phospholipids, ash, and enzymes. It is speculated 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] Meanwhile, natural rubber latex is generally used after being concentrated to approximately 30% to 60% of its volume at the time of extraction. Known 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 target 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 a certain extent, they have the drawback of requiring a large amount of energy and large-scale 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, denaturing the protein in the latex, and then removing the protein. 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 measured by the RRIM test method.

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

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

[0007] International Publication No. 2011 / 027739 Japanese Patent Application Laid-Open No. 2005-255907

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

[0009] One aspect of the present invention is a method for concentrating natural rubber latex, comprising the steps of: 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.

[0010] In one 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.

[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] It is preferable to add a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex, again introduce a gas containing at least 0.1 to 100% by volume of carbon dioxide into the natural rubber latex, allow the natural rubber latex to stand still, again cause phase separation into a cream phase and a serum phase, and recover the cream phase.

[0013] It is preferable to repeat the steps of adding a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex, again 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 and again causing phase separation into a cream phase and a serum phase, and recovering the cream phase, two or more times. Here, it is also preferable that the gas containing at least 0.1 to 100% by volume of carbon dioxide is exhaust gas.

[0014] A second aspect of the present invention is a method for producing concentrated natural rubber latex, 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.

[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 －４It 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] It is preferable to add a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex, again introduce a gas containing at least 0.1 to 100% by volume of carbon dioxide into the natural rubber latex, allow the natural rubber latex to stand still, again cause phase separation into a cream phase and a serum phase, and recover the cream phase.

[0018] It is preferable to repeat the steps of adding a surfactant and ammonia to the recovered cream phase to re-disperse the natural rubber latex, again 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 again, and recovering the cream phase, two or more times.

[0019] In this case, 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 concentrating natural rubber latex, 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; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to 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.

[0021] In the third aspect, 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] It is preferable to add a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex, add again a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to the natural rubber latex, allow the natural rubber latex to stand, and again cause phase separation into a cream phase and a serum phase, and recover the cream phase.

[0023] It is preferable to repeat the following process two or more times: adding a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex; adding again a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to the natural rubber latex; allowing the natural rubber latex to stand to separate again into a cream phase and a serum phase; and recovering the cream phase.

[0024] A fourth aspect of the present invention is a method for producing concentrated natural rubber latex, 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; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to 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.

[0025] In the fourth and third aspects, 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] It is preferable to add a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex, add again a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to the natural rubber latex, allow the natural rubber latex to stand, and again cause phase separation into a cream phase and a serum phase, and recover the cream phase.

[0027] It is preferable to repeat the following process two or more times: adding a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex; adding again a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to the natural rubber latex; allowing the natural rubber latex to stand to separate again into a cream phase and a serum phase; and recovering the cream phase.

[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.

[0029] FIG. 1 is a process diagram illustrating an example of the procedure for the method for concentrating natural rubber latex of the present 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 concentrating natural rubber latex, comprising: adding a surfactant, urea or a urea derivative, a compound selected from the group consisting of a hydroxide salt, ammonia and a salt 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.

[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 anti-corrosion 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 coagulation of the rubber component.

[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 Surfactants) Examples of anionic surfactants include carboxylic acid-based, sulfonic acid-based, sulfate-based, and phosphate-based surfactants. Examples of carboxylic acid-based 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-based 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 Surfactants) 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, polyglycerin fatty acid esters, and the like. Polyalkylene oxide adducts of these (e.g., polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene glycerin fatty acid esters, and the like) 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 surfactants 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 Surfactants) 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, alkylbenzenesulfonates, alkylnaphthalenesulfonates, 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 linear, branched, or Guerbet structure and typically having 8 to 22 carbon atoms.

[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 listed 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 to 5 phr, and more preferably 0.02 to 3 phr, based on 100 parts by mass of the solid content of natural rubber contained in the natural rubber latex. Here, phr refers to parts by mass of various additives per 100 parts by mass of rubber (part hundred 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 formula 1) RNHCONH ２(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. The urea derivative used in one embodiment includes a urea double salt, for example, HNO ３ CO(NH ２ ) ２ , H ３ P.O. ４ CO(NH ２ ) ２ , H ２ C ２ O ４ ・2CO(NH ２ ) ２ , Ca(NO ３ ) ２ ・4CO(NH ２ ) ２ , CaSO ４ ・4CO(NH ２ ) ２ , Mg(NO ３ ) ２ CO(NH ２ ) ２ ・2H ２ O, CaSO ４ ・(5-6)CO(NH ２ ) ２ ・2H ２ Examples include O.

[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 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 has the molecular formula NH ３The salt thereof is a salt produced by the reaction of ammonia with an acid or an acidic oxide and is also called an ammonium salt. 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 the natural rubber latex. When ammonia is added as a preservative for natural rubber latex, the concentration thereof may 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 may 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 It is preferable to add 50 phr.

[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-terminus 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 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 of two or more.

[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% by mass of the solids content of the 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 exceeds 30 phr relative to the rubber content, problems such as coagulation of the rubber content occur during the protein denaturation treatment step.

[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 the like, 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 the majority of its components are 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 a salt thereof, 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 cause phase separation 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 of 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. Preferably, the raw material natural rubber latex is diluted with water to a natural rubber concentration of approximately 30% by weight. A surfactant is first added to the natural rubber latex, followed by urea or a urea derivative. When ammonia-free natural rubber latex 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 diluted appropriately 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] A second embodiment of the present invention is a method for producing concentrated natural rubber latex, 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.

[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. The production of concentrated natural rubber latex does not require operations that require large-scale equipment, such as centrifugation or thermal evaporation, which consume a lot of energy.

[0061] A third embodiment of the present invention is a method for concentrating natural rubber latex, 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; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to 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.

[0062] A third embodiment is the method of the first embodiment, in which a creaming agent is directly added 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. Here, the creaming agent is an agent that promotes separation of the cream phase and serum phase of 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, a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof is again added to the natural rubber latex, the natural rubber latex is allowed to stand, and again phase separation into a cream phase and a serum phase occurs, and the cream phase is recovered. These operations can be repeated two or more times. By performing these operations, the concentration of natural rubber increases, and higher purity protein-free natural rubber can be obtained.

[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 that require large-scale equipment, such as centrifugation or thermal evaporation, which consume a lot of energy.

[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 Commercially available high-ammonia natural rubber latex was used as the raw latex, and this was diluted with water to a rubber concentration of 30% by weight. 3.3 parts by weight of an anionic surfactant (sodium dodecyl sulfate, hereinafter 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 became 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 content 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 the natural rubber latex for 3 hours, and after the introduction of carbon dioxide was stopped, the mixture was allowed to stand for 24 hours, and a second creaming was then performed.

[0070] The resulting cream phase was re-dispersed in a 0.1% SDS aqueous solution, and a third creaming was carried out in the same manner as the second creaming, thereby obtaining 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 to a rubber content of 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 to a rubber content of 6% by weight, and the mixture was stirred for 12 hours. [Example 4] A reduced-protein natural rubber latex was obtained in the same manner as in Example 1, except that 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 completed the modification treatment, the natural rubber latex was diluted with water to a rubber content of 6% by weight, and the mixture was stirred for 18 hours. [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 undergone the modification treatment, the mixture was stirred for 4 hours, 133 parts by weight of a 5% aqueous sodium hydroxide solution was then added, the mixture was stirred for a further 14 hours, and 133 parts by weight of 28% aqueous ammonia was then 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 undergone the modification treatment, and the mixture was stirred for 4 hours.

[0072] Example 7: 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 further stirred for 1 hour for modification.

[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 thereto, followed by standing for 22 hours to carry out 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 'SMR Bulletin No. 7', Rubber Research Institute of Malaysia (1973)) using the following procedure.

[0083] [RRIM Test Method (Kjeldahl Method)] A catalyst consisting of copper sulfate, potassium sulfate, and selenium and sulfuric acid were added to a solid natural rubber film, and the film was heated for about one hour to convert nitrogen to ammonia. An aqueous solution of sodium hydroxide was then added to make the film alkaline, and the liberated ammonia was subjected to steam distillation 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, and the like.

[0085]

[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 material 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 in 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%, and protein-free natural rubber that is substantially free of protein is prepared. 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. A method for concentrating natural rubber latex, 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 separate into a cream phase and a serum phase; and recovering the cream phase.

2. The solid mass of natural rubber contained in natural rubber latex is taken as 100, and the total mass of the natural rubber latex is 0.01-5 phr of surfactant, 0.01-5 phr of urea or urea derivative, and 10 －４ 2. The method for concentrating natural rubber latex according to claim 1, further comprising adding: -100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof; 3. 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. 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. The method for concentrating natural rubber latex according to any one of claims 1 to 4, characterized in that 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 allowed to stand, and again the natural rubber latex is separated into a cream phase and a serum phase, and the cream phase is recovered.

6. The method for concentrating natural rubber latex according to claim 5, wherein the steps of adding a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex, again 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 separate again into a cream phase and a serum phase, and recovering the cream phase are repeated two or more times.

7. 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. 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. A method for producing concentrated natural rubber latex, 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 separate into a cream phase and a serum phase; and recovering the cream phase.

10. A natural rubber latex containing 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 containing 100% solids. －４ 10 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof.

11. 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. 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. The production method according to any one of claims 9 to 12, characterized in that a surfactant and ammonia 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 allowed to stand, and again the phase separation into a cream phase and a serum phase occurs, and the cream phase is recovered.

14. The production method according to claim 13, wherein a surfactant and ammonia 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 allowed to stand, and again the phase separation into a cream phase and a serum phase occurs, and the cream phase is recovered, and the steps are repeated two or more times.

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

17. A method for concentrating natural rubber latex, comprising adding to natural rubber latex 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 mixtures thereof; allowing the natural rubber latex to stand to separate into a cream phase and a serum phase; and recovering the cream phase.

18. A natural rubber latex containing 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 phr of a urea derivative, based on the solid mass of natural rubber contained in the natural rubber latex being 100. －４ 18. The method for concentrating natural rubber latex according to claim 17, further comprising adding -100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof; 19. The method for concentrating natural rubber latex according to claim 17 or 18, characterized in that a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex, 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, and again the natural rubber latex is separated into a cream phase and a serum phase, and the cream phase is recovered.

20. The method for concentrating natural rubber latex according to claim 19, comprising the steps of: adding a surfactant and ammonia or a salt thereof to the recovered cream phase to re-disperse the natural rubber latex; again adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to the natural rubber latex; allowing the natural rubber latex to stand to separate again into a cream phase and a serum phase; and recovering the cream phase, the steps being repeated two or more times.

21. A method for producing concentrated natural rubber latex, 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; adding a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixtures thereof to the natural rubber latex; allowing the natural rubber latex to stand to separate into a cream phase and a serum phase; and recovering the cream phase.

22. A natural rubber latex containing 0.01-5 phr of a surfactant, 0.01-5 phr of urea or a urea derivative, and 10 phr of a urea derivative, based on 100% solids by mass of natural rubber contained in the natural rubber latex. －４ 18. The method for producing natural rubber latex according to claim 17, further comprising adding -100 phr of a compound selected from the group consisting of hydroxide salts, ammonia and salts thereof; 23. A method for producing natural rubber latex according to claim 21 or 22, characterized in that a surfactant and ammonia or a salt thereof are added to the recovered cream phase to re-disperse the natural rubber latex, a creaming agent selected from the group consisting of sulfates, carbonates, hydroxyethyl cellulose, and any mixture thereof is added to the natural rubber latex, the natural rubber latex is allowed to stand to cause phase separation into a cream phase and a serum phase again, and the cream phase is recovered.

24. The method for producing natural rubber latex according to claim 23, comprising the steps of: adding a surfactant and ammonia or a salt thereof 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 mixtures thereof to the natural rubber latex; allowing the natural rubber latex to stand to separate again into a cream phase and a serum phase; and recovering the cream phase, the steps being repeated two or more times.

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