JPH0314053B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing powdered rubber coated with calcium carbonate, and more specifically, a method for producing powdered rubber in which rubber particles are coated with calcium carbonate in a strong manner, without blocking, and having high fluidity. This is what we provide. The various synthetic rubbers that have been provided so far are produced by isolating rubber particles from rubber latex and forming the isolated rubber particles into relatively large lumps (blocks or veils) or chips by various means. It is supplied in these forms.
However, recently there has been a trend toward automating the supply of rubber to weighing machines or processing machines prior to processing.
For this purpose, it cannot be used in the form of lumps or the like. Therefore, for example, when rubber processing plants such as automobile tire manufacturing plants use block-shaped or bale-shaped rubber, they are currently shredded. This makes it possible to omit the shredding process, automate the supply of rubber to a weighing machine or processing machine prior to processing, and easily mix rubber with various compounded chemicals and fillers. Development of powdered rubber is desired. On the other hand, in recent years, especially for the purpose of improving processability, a masterbatch consisting of filler and synthetic rubber in which calcium carbonate, carbon black, white carbon, etc. are mixed in advance has been attracting attention. The advantage of this is that the filler is already mixed into the synthetic rubber, so there is no need to add a new filler during processing, which significantly reduces processing time. This also improves the hygiene of the working environment due to the scattering of chemicals. From this background and viewpoint, there has been a growing demand for powdered rubber containing fillers, and several manufacturing methods have been proposed to meet this demand. One proposed method is to add an aqueous dispersion of a filler to an aqueous solution containing powdered rubber, mix uniformly, and then dry the mixture. However, filler-containing powder rubber produced by these methods has poor adhesion between the rubber and filler and is easily classified, causing blocking of the rubber and poor fluidity, making it difficult to meet the above requirements. This is not something I can be completely satisfied with. As a result of intensive research to improve these drawbacks, the present inventors have completed a method for producing powdered rubber that does not block, has high fluidity, and is made by coating powdered rubber particles with calcium carbonate firmly. That's what I did. That is, the present invention is a calcium carbonate method characterized in that carbon dioxide is introduced into a dispersion containing rubber particles in which calcium hydroxide and/or calcium oxide are dissolved to produce fine calcium carbonate on the surface of the rubber particles. The present invention provides a method for producing coated powder rubber. The term "dispersion liquid containing rubber particles" as used in the present invention refers to an aqueous solution in which rubber is present in separated powder form. For example, (1) an aqueous solution in which rubber latex is separated into powder by forming a coacervation, which is a water-insoluble salt, with an anionic water-soluble polymer and a cationic polymer (Japanese Patent Application Laid-open No. 73244/1983); ). (2) An aqueous solution in which an acid is added to a mixture of rubber latex and an aqueous dispersion of a solid filler to make fine rubber particles and co-precipitate them (Japanese Patent Publication No. 54-4380, No. 56-
No. 32334). (3) An aqueous solution obtained by adding an aqueous calcium salt to a mixed liquid of rubber latex and alkyl cellulose and separating the powder into powder (Japanese Patent Application Laid-open No. 78785/1983). (4) A dispersion obtained by adding an alkali metal sulfate or carbonate and an alkaline earth metal chloride to a mixture of rubber latex and methylcellulose and separating the powder into powder (JP-A-54-7449). (5) An aqueous solution obtained by spraying aluminum polyhydroxychloride onto rubber latex and separating it into powder (Japanese Patent Application Laid-open No. 137241/1983). Dispersions such as the following can be mentioned. As the target rubber in the present invention, any rubber that can be obtained as an anionic or nonionic latex can be used. For example, natural rubber or polyisoprene rubber produced by conventional emulsion polymerization, polybutadiene rubber,
Homopolymers of conjugated diene compounds such as polychloroprene rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer, vinylpyridine-butadiene-styrene copolymer rubber, acrylic acid-butadiene copolymer rubber, methacrylic acid-butadiene copolymer rubber , copolymers of vinyl compounds and conjugated diene compounds such as methyl acrylate butadiene copolymer rubber, copolymers of olefins such as ethylene, propylene, isobutylene, and conjugated diene compounds, and the like. In the present invention, calcium hydroxide or/and calcium oxide are added to a dispersion containing these rubber particles, or a dispersion containing rubber particles is added to calcium hydroxide or/and calcium oxide, and carbon dioxide is added to the mixture. The main purpose of this method is to coat powdered rubber with fine particles of calcium carbonate using the rubber particles as cores. In order to prevent particle agglomeration, fine silica (e.g. colloidal silica) or/and higher fatty acids, alkali metal salts or ammonium salts of polycarboxylic acids are added before or/and after, preferably before, calcium carbonate is formed. It is effective to add at least one of the above and a water-soluble compound of a divalent or higher polyvalent metal. The particle size of the added fine silica is 10 to 20 g.
mμ, and the amount added is 1 to 50% by weight, preferably 3% by weight, based on the weight of the rubber in the separated liquid containing rubber particles.
Add powdered rubber dispersion to ~20% by weight. If the amount added is less than 1% by weight, sufficient adhesion of calcium carbonate to powdered rubber cannot be obtained, and the effect of preventing reagglomeration between rubber particles cannot be expected to be very high. If it exceeds 50% by weight, the properties of the rubber itself will be impaired, which is not preferable. Furthermore, it is essential to use at least one of higher fatty acids, alkali metal salts or ammonium salts of polycarboxylic acids in combination with a water-soluble compound of a divalent or higher polyvalent metal. Examples of the alkali metal salts of higher fatty acids include sodium salts, potassium salts, and lithium salts of capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid having a hydrocarbon group having 8 to 20 carbon atoms. The alkali metal salt of polycarboxylic acid is a low-molecular compound or oligomer having a long-chain alkyl group at the end of the molecule and two or more carboxyl groups in the molecule. Examples of the structural unit include sodium salts and potassium salts of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, and the like. The amount of these added is 1 to 10% by weight of the rubber weight in the separated liquid containing rubber particles. In addition, a polyvalent metal compound with a valence of 2 or more is
BaCl ₂ , CdCl ₂ , CaCl ₂ , CrCl ₂ , SrCl ₂ , FeCl ₂ ,
_FeCl3 , _CuCl2 , _NiCl2 , _BaCl2 , _MgCl2 , _BeCl2 ,
_ZnBr2 , _CdBr2 , _CaBr2 , _CoBr2 , _FeBr2 ,
Halides such as CuBr ₂ , NiBr ₂ , BaBr ₂ , MgBr ₂ , SnI ₂ , Zn(NO ₃ ) ₂ , Cd(NO ₃ ) ₂ , Cr
( _NO3 ) ₂ , Ca( _NO3 ) ₂ , Co( _NO3 ) ₃ , Sn( _NO3 ) ₂ ,
Fe( _NO3 ) ₂ , Fe( _NO3 ) ₃ , Cu( _NO3 ) ₂ , Pb( _NO3 ) ₂ ,
Ni( _NO3 ) ₂ , Ba( _NO3 ) ₂ , Mn( _NO3 ) ₂ , Mg
Nitrates such as ( _NO3 ) ₂ , _ZnSO4 , _Al2 ( _SO4 ) ₃ ,
( _NH4 )Al( _SO4 ) ₃ , KAl( _SO4 ) ₂ , _CdSO4 ,
_CaSO4 , _COSO4 , _FeSO4 , _CuSO4 , _NiSO4 ,
Sulfates such as MgSO ₄ and MnSO ₄ . These polyvalent metal compounds are used in an amount necessary to insolubilize the higher fatty acid or polycarboxylic acid salt. Furthermore, calcium oxide and calcium hydroxide added to the dispersion containing rubber powder are used in an amount of 10 to 100% by weight based on the weight of the rubber in the separated liquid containing rubber particles. In this case, it is desirable to add and stir calcium oxide or/and calcium hydroxide to a dispersion containing rubber particles and use it as a supersaturated aqueous solution, and an aqueous solution containing a suspension may also be used. In the powdered rubber obtained by the present invention, the generated microcrystalline calcium carbonate is uniformly and strongly adsorbed on the surface of the powdered rubber particles, thereby preventing the rubber particles from re-agglomerating and providing a powdered rubber with high fluidity. and,
By controlling the concentration of calcium oxide, calcium hydroxide aqueous solution, carbon dioxide gas blowing speed, stirring, reaction temperature, etc., it is possible to change the particle size of the calcium carbonate that is produced. Another feature of the present invention is that the calcium carbonate has a functional group introduced onto its surface and has reinforcing properties. The powdered rubber isolated and washed by the above operations is
A calcium carbonate-coated powder rubber can be obtained that can be easily dehydrated by centrifugation, has fluidity, and does not require pulverization or can be easily pulverized by a light pulverization operation. The material is then dried, but the drying method is not particularly limited, and methods such as ventilation drying, hot air drying, vacuum drying, and fluidized drying can be freely selected and used. In order to obtain a dry powdered rubber having a uniform particle size, it is preferable to use a fluidized drying method or a flash drying method that allows drying in a state of motion. In order to make the present invention easier to understand, the present invention will be described below with reference to examples, but the present invention is not limited thereto. All parts and percentages are by weight unless otherwise stated in the examples. Example 1 A dispersion containing rubber particles was obtained as follows. 30 kg of polychloroprene rubber (CR) latex with a dry weight of 39.6% is mixed with sodium carboxymethyl cellulose (hereinafter referred to as CMC) in an amount of 1% by weight based on the dry weight of CR latex, and the mixed solution is mixed with polyoxyethylene tallow alkylpropylene. Diamine (N-DT203 manufactured by NOF Corporation)
The rubber particles were added to 50 ml of an acidic aqueous solution containing 2% by weight at room temperature for 20 minutes with thorough stirring to obtain a dispersion containing rubber particles. To the dispersion containing the rubber particles, 1.2 kg of a 30% aqueous solution of fine silica (colloidal silica manufactured by Nissan Chemical Industries, Ltd.) was added at room temperature (15° C.) in an amount of 3% by weight based on the rubber portion in the dispersion. Next, the temperature was raised to 60°C, 118 g of sodium stearate was added, and after completely dissolving, 24 g of calcium chloride was added. The amounts of sodium stearate and calcium chloride were 1% by weight and 0.2% by weight, respectively, based on the rubber portion in the dispersion. Further, 2.4 kg (20% by weight) of calcium oxide was added to make a supersaturated aqueous solution, and then carbon dioxide was continuously blown in with stirring at a flow rate of 2.5/min for 180 minutes. After standing still, the supernatant liquid was removed by decantation and dehydrated using a centrifuge to obtain calcium carbonate-containing powder rubber that can be easily crushed. Table 1 shows the particle size distribution and physical property values of the powdered rubber. A free-flowing powdered rubber with a particle size of less than 1 mm was obtained. Example 2 In Example 1, 4.8 kg (40% by weight) of calcium oxide was added and carbonated to obtain powdered rubber containing calcium carbonate. Example 3 In Example 1, 8.3 kg (70% by weight) of calcium oxide was added and carbonated to obtain a powdered rubber containing calcium carbonate. Comparative Example 1 A dispersion liquid containing rubber particles similar to that in Example 1 was left to stand and dehydrated by decantation without adding a reagglomeration inhibitor such as fine silica, sodium stearate, or calcium oxide. Rubber in the form of granules was not obtained, but in the form of lumps. Comparative Example 2 Using a dispersion containing the same rubber particles as in Example 1, 1.2 kg of a 30% aqueous solution of fine silica was heated to 60°C,
118 g of sodium stearate was added, and after it was completely dissolved, 24 g of calcium chloride was added. After standing still,
The supernatant was removed by decantation and dehydrated using a centrifuge. Rubber in the form of granules was not obtained, but in the form of lumps. As shown in Table 1, the calcium carbonate-containing powder rubber obtained by this method had a particle size of 1 mm or less, was highly free-flowing, and did not block. Next, reference examples will be shown to show that the powdered rubber obtained by this method is an industrially very advantageous material. Reference Examples 1 to 3 Using the same CR latex as in Example 1, using rubber chips obtained by the usual freeze-drying method,
Calcium carbonate (Silver, Shiraishi Kogyo Co., Ltd.) was kneaded on a roll and its physical properties were measured. The results are shown in Table 2. Compared to the reference example using chip-shaped rubber, sufficient physical properties were obtained with the powdered rubber of the example with a kneading time of 1 minute. Also shown are cross-sectional photographs of vulcanized rubber sheets of Examples and Reference Examples. In the example, calcium carbonate was dispersed faster than in the reference example, and the cross section was homogeneous. Therefore, the powdered rubber of the present invention was an industrially advantageous material because a stable mixture could be obtained in a shorter time than with conventional rubber chips.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a cross-sectional photograph of a hot-flow rubber sheet. This is a photo of something.

Claims (1)

[Claims] 1. Adding or adding at least one type of fine silica or/and alkali metal salt or ammonium salt of higher fatty acid or polycarboxylic acid and a water-soluble compound of a divalent or higher polyvalent metal before and/or after producing calcium carbonate. Powder coated with calcium carbonate, characterized in that carbon dioxide is introduced into a dispersion containing rubber particles in which calcium hydroxide and/or calcium oxide are dissolved to generate calcium carbonate on the surface of the rubber particles. Rubber manufacturing method.