CEMENT COMPOSITION FOR EXTRUSION

Abstract: A cement composition for extrusion, which is produced by incorporating, into cement mortar, 3 to 15 weight % of crushed pulp fiber, 0.2 to 1 weight % of at least one member selected from an alkylcellulose and a hydroxyalkyl­ alkyllcellulose, 2% water solution having 80,000 cps or more viscosity, enables to cut production cost by reducing the loads of the binder material using a pulp fiber without carcinogenicitic asbestos fiber. Furthermore it allows to assure an excellent extrudability and to provide the moldings with such workability as nailing and sawing.

Description: The present invention relates to the cement compositions for extrusion and more specifically to those cement compositions for extrusion which contain pulp fiber. These cement compositions for extrusion provide excellent moldability and workability using binders in quantity equivalent to or less than the conventional one. Asbestos fiber reinforced cement boards or plates have so far been widely used as materials for outer walls, roofs, floors of buildings and so forth. Said cement boards or plates may be obtained by adding water into a mixture of cement on one hand and asbestos fiber and aggregates, etc. on the other on the order of 20 weight %, then kneading and extruding the whole into form by means of required dies. The asbestos fiber thus used is characterized by extremely excellent dispersing quality when kneading, and the kneaded materials obtained are good in shape and water retention when extruded. Further the heat resistance of the asbestos fiber displays to the full its performance as reinforcing fiber in the curing by steam autoclave to be worked out at 170°C or higher temperature to furnish the extruded materials with dimensional stability and required strength. Since the asbestos fiber is an unrivaled reinforcing fiber which satisfies, at the same time, the dispersing quality, shape retention, water retention and thermal resistance required when extruding, they have thus far been used exclusively for extrusion. In recent years however the asbestos fiber has become a social problem because of its carcinogenicity considered to derive from the fibrous shape peculiar thereto. It has therefore been required in an extrusion such as above not to use any asbestos. As a substitute for the asbestos fiber, first some synthetic fibers were considered, which however are poor in dispersing quality, shape and water retention. Furthermore these organic fibers are for the most part not good in their heat resistance, some being unable to be cured by the foregoing steam autoclave. The general trend is that more excellent the reinforcing effect the more expensive such fibers are as compared with the asbestos fiber. With this as background, we are now in such a situation where really satisfying materials cannot be found as substitutes for asbestos fiber. On the other hand, the pulp fiber, which is one of the organic but natural fibers, is less expensive and more excellent than other organic fibers, though it is inferior in dispersing quality to the asbestos fiber. The extruded materials to which a certain quantity of this fiber has been added is advantageous in it that they allow for such processing as nailing and sawing which could not be easily done on the conventional cement moldings containing asbestos fiber. A feature thereof facilitates to mount them as facing materials of buildings. They are now attracting a good deal of public attention as materials substituting for the conventional asbestos fibers. In the extrusion process of cement mortar compositions much pressure is in general applied thereonto when molding them. For this reason, such water retention characteristic, that the asbestos or pulp fibers in the cement compositions have, is not sufficient to hold water uniformly in the moldings. Since in their cases the compositions are made to adhere to each other with the water separated before the extruded moldings be set and solidified, it was much difficult to maintain the moldings discharged form dies as such in form. It has been proposed to use organic type binders in the compositions for extrusion molding in order to improve their moldability. For example in the Japapnese Patent Publication No. 43-7134 discloses a technology by which such binders as methylcellulose, and hydroxypropyl methylcellulose can be used cement compositions in containing an asbestos fiber for extrusion moldings. This method is generally adopted in use of binders. As such binders we can enumerate, in addition to the methylcellulose and hydroxypropylmethylcellulose disclosed in said publication; hydroxyethylcellulose, carboxymethyl hydroxyethylcellulose, polyethylene oxide, sodium polyacrylate, casein and so forth. Among those, the alkylcellulose and/or hydroxyalkylalkylcellulose, which are excellent in dispersing quality, water retention and tackiness, have been widely utilized in cement and aggregates. So far several propositions have been offered for compositions containing the pulp fiber for molding to which such binders as above were added. In the Japanese Patent Provisional Publication No. 55-51748, for example, it has been disclosed a composition comprising a glass fiber to which a small quantity of pulp (cellulose) fiber and such a binder as methylcellulose have been added. Another Japanese Patent Publication, No.63-1276 discloses that a molding allowing for riveting and sawing can be had by extruding a cement composition to which a pulp (cellulose) fiber were added, one-shot foamed s pherical resin and such binders as methylcellulose. It should be noted however that the use, as a binder, of such alkylcellulose and/or hydroxyalkylalkylcellulose as similar to those used in conventional cement containing asbestos fiber to be added to the compositions having pulp fiber, is problematical in it that it requires more loadings than conventional in order that we may have a regular and smooth extrusion molding. In the extrusion molding of the conventional cement compositions containing asbestos fiber, the cost ratio of required binder or binders in the total cost of the extruded molding is on the order of one fourth to a half. This implies that increased loads of binders will raise the total cost of materials to be molded, which places a high hurdle to the extrusion molding of the cement compositions containing the pulp fiber. With this as background it has been strongly desired to have such binders as allow for an excellent moldability by adding only small loadings equivalent to or less than the conventional ones in the extrusion molding of cement compositions containing the pulp fiber. As the result of our researches to control such disadvantages, we have eventually accomplished this invention finding such cement compositions containing pulp fiber for extrusion molding that are excellent in moldability and workability. The pulp fiber to be used in cement containing the pulp fiber according to this invention chooses a particular range of diameter and length. As a binder we use the alkylcellulose and/or hydroxyalkylalkylcellulose the 2% water solution of which has a viscosity of 80 Pa · s (80,000 cps) or more measured at 20°C by No. 5 JIS Ubbellohde viscometer. This binder requires only the quantity equivalnet to or less than that of the coventional alkylcellulose and/or hydroxyalkylalkylcellulose of which 2% water solution has a viscosity of 12 to 40 Pa · s (12,000 to 40,000 cps) measured at 20°C by the No. 5 JIS Ubbellohde viscometer, that were used in the conventional cement compositions containing asbestos fiber. The binder used in this invention allows to have more excellent extrusion moldability than conventional by adding only 0.2 to 1 weight % of the cement composition for extrusion molding as a whole. Furhter moldings containing the pulp fiber by this invention remarkably improves such workabilityas nailing and sawing with the conventional ones. The subject matter of the present invention is a cement composition for extrusion which is produced by incorporating, into cement mortar, 3 to 15 weight % of crushed pulp fiber being 5 to 20 microns in diameter and 1 to 10 mm in length, 0.2 to 1 weight % of the alkylcellulose and/or hydroxyalkylalkylcellulose, 2% water solution having a viscosity of 80 Pa · s (80,000 cps) or more measured at 20°C by No. 5 JIS Ubellohde viscometer. The alkylcellulose and/or hydroxyalkylalkylcellulose to be used as a binder for extrusion molding according to this invention have, in their 2% water solution, a viscosity of 80 Pa · s (80,000 cps) or more when measured at 20°C by means of the No. 5 JIS Ubbellohde viscometer. Examples of the alkylcellulose and/or hydroxyalkylalkylcellulose that can be used as such are, but not limited to; methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxyethylethylcellulose, and ethylcellulose. Their loads, which depend upon the quantity and dispersing quality of the pulp fibers used, are to be within 0.2 to 1 weight % of the cement compositions as a whole. These loadings permit the moldability and workability intended by this invention to display their effect to the fullest extent. Surpassing this weight percentage of 1% will lead only to cost increase without allowing any more effect. If the same percentage is less than 0.2 weight %, the extrusion molding will be impossible even with addition in small quantity of any pulp fiber excellent in dispersing quality. The raw material used for the pulp fiber will be either a chemical pulp from which the lignin in its lignified tissue has been chemically removed by means of sulfite method or nitrate method, or a mechanical pulp obtained by such treatment as pulp grinding of wood. The pulp sheet or chip as raw material is suitably crushed with impact type or crusher type grinder and then screened into 5 to 20 microns in fiber diameter and 1 to 10 mm in length through sieve before use. As pulp material mechanical pulp is preferable to be used due to its lower cost, but we may also fairly use chemical pulp in this invention. The loads of the pulp fiber as above should be 3 to 15 weight percents. If the diameter and the length of pulp fiber are smaller than the foregoing limits or if, even though these limits are cleared, the loadings are inferior to 3 weight %, the intrinsic effect of the pulp fiber as reinforcing one cannot be displayed. Even if the pulp fiber as such is added, it is disadantageous not only in its poor shape retention when molded, but also in improved workability such as nailing and sawing which cannot be expected in the products after curings. It should be noticed on the other hand that if the diameter and length of pulp fiber exceed said limits or if the loadings are too much, the pulp fiber will he poor in dispersing quality, which will bring obstacle to good molding and consequently to good extrusion moldings with good surface smoothness. Moreover the heat resistance worsened prevents it to be used in practice. The chief material of the cement composition according to this invention is composed of known cements, aggregates, water and additives. In addition to the ordinary Portland cement, we can use such special cements as alumina cement. As aggregates, we can use not merely perlite, vermiculite, flyash and other light-weighted aggregates usually employed in cement mortar, but equally quartz sand composed of silica, quartz sand No. 5 to No. 12 and/or quartz rock, silica material and silica fume of grain size equal to or less than that of cement. The present invention enables to cut production cost by reducing the loads of binder down to 0.2 to 1 weight percent of the material using a pulp fiber without carcinogenicitic asbestos fiber. Furthermore it allows to assure an excellent extrudability and to provide the moldings with such workability as nailing and sawing. In the following examples of the present invention and comparative examples are described perferred embodiments to illustrate the invention. It is however to be understood that the invention is not intended to be limited to the specific embodiments. Examples 1 - 6 and Comparative Examples 1-7 The components as below were prepared in quantities such as indicated in Table 1 and Table 2 attached hereto and then kneaded with a double arm kneader. They were then extruded into sheets 75 mm in width and 6 mm in thickness by means of a vacuum extruder Y-22 of Ishikawa-Ji K.K. made. Their moldability was compared by the following testing method, the results thereof are indicated also in Table 1 and Table 2, respectively, form hereafter. (Components) Cement: Asano-made normal Portland cement. Quartz rock: Toriyane-Sha made, class A, crushed, No. 30, (mean grain size: 9 - 12 microns). Pulp fiber I : A pulp sheet 2 mm in thickness and 80% or more in cellulose content was made from conifer from which lignin in lignified lignified tissue had been removed by sulfite process. This sheet was then cut into 5 mm x 5 mm square of chips, which were then crushed first with crusher type grinder "Victory Mill VP-1" (brand name of Hosokawa Micron K.K.) then with a compact type vibrating mill "B-3 type" (brand name of Chuoh Kakohki K.K.) for 0.5 hour. The crushed materials were screened with 4-mesh sieve for industrial use into grains of 8 to 15 microns in diameter and 1 to 3 mm in length. Pulp fiberII : After grinding the cut pieces of the pulp sheet as underI above with the crusher type ginder "Victory Mill VP-1" (of Hosokawa Micron K.K. made), they were screened by means of industrial 4-mesh sieve. The pulp fiberII contains a plenty of fiber thus obtained as oversize (20 microns or more in diameter and 10 mm or more in length). Pulp fiber III : After further grinding the pulp fiber I for 2 hours with the compact type vibrating mill "B-3 type" (brand name of Chuoh Kakohki K.K.), it was screened into a fiber 5 microns or less in diameter and 1 mm or less in length using a 42-mesh industrial sieve. Hydroxypropylmethylcellulose: 90SH type of the Shin-Etsu Chemical Co., Ltd. made. Hydroxyethylmethylcellulose: SEB type made by the same company. Methylcellulose: SM type made by the same. (Testing Method) Viscosity: 2% water solution of each cellulose ether was measured with No. 5 JIS Ubbellohde viscometer at 20°C. Moldability: Materials were processed by a vacuum extruder Y-22 (of Ishikawa-Ji K.K.) provided with a die 6 mm in thickness and 75mm in width. Moldings delivered with the cross section same as that of die were considered as "good" and those delivered with both ends cut off were designated as "bad". Surface condition: Those with uneven surface with pulp projected were designated as "bad". Nailing characteristic: Extruded moldings were cured first at 65°C under saturated steam and then at 180°C in an autoclave. The moldings thus cured were then nailed with nails 3 mm in diameter. Those without cracks were designated as "good", and those with cracks "bad". A cement composition for extrusion, which is produced by incorporating, into cement mortar, 3 to 15 weight % of crushed pulp fiber being 5 to 20 microns in diameter and 1 to 10 mm in length, 0.2 to 1 weight % of at least one member selected from an alkylcellulose and a hydroxyalkylalkyllcellulose, 2% water solution having a viscosity of 80 Pa · s (80,000 cps) or more, enables to cut production cost by reducing the loads of the binder material using a pulp fiber without carcinogenicitic asbestos fiber. Furthermore it allows to assure an excellent extrudability and to provide the moldings with such workability as nailing and sawing.

Claims: A cement composition for extrusion which is produced by incorporating, into cement mortar, 3 to 15 weight % of crushed pulp fiber, 0.2 to 1 weight % of at least one member selected from an alkylcellulose and a hydroxyalkylalkylcellulose, 2 % water solution having a viscosity of 80 Pa · s (80,000 cps) or more at 20°C, the crushed pulp fiber being 5 to 20 microns in diameter and 1 to 10 mm in length. A cement composition for extrusion according to claim 1 wherein the alkylcellulose is at least one member selected from methylcellulose and ethylcellulose. A cement composition for extrusion according to claim 1 wherein the hydroxyalkylalkylcellulose is at least one member selected from hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, and hydroxyethylethylcellulose.

Inventors: CHIBA, TOHRU SYNTHETIC TECHNOLOGY OF, HAYAKAWA, KAZUHISA SYNTHETIC TECHNOLOGY OF, NAKAMURA, SHIN-ICHIRO SYNTHETIC TECHNOLOGY OF
Applicants: SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1989
Main classification: C04B28
IPC codes: C04B28, C04B111