A process for production of hydraulic substances reinforced with high tenacity acrylonitrile fibers

Abstract: High tenacity AN fibers, a process for production thereof, hydraulic substances reinforced with the fibers and a process for production thereof are provided. The high tenacity AN fibers comprise AN polymers composed mainly of AN having an intrinsic viscosity of at least 2.5 and possess degree of crystalline orientation of at least 93% and a tensile strength of at least 10 g/d. The surface of the fibers is smooth. The high tenacity AN fibers are produced by extruding an AN polymer solution having an intrinsic viscosity of at least 2.5 into air or an inert gas through a spinning nozzle, introducing into a coagulating bath, subjecting the coagu­ lated filaments to washing with water, drawing and drying and then, drawing with dry heating at about 160 - 250° C under a drawing tension of about 0.5 g/d or more to make the total drawing magnification more than about 10 times per an initial length of the coagulated filaments. Hydraulic substances reinforced with the high tenacity AN fiber are produced by uniformly dispersing in water the high tenacity AN fibers having applied nonionic or cationic high molecular flocculants thereto, adding anionic high molecular flocculants thereto to flocculate and adsorb ce­ ment particles onto the surface of the AN fibers and. subjecting the resulting slurry to paper-making.

Description: AN fibers have been hitherto produced and sold for use for clothing items in large quantities. However, it is an actual circumstance that little AN fibers have been employed for use in technology and industry because of unsatisfactory mechanical strength. Many attempts to enhance or improve the mechanical properties of AN fibers have been proposed heretofore. For example, Japanese Patent Publication Nos. 19414/70 and 29891/71 propose a process for producing a high tenacity acrylic fibers for use in industry by introducing a solution of AN polymer into a coagulating bath through an inert gaseous medium to coagulate namely a dry-jet wet spinning method, which comprises forming coagulated threads by a dry and wet spinning process, subjecting the fibers to washing, hot drawing, an after-treatment and drying, then secondary drawing and further subjecting to a treat treatment under a shrinkage allowance, particularly under the conditions such as above-described two-stage drawing and high speed winding. Further, a process which comprises subjecting fibers obtained by a wet or dry spinning method to wet drawing, drying under a tension, and subsequently subjecting to contact drawing to make an effective total drawing ratio of 9 to 25 times is proposed in Japanese Patent Application KOKAI (= laying-open) Publication No 51810/82 (EP-A 044 534). It is described therein that high modulus AN fibers can be obtained by this process. Furthermore, a process which comprises subjecting a polymer having a relative viscosity of 2.5 to 6.0 to a dry or wet spinning method, washing or washing followed by wet drawing, drying on a heating roll in a tension state, drawing under dry heating and then heat-treating is proposed in Japanese Patent Application KOKAI Publication No 161117/82 (EP-A-0 061 117); it is described therein that high tenacity AN fibers can be obtained by this process. However, the strength of AN fibers obtained by the prior art is, for example, less than about cN/tex (10 g/d) at best in tensile strength. In addition, as the molecular weight or degree of polymerization of AN polymer employed increases, the AN fibers obtained often causes defects such as a mutual adhesion between the fibers etc. As a result of the defects, the AN fibers do not enhance or improve not only a tensile strength but also other mechanical properties such as an initial modulus, a heat strength etc. On the other hand, asbestos has been hitherto used as reinforcements of hydraulic substances such as cement or gypsum. Methods for producing asbestos-reinforced plane plates, corrugated plate slates, etc. include wet paper-making methods of cylinder mould type and fourdrinier type. Among them, a cylinder mould type paper-making method called a Hatcheck's method has received a reputation as a preferable method for past several ten years. The asbestos fibers for reinforcing cement have a very good affinity and a strong adhesion force to cement matrix. The presence of long fibers with short fibers in an appropriately mixed state enhances an efficiency of paper-making and makes a reinforcing effect satisfactory and, the asbestos fibers are thus ideal fibers for use in cement reinforcement. However, from a situation that harmful nature of asbestos fibers in handling becomes a problem on a world-wide basis, it has been actually expected to develop substitute materials for asbestos. As substitute materials for asbestos fibers, inorganic and organic fibers such as glass, polyethylene, polypropylene, nylon, polyacryl, polyvinyl alcohol, carbon, aramide, alumina fibers, etc. have been attempted to be utilized. In order to obtain a cement plate having an excellent reinforcing effect and durability in a paper-making method, the following requirements should be met, namely: (1) Fibers having a small diameter be separated from each other without being entangled and uniformly dispersed in a cement suspension (slurry). (2) Affinity of fibers to cement which greatly affects a paper-making property and a reinforcing effect be good and adhesion between fibers and a cement be strong. (3) Durability, particularly alkali resistance, be excellent; etc. However, the organic and inorganic fibers which have been attempted to be utilized heretofore did not satisfy all of the requirements described above. For example, fibers such as polyethylene, polypropylene nylon, etc. only have poor strength and poor modulus of elasticity. Further, adhesive force to cement matrix is weak. Thus, no satisfactory reinforcing effect can be obtained. Glass fibers have a poor alkali resistance and an unsatisfactory adhesion force. Further, aramide fibers and carbon fibers have poor dispersibility, weak adhesion force and are costly. Therefore, these fibers have not been adopted yet. Further, polyvinyl alcohol fibers and acrylic fibers promise a bright future as fibers substitutable for asbestos because alkali resistance is good and adhesion to cement matrix is strong. However, polyvinyl alcohol fibers encounter a problem in costs. Acrylic fibers have a poor tensile strength and a poor initial modulus of elasticity; accordingly, hydraulic substances having high efficiencies such as slates having a high bending strength, etc. cannot be obtained from these fibers. On the other hand, various methods for improving efficiencies, e.g., bending strength, etc., of hydraulic substances reinforced with the aforesaid acrylic fibers have been proposed in recent years. For example, in Japanese Published Unexamined Patent Application 170869/82, there is disclosed a hydraulic substance reinforced with acrylic fibers which contain 98 to 100% of acrylonitrile and have a tensile strength of at least 50 cN/tex (5.65 g/d) and a tensile elongation of at most 15%. However, acrylic fibers concretely described in the above-described publication are all obtained by subjecting acrylonitrile type polymers to wet spinning. The thus obtained fibers merely possess a tensile strength of at most 85 cN/tex (9.63 g/d) and a modulus of elasticity of at most 1510 cN/tex (171.1 g/d). A bending strength of cement reinforced with these acrylic fibers is considerably inferior to that of conventional asbestos-reinforced cement. In addition, a bending strength of a cement reinforced with acrylic fibers showing the highest tensile strength of 85 cN/tex (9.63 g/d) is not necessarily large but a relatively considerably low bending strength is merely obtained. Further, hydraulic substances reinforced with conventional asbestos are brittle due to remarkably small work load of rupture in bending and low impact strength, which often causes damages in building and construction sites. Furthermore, it is generally observed that an impact strength of hydraulic substances reinforced with synthetic fibers such as acrylic fibers, etc. described above would be improved. However, the improvement is unsatisfactory yet. It has thus been desired to develop hydraulic substances having not only an improved bending strength but also a high impact strength. On the other hand, various methods for enhancing an cohesion between fibers and cement particles in a slurry state of cement and improving a paper-making property have also been proposed. For example, in Japanese Patent Application KOKAI Publication No.62833/80, there is disclosed a process for producing a cement plate which comprises adding 10 to 800 ppm of a flocculant selected from strong anionic, medium cationic and weakly cationic flocculant to a cement slurry having formulated no asbestos fibers and then subjecting a cement plate to paper-making. However, cohesion between fibers and cement particles is hardly achieved and fibers are easily separated from cement particles by a shearing force at a paper-making step to cause heterogenecity of the slurry, while improvement in a paper-making efficiency is expected to a certain extent in this process because flocs of cement particles are formed by the addition of the flocculant and thus, outflow of cement particles from a wire cylinder is prevented at the paper-making step. After all, no improvement in property of the thus obtained cement plate after molding can be expected. Furthermore, a process for reinforcement of cement materials using polyvinyl alcohol synthetic fibers having coated thereon 0.01 to 3 wt% of anionic or/and nonionic surfactants and a cationic oil is disclosed in Japanese Patent Application KOKAI Publication No. 134553/81. Further in Japanese Patent Application KOKAI Publication No. 13455/81, a process which comprises using a cationic oil and a nonionic or amphoteric surfactant in combination as a treating agent is disclosed. However, when these processes are used, these processes encounter a drawback that due to unsatisfactory paper-making efficiency, namely, due to unsatisfactory cohesion between fibers and cement particles in a slurry state, paper-making cannot be performed efficiently while an effect of improving adhesion between fibers and cement particles in cement articles, that is, an effect of improving bending strength, can be expected to a certain extent. As described above, in the case of preparing cement plates through a paper-making process, it is important that cement particles be firmly fixed to the surfaces of fibers in large quantities at a paper-making step, a uniformly dispersed slurry be obtained and, at the same time, a felt material having good uniformity be formed by a cylinder mould machine or a fourdrinier machine while maintaining the firmly fixed state and the uniformly dispersed state. In the prior art processes, however, cohesion between fibers and cement particles in a slurry state or dispersibility of the slurry is insufficient so that paper-making efficiency is not always satisfactory. As a result, it has been prevented to improve properties of cement plate. As a result of extensive investigations on high tenacity AN fibers having improved and enhanced mechanical properties in total to a high degree, including tensile strength, an initial modulus, etc. of AN fibers, and hydraulic substances reinforced with these fibers, the present inventors have found the present invention. That is, an object of the present invention is to provide a process for production of at hydraulic substances wilt extremely good paper-making efficiency. These objects of the present invention can be achieved with the process of claim 1. The term "a degree of crystalline orientation" as used herein refers to a measure showing a degree of orientation of AN polymer molecular chains constituting the fibers at the fiber axis direction and is a value determined by the following measurement method. Method for measurement of a degree of crystalline orientation : The degree of orientation is a value calculated by the following formula using a half width value H determined by measuring distribution of diffraction strength in the azimuthal direction, paying attention to crystalline reflection having the maximum strength on the equator line at a scattering angle of 16 to 17. In an x ray diffraction pattern of AN fibers. a degree of orientation (%) = 180 - H 180 x 100 The characteristic feature of the present invention lies in AN polymers having a relatively markedly high degree of polymerization, namely, having at least 2.5 when expressed with an intrinsic viscosity, as compared with AN polymers constituting not only conventional, commercially available AN fibers and known AN fibers. Because fibers are composed of polymers having such a high degree of polymerization, not only a tensile strength exceeding about 88 cN/tex (10 g/d) is exhibited but also other mechanical properties show extremely large values. More importantly, notwithstanding that the AN fibers are constructed by polymers having such a high degree of polymerization degree, the AN fibers are fibers having a high degree of orientation of 93% or more measured by wide-angle x ray diffraction. Only by the facts that the fibers have such a high orientation and are constructed from the aforesaid highly polymerized polymers, super high tenacity mechanical properties that have not been considered for AN fibers heretofore are exhibited. That is, in conventional synthetic fibers, especially AN fibers, an increased polymerization degree of polymers which constitute fibers results in increase of a viscosity of a spinning solution so that spinning becomes difficult. It is thus required to decrease a concentration of a polymer. Decrease of the polymer concentration in a spinning solution is accompanied by desolvation in large quantities after forming filaments. Accordingly, a fiber structure becomes porous and tends to loose its transparency, which fails to achieve strength to a high degree. Further, the characteristic feature of the AN fibers of the present invention also lies in smooth fiber surfaces, specifically in smooth surfaces having a contrast glossiness of at least 10%, more preferably 15 to 30%. The term "glossiness of fiber surfaces" as used herein refers to a value determined by the following measurement method and, reflects smoothness of fibers at the surfaces thereof and at the same time, dense and homogeneous fiber structure. Method for measurement of glossiness at surface : A fiber bundle is arranged parallel. At this time, crimpled threads are treated with hot water of 90 to 100° C to remove crimp and make the threads straight. A light is given to the surface of this sample from one direction and, reflection lights are divided into a regular reflection component (a) and a diffuse reflection component (b). A ratio of both components is made a contrast glossiness. contrast glossiness = (1 - b/a) x 100 Namely, in case that polymers are generally dissolved in various solvents, the resulting polymer solution in solvents is used as a spinning dope and the dope is converted into fibers by applying means of wet dry or wet and dry spinning, etc., without subjecting polymers to melt spinning as they are, as in AN fibers, desolvation is required. Generally desolvation is performed using water, however, shrinkage in volume cannot be followed as desolvation proceeds and accordingly, voids are formed in order to remove the voids, drying is performed to make the dense and homogeneous structure fine. However, as pointed out in the Journal of Fiber Association, vol. 2, No. 8 (1973), a decreased polymer concentration results in coagulated filaments rich of voids. Accordingly, it is difficult to remove voids and properties of strength and elongation become poor, even after a drying step. On the other hand, an increased polymerization degree results in an increased viscosity of a spinning solution when a polymer is dissolved in a solvent. From viewpoints of stability of the spinning solution and fiber-forming property, it cannot be helped to decrease the polymer concentration. Therefore, it becomes difficult to make a dense and homogeneous structure due to adverse influence caused by reduction in a polymer concentration with a polymer having a high degree of polymerization. Thus, fibers having a high tenacity are not always obtained. The AN fibers are composed of a polymer of a high polymerization degree having an intrinsic viscosity of at least 2.5 and such a polymer of a high polymerization degree is highly oriented toward the fiber axis direction to a high value of 93% or more when expressed by x ray crystalline orientation degree. By the basic characteristic, superb mechanical properties, for example, physical properties such as a tensile strength of at least 88 cN/tex (10 g/d), preferably more than 106 cN/tex (12 g/d), an initial modulas greater than 1766 cN/t (200 g/d) and a knot strength of 19.4 cN/tex (2.2 g/d) or more, preferably more than 26 cN/tex (3.0 g/d) are exhibited. In addition, the fibers have a surface showing a high contrast glossiness of at least 10% or more, generally in the range of 15 to 30%, when expressed with contrast glossiness. In addition, the fibers are excellent in their fineness so that high mechanical fibers having a high initial modulus and further resistant to bending or friction can be obtained. To produce the fibers having excellent mechanical properties and efficiencies as described above, it is required that a polymerization degree of a polymer constituting the fibers be made markedly high and the polymer be highly oriented to the fiber axis direction. It is thus difficult to prepare the fibers of the present invention by a wet or dry spinning process most widely adopted for industrially producing AN fibers. It becomes possible to obtain super high tenacity AN fibers of the present invention only by a dry-jet wet spinning process described below in detail. That is, AN polymers are dissolved in solvents. The resulting spinning solution is once extruded into air or an inert gas, preferably in air, through a spinning nozzle. The extruded multifilaments are introduced into a coagulating bath via a gaseous minute space to cause coagulation there. In combination with this process, further specific steps for the production and for the conditions are adopted, thereby obtaining super high tenacity AN fibers of the present invention, Hereafter, the process for production of the super high tenacity AN fibers according to the present invention will be described in detail The AN polymers used in the present invention are AN homopolymers or AN copolymers containing at least 90 mol% of AN, preferably 95 to 100 mol% of AN and less than 5 mol%, preferably 0 to 5 mol%, of vinyl compounds copolymerizable with AN. When the ratio of the vinyl compounds to be copolymerized exceeds 5 mol%, heat resistance of the resulting fibers are reduced, which is not preferred for the purpose of achieving the objects of the present invention. Any compounds are usable as the above-described vinyl compounds in the present invention but are not particularly limited as far as the compounds are copolymerizable with AN. Preferred examples of copolymerizable components include acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate, vinyl acetate, sodium allylsulfonate, sodium methallylsulfonate, and sodium p-styrenesulfonate. These AN polymers are dissolved in solvents thereof such as organic solvents, for example, dimethylsulfoxide (DMSO), dimethylformamide (DMA), dimethylacetamide (DMAc), ethylene carbonate, and butyl lactone; a conc. aqueous solution of water soluble inorganic salts such as zinc chloride, calcium chloride, lithium bromide, and sodium thiocyanate. The thus obtained polymer solution is used as a spinning solution, i.e., a spinning dope. The polymer concentration of the spinning solution is in a range of 10 to 18 wt.%. When the polymer concentration is lower than 5 wt%, density and homogenity of the fibers becomes worse so that properties of strength and elongation are deteriorated and production costs become disadvantageous, which are not preferred. When the polymer concentration exceeds 20 wt.%, the viscosity of the spinning solution becomes excessively high so that the stability of the spinning solution and fiber-forming property become worse, which are not preferred. It is required that the viscosity of the spinning solution be at least 150 Pa.s (1,500 poise) at 45°C preferably 300 to 1000 Pa.s (3,000 to 10,000 poise). When the viscosity of the spinning solution is lower than 150 Pa.s (1,500 poise) at 45°C, a coagulation structure becomes worse so that strength decreases This concentration of the spinning solution is extremely important in the dry-jet wet spinning process adopted in the present invention. Only when the polymer concentration and viscosity of the spinning solution described above are within the ranges described above, it becomes possible to perform spinning stably and obtain high tenacity fibers having a high initial modulus in the dry-jet wet spinning process without causing troubles of drip, fiber breaking, etc. It is preferred that the temperature of the spinning solution be maintained generally in the range of 30 to 100° C because temperatures lower than 0° C cause drawbacks that the viscosity of the spinning solution becomes high so that gelation easily occurs to make spinning difficult and temperatures higher than 130 °C encounter drawbacks that stability of solvent or the spinning solution becomes poor. The thus adjusted spinning solution is subjected to the dry-jet wet spinning process. In this case, it is preferred that a distance between a nozzle surface and a liquid surface of a coagulating bath be set forth in the range of 1 to 20 mm, preferably 2 to 10 mm. When the distance is shorter than 1 mm, problems that the nozzle surface is contacted with the liquid surface tend to occur and such Is not preferred. When the distance exceeds 20 mm, extruded filaments tend to break and adhere or stick one another, which are not preferred In such a dry-jet wet spinning process, when a spinning draft ( = V 1 /V 0 , in which V 1 = the take-up speed of coagulated filaments and V 0 = the extruding speed of polymer solution through the spinning nozzle) is too large, filaments-breaking tend to occur, when the draft is too low, it causes cohesion between single yarns and unevenness of yarns. Accordingly, it is preferred that the spinning draft be in the range of 0.1 to 1.5, more preferably 0.2 to 0.8. As a coagulating bath, there is used water or an aqueous solution of the solvent for the aforesaid AN polymers in solvents used for wet or dry and wet spinning processes of known AN fibers, for example, an aqueous solution of the solvent having a concentration of 10 to 80 wt% and a temperature of 0 to 35° C. The thus obtained coagulated filaments are subjected to conventional, known post treatments, that is, treatments such as washing, drawing, drying, etc. In the present invention, it is required that the fibers after drying be subjected to dry drawing. Only by dry drawing the AN fibers obtained by the dry-jet wet spinning process, it becomes possible to convert AN fibers into the AN fibers having smooth surface composed of a highly polymerized polymer having an intrinsic viscosity of at least 2.5 or more and having a high orientation of 93% or more in the x ray crystalline orientation, i.e., the ultra high tenacity fibers. That is, the dry drawing in the present invention is a process which comprises, after coagulation, firstly drawing to about 2 to 10 times, preferably 3 to 6 times, and drying, then drawing the filaments in a heated air bath to a temperature of 160 to 250° C, preferably 180 to 220° C while maintaining the filaments in a drawing tension of 8,8 cN/tex (1 g/d) or more, preferably 13 to 22 cN/tex (1.5 to 2.5 g/d). When the magnification for the primary drawing is less than 2 times, dense and homogeneous filaments cannot be obtained; such is not preferred. When the magnification exceeds 10 times, cohesion tends to occur upon drying, which is not preferred. When the drawing tension is lower than 8,8 cN/tex (1 g/d) in the dry drawing described above, sufficient orientation is accompanied so that neither sufficient strength nor sufficient initial modulus can be obtained. When the drawing tension exceeds 22 cN/tex (2.5 g/d), no sufficient magnification for the drawing can be obtained, or, the drawing is accompanied by rupture; such is not preferred. Further when the temperature in the dry drawing is lower than 160 °C, no satisfactory magnification for the drawing can be obtained; such is not preferred. On the other hand, when the temperature exceeds 250° C, reduction in drawability based on insufficient heat resistance of fibers is accompanied; such is not preferred. As concrete means for dry drawing, it is preferred that drawing be performed using a tubular heating cylinder capable of supplying and exhausting heating air, while passing filaments through the heating cylinder maintained at a fixed temperature. The drawing magnification in the heat drawing varies depending upon drawing hysteresis of filaments to be subjected to heat drawing and is set forth in the range wherein the total drawing magnification of the drawn threads finally obtained becomes approximately 10 to 25 times. For example, in the case of filaments obtained by subjecting to the dry-jet wet spinning process, washing with water and then subjecting to primary drawing to approximately 4 to 8 times, heat-drawing is carried out to achieve 1.5 to 4 times, in the case of filaments not subjected to such drawing, the filaments are drawn to achieve the aforesaid total drawing magnificaton of 10 to 25 times, preferably 15 to 20 times, by performing heat-drawing at one step or multi-step. Further, it is preferred that a single yarn denier be less than 27 tex (3.0 d), preferably less than 18 tex (2.0 d). The thus obtained AN fibers show high orientation property of 93% or more in the x ray crystalline orientation and exhibit superb, high mechanical properties including a tensile strength. In addition, the fiber structure is extremely dense and homogeneous and the fiber surface is very smooth and futher defect at the surface is minimized. Because of these advantages, the AN fibers are used for reinforcing hydraulic substances. In order to obtain fiber-reinforced hydraulic substances having excellent bending strength and impact strength aimed at the present invention, it is important firstly to use the above-described high tenacity AN fibers having a high initial modulus, preferably a modulas of elasticity of at least 1766 cN/tex (200 g d), and secondly to use high tenacity AN fibers having a high initial modulus obtained by applying a nonionic high molecular flocculant or a cationic high molecular flocculant, as reinforcing fibers. It is desired that the length of the reinforcing fibers be in the range of 05 to 15 mm. Further it is appropriate that an amount of the fibers to be incorporated into a cement be in the range of 0 5 to 5 wt%. When the amount is less than 0.5 wt%, no sufficiently reinforcing effect is exhibited. When the amount exceeds the upper limit, dispersibility becomes worse so that any improvement in the reinforcing effect cannot be expected. The use of fibryl fibers such as pulps auxiliary in addition to the aforesaid AN fibers can prevent loss of cement at the paper-making step and as a result, an efficiency of paper-making is more improved. For the same purpose, AN type fibryl fibers, aromatic polyamide type fibryl fibers and a small quantity of asbestos, etc. can also be used in combination. The term "hydraulic substance" as used in the present invention refers to an inorganic substance which is hardened by hydration. Examples of such hydraulic substances include portland cement, alumina cement, slug cement, silica cement, gypsum, and calcium silicate. In order to impart a porous structure or a lightweight structure to these hydraulic substances, perlite, sand baloon, glass baloon, etc. may also be incorporated. The high molecular flocculants which can be employed in the present invention include the following: nonionic high molecular flocculants are high molecular electrolytes having many neutral polar groups such as a -CONH 2 - group, a -O- group, etc., for example, polyacrylamide, polyethylene oxide, starch, gujar gum. locus bean gum, gelatin etc. Of these, particularly preferred is polyacrylamide. Cationic high molecular flocculants are high molecular electrolytes having cationic functional groups such as an amine, a salt of an amine, a quaternary salt, etc., for example, polyalkylaminoacrylates or methacrylates, copolymers of aminoalkyl acrylate or methacrylates and acrylamide, Mannich-modified polyacrylamides, polyethyleneimine, polyamine, cyclized polymers of dially ammonium halides and copolymers thereof with sulfur dioxide, polyvinylimidazoline, water soluble aniline resin hydrochloride, hexamethylenediamine,epicfilorohydrin polycondensate, chitosan, etc. Of these high molecular flocculants, polyacrylamide type, polyacrylate type and polymethacrylate type are particularly preferred from viewpoints of alkali resistance and flocculating property. It is appropriate that a molecular weight of these high molecular flocculants be in the range of 1,000,000 to 15,000,000, preferably 3,000,000 to 10,000,000, from a viewpoint of bridging and adsorption to cement particles as will be later described. It is preferred that the pick-up of these high molecular flocculants onto the fiber be in the range of 0.01 to 1 wt%, desirably 0.05 to 0.6 wt%. When the pick-up is less than the lower limit, adhesion between cement matrix and fibers is poor. When the pick-up is larger than the upper limit, fibers are adhered to each other so that dispersibility of fibers in a cement slurry is seriously reduced. To apply the high molecular flocculants to fibers is effected by immersing fibers in an about 0.1% aqueous solution of a high molecular flocculant and then dehydrating appropriately by means of a squeezing roller, centrifugation, etc. In this case, it is desired that the dehydrated fibers are kept in moist state, after applying the aqueous solution of a high molecular flocculant to fibers results in reduction of dispersibility in water and cohesion between fibers and cement particles. As such, fiber-reinforced hydraulic substances are prepared by uniformly dispersing the high tenacity AN fibers having a high modulus of elasticity, to which the nonionic or cationic high molecular flocculant being applied in water together with a hydraulic substance such as cement or the like, then adding an anionic high molecular flocculant to the resulting slurry to make cement particles flocculate and adsorb to the surface of the aforesaid AN fibers, and subjecting the resulting slurry to paper-making. A method for cohesion between fibers and cement particles in the present invention involves utilization of a flocculating effect of the high molecular flocculant, which is effected by coagulation due to neutralization of electric charges and bridging by high molecular chains. That is, cement particles are flocculated with the anionic high molecular flocculant to form a floc. At the same time, the floc is adsorbed to and bridged with the nonionic or cationic high molecular flocculant at the surface of the fibers, thereby to effect cohesion between the fibers and the cement particles. Accordingly, the ionic nature of the high molecular flocculant to be applied to the fibers is desirably cationic but, nonionic high molecular floccurants can also be employed since the bridging effect of the high molecular chains also contributes to flocculation. However, when anionic high molecular flocculants having counter ions are applied to the fibers, electric repellation generates, resulting in failure to achieve cohesion between the fibers and the cement particles. In this sense, it is important in the cohesion of the present invention that the molecular chains of the high molecular flocculants be both sufficiently large. As the anionic high molecular flocculants which can be used for adsorption of cement particles to the surface of the fibers and bridging the same with the surface of the fibers, high molecular electrolytes containing a -CO 2 - group are preferred. Examples of such anionic high molecular flocculants include polyacrylamide partial hydrolysate, sodium polyacrylate, copolymer of sodium acrylate and acrylic amide, sulfomethylated polyacrylamide, sodium alginate, and CMC-Na, Of these, particularly preferred are polyacrylamide type such as polyacrylamide partial hydrolysate, copolymers of acrylic amide and sodium acrylate. It is preferred that the molecular weight be in the range of 1,000,000 to 15,000,000. When the molecular weight is outside this range, flocculation capability is markedly reduced, or, conversely floc becomes coarse to cause non-uniformity of the resulting slurry; these cause reduction in an efficiency of paper-making. On the other hand, when the molecular weight of the aforesaid anionic high molecular flocculants is particularly in the range of 4,000,000 to 9,000,000, a floc of cement particles adsorbed to and bridged with the surface of the fibers becomes a fine and appropriate size, dispersibility of the fibers and slurry is improved and bending strength of the obtained cement plate markedly increases. It is appropriate that the amount of these anionic high molecular flocculant to be added be 30 to 600 ppm based on the solid content in the slurry, in view of flocculating efficiency and paper-making efficiency. Further the use of inorganic flocculants in combination with the aforesaid anionic high molecular flocculant results in a fine floc which is to be formed when cohesion occurs. In addition, the floc becomes strong and has a strong resistance to a shearing force at a step of preparing a slate by the paper-making process. As a result, a paper-making efficiency is further improved. Examples of the inorganic flocculants used herein include substances which form cationic colloid ions in water, such as aluminum sulfate, sodium aluminate, ferrous sulfate, ferric sulfate, ferric chloride, and aluminum polychloride. Of these, aluminum sulfate is preferred. Further for purposes of exhibiting the efficiency of the aforesaid high molecular flocculants and inorganic flocculants and enhancing the effects of the flocculants, flocculating aids such as slaked lime, soda ash, sodium silicate, bentonite, fly ash, etc. can also be used, of course. The hydraulic substances of the present invention have not only a high bending strength but also a large work load of rupture in bending and a large impact strength, i.e., are excellent in capability of absorbing energy in rupture, since the hydraulic substances are reinforced with the high tenacity acrylic fibers having a high modulus of elasticity. The highly efficient hydraulic substances of the present invention are not ever achieved with conventional acrylic fibers but can be accomplished by using the high tenacity acrylic fibers having a high modulus of elasticity for the first time. This is assumed to be not only because the acrylic reinforcing fibers have a high tenacity and a high modulus of elasticity but also because both the smoothness at the surface of the fibers and the uniformity of the structure of the fibers in the inner and outer layers thereof would act effectively. Accordingly, the hydraulic substances reinforced with the acrylic fibers of the present invention have a bending strength comparable to conventional asbestos-reinforced substances and, at the same time, possess much far excellent impact resistance. In the present invention, a slurry in which large quantities of cement particles are fixed to the surface of the fibers, cohesion is extremely strong and dispersibility is good can be obtained by forming an aqueous suspension from AN fibers having applied thereto the nonionic or cationic high molecular flocculant and cement particles as described above and adding the anionic high molecular flocculant thereto. This slurry can sufficiently withstand the shearing force at the paper-making step. Accordingly, loss of cement which passes through a wire mesh upon paper-making is minimized, the solid content to be formed on the wire mesh increases and an efficiency of paper-making can be greatly improved. Further because of good dispersibility of the fibers and good adhesion to cement, the impact strength and the bending strength of the thus formed cement plate by paper-making is large and a highly reinforcing effect can be attained. Therefore, the process for production of the fiber-reinforced cement plate in accordance with the present invention is extremely useful for manufacturing various slate products, molding articles, etc. in building and constructing fields. Preparation of Fibers Examples 1 to 3 and Comparison Examples 1 to 7 100% AN was subjected to solution polymerization in DMSO to prepare 5 kinds of AN polymers having intrinsic viscosities of 1.3, 1.9, 2.6, 3.8 and 5.5, respectively. Viscosities (45° C) of these 5 polymers were adjusted to approximately 300 Pa.s (3,000 poise), respectively, to prepare spinning solutions. Using the thus obtained 5 spinning solutions, spinning was conducted by two processes, i.e., a wet spinning process and a dry-jet wet spinning process. In any spinning process, a 55% DMSO aqueous solution at 20° C was used as a coagulating bath. In the case of the dry-jet wet spinning process, the distance between a spinning nozzle and the liquid surface of the coagulating bath was set 5 mm apart from each other and, the distance from the liquid surface of the coagulating bath to a focusing guide was set forth 400 mm apart After washing the obtained undrawn filaments with water, the filaments were drawn by 5 times in hot water. After imparting an oil thereto, the drawn filaments were dried at 130° C to render the structure dense and homogeneous. Then, the filaments were drawn in a dry heating tube having a temperature atmosphere of 180 to 200° C. The drawing filaments were subjected to sampling and, physical properties of the fibers were measured. The results are shown in Table 1 below. The degree of crystalline orientations of the fibers obtained in Examples 1 to 3 were 94.7%, 94.5% and 94.5%, respectively. The contrast glossinesses were 20.3%, 22.5% and 23.1%, respectively, which were all higher than wide-angle of crystalline orientation of 91.7% and relative glossiness of 5.3% in Comparison Example 7. Spinning Method Intrinsic Viscosity Strength (g/d) cN/tex Initial Modulus cN/tex (g/d) Knot Strength cN/tex (g/d) Example 1 dry-jet wet 5.5 (13.1) 116 (231) 2040 (3.5) 30,9 Example 2 dry-jet wet 3.8 (12.8) 106 (225) 1987 (3.1) 27,4 Example 3 dry-jet wet 2.6 (10.8) 95,4 (214) 1890 (2.5) 22,1 Comparison Example 1 dry-jet wet 1.9 (8.5) 75,1 (172) 1519 (1.5) 13,3 Comparison Example 2 dry-jet wet 1.3 (6.9) 60,9 (153) 1351 (1.1) 9,7 Comparison Example 3 wet 5.5 (7.2) 63,6 (159) 1404 (1.7) 15,0 Comparison Example 4 wet 3.8 (7.3) 64,5 (161) 1422 (1.7) 15,0 Comparison Example 5 wet 2.6 (6.6) 58,3 (145) 1280 (1.5) 13,3 Comparison Example 6 wet 1.9 (6.2) 54,7 (131) 1157 (1.0) 8,8 Comparison Example 7 wet 1.3 (5.8) 51,2 (128) 1130 (0.9) 7,9 Example 4 and Comparison Examples 8 to 12 99.7 mol% of AN and 0.3 mol% of 2-acrylamido-2-methyl-propanesulfonic acid were dissolved in DMSO followed by solution polymerization to prepare AN copolymers having intrinsic viscosities of 3.3, 1.7 and 1.2. Polymer concentrations were adjusted to solution viscosities (45° C) of these copolymer solutions of about 400 Pa.s (4,000 poise) to prepare spinning solutions. The obtained spinning solutions were heated to 70° C and subjected to the dry-jet wet spinning process through a spinning nozzle having 500 holes, each 0.12 mm in diameter. The distance between of the spinning nozzle and the liquid surface of a coagulating bath was 3 mm The distance from the liquid surface of the coagulating bath to the focusing guide was set 500 mm apart. A rate of taking the extruded filaments up was set to 10 m/min. As the coagulating bath, a DMSO aqueous solution at 15° C was used. After washing the obtained coagulated filaments with water of 50° C, the filaments were drawn by 5 times in hot water and an oil was imparted thereto followed by drying at 120° C. Then, the drawn filaments were subjected to secondary drawing in steam under pressure or to secondary drawing with dry heating to obtain filaments drawn at 95% of the maximum drawing magnification. The mechanical properties of fibers were measured. The results are shown in Table 2 below. The filament fibers obtained in Example 4 showed a tension of 15,9 cN/tex (1.8 g/d) in the secondary drawing with dry heating at 190° C, the degree of crystalline orientation of 94.5% and contrast glossiness of 21.2%; whereas the filament fibers obtained in Comparison Example 8 showed a tension of 7,1 cN/tex (0.8 g/d) in the drawing described above, both the strength and initial modulus were poor. Intrinsic Viscosity Secondary Drawing Strength (g/d) cN/tex Initial Modulus (g/d) cn/tex Example 4 3.3 dry heating (13.1) 115 (237) 2039 Comparison Example 8 3.3 steaming (9.5) 83,9 (175) 1545 Comparison Example 9 1.7 dry heating (7.2) 63,6 (159) 1404 Comparison Example 10 1.7 steaming (6.1) 53,9 (138) 1219 Comparison Example 11 1.2 dry heating (6.4) 56,5 (160) 1413 Comparison Example 12 1.2 steaming (5.2) 45,9 (123) 1086 Examples 5 to 7 and Comparison Examples 13 and 14 99.5 mol% of AN and 0.5 mol% of 2-acrylamido-2-methyl-propanesulfonic acid were dissolved in DMSO followed by solution polymerization to prepare AN copolymer having a intrinsic viscosity of 5.2. Using the obtained copolymer solution, 5 kinds of spinning solutions having polymer concentrations of 4%, 6%, 8%, 10% and 12% were prepared, respectively. These spinning solutions were heated to 80°C and subjected to dry-jet wet spinning, respectively The distance between a spinning nozzle and the liquid surface of a coagulating bath was set 10 mm apart. As the coagulating bath, a 30% DMSO aqueous solution at 15°C was used. The spinning solution having the polymer concentration of 4% showed a poor spinnability in which single yarns were adhered to each other, resulting in unsatisfactory spinning. Therefore, the spinning solutions other than this spinning solution were subjected to spinning. Coagulated filaments obtained from the remaining 4 spinning solutions were drawn by 5 times in hot water, respectively. After washing with water, the filaments were strained at 110° C, dried and further subjected to secondary drawing using a dry heating tube at 190° C to obtain drawn filaments. The physical properties in fibers of the obtained filaments are shown in Table 3 below. The multifilament fibers obtained in Examples 5, 6 and 7 showed the degree of crystalline orientations of 94.5%, 94.2% and 94.1% and, contrast glossinesses of 22.1%, 18.9% and 18.1%, respectively. Dope Concentration of Spinning Solution Viscosity at 45°C Pa·s (poise) Strength (g/d) cN/tex Initial Modulus (g/d) cN/tex Example 5 12 960 (9600) (12.5) 110 (231) 2039 Example 6 10 512 (5120) (12.3) 109 (221) 1951 Example 7 8 209 (2090) (11.1) 98 (215) 1898 Comparison Example 13 6 125 (1250) (9.8) 86,5 (195) 1722 Example 14 4 350 (350) -- -- Examples 8 to 11 and Comparison Examples 15 to 17 100% AN was dissolved in DMSO followed by solution polymerization to prepare a polymer having an intrinsic viscosity of 3.2. The polymer concentration of the obtained polymer solution was adjusted to 15% to prepare a spinning solution having a solution viscosity of 370 Pa.s (3700 poise) at 45° C. The spinning solution was heated to 70° C and subjected to dry-jet wet spinning in a coagulating bath of a 50% DMSO aqueous solution at 15 C using a spinning nozzle having a pore diameter of 0.12 mm and a hole number of 200 H. The distance between the spinning nozzle and the liquid surface of the coagulating bath in the dry-jet wet spinning was modified as indicated in Table 4 below. Spinning state was observed and the results are also shown in Table 4 below. In the dry-jet wet spinning described above, the distance from the liquid surface of the coagulating bath from the focusing guide was set 700 mm. As shown in Table 4 below, the solution from the coagulating bath wetted the surface of the nozzle to render dry and wet spinning difficult, when the distance between the spinning nozzle and the liquid surface of the coagulating bath was 0.5 mm. On the other hand, when the distance exceeded 250 mm, adhesion between single yarns tended to occur before the extruded filaments went into the coagulating bath and, normal filament fibers could not be obtained. Namely, it is understood that stable dry-jet wet spinning becomes possible by setting the aforesaid distance between the spinning nozzle and the liquid surface of the coagulating bath in the range of 2 to 10 mm. Preparation of fiber reinforced hydraulic substances. Comparison Examples 12a to 14a and Comparison Examples 18 to 21 To 10 g each of AN fibers (obtained in Examples 1, 2 and 3 and Comparison Examples 2, 4 and 7) shown in Table 1, which had been cut into a fiber length of 5 mm, were added 10 g of craft pulp, 10 g of Ca(OH) 2 , 10 g of Al 2 (SO 4 ) 3 and 10 ℓ of water, respectively. After stirring the mixtures, 460 g of portland cement was added thereto followed by stirring again. Subsequently, 200 ppm each of anionic polyacrylamide type cement flocculants (made by Sanyo Kasei, "Sanfloc"® AH-330P was added to the mixtures, respectively, with stirring at a low speed to prepare slurries having formed a floc of cement particles on the surface of the fibers. Each of the slurries obtained was transferred in a mold of 20 cm x 25 cm on which a wire net of a 0.28 mm sieve mesh was put. After filtering, the system was pressed for 1 minutes under pressure of 9.8 MPa (100 kg/cm 2 ) to mold cement plates having a thickness of about 6 mm. An amount of the fibers to be mixed in each of the cement plates was 2 wt%, respectively. In the case of asbestos, a cement plate was mold only from asbestos (15 wt%) and cement. Next, curing was performed at 20° C at 100% RH for 1 day and then in water at 20° C for 6 days. Measurement of bending strength and work load of rupture in bending : A test piece was cut out of each of the cement plates. Bending strength was measured on the test piece in accordance with JIS-X-6911. Work load of rupture in bending was calculated from a stress-strain diagram in the bending rupture test. Measurement of impact strength : A test piece cut out of each of the cement plates was subjected to impact test in accordance with JIS-X-7111 to determine impact strength. Measurement of specific gravity : With respect to a test piece cut out of each of the cement plates, absolute dry weight, water holding weight and weight in water were measured. According to the following equation, a bulk density was calculated: specific gravity = absolute dry weight water holding weight - weight in water Properties of each of the cement plates are shown in Table 5 below. The cement plates of the present invention which had been reinforced with high tenacity acrylic fibers having a high modulus of elasticity possess a high bending strength that cannot be achieved with conventional acrylic fibers. At the same time, the fiber-reinforced cement plates of the present invention showed greatly increased work load of rupture in bending and impact strength and were excellent in capability of absorbing energy in rupture. In addition, the cement plates of the present invention exhibited the bending strength comparable to the conventional asbestos-reinforced cement plates and simultaneously showed much more excellent impact resistance. Property of Cement Plate Reinforcing Fiber Specific Gravity Bending Strength MPa (Kg/cm 2 ) Word Load of Rupture in Bending J/cm 2 (Kg·cm/cm 2 ) Sharpy Impact Strength J/cm 2 (Kg·cm/cm 2 ) Comparison Example 12a Example 1 1.59 22.5 (230) 0.278 (2.84) 0.298 (3.04) Comparison Example 13a Example 2 1.58 21.8 (222) 0.274 (2.80) 0.296 (3.02) Comparison Example 14a Example 3 1.60 20.9 (213) 0.259 (2.64) 0.279 (2.85) Comparison Comparison Example 18 Example 2 1.58 17.2 (175) 0.230 (2.35) 0.255 (2.60) Example 19 Example 4 1.58 17.2 (175) 0.120 (1.22) 0.202 (2.07) Example 20 Example 7 1.57 15.5 (158) 0.118 (1.20) 0.201 (2.05) Example 21 Asbestos 1.60 20.7 (211) 0.050 (0.51) 0.108 (1.10) Examples 15 to 17 and Comparison Examples 22 to 24 Using high molecular flocculants (Examples 15 to 17, Comparison Example 22), surfactants or oils (Comparison Examples 23 and 24) shown in Table 6 below, aqueous dispersions containing a 0.1% effective component were prepared. The AN fibers obtained in Example 2 shown in Table 1 were immersed in the aqueous dispersions at room temperature for 5 minutes. Using a centrifugal separator, excess moisture was removed. At this time, an amount of the flocculants, etc. to be applied was about 0.1 wt%. Then, the AN fibers were cut into a length of 5 mm without drying. In order to determine cohesion between the obtained fibers and cement particles, the following method was used for measurement. Namely, 0.2 g (provided that 0.2 g each of Al 2 (SO 4 ) 3 and Ca(OH) 2 was added only in Example 15) of the cut fiber obtained above was added to 0.2 ℓ of water. After stirring the mixtures, 9.2 g of portland cement was added to the mixtures followed by stirring again. Then, 200 ppm each of an anionic cement flocculant (polyacrylamide partial hydrolysate, made by Sanyo Kasei Co., Ltd., strongly anionic "Sanfloc"® AH-330P) was added to the mixtures, respectively, based on each of the solid contents while stirring at a low speed to fix cement particles onto the surface of the fibers. After each of the thus prepared slurries was stirred for 0 to 15 minutes using a stirrer of 400 rpm, the mixtures were filtered on a wire net of a 0.35 mm sieve mesh. The solids on the wire net were dried at 105° C and the weights were measured to determine a cement retention rate. The results are shown in Table 6 below. Next, cement plates were molded in a manner similar to Example 12 and, specific gravity and bending strength of each of the cement plates were measured. The results are also shown in Table 6 below. As is evident from the measurement results on Examples 15 to 17 and Comparison Examples 22 to 24 shown in Table 6 below, when the fibers to which the nonionic or cationic high molecular flocculants were applied as in the present invention were used, the systems of the present invention are excellent in paper-making efficiency since the cement retention rate was large and the cement particles were fixed firmly onto the surface of the fibers in large quantities. In addition, the bending strength is large and the coming out of fibers on the face of the ruptured cement plates are not observed. On the other hand, in the cement plate obtained in Comparison Example 22 to which the anionic high molecular flocculant was applied, the cement retention rate was small and the properties of the cement plate were also poor. Further, in the cement plates obtained in Comparison Examples 23 and 24 to which conventional water-dispersible surfactant or oil were applied, the cement retention rate was small and the properties of the cement plates were poor, irrespective of the ionic nature. Examples 18 to 22 and Comparison Examples 25 and 26 As AN fibers, the fibers obtained in Example 2 shown in Table 1 were used. As a cationic high molecular flocculant to be applied to the fibers, polydimethylaminoethyl methacrylate (strongly cationic sample H) having a molecular weight of 3,000,000 was used. As cement flocculants used for adsorbing and bridging cement particles onto the surface of the fibers, anionic, nonionic and cationic high molecular flocculants as shown in Table 7 below were used. Otherwise in quite the same manner as in Example 15, slurries were prepared and, measurement of cohesion, molding of cement plates and bending test on the cement plates were performed. Results of respective measurements are shown in Table 7 below. In case that cement particles were fixed onto the surface of the fibers using the anionic high molecular flocculants as in the present invention, the cement retention rate is large and, the bending strength of the cement plates is large. In case of using the anionic high molecular flocculants having molecular weight of 5,000,000 and 7,500,000, cement plates having high bending strength and good properties were obtained. On the other hand, in case that the nonionic or cationic high molecular flocculants are used as cement flocculants, the cement retention rate was small and the properties of the cement plates were poor. Comparison Examples 27 and 28 Using alkali-resistant glass fibers having a fiber length of 5 mm, a cationic high molecular flocculant, polydimethylaminoethyl methacrylate, having a molecular weight of 3,000,000 was applied thereto in a manner similar to Example 15 (except that the amount of the fibers to be mixed was adjusted to have the same volume percentage as in Example 15). As a cement flocculant, an anionic high molecular flocculant, polyacrylamide partial hydrolysate (strongly anionic sample B), having a molecular weight of 5,000,000 was used. Using this flocculant, cement particles were adsorbed to and bridged with the surface of the fibers to prepare slurries. Measurement of cohesion, molding of cement plates and bending test on the cement plates were performed. The results are shown in Table 8 below. The effect was less on the glass fibers. Both the cement retention rate and bending strength of the cement plates were poor.

Claims: A process for production of a fiber-reinforced hydraulic substance which comprises uniformly dispersing an AN fiber comprising an AN polymer containing 95 to 100 mol% AN having an intrinsic viscosity of at least 2.5, and having a degree of crystalline orientation measured by wide-angle X-ray diffraction of at least 93%, a tensile strength of at least 88.3 cN/tex (10 g/d), and a knot strength of at least 19.4 cN/tex (2.2 g/d), and having a surface smoothness which is at least 10% when expressed by contrast glossiness, the fiber being obtainable by a process which comprises once extruding a solution of said AN polymer in air or in an inert gas through a spinning nozzle, then introducing into a coagulating bath, subjecting the resulting coagulated filaments to washing with water, drawing and drying, and then drawing the filaments under a drawing tension of 8.8 cN/tex (1 g/d) or more with dry heating at 160 to 250°C in an heated air bath to make the total drawing magnification about 10 or more per initial length of the coagulated filaments, said solution having an AN polymer concentration in the range of 10 to 18 wt% and a viscosity at 45°C of at least 150 Pas (1500 poise) said fiber having applied a non-ionic high molecular flocculant or a cationic high molecular flocculant thereto in water, adding an anionic high molecular flocculant to flocculate and adsorb cement particles to the surface of the AN fiber and subsequently, subjecting the resulting slurry to papermaking. The process as claimed in claim 1, wherein said AN polymer is an AN polymer having an intrinsic viscosity of 2.7 to 3.3. The process as claimed in claim 1, wherein said tensile strength is at least 106 cN/tex (12 g/d) and the initial modulus is greater than 1766 cN/tex (200 g/d). The process as claimed in claim 1, wherein the spinning draft is in the range of 0.1 to 1.5. The process as claimed in claim 1, wherein the distance between the spinning nozzle and the liquid surface of said coagulating bath is 1 to 20 mm. The process as claimed in claim 1, wherein said coagulated filaments are primarily drawn to 2 to 10 times and, after dry heating, are secondarily drawn with heating under a drawing tension of 13.2 to 22.1 cN/tex (1.5 g/d to 2.5 g/d) to make the total drawing magnification greater than 15 times. The process as claimed in claim 1, wherein the filaments after drying are subjected to heat-drawing while passing through a tube containing heated air. The process as claimed in claim 1, wherein the molecular weight of said non-ionic or cationic high molecular flocculant to be applied to the surface of the fiber is 1,000,000 to 15,000,000. The process as claimed in claim 1, wherein the molecular weight of said anionic high molecular flocculant to flocculate and adsorb cement particles onto the surface of the AN fiber is 4,000,000 to 9,000,000. The process as claimed in claim 1, wherein said slurry of cement further contains pulp, a cationic inorganic flocculant and an inorganic flocculating aid.

Inventors: HIRAO KENICHI, SUZUKI MITSUO, TAKADA TAKASHI, TANAKA HIROYOSHI, HIRAO, KENICHI, SUZUKI, MITSUO, TAKADA, TAKASHI, TANAKA, HIROYOSHI
Applicants: TORAY INDUSTRIES, TORAY INDUSTRIES, INC.
Application year: 1985
Main classification: D01F6
IPC codes: C04B16, C04B28, D01F6, C04B20