JPH04245912A - Production of fiber for reinforcing cement - Google Patents

Abstract

PURPOSE:To produce an acrylic fiber excellent in the alkali resistance and in the affinity with cement. CONSTITUTION:A method for producing cement-reinforcing fiber strand having a single filament fineness of <=0.05 denier and a spinning oil extraction amount of 0.5-1% by wet-spinning a spinning dope comprising a dimethylformamide or dimethylacetamide solution of an acrylonitrile polymer having a weight- average mol.wt. of >=400000 and a polymer concentration of 3-8% and subsequently coagulating the spun fiber.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing reinforcing fibers for reinforcing cement, which have excellent adhesion to cement and mechanical reinforcing effects.

0002

BACKGROUND OF THE INVENTION Various methods are known for adding reinforcing materials to improve the strength of cement products. For example, methods using alkali-resistant glass and methods using asbestos are known. However, alkali-resistant glass-reinforced cement products are difficult to use in applications that require strong impact resistance, and asbestos-reinforced cement products have been restricted in use since the carcinogenicity of asbestos has been pointed out. It has become.

[0003] Therefore, various studies have begun to consider reinforcing cement products using general-purpose fibers. In this case, the most important requirements for cement reinforcing fibers are alkali resistance and compatibility with cement, as well as the ability of the reinforcing fibers to fibrillate during kneading with cement.

For example, DuPont's Kevlar (registered trademark), which is known as a high-strength fiber, has excellent mechanical properties, but because it uses a condensation polymer, it has low alkali resistance and poor adhesion to cement. It's bad. Therefore, when using Kevlar as cement reinforcing fiber, it is necessary to use surface-treated Kevlar (
(Japanese Patent Application Laid-Open No. 63-55142).

Acrylonitrile fibers are attracting attention as fibers that almost satisfy the three requirements of mechanical properties, alkali resistance, and cement adhesion, but ordinary acrylic fibers have low mechanical strength and do not have sufficient strength. I can't say it's effective.

[0006] It has been proposed to reinforce cement using acrylic fibers made of high molecular weight acrylonitrile polymer with improved mechanical strength (Japanese Patent Laid-Open Nos. 61-6160 and 61-61). -6161, 61-1
63149, 61-163151, etc.)
All of the fibers are insufficiently fibrillated during kneading with cement, and cannot provide a satisfactory reinforcing effect.

[0007]

[Problems to be Solved by the Invention] As a result of intensive research by the present inventors, the product has good alkali resistance and affinity with cement, and easily fibrillates during kneading with cement, making it easy to disperse uniformly in cement. He discovered a method for producing acrylic fibers and completed the present invention.

[0008]

[Means for Solving the Problems] The gist of the present invention is to obtain an acrylonitrile polymer containing 80% by weight or more of acrylonitrile units and having a weight average molecular weight of 400,000 or more, dissolved in dimethylformamide or dimethylacetamide. A spinning dope with a polymer concentration of 3 to 8% is spun using a wet spinning method, coagulated in a coagulation bath consisting of water and dimethylformamide or dimethylacetamide, and the resulting coagulated yarn is drawn to a single fiber fineness of 0.05 d. The present invention provides a method for producing a fiber aggregate for reinforcing cement, in which the extraction amount of the spinning oil is in the range of 0.5 to 1% of the weight of the fibers.

The acrylonitrile polymer used in the present invention must contain 80% by weight or more of acrylonitrile units and have a weight average molecular weight of 400,000 or more. If the acrylonitrile content in the acrylonitrile polymer used is less than 80% by weight, a large amount of monomers that easily react with the alkali in cement are present in the fibers, resulting in cleavage of the polymer main chain. Furthermore, even if the polymer main chain is oriented in the fiber axis direction, the orientation structure will be disturbed in the monomer unit part other than acrylonitrile, and water and alkali in the cement slurry will enter the fiber from that part. Since it becomes easy to diffuse, the CN group in the acrylonitrile polymer will be hydrolyzed during cement curing, and it will no longer function as a reinforcing fiber.

Examples of monomers that can be copolymerized with acrylonitrile include methacrylic acid, methyl acrylate or methacrylate, ethyl acrylate or methacrylate, n-, iso- or t-
Butyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, α-chloroacrylonitrile, 2-hydroxyethyl acrylate,
Examples include unsaturated monomers such as hydroxyethyl acrylate, hydroxyalkyl acrylate or methacrylate, vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl acetate, but any monomer that can be copolymerized with acrylonitrile may be used. , two or more types of monomers can also be used in combination.

Furthermore, it is necessary that the weight average molecular weight of the acrylonitrile polymer used is 400,000 or more. When using a polymer with a weight average molecular weight of less than 400,000,
Even if stretching is performed in the spinning process, it is not possible to orient the polymer molecules to the extent that the diffusion of water, alkali, etc. in the cement slurry into the fibers can be suppressed.

[0012] The method for producing the acrylonitrile polymer used in the present invention is not particularly limited;
For example, the method described in JP-A-61-111310,
That is, a mixture of 10 to 70% by weight of acrylonitrile, 15 to 60% by weight of an organic solvent, and 15 to 60% by weight of water is polymerized in the presence of a radical initiator, and then 1 part by weight of water or organic solvent is added to the monomer. A method in which 1 to 10 parts by weight of the acrylonitrile polymer is added and polymerized is preferred because it allows stable and efficient production of a high molecular weight acrylonitrile polymer suitable for fiber shaping. Examples of the organic solvent used in this method include dimethylformamide (DMF), dimethylacetamide (DMAc), γ-butyrolactone, and dimethylsulfoxide (DMSO).

In order to produce the acrylic fiber of the present invention with a single fiber fineness of 0.05d or less, it is necessary to lower the acrylonitrile polymer concentration in the spinning dope, and to adjust the linear velocity of the spinning dope from the spinning nozzle and the unstretched It is necessary to make the yarn speed ratio (spinning draft) as high as possible.

[0014] Therefore, it is necessary to set the concentration of the acrylonitrile polymer in the spinning dope in the range of 3 to 8%, but when the weight average molecular weight of the polymer used is less than 400,000, such Even if a spinning stock solution with a low concentration is prepared,
The viscosity decreases, and the spinnability decreases, making it difficult to continue spinning stably. Furthermore, if the concentration of the acrylonitrile polymer in the spinning stock solution exceeds 8%, the spinning draft becomes high and the spinning stability decreases. On the other hand, if the concentration of the acrylonitrile polymer is less than 3%, the viscosity of the spinning stock solution decreases, resulting in a decrease in spinning stability.

[0015] Next, such a spinning dope was prepared with a mesh opening of 10.
It is filtered through a filter medium of μ or less and discharged from a spinning nozzle. The smaller the hole diameter of the spinning nozzle is, the more preferably it is 50 μm or less, and more preferably 40 μm or less. The spinning method uses a mixed solution of dimethylformamide or dimethylacetamide and water, which is discharged from a spinning nozzle by a wet spinning method.

[0016] The obtained coagulated thread is then stretched while washing and removing the residual solvent. As for the stretching method, the stretching is carried out in boiling water or in warm water with a temperature gradient such that the temperature becomes higher in subsequent steps, while washing the organic solvent contained in the coagulated yarn.

Thereafter, a dispersion of a spinning oil agent is applied so that the extracted oil content of the resulting cement reinforcing fibers is 0.5 to 1% per fiber. When the amount of extracted oil in the resulting fibers is within this range, a fiber aggregate in which single fibers are appropriately bonded can be obtained.

[0018] If it is attempted to reduce the amount of extracted oil to less than 0.5%, the passability after the oiling step will be reduced. On the other hand, if the amount of oil extracted from the fibers exceeds 1%, this is not preferable because the adhesion between the single fibers in the resulting fiber aggregate is low and fiber balls are likely to form during cement kneading.

Subsequently, an oil dispersion is applied to the fibers and then dried, followed by dry heat stretching. The dry heat stretching method is as follows:
Any method such as a heat roll, a heat plate, a heat pin or a heat tube can be used.

[0020] Since the acrylonitrile fibers obtained in this way have fibers with a single fiber fineness of 0.05d or less attached, when added to cement slurry, friction with cement particles occurs during mixing with cement. The bonded single fibers can be loosened little by little and uniformly dispersed in the cement slurry, and as a result, cement products can be effectively reinforced.

In order to reinforce cement products using the fibers of the present invention, it is necessary to cut the acrylic fibers described above, add them to cement slurry, and then mold and cure them. As for the cut length, the fiber length is L, and the fiber diameter is D (D: fiber diameter when the fiber cross section is assumed to be a perfect circle).
When, L/D is preferably in the range of 500 to 5000. When L/D is less than 500, the reinforcing effect cannot be exhibited, and when it exceeds 5000, the fibers become entangled in the cement slurry, resulting in a small reinforcing effect.

The amount added to the cement slurry is preferably 0.1 to 3% by weight based on the cement. Added amount is 0
．． If it is less than 1%, the amount of reinforcing fibers will be small and the reinforcing effect will be extremely small. If it exceeds 3%, the dispersibility of the fibers in the cement slurry will be poor and the fibers will aggregate into fiber balls, resulting in a uniform reinforcing effect. is not obtained.

[0023]

[Examples] The present invention will be specifically explained below using Examples. 1. "Weight average molecular weight (Mw)" is determined by measuring "η" at 25°C using DMF as a solvent, and "η" = 3.35 x 10-4.
Calculated from (Mw) 0.72.

2. "Bending strength of cement products" is length 1
The three-point bending strength (δb) of a test piece measuring 5 cm and width 5 cm was measured using a large tensilon universal testing machine UTM-25T (manufactured by Toyo Baldwin Co., Ltd.).

[Math 1]

3. The extracted oil content of the fibers was measured by extracting methanol-soluble content from the fibers using methanol, drying the methanol solution, and determining the amount of the residue as the extracted oil content.

Example 1 An acrylonitrile polymer (100% AN units) with a weight average molecular weight of 450,000 obtained by a suspension polymerization method was dissolved in DMAc, and a spinning stock solution with a polymer concentration of 6% (30 poise/45°C) was prepared. was obtained and spun using a wet spinning method using a nozzle with a hole diameter of 30μ (number of holes: 50,000), and DMAc/water 30/70
(weight ratio), and coagulated in a coagulation bath at 55°C.

The obtained undrawn yarn was stretched 3 times in boiling water, an oil agent was applied by varying the oil bath concentration, dried with a heated roller, and finally heated with a heated roller at 200°C to be stretched 2 times. A fiber aggregate having a single fiber fineness of 0.05 d and a tow fineness of 2500 d was obtained. Furthermore, samples with different single fiber finenesses were obtained in the same manner. The results are shown in Table 1.

[0028]

[Table 1]

Comparative Example An acrylonitrile polymer (100% AN units) having a weight average molecular weight of 300,000 obtained by a suspension polymerization method was dissolved in dimethylacetamide, and spinning stock solutions were prepared by varying the polymer concentration. Thereafter, a spinning experiment was conducted under the same spinning conditions as in Example 1. The results are shown in Table 2.

[0030]

[Table 2]

Example 2 The acrylic fiber obtained in Example 1 was cut to a fixed length of 2 mm using a cutter to obtain short acrylic fibers. on the other hand,
4 parts of short acrylic fibers, 4 parts of pulp, and 800 parts of water were uniformly mixed using a mixer, and then 200 parts of cement was added and mixed uniformly again. The thus obtained cement slurry was filtered using filter paper and molded, and then cured at 25° C. for 15 days to obtain a slate board. The bending strength of the obtained slate plate was measured, and the results shown in Table 3 were obtained.

[0032]

[Table 3]

Claims (1)

[Claims] Claim 1: A spinning stock solution with a polymer concentration of 3 to 8% obtained by dissolving an acrylonitrile polymer having a weight average molecular weight of 400,000 or more and having 80% by weight or more of acrylonitrile units in dimethylformamide or dimethylacetamide is processed by wet spinning. The fibers are spun using a spinning method, coagulated in a coagulation bath consisting of water and dimethylformamide or dimethylacetamide, and the resulting coagulated fibers are stretched to obtain a single fiber fineness of 0.05d or less and an extraction amount of spinning oil of 0.05% of the weight of the fibers. A method for manufacturing a fiber aggregate for cement reinforcement in the range of 5 to 1%.