JPH04245913A - Production of fiber for reinforcing cement - Google Patents

Abstract

PURPOSE:To provide an acrylic fiber having excellent alkali resistance and affinity with cement. CONSTITUTION:An acrylonitrile polymer having a weight-average mol.wt. of >=400000 is mixed with cellulose acetate, polyvinyl alcohol or polymethyl methacrylate in a weight ratio of 60/40 to 90/10. The mixture is dissolved in a solvent, wet-spun and subsequently drawn in a ratio of >=6 times to provide a fiber which is liable to be fibrillated during kneading with Portland cement and which is used for reinforcing the cement.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is used for reinforcing cement.
The present invention relates to a method for producing reinforcing fibers that have excellent adhesion to cement and mechanical reinforcing effects.

0002

2. Description of the Related Art Various methods are known for adding reinforcing materials to improve the strength of cement products, such as using alkali-resistant glass and asbestos. 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 it has been pointed out that asbestos is a carcinogen. ing.

[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
No. 63149, No. 61-163151, etc.), but all of the fibers are insufficiently fibrillated during kneading with cement, and cannot produce a satisfactory reinforcing effect.

[0007]

[Problems to be Solved by the Invention] As a result of extensive research by the present inventors, we have found an acrylic fiber that is excellent for cement reinforcement because it has good alkali resistance and affinity with cement, and easily fibrillates during kneading with cement. found a manufacturing method and completed the present invention.

[0008]

[Means for Solving the Problems] The gist of the present invention is to combine an acrylonitrile polymer (A) containing 80% by weight or more of acrylonitrile units and a weight average molecular weight of 400,000 or more with cellulose acetate, polyvinyl alcohol, or polyvinyl alcohol. Methyl methacrylate (B) (A)/(B) is 6
A spinning stock solution in which a polymer mixture mixed at a ratio of 0/40 to 90/10 (weight ratio) is dissolved in dimethylacetamide or dimethylformamide is spun using a wet spinning method, and coagulated in a coagulation bath consisting of water and dimethylformamide or dimethylacetamide. The present invention provides a method for producing fibers for reinforcing cement, which comprises stretching the obtained coagulated thread by a factor of 6 times or more.

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 unit contained in the acrylonitrile polymer used is less than 80% by weight, a large amount of monomers that easily react with the alkali in cement will be present in the fibers, resulting in cleavage of the polymer main chain. It becomes more likely to occur,
Furthermore, even if the polymer main chain is oriented in the fiber axis direction, the oriented structure will be disturbed in the monomer unit parts other than the acrylonitrile units, and water, alkali, etc. in the cement slurry will diffuse into the fiber from that part. As a result, when curing cement, hydrolysis of the CN groups in the acrylonitrile polymer occurs and it no longer functions 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, hydroxyethyl acrylate, hydroxyalkyl acrylate or methacrylate Examples include unsaturated monomers such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl acetate, but any monomer that can be copolymerized with acrylonitrile may be used, and two or more monomers may be used. They can also be used together.

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, dimethylsulfoxide (DMSO), and the like.

Next, it is necessary to promote fibrillation in the cement reinforcing fiber of the present invention. Even when acrylonitrile-based polymers are used alone, it is possible to promote fibrillation of acrylic fibers by changing the coagulation conditions during the spinning process, but in that case, macrovoids may occur or The stretchability of the fibers decreases and the mechanical strength of the fibers decreases.

However, in the present invention, a dimethylacetamide or dimethylformamide-soluble polymer selected from cellulose acetate, polyvinyl alcohol, and polymethyl methacrylate is mixed with an acrylonitrile polymer. In this case, compared to the case where an acrylonitrile-based polymer is used alone, it is possible to promote only fibrillation with almost no deterioration in stretchability or fiber properties.

The mixing ratio of the acrylonitrile polymer (A) and the polymer (B) such as diacetate is preferably in the range of (A)/(B) from 60/40 to 90/10 (weight ratio). is necessary. The amount of acrylonitrile polymer mixed is 6
If it is less than 0% by weight, the drawability in the spinning process will be significantly reduced and the mechanical strength of the resulting fibers will be reduced. On the other hand, if the amount of acrylonitrile-based polymer mixed exceeds 90% by weight, fibrillation will hardly occur and cement cannot be effectively reinforced.

Next, to produce the cement reinforcing fiber of the present invention, a mixed polymer consisting of an acrylonitrile polymer (A) and a polymer such as cellulose acetate (B) is mixed with dimethylformamide or dimethylacetamide as the main component. Dissolve in solvent. In this case, the concentration of the polymer solution is 5 to 1
By setting it to 0% by weight, the viscosity becomes 50% at 45°C.
A spinning stock solution of ~500 poise is obtained. If the viscosity of the spinning dope is outside this range, spinnability decreases during wet spinning, making it impossible to ensure spinning stability.

Next, the obtained spinning stock solution is spun by a wet spinning method and coagulated in a coagulation bath consisting of water and dimethylformamide or dimethylacetamide.

In this case, the hole diameter of the spinning nozzle is preferably in the range of 30μ to 150μ. The hole diameter of the spinning nozzle is 30μ
If it is less than that, nozzle pressure increases and nozzle clogging tends to occur, making it impossible to continue spinning stably. On the other hand, if the hole diameter exceeds 150μ, the spinning draft determined by the discharge amount of the spinning stock solution and the take-up speed of the discharged yarn becomes high.
Thread breakage is likely to occur.

[0019] Subsequently, the obtained coagulated thread is stretched 6 times or more, preferably 8 times or more, to obtain the desired acrylic fiber. In order to achieve a stretching ratio of 6 times or more, it is possible to perform stretching in boiling water, but it is preferable to draw the coagulated fiber in warm water with a temperature gradient so that the temperature increases as the process progresses. It is preferable to carry out the stretching while washing the organic solvent, and then carry out the stretching at a temperature of 100° C. or higher.

[0020] As a stretching method at a temperature of 100°C or higher,
Examples include dry heat stretching, steam stretching, and stretching in a moist heat atmosphere using a high boiling point heating medium. Examples of the high boiling point heating medium include water-soluble polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, and glycerin.

The acrylonitrile fiber obtained in this manner has a tensile strength of 4 g/d or more, and is extremely susceptible to fibrillation because it uses a wet spinning method in which the spinning stock solution is directly extruded into a coagulation bath. is being promoted. Because the polymer chains in the fibril part are regularly arranged in the fiber axis direction, it is difficult for water and alkali in the cement slurry to diffuse into the fibers, and the -
It becomes possible to effectively reinforce cement with almost no decomposition of the CN group.

[0022]Furthermore, the fibrillation of the fibers of the present invention is greatly promoted, and as a result, the fibrils are scraped little by little during kneading with cement and dispersed in the cement, resulting in an excellent effect in reinforcing cement. It is something.

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. The cut length is preferably in the range of L/D from 100 to 1000, where L is the fiber length and D is the fiber diameter (D: fiber diameter when the fiber cross section is assumed to be a perfect circle). When L/D is less than 100, the reinforcing effect cannot be exhibited, and when it exceeds 1000, 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 3.0% by weight of cement. If the amount added is less than 0.1%, 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 and form fiber balls. Therefore, a uniform reinforcing effect cannot be obtained.

[0025]

[Examples] The present invention will be explained in detail with reference to Examples below. 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).

[Math 1]

Example 1 80 parts of an acrylonitrile polymer (AN unit 100%) with a weight average molecular weight of 400,000 obtained by suspension polymerization method and 20 parts of cellulose diacetate (acetylation degree 55%) were mixed and the mixture was subjected to DMA.
c to obtain a spinning stock solution (120 poise/45°C) with a polymer concentration of 9%, and a pore size of 75μ (number of holes: 25,000).
Spun using a wet spinning method from a nozzle, DMAc/water = 6
It was coagulated in a coagulation bath at a temperature of 0/40 (weight ratio) and 30°C. The obtained undrawn yarn was stretched 6 times in boiling water, and after applying an oil agent,
It was dried with a hot roller and finally heated with a hot roller at 200° C. and stretched 1.5 times to obtain fibers with a single fiber fineness of 1.0 d and a single fiber strength of 5.2 g/d.

Comparative Example 1 Using the same acrylonitrile polymer as in Example 1, D
A spinning stock solution with a polymer concentration of 9% was obtained by dissolving in MAc, and spinning was performed under the same spinning conditions as in Example 1 to obtain a single fiber fineness of 1.0.
d. A fiber with a single fiber strength of 6.1 g/d was obtained.

Comparative Example 2 80 parts of an acrylonitrile polymer (100% AN unit) with a weight average molecular weight of 250,000 obtained by suspension polymerization method and 20 parts of cellulose diacetate (degree of acetylation 55%) were mixed and mixed with DMAc. Dissolve the spinning stock solution with a polymer concentration of 10% (80 poise/45
°C) and was spun under the same spinning conditions as in Example 1 to obtain fibers with a single fiber fineness of 1.0 d and a single fiber strength of 4.6 g/d.

Example 2 The acrylic fibers obtained in Example 1 and Comparative Examples 1 and 2 were cut to a fixed length of 3 mm using a cutter to obtain short acrylic fibers. On the other hand, 4 parts of acrylic short 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 1 were obtained.

[0031]

[Table 1]

Claims (1)

[Claims] Claim 1: An acrylonitrile polymer (A) containing 80% by weight or more of acrylonitrile units and having a weight average molecular weight of 400,000 or more and cellulose acetate, polyvinyl alcohol or polymethyl methacrylate (B) (A)/
A spinning stock solution prepared by dissolving a polymer mixture of (B) in a ratio of 60/40 to 90/10 (weight ratio) in dimethylacetamide or dimethylformamide is spun using a wet spinning method, and coagulated from water and dimethylacetamide or dimethylformamide. A method for producing fibers for reinforcing cement, which comprises coagulating in a bath and stretching the coagulated fibers six times or more.