JP4005315B2 - Polypropylene fiber for cement reinforcement - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polypropylene fiber for reinforcing a cement molded body.
[0002]
[Prior art]
Conventionally, the use of various inorganic fibers and synthetic fibers as cement reinforcing fibers that replace asbestos has been proposed and put into practical use. One of them is polypropylene fiber. Polypropylene has been widely used in recent years because it is excellent in alkali resistance and is not easily embrittled even when a cement-molded body is cured at a high temperature.
[0003]
For example, JP-A-60-59113, JP-A-62-41331, and JP-B-3-20505 describe cement reinforcing fibers obtained by melt spinning a polypropylene resin. Japanese Patent Laid-Open No. 1-122943 proposes a reinforcing fiber obtained by splitting and opening a polypropylene resin film.
[0004]
The present applicant also pays attention to the excellent properties of polypropylene, and in order to provide higher-strength polypropylene fibers, the present applicant consists of highly crystalline polypropylene having a specific molecular weight, few low crystalline components, and extremely high stereoregularity. A fiber was proposed in JP-A-5-170497.
[0005]
[Problems to be solved by the invention]
As a recent trend, an increase in the heating temperature when the cement molded body is cured in an autoclave is recognized. This is due to shortening the curing time and trying to improve production efficiency. The optimum autoclave temperature is 180 ° C., but the conventional polypropylene fiber is significantly damaged in fiber form and the reinforcing effect is lowered.
[0006]
In other words, when cured at a high temperature, the fiber melts or softens and loses its shape, and cannot function as a reinforcing fiber in the cement molded body. For example, it is difficult to cure the molded body containing the above-described polypropylene fiber at 175 ° C. or higher.
[0007]
In order to avoid such inconvenience, it is sufficient to produce fibers using a resin having a high melting point. However, even if the melting point is high, the fiber is deteriorated by a chemical action even at a temperature below the melting point if it is not resistant to moisture and heat. For example, the melting point of the vinylon fiber is about 230 ° C., but when heated at about 110 ° C., the deterioration significantly proceeds due to the alkali component in the cement, and as a result, the reinforcing effect decreases.
[0008]
Thus, the actual condition is that only a small portion of cement reinforcing fibers suitable for autoclave curing at high temperatures is used. This invention is made | formed in view of this actual condition, and it aims at providing the polypropylene fiber especially suitable for the autoclave curing under high temperature.
[0009]
[Means for Solving the Problems]
The cement reinforcing fiber of the present invention has a Q value (Q: ratio of weight average molecular weight / number average molecular weight) of less than 5 and a boiling n-heptane insoluble content (HI; mass%) of 97 <HI <100, isotactic. Polypropylene resin having a pentad fraction (IPF; mol%) of 94 <IPF <100 and a residual ratio of fiber strength after autoclaving (180 ° C. × 10 hours) of 70% or more is melt-spun. A polypropylene fiber for cement reinforcement characterized by having a melt flow rate (MFR) of 1.5 to 3.0 and a fineness of 60 to 80 dtex.
The low MFR polypropylene fiber in the above range is less likely to flow even at high temperatures and easily maintains the fiber shape. When the MFR is less than 1.5 as a fiber, it is difficult to form a fiber from such a raw material polymer. In addition, it has a fineness of 30 dtex or more, so that the fiber form is maintained with respect to heat curing and there is no significant decrease in the reinforcing effect after curing, but if the fineness exceeds 80 dtex, one fiber is too stiff and the fiber from the cement board surface molded Since it comes to protrude, it is not preferable.
[0010]
The polypropylene resin forming the reinforcing fiber has a Q value (Q: ratio of weight average molecular weight / number average molecular weight) of less than 5 and a boiling n-heptane insoluble content (HI; mass%) of 97 <HI <100. The isotactic pentad fraction (IPF; mol%) is preferably 94 <IPF <100. A fiber made of such a highly crystalline polypropylene resin has a high breaking strength and a high rigidity. Therefore, the use of this fiber can further improve the strength of the cement molded body.
[0011]
The cement reinforcing fiber of the present invention preferably contains 2.0% by mass or less of a core material and / or a lubricant.
[0012]
The cement reinforcing fiber according to the present invention preferably has a fiber strength remaining ratio of 70% or more after treatment time of 5 to 16 hours in an autoclave (180 ° C.). Autoclave curing is generally used to efficiently obtain a molded cement product, but if the reduction in the reinforcing effect is within 30%, there is no practical problem.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The polypropylene used in the polypropylene fiber of the present invention has an MFR of 1.5 to 3.0 even if the viscosity decreases after spinning, but in order for the fiber to have such an MFR, the polymer polypropylene used as the raw material is MFR 0.5-2.5 is used. Further, the Q value (Q: ratio of weight average molecular weight / number average molecular weight) is less than 5, boiling n-heptane insoluble (HI; mass%) is 97 <HI <100, isotactic pentad fraction (IPF: mol) %) Is 94 <IPF <100, and the weight average molecular weight is obtained by the formula of Mw = [ΣNiMi ² ] / [ΣNiMi] using, for example, a light scattering method, a viscosity method, a super-extensive centrifugation, or the like. The number average molecular weight is determined by the formula Mn = [ΣNiMi] / [ΣNi] using, for example, a terminal group determination method, a freezing point depression method, a boiling point elevation method, and an osmotic pressure method. In general, the weight average molecular weight / number average molecular weight is used as a measure of polydispersity. As this value is larger than 1 (monodisperse), it means that the molecular weight distribution curve becomes wider (broad). Polymers with many branches are also high.
[0014]
Such a resin has a large boiling n-heptane insoluble content and a small amount of low crystallinity component. Therefore, even when stretched, the crystal orientation is not inhibited, the isotactic pentad fraction is large, and the stereoregularity is excellent. The crystal orientation due to is easily promoted, and since the Q value is low, there is an advantage that the stretchability is good and the film can be stretched at a high magnification.
[0015]
This resin is characterized in that it has a higher molecular weight than ordinary polypropylene and is highly easily oriented crystals. Therefore, at the time of fiber formation, in order to avoid molecular entanglement and cutting as in the case of ordinary polypropylene, melt spinning is performed at a temperature as low as possible, and the fiber is highly crystal-oriented by stretching at a temperature as high as possible at a high draw ratio. It is desirable.
[0016]
The cement reinforcing fiber of the present invention preferably contains 2.0% by mass or less of a core material and / or a lubricant. It is because the crystallinity can be further improved by adding these. If an amount exceeding 2.0% by mass is added, the fiber performance deteriorates. Examples of the core material include general sorbitol-based compounds, compounds containing benzoates such as sodium benzoate, and organic phosphates. Examples of the types of lubricant compounds include general primary amides such as stearic acid amide, secondary amides such as N-stearyl stearic acid amide, and ethylene bisamides such as N, N′-ethylenebisstearic acid amide. be able to.
[0017]
It is desirable that 0.05 to 10% by mass of a normal alkyl phosphate alkali metal salt having 8 to 18 carbon atoms adheres to the fiber surface of the cement reinforcing fiber of the present invention. Such a fiber treatment agent exchanges calcium ions present in a cement slurry or calcium ions leached from a fiber containing calcium carbonate to form a normal alkyl phosphate calcium salt on the fiber surface. Improve affinity with things.
[0018]
Moreover, it is desirable to be comprised from the polypropylene resin in which 2-20 mass% of calcium carbonate fine powder whose average diameter is less than 1 micrometer is contained in a polypropylene fiber. Since the specific gravity of the resin increases due to the presence of fine calcium carbonate powder, fibers having good underwater sedimentation can be obtained by using such a resin.
[0019]
The cement reinforcing fiber of the present invention comprises a core component and a sheath component, the core component is formed of a low MFR polypropylene resin not containing calcium carbonate, and the sheath component is a low MFR polypropylene resin containing calcium carbonate. It may be a core-sheath type composite fiber formed. According to this structure, since the core component not containing calcium carbonate ensures the strength of the fiber, it is possible to obtain a higher strength than the single fiber containing the calcium carbonate fine powder.
[0020]
If a cement molded body is manufactured by mixing the fibers as described above into a cement slurry, a high-strength molded body can be obtained even when the autoclave is cured at a high temperature.
[0021]
The content of the calcium carbonate fine powder is desirably 2 to 20% by mass in the fiber. More preferably, it is 6-12 mass%. If it is less than 2% by mass, the specific gravity of polypropylene hardly changes and the above-mentioned effects cannot be obtained. Moreover, the effect of the hydrophilic improvement by ion exchange with the specific fiber processing agent which is mentioned later is not acquired. If it exceeds 20% by mass, the spinnability is lowered and fibers cannot be stably obtained. It should also be noted that the strength of the fiber decreases as the content of fine calcium carbonate powder increases.
[0022]
The average diameter of the calcium carbonate fine powder is desirably less than 1 μm from the viewpoint of spinnability. More preferably, it is less than 0.6 μm. Further, it is desirable that the fine powder to be used does not contain particles having a diameter of 2 μm or more. This is because the presence of large particles causes a decrease in spinnability.
[0023]
The fine powder of calcium carbonate is mixed in the resin raw material stage. At this time, if a surfactant such as metal soap is attached to the fine powder in advance, the dispersibility in the resin is improved.
[0024]
The calcium carbonate fine powder may be contained only in the vicinity of the fiber surface. Such a fiber can be obtained by forming a core-sheath type composite fiber having a low MFR polypropylene resin containing calcium carbonate fine powder as a sheath component and a low MFR polypropylene resin not containing calcium carbonate fine powder as a core component. . According to such a structure, the strength of the fiber is ensured in the core portion that does not include the calcium carbonate fine powder, so that a fiber having higher strength than the single fiber made of the polypropylene resin containing calcium carbonate can be obtained.
[0025]
The composite ratio of the core-sheath type composite fiber is desirably a core / sheath = 2/8 to 8/2 in volume ratio. If the ratio of the core component is small, the strength of the fiber is lowered. Moreover, when the ratio which a sheath component accounts is small, content of a calcium carbonate fine powder will decrease and the target effect cannot be acquired.
[0026]
The ratio of the calcium carbonate fine powder contained in the sheath component is determined by how much the specific gravity of the whole fiber is increased. As described above, the effect of increasing the specific gravity is not recognized unless the proportion of the calcium carbonate fine powder in the entire fiber is 2% by mass or more. Therefore, it is necessary to determine the content of fine calcium carbonate powder in the sheath component by calculating from the composite ratio of core / sheath so as to be so. However, if the proportion of calcium carbonate in the sheath component exceeds 20% by mass, fibers cannot be obtained stably. Moreover, if the calcium carbonate fine powder of about 2% by mass is contained in the sheath component, the effect of increasing the specific gravity cannot be obtained, but the effect of improving the hydrophilicity by ion exchange with a specific fiber treatment agent described later is can get. Therefore, the proportion of calcium carbonate in the sheath component is desirably 2 to 20% by mass.
[0027]
The fineness of the cement reinforcing fiber of the present invention is 30 dtex to 80 dtex in either case of single type or composite type fiber. The smaller the fineness, the better the surface smoothness of the cement molded body. However, when using low MFR polypropylene resin, the melt viscosity is low, so the addition to the spinning extruder is large, and fine denier fibers are obtained. Is difficult. On the other hand, the greater the fineness, the better the fiber production efficiency. However, as the fiber becomes thicker, the surface smoothness of the cement molded body is impaired. Therefore, it is desirable that the fineness is within the above range. In particular, the reinforcing fiber of the present invention is suitable for roof tiles that do not require smoothness.
[0028]
The cement reinforcing fiber of the present invention is preferably treated with a fiber treating agent in order to improve the dispersibility in the cement slurry and increase the affinity with the cement composition. The fiber treating agent is preferably a monoalkyl ester or dialkyl ester phosphate salt having a normal alkyl group having 8 to 18 carbon atoms. Further, the normal alkyl phosphate salt is preferably an alkali metal salt such as a sodium salt or a potassium salt. When the fiber to which the fiber treating agent is adhered is introduced into the slurry, ion exchange with calcium ions in the slurry occurs, and the normal alkyl phosphate calcium salt adheres to the fiber surface, improving the hydrophilicity of the fiber.
[0029]
The normal alkyl phosphate salt is desirably deposited in an amount of 0.05 to 10% by mass with respect to the fiber weight. If it is less than 0.05% by mass, the desired effect cannot be obtained sufficiently, and if it exceeds 10% by mass, the effect does not change and it is uneconomical.
[0030]
In addition, when the fiber containing the above-mentioned calcium carbonate fine powder is treated with a normal alkyl phosphate salt, ion exchange between the calcium ions leached from the fiber and the normal alkyl phosphate salt occurs on the fiber surface in the presence of water. Therefore, even when dispersed in fresh water, the dispersibility of the fibers is good, and the fiber floating phenomenon is reduced. In addition, since the calcium ions in the fiber are exchanged, the calcium phosphate calcium salt is more firmly fixed to the fiber surface than in the case where the calcium ions in the slurry are exchanged. The affinity with the composition will be further improved.
[0031]
A phosphate salt may be further adhered to the fiber to which the normal alkyl phosphate alkali metal salt is adhered. By attaching the phosphoric acid salt, the aforementioned ion exchange is further promoted.
[0032]
Examples of the phosphate salt include dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, calcium dihydrogen phosphate, potassium pyrophosphate, sodium pyrophosphate, calcium pyrophosphate, potassium dihydrogen phosphate, Examples include sodium dihydrogen pyrophosphate, potassium metaphosphate, sodium metaphosphate, potassium tripolyphosphate, sodium tripolyphosphate, and the like. In use, only one type may be used, or two or more types may be mixed and used.
[0033]
It is desirable that the phosphate salt is attached in an amount of 1.5 to 25% by mass with respect to the fiber weight. If it is less than 1.5% by mass, the desired effect cannot be obtained, and if it exceeds 25% by mass, the effect remains unchanged and it is uneconomical.
[0034]
The fiber length of the cement reinforcing fiber of the present invention is preferably 3 to 15 mm in consideration of dispersibility in the cement molded body. The fiber of the present invention can be applied to reinforcement of ordinary Portland cement, blast furnace cement, silica cement, alumina cement and the like. It is also applicable when using hemihydrate gypsum, dihydrate gypsum and slag, or a mixture thereof with the above cement. Further, it can be used regardless of the molding method such as extrusion molding method, wet papermaking method, pouring method and the like. As described above, the fiber of the present invention is most suitable when the cement molded body is cured by autoclave, but exhibits an excellent reinforcing effect even when natural curing or steam curing is performed.
[0035]
【Example】
Hereinafter, the present invention will be described by way of examples.
[0036]
In the examples, the physical properties of the polypropylene resin and the physical properties of the cement molded body were evaluated by the following methods.
[0037]
(Melt flow rate (MFR)) Measurement was performed at a temperature of 230 ° C. with a nozzle passing amount (unit: g / 10 minutes, according to JISK7210, load weight 2.169 kg).
[0038]
(Q value) It measured on condition of the following using gel permeation chromatography (GPC).
(A) Measuring device name: Waters (ALC / GPC 150C type)
(B) Packing column: TSK-GER GMH6-HT (high temperature type)
(C) Solvent: Orthodichlorobenzene (ODCB)
(D) Temperature: 135 ° C
(E) Detector: differential thermorefractometer, flow rate: 1 ml / min
[0039]
(N-Heptane Insoluble) 5 g of a polypropylene sample was completely dissolved in 500 ml of boiling xylene, and these were put into 5 l of methanol, precipitated and recovered, dried, and then heated with boiling n-heptane. The time and the ratio of the extraction remainder after Soxhlet extraction were expressed in mass%.
[0040]
(Isotactic pentad fraction) The isotactic pentad fraction (IPF) is the "macromolecules" (Macromolecules, 6, 925 (1973) and 8, 687 (1975)) for n-heptane insoluble matter. Measured according to
[0041]
(Bending proportional limit strength, bending strength) A load was applied to each sample in accordance with JIS A 1408 to obtain a load-deflection diagram. The diagram shows the initial load that rises almost linearly-the load when the deflection line begins to fall (W ₁ kg) and the lowered load-the maximum load after the deflection line rises again (W ₂ kg). The bending proportional limit strength and bending strength were calculated from W ₁ , W ₂ , span (Lcm), sample width (bcm), and sample thickness (dcm) according to the following equations.
Bending proportional limit strength (kg / cm ² ) = 3W ₁ L / 2bd ²
Bending strength (kg / cm ² ) = 3W ₂ L / 2bd ²
[0042]
(Charpy impact strength) The Charpy impact strength was evaluated according to JIS B 7722.
[0043]
Example 1 After melt spinning at 285 ° C. using a polypropylene resin (trade name FL-7, manufactured by Nippon Polychem Co., Ltd.) having an MFR of 1.5, a Q value of 3.5, an HI of 98%, and an IPF of 97%, at 150 ° C. After dry stretching, 0.3% by mass of lauryl phosphate potassium salt was attached and cut to obtain a fiber having an MFR of 1.7, a fineness of 60 dtex, and a fiber length of 6 mm. Next, 1200 g of ordinary Portland cement, 800 g of silica sand, 20 g of methylcellulose, and 10 g of fibers were dry-mixed with a Henschel mixer, 400 ml of water was added, and the raw material obtained by wet mixing was put into an extrusion molding machine to form a cement molded body. Got. The molded body was then autoclaved at 180 ° C. for 10 hours.
As a result, the molded body density was 2.0 g / cm ³ , the bending strength was 2500 N / cm ² , and the Charpy impact strength was 34 N-cm / cm ² .
Only the fibers were autoclaved under the same conditions. The fiber strength was 397 cN before treatment and 353 cN after treatment, and the residual strength was 89%.
[0044]
[Comparative Example 1] MFR18, fineness of 60 dtex, and fiber length of 6 mm were spun in the same manner as in Example 1 except that MFR15 resin was used, and a cement molded body was prepared in the same manner as in Example 1.
As a result, the molded body density was 2.0 g / cm ³ , the bending strength was 2400 N / cm ² , and the Charpy impact strength was 1.2 N-cm / cm ³ .
Only the fibers were autoclaved under the same conditions. The fiber strength was 294 cN before treatment, 0 cN after treatment, and the residual strength was 0%.
[0045]
【The invention's effect】
Since the polypropylene fiber for cement reinforcement of the present invention has a low melt flow rate and a high fineness, it does not easily flow even when exposed to high temperatures, and maintains its fiber form. Even if the surface is melted, it takes a large amount of energy to flow, so it is difficult to flow. Therefore, since the fiber is rich in heat resistance, the superheating temperature can be increased when curing the autoclave. As a result, tobermorite crystals can be formed more efficiently, and an ideal cement board can be obtained.

Claims (4)

Q value (Q; ratio of weight average molecular weight / number average molecular weight) is less than 5, boiling n-heptane insoluble (HI; mass%) is 97 <HI <100, isotactic pentad fraction (IPF; mol%) ) Is 94 <IPF <100, and a polypropylene resin having a fiber strength remaining rate of 70% or more after the autoclave (180 ° C. × 10 hours) treatment is melt-spun, and the melt flow rate (MFR) is 1. A polypropylene fiber for cement reinforcement, having a fineness of 60 to 80 dtex.   2. The polypropylene fiber for cement reinforcement according to claim 1, wherein a core material and / or a lubricant is added in an amount of 2.0% by mass or less. A cement molded body in which the polypropylene fiber for cement reinforcement according to claim 1 or 2 is mixed. A cement molded body, wherein the cement molded body according to claim 3 is a roof tile.