JP3547780B2 - High strength, high modulus polypropylene fiber - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to high strength, high modulus polypropylene fibers .
[0002]
[Prior art]
Examples of reinforcing fibers such as resin composite materials and cement composite materials include organic polymer reinforcing fibers such as aramid fibers and high-strength polyethylene fibers, and inorganic reinforcing fibers such as glass fibers, carbon fibers, and whisker fibers. Among them, the organic polymer-based reinforcing fibers are excellent in that they have a lower density than the inorganic reinforcing fibers and can reduce the weight of the composite material. Polypropylene fiber is also known as a general-purpose material together with polyethylene fiber, and has higher heat resistance than polyethylene fiber, so if it has high strength and high elastic modulus, it can be used as an organic polymer-based reinforcing fiber. is there.
[0003]
For high-strength, high-modulus polypropylene fibers, see, for example, Journal Applied Polymer Science Vol. 28, p. 179 to 189 (1983), polypropylene was melted and extruded from a nozzle and cooled while being wound at an appropriate draft ratio to form a highly oriented crystalline undrawn yarn. The undrawn yarn was thermally drawn and molecular chains in the lamella crystal. It has been reported that a polypropylene fiber having a tensile strength of 0.76 GPa (gigapascal) and a tensile modulus of elasticity of 17.2 GPa can be obtained by unfolding the fiber and unfolding the fiber so that the molecular chain is elongated in the fiber axis direction.
[0004]
However, polypropylene fibers generally have poor adhesion to a matrix in a composite material, and the following (1) to (5) have been proposed as typical methods for improving the adhesion.
{Circle around (1)} Gypsum needle-like crystal fiber is mixed with polypropylene, melt-spun, drawn, and gypsum is projected on the fiber surface. (Japanese Patent Publication No. 57-8790)
(2) A polymer having a lower melting point than the reinforcing fibers is used as the matrix, and the matrix is thermally fused to the reinforcing fibers. (Japanese Patent Publication No. 4-4148)
{Circle around (3)} Spinning using a solvent, evaporating the solvent in the spun fiber to form a void on the fiber surface, and stretching the void by stretching to form a vertically elongated groove. (JP-A-60-174646)
{Circle over (4)} The surface of the reinforcing fiber is treated with a polyolefin containing an epoxy group or a carboxylic acid group. (JP-A-60-174646)
{Circle around (5)} The surface of the reinforcing fiber is subjected to plasma treatment or corona discharge treatment to form irregularities on the fiber surface. (JP-A-57-177032, JP-A-60-146078, JP-B-53-794, JP-B-58-5314)
[0005]
[Problems to be solved by the invention]
However, these methods have the following problems. That is, in (1), thread breakage easily occurs during thermal drawing, in (2), it is difficult to obtain good mechanical properties due to insufficient adhesion, and in (3), it is difficult to obtain good mechanical properties due to the residual solvent. In the case of (4), the matrix is limited, and in the case of (5), sufficient mechanical strength is hardly obtained due to a decrease in strength.
An object of the present invention is to provide a high-strength, high-modulus polypropylene fiber excellent in adhesion to a matrix in a composite material by melt spinning and hot drawing of polypropylene by solving such problems.
[0006]
[Means for Solving the Problems]
The present invention is a solid fiber without a hollow portion having a large number of micropores having an average pore size of 0.05 to 2 μm and a porosity of 20 to 90% on the fiber surface, and has a breaking elongation of 5 to 11%, A high-strength, high-modulus polypropylene fiber having a fiber diameter of 1 to 500 µm and a tensile strength of 0.5 to 0.8 GPa and a tensile modulus of 5 to 6 GPa .
[0007]
The polypropylene fiber of the present invention has a large number of micropores on the fiber surface, and the average pore diameter of the formed micropores is 0.05 to 2 μm. If the pore size is less than 0.05 μm, the adhesion to the matrix is insufficient, and if it exceeds 2 μm, the fiber strength is reduced. In addition, the micropores are present on the fiber surface by being opened, and the matrix and the polypropylene fiber of the present invention are firmly adhered to each other by the anchor effect of the opened micropores. In order to secure such adhesiveness, the open ratio of the micropores on the fiber surface, that is, the ratio of the total surface area occupied by the micropores to the fiber unit surface area is 20 to 90%, preferably 25 to 80%. There is a need. If the porosity is less than 20%, the adhesion to the matrix is insufficient, and if it exceeds 90%, the strength maintenance of the fiber becomes insufficient.
[0008]
The shape of the micropores is not particularly limited, but is preferably an elliptical shape or a slit shape extending in the fiber axis direction from the viewpoint of adhesion to the matrix.
[0009]
In the polypropylene fiber of the present invention, the micropores may also be present inside the fiber, and the distribution of the micropores is a solid fiber having no hollow portion from the viewpoint of securing the mechanical strength of the fiber. In this case, the micropores have a depth of 0.2 to 5 μm, preferably 0.2 to 2 μm from the fiber surface , and a nonporous portion and micropores in the center of the fiber cross section where no micropores are present. the ratio of the porous portion, of the fibers by existing distributed in a surface layer region ranging from 60 to 99.92% by the ratio of the non-porous portion radius r ₁ with respect to the fiber radius r ₂ as shown in Figure 1 machine The target strength is secured.
[0011]
The polypropylene fiber of the present invention has a breaking elongation of 5% or more and 11% or less, a tensile strength of 0.5 GPa or more and 0.8 GPa or less , and a tensile modulus of 5 GPa or more and 6 GPa or less. Has useful and effective mechanical properties.
[0012]
The form of the polypropylene fiber of the present invention is not particularly limited, except that it is a solid fiber having no hollow portion in a range of 1 to 500 μm, preferably 3 to 400 μm as an effective diameter for application as a reinforcing fiber, Further, the cross-sectional shape may be not only circular but also other than circular.
[0013]
The method for producing the polypropylene fiber of the present invention will be described below.
Isotactic polypropylene used to produce polypropylene fibers must have a melt flow index (MI value) in the range of 0.05 to 30. If the MI value is less than 0.05, the melt viscosity is too high and it is difficult to spin stably when obtaining fibers. If the MI value is more than 30, the melt viscosity is low and insufficient cooling occurs, resulting in stable spinning. Is difficult. The MI value is represented by a nozzle passing amount (unit: g / 10 min, load: 2.169 kg) at a temperature of 190 ° C. according to JIS K7210.
[0014]
Further, the isotactic polypropylene preferably has a tacticity of 96% or more. Here, the tacticity is a physical quantity indicating the degree of the arrangement of the side chain methyl group, and the macromolecules (Macromolecules) Vol. 6, p. 925 (1973) and Vol. 8, p. 687 (1975).
[0015]
Isotactic refers to an arrangement in which the side-chain methyl groups are arranged in the same direction. The higher the tacticity, the higher the crystallinity of the polymer. When a polymer having a tacticity of less than 96% is used, fine pores are not formed on the surface of the drawn fiber. Tacticity of 96% or more corresponds to crystallinity of 50% or more. Polymer Handbook, Willy, New York, 1975; Crystalline portion density 0.936 g / cm ³ according to V-23, the use of amorphous portions density 0.850 g / cm ^3, a crystallinity of 50% or more, corresponds to the mean density 0.890 g / cm ^3. The density of the polypropylene in the present invention indicates the average density, and it is necessary that the density is 0.890 g / cm ³ or more.
[0016]
In the present invention, the specific polypropylene is melt-spun using a nozzle for producing a solid fiber to prepare a highly oriented crystalline undrawn fiber.
[0017]
In order to stably obtain the polypropylene fiber of the present invention, the spinning temperature is desirably set to a temperature 30 to 80 ° C. higher than the melting point of the polymer. When spinning is performed at a temperature lower than this temperature range, the melting of the polymer is incomplete and melt fracture is likely to occur, and the stability in the drawing process is reduced. It is difficult to form holes.
[0018]
The polymer discharged from the nozzle is taken at a spinning draft ratio of 200 to 2,000 and is made into an undrawn fiber. At the time of drawing, if the spinning draft ratio is less than 200, highly oriented undrawn fibers cannot be obtained, and it is difficult to form micropores even when drawn. If the spinning draft ratio exceeds 2,000, the total draft exceeds 300%. Unstretched fibers capable of obtaining the amount of stretching cannot be obtained.
[0019]
The obtained undrawn fiber has a structure in which the crystal plane of the lamella crystal is perpendicular to the fiber axis and the lamella crystal is highly oriented and laminated. In order to make the oriented laminar structure of the lamella structure more complete, it is effective to subject the undrawn fiber to a heat treatment called an annealing treatment at 120 to 160 ° C., preferably 140 to 155 ° C. for 3 minutes or more. It is.
[0020]
In the present invention, the undrawn fiber prepared as described above can be drawn by any of the following methods.
(A) Cold stretching is performed, followed by hot stretching.
(B) Only hot stretching is performed without performing cold stretching.
[0021]
In the cold stretching in the method (a), the crystal structure is broken and microcraze is generated. In order to generate microcraze without causing crystal relaxation due to thermal vibration of the molecular chains in the crystal lamella, the temperature in the cold stretching is desirably 40 ° C. or lower. The cold stretching is preferably performed so that the stretching amount is 1 to 100%. After performing such cold stretching, hot stretching is performed. The hot stretching is preferably performed at 120 to 160 ° C. When the temperature in the hot stretching is lower than 120 ° C., the pore diameter becomes less than 0.05 μm, and the porosity becomes less than 20%, so that the desired micropores are formed. On the other hand, when the temperature exceeds 160 ° C., the fiber becomes transparent, and it becomes difficult to form desirable micropores. The heat stretching may be performed in only one step or in two or more steps, but the deformation speed is set to be more than 30% per minute, preferably more than 35% per minute in all the steps. . If the deformation rate is 30% or less per minute, holes are opened from the fiber surface to a deep region exceeding 5 μm, and the fiber strength is reduced.
[0022]
In the method (b), the thermal stretching is preferably performed at a thermal stretching temperature of 120 to 160 ° C., similarly to the method (a), and is performed in two or more stages. It is set so as to exceed 30% per minute, preferably, the first stage is set so that the deformation speed exceeds 30% per minute, and the second and subsequent stages are set so that the deformation speed exceeds 35% per minute. . In addition, the deformation rate at the time of the hot drawing in the present invention is a value obtained by dividing the drawing amount (%) in the drawing section by the time during which the fiber passes through the drawing section.
[0023]
In the present invention, the total amount of stretching is required to be 300% or more, preferably 500% or more, including the case where cold stretching is performed, in order to form micropores. However, since the elongation at break decreases with an increase in the total elongation, the upper limit of the total elongation is about 1000% in order to attain elongation at break of 5% or more.
[0024]
The heat-drawn fiber is a fiber whose stability in shape is almost secured and does not necessarily require a heat set for fixing a structure having a large number of micropores. In the same temperature range as the temperature, heat setting is performed while the length is fixed or contracted under stress.
[0025]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples.
[0026]
(Example 1)
An isotactic polypropylene having a tacticity of 98.8% and an MI value of 8 is discharged at a spinning temperature of 230 ° C. from a spinning nozzle having a hole diameter of 5 mm attached to a plunger type extruder, and in a 25 ° C. air under a 100 cm air gap. Thus, an undrawn fiber wound at a spinning draft ratio of 200 was obtained. This undrawn fiber was heat-treated in heated air at 145 ° C. for 8 hours. Next, after performing 40% cold stretching with respect to the initial length at room temperature, the deformation rate in each stage of the hot stretching was set to 50% per minute in five heating boxes heated to 140 ° C. The film was stretched to a total stretching amount of 300%.
[0027]
Subsequently, it was heat-set at a constant length for 1 minute in a heating box heated to 150 ° C. to obtain a drawn fiber. The obtained fiber has a diameter of 41 μm, and micropores having a minimum pore diameter of 0.5 μm, a maximum pore diameter of 0.7 μm, and an average pore diameter of 0.6 μm as measured by a mercury intrusion method are present on the fiber surface at an opening ratio of 40%. According to the electron microscopic observation of the fiber cross section, micropores were distributed from the fiber surface to the 1.5 μm layer, and the ratio of non-porous portion radius r ₁ / fiber radius r ₂ was 0.93. The fiber had a breaking elongation of 10%, a tensile strength of 0.7 GPa, and a tensile modulus of 6 GPa.
[0028]
(Example 2)
The undrawn fiber obtained in Example 1 was cold drawn at room temperature by 40% with respect to the initial length, and then the deformation rate at the time of hot drawing of each stage in 11 heating boxes heated to 140 ° C. per minute It was set to 32%, and it was drawn to a total drawing amount of 300% in 11 steps of drawing to obtain a drawn fiber. The obtained fiber had a diameter of 45 μm, and micropores having an average pore diameter of 0.4 μm as measured by a mercury intrusion method were present on the fiber surface at an opening ratio of 40%. Micropores were distributed throughout the cross section, and the ratio of the total micropore cross sectional area to the fiber cross sectional area was 40%. Further, this fiber had a breaking elongation of 10%, a tensile strength of 0.8 GPa, and a tensile modulus of 6 GPa.
[0029]
(Example 3)
In Example 1, a drawn fiber was obtained in the same manner as in Example 1, except that the undrawn fiber was not cold drawn after the heat treatment. The obtained fiber has a diameter of 45 μm, and micropores having a minimum pore diameter of 0.2 μm, a maximum pore diameter of 1 μm, and an average pore diameter of 0.6 μm as measured by a mercury intrusion method are present on the fiber surface at an opening ratio of 40%, According to electron microscopic observation on the fiber cross section, micropores were distributed from the fiber surface to the 1.5 μm layer, and r ₁ / r ₂ was 0.93. In addition, this fiber had an elongation at break of 11%, a tensile strength of 0.8 GPa, and a tensile modulus of elasticity of 6 GPa.
[0032]
( Example 4 )
After the undrawn fiber obtained in Example 1 was cold drawn at room temperature by 100% with respect to the initial length, the deformation rate at the time of heat drawing of each stage in 11 heating boxes heated to 140 ° C. per minute It was set to 60%, and it was drawn to 11% of the total amount of drawing by 300% to obtain a drawn fiber. The obtained fiber had a diameter of 30 μm, and micropores having an average pore diameter of 0.06 μm as measured by a mercury intrusion method were present on the fiber surface at an opening ratio of 45%. Micropores were distributed throughout the cross-section, and the ratio of the total cross-sectional area of the micropores to the cross-sectional area of the fibers was 50%. Further, this fiber had a breaking elongation of 10%, a tensile strength of 0.8 GPa, and a tensile modulus of 6 GPa.
[0033]
(Comparative Example 1)
After the undrawn fiber obtained in Example 1 was cold drawn at room temperature by 100% with respect to the initial length, the deformation rate at the time of heat drawing of each stage in 11 heating boxes heated to 140 ° C. per minute A drawn fiber was obtained in the same manner as in Example 1 except that the drawing was performed at 5% and the total drawing amount was 500% in 11 steps. The obtained fiber has a diameter of 40 μm, and micropores having a minimum pore diameter of 0.01 μm, a maximum pore diameter of 0.03 μm, and an average pore diameter of 0.02 μm as measured by a mercury intrusion method are present on the fiber surface at an opening ratio of 85%. According to electron microscopic observation of the fiber cross section, micropores were distributed over the entire fiber cross section, and the ratio of the total micropore area to the fiber cross sectional area was 95%. The fiber had a breaking elongation of 10%, a tensile strength of 0.0058 GPa, and a tensile modulus of 0.058 GPa.
[0034]
【The invention's effect】
The polypropylene fiber of the present invention is a fiber having a high strength and a high elasticity while being lightweight, because it has a large number of micropores opened on the fiber surface and is porous in addition to the original low specific gravity. It is extremely useful as a reinforcing fiber having excellent adhesion to a wide range of matrices such as resin, cement, and other composite materials such as resin composite materials and cement composite materials. The fiber is less damaged even by an instantaneous impact on the fiber, and has a high function-maintaining property as a reinforcing fiber.
[Brief description of the drawings]
FIG. 1 is an enlarged schematic cross-sectional view of an example of a polypropylene fiber of the present invention.
[Explanation of symbols]
1 Micropore 2 Non-porous part r ₁ Non-porous part radius r ₂ Fiber radius

Claims (1)

It is a solid fiber without a hollow portion having a large number of micropores having an average pore diameter of 0.05 to 2 μm and a porosity of 20 to 90% on the fiber surface, and has a breaking elongation of 5 to 11% and a A high-strength, high-modulus polypropylene fiber having a fiber diameter of 1 to 500 µm and a tensile strength of 0.8 GPa and a tensile modulus of 5 to 6 GPa .

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