JPH0672326B2 - Method for producing acrylic conjugate fiber having excellent crimp developability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for producing an acrylic conjugate fiber having excellent crimp-developing properties, particularly two or more kinds of acrylic polymers having different copolymerization compositions ( Hereinafter, the present invention relates to a method for producing an acrylic composite fiber by making a multilayer composite of an acrylic polymer).

[Prior Art] Conventionally, a composite fiber obtained by joining two or more kinds of acrylic polymers in a bimetal shape or a core-sheath shape with a composite spinneret has a unique and excellent structural crimp expression ability and therefore is used for clothing or Widely used in various fields such as futon cotton.

However, in this type of composite fiber, uneven dyeing due to the difference in the type and composition of the polymer and peeling between the composite polymers are likely to occur. Further, in order to obtain a composite fiber yarn having high bulkiness, it is generally necessary to increase the number of crimp occurrences,
Since the crimping degree does not increase in proportion to the number of crimps, the texture of the yarn tends to be hard, which is a drawback of the composite fiber product.

Furthermore, in terms of spinning technology, the spinneret equipment becomes more expensive as the spinneret structure becomes more complicated, which makes it difficult to manufacture composite fibers with a particularly fineness with high productivity. Furthermore, the composite state of the resulting composite fibers is relatively uniform. For this reason, there was a problem in that this warped only a material far from the texture of wool.

For such a conventional bimetallic or core sheath composite fiber, Japanese Patent Laid-Open Nos. 51-70322 and 51-75151 are available.
According to Japanese Patent Laid-Open Publication No. 2000-242242, a multi-layered composite fiber is proposed in which two or more stock solutions of acrylic polymers are introduced into a multi-layering device to be layer-divided, and then spun through a spinneret hole. It is said that the composite fiber suppresses the occurrence of yarn unevenness in the spun yarn or its product, and that the bulkiness becomes uniform.

However, the multilayer conjugate fiber obtained by such means is
Although the mixed spinning unevenness and bulkiness with other types of fibers are improved to some extent compared with conventional composite fibers, if the layer division in the multi-layering device becomes excessive, the peculiar cross-sectional structure and physical properties of the fibers are retained. The reason is that the theoretical number of layers in a single yarn (multilayering coefficient), which represents the statistical average number of inflow stock layers per single yarn, that is, per spinning hole of the spinneret, is 1.0 to
It was as low as 2.0, or in the range of 0.05 to 0.5.
For this reason, a large amount of fibers composed of a single-component polymer, that is, a single-component polymer among composite polymers, is mixed in the fibers. That is, since the layered composite of two or more polymer components is not sufficient, it is difficult to obtain desired crimp characteristics, and the crimp characteristics fluctuate remarkably. This tendency was more remarkable as the difference in copolymerization composition between the composite polymers was increased and the heat treatment temperature was increased to improve the crimping property. Moreover, as described above, when the mixing ratio of the single fiber composed of only one-component polymer in the composite polymer increases, naturally, uneven crimping characteristics and uneven dyeing occur, and thus the conventional multi-layer composite fiber is improved. Still had many problems.

[Problems to be Solved by the Invention] While the inventors of the present invention have been earnestly studying to solve the above-mentioned drawbacks in the conventional multilayer composite fiber, the increase in the number of logical layers in a single yarn in the multilayer composite fiber is generally increased. In the state of mixed spinning from composite structure (finally completely mixed like a single polymer,
(It does not become a composite fiber), and it is expected that it will be difficult to maintain the cross-sectional structure and physical characteristics peculiar to the composite fiber, but the distribution state of the spinning solution to be composited, the stabilization of the multilayer state in the multilayering device, Strictly controlling each process requirement such as the crimp expression method after dry densification of the fiber yarn has sufficient properties (especially, crimp expression ability) necessary for the composite fiber and the conventional composite. We found that the problems of fibers can be solved, and made a proposal earlier (Japanese Patent Application No. 62-170742).

In order to further improve the bulkiness of the final product, the present inventors have been investigating the relationship between mechanical crimping after dry densification and crimp development state, and among the two or more kinds of component polymers proposed above, Mechanical crimping after drying and densification is performed to improve crimp expression of a multi-layer composite fiber in which one-component polymer and another component polymer are laminated to form a multi-layer laminated structure in which the component polymer is continuous along the fiber axis direction. The inventors have found that the applying step and the crimp development processing step are very important, and have arrived at the present invention.

That is, an object of the present invention is to provide an industrial production method for improving the crimp expression of the acrylic multi-layered composite fiber and further improving the bulkiness and feel of the composite fiber product.

[Means for Solving Problems] An object of the present invention is to spin two or more acrylic polymers having different copolymer compositions and having a difference in the amount of the copolymer components of 1 to 10 mol%. The stock solution is layer-divided so that the number of theoretical layers in a single yarn represented by the following formula (1) is 3 or more, and is introduced into a spinneret through a filter having an opening of 10 μ or more to form a yarn,
Next, after drawing, washing with water, and drying and densification, the yarn is preheated under atmospheric pressure steam to give a mechanical crimp with a crimp number of 7 to 15 threads / 25 mm,
This can be achieved by a method for producing an acrylic composite fiber having excellent crimp-developing properties and level dyeing properties, which is characterized by performing a crimp-developing process, and then performing a re-drawing process and a mechanical crimp.

In the formula, K is a constant determined by the outer shape of the spinneret.

That is, as the acrylic polymer in the present invention,
Acrylic polymer having known fiber-forming property, namely, 30
A modacrylic polymer containing mol% or more of acrylonitrile (hereinafter, abbreviated as AN), an acrylic polymer containing 80 mol% or more of AN, and a copolymer thereof may be used, but are not particularly limited. When two or more kinds of polymers are selected as the composite polymer in the multi-layer composite fiber from the viewpoint of crimping property and level dyeing property, the difference in the amount of the copolymerization component between the polymers is about 1 to 10 mol%, preferably 1 to 5 mol. % Is what is meant. If the difference in the amount of copolymerization is less than 1 mol%, the crimp developability in boiling water tends to decrease, while
If the amount is more than mol%, the level dyeing property of the fiber tends to be deteriorated, and the crimp-developing property suitable for the soft texture of animal hair tends to be difficult to obtain.

The acrylic polymer copolymerization component includes, for example, acrylic acid, methacrylic acid and their lower alkyl esters, itaconic acid, acrylamide, methacrylamide, vinyl acetate, vinyl chloride, styrene, vinylidene chloride, and other vinyl-based compounds. In addition to the compounds, unsaturated sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, p-styrene sulfonic acid and the like, and same or different kinds of acidic monomers such as salts thereof can be used.

Further, the acrylic polymer includes acrylonitrile-styrene copolymer, cellulose acetate, methyl methacrylate-based polymer and the like in an amount of about 1 to 10% by weight based on the total polymer.
Preferably, if they are made to coexist in an amount of 2 to 5% by weight, it is possible to obtain a composite fiber having a water absorption performance due to the microporosity of the fiber.

The above acrylic polymers are dimethylformamide, dimethylacetamide, dimethylsulfoxide (hereinafter DMSO).
Abbreviated as), and rhodan lithium, potassium rhodan, sodium rhodan, and other alkali metal rhodan salts, rhodan ammonium, zinc chloride, perchlorate, etc. Use a spinning dope of 25% by weight. The spinning stock solution of two or more polymers to be composited is supplied to a multi-layering device to be layer-divided, and then discharged from a normal spinneret hole into a coagulation bath, or once air or air is discharged from the spinneret hole. After being discharged into an inert atmosphere, it is made into fibers by a dry-wet spinning method of introducing into a coagulation bath.

FIG. 3 is a flow sheet for explaining the process requirements at the yarn making stage of the present invention. In the figure, A and B are composite polymer spinning stock solutions, 1 is a guide device for individually introducing the composite polymer spinning stock solution, 2 is a multi-layering device, 3 is a filter, 4 is a spinneret, 5 is mechanical crimp Applying device (crimper), 6 is a crimp developing device for fiber yarns, 7 is a re-drawing device for temporarily removing the crimps developed by the crimp developing device 6, and 8 is a mechanical crimping device (crimper) Is.

In this method of the present invention, it should be particularly noted that the spinning solution of the composite polymer is sufficiently and stably layer-divided by the multi-layering device, and the obtained multi-layered state is stably maintained until it reaches the spinneret hole. It is to be.

That is, in order to achieve sufficient multi-layering in a multi-layering device, the number of theoretical layers in a single yarn is divided into 3 or more, preferably 4 to 15, more preferably 5 to 12, and then a single spinning spinneret is formed. It is to introduce.

The number of theoretical layers in the single yarn may be appropriately controlled by the structure in the multi-layering device, that is, the number and arrangement of the multi-layering elements, the twisting angle of the twisting blade, the number of passage tubes, the number of holes in the spinneret, and the like. .

The theoretical number of layers in a single yarn here refers to the statistical average number of undiluted liquid layers per spinning hole of the spinneret, and in the complete laminar basin, the theoretical value of the number of layers considered to be theoretically possible in a single fiber. Then, it can be obtained by the following equation.

In the above formula, K is a constant determined by the outer shape of the spinneret, and the square spinneret has a K value of 1, and the circular spinneret has a K value of 1.1.

Next, in order to stably form the spinning solution of the composite polymer in the multi-layering device, the viscosity difference between the spinning solutions at 60 ° C.
It is preferably 50 poises or less, more preferably 20 poises or less at 60 ° C. By setting this viscosity difference to 50 poise or less, the streamline is less likely to be disturbed in the multi-layering device, and the multi-layered state divided into layers becomes more stable.

When supplying the spinning dope to the multi-layering device, the spinning dope to be combined is not once joined and then supplied to the multi-layering device, but two or more kinds of spinning dope to be combined are not mixed with each other. As shown in FIG. 2, it is desirable to individually introduce the liquid by means of a stock solution guide device (inlet) provided at the inlet of the multi-layer device. Such an inflowing means of the spinning dope is completely different from the effect of reducing the number of the multi-layering elements by one, and surely and stably performs the multi-layering in the multi-layering device.

Further, in the multi-layering apparatus, it is desirable that the pitch (L / D) of the multi-layering elements is within the range of 0.8 to 2.5, particularly 1.4 to 2.0, as shown in FIG. If this pitch deviates from 0.8 to 2.5, the streamlines of the spinning dope that are multi-layered in the multi-layering device are disturbed and are easily mixed, and the multi-layered state tends to be unstable.

Examples of the multi-layering device used here include “High Mixer” manufactured by Toray Industries, Inc., “Static Mixer” manufactured by Noritake Co., Ltd., “Sukeya Mixer” manufactured by Sakura Seisakusho Co., Ltd.,
"Loss ISG mixer" manufactured by Tokushu Kako Kikai Co., Ltd. can be mentioned. Among these multi-layering devices, the constituent elements are not complicated, the flow resistance of the spinning dope is relatively small, and the effective cross-sectional area in the spinning dope flow path is little changed. In other words, the spinning dope stays abnormally inside the device. "Static mixer" and "Sukeya mixer" which are less likely to cause are preferably used.

The spinning stock solution that has been layer-divided into a predetermined range by the multi-layering device,
Although the conventional single spinneret is used, in the present invention, it is essential to interpose a specific filter between the multi-layering device and the spinneret. That is, a filter having an opening of 10 μm or more, preferably 20 to 50 μm is used for this filter. The smaller the mesh size of this filter, the better the filter effect or spinnability of the spinning dope, but on the other hand, the spinning dope can maintain the layer division by the above-mentioned multi-layering device due to the mixing or disturbing effect of the filter. Disappear. Therefore, the aperture of the filter should be 10μ or more.

The filter material of this filter is preferably a gauze fabric such as polyester or polyamide, or a lattice-like material such as a stainless wire mesh, mainly for the purpose of preventing mixing or disturbance after the above-mentioned layer division.

The above spinning dope which has passed through the filter is distributed to a single spinneret hole and discharged into a coagulation bath using an aqueous solution of the organic solvent or the inorganic solvent as a coagulant.

At that time, the polymer solution discharged from the spinneret may be directly introduced into the coagulation bath (wet spinning method), or the spinneret may be provided at a position of about 2 to 20 mm above the surface of the coagulation bath and the spinneret hole The so-called dry-wet spinning method may be used in which the spinning dope discharged from the vessel is made to travel in a minute space between the spinneret hole and the surface of the coagulating liquid, and then introduced into the coagulating bath.

The coagulated filaments drawn out from the coagulation bath are subjected to treatments such as washing with water or drawing at the same time as washing with water, stretching after drawing, washing with water, or drawing after washing with water, and then dried and densified.

Next, it is necessary to mechanically crimp the dried and densified yarn with a mechanical crimping device (crimper) prior to the subsequent crimping treatment and re-stretching treatment.

In this case, the number of mechanical crimps is 7 to 15 threads / 25 mm, preferably 9
~ 13 peaks / 25 mm. 15 crimps / 25mm
If the amount is larger, the number of crimps suitable for the bulkiness of the final product will be exceeded in the subsequent crimp development treatment step, and the texture will tend to be hard. On the other hand, if the number of mechanical crimps is less than 7 ridges / 25 mm, the crimp developability due to "pulling" in the subsequent crimp revealing process is poor, and the fiber movement does not proceed smoothly and the tension load is not uniform. This is not preferable because unevenness occurs, the number of crimps developed is small, and the bulkiness and soft feeling of the final product tend to be difficult to obtain. By applying a mechanical crimp within this proper range and then performing crimp development treatment, the bulkiness and texture of the final product will be further enhanced compared to conventional side-by-side type composite fibers and multilayer type composite fibers. An improved multi-layer composite fiber is obtained.

In order to impart the above mechanical crimp, a stuffing box type crimper (so-called push type crimper) or a gear type crimper which is generally used may be used. Further, in order to impart mechanical crimp sufficiently and easily, it is desirable to continuously preheat the dried and densified yarn under normal pressure steam of 65 to 90 ° C, preferably 70 to 80 ° C. At this time, when preheated at a temperature higher than 90 ° C., the fibers become soft and the fibers tend to stick to each other due to the pressure during mechanical crimping.
If the temperature is less than 5 ° C, it is difficult to apply mechanical crimp, so if the crimping conditions are tight and the crimp is forcibly applied, the fiber tends to be damaged.

The crimping conditions for applying mechanical crimp are as follows: tow density (D / W) 6.5 to 100,000 denier / cm, roller nip pressure 1.0
~4.0kg / cm ^2, is generally performed in the range of stuffing pressure 0.5~3kg / cm ^2.

Next, the crimp development treatment is performed under steaming in a relaxed state, and the steaming heat treatment temperature at that time is preferably 105 ° C. or higher, particularly 108 to 125 ° C. By this steaming treatment, the latent crimp of the fiber yarn can be sufficiently developed.

The re-stretching treatment is carried out to make latent the crimps sufficiently developed by the crimp developing treatment, but the re-stretching condition is that the temperature is lower than the heat treatment temperature in the crimp developing treatment time. It is desirable to re-stretch,
Usually, under wet or steam heat of 80 to 115 ℃, draw ratio 1.05 to 1.
It is generally set to 25 times the range.

Further, the yarn after the re-drawing treatment is further mechanically crimped in order to improve the entanglement property of the web or the sliver in the carding or knitting yarn in the subsequent spinning step. In this case, the number of mechanical crimps is 7 to 15 threads / 25 mm, preferably 9 to 13 threads / 25 mm
However, other conditions for applying mechanical crimps may be based on the mechanical crimps applied to the dried and densified yarn.

As described above, in the present invention, in addition to the above-described multilayer structure of the composite polymer, mechanical crimping-latent crimp expression treatment-
For the first time, by further integrating the re-drawing treatment (hidden crimping) -the mechanical crimping process, the crimping properties of the multi-layer composite fiber, especially the crimping ability in the step of commercializing the fiber is further improved. Can be done.

Hereinafter, the present invention will be described in more detail with reference to Examples.

In this example, the level dyeing degree, the number of crimps after the boiling water treatment, the degree of crimp, the variation rate of the number of crimps, and the feel were determined as follows.

Level dyeing: A standard fiber and a test fiber are dyed in the same bath using a package dyeing machine with the following three dyes having different dyeing speeds at 100 ° C. for 60 minutes.

Staining conditions: Astrazon Golden Yellow GL 1.0% owf Maxilon Red 0.5owf Malachite Green 0.22% owf Cationogen L 0.5% owf Sodium acetate 0.5% owf pH = 4 2g of each dyed fiber bundle was collected and 102m
After cutting to m, the color difference and density difference of the opened cotton are visually judged in 0.2 steps under daylight, and the dye difference between the maximum and minimum values of color and density is evaluated as the level dyeing degree. It is best that there is no difference in dyeing, and if it is 2.0 or more, uneven dyeing in the fiber bundle can be clearly seen.

The standard fiber here is a fiber obtained by mixing a spinning polymer obtained by mixing composite polymers having different copolymerization compositions almost completely like a single polymer under the same spinning conditions as the fiber of the present invention. .

Number of crimps and degree of crimp after boiling water treatment: According to JIS-L1015.

The rate of crimp number variation (%), which represents the variation in the number of crimps, is calculated by the following equation.

However, σ; standard deviation; average value Feeling: 4th spun roving yarn was prepared from the test fiber. This roving is bulked in steam (100 ° C x 10 minutes),
After drying, the bulkiness and softness were evaluated by sensory evaluation. This was used as a measure of the bulkiness after dyeing of the spun yarn (crimp expression under constraint) and the softness.

⊚: Very good ○: Good Δ: Slightly good ×: Poor XX: Very poor Example 1 AN95.4 mol%, methyl acrylate 4.3 mol% and sodium methallylsulfonate 0.3 mol% in DMSO Solution polymerization was carried out to prepare a spinning dope (A) having a solution viscosity of 128 poise / 60 ° C. and a concentration of 22.3% by weight.

On the other hand, AN91.7 mol%, methyl acrylate 8.0 mol% and sodium methallylsulfonate 0.3 mol% were similarly solution polymerized, and the solution viscosity was 123 poise / 60 ° C and the polymer concentration was 22.1 wt% (B). Was produced.

"Static mixer" (pitch diameter L / D1.5 of multi-layered element) equipped with a stock solution inlet guide device 1 as shown in Fig. 3 in which equal amounts of the above two spinning stock solutions (A) and (B) are used. , And after layer separation, through a polyester gauze fabric filter (opening: about 30μ) provided immediately near the spinneret,
By shape single spinneret towards a pore size of 0.055 mm ^phi (hole number 56,000H), and the discharge-coagulated yarn in a coagulation bath to 55 wt% of DMSO solution and the coagulating liquid.

At this time, the number of stacked layers of the multilayer element is controlled to
The number of theoretical layers in a single yarn as shown in the table was used.

The spinning draft was 0.48, and the take-up speed (spinning speed) of the solidified yarn was 10 m / min.

The coagulated yarn was drawn 6.4 times in hot water at 98 ° C, the drawn yarn was thoroughly washed with warm water, and then dried and densified at 160 ° C.

This dried and densified yarn is preheated under atmospheric pressure steam (the yarn temperature is 75 ° C), and after being mechanically crimped with a crimping type crimper with 12 crimps / 25 mm, it is guided to a crimp developing machine at 113 ° C. Was subjected to crimp development treatment in a relaxed state in pressurized steam.

Next, the yarn after the crimping expression treatment is heated at a steaming temperature of 101 ° C.,
Re-stretch at a draw ratio of 1.16 to eliminate crimps, and to improve entanglement during spinning, push-down crimper 11-12 threads / 2
A mechanical crimp of 5 mm was applied and dried with hot air at 70 ° C. to obtain an acrylic composite fiber having a single fiber fineness of 2 denier.

The number of crimps after the boiling water treatment, the degree of crimps, the rate of change in the number of crimps, the degree of uniform dyeing, and the feel of the obtained fibers were examined and shown in Table 1.

As the results show, the fibers produced by the method of the present invention have a high number of developed crimps and a high degree of crimp, and feel (bulkiness and softness).
It is found that the dyeing properties are excellent and the leveling property at the time of dyeing is also good.

Example 2 In Example 1, the polymerization time and the polymer concentration at the time of preparing the spinning dope were controlled, and the solution viscosity difference from the spinning dope (A) was changed as shown in Table 2. Otherwise, in the same manner as in Example 1, an acrylic multilayer composite fiber having a single fiber fineness of 2 denier was obtained (however, in this case, the number of theoretical layers in the single yarn is 8.
7).

The number of crimps, the degree of crimping, the fluctuation rate of crimping number, the degree of uniform dyeing, and the feeling of the obtained fibers were examined and shown in Table 2.

Example 3 In Example 1, the opening diameter of the stainless wire mesh filter was changed as shown in Table 2, and the crimp development treatment temperature was changed to 114 ° C. Except for this, a composite fiber having a single fiber fineness of 2 denier was obtained in the same manner as in Example 1 (however, the theoretical number of layers in the single yarn in this case was 8.7).

In this case, the spinnability (spinnability) and the number of crimps after the boiling water treatment of the obtained fibers, the degree of crimping, the fluctuation rate of the number of crimps, the degree of dyeing, and the feel were examined and shown in Table 3. .

Example 4 In Example 1, a dry densified yarn was subjected to a preheating temperature of 77 ° C., a tow density of a push-in type crimper, a roller nip pressure,
By controlling the stuffing pressure and the like, the number of mechanical crimps was changed as shown in Table 3, and crimp development treatment was performed. Except for this, a composite fiber having a single fiber fineness of 2 denier was obtained in the same manner as in Example 1 (however, the theoretical number of layers in the single yarn in this case was 8.7).

The number of crimps after the boiling water treatment of the obtained fibers, the degree of crimp, the fluctuation rate of the number of crimps, the degree of dyeing, and the feel were examined and shown in Table 4.

As is clear from these results, the multilayer conjugate fiber according to the method of the present invention can be made latent by the occurrence of crimps in the crimp expression treatment step by imparting appropriate mechanical crimps. Therefore, the bulkiness and texture of the final product are further improved.

Example 5 In Example 1, the crimp development treatment temperature was changed as shown in Table 4. Except for this, a composite fiber having a single fiber fineness of 2 denier was obtained in the same manner as in Example 1 (however, in this case, the number of theoretical layers in the single yarn was 8.7).

The number of crimps, the degree of crimp, the degree of crimp number variation, the level of dyeing, and the feel of the obtained fiber after boiling water treatment were examined and shown in Table 5.

Example 6 In Example 1, the re-stretching condition after the crimp expression treatment was changed to the sixth condition.
Changed as shown in the table. Except for this, an acrylic multilayer composite fiber having a single fiber fineness of 2 denier was obtained in the same manner as in Example 1 (however, in this case, the number of theoretical layers in a single yarn was 8.7).

The number of crimps, the degree of crimps, the degree of crimp number variation, the degree of dyeing, and the feel of the obtained fibers after boiling water treatment were examined and shown in Table 6.

[Advantages of the Invention] As described above, the multilayer conjugate fiber as shown in Fig. 1 obtained by the method of the present invention is subjected to a crimp development treatment thereafter by applying mechanical crimps prior to the crimp development treatment. Since a higher degree of crimp development occurs, a remarkable effect is obtained in that the bulkiness of the final product is further improved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional photograph of a multi-layer composite fiber according to the present invention,
FIG. 2 is a partial cross-sectional photograph of a conventional multi-layered composite fiber, FIG. 3 is a flow sheet for explaining the process requirements of the fiber of the present invention in the yarn making stage, and FIG. 4 is a schematic view of a multi-layering element in a multi-layering device. is there. A, B: Spinning solution for composite polymer 1: Guide device for composite polymer 2: Multilayer device, 2 ': Multilayer element 3: Filter 4: Spinneret 5: Mechanical crimping device (crimper) 6: Crimping manifestation Device 7: Re-stretching device 8: Mechanical crimping device (crimper) D: Diameter of multi-layered element L: Length of one multi-layered element

Continuation of the front page (56) References JP-A-51-75151 (JP, A) JP-A-51-70322 (JP, A) JP-A-59-36720 (JP, A) JP-A-59-53715 (JP , A) Actually open 57-128219 (JP, U) Actually open 54-96139 (JP, U) Actually open 48-28707 (JP, U) Special public Sho 57-34363 (JP, B2) Special public Sho 58-18448 (JP, B2)

Claims (1)

[Claims] 1. A theoretical single yarn yarn layer represented by the following formula (1), which is a spinning stock solution of two or more acrylic polymers having different copolymerization compositions and having a difference in the amount of copolymerization components of 1 to 10 mol%. The number of layers is divided into 3 or more, and it is introduced into the spinneret through a filter with an opening of 10μ or more to form a yarn, and then stretched, washed with water, dried and densified. Is preheated to give mechanical crimps with 7 to 15 threads / 25 mm, then crimp development treatment, re-stretching treatment and mechanical crimping are performed. A method for producing an acrylic composite fiber having a level dyeing property. In the formula, K is a constant determined by the outer shape of the spinneret.