IL33801A - Acrylic fibers of improved brightness and process for same - Google Patents

Description

ACRYLIC FIBERS OF IMPROVED BRIGHTNESS AND PROCESS FOR SAME This invention relates to acrylic fibers of improved brightness having a novel cross-sectional shape and to a wet-spinning process for preparing them. More particularly, this invention relates to fibers having a generally triangular cross-section with undulating sur-faces . The process particularly involves wet-spinning through Y-shaped orifices using delivery ratios of 0.5 to 3.0 in a process wherein the inorganic salt concentration in the spinning solution and in the coagulant are interrelated and the various stretching ratios are with-in prescribed ranges .

Many attempts have been made to improve the brightness of synthetic fibers by forming their cross-sections into shapes that are non-circular thus including many different shapes. For example, in Japanese patent Publications No. 20770/1961 and No. 5268/1962, it is mentioned that a textile filament of a cross-section that is tri-lobal and substantially symmetrical with respect to the lobes has excellent brightness. The process for producing such trilobal filament, however, involves a melt-spinning technique, which technique can maintain a comparatively high degree of correlation between the cross-sectional shape of the spinning orifice and the cross-sectional shape of the spun fiber. However, wet-spinning techniques generally show poor cor-relation between cross-sectional shape of the spinning orifice and the cross-sectional shape of the spun fiber, and the cross-sectional shape of the fiber in wet-spinning is influenced by the desolvating velocity when the spinning solution is extruded into the coagulating bath, the diluting velocity of the solvent, and skin-core formation. Accordingly, since the cross-sectional shape of fibers obtained by wet-spinning cannot be controlled satisfactorily by cross-sectional shape of the spinning orifice, alternative methods for cross-sectional shape control in wet-spinning processes must be employed.

In Japanese Patent Publication No. 14424/1962, it is disclosed that a non-circular cross-section is obtained in acrylic fibers by maintaining the stretching rate in the coagulating bath in a particular range with a view to increasing, adsorption velocity of dyes and improving dyeability of the fibers. Also, in Japanese Patent Publication No. 22688/1964, the concentration of salt used in the coagulating bath is reported to be a factor in the formation of acrylic fibers of triangular cross-section which are low in extent of deformation .

In accordance with the product aspect of the present invention, there is disclosed an acrylic fiber of improved brightness having a triangular cross-section obtained by wet-spinning characterized by. having sides of said triangular cross-section that undulate in a manner defined by the formulas: wherein 1 is the distance in microns between two apexes of said triangular cross-section when measured as a straight line connecting the two apexes, a is the minimum amplitude of an undulation in microns when measured in a direction perpendicular to the straight line connecting the two apexes of said triangular cross-section, p is the minimum length of the undulation in microns when measured in a direction parallel to the straight line connecting the two apexes of said triangular cross-section, and d is the monofilament fineness of the fiber in deniers . In accordance with the process aspect of the present invention, there is disclosed a process for producing the acrylic fiber of improved brightness which comprises extruding a solution of an acrylonitrile polymer in an aqueous inorganic salt solution through a spinnerette having substantially Y-shaped orifices into an aqueous inorganic salt coagulant at a temperature of P -10 to 15 °C . at a suitable delivery rate defined as the average flow velocity of the polymer solution through the spinnerette orifices divided by the pull-out velocity, and subjecting the thus-formed fiber to a cold-stretching at room temperature, to a primary hot-stretching in hot water, and to a secondary hot-stretching in steam characterized by (1) adjusting the inorganic salt concentration in the polymer solution and in the coagulant to be in the range of: -2 ≤ x--#-= 3 (3) » y = 9 (4) wherein y is the concentration of inorganic salt in the polymer solution in percent by weight and x is the con-centration of inorganic salt in the coagulant in percent by weight; (2) maintaining the delivery ratio in the range of 0.5 and 3·0$ and (3) carrying out stretching in a manner represented by the formula: wherein χχ is the cold-stretching ratio at room temperature, x2 is the primary hot-stretching ratio in hot water, and x3 is the secondary hot-stretching ratio in stea .

In order to obtain the acrylic fibers of im-proved silky brightness by a wet-spinning process, it is thus necessary to adopt certain limiting conditions in the series of fiber-producing steps, beginning with delivery of the polymer solution to the coagulant and extending to steam stretching, and to combine into the integral process those steps involving the limiting conditions . The improved brightness cannot be achieved " by individual factors such as solvent concentration or stretching in the coagulating bath.

In order to appreciate the fine structure of the cross-section of the acrylic fibers of the present invention, reference should be made to the accompanying Figure 1. In Figure 1 is shown a typical cross- section of the acrylic fiber of the present invention showing the generally triangular structure represented by the figure ABC. The structure is made up of three sides, AC, AB, and BC and the apexes are indicated as A, B, and C. It should be noted that each of the sides enumerated presents an undulating surface similar to the others . The distance between apexes is indicated as £ and represents the length of the straight line connecting two apexes. The amplitude, or height, of an undulation is indicated by a and the length of an undulation is indicated by p. In order for the silky brightness of the acrylic fibers obtained by wet-spinn- ing to be obtained, it is not only necessary for the cross-section of the fiber to be generally of triangular shape, as indicated by the structure ABC, but it is also necessary for the sides of the structure ABC to present the undulating surfaces defined by Equations (1) and (2) above.

The brightness of the fibers of the present invention is conveniently measured as the 60-degree mirror-surface luster defined in JIS Ζ-βτ4ΐ as a mirror- surface luster of an angle of incidence of 60 degrees . The 60-degree mirror-surface luster in the present invention is measured according to the method described in JIS Z-87 1 using a GM-5 luster meter (manufactured by Murakami Color Technical Laboratory) . In the test, a rectangular piece of cardboard 6 centimeters by .5 centimeters was used as a base upon which were mounted fiber bundles . The fibers making up the bundles were tensioned and straightened under heat to remove the crimps and then arranged in parallel for mounting. Measurements of luster were obtained with the angle of incidence parallel to the axial direction of the fiber. whether or not the required undulating surfaces presented by the sides of the triangular cross-section are obtained in the fibers is indicated by the numerical value of the 60-degree mirror-surface luster defined by JIS Z-87 1 . It can be readily confirmed by microscopic examination that when the numerical value of the 60-degree mirror-surface luster is at least 35 * the undulating surfaces presented by sides of the triangular cross-section of the fiber are within the limits defined by Equations ( 1 ) and ( 2 ) . Thus, for purposes of the present invention, the fibers of improved brightness are those having a 60-degree mirror-surface luster of at least 25 > measured by the method of JIS Z-87^1 .

The acrylic fibers of the present invention in-elude single polymer component fibers and composite fibers formed by bonding two polymer components differing in thermoshrinking behavior in a core-sheath form or side by side form. As polymer components are included homopolymers of acrylonitrile or copolymer of acrylonitrile containing at least 80# by weight of acrylonitrile and the balance of one or more monomers copolymerizerable with acrylonitrile . The obtained fibers may represent either staples cut to predetermined length or monofilaments or multifilaments spun in the form of continuous ilaments .

Although only certain steps in the conventional procedures for producing acrylic fibers by wet-spinning require limiting conditions «in order to produce fibers of improved brightness, other steps can also be employed in the fiber-producing procedure without detracting from the improved brightness . Such other steps include water-washing for desolvating, drying between primary stretching in hot water and secondary stretching by steam, and heat relaxing after the secondary stretching, as are conventionally employed .

In carrying out the wet-spinning procedure of the present invention, it is preferable that the temperature of the polymer solution be in the range of 40 to 8o°C. If the temperature is below o°C, the back pres-sure on the spinnerette will rise and interfere with continuous smooth spinning. If the temperature is above 8o°C, the polymer composition will become colored and reduce commodity value of the fiber obtained. The temperature of the coagulant will be in the range of -10 to 1 °C. as is conventionally employed.

Further, in carrying out the wet-spinning proce -dure of the present invention, if the range of inorganic salt concentration in the polymer solution and in the coagulant is below that indicated in formulas (3) and (4) above, the coagulating velocity of the polymer f solution will be accelerated to excess, a skin-core structure will be formed and it will be prevented from imparting the desired undulating surface of the sides of the triangular cross-section. On the other hand, if the range of inorganic salt concentration in the polymer solution and in the coagulant is above that indicated in formulas (5) and (4) above, the coagulating velocity will be reduced, the fiber filaments will become glued to each other and prevent continuous spinning, and even where spinning continues the obtained gel fiber will be water-washed as uncoagulated and will therefore become devitrifled and be of poor quality. It is also necessary to maintain the delivery ratio between 0.5 and 3.0 in order to maintain stabilized spinning. In case the delivery ratio exceeds J>.0, even if substantially Y-shaped orifices are employed, the cross-sectional shape of the obtained fiber will usually be approximately circular and the brightness will be considerably reduced .

The fiber filament having passed through the coagulating bath is then subjected to a series of stretching steps defined in Equation 5* above. Among these stretching steps, the cold-stretching and primary hot-stretching give a substantial elongation to the fiber filament without destroying the skin-core structure formed mostly in the coagulating step, accelerate the orientation of the fiber-forming components, give a required strength to the fiber filament and become factors in forming the proper undulating surface presented by the sides of the triangular cross-section. The fiber filament subjected to the primary hot-stretching is dried according to conventional procedures and is then led into a steam heat medium for secondary stretching. Such secondary stretching is to stretch the fiber further so that the desired value of 60-degree mirror-surface luster will be obtained. It will be understood from Equation 5 that, in order to elevate the value of 60-degree mirror-surface luster, it is effective to set the cold-stretching ratio and the primary hot-stretching ratio to be as low as possible and to set the secondary hot-stretching ratio to be as large as possible and, particularly, to make the cold-stretching ratio small.

As monomer compounds copolymerizable with acr lonitrile in forming the polymer component, there can be enumerated such acrylic esters as methyl acrylate and ethyl acrylate; such methacrylic esters as methyl methacrylate and ethyl methacrylate; such carboxylic vinyl esters as vinyl formate and vinyl acetate; styrene, x-methylstyrene; vinyl chloride, vinylidene chloride; methacrylonitrile; such amides as acrylamide, meth-acrylamide and methylene bisacrylamide and their N-sub-stituted derivatives; such unsaturated mono- and dicar-boxylic acids as acrylic acid, methacrylic acid, itaconic acid, and maleic acid and their salts; such unsaturated sulfonic acids as allylsulfonic acid, methallylsulfonic acid and styrenesulfonic acid and such unsaturated monomers containing basic nitrogen as vinylpyridine and its derivatives, vinyl pyrrolidone, dimethylaminoethyl methacrylate, 2-hydroxy- and 3-methacryloxypropyltrimethyl-ammonium chloride .

As inorganic salts used in preparation of the polymer solution and coagulant, there may be employed such thiocyanates as sodium, potassium, calcium, and ammonium thiocyanates. Such salts as zinc chloride, calcium chloride, sodium perchlorate and potassium per-chlorate may also be employed .

As has been stated earlier, the fibers of..the present invention are improved in brightness and , accordingly, find increased use in those applications where such property is desirable. Additional benefits possessed by the fibers of the present invention are improved hand and bulkiness .

The invention is illustrated by the following examples wherein the percentage is baced on weight un-less otherwise specified .

Example 1 Two solutions of copolymer concentration of ll.j5$ and NaSCN concentration of 27$ prepared by respectively dissolving in a concentrated aqueous solution of NaSCN a copolymer made by copolymerizing acrylonitrile, methyl acrylate and sodium methallylsulfonate at a ratio of 91/8 .73/0.27 in one case and a copolymer made by copolymerizing acrylonitrile and vinyl acetate at a ratio of 89/II in another, as acrylic fiber-forming components were heated to a temperature of 70°C. and were delivered into a coagulating bath consisting of an aqueous solution of 12$ NaSCN at a temperature of -3°C by using a spinnerette having the below-mentioned cross-sectional shape.

As a spinning device, there was used a gold- platinum spinnerette in which were made 50 Y-shaped orifices in each of which three rectangular slots were radially arranged so that the phase difference was 120 degrees, the length from the center of the crossing zones of the radial slots to the end of the slot in the lengthwise direction was 0.15 mm. and the width of the slot was 0.003 mm. The value of the delivery ratio of said spinning solution in the coagulating bath was 1 .8 . The final spinning velocity through the outlet of the steam stretching machine was IhO m./min. The spun fiber filament was subjected to the coagulation in the coagulating bath, cold-stretching at the room temperature, water-washing, primary hot-stretching in boiling water, drying under the temperature conditions of a dry bulb temerature of 11 °C. and wet-bulb temperature of 70°C, collapsing, secondary stretching by steam heat at 120 °C, relaxing heat-treatment in a steam heat atmo sphere at 127 °C. and drying treatment under a dry-heating action of 105 °C. to make an acrylic fiber having a triangular cross-section.

The cold-stretching ratio Xx, primary stretching ratio X2 and secondary stretching ratio X3 were varied . The 60-degree mirror-surface luster values of the obtained acrylic synthetic fiber are shown in the following Table 1.

Total Fiber forming stretch- 60-degree m o . components i 2 3 ing ratio surface lus Acrylonitrile/ methyl aerylate 1 /sodium metha- 1.5 1.5 4.44 10 58 llylsulfonate 2 II 1.5 2 3.33 10 53 3 It 1.5 3 2.22 10 46 4 II 1.5 1.66 10 32 II 1.2 2 5.2 12.5 59 6 11 1.5 2 5.2 I .6 57 II 2 2 5.2 20.8 39 II 2.5 2 5.2 26.0 42 II 2 2 3.0 12 40 It 2 2 4.0 16 40 1 II 2 2 6.0 24 51 2 It 2 2 4.7 18.8 52 II 2 2 6.3 25.2 58 Acrylonitrile/ vinyl acetate 2 2 4.7 18.8 40 It 2 2 6.3 25.2 42 Further, in order to make the monofilament fineness of the finally obtained acrylic synthetic fiber 5 denier, the delivery ratio in the above mentioned spinning conditions was varied in spinning. The values of/, p and a representing the peculiarity of the cross-sectional shape of the obtained fiber were measured and the 60-degree mirror-surface luster degree were measured. They are shown in Table 2.

Table 2 ^3 Cold . Stretching Steam Total 60-degree stretching ratio in stretchstretchmirror-surfac ratio hot water ing ratio ing ratio luster value 1.2 2 5.2 12.5 59 1.5 2 5-2 15.6 57 .2 2 3 12 40 Example 2 A spinning solution of copolymer concentration of 11$ and NaSCN concentration of $ was prepared by dissolving in a concentrated aqueous solution of NaSCN a copolymer made by copolymer!zing acrylonitrile, methyl acrylate and methallyl sulfonic acid at a ratio of 91/8.7 O.3 as acrylic synthetic fiber forming components. The spinning solution at a temperature of 60 °C. was delivered into a coagulating bath consisting of an aque-ous solution of NaSCN at a temperature of -3°C. while maintaining a delivery ratio of 1.5 of the spinning solution. As a spinnerette, there was used a gold-platinum spinnerette having l8o Y-shaped orifices in each of which three rectangular slots were radially arranged so that the phase difference might be 120 degrees, the length from the center of the intersection of the radial slots to the end of the slot in the lengthwise direction was 0.16 mm. in each of the two sides and 0.20 mm. in the remaining one side and the width of each slot was 0.03 π∞· The spinning conditions except the stretchi g ratios were the same as in Example 1.

The variation of the 60-degree mirror-surface luster value with the variation of the stretching multiplication is shown in Table 3.

Table 5 Cold Stretching Steam Total 60-degree Stretch- ratio in stretch- stretch- mirror-sur ing ratio hot water ing ratio ing ratio luster 1 6 18 68 1 6 24 *9 1.5 2 6 18 55 1.5 6 27 51 2 2 6 24 50 1 2 6 12 77 1 2 5 10 72

Claims (2)

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is :

1. An acrylic fiber of improved brightness having a triangular cross-section obtained by wet-spinning characterized by having sides of said triangular cross-section that undulate in a manner defined by the formulas : wherein L is the distance in microns between two apexes of said triangular cross- section when measured as a straight line connecting the two apexes, a is the minimum amplitude of an undulation in microns when measured in a direction perpendicular to the straight line connecting the two apexes of said triangular cross-section, p is the minimum length of the undulation in microns when measured in a direction parallel to the straight line connecting the two apexes of said triangular cross- section, and d is the monofilament fineness of the fiber in deniers .

2. A process for preparing the fiber of Claim 1 which comprises extruding a solution of an acryloni- salt trile in an aqueous inorganic solution through a spin- nerette having substantially Y-shaped orifices into an aqueous inorganic salt coagulant at a temperature of -10 to 15 °C. at a suitable delivery ratio defined as the average flow velocity of the polymer solution through the spinnerette orifices divided by the pull- out velocity, and subjecting the thus-formed fiber to r stretching in steam characterized by (1) adjusting the inorganic salt concentration in the polymer solution and in the coagulant to be in the range of: 35 - y =^ 9 wherein y is the concentration of inorganic salt in the polymer solution in percent by weight and x is the concentration of inorganic salt in the coagulant in percent by weight; (2 ) maintaining the delivery ratio in the range of 0.5 to 3 ·0; and (3 ) carrying out stretching in a manner represented by the formula: wherein X is the cold-stretching ratio at room temperature , X2 is the primary hot-stretching ratio in hot water, and X3 is the secondary hot-stretching ratio in steam . Agents for Applicants -10-