IL31886A - Naturally crimped textile fibers - Google Patents

Description

NATURALLY CRIMPED TEXTILE FIBERS This invention relates to synthetic textile fibers having incorporated within the fiber matrix aggregations of submicroscopic metal oxide particles and to a method for preparing the same . More particularly, this invention relates to such fibers which have im-proved anti-soiling properties and, if desired, natural crimp, as well as to the necessary process variations for preparing the same.

A substantial portion of the textile industry is presently concerned with the production of yarns and fabrics from synthetic fibers. Certain physical characteristics common to the natural fibers such as wool and cotton, are not present in these synthetic filaments . As an example the fibers of wool in their natural form contain a plurality of crimps consisting of waves with the number of crimps per inch in the individual fibers varying widely within the different grades of wool. It has been determined that these crimps are primarily responsible for the soft hand, high bulk, covering power and excellent textile processing properties of wool . Furthermore, the peculiar elastic qualities of wool are thought to stem from these crimps in that, when such fibers are stretched, the crimps are subject to a straightening influence which imparts internal stresses, the net effect of which are to urge the fibers to assume their original crimp configuration.

Various well-known techniques, primarily physical or mechanical, exist for performing an operation called "crimping" upon strands of synthetic textile fibers. These include the application of external mech-anical forces usually at elevated temperatures . For example, "gear crimping" by passing a bundle of the fibers between a pair of co-acting gears. Another is "stuffer crimping", which relies upon the bending back and forth of a strand as it is forced into a stuffing box or con-fining chamber. Yet another involves "twist-crimping" whereby the filaments are twisted and untwisted to produce a more or less disturbed helical configuration. More recently, improved crimping techniques have employed the use of bicomponent spinning, whereby two polymers of different composition are extruded simultaneously through the same orifice. The composite filament that is formed is subjected to the action of a shrinking agent such as boiling water, whereby the filaments develop a helical crimp.

The complexity of some of these various pro- cesses and apparatus tends to deter their adoption for commercial practice. Additionally none has produced the permanency of crimp and softness of hand such as is associated with fabrics of natural fibers .

In accordance with the present invention synthetic textile fibers having improved anti-soiling properties are obtained when they have properly incorporated within the formed matrix thereof at least 1# by weight or silica of metal oxide/ particles, said particles being in the form of elongated aggregations having a length to width ratio of at least 10 to 1. The fibers thus described will also have permanent crimp derived from the incorporated metal oxide when the formed fibers are subjected to relaxation shrinkage after both stretching and drying steps are carried out in the fiber forming process. The desired fibers can be prepared by forming in the spinning composition loose aggregates of submicroscopic metal oxide particles havin chain-forming surface reactive groups, and spinning the thus-modified spinning composi-tion by any conventional spinning process including stretch-orientation, drying, and relaxation shrinkage steps, with the order of steps mentioned being in the sequence given when permanent crimp is desired. or silicas The metal oxides/ generally useful in the prac-tice of the present invention may be described as pigmentary colloidal particulate materials. The colloidal state of subdivision of matter encompasses particles having sizes ranging from 0.1 to 0.001 micron. Since or silica the metal oxide/ particles useful in the present inven-tion range from about 0.007 to 0.014 microns, they are within the colloid range. A pigment is a finely- -powdered insoluble material used suspended in a vehicle. The metal oxides of the present invention are used in a spinning composition and are insoluble therein. They also are colorless or white in preferred form and are inert to the usual materials with which they come in or silicas contact. Accordingly, the metal oxides /are pigmentary type as the definition is given above . Typical of the type of metal oxides included are alumina, silica, titania, vanadia, and similar oxides .

We have found, surprisingly, that not all or silicas types of these metal oxides/ may be employed to form elongated aggregations . A particular type of metal oxide or silica / particles useful in the present invention are those gen- erated in a gaseous environment, that is by a vapor phase reaction. The vapor phase reaction is carried out ΟΪ* siliCcLs by flame hydrolysis and leads to pyrogenic metal oxides/ This method of making pyrogenic silica is described in detail in "Industrial and Engineering Chemistry", Volume 51, Page 252, March 1959. The method which produces pyrogenic silica can also be used to produce other metal oxides such as A1203, Zr203, Fe203 and Ti02. or silicas Not all pyrogenic metal oxides/ are capable of producing the combination of improved anti-soiling pro- or silica perties and permanent crimp. Only metal oxide/ particles having surface reactive groups leading to the formation of chain-like aggregations are useful. Typically such metal ox£Sesparticles have a hydroxyl surface area or a number of hydroxyl groups per particle. In such in- stance, the hydroxyl surface area is indicated by pH and acid number. However, other surface reactive groups are possible and appropriate indications thereof are or silica obtainable. In particular, the useful metal oxide/ particles are those which when in the matrix of the formed fiber form chain-like aggregations having a length to width ratio of at least 10 to 1.

This invention contemplates formation of these or silica elongated aggregations by stirring metal oxide/particles into a spinning composition prior to extrusion of the spinning composition into fibers . Preferably, low shear stirring is employed in order to form loose aggregations of the metal oxide particles in the spinning composition. The aggregations become elongated while passing through the orifices of the spinnerette and during a subsequent conventional stretch-orientation step. Normally, in the spinning of synthetic fibers, a relaxation step is provided following the stretching step, and it is during relaxation that these fibers develop their crimpi-ness, if drying is carried out following stretching.

We do not fully understand why the present treatment provides the unusual results of causing the fiber to crimp. A theoretical explanation of why the results are obtained is not necessary however, to an understanding of the invention. We believe that these elongated aggregations within the fiber matrix provide relatively more rigid regions which shrink differentially to the fiber matrix during relaxation. We have noted that when the dimensions of the aggregations are such that the length is less than about 10 times the width, then acceptable crimping does not occur. We believe, that there is an intimate or interlocking relationship between the aggregations and the fiber matrix which prevents slippage of the fiber matrix in the vicinity of the aggregates. The above explanation is not intended in any way to limit the scope of this invention but is offered only as one plausible theory to explain the results .

The fibers of this invention, whether in their permanently crimped or uncrimped state are sur-prisingly resistant to soiling. Although these fibers have a high degree of luster or specularly reflected light, the amount of light transmittance through the fiber is low. Such combinations of optical properties are desirable in obtaining improved apparent soiling properties. However, it is highly unpredictable that fibers of the type envisioned by this invention should have such optical properties . By alteration of the fiber spinning procedure, it is possible to obtain fibers having elongated aggregates of silica particles which are not crimped but which have improved anti-soiling properties. The preferred fibers, however, are the naturally crimped fibers of this invention which also have improved anti-soiling properties in addition to improved bulk, cover, etc .

For a clearer and more complete understanding of this invention, reference may be made to the following detailed description of a preferred embodiment thereof along with the accompanying drawing wherein: Figure 1 is an electron micrograph of a suit-able dispersion of silica particles in a film cast from a spinning solution magnified about 5*000 times; and Figure 2 is an electron micrograph of a longitudinal section of part of a finished fiber containing elongated aggregations of silica particles magnified about 5*000 times.

This invention will now be described in more detail with respect to a presently preferred polymer composition and fiber-making process* as well as with specific reference to silica particles. However, it is clear that the invention is not limited to the specific details of this preferred embodiment.

It is well known that acrylonitrile polymer compositions may be dissolved in suitable solvents and spun into textile fibers having excellent properties . It is equally well known that such suitable solvents include concentrated aqueous solutions of certain metal salts, e.g., the thiocyanates, chlorides, etc. which are disclosed in Rein, U.S. Patent 2,140,921, among others. Such acrylonitrile polymers can be formed into fibers by "wet spinning" techniques of the kind proposed by Cresswell, U.S. Patent 2,558,730, and others. "Wet spinning" involves extrusion of a spinning solution of the polymer in a solvent through a spinnerette into an aqueous coagulant to form a "wet gel" fiber which there-after may be washed, stretched, irreversibly dried and then relaxed.

The fibers of the present invention may be accomplished in a "wet-spinning" process as described above by adding one or more of the desired silica pro-ducts to the spinning solution in such a manner that loose aggregates of silica particles are formed.

Thereafter such spinning solution is formed in the conventional manner into fibers which have improved anti-soiling properties and may have naturally formed crimp following the final relaxation step. Some wet-spinning processes employ the relaxation step prior to drying, which is known as "gel relaxation" . We have found that when "gel relaxation" is employed the desirable crimp is not obtained. To obtain this natural crimp the fib-ers must be dried prior to being relaxed .

The silica particles employed according to this invention comprise submicroscopic particles averaging in diameter by grade from about 70 to 140 Angstroms clustered together in chain-like formations . These chains are branched and have surface areas generally of 2 2 about 400 M /g to about 200 M /g . This unique chain- -like form distinguishes the desired silicas useful for the present invention from the undesired silicas which do not provide these novel fibers . The ability of the preferred silicas to form chain-like formations appears to be due to reactive groups, e.g. hydroxyl groups, residing on the surface of the silica particles . The degree of hydroxylation cannot be specified exactly since the amount required varies with respect to the surface area of the particle and the like. It is essential to the present invention only that the particles 5¾¾ elongated aggregations within the matrix of the fiber and that said aggregations have a length-to-width ratio of at least 10 to 1. To this end, silica particles which do not form such aggregations are not useful for the purposes of the present invention.

The amount of silica added to the spinning composition or solution should exceed 1 percent based upon the amount of polymer present. There is no upper limit with respect to crimp development, however, obviously, one should not add so much as to cause deterioration of such fiber properties as strength, optical properties, etc. We have found that best results are obtained when using between about 1 and 10#, and pre-ferably from about 1.5 to #> of silica on weight of polymer. Specific examples of the preferred silica pro-ducts are certain of the fumed silica such as Cab-0-Si.H sold by the Cabot Corporation and Aerosir^ sold by Degussa, Inc . Not all products sold under these trade-marks are suitable, however, since not all have the required amount of reactive surface hydroxyl groups .

Specific reference to those found useful to date will be found in the examples to follow.

Particular care must be employed in the manner in which the silica is incorporated in the spinning composition or solution in order to obtain a proper dispersion. We have found, for example, that gentle stirring or mixing of the solution following addition of the silica is best for forming the desired loose formations of the particles. This condition is illustrated in Fig. 1, which is an electron micrograph of a suitable dispersion of silica particles in a film cast from a spinning solution and magnified about 5,000 times. Fig. 1 substantially represents the dispersion as it would exist in the spinning solution. If rapid stirring or high shear mixing is employed, dense aggregates of the silica are formed which do not become elongated during subsequent spinning procedures.

The spinning solution so prepared is next ex-truded through spinnerette orifices into a suitable coagulant, preferably aqueous, which is a non-solvent for the polymer. A fiber gel is formed which is washed free of residual solvent and then stretched in hot water, air, steam, or the like at least 2 times and sometimes 4 to 15 times or more which causes the polymer molecules in the gel to orient themselves longitudinally with the fiber axis to impart strength. Optionally, a "solvent" stretch may be used prior to the washing step in combination with the hot stretch. Next the stretched fibers are irreversibly dried, usually under controlled temperature and humidity such as is described in Robertson et al., U.S. Patent 2,984,912, which serves to collapse the fiber from its highly swollen gel state to a dry, dense structure. The dried fibers are then relaxed in a free-to-shrink condition while exposed to a treatment which allows shrinkage, such as high temperature steam under pressure, shrinking agents, etc. It is during this relaxation, i.e. the shrinkage treatment, that the fibers of this invention assume a naturally crimped configuration. Fig. 2 is an electron photomicrograph at 5,000X of a longitudinal section of finished fiber prepared in the above described manner, clearly illustrating the inclusions of elongated aggregates of silica particles. Fibers which are relaxed prior to the drying state are not naturally crimped but still have desirable anti-soiling properties and are useful in those applications where high bulk and cover are not important considerations.

Generally, the degree of crimp or crimp pro-duct; i.e., the number of crimps per unit length times the amplitude of this crimp, increases with an increase in the amount of silica up to about one percent on the weight of fiber and also increases with an increase in the amount of fiber shrinkage obtained during relaxation. Above about one percent, crimpness is not affected significantly by the amount of silica but continues to increase with increased shrinkage. Characteristically, the crimp obtained is one of medium frequency and relatively low amplitude.

The present invention does not exclude the application of mild mechanical crimping of the fibers, in addition to the naturally obtained crimp. As stated earlier, the naturally obtained crimps are permanent to conditions of dyeing; i.e., boiling water, etc. ech-anical crimping is generally not permanent. It may be desirable, therefore, to impart mechanical crimps to the fibers as a textile processing aid while depending upon the natural crimps to yield improved fabric properties .

While, as previously stated, the preferred fibers are acrylonitrile polymer fibers that are wet spun from fiber-forming acrylonitrile polymers that contain at least about 70 weight percent polymerized acrylonitrile, it is apparent that other types of fibers can also be similarly improved by incorporation therein of elongated aggregations of silica particles in accordance with the teachings of the present invention.

In order to further illustrate this invention, reference is made to the following examples which are presented by way of illustration only and which are not intended to limit the invention in any way.

Example 1 A spinning solution was prepared comprising 11.2 percent of a copolymer of 10.2 percent methyl methacrylate and 89.8 percent acrylonitrile, 41.0 percent of sodium thiocyanate, and 47.8 percent of water.

A quantity of silica having the following properties was treated at 150°C. for 1-1/4 hours and then transferred to a vacuum desicator to remove any re-sidual moisture.

Cab-0-Si3^ EH-5 grade 2 + Surface Area M /g (BET) = 590 _ 40 Particle size Microns » 0.007 Density lbs/cu. ft. = 2-5 max 3.36 Grams of the thus dried silica was added to 1000 grams of the spinning solution and stirred until mixed. The mixture was placed in a sealed container which was next rolled on rollers for approximately one hour to complete a thorough mixing of the silica in the solution.

After deaerating, the spinning composition comprising the polymer solution and silica was extruded through a spinnerette having 10 orifices measing lj50u each into a 10 percent aqueous NaCNS coagulation bath cooled to 0°C, thus forming gel filaments.

The gel filaments were continuously withdrawn from the bath, stretched 2.5 times in air and thereafter washed with water until free of residual NaCNS. The washed filaments were next stretched 4 times in water at approximately SQ°C. and then dried in a free-to-relax condition in an oven at 127°C. (dry bulb) and 60°C. (wet bulb). During drying, the filaments shrunk 28 percent of their stretched length. The dried filaments were then subjected to pressurized steam at 127°C. which fur-ther shrunk the filaments by an overall 35$ of their stretched length. The fiber had a final denier of 18.0. The fibers so prepared had a naturally acquired crimp. By measurement, the crimp frequency was 9.5 crimps per extended inch of fiber and a crimp product was 12.7. By ash analysis, the fiber contained 2.1 percent SiOa.

Electron photomicrographs of longitudinal crosssections of the fiber showed that the silica was present in the fiber as elongated aggregations in chain--like configurations of Si02 particles, similar to that shown in Fig. 2.

An identical spinning of the same spinning solution, without the added silica, produced essentially straight fibers having no crimp.

Example 2 A series of fibers were made containing various amounts of the silica compound of Example 1 utilizing substantially the same procedure as Example 1, which show that crimp is obtained in all cases when more than about 1 percent silica on weight of fiber is incorporated therein. It will be noted that the amount of silica above 1 percent does not significantly affect the amount of crimp obtained. The results are as follows: Shrinkage SiO* In After Steam Crimp Crimp Fiber 127°C. Frequency Product 0.5 3 Very Slight 1.2 37 8.4 9.0 1.6 32 6.4 ' 8.1 2.1 34.5 9-3 10.5 .5 36 11.7 15.0 2.4 33 8.2 8.4 4.2 32 17.1 11.5 .7 32 13.5 14.0 As the data suggest, the amount of shrinkage affects the amount of crimp obtained . To confirm this the samples containing 4.2$ and 5 ·7# Si02 were steamed at higher temperatures to determine the effect on crim .

Steam Temp . Crimp Crimp % Si02 °C. Shrinkage Frequency Product 4.2 128.5 36 17.1 8.5 4.2 130.O 40 19. 12.8 .7 128.5 36 15.7 13.1 -7 130.O 40 18.0 18.6 Example 3 Following the procedures of Example 1, other silica products having similar properties to the silica of Example 1 were successful in preparing naturally crimped fiber. These products are given below along with their respective properties and the results obtained on spun fiber: Product jo SiOa Sh + Cab-O-Sil H-5 325 _ 25 0.007 1.3 it H-5 " " 3.6 33 HS-5 2.5 3 " M-7 200 25 0.012 2.5 (Est.) 36 200 200 5 0.012 3.1 3 38Ο 38Ο 0.005 2.6 3 (1) Surface Area M /g; (2) Particle size Microns; (3) Density lb/cu.ft.

( Crimp Frequency Crimp Product (Est. = estimated) Example k This example represents a reduction to practice of the present invention in which several hundred pounds of product was made . The product was tested with respect to critical characteristics, such as physical properties, crimp permanence in boiling water and anti-soiling performance. This fiber was spun by injection of a masterbatch of concentrated silica into a spinning solution not containing silica prior to extru-sion . Details are as follows .

A masterbatch was prepared consisting of 11 lbs . of Cab-0-Sil EH-5 mixed into 13 lbs . of the polymer of Example 1 dissolved in a solution of 15^ .5 lbs. of NaC S and 135 .5 lbs. water. This masterbatch con-taining about 3 «5 silica and about k .1$ polymer was continuously injected into a spinning solution containing 11 .2 of the same polymer in amounts necessary to yield approximately 2 .0$ silica on the total weight of polymer from the combined streams . A conventional line mixer was used to thoroughly combine the two streams prior to extrusion and subsequent spinning as described in Example 1. The fibers were relaxed in drying and steaming to a total overall shrinkage of approximately 36 percent of their stretched undried length. Crimp frequency and crimp product were variable along the fiber length with the crimp frequency ranging from about 10.0 to about 16.5 crimps per inch and the crimp product varying between about 7.5 and about 18.0.

Samples of these fibers were exposed to boiling water to determine the amount of crimp retention and perman- ency to such a treatment. The following table indicates little or no crimp is lost, and there is some in dication of an increase in crimp amplitude in all but one case with a corresponding decrease in crimp freq-uenc .

Before Boiling After Boiling C.F. CP. C.F. CP. .9 10.3 10.4 16.2 .3 17.8 16.3 16.6 16.0 11.5 12.7 16.9 1 .9 7.5 13.0 13.4 16.4 9 .0 15 .7 12.1 16.4 10.3 14.4 16.0 13 .8 9.6 12.5 10.1 Many analyses of the fibers were made for silica content. The distribution was not uniform and ranged from 1 .2$ to 2 .76$, averaging about 1.9$ in most cases.

The fibers produced in this example, like those of the other examples, have a very desirable translucent luster. When measured for light transmission, the fibers of this example transmitted generally less than 15 percent, and often less than 10 percent of the light. This combination of high luster or specular reflection and low transmission is desirable in obtain-ing improved apparent anti-soiling properties . The degree of soiling of a fiber is calculated from measurements on a "Color Eye" (a colorimeter made by Instrument Development Labs.). Each fiber smaple is measured before and after soiling from which a Kubelka-Munk (K S) value is obtained by log [Y value x 0.8813 ] where Y is a measure of greenness in the sample . The di ference in (K/S) between a soiled and an unsoiled sample (Δ K/S) is, therefore, indicative of the degree of soiling. Then the fibers of this example were compared with identical fibers without silica by this test, it was found that the fibers containing silica had vastly improved anti-soiling characteristics .

The test was conducted as follows; in separate tests, ten grams of fiber were washed for 1 minute in 1000 ml. of either (A) water containing 0 .5 g. of synthetic dirt, or (B) benzene containing 0.3 g. of synthetic dirt, and then dried. Next, the fibers were measured on the Color Eye to determine their respective K/S values. The following A(K/S) values indicate the results of this test using the fibers of this example and an untreated fiber .

Carrier Untreated Treated Benzene 1 .10 (Very Soiled) 0 .08 (Very Light Soil) Water 0.18 (Light Soiling) 0 .12 (Light Soil) Another test was conducted on additional quantities of these same fibers. Treated fibers made by the process of this example were further processed into yarn which was mock dyed and then processed into tufted carpets. Also, untreated fibers (without silica, but otherwise identical) were made into comparison carpets of identical construction. Both carpets were placed on the floor of a laboratory corridor for floor testing. After about 10, 000 traffics, the K S values on the soiled carpets were determined as above . Then the carpets were cleaned by a commercial cleaner utilizing their standard carpet cleaning procedure. The K S values were also determined on these cleaned carpets. The differences between these K/s values and the K S values of the original carpets prior to floor testing are reported in the following table of the A(K S) values .

Treated Untreated After 10,000 traffics .291 .617 After cleaning .183 .363 From these tests, it is seen that the fibers of the present invention appear to resist soiling better than untreated fibers which are otherwise identical and also appear to be less soiled after identical operations .

The development of crimp, of course, has nothing to do with the fiber optics and such anti-soiling improvements will be obtained whether crimp is intentionally developed or not.

Although certain specific examples have been given for purposes of illustration, other silica or metal oxides having similar properties and producing a similar effect may be used. The invention may be adapted to various uses as will occur to one with skill in the art .

Claims (9)

1. . A naturally crimped fiber having incorporated therein at least 1 percent (on the weight of fiber) of a pigmentary colloidal particulate or silica metal oxide/ in the form of elongated aggregations having a length-to-width ratio of at least 10 to 1 .

2. . A fiber as defined in Claim 1, wherein or silica said metal oxide particles have chain-forming surface reactive groups, an average diameter of less than about 150 angstroms and a surface area of at least about 200 square meters per gram.

3. . A fiber as defined in Claim 2, wherein said surface reactive groups are hydroxy 1 groups .

4. . A fiber as defined in Claim 2, wherein the particulate xi t4 oxide is a silica as exemplified by products available under the trade-names H-5 , Cab-O-Sil HS-5 , Cab-O-Sil EH-5 , Cab-0-Sil M-7, Aerosil® 300, Aerosil 380, and Aerosil 200 .

5. A fiber as defined in Claim 1, wherein said fiber comprises an acrylonitrile polymer .

6. A synthetic textile fiber having incorporated therein at least 1 percent (on the weight of or silica fiber) of a pigmentary colloidal particulate metal oxide/ in the form of elongated aggregations having a length-to-width ratio of at least 10 to 1, said fiber having improved anti-soiling properties .

7. . In the process of spinning fibers by dissolving an acrylonitrile polymer in an aqueous saline solvent to form a spinning composition and spinning said spinning composition into fibers by steps including extruding said spinning composition into an aqueous coagulant to form wet gel filaments, washing, stretching, and drying said wet gel; the improvement which comprises forming in said spinning composition loose aggregations or silica of a pigmentary colloidal particulate metal oxide/having chain-forming surface reactive groups, said metal oxide particles comprising at least 1 percent of the weight of the polymer present in such spinning composition and relaxing said fiber.

8. A process as defined in Claim 7* wherein said relaxing step is performed on the wet gel after stretching and prior to drying whereby fibers of improved anti-soiling properties are obtained.

9. A process as defined in Claim 7> wherein said relaxing step is performed on the dried fiber after both the stretching and drying steps whereby naturally crimped fibers are obtained.