PROCESS FOR SELECTIVELY NAPPING FABRIC

Abstract: A process for selectively napping fabric and a product derived therefrom. The process permits the large-scale manufacture of sculptured fabrics. The fabric is selectively coated with a nap-resisting solution (24) which is allowed to solidify (26) and adhere to the coated portions of the fabric. The fabric is then napped (28), causing the filaments of the fabric to be broken in the uncoated portions. The nap-resisting solution is removed (34, 36) and a sculptured fabric is the result.

Description: P OCESS FOR SELECTIVELY NAPPING FABRIC Technical Field The present invention relates to processes for producing selectively napped or sculptured fabrics, that is, fabrics having a pile or nap of varying height. Background of the Invention In certain applications it is desireable to pro¬ duce a subtle design in a fabric. To obtain this objec¬ tive sculpturing of the fabric may be employed because the three-dimensional aspect of the fabric will show a design without the need for actually printing the design in the fabric with a separate color dye. It is possible to produce a sculptured effect in fabric having a high pile by mechanically shearing selected areas of the pile to a shorter length. The varied pile heights produce the sculptured effect. This mechanical shearing technique can produce visible patterns in the fabric without the need for highlighting the pat¬ tern with a separate color dye process. Mechanical shearing, however, is not well suited to high production manufacture because of the slowness of the process and the substantially increased costs involved. Furthermore, the complexity of the design is also limited by the physical parameters of the mechanical system. To overcome these technical problems it has been generally proposed that a plain undyed fabric be coated with a paste and thereafter the fabric be raised or napped so that the unpasted portions will have a higher pile than those areas covered with paste. As this proposed process is understood, the paste is intended to serve as a "nap resist" material or nap-resisting partial coating of the fabric. There can be many technical problems associated with a "nap resist" approach also. It may be difficult to apply complicated designs. "Resist" materials may fail to provide good definition, even of simple designs. The "nap resist"-coated areas may break down during napping, and thus fail to shield the fabric substrate while the nap or pile is being raised on the uncoated portions of the fabric. Ideally, it should be possible to completely remove the "resist" material from the fabric rapidly and without harm to the predyed material. It is further to be desired that at least some of the steps of the entire coating, nap-resisting, and nap-raising process be capable of being practiced continuously and quickly, so that large rolls of fabric can be continuously unwound and treated, then wound up again on a core when the treatment is com¬ pleted. Brief Summary of the Invention The present invention is directed to a process and ' a product derived therefrom for selectively napping fabric, including the steps of selectively coating the fabric with a nap resist in the form of a solution (preferably aqueous); allowing the solution to form a generally dry, solid, nap-resisting residue; napping the fabric; and rinsing the fabric to remove the residue. According to further aspects of the invention, a process and a product derived therefrom for making sculptured fabric is disclosed, including the steps of selectively coating the fabric with the nap resist solu¬ tion, forming the solid residue from the solution (e.g. by evaporation, which can occur spontaneously or be acceler¬ ated by heating or air blasts), napping the fabric, rinsing the fabric to remove the residue, drying the fabric, and shearing the napped pile to a uniform height. The preferred nap resist solutions comprise a synthetic organic substantially water-soluble prepolymer substantially dissolved in an aqueous medium, which aqueous medium can be thickened with a suitable thickening agent to adjust its viscosity to a level suitable both for good definition of patterns and for ease of flow through pattern- pplying equipment. Specific steps of the process of this invention - or the entire process, if desired - can be carried out continuously. Brief Description of the Drawing The Drawing is a schematic illustration of a process which forms a portion of the preferred embodiment of the present invention. Detailed Description of the Invention The preferred embodiment of the present inven¬ tion is directed to a commercially feasible process for mass-producing selectively napped or sculptured fabric. The pattern reproduced on the fabric can be delicate and include very fine detail; on the other hand, there are no commercially significant limitations as to the size or coverage of the pattern on the fabric. The present invention employs the so-called napping technique, wherein the fabric is passed under a plurality of napping wires in a machine that resembles the claws of a cat, so as to break the filaments of the fabric and produce a furlike appearance. This system has been extensively used and is the standard method of producing velour-type fabrics. After the napping step, it is typi- cal to shear the fur-like filaments to a uniform height in a cropping machine. In order to produce the three-dimensional effect of sculptured fabric, it is necessary to prevent the napping wires from touching the fabric in specified regions. These regions make up the pattern which will have a lower pile than the remaining areas of the fabric, which will have a raised pile due to the napping effect. A significant aspect of such a process is the selection of the appropriate chemical formulation capable of protecting the fabric from the effect of the napping wires while having high adhesion, a controlled viscosity, low migration, and ease of removal as properties. O PI, In the method of this invention, the most effec¬ tive and practical type of nap resist material is a solu¬ tion, preferably an aqueous solution, so that solvent recovery procedures and equipment will be unnecessary. The preferred solutions dry readily to a solid residue or deposit which will adhere to most fabrics without damaging them or leaving a permanent residue. Indeed, the pre¬ ferred solutions dry to residues that are readily redissolved in aqueous media and can be rinsed essentially completely from the fabric in a matter of minutes or, more preferably, seconds. In the nap resist solutions of this invention, a substantially water soluble solid solute provides the solid residue when the solution dries, the preferred solutes being synthetic organic compounds having hydro- philic substituents such as free hydroxyl groups, particularly of the alkylol type. As is known in the art, other types of substituents can have water solubilizing effects, e.g. salt groups, acid groups, ester groups, recurring oxyethylene units, and other polar functional groups, both pendant and chain-forming. Some of these kinds of substituents, such as. the recurring pendant salt groups or carboxylic acid groups of the polyacrylates can have a marked tendency to increase the viscosity or the thixotropy (shear-dependent viscosity) of aqueous media. Some degree of thickening or thixotropy or both is usually desirable in any coating composition. Absent such vis¬ cosity-increasing effects, even a high-solids water solution could have a viscosity approaching that of water itself, e.g. in the low hundreds of centipoise (cps). For many types of commercial coating or transfer or printing operations (including silkscreening), viscosities above 1000 cps are desirable, e.g. 3000-10,000 cps at room temperature (20-25° C). There are coating heads which can handle viscosities in the hundreds of thousands of centipoise or even higher, but the coating materials must then be metered and pumped with special equipment. In this invention, it is preferred to make use of conven¬ tional silk screen printing equipment for the coating or application of the nap resist solution, and nap resist solutions with good flowability at room temperature are desired, provided their viscosities are not so low as to result in migration over the surface of the fabric and poor definition of coated patterns. The preferred approach to the desired viscosity control is to use a thickener or thixotrope in combination with a water-soluble organic solid which provides the desired adherent, nap-resisting residue. Alternatively, the organic solid may itself be a thickener (e.g. a poly- acrylate or a polyvinyl alcohol), but the desired viscosity range for silk screen printing is believed to be more difficult to arrive at in this manner; in addition, some of these polymers may have a tendency to coat the mesh used in printing the pattern, thereby interfering with the coating or printing step of the process. This thickener or thixotrope is preferably as easy to wash out of the fabric as any other part of the solid residue. Alternatively, the thickener is effective in small quan¬ tities and forms less than about 30% by weight of the residue, more typically 0.110% by weight. Ideally, the thickener is both easy to wash out and effective in small quantities. It need not be a synthetic material (some synthetic polymeric thickeners may be allergenic or derma¬ titis-causing) and can be a natural or synthetic gum or a modified cellulose. Natural extracts such as soybean extract have been used in the art as thickeners and are fully effective in this invention. The principal solid ingredient of the nap resist solution is preferably a synthetic organic prepolymer which is substantially soluble in aqueous media and which can be dissolved in such media at levels of concentration above about 10% by weight without raising the viscosity of the resulting solution any higher than 10,000 cps (or¬ dinarily 8500 cps may even be too high) at normal ambient temperatures. The preferred prepolymers of this inven¬ tion, even in the presence of soybean extract thickener, do not raise the nap resist solution viscosity substan¬ tially above 10,000 cps even at a 50 or 60 weight-% solids level. In the context of this invention, the term "prepolymer" refers to a compound which contains no repeating units or only a small number of repeating units and is capable of being polymerized or further polymerized (chain-extended and/or crosslinked) to a relatively higher molecular weight material. Among the most readily available of the prepolymers which meet the criteria of this invention are the relatively low molecular weight solid condensates which, upon polymerization, form pheno- plast or aminoplast resins, which are usually highly crosslinked. In this invention, it is highly undesirable to permit such polymerization to occur, since any degree of crosslinking can drastically effect solubility in aqueous media. Some aminoplast resins are now used in fabrics as permanent press agents. In the permanent press art, these aminoplasts are typically applied as low mole¬ cular weight, water-soluble "amine"/aldehyde (actually amidine or amide/aldehyde) condensates. The low molecular weight condensate can be cured or crosslinked to a thermo- set resin, and such curing reactions permanently insolubilize the resin and . anchor it to the fabric. Amino¬ plast precursors used in this invention are kept at their low or negligible level of polymerization, so that exactly the opposite effect will be achieved - residues or deposits of these precursors on fabric are temporary only, resistant to mechanical removal but easily washed out of the fabric. Generally speaking, preferred prepolymers of this invention are solid condensates having hydrophilic character due to a plurality of methylol groups, e.g. amine- or amide- or amidine-formaldehyde condensates. It is preferred to select prepolymers or condensates which dissolve in neutral aqueous media since some fabrics are adversely affected by acids or bases. For this reason, the alkali-soluble phenol-aldehyde condensates are less pre¬ ferred. On the other hand, so-called amine-aldehyde condensates may be dissolved in neutral aqueous media, including plain water. The first stage in the synthesis of these condensates typically involves condensing a plurality of moles of an aldehyde such as formaldehyde with a mole of an amide or amidine such as melamine, urea, thiourea, an aromatic amine, or an aromatic sulfonamide. The simplest products of such condensation reactions - compounds such as dimelylol urea and trimethylol melamine are water-soluble solids. Further reactions can occur which advance these compounds to higher stages of conden- sation or chain extension without causing them to become thermoset resins. Virtually any of these intermediate but higher stages can be used in this invention, so long as water solubility of the intermediate-staged polymers has not been lost. In addition to the solvent (preferably water), the residue-forming solute (e.g. the prepolymer)and any thickener, the nap resist solution can contain surface tension-lowering or other surface active agents, coloring agents, and various miscellaneous ingredients - normally those which leave no permanent residue or can be washed out of the fabric. The amount of water in the solution ranges from 35 to 90% by weight, amounts in excess of 50 weight-% being preferred to keep the viscosity and the solids content within the desired range. For water solubility, good viscosity control (typically with the aid of a thickener), resistance to pattern migration, penetration and adherence to fabric, ease of removal with water, and resistance to napping wires as a solid residue, excellent results have been obtained with an aqueous solution of an aminoplast pre¬ cursor or prepolymer, particularly a melamine-formaldehyde condensate commercially available from American Cyanamide Corporation and known as "AEROTEX" Resin M-3 (trademark), preferably in a concentrate of 10-35% by weight of the resin, an amount of thickener sufficient to bring the viscosity into the most desirable range (e.g. 5000-8500 cps, determined on a Brookfield Viscometer), and a suit¬ able amount of water or aqueous medium, e.g. up to about 90% by weight. The optimum level of resin concentration in the resist solution appears to be in the range of 20-30% by weight, e.g. 25 wt.-%. In the preferred embodiment I utilized pre¬ viously dyed fabric to the nap-resisting technique. It is, of course, possible to dye the fabric after the pro¬ cess has been completed; however, this is not desirable in that the broken filaments of the nap areas may absorb dye in a different way than the protected areas, leaving an uneven color distribution. Furthermore, there is con¬ siderable longitudinal stretching and lateral shrinkage during the dyeing process and thus a pattern impressed into the fabric by the selective napping technique before dyeing would be highly distorted after the dyeing process by these factors. Typically, an undyed fabric begins at 168 inches (427 centimeters) in width, and results in a finished product of about 105 inches (267 centimeters) in width. Referring to the Drawing, the preferred embodi¬ ment of the process of the present invention is shown in schematic form. The preferred embodiment illustrates a continuous process although a batch process is also pos¬ sible. As mentioned above, dyed stock 20 is preferred for this process. The process is usable on any fabric suscep¬ tible to napping such as tricot and other knit fabrics, including both cellulosic and synthetic fiber knits. The next step in the process involves screen printing 22 wherein a mesh or silkscreen technique is used to define areas of the fabric which will become coated with the resist solution 24, thus defining the pattern. In order to achieve a commercially acceptable process, it is necessary to produce a resist solution which has suffi¬ ciently low viscosity to permit it to be pumped into the printing machinery. Adequate results were achieved through the use of a mixture of 50 wt.-% AEROTEX M-3, 47 wt.-% water, and 3 wt.-% "INDALCA" thickener (a soybean extract), which had an approximate room temperature Brook- field viscosity of about 8500 cps. As the percentage of M3 increased, the ability of the solution to flow through the printing device was reduced, but dilution of the M-3/ thickener levels improved flow. At 36 wt.-% resin, the Brookfield viscosity was about 7500 cps; at 20-30 wt.-%, about 6000-7000 cps. On the other hand, when the percen¬ tage of M-3 dropped substantially below 20 wt.-%, such as 10%, breakdown of the solution under napping became more likely, as was pattern migration. The viscosity at this solids level had dropped to about 5000 cps. Optimum results, as noted previously, were achieved with a solu¬ tion of about 25 parts by weight AEROTEX, about 75 parts by weight water, and a suitable amount of thickener. With this degree of dilution, migration of the resist solution 24 was kept to a minimum such that the printed pattern could have lines as narrow as approximately 0.5 cm in width, in some cases even as narrow as 0.3 cm. Further¬ more, it was found to be possible to cover about 80% of the fabric surface with resist solution using the process of this invention. During the -printing process, the preferred solution (i.e. the aminoplast precursor dissolved in water) is allowed to soak into the fabric thoroughly even through to the other side. This ensures that the solution will firmly adhere to the fabric during the napping pro¬ cess so that the napping wires do not rip out the solution and ruin the intended pattern. The preferred method of printing is of course by a silk screen method. However, the solution " may be applied by any other printing, coating, or transfer means including roller application, spraying, use of a coating head, etc., depending upon the type of pattern which is to be applied. The next step is the drying process shown as block 26 in Figure 1, where the resist solution is allowed to solidify or harden to a substantially solid residue to meet the requirements stated above. In the preferred embodiment, the fabric is passed through an environment preferably at a temperature which will facilitate water evaporation without damaging the fabric or polymerizing the aminoplast precursor. Accordingly, temperatures above 100° C. and below 175° C. are preferred. The drying takes place in a matter of minutes or seconds, depending upon the temperature (e.g. less than 60 minutes). The fabric can be pulled through the printing and drying steps con- tinuously at several meters per second, e.g. over 30 m/minute. The next step napping 28 involves napping which can be done by any conventional means, including passing the fabric under a set of napping wires 30 to rip the filaments of the fabric. In the preferred embodiment, the fabric was passed through the napping machine three times to ensure sufficient raising without subjecting the fabric to the extreme pressure that might be required if a single pass was employed. The napping step is, of course, stan- dard procedure with velour-type fabrics. In this case, there was employed 28/32 double-acting wires in the first two passes and 32/34 wire in the last pass. The fabric was then sheared 32 by a cropping machine to a maximum height of approximately 0.05 cm. Of course, the portions covered by the resist were not affected by the shearing steps. After the shearing step the first wash 34 is used to substantially remove the resist solution. In the first wash (34) the fabric was passed through a tank having hot water preferably at or near boiling for an effective or resist-removing dwell time of less than a minute, e.g. 9 seconds. The first wash contained a rinsing or scouring agent known as "Strodex V8" (trade¬ mark) in a conventional use concentration. Various anionic and nonionic surfactants are useful as scouring agents, neutral or mildly basic agents being normally preferred. "STRODEX" (trademark) agents are alkali metal salts of complex organic polyphosphoric acid esters or phosphate esters. The second wash 36 was a tank of water heated above room temperature but below boiling (e.g. 50-90° C), the dwell time being similar to the first wash (e.g. 9 seconds). The tank had a continuous water inflow and an overflow tube to remove any scum which might form on the surface of the water. The fabric was run on a dye beam with the pressure kept as low as possible. It is advantageous to keep the dwell times and temperatures as low as possible to avoid color changes. Time and tempera¬ ture are, of course, interrelated in this context. A room temperature (20-25° C.) wash is technically effective but commercially undesirable because of the long dwell time. The extraction step 38 involves placing the fabric rolls onto a dye beam in a machine which draws air through the center of the beam. The vacuum action draws air through the fabric, removing most of the water. The final step heat-set 40 is typically done at a temperature above the temperature of wet steam but below the degradation temperature of the fabric (e.g. at 190° C. ) with the fabric traveling through the heated environ¬ ment at a somewhat slower speed, but still preferably above 10 m/minute. The heat-set procedure returns the pile to its correct height by injecting steam beneath the fabric penetrating through to the pile. Because the fabric is still wet after extraction, the inner turns of fabric on the dye beam are somewhat wetter than the outer turns and the heat setting speed slows from, say, about 15 meters per minute on the outer turns to a slower speed approaching 10 m/minute or less toward the center of the spool, e.g. about 13 m/minute. It has been determined that the use of amino¬ plast precursors as the adherent residue-forming resin is desirable especially in that even white fabrics, are not stained by their use and the resin can be completely washed out of the fabric if its crosslink density is not permitted to increase above the virtually uncrosslinked level characteristic of aqueous aminoplast solutions. Small amounts of thickeners (e.g. 1-10% by weight) are effective with these resins to build the viscosity to the optimum level. The pH of the solution of aminoplast precursor is preferably kept near neutral, so that "acid colloids" are not formed. While "acid colloids" may be useful in this invention, their residues are more diffi¬ cult to remove with aqueous rinses, particularly as compared to the preferred water-soluble prepolymers. The following Example illustrates a preferred embodiment of a nap resist solution. Example A water solution of "AEROTEX" Resin M-3 (trade- mark), a melamine-formaldehyde condensate was adjusted to a 25 wt.-% concentration with water. No accelerator or catalyst or acid or base was added to the solution. Prior to dilution with water, 6 parts by weight of "INDALCA CD 30" (trademark for soybean extract thickener) were added for each 100 parts by weight of solid resin, so that the diluted solution contained 25 wt.-% resin and 1.5 wt.-% thickener, the balance being water. Excellent overall nap resisting performance was obtained with this formulation. The viscosity of this formulation was found, to be within the desired 6000-8000 cps range when measured with a Brookfield Viscometer, No. 6 spindle, at 20 r.p.m. The wet thickness of nap resist coatings did not appear to be critical; drying occurred with adequate effi¬ ciency at various wet thicknesses. The resulting dry thickness of the nap-resisting residue was considerably less than the height of the pile after the napping step.

Claims: WHAT IS CLAIMED IS: 1. A process for making selectively napped fabric including the steps of: (a) selectively coating fabric with a nap resist solution to obtain a fabric having selectively coated portions; (b) allowing said solution to form a generally nap-resisting residue essentially limited to and adhered to the selectively coated portions of the fabric; (c) napping the fabric; (d) rinsing the fabric to remove said generally nap-resisting residue. 2. The process of claim 1 wherein said fabric is coated with nap-resisting solution through a mesh screen so that a predetermined pattern may be covered by said solution. 3. The process of claim 1 including the subsequent step of drying the fabric. 4. The process of claim 1 wherein said napping step includes passing napping wires over said fabric so that only portions not coated with said solution will be ripped by the wires. 5. The process of claim 1 wherein said rinsing step includes passing said fabric through a rinsing agent. 6. The process of claim 5 wherein said rinsing agent includes a surface active agent. 7. The process of claim 1 wherein said rinsing step includes the steps of rinsing the fabric first in hot water and then rinsing the fabric in a rinsing agent. 8. The process of claim 1 wherein said solidifica¬ tion step includes allowing said solution to dry. 9. The process of claim 1 wherein said coating step includes allowing said solution to impregnate said fabric in said selectively coated portions prior to step (c). 10. The process of claim 1 further including the step of drying the fabric. 11. The process of claim 10 wherein said drying step includes removal of water from said fabric by vacuum means. 12. The process of claim 1 further including the step of•heat setting the fabric by passing steam through the fabric while maintaining the fabric in a hot environ¬ ment so that the pile of the fabric is restored. 13. A process for making selectively napped fabric including the steps of: (a) selectively coating an area of fabric with an aqueous solution comprising a substantially water- soluble synthetic organic resin; (b) allowing the aqueous solution in said area to form a substantially dry, solid nap-resisting residue which adheres to the fabric, said nap-resist¬ ing residue comprising the water-soluble synthetic organic prepolymer; (c) napping the fabric whereby filaments of the fabric will be broken in uncoated areas; (d) rinsing the fabric with an aqueous medium at a temperature above 50° C. to substantially remove the nap-resisting residue. 14. The process of claim 1 wherein said coating step includes impregnation of the fabric to cause the resulting nap-resisting residue to adhere more strongly to the fabric. 15. A process for making selectively napped fabric including the steps of: (a) continuously selectively coating an area of fabric with an aqueous solution capable of being absorbed into the fabric without substantial migra¬ tion so that defined coatings of approximately 5 mm in width are achievable, said aqueous solution com- prising a substantially water-soluble synthetic organic prepolymer and a thickening agent; (b) continuously allowing the aqueous solution in said area to dry to a substantially solid water- soluble residue comprising the synthetic organic prepolymer so that the residue adheres to the fabric and forms a coating which shields said area of the fabric; (c) napping the fabric whereby filaments of the fabric will be broken in uncoated areas; (d) rinsing the fabric in water heated to a temperature above about 50°; (e) extracting water from the fabric; (f) heat setting the fabric by injection of steam therethrough while maintaining the fabric at a temperature at least, as high as the ambient steam temperature. 16. A process for making sculptured fabric including the steps of: (a) selectively coating an area of fabric with a nap resisting solution, said area being up to 80% of the total area of the fabric; (b) allowing the solution in said area to form a nap-resisting solid residue; (c) napping the fabric; " ( ) rinsing said solid residue out of the fabric; (e) drying the fabric; (f) shearing the fabric so that napped areas are cut to a uniform height. 17. The process of claim 1 wherein said solution comprises about 10% to about 60% by weight, based on the weight of the solution, of substantially water soluble solid synthetic organic prepolymer dissolved in an aqueous medium. 18. The process of claim 17 wherein said solid synthetic organic prepolymer is an aminoplast-forming condensate. 19. The process of claim 18 wherein said condensate is a substantially non-crosslinked melamine-formaldehyde condensate. 20. A selectively napped product made according to the process of claim 1 or 13 or 15 or 16.

Inventors: DALE DAVID
Applicants: DALE DAVID, MUNSINGWEAR INC
Application year: 1981
Main classification: D06C23
IPC codes: D06C23