US2774128A - Felt-like products - Google Patents

Description

Dec. 18, 1956 H. A. SECRIST FELT-LIKE PRODUCTS Filed Nov. 4, 1950 INVENTOR. A aPAz-E /Z Sac /57? United States Patent FELT-LIKE PRODUCTS Horace A. Secrist, Dedham, Mass, assignor to The Kendall Company, Boston, Mass, a corporation of Massachusetts This invention relates to non-Woven fabrics and feltlike sheet materials comprising interlocking cotton fibers and fibers having latent coalescent properties.

Many attempts have been made to manufacture nonwoven fabrics by mixing cotton fibers and fusible fibers by some suitable means and thereafter activating the fusible fibers. Among the successful materials made in this manner is the fabric disclosed by Reed in U. S. Patent 2,277,049. According to the preferred process of Reed carded webs of intermingled cotton fibers and plasticized cellulose acetate fibers are unified by heat and pressure to form a fabric. Although this material and structures similar to it have enjoyed a wide variety of commercial uses, they still suffer from certain undesirable characteristics. The heat and pressure usually required to produce a strongly unified sheet material have caused the mixed fiber products of the prior art to lose thickness and have a somewhat harsh and papery feel. The primarily lengthwise alignment of fibers obtained by the carding or gametting process persists through to the finished product resulting in a highly directional fabric with a high ratio of lengthwise to widthwise strength, often of the order of 9 or 10 to 1. The extensibility is of the same order of magnitude as that of an untreated web or bat, namely or less.

It is the primary object of this invention to provide a novel soft, porous, extensible felt-like sheet material having various advantages over'the product'just described and it is a special object of this invention to produce a reinforced cotton felt of high tensile strength in both the wet and dry states.

I accomplish these objects and others by supplying a sheet material comprising a network of intermingled cotton fibers and fibers having latent coalescent properties, the cotton fibers being frictionally entangled and interlocked with each otherand with the fusible fibers in situ by artificially induced kinks, bends, twists and curls, and the fusible fibers being bonded to one another and/ or the cotton fibers by coalescence. Depending upon the conditions of caustic treatment, the percentage of fusible fibers and the extent of activation thereof, the felt-like products of my invention may vary from soft, fluffy, absorbent, highly extensible materials to structures of limited extensibility and/ or increased stiffness.

These and other characteristics of my invention will be more readily appreciated from the following description of an embodiment thereof selected for the purposes of illustration, and showninthe accompanying drawings in which:

Figure l is a plan view of a section of a fabric of my invention, and

Figure 2 is a cross section along line 2-2 of Figure 1.

As shown in these drawings, the fabric is made of a three-dimensional network consisting essentially of cotton fibers 10 which are frictionally interlocked and entangled with'themselves and each other as a result of chemically induced random kinks, twists, bends and curls of said Patented Dec. 18, 1956 cotton fibers, and coalescent fibers 12 which are commingled with the aforementioned cotton'fibers, and which are adhesively bonded to some, at least, of the points of intersection of said coalescible fibers with each other and with the said cotton fibers.

The source of the integrity and coherence of my sheet materials is the frictional interlockingv provided by the network of the curled and kinked cotton fibers, and the positive adhesive fiber-to-fiber bonding supplied by the fusible fibers which co-operate to give my products a combination of conform-ability, extensibility and strength. The adhesive bonds act as a framework permeating the structure, impeding and damping the inter-fiber adjust ments which take place as my sheet materials are stressed. As the curled and kinked cotton fibers straighten, extend, and slip past one another, they assume in many cases new positions of entanglement with each other and with the fusible fibers, thus stabilizing the fabric and providing capacity for further extension before break.

Even though my finished fabrics are usually prepared from highly oriented carded webs, they are usually substantially more balanced than the fused fiber webs of the prior art because the three-dimensional frictional interlocking and entanglement of the cotton fibers in situ tends to randomize the orientation of the fibers. Individual fibers are less likely to be displaced or removed from the structure by abrasive forces, and in a direction normal to the plane of the sheet material the entanglement of the fibers greatly enhances the resistance to delamination of my products, particularly in those instances in which they have been prepared from a pluralityofcardedwebs,

Because of their substantial tensilestrength and other characteristics, my products are useful in themedical and surgical field as-sponges, dressing pads, bandages and the like. No separate fusing treatment may be required because theactivation of sotnefusible fibersmay be efiected by standard heat sterilization procedures employed in the preparation of bandages and the like in hospitals. Many of the sheet materials of this invention, prior to substantial activation of the fusible fibers, have distinct advantages in the manufacture of shaped liner or covering materials, stiffeners, and stiffened shaped articles. Their conformability and extensibility enable them to be easily molded or drawn to the desired shape, and thereafter the fusible fibers may be activated by heat or the action of appropriate solvents, thereby stabilizing the material in its molded shape and producing a surface with a high resistanceto deformation.

My novel sheet materials are particularly adapted for use in the manufacture of end products where both high marginal tear resistance and interior softness and absorbency are required, as for example sanitary napkins and diapers. In making such products, the sheet material may be cut to the desired shape 'andheat pressed at its edges only, thereby activating the fusible fibers in these areas I while leaving a soft, fluffy absorbent interior region.

The fusible fibers contained in my structures may be selected from a very wide variety of materials. For example, various fibers comprising esters and others of cellulose are suitable, such as those made of cellulose ace;v tate, cellulose propionate, cellulose butyrate, ethyl cellulose and benz yl cellulose. Fibers made of mixed esters such as cellulose acetate propio'nate also" are very. useful. Others of an entirely different chemical nature, however, may be'employed, such ast hose madeofvinyl polymers,

7 for example, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, or vinyl copolymers, and those of the polyamide type, an'impr ant' example of which is that commercially known as nylon. The above mentioned fusible fibers maybe classifiedas'thermosensitive, that is, they have the property of being softened by heat and hardening upon eooling'again, although they may be also hydroxide and the like.

w i In rm yprefe'tredkmaterial plastic in character ar d ;su sltantially inert to my alkalinev f, treatingfagent under the/temperature,concentration, and time duration condition-of my' process, The duration'of rendered tacky by the use of appropriate organic solventsv Under certain conditions, to be described hereinafter, I may also use fibers which are" not classified as thermosen- 'sitive.

I have found that thei' felt-like-sheet materials of'tliis invention can be produced by rrrixingthe, cotton fibers with fibers having laten't coalescentproperties toformaweb v and subjecting the web or a plurality of suchwebs to treatment with alkaline liquids having a substantial swelling action on cellulosein sucha manner :as to permit shrinkage ofthe structure, these stepsof the process and an apparatus useful in carrying vthese out being more fully be activated by the alkaline treatment, by theheat employed in the dryingprocess, by subsequentheat treatment or by the action of appropriate solvents or by suitable combinations thereof. Pressure may be usedto increase the bonding by the activated fibers; The preferred treating chemical forthe cotton fibers is an aqueous solution of caustic alkalisuch as sodium, potassium or lithium hydroxide, but other-basic celluloseswelling agents may be employed, such as solutions of sodium zinca-te, :quaternary ammonium bases such as benzyl trimethyl'ammonium 'Using aqueous sodium hydroxide solutions satisfactory 'results have been {obtained,withsolutiou concentrations of at least 8% and less than 30% NaGH at temperatures from justiabove the freezing pointof the-solution to +25";

Cg; It should be understood'itha-t temperature-and concentration are mutually dependent variables and that the selection of a particularvalue-for one maytfix the operating' range of the otheru Preferably and .for best results i ,such' solutions. are used in concentration of at least 10% i and less than 18%; NaOHattemperatures hom -110" C. "to +15 C. Otherfreagentsmay bee'mployed at-corresponding eflective strength andrtjetnperature. I The maximum felting con tractive efiectsg1of :tliechein'i cal are realized'in a shortitime, normally .to'3' minutes and the fiber sheet-is'the'n removed from the vat and treated to :remove theg'chemical; preferably promptly desirable gelatinization-of the fibers;

The extent of fiber curling, kinking, a'ndientanglement V fisfactory results-have been obtained When-this contraction" j is of theorder of fiopercenforgreatenalthough products l vhose area shrinkages areless may possess some or many wof the features of this invention,

. eam'ount'of shrinkage iob ained-depends on'a -nurri r b ret factors, the most important of which are the weight} per unit area of the fibrous; a ssembly robe-treated, the; ,ratio by weight of the cotton fibers; tortlre fusible fibers, andfthe temperature and coneentration ;of,-theiicaustic. i

solution; Other thingsl being,equ al,;-the:area'shrinkages V decreaseZif; either theweightof theassenrblylofithe relative 1 5 proportionof fusible fibers to cot-ton fiberslisiincreased.

' ,For' most 'prqdu'titsi'of this sinventiomlthe j cotton fibers shouldbein major proportion in'orderitohaveSthelgreat 1 est .flexibility of operating cond tions,j although satisfac V tory shrinkages-havebeen obsenved ith;cotton fiber con' 'centration'sf somewhat lower than;

tion with'optimum'values of therother-factors.influencing r percent-in conjuncareatr eontractio'n of the-assembly, #1

the f sibleifibers amassas' over; long exposure to the. chemical may produce 1111-.

contact or" the, fusible fibers with the treating solution is particularly important in the case of thermoplastic fibers of a cellulosic nature such as cellulose acetate where pro longed contact might radically change the characteristics of thetfibers, reducing or destroying their thermoplastic properties. Also, fibers of this type may in some instances be rendered coalcscent in the caustic solution, depending V i on the particular'fiber and'conditions of treatment, causing bonding of the fibers prior to heat or solvent'activa. j

tion. Usually, however, the bondingv supplied byxth'e' fusible fibers as a result of the caustic-'treating stage of my.

process is only incidental, and the fusible fibers retain their latent coalescent properties toia substantial extent. The particular type or" the'rmoplasticfiber chosen de pends primarily on the character of the product desired." ln order to produce a flufiyQhighly. extensible structure the fusible fibers of which are to be activated at. some point in the end use of the material, lselecta'fiisiblejiber which becomes tacky and coalescent atarelativelyhigh temperature so as to minimize thenactivationnfthe fusible fibers in the drying rof the sheet material following caustic treatment. Itis .possiblefof course, to achieve these same results with. fibers which become tacky'at, .lower temperatures by reducing the dryingtemperature,

but this is inefficient from an operating viewpoint; Conversely, if a product is desired in Which'the fusible fibers are partially or completely activated, the drying temperature maybe increased, or a fusible, fiber'may'be selecte'drwnich becomes tacky and coalescent ata relatively low temperature. 1 a i The operation of activatingr the fusible fibers. should be controlled'in accordance with the nature of the binder .fibersus ed, the proportion of such fibers and the charac j teristics'of thefinal product desiredf During thermixing 'tep these fibers caulbe in'a' dry' free condition suitable for dryass'embly,,picking, carding orlike processes. ..Co'n-f seguently, the process of activation necessarily: requires V that'the binderfibersjbe' softened, to a suitable degree.

Any appropriate activating agent maybe used which will 7, I produce good softening action.'*:T-hose;found mostpprac tical consist of heat, solvents or those substances ,suchfas plasticizers which'eXert aj softening action, or-some combination of the foregoing -jwhere the binder fibers are thermosensitive, havin-gthe property of being softened '1 by heat and hardening uponcooling agai1i,;these"changes '7 in I the physical condition c-rdinarily. take place without any material chemical deterioration. 7 Accordingl a convenient method of effecting activation is} to pass the sheetmaterial through a heating chamber, bet-weenheated plates or heated rolls, orthrcugh ranyother suitable ap p'aratus, such as a .dielectricheat ing unitfcapable of raising the'temperature of the fibers to thedesired degreer "Where the binder fibers used taresolublerin ornnay ,be.

softened by' organic solvents whichtdo notialfect'the cotton fibers to any substantial degree; another method of producing the' desired union fofthejfibers crihs'ists in subjecting the materialaftercaustic]treatment to. the action of such a s elvent, 'orj to asolvent 'vapsr or gas, which' wi ll develop in situthe' adhesive orfb'ounding propg erties of the fusible fibers, For. instance," if the-sheet 1 materiahconsists' of a mixturesof cotton and cellulose t acetat'e fibers it may be treated with a mixture of acetcn'e and methanol, to supcr'ficiallvdissclve '01:; soften "the; fusible fibers. -'The 'web may then be passedbetween' v pressure rolls. The'mature of. easements employed necessarily vzill be determined by the :cha'racte' off th binder fibers and other practical considerations. 9

variety of solvents for*the'yarious'binderffibeiis process will depend chiefly upon the nature of the fusible fibers used and of the character of the final product desired. Pressing necessarily results in bringing a single fusible fiber in contact with a greater number of contiguous fibers of both kinds than otherwise would be the case and thus to increase the number of individual bonds with accompanying increase in strength. It tends to reduce the softness, flexibility and draping qualities of the product and to give it lgreater firmness and rigidity. Whether to use pressure and the degree of pressure to be employed, if it is used, therefore will depend upon results desired, the nature of the fusible fiber and softening agent used and other practical considerations.

That the nature of the bonding, coalescence or association of the fibers with each other produced by the activation process may take several forms will be evident from the character of the activation processes herein described. For example, in subjecting the sheet material to a suitable temperature the thermoplastic fibers wiil attain a softening stage which is sufiicient to develop the coalescent properties. Or with some types of binder fibers, the heating step may be carried further until the surfaces of the fiber become sticky so that when the web is pressed the binder fibers will adhere or weld firmly to other binder fibers, and they likewise adhere to the non-binder fibers with which they are in contact. Or with some kinds of fusible fibers the heating step may be continued still further until the form of the binder is further broken down and the fibers are converted into almost a liquid state in which case they will wet intersecting non-binder fibers and will unite them upon subsequent cooling. In any of these extremely soft conditions more or less spreading the binder constituent may be effected, if desired, and even to such a point as to convert some or almost all of the fusible fibers into discreet particles or a discontinuous or continuous non-fibrous film.

In those instances where heat is employed as an activating agent for the fusible fibers it is possible to obtain more uniform bonding action throughout the sheet material by matching the -thermo-softening point of the fusible fibers to the temperature gradient throughout the thickness of the Web. This matching may be accomplished by incorporating different amounts of plastioiz er into fusible fibers in the various strata of the sheet ma terial or by selecting chemically different fusible fibers with varying softening temperatures.

When my products are prepared with a relatively high proportion of thermoplastic fibers at at least one surface of the material, they are useful for purposes to which heat sealability is desired, as for example, in porous or permeable containers. Sheet materials which exhibit di ferent surface characteristics because the fusible fibers occur in predetermined diiferent proportions on opposite surfaces arerparticularly useful as adhesive tape backings because good interface adhesion and resistance to picking on unrolling are secured.

By incorporating yarns or woven fabrics into my structures prior to caustic treatment it is possible to manufacture products similar to those described in my copending application S. N. 191,933, filed October 24, 1950. In these products the positive adhesive bonding supplied by the fusible fibers considerably strengthens the frictional entanglement of the spun and upspun fibers.

A class of fusible fi ers may be used which are not thermosensitive but which swell and become gelatinous and tacky in the presence of the alkaline treating agents of my process. Examples of this class are fibers of regenerated cellulose manufactured according to the viscose or cupranirnonium processes. One advantage inherent in the use of this class of fibers is that no after-treatment of the material is required. The cotton fibers are'curled andkinked and the fusible fibers activated by the same treating solution: The extent of activation of this type of fusible fiber may be controlled by varying the temperature and concentration of the caustic, or by adding varying amounts of sodium chloride to the wash water, or to the caustic. Products of this type have a high degree of stability, because the adhesive bonding provided by the regenerated cellulose fibers is substantially unaffected by heat or the action of a wide variety of organic solvents.

The following examples are given as illustrative of the products of my invention:

Example 1 Nineteen parts by weight of bleached cotton fibers were mixed in a picker lapper with one part Vinyon fibers VYHH-Z (a co-polymer of vinyl acetate and vinyl chloride distributed by The American Viscose Company). The lap was fed to a card which carded the fiber mixture and worked it into the form of a web. Several such webs were superposed to form a fibrous sheet weighing approximately grams per square yard. The fibrous sheet was cold-pressed by passing it between calender rolls at a pressure of about 1000 pounds per inch of roller inch of roller width and then treated in a bath of 14% NaOH at a temperature of 4 C. for a period of about 35 seconds. The material was removed from the bath, rinsed with water, neutralized with dilute acetic acid, again washed, and dried in air. An area shrink of 77% was noted. Half of each sample was fused between layers of cheesecloth at 300 F., for five minutes without pressure and the following physical properties determined. I

CORRECTED STRENGTH l 1 Corrected strength: In making comparisons between felts of different thicknesses and densities I make use of what I term"c0rrected strength, which is the actual load at break (in pounds per inch of width of the sample tested) divided by the weight in pounds of one square yard of the felt. This corrected load takes'into account differences in weight of the compared felts, in effect, giving the approximate strength of a unit quantity or weight of fibers on difierent felts.

Example 2 A fibrous sheet material containing 10% by weight Vinyonfibers and 90% cotton fibers was prepared, treated, and tested as in Example 1. The area contraction was 66%.

' I CORRECTED STRENGTH Unfused Fused Dry Wet Dry Wet Lengthwise 2. 52 9. 60 4. 24 Widthwise.-- 1 83 .970 2 96 1.55 Ratio (Lengthwise to Widthwlse) 2. 60 2. 74

" ELONGATION, PERCENT Lengthwise. Widthwise...

Example 3 A fibrous sheet material containing 20% .by weight Vinyon fibers and cotton fibers was prepared,

treated and tested as in Example 1'. The area contraction was5 1 CORRECTED STRENGTH Example: I

A fibrous sheet material containing. 40%:by weight :Vinyon fibers and 60% cotton fibers. was prepared,

treated and tested as in Example 1:. r The. area conttac CORRECTED STRENGTH Uutused Iused.

Dry Wet Dry Wet Lengthwise.- 2. 49 2.9.9 '17.? Widthwise A V, .853 8.03 4. 72 7 Ratio (Lengthwise to Widthwise) 2. 92 3.72 3.75

ELONGATION, PERCENT Lengthwise 26 V 37 25 as Widthwise -1 83 131 r 57 42 Example 5 A fibrous sheet weighing '60. gramsper square yard containing 10% by-weight Vinyonfihers and- 9.0%: cottonfibers was prepared and treated' as in. Example 11'. except.

. thatinip rolls at a pressure: of ahoutjterr pounds per inch.

'of'roller width were substituted for thejiheavy calender rolls. The area contraction ofthe. air-dried material was 75 Example 1 q i it through nip rolls at, a pressure of about. ten. pounds per inchv oi roller width. 7 The sheet was then. treated-Q in a bath of 18.42; lfIaOH at 1 0.? C.}:washed with'water; neutralized withdiluteacetieacid; and againwashed with water. Anarea contraction of about 38%" was observed.

: 1' A portion of the material was air-dried and the remainder dried on a steam can maintainedat about 225 F. Part fo f lthe candried portion'was subjected fora ofione minute to a pressure b1 386 pounds per square incinbe 8 r tween metal plates heated to 295 F. The following physical properties of each material were determined:

' oonnnornn STRENGTH I Air Can. Hot

. Dried Dried V Pressed Lengthwise; 11.6 10.8 41; 2 Widthwise 1. 1o 1. 13 6.09 7 Ratio 10.5 9.58 6. 7G 10- ELONG-ATION, PERCENT Lengthwise 20. 9 20. 9 13. 9 Widthwise V 44.1 72.4 6.2

' I 7 Example 7 A 40% Vinyon,.60l% cottonfibroussheet weighing 108 7 grams per. square yardwas prepared accordingto the. method of Example 1 'and given a light .press by passing it through nip rolls at a pressure of about ten pounds per inch of roller width; The sheet wasthen treated in a .bath of'1 3.8%' NaOI-I at 4 C., washed with water, neutralized with diluteacetic acid, and again Washed with water. Arr area shrink of 62.5% was noted. A'portion 0f the material was, air dried and the remainder dried on a steam can at a temperature of. about 225 5. Part of the can-dried portion was 'subjeeted for a period of one minute to a pressure of 2211, pounds per s'quare inch between. metal plates heated to 290 F- The following physicalpropcrties of each material Were determined:

CORRECTED STRENGTH I Air 7 Can Hot 7.

; Dried Dried Pressed V V V V 'Lengthwise 8. 60 15. 6 75 Widthwise'. 1. 40 1. 55

Ratio 7 7 6.15 10.1 V

40 VVELONGATIONQPERCENT Lengthwisel- 1o. 2 V 9. 0 1s. 0

Widthwise" .7 47.4 V p 7.6

I Example 8 sisting"; oi 80i% b1eached cotton fibers, and 20 percent fusihle fibers composed oftwo partsfc ellulose acetate and 725%, Th foll win phy i flip nj were id I pressby passingit; through nip. rolls at a pressure of about mined 2 a Y i e t'en-ip'ounds perinch' of rollerwidth. The sheetjwas then 1 1 treated inra bath. of 11.7% NaOH'at'-2 Cz wa shed V j j V r Corrected strengm water, neutralized with dilute acetic acid,: and again V Lengthwi e 8A8 Washed with. water An area shrink of 62.3%. was. obw 3 served. A portion of the material wasair dried and the j 359 rem inder dr iedien a steamcan maintainedatabout p q i a V V i" V Elongationypercem 22511 'Part of the can driedportion' was'sprayedwith V Lefigthwisa a etone, pressed-with a cardboard-roller under handpres- 6O su-re'andl'dried'.onthesteam. can; The product washoniceably stifier and stronger than either of thefother. samples; The: following .phys'ical properties of'each ma- V terial were determined:

' ORRECTED. STRE GTH;

" i Errors Garters, PERCENT fibrous sheet weighing 44 grams per square yard con- 9 Example 9 A fibrous sheet weighing 94.5 grams per square yard consisting of 60% cotton fibers and 40% viscose rayon fibers was prepared according to the method of Example 1 and given a light press by passing it through nip rolls at a pressure of about ten pounds per inch of roller width. The sheet was then treated in a bath of 20% NaOH at 21 C., washed with water containing 10% sodium chloride, neutralized with dilute acetic acid, again washed with water and dried on a steam can. An area contraction of approximately 30% was observed. The following physical properties Were determined:

Corrected strength lengthwise 2.97

Example 10 A fibrous sheet weighing approximately 91 grams per square yard consisting of 60% cotton fibers and 40% viscose rayon fibers was prepared according to the method of Example 1 and given a light press by passing it through nip rolls at a pressure of about ten pounds per inch of roller Width. The sheet Was then treated in a bath of 20% NaOH at 21 C., washed with water, neutralized with dilute acetic acid, again Washed with water and dried on a steam can. An area contraction of 56% was noted. The following physical properties of the material were observed.

I claim:

As an article of manufacture, a unitile, coherent, integrated, shrunken textile sheet material having substantial extensibility, conformability, integrity, and resilience and consisting essentially of fibers having latent coalescent properties and unspun cotton fibers, said unspun cotton fibers being chemically swollen, said fibers having latent coalescent properties and said unspun cotton fibers being mutually integrated and frictionally interlocked by chemically induced permanent deformations of said unspun cotton fibers, said deformations being in the form of random kinks, bends, twists, and curls in substantially all threedimensional directions and being in excess of the deformations normally present in cotton fibers, the unspun cotton fibers being entangled with themselves and with each other and with said fibers having latent coalescent properties, the entanglement being substantially continuous and uniform throughout the sheet, said fibers having latent coalescent properties being adhesively bonded at some at least of their points of contact with each other and with said cotton fibers by the activation of their coalescent properties.

References Cited in the file of this patent UNITED STATES PATENTS 2,181,043 Boeddinghaus Nov. 27, 1939 2,277,049 Reed Mar. 24, 1942 2,321,108 Schneider June 8, 1943 2,336,797 Maxwell Dec. 14, 1943 2,348,079 Lichtenthal May 2, 1944 2,395,371 Dockerty Feb. 19, 1946 2,496,873 Hoffman Feb. 7, 1950 2,528,793 Secrist Nov. 7, 1950

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