CA1076429A - Non-woven fabrics - Google Patents

Abstract

Abstract of the Disclosure A process for the production of thermally segmentally bonded non-woven fabrics by calendering between rolls at least one of which bears a pattern formed by groups of lands of different density, the difference in density resulting, for example, from grouping lands of different sizes of different numbers per unit area.

Description

1~76~Z9 This invention relat~ to bonded non-woven fabrios and, in par-ticular, to the produotion of segmentally bonded non-woven fabrios.
Many methodY for the produotion of bonded non-woven fabrics have been propoaed inoluding the applioation to a non-woven web of adhe~ives or heat if thermoplastic materials are included in the web~ In particular it is known to apply heat and pres~ure for bonding at limited area~ of the web by pa~sing it through the nip between oalender rolls at laast one of which i8 heated and carries a pattern of lands and depressions on its surfaoe. Where the fabrio i~ nipped between tha roll surfaoe~ heavy or primary bonding is effeoted at separated segments of the fabric resulting in a segmentally bonded fabrio. Of the roll pair u0ed as the calender roll~ either one roll or both rolls may carry patterns of lands and depressione; in the former case the seco~d roll being a plain -, unpatterned one. In the former case the plain roll especially ~hen directly heated also tends to cau~e ~ome le8~ heavy or ~eoondary bonding over the remainder of the fabric where it ha~ not been nipped ,- between the rolls. This overall secondary bonding on one face of the fabric tends to stiffen the fabric. In the latter cas. ~hen both roll~ are patterned it i8 known to use patterns in the form of oircumferential rings or helices which cannot intermesh. Calendering with such roll~ does not cau~e ~econdary bonding over the whole of a fabric face but only at those places in each face where the fabric ha~ been touched by a land on one side only. However this more limited ~econdary bonding ia achieved at the e~pen~e o~ the di~advantage .' '~ .

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that only a llmited r~lge of re~ular patterns of primary bonds oan be produced, at the land croas over pointa as the rolls rotate.
Cal~.ndering a web between two rolls each bearinæ patternF.
of land~. which were maintained sufficiently accurately in regi~ter with each oth~r could produce any desired pattern of both primary and secondary bonding; but maintenance of such accurate registsr i.s. not practicable~ or is at best very expensive~ when using rolle big enough to produce wide fabrics and with lands small enough to produce fabrics with useful ~roperties and pleasing appearance.
The physical a~.d visual properties of the bonded fabric are related to the amount of bonding some directly and some inversely and accordingly the properties obtained in a fabric are the result of a compromise. Hitherto available fabrios have not achieved the best combination of properties for all purposes, in partioular as fabrics for apparel purposes where properties closely resembling conventional woven and knitted fabrics and an attractive appearance are desired.
Such known fabrics generally carried a geometrically regular pattern of primary bonds which is aesthetically unattractive~
~ Acoording to this invention we provide a process for the s 20 production of a thermally segmentally bonded fabric wherein a fibrous ~ web including at least some distributed thermally bondable material }- is pa~sed through the nip between co~operating calender roll~ at least one of which is heated to a bonding temperature and at least one of which has on its surface a pattern of lands formed by groups of lands of different den~ity.
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: ' ' :~ ' ~L~76429 Fibxous webs for use in this invention may comprise staple fibres or continuous filaments or even mix-tures of these. Staple fibre webs are conveniently prepared by carding a mass of staple fibres or they may be prepared by a random air laying method and continuous ~i.lament webs may be prepared by a conventional air laying method using a jet of air to transport the filaments from some source and to spread ~hem in a randGm array on a or-aminous conveyor, An electrostatic charge may be applied to the filaments to enhance their separation prior to laying on the conveyor, thermally bondable material included in a web used in this invention may comprise particles of the material distributed throughout the web of fibres or preferably it may take the form of distributed fibres of lower softening or melting point than the other web fibres or most preferably the web may consist wholly or in part of bicomponent fibres one of the components being at least in part present at the surface of the fibres and being of lower softening or melting point than the other component.
The fibres of a web may include natural, artifical or synthetic fibres from linear organic polymeric materials as for example polyesters, polyamides and copolymers of these classes of organic linear polymers, The working temperature of the calender roll or rolls if both are heated to a bonding temperature, is in the region of the softening or ~-melting point of the bondable material and is such that together with the pressure between the calender roll surfaces forms primary bonds in fabric segments nipped between the ... . .
s~ 30 roll surfaces~
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In thlo inveJItion one or both of the oalender roll~ pair iB formed with a pattern of land groups of different density and ln suoh rolls the diff~rent donsity may be produced by varying the ~ize of the land~ in the different group~ or by varying the number of uniform si~e lands per unit area of the diffsrent groups~ These pattern~ may be formed on a oalender roll by~ for example~ engraving prooesses whioh begin with a oontlnuous tone positive or negative of the overall pattern~ breaking this up into a half tone ne~ative or positive by a suitable soreen printing prooess using for example a chequerboard or ruled line screen and transferring the half tons pattern to the roll by photo-etohing or mill-engraving methods which reproduc~ the overall pattern as groups of la~d~ with depre~sions betwaen~ of different densityO In order to produoe a bonded fabric having desired properties the overall amount of bonding must be oontrolled so that fabrics are not produced which are either unduly atiff by reaoon of a high percentage bonded area of ths fabrio surfaoe or which are insufficiently resistant to surfaoe abrasion and wear by rea~on of a low percentaee bonded area. At the same time it is desired to have a low .
percentage bonded area to favour the more aesthetic properties of handle ~ 20 and drape and high bonded arsa to favour physica1 propertie~ suoh as - abras1on and tensils strength.
A very important advantage of the present invention is that it makes possible an easier selection of bonded area to effect a compromise ~- between the foregoing oonflicting effect~ Thi~ is besause at least throe value~ of bonded area are involved in the final re~ult obtained~

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~7~29 Thus if groups of lands of only two different (len~ities is involved in makinæ up the overall pattern then the final result derives from the percentage bonded area at eaoh density and the relative amount and distribution of each group of lands of the two densities~ It oan therefore be appreoiated that the flexibility of control iB grsatly inoreased over that possible with the regular patterns of lands previously used.
At the aame time the regularity of patterning of the fabric by the known land patterns~ ~uch as chaquerboard~ olosed or open eohelon and similar patterns of lands of reotilinear outline i8 broken up a~d replaced by a more aesthetioally pleasing pattern in the present . .
inventionO ' ~ ' To obviate or reduce the occurence of ~tiff spot~ in a bonded fabric due to very dense groups of lands on a roll for use in the present invention it is preferred that a very ooarse soreen ia uaed in making a half tone negative or positive if this method i9 used and the screen will be much coarser than those normally used in half tone reproduction.
It wa~ therefore unsxpected and surprising that with such coarae soreens a good likeness of an intricate pattern could ~till be disoerned in the bonded fabrio a~ is found to be BO even on olose inspection of the bonded fabrio. The ooaraeness of the pattern used also faoilitates reproduction !'~', aa à pattern of lands on a roller by other methods of engraving.
~hatever process is used to reproduce the pattern of lands on a roll it is effected so as to reproduce the pattern on the roll with a depth of depressions between land~ such that these will penetrate into ., .''.'' ' ~ _ 6 ' ~1, .~ .

1(3~6~Z9 a fibrous ~eb in the bondin~ process substantially without contact between the web anl the roll surface at the base of the depres~ion~.
The second roll of a calender pair~ if not of the diEferent density patterned kind juYt described, may be a plain roll or one bearing a simple regular pattern of lands and depres~ions, as for example a chequerboard pattern~ a pattern of rings~ helices or splinss or a pattern of parallelogram shaped lands in closed or open echelon, provided that in operation the lands on the simple regular patterned roll provide sufficient overlying contaGt with lands on the other patte~ned roll to produce a defined pattern of primary bonds at least resembling the groups of different pattern dennity. The pattern on the second roll and/or the surface temperature of this roll should also be such a6 not to impair the bonded fabric properties by contributing an undue amount of econdary bonding. I~ this way the undesirable regularity of bond patterns produced in previously known methods may be replaced by the dominating pattern of primary bond groups of different density~ presenting a very much ~ore attractive appearance which may be enhanced or accentuated by colourat-ion~ as by dyeing or transfer printing since the primary bonds will exhibit a different affinity for dyestuff from that shown by the le~3 heavily bondad or un~onded parta of the fabric. Such colouration may be effected simultaneously with bonding by pas~i~g a dya transfer ~; sheet through the calender nip w1th the fibrous wab a3 described in our patents U.K. Patent No. 1498254 and U.S. Patent No. 4086112.
Pattern group~ of diffsrer.t density may take ~ariou~ ~orm~;
For e~ample they may b~ reali~tic in that -~everal group9 togather . .
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' ' ~ '''''''"'";'~'' ' ~076~ 9 represent real object~, ~uch as flowers for example or th~y may be surrealistic or ~lon-representational of real object~ whila still pre~enting an overall pattern of different den~ity groupsO
The aocompanying drawings illustrate p~tterns defined by groups of different density whorein~
Fig 1 represents a pattern formed of lands of circular cross ~ection, and Fig 2 represents a pattern formed of linear landa whioh may be circumferential rings or helice~ or longitudinal splines.
Heferring to Fig 1 this repre~ents portion of a floral pattern wherein floral representation6 of different tones are ahown by land groups of different density against a background of uniform density.
~` 15 Fig 2 i~ a representation of a floral and leaf patter~
wherein the different density groups are produced by YariatiOn of the thickness of the line patterns~
Fig 3 is a chess-board pattern also formed by variation of the thickness of the line patterns.
In an embodiment of this invention a carded web wei~hing .
141.6 ~ m2 consisting of 393 decitex 58 mm staple fibres of polyamide csnjugate filaments (50s50 by weight sheath/oore nylon 6/nylon 66) is passed at 3 ~ min through the nip between calender rolls each at .
~urface temperature of 215C and with a linear nip pressure of 180 lb/in.
~he upper roll i8 patterned as in Fig 3 the thicker lands having a width ~`' ' ' , :~ j :, . ~: .
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1~76~g 0.5 A of 1.1 mm and the thinner land~ a width of ~ mM. Each group oon9i8ta of seven line~ in a 1207 mm ~quare and the % roll ~urface area formed by these line~ ie 6C/' and 2l5~ for the denser and lee~ dense areac respectively. The lower roll i8 a thin walled tube whioh yields ~uffioiently to equalise ar~ small surface irregularities and thus equalise nip pressure along the nip. Thia ro~l bear~ a 6imple pattern of longitudin~l splines having a width of 5LA~ mm~ there being 16 suoh spline~ per 25 ~m of roll circumference oorresponding to a land area of 50'~0. The combined effect on the fibrous web passed betwsen these roll8 i8 to produoe 3 ~ primary bonded area in tha dense regions and 14 in the lighter regiono and to produce a bonded fabrio having the following propertiess Breaking load, Kg22~2 (MD) ~ Extension at break~ ~ 27 (~D) r; 15 Taar strength~ Xg1.7 (~D) 1.9 (CD) `s Bending length~ om5.1 (~D~

: 307 (CD) .~ MD . Machine direction ~ CD 8 Cross direction.
~hese measurements are made by the following methods:
~ - ~b-~; The bending length is measured according to British Standard - B~3356 : 1961. Bending length (Gm) is the cube root of the ratio of flexural rigidity to the weight per unit areaS
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Ten~ile Stren th The tenaile strength iB measured as the breaking load of 25 mm wide strips of fabrio when strained at a constant rate of 100 mm/
min (on an In~tron ten~ile tester~ from an initial gauge leng~h of 100 mm.
The exten~ion at break is simultaneously recorded.
~b i The load raquired to tear a sample iB measured on an In~tron Tensile Tester~ A rectangular sample 100 mm by 50 mm iB prepared by making a ~traight cut in the centre of a shorter Yide for 75 mm parallel to the long ~ides. The two 25 mm wide ends ~o formed are secured~ one in eaoh of the Instron jaw~ which are spaoed 50 mm apart~ On ~eparating the jaws at r1ght ang}es to the plane of the fabric at 50 mm/min the aample iB torn and the maximum load tor the mean level if several peaka were noted) ia recorded.

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Claims (11)

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A process for the production of a thermally segmentally bonded fabric wherein a fibrous web including at least some distributed thermally bondable material is passed through the nip between co-operating calender rolls at least one of which is heated to a bonding temperature and at least one of which has on its surface a pattern of lands formed by groups of lands of different density,

2, A process according to Claim 1 wherein the groups of lands of different density differ in the size of the lands in the different groups,

3, A process according to Claim 1 wherein the groups of lands of different density differ in the number of lands of uniform size percent area of the different groups.

4. A process according to Claim 1 wherein both rolls bear a pattern of lands formed by groups of lands of different density,

5. A process according to Claim 1 wherein one roll is a plain roll.

6. A process according to Claim 1 wherein one roll bears a regular pattern of uniform size lands.

7. A process according to Claim 1 wherein the thermally bondable material consists of fibres or filaments of an organic polymeric material.

8. A process according to Claim 7 wherein the bondable material consists of bicomponent fibres or filaments,

9. A process according to Claim 8 wherein the web consists wholly of the thermally bondable material.

10. A process according to Claim 1 wherein the web includes natural fibres.

11. A process according to Claim 1 wherein the web is coloured simultaneously by passing a dye transfer sheet through the nip with the fibrous web.