CA1279982C

CA1279982C - Stitched polyethylene plexifilamentary sheet

Info

Publication number: CA1279982C
Application number: CA 550858
Authority: CA
Inventors: Dimitri Peter Zafiroglu
Original assignee: EI Du Pont de Nemours and Co
Current assignee: Xymid LLC
Priority date: 1986-11-05
Filing date: 1987-11-03
Publication date: 1991-02-12
Anticipated expiration: 2008-02-12
Also published as: EP0267030A2; JPS63152445A; BR8705928A; DE3783329D1; US4704321A; EP0267030A3; MX159755A; KR940010901B1; EP0267030B1; KR890008377A; DE3783329T2; FI874872A0; FI874872A; IL84370A; IL84370A0; JP2596947B2

Abstract

ABSTRACT
A nonwoven fabric is provided which comprises a layer of nonbonded, polyethylene, plexifilamentary film-fibril strands, which layer is multi-needle stitched with a stitching thread that forms spaced-apart, parallel rows of stitches in the fabric.
Stitching thread of spandex yarn which causes the fabric to contract to 35 to 70% of its original area is preferred. The nonwoven fabric is particularly suited for use as a wipe-cloth.

Description

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TITLE
Stitched Polyethylene Plexifilamentary Sheet E~ACRGROUND OF THES INVENTION
Field of the Invention This invention concerns a multi-needle 6titched S layer of nonbonded, polyethylene, plexifil~mentary film-fibril ~trands, which forms a nonwoven ~abric that i8 partioularly useul ~s a wipe-cloth. The invention also concerns a process for making the nonwoven fabric.
Description of the Prior Art Many types of woven and nonwoven materials have been used ~nd suggested for use as a wipe-cloth (also sometimes called a ~dust-cloth"). Superior wipe-cloths should possess 6everal important characteri6tics. Such wipe-c}oths should absorb or lift dust and oily films from a surface without leaving lint or a residue on the wiped surface. The cloths ~hould be 60ft to prevent scratching of the surface being cle~ned. Further, the cloths should have sufficient stability to permit thorough rubbing of the surface without lintlng or destr~ction of the cloth. Removed dust should be retained by the wipe-cloth and not drop off the cloth until the cloth is vigorously shaken. Some known dust-cloths are impregnated with an oily ~ubstance to assist in dust particle pickup and retention, but these often leave a residual film on the wiped surface.
Nonwoven 6heets made from plexifilamentary strands of polyethylene film fibrils are known. Blades et al, United States Patent 3,081,519, disclosesj flash spinning of plexifilamentary 6trand6 of polyethylene fllm fibrils. Steuber, United States Patent 3,169,899, discloses depositing such strands onto a moving receiver to form a nonwoven sheet. Methods of assembling ~trand~
deposited from a plurality;of~positions are dlsclo~ed by ~ne~, United States Patent 3,402,227. Improved method~
~ for~depositin~ flash-spun plexifilamentary strands and '~

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forming them into ~heets are di6clo6ed by Pollock et ~l, United State~ ~atent 3,497,918. ~onded 6heet6 ere di~clo~ed by David, United States Patent 3,532,589.
The aforementioned ~ethods hAve been used commercially in the nanuf~cture of nonwoven ~heet of polyethylene plexifila~ent~ry ~tr~nds. ~heet product, sold under the trade~ark ~Tyvek~ spunbonded polyolefin by E. I. du Pont de Nemours & Co., has been found useful in many applications. ~owever, Applicant has found that when these ~heet6 were ~ried for u~e a6 wipe cloths, the sheets were unsatisfactory. Such sheet~ in bonded form did not pick up or retain dust ~dequately. Nonbonded ~heets did not have ~ufficient ~urface ~tability to permit any cignificant 6crubbing or rubbing without destruction of the zheet 6urace.
Multi-needle stitching m~chine~, generally known ~s Arachne~ or /Mali~ machines (including Malimo~
Malipol*and Maliwatt machines~ are known and have been used to in~ert 6titches lnto a wide variety of fibrous ~ubstrate~. Such ~achines and ~o~e of the fabric~
produced therewith are disclos~d by ~. W. 3ahlo, rNew Fabric6 Without Weaving", Paper6 of the American Association for Textile Technology, Inc., page~51-54 tNovember~ 1965). Other disclosurefi of the u~e of 6uch machines appear for example, in ~loch et ~l, United States Patent 3,769,81~, ~ughes, United States Patent 3,649,428 ~nd Product ~icensing Index, Research Disclo6ure, ~ Stitchbonded product of continuou~
filament nonwoven websn, page 30 ~June 1968). However, none of these disclo~ure~ concern 6titching of 6heets of polyethylene plexifilamentary film-fibril str~nd~.
~ An object of the pre~ent invention is to provide a nonwoven fabric which overcomes the 6hortcomings as60c}ated with 6heets of polyethylene plexifila~entary film-fibril str~nds and indeed provides a superior material or use as ~ wipe-clo~h.
* denotes trade mark 2 9~

SUMMARY OF THE INVENTION
The present invention provide~ a nonwoven ~abric which comprise6 a layer of nonbonded, polyethylene plexifilamentary film-fibril ~tr~nd~, the layer being ~titched through with thread th~t ~orme ~paced apart row~ of ~titches extending along the length of the fabric, the row ~pacing being in the range of 2 to 10 rows per centimeter, preferably 3 to 6 per cm, and the ~titch ~pacing beinq in the range of 2 to 15 stitches per centimeter, pr~fçrably 4 to 12 per c~.
U6ually, the nonbonded layer of polyethylene 6trands has a unit weight in the range of 30 to 200 grams per ~quare meter, preferably 50 to 150 g/m2. The 6titching thre~d u~ually amounts to 2 to 40~, preferably 5 to 10%, of the total weight of the nonwoven fabric. A preferred 6t~tching thread is a ~pandex ela6tomeric y~rn.
The present invention al~o provides ~ process for making the above-described nonwoven fabric, wherein a lightly consolidated nonwoven sheet of flash-6pun, polyethylene plexifilamentary film-fibril ~trands is multi-needle ~titched with 6titching thread that forms spaced-apart, parallel rows of 6titches in the sheet, the needl~ spacing being in the range of 2 to 5 needles per c~, and the ~titche~ within each row being inserted at a ~pacing in the range the range of 1 to 7 stitches per centimeter, preferably 2 to 5 stitches per cm.
Preferably the stitches are formed with ~ s~itching thread that is under sufficient tension to eIongate the thread in the range o~ 100 to 250~. Then, relea~e of the tensi~n permit6 the thread to retract ~nd cause the fabric to contract. In a preferred process, the fabric area after release of the tension is in the ranqe of 35 to 70% o~ the original area of the con~oiidated ~heet.
DETAILED DE5CRIPTION OF PREFERRED EMBODI~NT_ The invention:will now be illu~trated ~n detail with regard to~a preferred nonwoven fabric made rcm a , , ~ ~ 7 g ~

layer of nonbonded polyethylene plexifilamentary film-fibril ~trands which is multi-needle stitched.
As u~ed herein, the term "polyethylene" ig intended to embrace not only homopolymsr~ of ~thylene but also copolymers wherein at least B5% of the recurring unit~ are ethylene unit6. The pr~ferred polyethylene polymer i~ a homopolymeric linear polyethylene which has ~n upper limit of ~eltinq r~nge o~ about 134 to 135C (as measured with ~ differential thermal analyzer operated ~t a heating rate of lOQC per minute), a den~ity in the range of 0.94 to 0.96 gjcm3 and a melt index (as defined by ASTM D-1238-57T, Condition E) of 0.1 to 6Ø
The ter~ "nonbonded", a6 u6ed herein, with regard to the ~heet of polyethylene plexifilamentary lS film-fibril ~trands, ~ean~ that the ~trand6 are not bonded to each other by chemical or thermal action.
The plexifilamentary film-fibril str~nds of which the sheet oP the invention i6 composed are of the type di6closed in Blade~ et al, United State~ Patent 3,081,519. The film fibril are very thin ribbon-like fibrous element, which usually ~re le~6 than 4-micron~
thick, as measured by interference microscopy. The film fibril6 are interconnected and form an in~egral network within the plexifilamentary strand.
The preferred tartin~ nonwoven layer of polyethylene plexifilamentary film-fibril strand~ u6ed for preparing the~nonwoven fabric of the invention i6 preparèd by the general methods disclosed by Steuber, United State Patent 3,081,519. The preferred layer i~
a nonbonded ~heet. The 6heet i6 only lightly con~olidated. To prepare the preferred ~tarting ~heet, linear polyethylene having ~ denslty of 0.95 g/c~3, a .
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~elt index of 0.9 ~nd ~n upper limit of the ~elting range of about 135C, is flash-6pun from a 12.5%
solution of the polymer in trichlorofluoromethane. The ~olution i6 sontinuou~ly pumped to ~pinneret ~emblie~
~t a temper~ture of 179C and ~ pre~uro ~bove about 8610 kPa. In each ~pinneret assembly, the ~olution 1 pa~sed through a fir~t orifice to a pres~ure let-down zone and then through ~ ~econd orifice ~nto the 6urrounding atmosphere. ~he resulting film-fibril ~trand i6 6pread and oscillated by means of a ~haped rotating baffle, is electro~tatically ~harged and then is deposited on a ~oving belt. ~he spinneret a6semblies are ~p~ced to provide overlapping inter6ecting depo6its on the belt to form ~ batt. The batt is lightly compre6sed by pa~sage through a nip that applie6 ~ load o~ 17.6 N/cm of batt width to form a lightly consolidated sheet, which serves as starting material for the stitching ~tep of the present invention.
Further details concerning the fabrication of the lightly consolidated, nonbonded ~heet of polyethylene ~ilm-fibril çtrands are disclosed in ~ee, Un~ited States Patent 4,554,207, column 4, line 63, through colu~n 5, line 60. Generally, ~or u~e in the pre~ent invention, ~uch lightly consolidated ~heet h~s a unit weight in the range of 20 to 150 9/m2 and a density in the r~nge o~
0.15 to 0.3 g/cm . The thu~ly prepared ~heet i6 U8Ually wound up a~ a roll. ~hen heavier final product~ of the invention ~re desired, layers of 6uch ~heet can be positioned upon each o~her in preparation for the 6ubsequent ~titching 6tep. Two or more layer~ can be used to make up the required sheet of polyethylene plexifilamentary film-fibril 6trand6 that 6ubseguently will be 6titched to for~ the fabric of the invention.
However, one layer of lightly consolidated 6heet ~8 preferred~for processing ease and economy.

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In ~ccordance with the process of the pr~ent invention, the stitching operation can be carried out with conventional muti-needle stitching equipment, for example of the M~li type ~entioned hereinbefore. Mali~o multi-needle ~titching ~achines are particularly useful for ~aking ~he nonwoven f~brics of the pre6ent invention. In the ~titching step, ~paced apart rows of ~titches, gener~lly extending along the length of the ~abric, penetrate the nonbonded sheet of polyethylene plexifilamentary film-fibril strands. Thi6 type of multi-needle ~titching $s sometimes referred to in the art as ~stitch bondingn.
Substantially any thread is 6uitable ~5 the ~titching thread for use in the present invention.
However, preferred threads are those that can provide a force that will c~u~e to polyethylene plexifilamentary 6trand layer to contract or pucker. For example, conventional stretch yarns that can elongate ~nd retract (e.g., spandex yarns) or yarns that can be made to 6hrink after ~titching (e.g., heat or steam shrinkable yarns) can be used satisfactorily to form the required stitching pattern. Al60, the retractive force of the stitching can ~o~etimes provided by a ~echanical pre-treatment of the yarn (e.g., stuffer-box crimped or other textured yarns) to form retractive forces that can be activated by a thermal or chemical treatment that does not adversely affect the polyethylene substrate, but causes the yarns to shrink and apply the desired retractive force.
A particularly preferred stitching thread is $ormed from spandex yarn which has high elongation and high retractive power. Such preferred yarns are available commercially (e.g., Lycra* ~pandex yarn manufactured by E.~I. du Pont de Nemours and Company).
The spandex yarn can be inserted into the ~heet under tension in stretched condition, so that when the tension * denotes trade mark 6 :: :

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is released, the retractive forces o~ the yarns cause the sheet to contract and pucker. Preferred yarns can elongate and retract in the range of 100 to 250%.
Stretch yarns, for example of nylon or polyçster, c~n function in a somewhat ~imilar manner to spandex yarns, but usually with considerably less elongation ~d retraction.
In a preferred stitching step of the process, the multi-needle stitching machine forms parallel chains o ~nterlocked loops on one ~urface of the nonwoven polyethylene plexifilamentary sheet and a parallel series of zig-zag tricot stitches on the other surface.
Such rows of ~titches are typical of those ~ade by a ~Mali" or ~n "~rachne" multi-needle ~titching machine.
Alternatively, the ~titching can form substantially parallel rows of chaln stitches ~long the length of the fabric. In embodiment~ of the invention in which fabric area contraction is caused by ~hrinkage or retraction of the 6titching, chain stitches cause ~lmost all the contraction to take place in the direction of the stitching (i.e., along the length of the fabric) whereas tricot ~titches cause contraction acros~ the width a6 well as the length o~ the fabric. The rows of titches are inserted~by needles having a 6pacing in the range of 2 to ~ needles per cm and the stitches in each row are inserted at a spacing in the range of l to 7 stitches per c~, preferably 2 to 5 stitche per cm.
The nonwoven fabric of the invention, as shown in Examples 1-3 below, is particularly especially suited for use as ~ wipe-cloth. When the nonwoven fabri~ is fashioned into a simple mitten, an especially use~ul ~orm of~dust-cloth results. The fabric also has utility in other applications. For example, because of its 6tructure, ~the nonwoven fabric has a high insulating valu~e~and therefore is suitable for use in thin 5 lnsulative gloves, in thermal underwear, and the llke.

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These examples illustrate the fabriGat;on of three fabrics of the invention. The advantages o~ these fabrics as wipe-cloths are demonstrated by ~omparing their wiping performance with 60me commercial and other known wipe-cloths.
The 6tarting ~aterial for each o the three - fabrics of the invention was a layer of nonbonded, lightly consolidated, flash-spun strands of polyethylene film fibril~. The layer weighed 40.7 grams/m2 and was prepared by the method described in detail hereinbefore with regard to the process for preparing a preferred starting nonwoven layer of polyethylene plexifilamentary film-fibril strands in accordance with United States Patent 3,081,519-.
A roll of the polyethylene plexifilamentary ~tarting 6heet, measuring 50.~-cm wide, was mounted for feeding in the machine direction of a Malimo multi-needle stitching machine. A spandex yarn ("LYC~A"
type-126, availabIe commercially fron E. I. du Pont de Nemours and Company) was used as the ~titching yarn for each fabric. A stitch length of 2mm (i.e., 5 per cm) ~nd a 12 gauge needle bar;~i.e., l~ needles per 25mm) were employed.~Sufficient tension was placed on the yarn to provide a thread elongation of about 200~ or more.
The machine was operated to form 750 courses per minute which corresponded to ~titching a length about 1.5 ~eters of polyethylene sheet layer per ~inute.
T~ble I summariæes the~manufacture of~the nonwoven fabrics. In particular, the Table~lists the type of 8titch inserted (i.e., chain 6titch or tricot stitch), ~the number of stitches per cm in eaoh row, the row ~pacing, the amount of ~tretch imparted ~o the stit~ch~ing~yarD as it was~6titched through thé
~ consolidated layer~,~and the amount of area~contraction experienced~by the polyethylene film-~ibr~l layer, etc.
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Table I
Fabrication of Nowoven Fabrics of the Invention Example number 1 2 3 P~lyethylene l~yer ~eight, g/m2 40.7 40.7 40.7 Spandex stitching yarn Stitch type chain chain tricot dtex 156 44 156 ~ 6tretch(l) 250 200 190 Finished fabric 1~ Stitches per cm ~long Iength 12.2 10.2 9.5 along width 4.9 4.9 6.9 Weights, g/m2 Polyethylene 119 115 139 Stitching 21 5.8 31 % ~titching 17 5 22 Contracted dimensions~2) Length, % 49 51 53 Width, ~ 97.5 97.5 70 Area, S 40 48 37 Notes:
(lt ~ elongation imposed on ~titching thread by tension during stitch formation (2) all contracted dimension ~re expressed 25as ~ percentage o~ the original dimension, e.g., contracted ~rea, %:- (fini~hed ~heet area/original area)~100)~
The performance each of the three fabrics of the invention as~a wipe-cloth was compared to that of 6everal commerci~1 dust-cloths by a dust-pickup test. In this test, a synthetic~dust was 6pread on a smcoth, polished:surface of~dark, smoky, ~cratch-re~i6tant Lucite*:SAR and:then wiped by hand with the te~t cloth.
The 6ynthetic dust con~isted of about 75 parts by volume home-laundry-drie;r lint and 25 parts of automotive * denotes trade mark : , .

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air-cleaner test du~t (the latter, a product of AC Delco Division of General Motors Corporation). ~he ~ynthetic dust was placed in ~ large "6alt ~haker~ ~nd sprinkled therefrom onto the surface in A thin l~yer. Performance of the test eloth in picking up du6t, ~n retaining the du~t on the cloth, and in not leaving any 11~ ~n the ~urface was subjectively rated: 1 for excellent; 2 for fair; ~nd 3 for poor. The test sample~ of ~nvention were rated against the following control ~aterials:
A. Sontara* Etyle 8803, 80/20 woodpulp/polye~ter nonwoven industrial wipe ~ade by E. I. du Pont de Ne~our6 & Co., Wilmington, Delaw~re.
B. Economizers* Brand no. 05800, disposable wipe ~ade by Scott Paper Company, Philadelphia, Pa.
C. Yellow nonwoven cloth with lemon oil on it made by Scott Paper Company.
D. Guardian One-Wipe* dust cloth with çome oil in it ~ade by Guardian Chemical~ Inc., Consumer Products Div., Grand Rapids, Michigan.
E. 'Masslinn* 6ports towel ~ade by Chicopee, Milltown., New Jersey.
F. Chamois cloth made by Drutan Products, ~radford, Malne.
The results of the tests are given in Table~II.
Table II
~e Test Dust Du~t Film Sample Pickup RetainResidue D 2 ~ 1 3 E ~ 3 3 F
* denotes trade mark 10 :: : :~:

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As shown by Table 2, the fabrics of the invention were rated "excellent" in picking up and retaining picked-up du~t, a6 well as in leaving no oily film on ~he ~urface. In contrast, comparison E~mples C
and D left an oily film on the surface. ~nly the test ~amples of the invention were able to easily remove the oily film left by 6uch comparison samples. The only other material that rated "excellent" in the three rated categories was chamoi6 cloth (~ample F), a much more expensive natural product that ~till could not remove oiiy films from the surface as readily ~s could the nonwoven fabric~ of the invention.
When-6amples of the inventlon, whi~h were made without significant area contraction, were ~ubjected to the above-described test~, they also were rated nexcellent~, but required somewhat more rubbing to remove residual films left by wipes, such as C and D.
All the fabrics of the invention were excellent in being able to wipe oily films from the polished ~urface, such as tho~e caused by fingermarks or thin layer~ of fine lubricating oils.

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Claims

1. A nonwoven fabric which comprises a layer of nonbonded, polyethylene plexifilamentary film-fibril strands, the layer being stitched through with thread that forms spaced-apart, parallel rows of stitches in the layer, the row spacing being in the range of 2 to 10 rows per centimeter and the stitch spacing being in the range of 2 to 15 stitches per centimeter.

2. A nonwoven fabric of claim 1 wherein the nonbonded layer of polyethylene strands has a unit weight in the range of 20 to 200 grams per square meter.

3. A nonwoven fabric of claim 1 wherein the row spacing is in the range of 3 to 6 rows per cm, the stitch spacing is in the range of 4 to 12 stitches per cm and the unit weight of the nonbonded layer is in the range of 50 to 150 grams per square meter.

4. A nonwoven fabric of claim 1, 2 or 3 wherein the stitching thread is an elastomeric yarn and amounts to 5 to 10% of the total weight of the fabric.

5. A process for making a nonwoven fabric of claim 1 wherein lightly consolidated, nonwoven sheet of flash-spun, polyethylene plexifilamentary film-fibril strands, is multi-needle stitched through with stitching thread that forms spaced-apart, parallel rows of stitches in the sheet, the needle spacing being in the range of 2 to 5 needles per centimeter and the stitches within each row being inserted at a spacing in the range of 1 to 7 stitches per centimeter.

6. A process of claim 5 wherein the stitch spacing is in the range of 2 to 5 stitches per centimeter.

7. A process: of claim 5 wherein the stitching is formed with stitching thread which, when activated, exerts sufficient retractive force to cause the nonwoven sheet to contract to a finished area that is in the range of 35 to 70% of the original fabric area.

8. A process of claim 7 wherein the retractive force on the stitching thread in the thusly formed multi-needle stitched sheet is activated.

9. A process of claim B wherein the stitches are inserted with the stitching thread under a tension that elongates the stitching thread in the range of 100 to 250% and then the tension is released to permit the fabric to contract.

10. A process of claim 7, 8 or 9 wherein the stitching thread is a spandex yarn.