US2859472A - Apparatus for reducing shrinkage and creep of thermoplastic yarns - Google Patents

Description

1958 R. c. WINCKLHOFER 2,859,472

APPARATUSFOR REDUCING SHRINKAGE AND CREEP 0F THERMOPLASTIC YARNS Filed I Oct. 5. 1955 UNDRAWN YARN TOP ROLL ASSEMBLY i l I l l- I l \5 FEED I 1| ROLL ,1 ASSEMBLY i '7 GUIDE9 i l l I l r" DRAW ROLL IPQ\I AND HEATER I \i ASSEMBLY RING AND TRAVELER WIND'UP IO INVENTOR ROBERT C.W|NCKLHOFER BY W 61 MW ATTORNEY United rates Patent 2,859,472 APPARATUS FOR REDUCING SHRINKAGE AND CREEP 0F THERMOPLASTIC YARNS Robert C. Wincklhofer, Irvington, N. J., assignor to Allied Chemical Corporation, a corporation of New York Application October 5, 1955, Serial No. 538,734 3 Claims. (Cl. 131) This invention relates to operations for reducing heat shrinkage of thermoplastic filament, yarn and the like, hereinafter broadly referred to as filament or filamentary material; and for reducing creep of said filament, or filamentary material, i. e. contraction when said filament is unwound from a supporting package such as a bobbin.

In particular this invention relates to apparatus for treating molecularly oriented thermoplastic filament by heating the filament under tension preventing shrinkage of more than about as measured by increase in denier, especially so heating in stages; and for contacting the hot filament with a relatively cool solid surface moving at about the linear speed of the filament, said cool surface being designed to have frictional contact with the filament varying with the tension exerted upon the filament.

My invention comprises apparatus for use in the process steps, in combination, of subjecting a molecularly oriented thermoplastic filamentary material to initial tension of at least 1 gram per denier and tension permitting no more than at most about 10% increase in the denier of said filamentary material, as compared to the denier of a like standard filament similarly handled but without the heating treatment recited below; passing said material under said tension through a heating zone at temperature and contact time which would shrink the filamentary material and increase its denier as compared to the standard filament by at least 5% under Zero tension; then reducing tension on the hot filament while maintaining denier as aforesaid. In particular, in accordance with my invention the hot filament can be brought at less than 1 gram per denier tension into contact with a relatively cool solid coarse or bumpy surface moving at about the linear speed of the filament as it is fed from the heated surface to said relatively cool surface, said coarse surface having bumps contacting the filamentary material. Preferably in said heating step the filamentary material is heated in at least two stages to progressively higher temperatures and the tension on the filamentary material traversing at least one heating stage is maintained lower than in the next earlier heating stage. Preferably the tension is reduced until not above about 1 gram per denier tension is being applied. Preferably this reduction of tension is effected by bringing the filament into frictional contact with a solid, relatively cool, moving surface such as a polished draw roll.

I have found that apparatus giving particularly advantageous results in accordance with such process comprises a stationary shoe type heater fitting between the draw roll and associated separator roll of a filament tensioning apparatus, said draw roll having a take-off end with a bumpy surface, e. g. a sand-blasted surface.

Preferably the heater surface is generally cylindrically curved with a relatively narrow are, measured in degrees,

contacted by the filament thus producing only small to moderate frictional drag of the filament over the heater. Preferably the tension is not above about 1 gram per denier in the filamentary material entering on the bumpy surface. v

Important features of my operations are:

(1) The heating step is performed on molecularly oriented filament, i. e. filament which has substantially 4 2,859,472 Pateiitd Nov. 11, 1958 reached the desired degree of molecular orientation, and not on filament while it is being stretched enough to acquire substantial permanent elongation, i. c. more than 10% decrease in denier after the treatment is completed.

(2) Nevertheless the heating is performed with the filament under tension permitting no more than at most 10% increase in denier of the filamentary material. Preferably the initial tension is about the draw tension, i. e. the tension needed to confer upon unoriented filament the molecular orientation of the filament being treated. Thus, preferably the treated filamentary material has about the same denier as a control molecularly oriented under the same initial tension but not heat treated.

(3) The bumpy or coarse surface is contacted by the filament while the filament is still hot from the heating step and this surface is relatively cool.

(4) The hot filament entering on the coarse surface is under low tension, less than 1 gram per denier.

These conditions produce a yarn with boil shrinkage (i. e. shrinkage in boiling water) and creep each sub-- stantially reduced, yet with substantially the original length (i. e. denier), tensile strength, and elongation to break (ultimate elongation) of a control treated the same except not heated.

While I do not intend to define my invention by any theory, I believe the principle involved in the heating step is that atoms and groups of atoms, which have been left in positions causing internal strain by the stretching step (for imposing molecular orientation), readjust their positions when endowed with thermal energy by heating; and when so heated while still in the form of a filament under tension but without more than 10% further stretching, they find positions of reduced internal strain without serious loss of the molecular orientation. In the preferred heating procedure wherein heating is in stages with tension reduced in successive stages, I believe optimum results are realized because the progressively lower tensions permit using progressively higher temperatures without stretching the filament; the progressively higher temperatures and lower tensions permit progressively more complete relief of internal strain; and the progressive relief of internal strain permits use of progressively lower tensions without more than 10% contraction of the filament. The periodic relatively small increase in tension due to drag of each wrap of filament over the stationary heater are believed to contribute to the accomplishment of optimum results in the preferred method of operation.

In the step of contacting the hot filament at low or Zero tension with a coarse surface, I believe the filament may be given a chance to set by cooling free of strains; the coarse surface probably allows slight slippage when only a light tension is applied, allowing a general relaxation of stretch in the filament. If the wind-up mechanism at any time should jerk the filament, the filament probably hugs the coarse surface tighter, with greater are of contact between the bumps on the surface and the filament, so that the friction due to contact increases as the tension goes up, and no high tension from the jerk is transmitted to the filament entering onto the coarse surface and there undergoing setting and relaxation of stretch. The initial tension in my operations should be at least 1 gram per denier; and in carrying out the process withv molecularly oriented filaments such as certain nylon filaments having boil shrinkage near to 10%, or below 10%, the tension during heat treatment in accordance with my invention should preferably be sufficient to prevent contraction greater than about 5%.

In the accompanying drawings, Figure 1 shows, par tially schematically, preferred heater and draw roll apparatus in accordance with my invention. Figure 2 shows,

the steps involved in the process.

In Figure 1, reference numeral 1 designates a cylindrical separator roll. Reference numeral 2 designates 4 inch to about .005 inch and depth measured as an arithmetical average of about 65-70 microinches; they defined irregular bumps or ridges between them.

The radius of curvature of each half of the heating a generally cylindrically curved stationary shoe type 5 surface was about 16 inches; their combined length was heater, electrically heated, fitting in two halves between about 7 inches; and their width was about 1% inches. 21 cylindrical-draw roll and its separator roll. The curved The length of heater surface contacted by one wrap of. heater surface intersects the common tangents between yarn was 7 inches and the corresponding length of draw' thecylindrical surfaces of said draw roll and separator roll surface was 7.1 inches. Thus the contact are of each roll, sothat these common tangents aresecants of the arcs 10 wrap on the heater surface was radian or about 27 described by the heating surface-s. These arcs bulge and that on the draw roll surface was 7.1/1.9 radians or away from each other to make a double lobe. about215".

The axial length of'the separator roll 1, heaters 2, and The apparatus was run at a speed of wind-up on the draw roll polished surface 3 is sufiicient to permit sevbobbin of 1300 ft. per minute with /2 twist per inch. The eral non-interfering helical wraps of filament around the resulting time of treatment of the yarn was about 0.4 whole assembly. The degrees of arc of contact between second for 7 wraps of yarn. the filament and heating surface is preferably smaller The tension on the yarn as it reached the draw roll than the degrees of arc of contact between the filament was about 4 grams per denier. This tension dropped at and the draw roll below the heater. Thereby the desired successive wraps due to frictional contact of the yarn drops in tension are effected on the roll between the heat- 20 with the draw roll. The tension on the yarn entering on ing stages; and dragacross. the heater is kept suitably the sand-blasted take-off end of the draw roll was about low to avoid damage to the filament. 0.1 gram per denier, and the normal tension of the yarn Reference numeral 3 designates a polished cylindrical l aving the take-off end of the draw roll for wind-upsurface of the draw roll, and reference numeral 4 desigwas about 0.1 gram per denier.

Hates a cqarsely fi i h d tak -off end f th draw roll. The heater was maintained at the temperatures shown In the operations represented in Figure 2, undrawn for each test in the table below. yarn on package 5 passes over a top roll assembly 6 which The draw roll was unheated and remained relatively unwinds the package, and thence passes to feed roll as- 0001 compared to the heater,

.sembly 7. The yarn is stretched and molecularly oriented The table below summarizes the results for change in as it passes from feed roll assembly 7 to draw roll and shrinkage and creep obtained with the heater and with heater assembly 8, which are as described in connection and without the sand-blasted take-off end; the correspondwith Figure 1. The yarn slides across the heater surface ing figures for the controls were obtained by subje ting and makes frictional contact with the polished surface of the ImdfaWH Y t0 the Same Stretching between r0115 the draw roll. After leaving the coarsely finished surface h t either heater or sand-blasted roll.

of the draw roll the yarn passes through guide 9 to a The gures appearing in the table have the following ring and traveller wind-up apparatus 10 which winds the SIgIIifiC-BIICBI O Or more sets of figures bracketed yam Onto b bbi 11 means substantially the same results were obtained using Theapparatus and procedure used in the examples were these 3611s Of COlldlflOIlS. The first figure under Wraps as i l m i the figures above d ib d is wraps in contact with both the polished surface of the- The following examples are specific examples of the draw rollandthe surface of the heater; and the second mode of operation of my invention, illustrative of the is number of Wraps in Contact With las d take' best mode contemplated by me for carrying out the in- Off end of the draw roll, the last of the designated wraps vention, but are not to be construed in a limiting sense. on the take-Off end being a partial rather than a comple Example 1.Theyarn used in the tests summarized pbelow was undrawn epsilon-'caprolactam polymer nylon The heading 11163115 boil Shrinkage yarn of 32' filament count. The control, i. e. said yarn tefminedby a Standard test in boiling Watefwhen molecularly oriented 'by stretching to its desired The heading Creep means percent change in length permanent length and denier, was; about 6970 denier; 0f Y Under 10 t nsi n as compared to length of yarn had tensile strength at break (UTS) of about 5.5-5.7 When wound in a-package, measured byastandard test. grams perdenier; and had elongation at break (UE) of UTS and UE mean, respectively, tensile strength about 27-28%. Its moisture content was about 4% and at r ak in grams, per denier of unstressed filament; and its lactam monomer content was about 2.5%. The meltelongation at break in percent increase beyond length of ing point of the polycaprolactam composing this yarn unstressed filament. was about 2l9224 C. The figures given in the table are all averages of 2 to 5 The draw roll had diameter of 3.8 inches and width tests under comparable conditions. The yarn samples used of 2.125 inches; the take-off end was finished by sandin all tests were similar; the differences for the two conblasting over a width of about 0.54.0 inch. The craters trols represent the expected. range of variation betweenthus produced had diameters in the range of about .0005 random samples of similar yarns.

TABLE Heater Alone Heater and Sand-Blasted N0 Heating or Sand-Blasted End Temp. of Roll (Control Control Heater, C. Denier Wraps NBS Creep Wraps NBS Creep UTS UE' NBS Creep (a) 180 7-0 7.5 0. 30 6-1 6.0 0. 28 5.7 28 13.5 2.0. (b) 3:: l 9.3 1.3 14o Q 8.0 1.2 ii i 5.5 '27 12.0 4.2 69' iso gig} 6.2 0.9 I 200 Eff a1 0.8

The tensile strength at break (UTS) and elongations at break (UE) of all heat-treated filaments shown in Example 1 were substantially those of the controls given above; the denier of all the heat-treated samples was slightly below the controls, being about 68 vs. 70. The range of variation observed with various similar yarns is indicated by the figures under (a) compared to those under (b) at 180 C.

Example 2.Undrawn acrylonitrile polymer yarn samples were run on a drawtwister with essentially the procedure described in Example 1 above, except as specifically noted below. All the samples were taken from the same spin sleeve and drawn at approximately 3:1 draw ratio at 1200 ft./min.

Sample I was stretched over a surface heated to 250 C. but not passed over a heater after stretching was completed. Sample 11 was stretched in the same way and then passed over a heating shoe in several wraps as in Example 1.

The residual shrinkage recorded is the total shrinkage and is roughly the sum of the creep and the net boiling shrinkage.

I. Hot stretched (250 C.); no heater after stretching Denier UE UTS Residual Shrinkage II. Hot stretched (250 C.); and passed over a heater having surface at 250 C.

The specific polymer used was a 90:10 by weight copolymer of acrylonitrile with methyl acrylate.

Examples of types of molecularly orientable thermoplastic filamentary materials which can be similarly treated to reduce shrinkage and/or creep include polyamides such as polycaprolactam and diamine-dicarboxylic acid condensation polymers such as polyhexamethylene adipate; polyesters such as ethylene glycol terephthalate polymer; vinylidene halide polymers such as vinylidene chloride polymers and copolymers; acrylonitrile homopolymers and copolymers; etc.

In the preferred operations above illustrated, the filament was heated in stages as it was drawn in successive wraps around the heater, and the tension on the filament was reduced between successive heating stages by bringing the filament into frictional contact with the solid polished surface of the draw roll at each wrap. Thus as heating progressed the filament was under progressive ly lower tension, so that it was not at any time strained or stretched to decrease denier by more than 10% as it got to higher temperatures; but at the same time its tendency to shrink was reduced at each stage, so that the tension at all times remained high enough to prevent any contraction of the filament due to the effect of temperature. Short range elongation and contraction of purely elastic character probably occurred as tension was in- 6 creased by drag over the heater and decreased by contact with the draw roll.

The above results can be achieved with a series of separate heaters and tension-controlling means between at least two of them, but are generally more conveniently obtained as above outline using a double heater, a single separator roll above the heater, and a draw roll assembly below the heater. The heated surfaces can 'be heated in any convenient manner, including radiant heat, fluid heat, etc., and can be flat, grooved, or curved otherwise than specifically described above; these other forms will be generally effective in the same way as the above.

Other types of coarse or bumpy surfaced roll can be used instead of a sand-blasted roll, e. g. a randomly scored roll or the like.

Generally it is preferred to use at least three stages of heating with tension reduced between them. Preferred total treating times are not more than about 1 second. As illustrated in the examples, preferred temperatures are in the range between about C. and 250 C.

In the preferred operations wherein a yarn is wrapped around a contact heater and a draw roll with coarse surfaced take-ofi end, the major filament-contacting surface area of the draw roll is preferably polished to permit good frictional contact with the yarn. Enough wraps are taken on the draw roll to hold the filament under the desired drawing tension; and at least a partial additional wrap is taken on the coarse surface, with are of contact with the coarse surface of at least 5.

A few empirical tests can readily be made to determine suitable operating conditions. In particular, conditions on the heater can be regulated in combination with conditions of contacting the filament with the coarse surface after the filament finally leaves the heater so that at least one of the properties, heat shrinkage and creep of the filament is further reduced upon contacting the filament, while still hot, with the relatively cool, solid, coarse, moving surface.

I claim:

1. Apparatus for reducing the heat shrinkage and creep of molecularly oriented, thermoplastic filamentary material comprising a filament tensioning apparatus including a draw roll and an associated separator; and a heated solid stationary surface positioned to contact the filament as it moves between draw roll and separator between said draw roll and separator; said draw roll having a bumpy take-ofl? end surface.

2. Apparatus as defined in claim 1 wherein the draw roll and separator are substantially cylindrical; the heating surface is stationary and generally cylindrically curved, and is positioned to make at least one of the common tangents between the cylindrical surfaces a secant of the arc described by the heating surface; and the takeoff end surface of the draw roll is a sand-blasted surface.

3. Apparatus as defined in claim 2 wherein heating surfaces are fitted above both sides of the draw roll, and the separator is a roll; and the arcs described by the heating surfaces bulge away from each other.

References Cited in the file of this patent UNITED STATES PATENTS 2,244,461 Kettley June 3, 1941 2,517,570 Irons Aug. 8, 1950 2,611,923 Hume Sept. 30, 1952

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