US 3819402 A
An improved process is disclosed for the heating or heat treatment of a substrate, particularly a textile material in an oscillating electromagnetic field. The addition of ionic compounds to the material to be heated greatly enhances the heating or heat treatment of the material when subjected under proper moisture conditions to the effects of an oscillating electromagnetic field.
Description (OCR text may contain errors)
United States Patent 1191 Thrower, Jr.
[ PROCESS FOR HEAT SETTING CRIMPED SYNTHETIC POLYMERIC FIBER TOW  Inventor: Herbert T. Thrower, Jr.,
 Assignee: Hystron Fibers Incorporated,
 Filed: July 29, 1971,  Appl. No.: 167,156
 US. Cl. 117/931 DH, 57/157 TS, 34/1, 1l7/l38.8 F, 117/1395 CF, 117/1395 co, 219/1061 51 111 ,01. B06111 1 1/11 1, H05b 9/00  Field of Search. .ll 7/93 ,1 on, 139,511, 138.8 F, 117/1395 CF, 139.5WCQ;734 /1; 162/192;219/10.61; 57/157 TS  References Cited UNITED STATES PATENTS 2,473,251 6/1949 Hsu l17/93.I DH
5 16 X Z 5 12 U) 0! L 8 CD I 1111 3,819,402 June 25, 1974 2,618,796 11/1952 Brophy l17/93.1 DH 2,730,481 l/l956 Day 1l7/93.l DH 2,865,790 12/1958 Baer 117/93,] DH
OTHER PUBLICATIONS Von Hippel, Dielectric Materials and Applications, John Wiley & Sons Inc., New York, p. 361, (1954).
Primary Examiner-William D. Martin Assistant Examiner-John H. Newsome Attorney, Agent, or Firm-Wellington M. Manning, Jr.
[ 5 7] ABSTRACT 3 Claims, 1 Drawing Figure RELATIVE LOSS FACTOR OF FINISH, KIIX 1o" EFFECT OF LOSS FACTOR OF FINISH 0N HOT AIR SHRINKAGE OF FIBER HEAT-SET IN AN OSCILLATING ELECTROMAGNETIC FIELD PAIENIED 3. B 1 9,402
2 I6 g I2 U) g 8 1/ 3 RELATIVE LOSS FACTOR OF FINISH, KX IO EFFECT OF LOSS FACTOR OF FINISH ON HOT AIR SHRINKAGE OF FIBER HEAT-SET IN AN OSCILLATING ELECTROMAGNETIC FIELD INVENTOR. HERBERT T. THROWER,JR.
ATTORNEY BACKGROUND OF THE INVENTION The use of an oscillating electromagnetic field for the heat treatment of various and sundry materials has long been known. Depending upon the particular material or load being treated, numerous variations and modifications have been made to the apparatus for creating the electromagnetic field, to the design of equipment for a particular application of the electromagnetic field, preconditioning of the material to be subjected to the electromagnetic field, and the like. Oscillating electromagnetic fields have been employed to dry paper, textiles, foods, and the like; to heat set textiles; to treat packaging materials; for moisture leveling; and other wide and varied uses.
More particularly, the application of an oscillating electromagnetic field to the various products may involve an arrangement of apparatus whereby opposite plates or grids are provided in parallel or angular relationship with the load to be treated passing therebetween. Likewise, rods may be positioned in a side by side relationship with the material passing adjacent thereto or parallel rods may be deployed side by side and apart from each other in opposite banks with the material passing therebetween. Depending upon the particular product being subjected to the effects of the field, one of the above referred to arrangements could be employed.
Numerous variations have been made in the use of oscillating electromagnetic fields for the treating or drying of paper, textiles, food and the like. For example, substantial work has been conducted on the particular arrangement of the field producing apparatus. Such work was superficially mentioned above wherein opposite plates or grids, side by side rods or opposite banks of side by side rods have been used. Additionally, it has been found by some that a particular end result may be obtained by varying the attitude of the load (the material being treated) with respect to the electromagnetic field. As such, the load could be physically arranged to maintain a particular relationship to the geometry of the electric field. Moreover, frequency variations have been found to be useful in drying where it has been stated that as the moisture content of the load becomes lower, the frequency should be increased to continue to remove a desired amount of moisture. In certain cases, the oppositely positioned plates are angled in at one end, toward each other whereby the voltage gradient increases with the decreasing space between the plates. It has further been stated that certain conditioning of the load prior to exposure to the electromagnetic field will achieve a certain end result.
Generally speaking, the prior art has been quite inconsistent in the theoretical aspects of preconditioning of a substrate prior to passage through an oscillating electromagnetic field for the heating or otherwise treating of the substrate. For example, statements have been made in the prior art to the effect that the dielectric. constant of a material appliedto a load and subjected to an oscillating electromagnetic field is completely determinative of the improved heating of the load in the field. Further. statements have been made that relate a material having a high dielectric constant to also having a high loss factor to thus improve drying, etc. of a load under the effects of an oscillating electromagnetic field. Voltage variation across the electrodes that are utilized to create the electromagnetic field has also been taught to afford improvement. Hence, as a mate- 5 rial loses moisture, its power factor decreases thus necessitating a higher voltage to maintain a relatively uniform effect on the material. Dipole moment of a material used to finish a textile substrate has also been stressed as an important factor in improved effects on the substrate in oscillating electromagnetic fields. For example, one source stated that a material having a high dipole moment, such as water, experiences extreme molecular vibration in accord with the rapidly reversing polarity of the electrodes, thereby creating increased heat on the load.
All of the above statements prior to a vast amount of work that has been done in the field of oscillating electromagnetic energy for industrial or other use. The present invention is still a further advance in this particular art, and teaches an improved process for the heating or otherwise heat treating of substrates, particularly textile materials by the addition of certain ionic ingredients thereto.
While the prior art is quite sizeable and contains teachings pertinent to the heating of materials in an oscillating electromagnetic field, there is no teaching or suggestion in the prior art of the present invention. The prior art is exemplified by U.S. Pat. No. 2,390,572 to Brabander; U.S. Pat. No. 2,503,779 to Story; U.S. Pat. No. 2,530,680 to Burkholder; U.S. Pat. No. 2,709,856 to Hunter et al; U.S. Pat. No. 3,205,334 to Manwaring; U.S. Pat. No. 3,292,270 to Spunt; U.S. Pat. No. 3,399,460 to Russell; U.S. Pat. No. 3,435,534 to Knobloch et al; U.S. Pat. No. 3,484,179 to Adams et al; U.S. Pat. No. 3,485,984 to Cerutti and U.S. Pat. No. 3,531,551 to McDonough and British patent 1,009,586 to L & L'Manufacturing, lnc.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved process for the heating of textile materials in an oscillating electromagnetic field.
Another object of the present invention is to provide an improved process for the heat setting of synthetic polymers under the effects of an oscillating electromagnetic field.
Still another object of the present invention is to provide an improved process for the heat treatment of a dielectric material in an oscillating electromagnetic field.
Another object of the present invention is to provide an improved process for the heat treating of synthetic polymeric fibers in an oscillating electromagnetic field.
at least 4 per cent based on dry weight of the substrate.
Textile materials that may be treated by the process of the present invention include, but are not limited to filament, yarn, tow, staple, nonwoven, knit, woven, etc.
substrates. Furthermore, the textile material may be a natural material, a synthetic polymer or a combination of the two. Exemplary of suitable synthetic polymeric materials that may also be treated according to the present invention are polyesters, polyamides, polyolefins, polyacrylonitriles and the like.
The process of the present invention may thus be utilized for the heating of textile materials either as piece goods or in a continuous manner as in a process line. Furthermore, the process of the present invention is ideally suited for the heat setting of textile materials containing or consisting of high molecular weight syn- .thetic polymeric materials such as polyester fibers or filaments. The process of the present invention is further suited for generating heat in a material suitable for the bonding of lamina to form a laminate; heat sealing of plastics; for the application, drying, or curing of textile finishing compositions, coatings, films and the like.
. Moreover, the process of the present invention may be controlled in such a manner to heat a substrate without causing damage to the substrate and in particular to heat a textile material having a particular finish thereon to remove a carrier from the finish without activating other ingredients of the finish as might be required prior to curing a textile resin, for example, for permanent press applications or even curing the textile resin, if desired.
The present invention is thus directed to the addition of ionic materials in a carrier such as water to amaterial to be treated in an oscillating electromagnetic field. Ionic materials having a high loss factor in the particular operating frequency improve heat conversion in the electromagnetic field. These ionic materials may be cationic, anionic, or may be of an organic or inorganic nature.
The operating frequency range of the oscillating electromagnetic field can be set as desired. It has been determined, however, that the process of the present invention performs best at lower frequencies. Accordingly, an operating frequency for the oscillating elec tromagnetic field is preferred in a range up to about 300 megahertz.
BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a graphical presentation of the effect of loss factor of a finish composition on residual shrinkage of a heat treated polyester fiber.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS The process of the present invention is suitable for the heating of numerous substrates, particularly textile substrates including both natural and synthetic textile materials. For example, cotton, wool and rayon exemplify natural textile materials. Polymers, copolymers, terpolymers, etc. containing polyesters, polyamides, polyolefins, polyacrylonitriles, and the like including the possible modifications thereto, typify synthetic polymers that may be treated by the present process. Additionally, blends of natural and synthetic material may likewise be treated. Insofar as the type of substrate, per se is concerned, the process of the present invention may be advantageously utilized for fibers, yarns, staple, tow, fabrics, garments, films, coatings, laminates and the like.
strued to include the removal of moisture from a load,
heat setting of the load or portions thereof, curing of a load or the like. In fact, a preferred use of the process of the present invention is to heat set wet crimped polyester fiber tow which is measured by resulting shrinkage of the fiber in hot air or water. As such, the present process willbe hereinafter described with relation to heat setting of polyester filament tow, though the principals alluded to equally apply for conventional drying or other heat treatment of the materials and substrates hereinbefore mentioned.
A finish containing a certain amount of the active ionic ingredient is applied to the textile material, in this case, a polyester filament tow which is to be heat set. Preferably, the finish composition will be applied in an aqueous mixture though numerous other carriers or bases may be utilized to obtain the same or similar results. The textile material having the particular improved finish thereon is passed through an oscillating electromagnetic field under proper moisture conditions where improved heat setting of the polyester filaments takes place. In the sense of application of the finish to the substrate, in general, the ionic constituent may be applied to the textile material at any point prior to treatment in the oscillating electromagnetic field, provided that, prior to treatment in said field, the substrate has a proper moisture content. Hence, the ionic compound may be applied in an aqueous composition, may be incorporated into the polymer, may be added in a paste, semi dry or dry state or the like. Thereafter, if the substrate does not contain the proper moisture content, moisture must be added to achieve same. Likewise, the ionic constituent may be included in a stretch finish bath or the like either alone or with other constituents as might be desirable for a particular result.
Moisture conditions according to the teachings of the present invention are an important variable in the process. A dry substrate, one having an initial moisture content below about 4 per cent by weight, will not perform satisfactorily according to the teachings of the present invention. It is thus necessary to present the substrate to the electromagnetic field, at a moisture content of at least about 4 per cent by weight of the substrate. Preferably, the moisture content of the substrate should be at least about 7.5 per cent by weight of the substrate. Beyond about 20 per cent moisture based on the weight of the substrate, however, the improved effects became uneconomical due to the cost of moisture removal. As such, after application of the finish, the moisture content should preferably be con-' trolled in the range of about 4 to about 20 per cent based on the weight of the substrate. Thus liquid may be added to the substrate or expelled from the substrate prior to subjecting the substrate to the oscillating electromagnetic field. Moisture as referred to herein in-' cludes any liquid carrier that is compatible with both the ionic compound and the substrate without adverse effects thereto, and that can be removed by the electromagnetic field. r
The ionic materials added to the substrate to bring about the improved heating conditions according to the teachings of the present invention should yield a finish composition having a higher relative loss factor than that of water. Much of the prior art refers to water as being the key to success of electromagnetic fields with out any definition as to the particular water being used. Demineralized water for example gives no effect whatsoever, though much of the prior art credits water as the active component for improved heating. It can be hypothesized that the water being used according to the prior art contained a certain ion concentration such that some effect was obtained. Such is, however, far from a teaching of the present invention. Tap water varies considerably from one area to another. Moreover, tap water in the same area will vary considerably in ion content at different times of the year. Hence what might improve the effects of an oscillating electromagnetic field at one time of the year will have little or no effect at a different time of the year. The present invention has now precisely determined the active ingredients that improve the heating effects on a substrate in an oscillating electromagnetic field. With the teachings set forth herein, one can now completely and consistently control the improved heating to realize an anticipated result.
it has been determined that ionic materials having a high loss factor at the operating frequency of an oscillating electromagnetic field improve the heating effects of the field when added to a material being subjected to the field.
Theoretically, the heating in an oscillating electromagnetic field is predicated upon the ability of the load to convert available electrical energy into heat. Moreover, a load placed between the plates of a radio frequency generator may be considered analogous to a capacitor and resistor in paralleL'Current flowing through the capacitor is considered as charging current and current through the resistor is considered as loss current. The loss current is that portion that is converted into heat. Total current flow in the field may thus be defined according to Von Hippel, Dielectric Materials and Applications, pp 3, 4. M.l.T. Press (1954), as
l total l charging l loss where:
1 total total electrical current through the electromagnetic field l charging charging current component that leads by a temporal phase angle of 90 l loss loss current component in phase with voltage j= a complex algebra vector operator w angular frequency of applied current C capacitance of the load C capacitance of free space G reciprocal of load resistance V applied voltage e permittivity of the load e, permittivity of free space e'/e,, relative permittivity k v Total current flow may thus further be defined as 1 total jwk*C0V relative dielectric constant e'/e tan 5 loss tangent or dissipation factor 1 loss loss current component in phase with voltage l total (/wk' w COV (8 Hence, comparing equations 3 and 8, it is seen that the product of the loss factor and the frequency, called the dielectric conductivity, determines the amount of electrical energy that is transformed into heat. To increase the heating of a load under the effects of an electromagnetic field operating at a set frequency, the loss factor associated with the load should thus be increased. Further, depending upon the magnitude of the operating frequency, the loss factor of a material has been found to be substantially independent of its dielectric constant.
Ionic finishes suitable for application to polyester filaments according to the teachings of the present invention may be anionic or cationic in nature and further the ionic constituent may be an organic or inorganic compound. Examples of suitable ionic compounds that may be added to the fiber finishes and applied to the filaments include, but are not limited to, sodium nitrite, magnesium chloride, sodium sulphate, Parastat C-2, a cationic diethyl sulfate imidazoline, produced by Trylon Chemical, lnc., Mauldin, South Carolina and Tryfac 525K, an alkyl ethyoxy potassium phosphate, produced by Trylon Chemical, Inc., Mauldin, South Carolina. Each of the compounds listed above, when added to polyester filaments in an aqueous finish composition, brought about a noticeably improved heating of polyester filaments to the point of heat setting the previously crimped filaments. in addition to the ionic compounds applied to the textile substrate, other ingredients may be simultaneously applied therewith. For example, a normal finish for a synthetic polymeric fiber or filament may include not only the ionic constituent therein, but also dyestuffs, antistats, lubricants and other finishing compounds such as textile resins and the like. Also, as mentioned above, while the composition is preferably an aqueous composition, other liquid carriers may be employed.
The presence of the ionic compound in the finish improves the conversion of electrical energy into heat whereby the previously crimped filaments are heat set. The degree of heat setting is evidenced by the per cent fiber shrinkage in hot air at 392F. A low per cent shrinkage indicates good heat setting. It has been shown that an ionic material containing composition having a high relative loss factor measured at room temperature and a frequency of 15 megahertz will, when added to a load, improve the conversion of electrical energy into heat when the load is passed through an oscillating electromagnetic field. The degree of heating of the load may thus be empirically predicted by control of ion concentration in the finish composition, operating frequency of the oscillating electromagnetic field, voltage gradient across the field and moisture content of the load.
Though as mentioned above, a relative loss factor greater than water shows improvement, it is preferred according to the teachings of the present invention that the composition applied to the load have a relative loss factor of at least about 300 when measured at room temperature and 15 megahertz. A finish composition having a relative loss factor of at least about 300 at the previously mentioned conditions converts sufficient electrical energy into heat to heat set the previously crimped polyester filaments. Temperatures significantly higher than 212F. are generally required for suitable heat setting of polyester filament tows, and though an aqueous finish composition has been used predominantly, it is hypothesized that as water is evaporated, the concentration of ions increases to thus raise the boiling point of the remaining aqueous medium. As such, the higher heat setting temperatures are reached in the field. It is not intended, however, that the present invention be limited to this theory.
Addition of ionic compoundstoa finish increases the electrical conductivity of the finish. Hence, sufficient ionic material should be added to the finish to permit conductance of the electrical energy to be converted into heat. There is not, however, a direct relationship between finish conductivity and heat generation in the electromagnetic field. Instead, for each particular system, there is a level of conductivity at which sufficient current may pass and beyond which, increases in conductivity though helpful, are not appreciably additive towards further heat generating capability. Beyond about 0.4 millimhos per centimeter, for example, a higher ion concentration will not appreciably add to the heat generation capability in the electromagnetic field. Also, high conductivity in a finish having a low relative loss factor will not perform satisfactorily according to the teachings of the present invention. riieo seiaiifigfreqtifieyafifi electromagnetfifild is a further important consideration. Improved effects due to the addition of ionic materials to the load should be noticed at any operating frequency. The greatest improvement has been noticed, however, in the lowerfrequency range of the spectrum. Hence, an electromagnetic field oscillating at a frequency of up to about 300 megahertz is preferred for practice of the process of the present invention. A frequency range of from about 0.1 to about 30 megahertz is further preferred. The lower frequency level is more economical and more effective during operation.
Voltage gradient across the electromagnetic field must also be considered for the process can be rendered unsuccessful by use of an incorrect voltage gradicut for the particular material being treated. Too high a voltage gradient or inadequate vapor removal capacity for example, can cause arcing between the electrodes which will deactivate the field producing generator. Hence, a proper voltage gradient for a particular system (load and finish) should be that gradient as high as possible without causing arcing across the electrodes. Such a condition cannot be numerically expressed due to the large variance in materials that may be treated and ionic compounds being used. Likewise, there is great divergence in the expected end result. For the heat setting of high molecular weight synthetic polymer fibers and filaments, a voltage gradient in the range of from about 0.2 to about 5.0 kilovolts per centi-' meter spacing between the electrodes is preferred.
Having discussed parameters of the present invention, the following examples are submitted to more fully describe the specifics of the invention and to permit a better understanding thereof.
quency oven, Model HFV60, manufactured by Siemens, AG, Erlangen, Germany, and passed therethrough at a rate sufficient to permit a residence time of 65 seconds in the oven. Plates in the oven were set at a gap of 13 centimeters at entrance and tapered to a 9 centimeter gap at exit. Applied voltage was 15,000 volts and operating frequency was 15 megahertz. Measured current through the oven was 1.1 amps. The tow entering the oven exhibited a moisture content of 6 per cent by weight and a fiber shrinkage of 22 per cent in hot air at 392F. Samples were taken from the tow at the exit end of the oven and analyzed for shrinkage in hot air at 392F. Hot air shrinkage of the filament samples averaged 21.1 per cent. Hence, though some of the water may have been removed from the tow during passage of the tow through the oven, the tow was still moist to the touch and the 21.1 per cent shrinkage in hot air after passage through the ovenindicated virtually no heat setting of the crimped filaments. Data and results from Example I are reported in Table I.
" amnesia Example I was repeated under identical conditions except for finish composition. In Examples 2-16, various organic and inorganic ionic compounds were added to a finish which was applied to the tow prior to stretching in steam. Data and results from Examples 2-16 are set forth below in Table I. 7 W
Normal shrinkage for this particular polyester fiber is in the range of 20 to 22 per cent. From Table I, it can readily be seen that low fiber shrinkage and thus good heat setting was achieved when certain ionic compoundswere added to the finish. Note, however, although urea has a high dipole moment, it has a relatively low loss factor and thus performed only slightly better than demineralized water. Also note that arcing occurred when sodium acetate was added. The arcing was presumed to be due to rapid decomposition of the sodium acetate, yielding conductive vapor betweenthe electrodes. Aluminum sulfate also showed only a slight improvement over demineralized water. As can be seen below, both aluminum sulfate and urea solutions were analyzed to have relatively low loss factors.
Results from Table 1 thus show ionic compounds, both organic and inorganic, as contributory to improved heat setting of polyester fibers under the effects of an oscillating electromagnetic field. Low fiber shrinkage as mentioned above, is evidence that the fiber underwent sufficient heating to set the molecular structure of the fibers in the crimped state. An acceptable residual shrinkage for the particular polyester fiber treated is in the neighborhood of 6 per cent or less. Hence, Examples 2l6 dramatically illustrate the improvement obtained by adding an ionic compound to a the finish. By so doing, the proper heat setting may take place in the RP. oven and conventional drying can be avoided thereby. Stretch line speed can therefore be TABLE I EFFECTS OF IONIC FINISHES ON POLYETHYLENE TEREPHTHALATE FIBER SHRINKAGE EXAMPLE FINISH SPECIFICATION CURRENT FIBER SHRINKAGE NO. IN OVEN AFTER TREATMENT Component Solids Conc. Conductivity millimhos/cm amps 1 Demineralized H O 0.0 0.003 1.1 21.1 2 Urea 0.39 0.0387 1.1 18.4 3 NaNo 0.044 1.347 1.5 8.9 4 do. 0.020 0.449 1.95 5 .3 5 do. 0.044 0.587 1.6 6.1 6 do. 0194 2.034 1.95 3.6 7 do. 0.44 4.738 1.8 3.1 8 NaAc 0.53 0.042 Arcing 18.3 9 MgCl, 0.66 4.389 1.95 2.1 w mas n. 9-64 90.35 1-2 1 l Nil-2S0. 0.046 0.542 1.9 5.6 12 Parastat C-2 3.2 0.570 1.9 3.2 13 do 1.0 1.211 1.75 5.9 14 Parastat C-2 1.0 0.287 1.8 6.2 15 Tryfac 525K 1 0 3.323 1.7 6.1 16 Tryfac 525K 5 0 2.412 1.8 g 5.3
V 1 Fiber shrinkage measured in hot air at 392F. 2 Parastat C-Z is a cationic diethyl sulfate imidazoline. Tryfac 525K is an anionic alkyl potassium phosphate. pH= 5.0
increased substantially over conventional dryers" and also over a conventional dryer in tandem with a radio frequency oven. Moreover, power consumption of the radio frequency oven is low compared to conventional heat setting of the polyester fibers.
EXAMPLE I? 4 dure was used to measure the dielectric properties of 5 the solutions. Tabulated data and results of the analyses. are presented in Table II below. Also for comparative purposes, the fiber shrinkage data from Table l is reproduced beside the appropriate materials. 50
TAELE II A plot of relative loss factor for ionic compositions versus fiber shrinkage in hot air at 392F. is shown in FIG. 1. The solid line drawn through the points clearly indicates a definite correlation between loss factor of the finish and heat effect on the fiber load. Hence, the experimental data of Table I is reinforced by the analytical data of Table II to definitely relate the loss factor of the finish at the operating frequency to the heating effect on a load subjected to an oscillating electromagnetic field.
Having described the present invention in detail, it is obvious that one skilled in the art will be able to make variations and modifications thereto without departing from the scope of the invention. Accordingly, the scope of the present invention should be determined only by the claims appended hereto.
What is claimed is:
1. An improved process for continuously heat setting high molecular weight synthetic polymeric fiber tow comprising the steps of:
a. applying a finish composition onto said tow, said finish composition having a relative loss factor of at least about 300 when measured at room temperature and 15 megahertz;
b. crimping said tow; and
RELATIVE LOSS FACTOR FOR SPIN FINISHES Fiber shrinkage measured in hot air at 392F. Parastat O2 is a cationic dicthyl sulfate imidazoline. l'ryfac 525K is an anionic alkyl potassium phosphate.
lar weight synthetic polymeric fiber tow as defined in claim 1 wherein the tow is a polyester fiber tow.
3. The process as defined in claim 1 wherein the composition contains anionic constituent selected from the group consisting of sodium nitrite, magnesium chloride, sodium sulfate, an alkyl sulfate imidazoline and an alkyl ethoxy potassium phosphate.