US2346324A - Treatment of fibrous insulating materials - Google Patents

Description

purpose.

the wire either in selected single colors or in Patented Apr. 11,

- UNITED STATES 2,346,324 TREATMENT OF FIBROUS INSULATING MATERIALS Thomas E. ODonnell, Westfleld, N. 1.,

to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application August 1:. 1941,

Serial No. 406,724

6 Claims.

This invention relates to the treatment of fibrous insulating materials, and more particularly to methods for treating fibrous materials for use as insulation on electrical conductors.

Electrlcalconductors employed in electrical apparatus, such as communication equipment, are often provided with fibrous insulation, such as silk or cotton, and the type of fibrous material used in each instance depends primarily upon service requirements and.cost considerations. It is, of course, desirable to use the more plentiful and less expensive cotton wherever possible and a primary consideration which normally governs and restricts the use of cotton for this purpose is the fact that its electrical insulating characteristics tend to vary widely with service con- -(iltion s.- Ordinarily, cotton possesses fairly good insulating properties in a relatively dry state,

but its insulation resistance values are lowered substantially when the cotton is exposed to moist air. Consequently, it is desirable to improve the insulation resistance of the cotton, particularly in the presence of moisture, in order to permit its use on conductors which encounter such conditions in service.

In many cases it is desirable to provide insulated wires with some'identifying marking and when fibrous insulation is used on the wires it is convenient to employ colored materials for this 'Ihe colored materials are applied on color combinations as a means of identifying in-. dividual wires in the, apparatus or circuits. in which they are eventually incorporated.

The present invention is particularly adapted to the production of cotton in a variety of colors for use as insulation on electrical conductors that require high insulation resistance values over a wide range of operating conditions.

An object of this invention is the provision of improved methods for treating fibrous materials, such as cotton in strand or textile form, to incorporate a durable and fast dye in the cotton and also improve the electrical insulating char- .4

acterlstics of the cotton.

In accordance with one embodiment of the invention, fibrous material, such as cotton strand, is enclosedin a pressure chamber and a hot aniline dye liquor containing calcined gypsum in solution is circulated under pressure through the fibrous material for a predetermined period, after which the liquor is-drained from the pressure chamber and a dilute aqueous carbonic acid solution ,then circulated through the pressure chamber and the cotton for a definite time period.

The cotton may be then washed with clear water and thoroughly dried to complete the process.

The invention can be practiced conveniently in a conventional dyeing machine, such .as the Franklin dyeing machine, the Thies dyeing machine" or the Obermaier dyeing machine,

all of which are well known and are employed generally for dyeing textile materials. All of these machines operate on a similar principle 10 and comprise a sealed pressure chamber which contains a plurality of perforated hollow spindles which support the textileand which are connected in a fluid supply system whereby fluids are fed under pressure, from a pump into the perforated spindles or into the pressure chamber adjacent to the spindles. The textile, usually strand wound somewhat loosely into cylindrical packages, is mounted on each perforated spindle. The pressure chamber is then sealed andthe fluid forced, under pressure from-the pump, through the perforated spindles, the textile and the pressure chamber, after which the fluid is returned to, the pump and recirculated continuously as long as the process is continued.

'These machines are provided with a suitable system of piping'and valves to permit circulating of the fluid through the cotton either outwardly from the spindle or inwardly to the spindle. In the first instance, usually designated as circulating from inside to outside, the fluid from the pump is forced through the perforated spindle, through the textile, through the pressure cham- 'ber, and back to the pump in that order. In the second instance, which is termed circulation from outside to inside, the path of fiuid flow runs from the pump into the pressure chamber, through the textile, through the perforations in the hollow spindle. and down through the spindle to a pipe running to the pump.

For the process of this invention, a number of the wound packages are inserted over each spindle of the above described apparatus and the packages on each spindle are then clamped to- .gether in end to end engagement. The tubes have bevelled end portions and are longitudinal- 1y compressible to a slight extent so that clamping the tubes on the spindle provides essentially tight Joints between successive packages with the as quantity of dye of the desired color is first added to hot water and stirred until the dye dissolves or forms a satisfactory suspension. The prepared dye liquor is then placed in the apparatus and brought to a. temperature of about 160 F., by either cooling or heating as required, and circulation of the liquor through the cotton packages, as above described, is then started.

Shortly after circulation of the dye liquor is started, a quantity of calcined gypsum is added anddissolved or suspended in the liquor or solution. The best grade of calcined gypsum is used for this purpose.

The quantity of calcined gypsum to be added at this stage of the process depends upon the quantity of cotton being processed and a quantity of calcined ypsum equal to .25% of the total weight of the cotton in process, in the pressure chamber, is added to the liquor shortly after circulation of the liquor through the cotton is started. Circulation of the liquor, which is then at a temperature between 155 F. and 165 F., preferably 160 F., is continued for about 15 minutes to provide a low temperature treating and dyeing period.' At the termration of this low temperature treating period, the temperature of the liquor, or treating solution, is raised gradually, conveniently by introducing live steam thereto, until it attains a temperature between 195 F. and 205 F., preferably 200 F. Circulation of the treating solution through the cotton is continued during this heating period and the addition of heat is controlled so that about 15 minutes, equal to the low temperature treating period, is required for the specified temperature rise. After the liquor reaches a temperature of 195-205 F., it is maintained at that temperature, by introduction of steam for example, and circulation of the solution through the cotton continued at that temperaturefor about one-half hour, or about twice the low temperature treating period. The exact durations of these temperature periods may vary from the given values but they should be coordinated and the above ratios .should be maintained with the low temperature and the heating periods of equal length and the high temperature treating period being twice the length of the low temperature treating period.

As stated above, the amount of calcined yp um added to the liquor near the beginning of the process depends upon the quantity of cotton in process, and a unit quantity equal to .25% of the cotton weight is added at that time. The total quantity of gypsum to be added during the complete process depends also upon the color of the dye being applied to the cotton. For certain colors, such as yellow and blue, no further additions of calcined gypsum are needed after the first addition is made near the start of the process and the unit" quantity added at'that time is adequate. For other colors, however, further additions of calcined gypsum are needed as the process progresses. For such colors as black,

brown, green, orange and red, three further additions of calcined gypsum, each equal to the unit quantity, or .25% of the cotton weight, are made during the operation, making a total of four additions. These unit quantities are added at uniform intervals, or roughly at the end of each 15 minute period. Thus, the first addition is made near the beginning of the process with the liquor at about 160 F., the second is made approximately 15 minutes later when heating of the solution to increase its temperature begins, the third addition is made at about the time the solution attains its maximum temperature, and the final addition is made at about the mid-point of circulation at the maximum temperature, or the high temperature treating period. Although no close coordination between the total volume of solution and amount of gypsum is required, the total quantity of gypsum added in four unit quantities, equal to 1% of the-cotton weight, will saturate the volume of liquor used with the corresponding weight of cotton.

During this operation, the direction of flow of the treating solution is reversed periodically, by proper regulation of the valves, to force the liquor successively from the inside to the outside of the cotton packages and from the outside to length of time, the pump is stopped and the liquor is removed from the pressure chamber. The cotton is then washed or flushed with clear water heated to a temperature of about 140 F. and in this operation the clear water is circulated through the apparatus and forced through the packages in the same manner employed for circulation of the treating solution.

In the next step in the process, the cotton is treated with a purifying liquid or solution which may be prepared by dissolving carbon dioxide gas in water to form a dilute aqueous solution of carbonic acid having a pH from 4 to 5. The usually available tap water is suitable for this purpose and the carbon dioxide gas is introduced to the water under suitable pressure to cause the necessary quantity of gas to dissolve and remain dissolved in the water.

The pH of tap water varies somewhat, depending mainly upon the water source and in some cases treating processes that are applied to the water supply, but most commonly available waters can be used for preparation of the purifying liquid by dissolving in the water a sufiicient quantity of carbon dioxide gas to provide a solution having the desired pH value.- Best results are obtained when the purification liquid, or agent, has apH 01' 4.5 and this exact value is used preferably, though the pH of the agent can vary between the limits of 4 and 5. For different tap waters, I different additions of CO2 are, 01' course, required to produce the desired pH- values but after the quantity of carbon dioxide required per unit volume of any particular tap water has once been established, it is convenient to prepare the purifying liquid in any desired quantities by merely combining the components in the established proportions.

The aqueous solution of carbonic acid is prepared in a suitable container and then introduced to the apparatus, wherein it is circulated through the pressure chamber and the cotton packages, as above described. During preparation of the solution, during any necessary storage period and while the solution is in the apparatus, it is maintained constantly under a suitable pressure to prevent escape of the carbon dioxide from the process. Circulation of the purifying solution is continued, with periodic reversals of circulation direction, for about one hour.

After completion of the washing operation, the cotton-may be flushed with clear water, after which it is removed from the apparatus, thoroughly dried and is then ready for subsequent operations.

The resultant product exhibits electrical insulating properties which are greatly superior to those possessed by ordinary cotton. This improvement is due partly to the removal from the cotton of certain ionizable impurities or electrolytes, such as compounds of the alkali metals, which occur naturally in cotton. The successive application to the cotton of the calcined gypsum and the carbonic acid solutions effectively removes these ionizable impurities and otherwise improves the electrical insulating properties of the cotton.

The manner in which these agents perform their respective and combined functions is not clearly understood. However, it appears that the cotton fibres have a high aifinity for the calcium cations present in the calcined gypsum solution and that the gypsum is carried into the fibres to replace portions of the more readily soluble and ionizable impurities found naturally in the cotton. The subsequent introduction of the carbonic acid solution accomplishes a further removal bf these ionizable impurities from the cotton and apparently also aflects the condition of the calcium deposits in the fibres with the re-- sult that they are irreversibly adsorbed by the fibres. Whatever the exact action of these agents may be, their use in accordance with this process results ma suificient improvement in the electrical insulating properties of the cotton to permit its adoption in many electrical circuits and apparatus.

The use of calcined gypsum in the dye liquor also improves the dyeing action and the condition of the dye deposit. As stated above, the cotton is supported in rigid packages on rigid perature approximately 160 F. and containing tubes in the processing apparatus. The addition of the calcined gypsum to the dye liquor, and the coordinated temperature cycles above described, assist the depositing of the dye in the cotton. The dye deposit in the cotton fibres is fast and durable and no appreciable bleeding of the dye occurs during the subsequent treatment with the carbonic acid solution and final washing with water.

Although the processes herein described are particularly adaptable for treating cotton in the form of strands wound into packages, the process is also suitable for treating fibrous materials in other forms, such as woven fabric. apparent that other adaptations and modifications of the process are feasible and it is to be understood that the invention is limited only by the scope of the appended claims.

What is claimed is:

1. In a method of preparing cotton for use as electrical insulation, the steps of treating the cotton with a water solution of dye heated to a temperature between 155 F. and 165 F. and containing a unit quantity of calcined gypsum for an initial treating period of predetermined length, then adding a second unit quantity of calcined gypsum equal to said first unit quantity i will be a unit quantity of calcined gypsum dissolved 'therein for a low temperature treating period of predetermined length, then adding a unit quantity of calcined gypsum to the liquor and simultaneously adding heat to the liquor to increase its temperature to about 200 F., adding another unit quantity of calcined gypsum to the liquor at the time the liquor attains a temperature of about 200 F., maintaining the liquor at a temperature of about 200 F. and treating the cotton therewith for a high temperature treating period of twice the length of the low temperature heating period, adding another unit quantity of calcined gypsum to the liquor at about the mid-point of said high temperature heating period, and finally treating the cotton mass with an aqueous solution of carbonic acid.

3. In a method of preparing cotton for use as electrical insulation, the steps of enclosing a mass of the cotton in a pressure chamber, forcing a water solution of dye heated to a temperature between F. and 155 F. and containing a unit quantity of calcined gypsum equal to approximately 25% of the weight of the cotton mass through the chamber and the cotton mass for a low temperature treating period of predetermined length, adding a second unit quantity of calcined gypsum to the treating solution and simultaneously adding heat to the solution to raise its temperature to 195 F.-205 F., adding a third unit quantity of calcined gyp um to the solution at the time the solution attains the higher temperature, maintaining the solution at the higher temperature range and forcing the solution through the chamber and cotton for a high temperature treating period .of substantially twice the length of the 10w temperature treating period, adding a fourth unit quantity of calcined gypsum to the solution at about the mid-point of said high temperature treating period, and finally forcing an aqueous solution-of carbonic acid through the chamber and cotton mass.

4. In a method of preparing cotton for use as electrical insulation, the steps of enclosing a mass of the cotton in a pressure chamber, forcing a water solution of dye heated to a temperature between 155 F. and F. and containing a unit quantity of calcined gypsum on the order v of 25% of the weight of the cotton mass through the chamber and the cotton mass for a low temperature treating period of definite length, then adding a unit quantity of calcined gypsum to the solution and simultaneously adding heat to the solution, said heat being added at a suitable rate to cause the solution to attain a temperature. between 'F. and 205 F. in a length of time equal to about the length of the low temperature treating period, while the solution is being forced through the cotton mass, adding a unit quantity of calcined gypsum to the solution at the time the solution attains. the higher temperature,

ture range and forcing the solution through the cotton mass for a high temperature treating period of twice the length of the low temperature treating period, adding a unit quantity of calcined gypsum to the solution at about the mid-point of the high temperature treating period, and subsequently forcing through the chamber and the cotton mass an aqueous solution of carbonic acid.

5. In a method of preparing cotton for use as electrical insulation, the steps of enclosing a measured mass of the cotton in a pressure chamber, forcing a water solution of dye heated to a temperature around 160 F. and containing a unit quantity of calcined gypsum equal to substantially 25% of the cotton mass weight through the chamber and the cotton mass for an initial treating period, then at the end of the initial treating period adding a unit quantity of calcined gypsum to the solution and simultaneously adding heat to the solution at a suitable rate to cause the solution to attain a temperature around 200 F. in a length of time equal to the initial treating period while the solution is being forced through the cotton mass, adding a unit quantity of calcined gypsum to the solution as soon as it attains the higher temperature, maintaining the treating solution at the higher temperature and forcing it through the cotton mass for a period of time equal to twice the length of the initial treating period, adding a unit quantity of calcined gypsum to the solution at about the mid-point of the period during which the solution is maintained at the higher temperature, and finally forcing through the cotton mass an aqueous solution of carbonic acid.

6. In a method of preparing cotton for use as electrical insulation, the steps of enclosing a mass of the cotton in a pressure chamber, initially treating the cotton for a period of about 15 minutes with a dye liquor heated to a temperature around 165 F. and containing a unit quantity of calcined gypsum equal to approximately 25% of the weight of the cotton mass, then adding a unit quantity of calcined gypsum to the liquor and simultaneously adding heat to the liquor to cause the liquor to attain a temperature between 195 F. and 205 F. in a period of about 15 minutes while treatment of the cotton with the liquor is continued, adding a unit quantity of calcined gypsum to the liquor at the time the liquor attains a temperature between 195? F. and 205 F., treating the cotton with the liquor at the higher temperature for a period of about 30 minutes and adding a unit quantity of calcined gypsum to the liquor at about the mid-point of said 30 minute period, and finally forcing through the cotton mass an aqueous solution of carbonic acid having a pH between 4 and 5.

THOMAS E. O'DONNELL.