Tampon Coated With Insertion Aid And Method For Coating

Abstract

A compressed absorbent tampon provided with an improved insertion-aid coating on at least the tip portion and a method for applying the improved coating and similar coatings to the tampon. The improved coating comprises a normally solid polyethylene glycol containing at least one stabilizing agent. Suitable agents include water-insoluble metal stearates and/or fumed silica.

Description

BACKGROUND OF THE INVENTION

In the manufacture of compressed absorbent tampons, and especially those of the type which are inserted into body cavities without the aid of an insertion tube or a lubricous cover and thus present an inherently dry surface to the body, it is desirable to coat at least the leading end or tip of the tampon with an insertion-aiding lubricant. A problem which has long plagued the industry is to find a suitable coating which will retain its lubricating ability under the severe temperature variations to which tampons are subjected during normal shipping and warehousing and yet which will dissolve readily under use conditions. The patented art is replete with proposed solutions to this problem. While some aspects are successfully solved by the various proposals, others seem to appear with vexing regularity. It is well known, for example, as described in assignee's U.S. Pat. No. 3,428,044 of Feb. 18, 1969, that normally solid polyethylene glycols of an average molecular weight of about 1,000 and above, when coated on the tip of a precompressed tampon will provide a surface lubricity suitable for use as an insertion aid. However, it was found that at the elevated temperatures which frequently occur in warehousing and shipping, this type of coating softens enough to permit migration of the coating into the body of the tampon. Under such conditions the surface where the coating had been applied then eventually reverts in appearance and feel to that of an uncoated tampon. As a result the desired lubricity is lost. In assignee's U.S. application Ser. No. 807,490 filed Mar. 17, 1969 and now U.S. Pat. No. 3,595,236 a more stable polyethylene glycol coating is described in which the stability and opacity of mixtures of specified molecular weight polyethylene glycols are improved by the addition of starch. While this composition was found to be an improvement over earlier type coatings, it still lacked the desired long term stability. This invention is directed to a polyethylene glycol coating formulation which overcomes most of the disadvantages formerly encountered. A preferred method of applying the coating to a tampon tip is also disclosed.

Accordingly, an important object of the present invention is to provide an improved insertion-aid coating for precompressed tampons which coating remains stable during long term shipment and storage.

Another object is to provide a suitable method for applying the improved coating and similar coating materials to precompressed tampons.

SUMMARY OF THE INVENTION

A polyethylene glycol lubricant material which is normally solid at room temperature, is heated and thereby melted to a mobile fluid state. An adjuvant material selected from the group consisting of water-insoluble metal stearates and fumed silica or mixtures thereof is dispersed in the melted polyethylene glycol. A small metered amount of this melted mixture is injected into a smooth-surface die having a cavity of a configuration conforming to the configuration of the tip of a precompressed tampon which is to be coated. The die is maintained at a temperature less than the melting point of the mixture. When the mixture is injected into the cooled die cavity it forms a bead which becomes partially congealed on its outer surface due to contact with the cooled cavity, but the major portion of the interior remains fluid and mobile. The tip of the precompressed tampon is pressed into the cavity containing the internally mobile mixture whereby the mixture is molded around the tampon tip to form a smooth cast coating. When the tampon is withdrawn, the molded coating readily releases from the cavity without leaving residue. Apparently this is due to the lubricating properties of the adjuvant as well as the slight shrinkage of the coating as it hardens. The tampon tip is thus provided with a smoothly molded coating. The tampon may also be axially rotated in the die during the molding operation. This axial rotation step speeds up the setting or hardening of the coating, which is desirable when using lower molecular weight polymers. It also results in a dull, matte surface rather than the smooth cast surface noted above.

In addition to facilitating residue-free release from the cavity the dispersed adjuvant has other functions which improve performance and appearance of the finished tampons. One is that it stabilizes the polyethylene glycol coating so that the coating remains in fresh condition and does not migrate into the tampon or leave a dry surface even after a prolonged exposure at temperatures of 150.degree.F. Another is that it provides an opaque color and cosmetic appearance to the coated surface.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic illustration of a means suitable for carrying out the method for coating tampons in accordance with this invention.

FIG. 2 is a section of a die cavity taken at 2--2 of FIG. 1 showing a metered amount of lubricant mixture disposed therein.

FIG. 3 is a section similar to FIG. 2 taken at 3--3 of FIG. 1 showing a tampon pressed into the die cavity with the lubricant mixture molded around the tampon tip.

FIG. 4 is a perspective view of a tampon with a cast coating of lubricant on the tip thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated above, this invention is particularly directed to an improved insertion-aid coating for precompressed self-sustaining tampons and a method for applying the coating while in a mobile condition to the tip portion of the tampon. The primary coating material is a normally solid polyethylene glycol and the improvement comprises the addition of particular stabilizing agents to the polyethylene glycol.

As shown in FIG. 4 of the drawings, the preferred tampon 30 comprises a body of absorbent material compressed to a self-sustaining cylindrical shape with a substantially hermispheric frontal portion or tip, and having a withdrawal string 31 attached to the rear portion. The tampon may be adapted for use for stick insertion by having an axially extending socket 32 centrally drilled part way into the rear portion into which a removable stick 33 may be seated. For digital insertion, the socket is not required.

FIG. 1 illustrates one method for carrying out the invention. The numeral 11 generally indicates a melting, mixing and injecting device for the polyethylene glycol. The device as shown comprises a heated tank 12 into which a normally solid polyethylene glycol is melted to a fluid state as indicated at 13. A small amount of a finely-powdered water-insoluble adjuvant selected from the group consisting of metal stearates and/or fumed silica is introduced into tank 12 through port 14 and dispersed in the melted polyethylene glycol by mixing device 15 driven by motor 16. Preferably the mixer is run continuously to provide a uniform dispersion. Connected to tank 12 is an extruder or ejector means 18 which is also equipped with a metering device 17 for metering the amount of the fluid polyethylene glycol mixture it is desired to eject.

A rotatable turntable 19 is disposed beneath ejector 18. The upper face of turntable 19 is provided with series of die cavities 20 disposed adjacent the circumference. Each die cavity 20 has an interior configuration which substantially conforms to the shape of the tampon it is desired to coat. The cavity shown is hemispheric and conforms to the rounded tampon tip shown in the drawings. The interior of turntable 20 is hollow and is preferably filled with a circulating coolant fluid 21 (FIGS. 2 and 3) which surrounds the outer wall of cavities 20 depending from the top wall of turntable 19 to maintain the dies 20 at a temperature below the melting point of the polyethylene glycol mixture. The coolant is fed through axially disposed tube 22 and removed at 23 through a concentric channel as indicated.

In operation, a metered amount 24 of the melted polyethylene glycol mixture containing the specified adjuvant is injected in timed sequence into each of the cavities 20 on turntable 19 as each cavity is rotated underneath ejector means 18. The turntable 19 may, of course, be rotated continuously or intermittently as desired.

The ejected fluid 24 forms a bead 25 in the bottom of the cavity as shown in FIG. 2. It will be seen that in this condition only a small portion of the bead surface is in contact with the cooled surface of the die cavity, so that only a small surface area of the bead 25 will congeal or start to solidify while the major portion remains mobile. After each cavity receives an injection of the coating mixture, the turntable continues to rotate past the ejection device, and the tip of a tampon 20 is pressed into the mixture-containing cavity at station B. As the tampon tip is pressed into the cavity it causes the polyethylene glycol mixture to flow and mold itself around the tampon tip in the form of a thin cast coating as shown at 34 in FIGS. 3 and 4. As the turntable 19 continues to rotate the cooling liquid 21 surrounding the die cavity reduces the temperature of the molded polyethylene glycol mixture below its melting point, causing the mixture to rapidly congeal and harden into a solidified condition. The coated tampon with a molded cap 34 of the polymer mixture on the tip thereof, as shown in FIG. 4, is then removed at station C. If desired the tampon may also be rotated axially on itself as turntable moves the tampon from station B to station C. This axial rotation step speeds up the hardening of the coating, but results in a dull, matte finish.

In the above-described process, it was found that the use of the specified adjuvant permits easy removal of the coated tampon from the die, leaving no residue. This easy release may be attributed to the additional lubricating ability contributed by the adjuvant, but may also come from the fact that the polyethylene glycol takes a firmer set with the adjuvant mixed therein.

The following Examples will set forth several specific embodiments of the invention.

Tampons with hemispherical tips as shown in the drawings were coated in the manner described with each of the formulations described below. In these formulas, polyethylene glycol with an average molecular weight of 1,000 is identified as PEG 1,000 and polyethylene glycol with an average molecular weight of 4,000 is identified as PEG 4,000. All parts are parts by weight. In each instance, the PEG 1,000 was heated to about 158.degree.F. to reduce it to a fluid state. The die cavity was maintained at about room temperature.

Example A. PEG 1,000 alone.

Example B. Ten parts PEG 1,000, 1 part fumed silica.

Example C. Ten parts PEG 1,000, 1 part fumed silica, 1 part magnesium stearate.

Example D. Ten parts PEG 1,000, 1 part fumed silica, 1 part aluminum stearate.

Example E. Ten parts PEG 1,000, 1 part fumed silica, 1 part zinc stearate.

Example F. Ten parts PEG 1,000, 1 part fumed silica, 1 part calcium stearate.

Example G. Ten parts PEG 1,000, 1 part magnesium stearate.

Example H. Ten parts PEG 1,000, 1 part aluminum stearate.

Example I. Ten parts PEG 1,000, 1 part zinc stearate.

Example J. Ten parts PEG 1,000, 1 part calcium stearate.

After tampons were coated with each of these mixtures, they were placed in a forced air oven at 150.degree.F. for 16 hours. At the end of that time, the Example A coating consisting of PEG 1,000 alone had completely migrated into the tampon. The coating formulations consisting of PEG 1,000 and fumed silica (Example B) as well as those containing PEG 1,000, fumed silica and a metal stearate (Examples C, D, E, F) all remained on the surface of the tampons and retained essentially all of their original smoothness and lubricity. Those formulations containing PEG 1,000 and a metal stearate (Examples G, H, I, J) remained on the surface of the tampon but appeared to lose some lubricity. However, this loss was not enough to make the coating defective. The coatings containing PEG 1,000 and the zinc stearate, the magnesium stearate, and the calcium stearate were a little drier and stickier than similar coatings which also contained fumed silica, while the coating containing PEG 1,000 and aluminum stearate took on a somewhat mottled appearance which was absent in the same coating containing fumed silica. In each case, however, the desired stability was present.

It will be noted therefore that while the metal stearate may be used alone, the combination of stearates with fumed silica is superior.

The above experiments were repeated except that in each of the formulations PEG 4,000 was used instead of PEG 1,000. Each of the coated tampons were heated for 16 hours at 150.degree.F to test stability. The results were substantially the same as those obtained when PEG 1,000 was used in the formulas.

In each case the metal stearate and fumed silica is added to the coating by simply blending it into the hot PEG melt. The fumed silica has been found to exert a thixotropic effect upon the formulation. That is, the formulation containing fumed silica remains very fluid while it is being stirred but when stirring stops, the formulation begins to thicken, eventually reaching a marshmallow type consistency. Upon stirring, the structure is rapidly broken down and the formulation becomes very fluid once more.

This thixotropic effect has been found to be advantageous for tampon coatings. The tampon is coated with the formulation in the hot fluid state so that the mixture readily flows around the tip as it is pressed into the die. However, because it is thixotropic when containing fumed silica, the coating does not become fluid when similar temperatures are reached during storage of the coated tampon due to the absence of physical agitation. It is believed this phenomenon also aids in preventing migration of the coating into the body of the tampon.

Fumed silica is silicon dioxide formed by the vapor phase hydrolysis of silicon tetrachloride. It is supplied as a low density water-insoluble powder with extremely small particle size and a large surface area. Although it is insoluble, the powder forms a clear, colloidal suspension in water. The grade of fumed silica used in the Examples described is sold under the trademark CAB-O-SIL by Cabot Corporation. It has been approved by the FDA for use in foods and pharmaceuticals.

The metal stearates may be used in their conventional commercial form which are water-insoluble powders. FDA approved grades should of course be used.

As indicated above, the polyethylene glycol should be one that is normally solid at room temperature. While PEG 600 has a melting point range of about 68.degree.F to 77.degree.F and can meet the definition, it is marginal in performance, and it is preferred that polyethylene glycols with an average molecular weight of about 1,000 and above be used. The preferred range is from about 1,000 to about 6,000. Lower molecular weight polymers may of course be used in admixture with higher weight polymers to obtain average molecular weights in the preferred range. Methoxy polyethylene glycol with an average molecular weight of about 750 may also be used.

While the description of the specific examples have been confined to polyethylene glycol and adjuvant mixtures, it will readily be seen that the method of application itself can readily be used for other coatings which are solid at room temperature but fluid at elevated temperature.

The described method has been found to be superior to the older methods of dipping the compressed tampon tip into the molten polyethylene glycol or of spraying partially congealed material onto the tip. By the described method much better control over the thickness and uniformity of the applied coating is possible. In addition, less coating material is required, providing advantages in both economy and performance.

While the resulting coating dissolves somewhat more slowly in body fluids than fresh polyethylene glycol coatings lacking a stabilizer, the fact that the method provides better control in applying a smaller amount of stable coating in a small confined area of the tip overcomes any disadvantage the slower solubility may have. As a result, the overall absorbence of the tampon is not deleteriously affected.

Claims

What is claimed is:

1. An absorbent cylindrical tampon having a stabilized insertion-aid coating on at least the tip portion thereof, said tampon comprising a compressed self-sustaining body of absorbent material and said coating comprising a molded cap of normally solid polyethylene glycol having dispersed therethrough a minor portion of a finely-powdered water-insoluble adjuvant selected from the group consisting of metal stearates and fumed silica.

2. The coated tampon of claim 1 wherein said metal stearates are selected from the group consisting of aluminum, calcium, magnesium and zinc stearate.

3. The coated tampon of claim 1 wherein said adjuvant is present in said mixture in the amount of from about 5 percent to about 15 percent by weight.

4. The coated tampon of claim 1 wherein said polyethylene glycol has an average molecular weight in the range of about 1,000 to about 6,000.

5. The coated tampon of claim 1 wherein said polyethylene glycol is a methoxy polyethylene glycol with an average molecular weight of about 750.

6. The coated tampon of claim 1 wherein said adjuvant comprises fumed silica and a metal stearate selected from the group consisting of aluminum, calcium, magnesium and zinc stearate.