MXPA97008499A - Thin wall pipe having an inte rib - Google Patents

Abstract

A thin-waltube is described having a wall which extends between the first and second ends. The wall has a thickness of less than about .03 inches. The tube also has a longitudinally extending rib formed on an inner periphery thereof. The rib allows the thin tube to be injection molded from a thermoplastic material using standard temperature ranges and relatively short cycle times

Description

TOBO DK THIN WALL HAVING AN INTERNAL RIB FIELD OF THE INVENTION This invention relates to a thin walled tube having an internal rib which can be injection molded of a thermoplastic material. More specifically, this invention relates to a thin-walled tube which has a longitudinally extending rib formed on an inner periphery thereof which facilitates distribution of the melted plastic to the ends of the tube during the molding process.

BACKGROUND OF THE INVENTION The tubular thermoplastic members have been manufactured by both extrusion molding and injection molding. Such tubes can be used in many different products and can vary in designs and dimensions. If a tube has a uniform cross-sectional configuration it can be cheaper and cost effective to form it by extrusion molding. However, if the tube has a non-uniform cross-sectional configuration it may be advantageous to form it by injection molding. It has been found that when it is necessary to produce pipes having a wall thickness of less than about .03 inches (about .76 mm) that injection molding may be the best to give consistent quality pipes which exhibit deviations standard lower along the main and / or minor diameters. However, even when the tubes are injection molded, difficulties have been encountered during the molding process when the wall thickness is relatively thin and the overall length is equal to or greater than about 2 inches (about 50 mm). Such difficulties increase when one wishes to mold such tubes by injection using a very short cycle time. Under these conditions, the molded plastic can solidify before the tube is completely molded.

The lack of ability to quickly move the melted plastic to the ends of the tube becomes more pronounced when the wall of the tube tapers in thickness, especially when tapering down from one end to the other end. To overcome this problem, one can change the characteristics of the plastic, for example, one can use a plastic exhibiting a superior melting point. Other solutions to the problem include increasing the cycle time, raising the operating temperature of the injection molding, using smaller cavity molds where possible, or using a combination of the above-identified characteristics to mold an acceptable tube by injection. Each of these changes will increase the cost of the finished tube. In addition, when the temperature of a mold rises, it is normal to increase the cooling cycle time in order to form a finished article. The operation of an injection mold at a higher temperature can also limit the types of thermoplastics which can be used to those having a relatively high melting point. Plastics with superior melting points can be more expensive.

One use for tubes having a thin panel structure is in the manufacture of plug applicators. Cap applicators are used by women to place a catamenial plug inside their vaginas. Such applicators are commercially available in either a single-tube design or a two-piece design. In the two-part applicator, the absorbent plug is retained in an outer tube and can be expelled therefrom by an inner tube or plug which is telescopically assembled there. The inner tube can be constructed with a very thin wall because most of the applied forces are directed along its longitudinal central axis. Since millions of such tubes are manufactured annually, any reduction in the amount of material needed to build a single tube can result in substantial cost savings.

For a common style of two-piece applicator, the inner tube or plug has its ends flared after assembly with the outer tube so that the two members do not separate. It is easy to flare the ends of the inner tube when the wall thickness of the inner tube is relatively thin.

A thin-walled tube having an internal rib has now been invented which can be injection molded of a thermoplastic material at commercial speeds and at an effective cost and in an efficient manner.

SYNTHESIS OF THE INVENTION Briefly, this invention relates to a tube having a thin wall which can be injection molded. The tube has a first end and a second end and the wall tapers to a smaller thickness adjacent to one of the ends. The tube also has a rib formed on its inner periphery which extends along at least a part of the entire length of the tube. The rib facilitates the distribution of melted plastic to both ends of the tube during the molding process.

The general object of this invention is to provide a tube having a thin wall which can be injection molded from a thermoplastic material. A more specific object of this invention is to provide a thin walled tube which has a longitudinally extending rib formed on the inner periphery thereof which facilitates the distribution of the melted plastic to the tube ends during the molding process .

Another object of this invention is to provide a tube having a wall thickness of less than about .03 inches (.76 mm).

A further object of this invention is to provide a thin walled tube having a constant external configuration and having a variable thickness.

Still another object of this invention is to provide a thin walled tube which can be economically and efficiently injection molded.

Yet another object of this invention is to provide a thin-walled tube which can be used as the inner tube of a two-piece plug applicator.

Other objects and advantages of the present invention will be more apparent to those skilled in the art in view of the description that follows and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a planar view of a cylindrically shaped and straight tube.

Figure 2 is a cross-sectional view of the tube shown in Figure 1 showing the rib extending longitudinally.

Figure 3 is an end view of Figure 2 showing the circular configuration of the tube.

Figure 4 is another embodiment of the cylindrically shaped and straight tube having a rib configured convolutely.

Figure 5 is an end view of Figure 4 showing the circular configuration of the tube.

Figure 6 is a planar view of an arcuately shaped tube.

Figure 7 is a sectional view of the arcuately shaped tube shown in Figure 6 exhibiting a tapered wall and a rib formed on the inner periphery of the wall.

Figure 8 is a straight end view of Figure 7 showing the oval cross-sectional configuration of the arcuate shaped tube.

Figure 9 is a planar view of an arcuate shaped tube having a thick area which serves as a rib extending from one end to the other end.

Figure 10 is an end view of the tube shown in Figure 9 taken along line 10-10 exhibiting a circular exterior configuration.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring to Figures 1-3, a tube 10 is shown which can be injection molded from a thermoplastic material. The tube 10 is a hollow cylinder coaxially aligned about a longitudinal axis and straight A-A. The tube 10 is formed of a molded thermoplastic material such as polyethylene, of polypropylene or of some combination thereof. Other kinds of thermoplastic materials can also be used. The material may have a high density or a low density and must have a melting point which is high enough to avoid burning or singeing during the injection molding cycle. High density polyethylene is one such material that is desirable to form a thin-walled tube which can be used as the inner tube or plug of a two-piece plug applicator. High density polyethylene is available from a number of sources. Two such sources include Union Carbide Chemicals and Plastics Company, Inc., having sales office at 3030 Warrenville Road, Suite 870, Lisie, Illinois, 60632 and Quantum Chemical Corporation, USI Division, 11500 Northlake Drive, Cincinnati, Ohio 45249 .

The tube 10 has a wall 12, see figure 2 and a predetermined section which extends from a first end 14 to the second end 16. The length of the tube 10 can vary as can the shape and the overall dimension of the tube . When the tube 10 is to be used as the plug member of a two-piece plug applicator, it must be at least 2 inches long (at least 50 mm), preferably at least 2.5 inches long. (at least 64 ram), and more preferably, about 3 inches (about 76 mm). The tube 10 is shown as having a circular or round cross-sectional configuration with a constant internal and external radius. It should be noted that the tube can be molded into other shapes if desired. For example, the tube may have a cross-sectional configuration in the form of an ellipse, an oval, a square, a rectangle, a triangle, etc. Since the tube is designed to be injection molded, corners or sharp or pointed surfaces should be rounded or removed. The tube must also have a scaled exterior configuration or some other non-uniform interior and / or exterior shape. It is also possible to form grooves or indentations on the inner and / or outer surfaces of the tube to help facilitate the release of the tube from the injection mold.

Referring to Figure 3, the tube 10 is shown having a circular or circular cross-sectional configuration with an internal periphery 18 formed on a radius ri and an outer periphery 20 formed on a radius r2. The outer periphery 20 should preferably be smooth.

Although the tube 10 is shown to be straight over its entire length, it can also be molded to have an arched or curved profile. Any non-linear, curved or bent form is within the scope of this invention. The particular curvature of the tube can be varied to suit the particular needs of one.

The wall 12 of the tube 10 is shown as having a thickness wt "which is uniform between the first and second ends, 14 and 16. For some applications, it may be necessary to use a wall of non-uniform or variable thicknesses. For example, the wall can be formed with a taper where the thickness decreases in only one direction, say from the first end 14 to the second end 16. It is also possible to mold the wall so that it has a maximum thickness located at or near of the central part of the tube and have a minimum thickness towards the ends 14 and 16.

The wall 12 is thin having a thickness of less than about .03 inches (about .76 mm). The thicknesses can range from between about .03 inches (about .76 mm) to down to .005 inches (about .13 mm). Preferably, the thickness is less than about .02 inches (about .51 mm) and, more preferably, it is less than about .015 inches (about .38 mm).

Referring again to Figure 2, the tube 10 also contains a rib 22 which is formed on the inner periphery 18 of the wall 12. In Figure 2, the rib 22 is shown extending along the entire length of the tube 10 from the first end 14 to the second end 16. However, the rib 22 must extend at least along half the length of the tube 10, and preferably it should extend along a main part of the length of the tube 10. By "main part" is meant a distance equal to at least 75 percent of the length of the tube 10.

The rib 22 is shown as a straight member formed parallel to the central axis length A-A. The rib 22 has a height "h" which is equal to the thickness wt "of the wall 12. However, it is possible to make the height wh * of the rib 22 less than or equal to or greater than the thickness wt" of the wall 12. Preferably, the height "h" of the rib 22 will be equal to or greater than the minimum thickness wt "of the wall 12. The reason for this is that when the wall 12 is very thin, the rib 22 is designed to act as a conduit for moving or transporting the melted thermoplastic material to both ends, 14 and 16, respectively so that the tube 10 can be formed completely.Therefore, the rib 22 acts as a channel or path for the melted plastic.As mentioned above, the The general shape of the rib 2 may vary but the semicircular cross-sectional configuration is preferred Other cross-sectional configurations may include square or rectangular shapes with rounded corners, or a teardrop shape, an elliptical shape, etc.

Since the dimensions of the rib 22 do not have to conform to narrow tolerances which are normally assigned to the outer periphery 20 of the tube 10, the rib 22 can be constructed almost in any desired shape and size. For example, when the tube 10 is designed to serve as the plunger member of a two-piece stopper applicator, the shape and dimension of the outside of the tube has to be molded by observing very close tolerances in order to allow the two members to interact telescopically The height, width and general configuration of the rib 22 can vary over its entire length, but preferably, all dimensions will be constant.

For best results, the rib 22 will have a height "h" which is at least equal to the minimum thickness of the wall 12. For very thin walls, having a thickness in the range of about .015 inches (about .38 mm) to about .02 inches (about 51 mm), the height wh "of the rib 22 can be increased to about two to three times the thickness wt "of the wall 12. This will ensure an adequate flow of the melted thermoplastic material at both ends 14 and 16 of the tube 10.

Referring again to FIGS. 1 and 2, the tube 10 has a gate 24 formed on the outer periphery 20. The gate 24 represents the location of the injection nozzle through which the melted thermoplastic material is introduced into the interior. mold cavity. In order to facilitate the molding of the tube 10, the gate 24 must be located approximately halfway between the first and second ends 14 and 16, respectively when the tube 10 is straight and the wall 12 has a constant thickness. For arched tubes and tubes having strange shapes or characteristics, especially for tubes having a varying wall thickness, the gate 24 may be offset to one end. Preferably, the gate will be located so that an approximately equal volume of molten plastic will flow in opposite directions towards the distally spaced ends 14 and 16. The depth of the gate 24 may vary but will normally be as low as possible. Preferably, the depth of gate 24 will be so sparse that it will apparently not be visible except for those familiar with the injection molding process.

Referring to Figures 4 and 5, an alternate modality of a thin-walled tube is shown 26. The tube 26 is a straight cylindrical member coaxially aligned about a longitudinal central axis B-B. The tube 26 has a wall 28 which extends between a first end and a second end 32. The wall 28 has a circular or round cross-sectional configuration with an inner periphery 34 formed on a radius r3 and an outer periphery 36 formed on a radius r4. The tube 26 also contains a rib 38 which is convolutely or spirally formed on the inner periphery 34 of the wall 28. The rib 38 extends along the entire length of the tube 26 from the first end 30 to the second end 32 The twisted or spiral rib 38 not only facilitates the distribution of the melted plastic at both ends 30 and 32 of the tube 26 but also provides structural rigidity to the tube 26 once the material forming the rib 38 solidifies. When such a tube 26 is injection molded it may be necessary to rotate either the inner core, the tube or both in order to release the finished molded tube without damaging the rib 38. The spiral or convoluted configuration of the rib 38 tends to providing the tube 26 with a more consistent and uniformly distributed compressive strength compared to the tube 10 shown in Figures 1-3.

Referring to Figure 5, the tube 26 is shown exhibiting a wall 28 which is thinner than the wall 12 shown in Figure 3. The wall 28 is formed on a radius r3 which is larger than the radius ri and has a thickness t2 which is much smaller than the thickness t3 of the rib 38. In fact, the maximum thickness t3 of the rib 38 is shown as being approximately three times the thickness t2 of the wall 28. Another difference in this embodiment is that the spirally formed rib 38 rotates through a circular arc of at least 360 ° on the inner periphery 34. The actual inclination of the spiral can vary depending on one's needs.

Referring now to Figures 6-8, a third embodiment is shown wherein an arcuate shaped tube 40 is shown formed on a curved center line C-C. The arcuately formed tube 40 has a wall 42 and a length which extends from the first end 44 to a second end 46. The arcuately shaped tube 40 can be formed on a curved path of any desired length. The arcuately shaped tube 40 is shown as having an oval cross-sectional configuration with an inner periphery 48 and an outer periphery 50. It should be noted that other profiles may be used in cross section, eg, a circular or round configuration. The configuration in oval cross section will have a larger dimension and a smaller one. The inner periphery 48 and the outer periphery 50 can have either a uniform or non-uniform profile along the length of the tube 40. Preferably, the outer periphery 50 has an essentially constant profile when the arcuately shaped tube 40 is to be used as the plunger member of a two-piece plug applicator.

Referring to Figure 1, the wall 42 tapers in thickness over the length of the tube 40. The wall 42 is thicker on one side of the first end 44 and tapers down to a narrower thickness on one side of the second end 46. This means that the second end 46 has larger internal dimensions than the first end 44. When an arcuate shaped tube 42 is injection molded and a core mold core is required to form the inner periphery 48, it is advantageous to tape the thickness of the wall 42 in order to facilitate the removal of the central mold core. The core mold core can then be retracted from the finished molded tube 40 by means of the second end 46. The thickness of the wall 42 can be tapered down from a thickness of about .03 inches (about 0.76 mm) to up thickness of around .005 inches (around .13 mm) The arcuately shaped tube 40 also contains a rib 52 which is formed on the inner periphery 48. The rib 52 is shown to extend almost to the full length of the tube 40. The rib 52 can extend to the full length of the tube 40 from the first end 44 to second end 46, if desired. The rib 52 stops just near both the first and second ends, 44 and 46 respectively, in order to allow the ends to be flared in a subsequent operation.

In order to facilitate the flare operation, it is beneficial to use a thin-walled structure. For this reason, the inner periphery 48 is believed to form an inclined surface 54 near the first end 44. The second end 44 already has a tapered wall thickness and therefore does not have to be chamfered. It should be noted that when the tube 40 is to be used, the plunger member of a two-piece plug applicator, which one way to ensure that the permeable inner tube 40 will be connected to the outer tube is to flare the ends of the tube. inner tube 40 after the tubes are assembled. The flared ends will prevent the inner tube 40 from being pushed or pulled in or out of the outer tube except by the exercise of extreme force. It should be noted that the rib 52 can be designed to extend to either or both ends 44 and 46 respectively, if desired.

The rib 52 has a height "hi" which is shown as being constant along the length of the tube 40. The rib 52 can vary in height if desired. The height wh? "Of the rib 52 may be less than, equal to or greater than the thickness of the wall 42. Since the thickness of the wall 42 varies, it is possible to assume that at some point the height x% h?" of the rib 52 will be less than, equal to or greater than the thickness of the wall 42. Preferably, the height Mh "of the rib 52 will be equal to or greater than the thickness of the wall 42 over a length of the tube 40 that represents at least half the length of the general tube The maximum thickness of the wall 42 should be less than about .03 inches (about .76 mm).

The arcuate shaped tube 40 also contains three grooves 56 formed in the outer periphery 50 which are located on one side of the first end 44. Three similar grooves 58 are located on one side of the second end 56. The grooves 56 and 58 are designed to engage with the semicircular rings (not shown) placed in two matching mold blocks. Upon joining the pair of mold blocks, the outer surface of the tube 40 is defined. Even when two sets of three slots 56 and 58 are shown, it is only necessary to have a single slot, either 56 and 58, formed in the outer periphery 50 on one side of only one of the ends 44 or 46. When only a single groove 56 or 58 is used, it is preferable to locate it on one side of the first end 44. The purpose of the groove or grooves 56 and / or 58, is to keep the molded tube 40 stationary when the core is removed. central mold (not shown) after the melted material forming the tube 40 solidifies. The presence of more than one slot 56 and / or 58 provides an added assurance that the molded tube 40 will remain stationary until the core mold core is completely removed from the inner periphery 52. In the embodiment shown in Fig. 7, two sets of three slots 56 and 58 are present at the respective ends 44 and 46 because the tube 40 is relatively long and is designed to serve as the plug member of a two-piece plug applicator. In this use, the slots 56 and 58 will be visible to the consumer and it is therefore highly recommended to provide the tube 40 with a balanced aesthetic appearance.

In Figures 6-8, the slots 56 and 58 are shown as being circular and extending completely around the outer circumference of the tube 40. Each slot 56 and 58 has a depth which is at least 25 percent of the thickness of the wall 42. Preferably, the depth of the grooves 56 and 58 is at least half the thickness of the wall 42 at the location where each slot 56 and 58 is formed. The cross-sectional profile of each slot 56 and 58 may vary. However, a trapezoidal profile with a flat bottom and the opposite sides sloping downwards and inwards towards the central longitudinal axis C-C work well and are easy to form.

The arcuately shaped tube 40 also includes a gate 60 formed in the outer periphery 50.

The gate 60 represents the location of the injection nozzle through which the melted thermoplastic material is introduced into the mold cavity. In order to facilitate the molding of the arcuately shaped tube 40 having a tapered wall 42, the gate 60 must be located at a point halfway between the amount of material necessary to form the tube 40. In Fig. 7, it is obvious that the gate 60 is located closer to the first end 44 since the wall 42 is thicker at this end and requires more material to form it. By locating the gate 60 at a point where half the volume of the melted material can flow to the ends 44 and 46, one can ensure that the tube 40 can be formed completely and that the partially formed tubes are kept to a minimum .

Referring to Figures 9 and 10, a fourth embodiment of a thin-walled tube 62 is shown. Tube 62 is arcuately shaped along a curved center line D-D. The tube 62 has a wall 64 and a length which extends from a first end 66 to a second end 68. The arcuately shaped tube 62 can be formed on a curved path of any desired length. The arcuately shaped tube 62 is shown as having an inner periphery 70 and a circular or rounded outer periphery 72. The wall 64 varies in thickness in the plane in cross section. However, the inner and outer peripheries, 70 and 72 respectively, have a uniform profile along the length of the tube 62. The wall 64 varies in thickness along its length. A main part of the wall 64 may have a thickness of less than about .03 inches (about .76 mm) and preferably, less than about .015 inches. (around .38 mm). The tube 62 also contains a thickened portion 76 which is formed on the inner periphery 70. The thickened portion 74 is an alternative configuration for the rib 52 shown in Figs. 6-8. The thickened part 74 has a constant height "h2" which is greater than a part of the wall thickness. The thickened portion 74 extends to the full length of the tube 62, extending from the first end 66 to the second end 68. The shape of the thickened portion 74 may vary but must be thick enough to serve as a conduit for the thermoplastic material melted so that the melted material can be directed to opposite ends 66 and 68.

The arcuately shaped tube 62 further includes a gate 76 formed on the outer periphery 72. The gate 76 represents the location of the injection nozzle through which the thermoplastic material is introduced into the mold cavity. In order to facilitate the molding of the arcuately shaped tube 62, the gate 76 must be located at a mid point between the first and second ends 66 and 68 respectively. Since the tube 62 has a constant wall thickness along its length, the gate 76 can be located at an equal distance between the ends 66 and 68.

Finally, the arcuately shaped tube 62 contains a single groove 78 formed in the outer periphery 72 which is located on one side of the first end 66. The purpose of the groove 78 is to hold the molded tube 62 stationary when the core is removed of central mold (not shown) after the melted material forming the tube 62 solidifies. The groove 78 has a trapezoidal profile with a flat bottom and the opposite sides which are inclined downwards and inwards towards the central longitudinal axis D-D. As indicated above, another slot can also be formed in the outer periphery 72 of the tube 62 at one side of the second end 68 if the aesthetic appearance is important.

Although the invention has been described in conjunction with several specific embodiments, it should be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Therefore, this invention is intended to encompass all those alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Claims (24)

RE I VI ND I CAC I ONE S

1. A tube comprising a wall and having a length extending from a first end to a second end, said wall having a thickness of less than about .03 inches and a rib formed on an inner periphery of said tube extending along of at least a part of said length.

2. The tube as claimed in clause 1, characterized in that said rib has a constant height.

3. The tube as claimed in clause 1, characterized in that said rib has a semicircular cross-sectional configuration.

. A tube as claimed in clause 1, characterized in that said wall is tapered in thickness between said first and second ends.

5. A tube comprising a wall extending from a first end to a second end, said wall having a non-uniform thickness and a longitudinally extending rib formed on an inner periphery of said tube which extends along the length of minus a part of said length.

6. The tube as claimed in clause 5, characterized in that said wall has a thickness of less than about .03 inches and said wall is tapered downward in thickness when approaching at least one of said ends.

7. The tube as claimed in clause 5, characterized in that said wall narrows in thickness from the second end to the first end.

8. The tube as claimed in clause 5, characterized in that said rib has a height which is greater than at least a part of said wall thickness.

9. The tube as claimed in clause 5, characterized in that said rib has a length which is smaller than the distance between said first and second ends.

10. An arcuately shaped tube comprising a wall and having a length extending from a first end to a second end, said wall being tapered to a smaller thickness on one side of at least one of said ends and a rib formed on one end. inner periphery of said tube extending along at least a part of said length.

11. The tube arcuately shaped as claimed in clause 10, characterized in that said rib extends from the first end to the second end.

12. The tube arcuately shaped as claimed in clause 10, characterized in that said rib extends along a main part of the length of said tube and is spaced outwardly from at least one of said ends.

13. The tube arcuately shaped as claimed in clause 10, characterized in that said wall has a constant outer profile and a thickness of less than about .03 inches.

14. The tube arcuately shaped as claimed in clause 10, characterized in that said tube has an oval configuration in cross section.

15. The tube arcuately shaped as claimed in clause 10, characterized in that said tube has a circular configuration in cross section.

16. An arcuately shaped tube comprising a wall and having a length extending from a first end to a second end, said wall having a non-uniform thickness and a rib formed on an inner periphery of said tube extending along a length of main part of said length.

17. The tube arcuately shaped as claimed in clause 16, characterized in that said tube is formed of high density polyethylene.

18. The tube arcuately shaped as claimed in clause 16, characterized in that said tube is formed of low density polyethylene.

19. The tube arcuately shaped as claimed in clause 16, characterized in that said wall has a thickness of less than about .03 inches.

20. The tube arcuately shaped as claimed in clause 16, characterized in that said wall has a thickness of less than about .015 inches.

21. The tube arcuately shaped as claimed in clause 16, characterized in that said wall has an outer periphery and at least one groove is formed on the outer periphery at one side of one end thereof.

22. The arcuately shaped tube as claimed in clause 16, characterized in that said wall has an outer periphery and at least one groove is formed in said outer periphery adjacent to each end thereof.

23. A tube comprising a wall and having a length extending from a first end to a second end, said wall having a thickness of less than about .03 inches and a thickened portion formed on an inner periphery of said tube extending along at least a part of said length.

24. The tube as claimed in clause 23, characterized in that said thickened part has a constant height. SUMMARIZES A thin-walled tube having a wall which extends between the first and second ends is described. The wall has a thickness of less than about .03 inches. The tube also has a longitudinally extending rib formed on an inner periphery thereof. The rib allows the thin tube to be injection molded of a thermoplastic material using standard temperature ranges and relatively short cycle times.