FIELD

This invention relates to hollow injection molded plastic articles such as tape dispensers having curvature in three dimensions and, in another aspect, to methods for making hollow injection molded plastic articles having curvature in three dimensions.

BACKGROUND

There are many commercially available hand held tape dispensers. One piece tape dispensers such as those disclosed in U.S. Patent Nos. 5,328, 1 15 and 5,083,717 are relatively simple and easy to manufacture. One piece tape dispensers tend to be linear in the z-axis (that is, the axis parallel to the tape as it unwinds). They therefore have a relatively hard sharp edge that can be uncomfortable in the user's hand during use.

Some two piece tape dispensers such as those disclosed in U.S. D540870 are known to have curvature in the z-axis. This curvature makes the dispenser more visually interesting as well as more comfortable in a user's hand. However, manufacturing and assembling two piece tape dispensers is more costly and complicated than manufacturing and assembling one piece tape dispensers. For example, after a roll of tape is placed in one half of the dispenser, the second half of the dispenser must be precisely lined with the first half so that they meet properly. This can substantially reduce cycle time during manufacturing/ assembly.

SUMMARY

In view of the foregoing, we recognize that there is a need in the art for one piece tape dispensers having curvature in the z-axis.

Briefly, in one aspect the present invention provides a tape dispenser comprising a housing comprising a face portion and a sidewall proximate the face portion. The face portion and the sidewall each comprise an inner surface and an outer surface. The outer surface of the sidewall is curved in the x- y plane, contains no undercuts and comprises a plurality of ribs extending across it. The ribs are convexly curved in the z-axis. The inner surface of the sidewall is linear in the z-axis. The inner surface of the face portion comprises a tape holding portion adapted to hold a roll of tape therein. The curvature of the inner surface of sidewall encircles more than half of a roll of tape held by the tape holding portion. The housing is integrally molded from a polymeric material.

The tape dispensers of the invention meet the need in the art for tape dispensers having curvature in the z-axis. In addition, the ribs on the dispenser are not only aesthetically appealing, but they are comfortable in the hand and help the user grip the tape dispenser.

In another aspect, the present invention provides hollow plastic articles comprising an inner surface curved in the x-y plane, and an outer surface curved in the x-y plane and comprising a plurality of ribs. The ribs are convexly curved in the z-axis at a first end and linear in the z-axis at a second end. At least a portion of the inner surface is curved more than 180° in the x-y plane. The inner surface contains no undercuts. The article is integrally molded from a polymeric material.

In yet another aspect, the present invention provides a method of making hollow plastic articles. The method comprises: (a) providing a mold having an A plate and a B plate, wherein at least a portion of the mold is configured to form curvature in the x-y plane and z-axis using a plurality of ribs that are convexly curved in the z-axis at a first end and linear in the z-axis at a second end, and the parting line of the A plate and B plate at the centerline of the curve, (b) injecting heated polymeric material into the mold, (c) allowing the polymeric material to cool and form a molded article, (d) moving the A plate away from the molded article, and (e) ejecting the molded article from the B plate. The method does not involve the use of collapsible cores or slides and lifts in creating the ribs.

In the injection molding art, it is known to use collapsible cores or slides (that is, mold pieces that slide into the part cavity through the side of the mold) and lifts to make undercuts and other part features. The use of collapsible cores and slides both have limitations, however. Collapsible cores, for example, are only useful in making round or 360° undercuts. On the other hand, it is difficult to use slides and lifts for undercuts having more than a 180° curve or a half circle. When making a half circle or less, a lift can be easily pulled out of the mold and removed, but when making more than a half circle, the slide hits the other side of the mold when it is pulled out. Slides therefore need to be segmented in order to make undercuts having more than a 180° curve. Thus multiple pulls of the slide are required, leaving visually undesirable witness lines and also increasing molding cycle times.

The method of the invention enables injection molding of hollow plastic articles curved in the x-y plane and the z-axis. The method does not require the use of collapsible cores or slides and pulls in creating the ribs. Because slides and pulls are not utilized, no witness lines are created in making the curved undercuts. (There will be one witness line where plate A and plate B came together.) The method of the invention is useful for making hollow plastic articles including, but not limited to, plastic tape dispensers.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a tape dispenser of the invention.

Fig. 2 is a front view of a tape dispenser of the invention.

Fig. 3 is a back view of a tape dispenser of the invention.

DETAILED DESCRIPTION

Figs. 1 - 3 show different views of exemplary tape dispenser 100. Fig. 1 is a perspective view of tape dispenser 100. Fig. 2 shows the front of tape dispenser 100 and Fig. 3 shows the back of it.

Tape dispenser 100 comprises housing 102, which includes face portion 104 and sidewall 106. Housing 102 is integrally molded from a polymeric material and is hollow. Therefore face portion 104 has an outer surface 108 and an inner surface 110 and sidewall 106 has an outer surface 112 and an inner surface 114. Inner surface 110 comprises tape holding portion 116 adapted to hold a roll of tape (not shown). As depicted, tape holding portion 116 includes posts 118, but any useful configuration for holding a roll of tape may be utilized.

Sidewall 106 is curved in the x-y plane so that it encircles or surrounds at least a portion of a roll of tape when the tape is placed in tape holding portion 116 for use. Preferably, sidewall 106 encircles more than half a roll of tape. As used herein, and as depicted in the figures, the term "encircles" includes various curvatures and is not limited to 360° curves.

Inner surface 114 of sidewall 106 is linear in the z-axis. Outer surface 112 of sidewall 106 comprises a plurality of ribs 120. Ribs 120 are convexly curved in the z-axis as can be seen in Fig. 1.

Ribs 120, are linear in the z-axis, however, at the inner surface In some embodiments of the tape dispenser of the invention, the ribs are re from about 0.1 inches to about 0.5 inches tall at their centerline.

In some embodiments, the ribs are wider at the centerline of the sidewall than at the edges of the sidewall.

The distance of the gaps between the ribs can vary. Widening the gaps between the ribs can make molding the part easier, but the comfort of the article in a user's hand can be decreased as the gaps become too wide. A skilled designer will therefore balance these considerations when designing the ribs for a particular article.

In some embodiments, as shown in Figs. 2 and 3, it is desirable to have some flat ribs such as rib 122 at the bottom of the dispenser so the dispenser can stand up.

Tape dispensers of the invention such as tape dispenser 100 and other hollow plastic articles of the invention can be made by injection molding. In injection molding, heated polymeric material is forced into a mold cavity wherein it cools and hardens to the configuration of the mold cavity. Typically, the molds are made from a metal such as steel or aluminum. Molds comprise an injection mold plate (the "A" plate) and an ejector mold plate (the "B" plate). Once the polymeric material injected into the mold cools, the A plate is moved away and the resulting plastic part is ejected from the B plate.

The method of the invention simplifies making hollow plastic articles with curved walls. The inner surface of the wall has no undercuts. The parting line of the A plate and the B plate is at the middle or centerline of the curve. When there is a curve in the z-axis and a linear inner surface formed without ribs, there is a thick mass of plastic that could cause long cooling cycles or sink marks in the plastic. To overcome this problem, ribs are formed to create a wall thickness that is more similar to the thickness of the face portion of the article.

Numerous polymeric materials including thermoplastic and thermosetting plastic materials can be injection molded. Any useful polymeric material may be used to make the tape dispensers and hollow plastic articles of the invention. Preferably, hard plastic materials are used. Examples of hard plastic materials include polystyrene, polycarbonate, acrylonitrile butadiene styrene (ABS), and the like. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments set forth herein and that such embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.