PE CAP This invention is concerned with writing instruments, and in particular relates to pen caps. It is usual to provide a pen with a retraction mechanism to enable the writing point to be withdrawn into the pen barrel when the pen is not being used, or to provide a detachable cap for covering the writing tip when the pen is not in use. Some pens require the writing point to be enclosed within a sealed space to prevent the ink stored within the pen drying out due to evaporation, and a removable cap is generally employed to define this space. The caps perform this function very well, but it is considered that detachable pen caps can be hazardous to children who may put the caps into their mouths. It is not unknown for a child accidentally to inhale a pen cap, as a consequence for the air passage to the lungs to be seriously obstructed or blocked. It has been proposed that pen caps should be made so that air can still flow through should a pen cap become lodged in a childs trachea. The need to define an air passage is, of course, contrary to the main purpose of a pen cap, i.e. to form a sealed enclosure around the writing tip of the pen, which means there are conflicting requirements imposed on the cap design. In EP-A-0330877 there is disclosed an integral pen cap having a tubular main part for receiving a forward end portion of the pen barrel, and a hollow stem attached to one end of the main part by radial fins which also extend the length of the hollow stem. The

fins form external flutes for defining air passages while the hollow stem defines an enclosure for sealing around the writing tip when the cap is fitted to the pen. The effectiveness of external flutes, and other possible methods of defining an air passage along the outside of a cap, is very uncertain due to the unpredictable effects of tissue swelling in the trachea. Another drawback of this cap is that it is only suitable for pens with a small diameter at the tip, otherwise the cap needs to be of large diameter.

The present invention has for its aim to provide a pen cap of simple and economic manufacture which will ensure in reliable manner an effective passage for air through the interstices of the cap when the cap is detached from a pen.

In accordance with the invention there is provided a pen cap comprising a tubular casing having an open forward end for receiving a front end portion of a pen, inwardly projecting abutment means at the rear end of the casing, and a rearwardly facing abutment shoulder spaced axially from the rear end of the casing, and an insert accommodated in the casing and providing a cup- shaped core to define a sealed enclosure around the writing point of the pen, an air passage being defined between the core and the casing along the length of the core, and a projection on the core engaged with said abutment shoulder whereby the insert is held against axial movement by engagement between said inwardly projecting abutment means and said abutment shoulder. In a preferred construction the casing has at the rear end thereof an inturned circumferential lip and a longitudinally extending slot. A lateral projection on the core of the insert engages in the slot of the casing to limit forward movement of the insert and the insert is held against rearward movement by abutment with the lip.

A pen cap embodying the invention can be

assembled easily from two injection moulded plastics parts, namely the casing and the insert, by pushing

•V f the insert through the open rear end of the casing until it snaps behind the casing lip. A longitudinal air 5 passage between the casing and insert is ensured. For this purpose the insert is conveniently formed with longitudinal spines or ribs distributed around the core to position the core centrally in the casing and define a plurality of air passages between the casing and 10 insert. The ribs can be arranged to abut the casing lip to secure the insert within the casing.

The projection which engages in the casing slot conveniently serves to carry a pocket clip which can be made integrally with the insert. 15 To assist a clear understanding of the invention an embodiment will now be described in greater detail with reference to the accompanying drawings, in which:-

Figure 1 is a longitudinal section through a 20 pen cap constructed in accordance with the invention; Figure 2 is a rear end elevation of the pen cap shown in Figure 1;

Figure 3 is a transverse cross-section taken along the line III-III in Figure 1; 25 Figure 4 is a rear end view of the cap insert; and

Figure 5 is a rear end view of the cap casing. The cap illustrated in the drawings is assembled from two parts, namely a casing 1 and an 30 insert 2 , each made as an injection moulding. The casing is tubular with a through bore, and at its rear end is formed with a small inturned flange or lip 3 and a longitudinally extending slot 4. On its interior the casing is provided with pips 5 intended to cooperate 35 with a groove in the pen barrel to retain the cap on the pen, and on its exterior the casing is formed with a projection 6 for cooperation with the pocket clip of the

pen cap as described below.

The insert 2 comprises a generally cup-shaped core having a cylindrical open end section 8 and a frusto-conical closed end section 9. Integral with the core and uniformly distributed thereabout are longitudinal ribs 10, the ribs being four in number in the exemplary embodiment. The ribs engage the inner surface of the casing and support the core coaxially within the casing so that longitudinal passages 11 for flow of air are defined between the insert and the casing intermediate adjacent ribs. As the rear end of the core is tapered there are ensured large air openings 12 at the rear of the cap, and the flow of air through the passages is not restricted by the lip 3 of the casing. The rear ends of the ribs (except the rib aligned with the casing slot 4) abut the lip 3 to retain the insert securely within the casing.

The insert includes an integral pocket clip 14 which extends parallel to the casing to a forward end located adjacent the projection 6 for gripping a piece of cloth, in particular the edge of a pocket, between the clip and the casing. The clip is attached to the frusto-conical section of the core by an arm formed by a pair of parallel lugs 16 which project laterally from the core and through the slot 4 of the casing. The lugs abut against the shoulder defined by the front edge of the slot 4 to limit the forward displacement of the insert 2. The hole 17 defined between the lugs 16 at the rear end of the cap can help provide an additional flow way for air which may pass along the cap between the pocket clip 14 and the casing 1.

To assemble the pen cap, the insert is merely pushed into the rear end of the casing with the clip arm aligned with the slot 4, until the arm engages the forward end of the slot and the ribs 10 snap behind the lip 3. The forward ends of the ribs 10 are tapered to facilitate insertion of the insert 2 into the casing.

When the cap is fitted onto the front end portion of a pen, the writing tip is positioned within the hollow core and the open end of the core seals against the pen barrel to form a sealed enclosure around the writing tip. If the pen cap should be accidentally inhaled the passages 11 defined between the casing and insert will ensure adequate flow of air until medical attention can be given. The external passage between the pocket clip and casing may enable even greater air flow to be sustained.

The pen cap of the invention is simple to manufacture and assemble, and is effective in use while still meeting with safety demands. The casing can be made of a substantially rigid material whereas the insert is made of more resilient material to ensure the clip 14 has the required resilience, to facilitate insertion of the insert into the casing and to form a good seal about the writing tip. The insert occupies only a minor part of the length of the casing, which means the cap can be used with pens having barrels of relatively large diameter without requiring the cap to be exceptionally large. Of course modifications are possible without departing from the scope of the appended claims. For example, the lip does not need to be a continuous flange and individual inturned projections for cooperation with the respective ribs would be adequate.