2. Description of the Prior Art A conventional writing utensil have a cap for covering the tip end, while the writing utensil is not used, to prevent ink from being dried. However, the writing utensil having the cap has a problem in that it is non-efficient and can be easily lost.

Accordingly, there exists a technology about a writing utensil which automatically closes the tip end as the writing utensil is not used in order to eliminate the necessity of the cap.

For example, Japanese Utility Model publication so 42-21538 and laid-open Publication so 62-87882 disclose writing utensils including a sleeve formed with a magnet disposed toward a front end of the body, a front end of a barrel having a writing nib and an ink container shaped in a ballpoint refill container and forwardly shrinkable from the sleeve through an extended bore, and closer formed in a ball or a plate and magnetically attachable on the front portion of the sleeve to close the bore as the front end of the barrel is shrunk.

Japanese Utility Model publication so 38-18620 and 41-13855 disclose instruments in which a closer is connected to a sleeve by an elastic member and, in an elastic part, the closer is pressed to be contacted with the front end of the sleeve

in an elastic force and then to close a sleeve bore in an elastic part.

However, in the writing utensils disclosed in Japanese Utility Model publication so 42-21538 and laid-open publication so 62-87882, since a closer is attracted to a sleeve by a magnetic force of the sleeve, for example, as a front portion of a barrel is forwardly protruded after a closer rises over 90 degree, or as the barrel is retreated to a position where the writing utensil moves downwardly to be inserted, the closer is not completely restored to an original sealing position and does not close a bore completely.

Particularly, as the barrel moves forwardly with a front portion of the writing utensil moved downwardly, the closer pressed away from the sleeve closes a front opening of the writing utensil, so that protrusion of a barrel end is interrupted. If the writing utensil is forced to be protruded, a big load is applied to the barrel end, causing the barrel to be broken.

In the meantime, in a writing utensil disclosed in Japanese Utility Model Publication so 38-18620 and 41-13855, since a closer is pressed against a sleeve with an elastic restoration force of an elastic member, the elastic member should have a considerable restoration force for a complete closing of the writing utensil.

Accordingly, in case of the disclosed writing utensil, when protruded, the barrel end experiences a considerable resistance provided by the elastic member. Such resistance increases greatly as the elastic member is deformed, the increased resistance is applied to the tip of the writing utensil, causing the tip to be destructed.

Reversely, as the elastic restoration force is small, the writing utensil is not closed completely.

Further, Korean Patent No. 95-1695 discloses a writing utensil which includes a sleeve having a sealing portion of a sealing member and a closer. A front end

portion of the sleeve and the closer have magnets to magnetically attract each other. However, the writing utensil has a complicated structure and needs many components to cause difficulty in its assembling process, so that the production cost increases. Acc. ordingly, there exists a problem in that the writing utensil can not be provided to users in a low price.

Lastly, in a writing utensil disclosed in Korean Patent laid-open Publication 98-1341, a ring member of a flexible hose forming a junction portion which has plural wrinkles and pen-end outlet is inserted into a upper jaw of a front portion of a writing member which is inserted in a outer tube, and a screw portion of a front end cap is engaged with a screw portion of a front end of the outer tube. However, in the above writing utensil, there exists a problem in that an operation tip is damaged when repeatedly used for a long time since the operating tip is contacted with the junction portion.

SUMMARY OF THE INVENTION In order to overcome the above-mentioned problems, it is an object to provide a writing utensil having a simple structure.

In order to achieve the above object, a writing utensil having an expander for exposing an operating tip to allow contents for work to be discharged comprises a housing having the operating tip therein; an opening/closing part mounted on one end portion of the housing for allowing the operating tip to move in and out, and for sealing the tip to prevent the contents from being evaporated in a closing state that the tip is not exposed, and for exposing the tip in an opening state that an operation for work is performed; and an expender mounted on the end portion of the housing through which the operating tip moves in and out, and for opening the

opening/closing part by overcoming elasticity of the one end portion while protecting the operation tip when an operation is performed to convert the sealing state of the tip to the exposing state of the tip.

Preferably, the expander is formed in a hollow and cylindrical shape for accommodating the operating tip, presses the one end portion earlier than the operating tip when an operation is performed to convert the sealing state of the tip to the exposing state of the tip, and opens the opening/closing part to opposite directions if pressed by the expander.

Further, the opening/closing part may be formed in any shapes, but preferably, in a dome shape. The housing may be also formed in various shapes, but preferably in a cylindrical shape for a user to hold it with ease.

The writing utensil may be used for stationery which has an operating tip, inclusive of cosmetics, correction fluid containers, water-based pens, oil-based pens, bar-type paste, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS The above object and other advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings, in which: FIG. 1 is a perspective view for showing a tip end portion in a state that an opening/closing part is closed according to an embodiment of the present invention; FIG. 2 is a perspective view for showing a tip end portion in a state that an opening/ciosing part is opened according to an embodiment of the present invention; FIG. 3 is a cross-sectioned view for a tip end portion in the state of FIG. 1; FIG. 4 is a cross-sectioned view for showing a state that an expender presses

an opening/closing part to be opened; FIG. 5 is a cross-sectioned view for showing a state that an operating tip is exposed according to an embodiment of the present invention; and FIG. 6 is a view for showing a writing utensil according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings, but the present invention is not defined to this embodiment.

FIG. 1 is a perspective view for showing a tip end portion in a state that an opening/closing part is closed according to an embodiment of the present invention.

As shown in FIG. 1, one end portion of a housing 8 includes an opening/closing part.

An expender in a hollow and cylindrical shape 4 is mounted inside the housing 8, and an operating tip 6 is mounted in the expander 4. The operating tip according to an embodiment of the present invention may be a bar-type paste of which hardness is lower than other writing utensils such as ballpoint pens or the like.

An opening/closing part 2 may be transparent plastics and is formed in a dome shape. As the opening/closing part 2 is parted to opposite directions from each other, the operating tip 6 is outwardly protruded between the parted opening/closing part 2. The opening/closing part 2 has elasticity so that it is closed by the elasticity to seal the tip end portion as no external force is applied. In the present embodiment, even though any elastic material is not provided for the opening/closing part 2, in order to step up a sealing effect, an iron plate may be used together with packing mounted on the joints of the iron plate instead of the transparent plastics, or

a spring may be provided to the opening/dosing part 2. Further, in the present embodiment, the opening/closing part 2 is composed of two pieces of plastics to be parted to opposite directions when pressed by the expander 4, but the opening/closing part 2 may be composed of three or more pieces to be radially opened and closed.

In the present embodiment, the expander 4 is made up of plastics, and the operating tip is mounted inside the operating tip 6. When the expander 4 opens the opening/closing part 2, in order to prevent the opening/closing part 2 from being broken, the portion of the expander 4 which are contacted with the opening/closing part 2 is formed in a smooth shape.

In the present embodiment, a bar-type paste is used as the operating tip. In general, the bar-type paste is not solid, and hardened without moisture so that it can not be used as paste. However, the writing utensil according to the embodiment of the present invention keeps the opening/closing part 2 in a sealed state to prevent the paste from being dried while the bar-type paste is not used, enabling the function of the paste to be kept.

The present embodiment has not additional elastic members since plastic material can provide an enough elastic force, but, in order for the sealed state to be more secured, metal instead of plastic material may be used for the opening/closing part 2, or an elastic member such as a spring may be additionally provided.

Hereinafter, operations will be described for the embodiment of the present invention.

FIG. 3 is a cross-sectioned view for a tip end portion in the state of FIG. 1. As shown in FIG. 3, in a writing utensil according to an embodiment of the present invention, the operating tip 6 and the expander 4 are mounted in the opening/closing

part 2. In the state as shown in FIG. 3, a user operates the writing utensil to expose the operating tip 6, as shown in FIG. 4, the expander 4 presses the opening/closing part 2 to be parted in opposite directions, so that the opening/closing part 2 is opened. After the operating tip 6 and the expander 4 are moved together up to a certain length, as shown in FIG. 5, only the operating tip 6 is outwardly exposed.

FIG. 6 is a view for showing a writing utensil according to another embodiment of the present invention. The embodiment shown in FIG. 6 is the same as in the embodiment describe in connection with the FIG. 1. However, the opening/closing part 2 is not straightforwardly divided, but has steps 10 and 11 on end portions thereof in order to elevate the sealed effect. That is, as stated above, the end portions of the opening/closing part 2 are formed in any shapes.

In the embodiment as above-mentioned, mechanism which exposes the expander 4 and the operating tip 6 may be the same as in a conventional art, and has been disclosed to the public, so that the description on the mechanism will be omitted.

Various changes and modifications can be made with the spirit and scope of the present invention, and all of such changes and modifications belong to the technical scope of the present invention. That is, the exposing tip may be a water- based pen tip or an oil-based pen tip, the transparent plastics may be replaced with an opaque plastics or rubber, the expander in the hollow and cylindrical shape may be replace with an expander in a round bar shape, and so on.

The writing utensil of the present invention has a seal effect which prevents contents thereof from being volatilized or evaporated without a cap. In addition, aesthetic feeling different from conventional writing utensils can be roused since the opening/closing part 2 is made up of transparent plastics.