Pleated filter medium

Pleated filter medium and filters having pleated filter medium are provided. In one embodiment, a pleated filter medium is provided having pleats with rectangular sides and a length direction parallel to the fold between the two sides of a pleat. comprising several rows of distance elements extending in a cross direction relative to the folds in the pleated filter medium The rows are distanced from each other along a length direction, whereby each row of distance elements is constituted of a line of glue elements distanced from each other and applied to a side of the filter medium. Rows of glue elements are applied to both the inside and the outside of the filter medium, the rows on the inside being displaced in the length direction in relation to the rows on the outside.

TECHNICAL FIELD

The present invention relates to a pleated filter medium having pleats with rectangular sides and a length direction parallel to the fold between the two sides of a pleat, comprising several rows of distance elements extending in a cross direction relative to the folds in the pleated medium, said rows being distanced from each other along a length direction, whereby each row of distance elements is constituted of a line of glue elements distanced from each other and applied to a side of the filter medium. The invention also relates to a filter using such a filter medium.

BACKGROUND OF THE INVENTION

Pleated filter media can be used for producing conical filters by being applied around end pieces having different diameters and by affixing the two free sides of end pleats to each other along the length thereof. When the length of the filter, the length direction being the axial direction of such a conical filter, reaches a certain length the pleats in the filter medium must be stabilised. One way of accomplishing such a stabilising is to glue one or more continuous cords around the periphery of the applied filter medium. The stabilising of the pleats thus requires a separate process step being made after the applying of the filter medium to the end pieces.

The objective of the present invention is a pleated filter medium which can be applied to end pieces to form a conical filter without the need for a separate stabilising step after forming of the conical filter.

SUMMARY OF THE INVENTION

This objective is accomplished by a pleated filter medium having pleats with rectangular sides and a length direction parallel to the fold between the two sides of a pleat, comprising several rows of distance elements extending in a cross direction relative to the folds in the pleated filter medium, said rows being distanced from each other along a length direction, whereby each row of distance elements is constituted of a line of glue elements distanced from each other and applied to a side of the filter medium, characterised in that rows of glue elements are applied to both the inside and the outside of the filter medium, the rows on the inside being displaced in the length direction in relation to the rows on the outside. Such a filter medium can be used to manufacture a conical filter without the need of a separate pleat stabilising step after forming of the filter.

In a preferred embodiment, the glue elements in each row of glue elements are distanced from each other in such a way that a glue element is applied to every side of a pleat, and successive rows of glue elements on the inside and the outside of the filter medium are spaced the same distance from each other in the length direction, and the rows of glue elements on the outside of the filter medium are displaced half said distance from the rows of glue elements on the inside of the filter medium.

At least one continuous glue line is preferably applied in the cross direction in one of the end portions of the filter medium.

The length of the glue elements in the cross direction is preferably 10-80% of the width of the side of the pleat.

The invention also relates to a filter, characterised by having such a pleated filter medium, the opposite ends of the filter medium being applied around the periphery of an end piece and sealingly attached thereto. One of the end pieces can have a larger diameter than the opposite end piece so that the filter has the shape of a truncated cone.

DESCRIPTION OF EMBODIMENTS

InFIG. 1, a small piece of a pleated filter medium1according to a preferred embodiment of the invention is schematically shown. This piece of filter medium is shown with the pleats of the filter medium in a somewhat out-folded state compared with the end position of the pleats. InFIG. 1only three pleats2are shown but a filter medium assembled in a filter contains a lot of pleats. The pleats all have the same dimensions. Furthermore, inFIG. 1only an end portion of the filter medium1is disclosed. The length direction L of the filter medium1is parallel to the direction of the pleats2and the cross direction C is perpendicular thereto. The outside of the filter medium1is proximal to the viewer ofFIG. 1and the inside of the filter medium is distal to the viewer.

Successive rows of distance elements3extended in the cross direction C are applied to the inside of the filter medium1along the length direction L thereof. The distance elements3in each such row are equispaced from each other so that a distance element3is located on every second side of a pleat2. The function of these distance elements3is mainly to prevent the sides of the pleats2from being pressed together by airflow during use of the filter. The distance elements3consist of glue spots and have preferably a thickness of 1-4 mm. The extension of each distance element3in the cross direction C is preferably about 10-80% of the width of a side of a pleat2.

Successive rows of glue spots4extended in the cross direction C are applied to the outside of the filter medium1along the length direction thereof. The glue spots4in each such row are equispaced from each other so that a glue spot4is located on every second side of a pleat2, in the shown example the spots4are applied to the same side of a pleat2as the spots3but on the outside thereof instead of the inside. Depending on the filter media and the glue, the glue spots may be applied on every side of the pleats.

When the filter medium1is produced, the pleats are accomplished by a multi-pleat machine, in which the pleats are formed and the adjacent sides of two adjacent pleats are pressed towards each other so that the pleats2are attached to each other by the glue spots4and also distanced from each other by the spots4. The function of the glue spots4is mainly to stabilise the pleats2but the presence of spots4will of course reduce the risk that portions of the pleat sides will be pressed together. Also the sides of the pleats will be pressed towards each other so that these sides will be attached to each other by the glue spots3.

The rows of glue spots3on the inside of the filter medium1and the rows of glue spots4on the outside are displaced in relation to each other in the length direction L so that each row of glue spots4in the length direction is located between two successive rows of glue spots3. Preferably, the spots3and4are located on opposite sides of a line extending midway between the tops5and the troughs6. More preferably, the spots4are also distanced from the top 5 of a pleat2by the same distance as the spots3are distanced from the bottom of a trough6.

In the shown end of the filter medium1two continuous glue lines7,8are applied to the inside of the filter medium.

The filter medium1consists of a foldable material, preferably paper such as Glass Paper, from Sojitz Pla-Net Corporation, Tokyo, Japan, but any material used for air filters can be used. The glue used is preferably a hot melt adhesive, for example Technomelt from Henkel, Heidelberg, Germany but any other glue used for air filters can be used as well.

The distance between successive rows of glue spots3can be 50 mm and the distance between successive rows of glue spots4is the same. The displacement in the length direction between rows of glue spots3and rows of glow spots4is preferably half the distance between two successive rows of glue spots3, i.e. 25 mm.

A filter medium1as described above is to be used together with end pieces to form a cylindrical or conical filter.

A filter9having the shape of a truncated cone is schematically shown inFIG. 2. Such a filter is made by wrapping the cross directional end portions of a rectangular, pleated filter medium1around cylindrical end pieces10,11and by sealingly attaching the wrapped filter medium to the end pieces10,11and attaching the length directional ends of the filter medium to each other along the length thereof.

As is evident fromFIG. 2, the end piece10has a smaller diameter than end piece11which means that in the wrapped condition the initially rectangular pleated filter medium has taken the shape of a cut triangle. Specifically, this change in shape is accomplished by a gradual enlargement in the cross direction of the filter medium starting from the end wrapped around the end piece10with the smallest diameter. It is easy to realize that such an enlargement in a pleated filter medium can be obtained by gradually folding out the pleats in the length direction. However, since the pleats2are held together by the rows of glue spots4and rows of glue spots3such a simple folding out of the pleats is not possible in the present case. Instead, the gradual enlargement in the cross direction, i.e. the circumferential direction in the assembled filter9schematically shown inFIG. 2, is accomplished by gradually larger bending out of the portions of the adjacent sides of two adjacent pleats2lying between adjacent rows of glue spots3and a gradually larger bending out of the portions of the two sides of the pleats2lying between adjacent rows of glue spots4in a direction from end piece10towards end piece11. The bending out of the portions of the adjacent sides of two adjacent pleats2lying between adjacent rows of glue spots3will move the glue spots3somewhat closer to each other also move the glue spots4in the cross direction and the bending out of the portions of the two sides of the pleats2lying between adjacent rows of glue spots4will move the glue spots4closer to each other and also the glue spots3in the cross direction. Therefore, the fold lines in the tops and troughs will not run in a totally straight line from the end piece10to end piece11but run in a slightly tortuous line.

With a conical filter9having a pleated filter medium1as described above it is not necessary to provide the pleats2with one or more continuous glue strings around the periphery of the filter medium after assembly of the filter medium onto the end pieces10,11in order to stabilise the pleats. Due to the rows of glue spots3,4a stable filter medium is obtained.

A conical filter according to the present invention will thus be much easier to manufacture than a conical filter in which the pleats have to be stabilised in a second step after assembly of the filter. The manufacturing costs of a conical filter according to the invention will thus be significantly lower than for the known filter.

The described filter medium can of course also be used for a filter having a cylindrical shape.

The described embodiment can be modified in several respects without leaving the scope of invention. The distances between the rows of glue spots can be different than described. It is also possible that the rows of glue spots applied to the outside of the filter medium are fewer than the rows of glue spots applied to the inside thereof, however the rows on the outside should still be located between rows on the inside. Furthermore, the glue spots on the outside can be displaced in the cross direction relative to the glue spots on the inside. Other materials for the filter medium than mentioned above can be used and other types of glue. It is not necessary to use the same type of glue for the rows of glue spots on the outside and inside of the filter medium even if this is preferred. The scope of invention shall therefore only be limited of the content of the enclosed patent claims.