Patent Description:
Various deflectors, sometimes referred to as end deflectors, are available, such as disclosed in <CIT>, <CIT> and <CIT>. <CIT>, <CIT> and <CIT> disclose deflector units having the precharacterising features of claim <NUM>.

The present inventor has recognized that existing end deflectors suffer from a number of drawbacks, in causing disruption of the print medium roll at the lateral ends of the printing blade, and also in causing coining of the printing screen, where the end deflectors dig into the printing screen with repeated operation.

It is an aim of the present invention to provide improved end deflectors for printing blades, typically squeegee blades, in preventing the escape of print medium beyond the lateral ends of printing blades in a printing operation.

It is also an aim to enable simplified deflector switching methods for different print media, such as printing paste and adhesive.

It is a yet further aim to provide a deflector which is resistant to damage from paste contamination.

In one aspect the present invention provides a deflector unit in accordance with claim <NUM>.

Advantageously, the biasing element may comprise a compression spring.

Advantageously, the deflector includes a deflector member, which engages a surface of the printing screen in a printing operation.

Preferably, the first surface extends over a substantially flat plane.

The second surface may extend over a substantially flat plane, or alternatively the second surface may be a curved or arcuate surface.

The second surface may have a first, rear edge and a second, forward edge, and a chord between the edges which encloses an angle (β) of less than about <NUM> degrees with the first direction of printing, optionally less than <NUM> degrees, optionally less than <NUM> degrees.

Preferably, the angle (β) may be greater than <NUM> degrees, optionally greater than <NUM> degrees, optionally greater than <NUM> degrees.

The second surface may extend substantially parallel to the first axis, optionally in a substantially vertical direction in use.

Preferably, the distance between the first and third surfaces is at least <NUM>.

Preferably, the distance between the first and third surfaces is at most <NUM>, optionally at most <NUM>, optionally at most <NUM>.

Preferably, the junction of the second and third surfaces encloses an angle of less than <NUM> degrees, optionally an angle of less than <NUM> degrees, optionally an angle of about <NUM> degrees.

The third surface may extend over a substantially flat plane. Alternatively, the third surface may be an arcuate or curved surface.

In another aspect the present invention provides a printing head in accordance with claim <NUM>.

The deflector units may be separable from the support.

The support and the deflector units may be integrally formed.

Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which:.

The printing head comprises a support <NUM>, which is attached to a screen printing machine (not illustrated), a printing blade <NUM> which is attached to the support <NUM>, and first and second end deflector units <NUM>, which are attached to opposite ends of the support <NUM> to prevent print medium passing laterally beyond the respective ends of the printing blade <NUM> during a printing operation.

In this embodiment the print medium is a paste, such as a solder paste.

In this embodiment the support <NUM> comprises an elongate member <NUM> to which the printing blade <NUM> is attached.

In this embodiment the printing blade <NUM> has a first, lower edge <NUM> which contacts a printing screen PS in a printing operation, and the printing blade <NUM> depends downwardly from the support <NUM> to engage the printing screen PS, with a forwardly-inclined relation so as to create a main roll <NUM> of print medium, having an effective diameter of approximately d1, forwardly of the printing blade <NUM> in a direction of printing D1, at the junction of the printing blade <NUM> and the printing screen PS.

In this embodiment the printing blade <NUM> comprises a squeegee blade.

In this embodiment the end deflector units <NUM> each comprise a body <NUM> which is attached to a respective one of the ends of the support <NUM>, a deflector <NUM> which is movably disposed to the body <NUM> for a range of travel along a first, substantially vertical axis X and is disposed adjacent a respective one of the ends of the printing blade <NUM> so as to contain the print medium within the lateral extent of the printing blade <NUM>, and a biasing element <NUM> which acts to bias the deflector <NUM> in a downward direction D2 along the first axis X.

In this embodiment the biasing element <NUM> is a compression spring.

In this configuration, with the deflector <NUM> being movably coupled to the support <NUM>, different pressures, which are applied to the printing blade <NUM> in various printing operations, can be accommodated, thereby providing that the deflectors <NUM> are self-adjusting and avoiding coining of the printing screen PS.

In this embodiment the body <NUM> includes a guide recess <NUM>, here an elongate bore, which receives a counterpart guide member <NUM> of the deflector <NUM>, as will be described in more detail hereinbelow. The guide recess <NUM> comprises two sections, a first, lower section in which the guide member <NUM> is accommodated, and a second, upper section in which the biasing element <NUM> is accommodated. The lower section is preferably of non-circular cross-section, which acts to prevent rotation of the guide member <NUM>, and hence deflector <NUM>, relative to the body <NUM>. The upper section is preferably of circular cross-section, for accommodating and allowing compression and extension of the compression spring biasing element <NUM>. It will be noted that this difference in cross-sections prevents the biasing element <NUM> from falling out of the body <NUM> if the deflector <NUM> is removed therefrom. The two sections are aligned and connected, such that the distal end of the guide member <NUM>, i.e. that end which extends furthest into guide recess <NUM>, contacts the biasing element <NUM> and is thereby biased in a downward direction. In this way the deflector <NUM> is biased towards the printing screen in use.

In this embodiment the biasing element <NUM> is held captive by a fixing <NUM>, here a screw fixing, which completely closes the upper section end of guide recess <NUM>.

In this embodiment the body <NUM> includes a lateral bore <NUM>, arranged generally orthogonally to the length of the guide recess <NUM> and in communication therewith, for receiving an engagement member <NUM>, as will be described in more detail hereinbelow.

In this embodiment the deflector <NUM> includes a deflector member <NUM> which engages a surface of the printing screen PS in a printing operation, and a guide member <NUM>, here an elongate shaft, which is counterpart to the guide recess <NUM> and is slidingly-disposed within the guide recess <NUM>, such that the deflector <NUM> is constrained to move along the first axis X in relation to the body <NUM> along its range of travel. The cross-sectional shape and dimension of the guide member <NUM> conforms closely to that of the guide recess <NUM>, which prevents paste or adhesive from entering the guide recess <NUM>, thus preventing contamination.

In this embodiment the deflector member <NUM> has a first, engagement surface <NUM> which engages the printing screen PS in a printing operation, and a second, inwardly-facing surface <NUM> which extends from the engagement surface <NUM> and flares or tapers laterally outwardly in the direction of printing D1.

In this embodiment the first surface <NUM> is a substantially planar surface.

In this embodiment the first surface <NUM> is profiled or textured, in the manner of tyre tracks, which promotes the transfer of any print medium at the first surface <NUM> laterally inwardly towards the printing blade <NUM>.

In this embodiment the second surface <NUM> is a substantially planar surface.

In another embodiment the second surface <NUM> could be a curved or arcuate surface.

In this embodiment the second surface <NUM> has a first, rear edge <NUM> and a second, forward edge <NUM>, and a chord between the edges <NUM>, <NUM> encloses an angle β of less than <NUM> degrees with the direction of printing D1.

In this embodiment the angle β is <NUM> degrees.

In one embodiment the angle β is less than <NUM> degrees.

In another embodiment the angle β is less than <NUM> degrees.

In a further embodiment the angle β is less than <NUM> degrees.

In one embodiment the angle β is at least <NUM> degrees.

In another embodiment the angle β is at least <NUM> degrees.

In a further embodiment the angle β is at least <NUM> degrees.

In this embodiment the second surface <NUM> extends substantially perpendicular to the contact edge <NUM> of the printing blade <NUM>, here substantially parallel to the first axis X, in a substantially-vertical direction.

With this configuration, second, subsidiary rolls <NUM> of the print medium are developed at the respective deflectors <NUM>, having an effective diameter of approximately d2, smaller than diameter d1, which act to return the print medium which passes outwardly of the respective ends of the printing blade <NUM> back into the main roll <NUM> of print medium with little disturbance to the uniformity of the main roll <NUM> of print medium.

In this embodiment the deflector member <NUM> includes a third, downwardly-facing surface <NUM> which joins the second surface <NUM> at a distance d3 from the lower surface <NUM> thereof.

In this embodiment the distance d3 is <NUM>.

In one embodiment the distance d3 is at least <NUM>.

In one embodiment the distance d3 is at most <NUM>.

In this embodiment the junction of the second and third surfaces <NUM>, <NUM> is a substantially square junction.

In this embodiment the junction of the second and third surfaces <NUM>, <NUM> encloses an angle of about <NUM> degrees.

In another embodiment the junction of the second and third surfaces <NUM>, <NUM> encloses an angle of less than <NUM> degrees.

In a further embodiment the junction of the second and third surfaces <NUM>, <NUM> encloses an angle of less than <NUM> degrees.

In this embodiment the third surface <NUM> extends is a substantially flat surface.

In this embodiment the third surface <NUM> extends in substantially perpendicular relation to the second surface <NUM>.

In an alternative embodiment the third surface <NUM> could be an arcuate or curved surface.

The third surface <NUM> acts to prevent upward movement of the paste in use. This helps to prevent paste from entering the guide recess <NUM> at its lower end. Furthermore, the combination of third surface <NUM> and the angled second surface <NUM> acts to constrain the paste to create the rolls <NUM>, having a height approximately equal to d3, during the printing operation. This constrains the paste, reducing wastage and simplifying re-use.

In this embodiment the guide member <NUM> includes a recess <NUM>, here an elongate slot which extends axially along the guide member <NUM>, which defines first and second limit stops <NUM>, <NUM>. Each body <NUM> of respective end deflector units <NUM> further comprises a detent <NUM>, which extends into the recess <NUM> in the guide member <NUM> to define the limit of travel of the deflector <NUM> along the first axis X by engagement with the limit stops <NUM>, <NUM> of the recess <NUM>.

In this embodiment, the detent <NUM> is provided by an engagement member <NUM>, which is disposed in the bore <NUM> in the body <NUM>.

In this embodiment the engagement member <NUM> takes the form of a screw, which is threadedly engaged in the bore <NUM> and completely closes the same. This arrangement allows the position of the detent <NUM> with respect to the body <NUM> and recess <NUM> to be adjusted by rotation of the engagement member <NUM> within the bore <NUM>, whereby the detent <NUM> may be adjusted to provide sufficient engagement with the end stops <NUM>, <NUM> to delimit the travel of the deflector <NUM> along the first axis X, such that the detent <NUM> is captively located within the recess <NUM>.

In this embodiment the guide member <NUM> includes a groove <NUM> which extends axially along the guide member <NUM> from the recess <NUM> to the distal end thereof, that is the end opposite to the deflector member <NUM>.

In this embodiment the groove <NUM> is a V-shaped groove.

By suitable adjustment of detent <NUM> by rotation of the engagement member <NUM>, the detent <NUM> can be drawn out of the recess <NUM> by manual application by an operator and along the groove <NUM>, against the frictional resistance with the groove <NUM>.

In this way, the groove <NUM> allows the deflector <NUM> to be fitted to and removed from the body <NUM> without requiring any tools, with the groove <NUM> being shaped and/or sized to allow an operator manually to overcome the frictional resistance with the detent <NUM>. With this configuration, an operator can readily change the deflectors <NUM>, such as for cleaning or replacement. This design also enables different types of deflector to be fitted in a modular fashion, for example to interchange between deflectors more suitable for paste application and deflectors more suitable for adhesive application, or to allow separate deflectors for leaded and lead-free paste. Furthermore, the inclusion of groove <NUM> on only one side of the guide member <NUM> prevents the guide member being inserted by an operator into the body <NUM> in an incorrect orientation.

It will be apparent that with the above-described configuration, the biasing element <NUM> is located internally of, and wholly enclosed within, the body <NUM>, throughout the deflector's range of travel, and that paste or adhesive, or indeed any other potential contaminant, is prevented from contaminating the biasing element <NUM>. In particular, no paste may enter the guide recess <NUM> at its lower opening due to the close conformance of the first section's cross-section with the cross-section of the guide member <NUM> and the barrier effect provided by third surface <NUM>, no paste may enter the guide recess <NUM> at its upper opening due to the closure by fixing <NUM>, and no paste may enter the guide recess <NUM> via lateral bore <NUM> due to the closure by engagement member <NUM>.

<FIG> illustrates a printing head in accordance with another embodiment of the present invention.

The printing head of this embodiment is very similar to that of the above-described embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs.

The printing head of this embodiment differs from that of the above-described embodiment in that the support <NUM>, the printing blade <NUM> and the end deflectors <NUM> are formed as an integral unit.

<FIG> illustrates a printing head in accordance with a further embodiment of the present invention.

The printing head of this embodiment is quite similar to that of the first-described embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs.

The printing head of this embodiment differs in that the deflector members <NUM> omit the second and third surfaces <NUM>, <NUM>.

Although the omission of the second and third surfaces <NUM>, <NUM> from the deflector members <NUM> does not allow for the formation of the subsidiary rolls <NUM> of the print medium at the lateral ends of the main roll <NUM> of the print medium, the deflector members <NUM> still advantageously are self-adjusting, independent of the pressure as applied to the printing blade <NUM>, thereby preventing coining of the printing screen PS.

This embodiment has particular application to print medium in the form of glues and inks.

Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the invention as defined by the scope of the appended claims.

For example, in one embodiment, as illustrated in <FIG>, the deflector member <NUM> could include a raised, elongate projection <NUM>, which is inclined substantially in parallel relation to the printing blade <NUM>, and acts to reduce the pressure of the print medium at the junction of the second surface <NUM> and the printing blade <NUM>. This helps to reduce the formation of "snail trails", i.e. thin trails of paste left in the wake of the printing blade <NUM> during the printing operation.

In this embodiment the projection <NUM> has the form of a ridge or bead, optionally a rounded ridge or bead.

Although illustrated in relation to the deflectors <NUM> of <FIG> and <FIG>, the projection <NUM> could have equal application to the embodiment of <FIG>.

For example, in another embodiment, as illustrated in <FIG>, the deflector <NUM> could include an inwardly-projecting member <NUM> at a rear, trailing edge in the direction of printing D1, which is located rearwardly of the printing blade <NUM> and includes a surface <NUM> which acts to transfer any print medium which remains on the printing screen PS after traversal of the print head <NUM> laterally inwardly into the printing region of the printing screen PS. This also helps to reduce the formation of "snail trails".

Claim 1:
A deflector unit for use with a printing blade (<NUM>) in printing a print medium through a printing screen (PS), the deflector unit (<NUM>) comprising:
a body (<NUM>) which is disposable adjacent a respective one of the ends of a printing blade (<NUM>);
a deflector (<NUM>) which is movably disposed to the body (<NUM>) for a range of travel along a first axis (X) and acts in use to contain print medium within a lateral extent of the printing blade (<NUM>); and
a biasing element (<NUM>) which acts to bias the deflector (<NUM>) from the body (<NUM>) along the first axis (X);
characterised in that the biasing element (<NUM>) is wholly enclosed within the body (<NUM>) throughout the range of travel of the deflector (<NUM>);
and wherein the deflector (<NUM>) includes a guide member (<NUM>) having a cross-sectional shape and dimension, and the body (<NUM>) includes a guide recess (<NUM>) in which the guide member (<NUM>) is slidingly disposed, such that the deflector (<NUM>) is constrained to move along the first axis (X) in relation to the body (<NUM>), the guide channel having a cross-sectional shape and dimension which conforms to that of the guide member (<NUM>) to prevent contamination of the biasing element (<NUM>) by the print medium in use.