Constant bevel doctor blade and method and apparatus using same

A method of making a doctor blade for wiping excess ink from a printing surface of a printing form in lieu of a conventional doctor blade of a type having a constant blade thickness between two mutually parallel blade surfaces and a generally wedge-shaped tip portion including a run-in blade bevel having an optimum tonal quality size and extending from one of said blade surfaces at an angle corresponding to an angle of attack of the doctor blade relative to said printing surface, and an inclined wedge surface extending from said blade bevel to the other of said blade surfaces, whereby the effective area of said blade bevel would increase from said optimum size through progressive wear of said tip portion during use of said conventional blade to sizes eventuating in progressive degradation of print quality, comprising in combination the steps of:

• providing a doctor blade blank having said blade thickness between said parallel blade surfaces;
• shaping a marginal portion of said blank into a blade tip portion, providing the latter blade tip portion with a shaped blade bevel essentially identical to said run-in blade bevel having said optimum tonal quality size and providing the latter blade tip portion throughout a useful depth of said latter blade tip portion with a constant blade tip thickness equal to the height of said shaped blade bevel measured essentially perpendicularly to said useful depth, with said useful depth being made equal to several times said shaped blade bevel height whereby the effective area of said shaped blade bevel remains constantly at said optimum size despite progressive wear of said shaped blade tip portion in the direction of and throughout said useful depth during said excess ink wiping.

A doctor blade for wiping excess ink from a printing surface of a printing form in lieu of a conventional doctor blade of a type having a constant blade thickness between two mutually parallel blade surfaces and a generally wedge-shaped tip portion including a run-in blade bevel having an optimum tonal quality size and extending from one of said blade surfaces at an angle corresponding to an angle of attack of the doctor blade relative to said printing surface, and an inclined wedge surface extending from said blade bevel to the other of said blade surfaces, whereby the effective area of said blade bevel would increase from said optimum size through progressive wear of said tip portion during use of said conventional blade to sizes eventuating in progressive degradation of print quality, comprising in combination:

• a doctor blade body having said blade thickness between said parallel blade surfaces, and a marginal blade tip portion adjacent said doctor blade body having a shaped blade bevel essentially identical to said run-in blade bevel with said optimum tonal quality size, and having throughout a useful depth of the latter blade tip portion a constant blade tip thickness equal to the height of said shaped blade bevel measured essentially perpendicularly to said useful depth, with said useful depth being equal to several times said shaped blade bevel height, whereby the effective area of said shaped blade bevel remains constantly at said optimum size despite progressive wear of said marginal blade tip portion in the direction of and throughout said useful depth during said excess ink wiping.

In a printing apparatus of a type wherein excess ink is wiped from the printing surface of a printing form with a doctor blade having conventionally a given constant blade thickness between two mutually parallel blade surfaces and a generally wedge-shaped tip portion including a run-in blade bevel having an optimum tonal quality and extending from one of said blade surfaces at an angle corresponding to an angle of attack of the doctor blade relative to said printing surface, and an inclined wedge surface extending from said blade bevel to the other of said blade surfaces, whereby the effective area of said blade bevel would increase from said optimum size through progressive wear of said tip portion during use of said blade to sizes eventuating in progressive degradation of print quality, the improvement comprising in combination:

• a marginally shaped doctor blade in lieu of said conventional doctor blade, including a doctor blade body having said blade thickness between said parallel blade surfaces, and a marginal blade tip portion adjacent said doctor blade body having a shaped blade bevel essentially to said run-in blade bevel with said optimum tonal quality size, and having throughout a useful depth of the latter blade tip portion a constant blade tip thickness equal to the height of said shaped blade bevel measured essentially perpendicularly to said useful depth, with said useful depth being made equal to several times said shaped blade bevel height, whereby the effective area of said second blade bevel remains constantly at said optimum size despite progressive wear of said marginal blade tip portion in the direction of and throughout said useful depth;
• means operatively associated with said marginally shaped doctor blade for applying said marginally shaped doctor blade to said printing surface at an angle essentially equal to said angle of attack and placing said shaped blade bevel into contact with said printing form;
• means operatively associated with said printing form for applying said ink to said printing surface and printing form;
• means operatively associated with said printing form for effecting relative movement between said printing form and said marginally shaped doctor blade whereby said marginal blade tip portion is caused to wipe excess ink from the printing surface at said optimum size shaped blade bevel;
• and
• means operatively associated with said blade applying means for advancing said marginally shaped doctor blade toward said printing form to compensate for wear of said marginal blade tip portion and to maintain said marginally shaped doctor blade continuously in contact with said printing form via a shaped blade bevel maintaining continuously said optimum size throughout said useful depth of said marginal blade tip portion.