US2699720A - Half tone engraving process - Google Patents

Description

Jan. 18, 1955 w. c. HOWEY HALF TONE ENGRAVING PROCESS Filed April 13, 1950 Fig.1 I

' INVENTOR. Wqher L. Home BY United States Patent HALF TONE ENGRAVING PROCESS Walter C. Howey, Boston, Mass.; Winfield S. Brooks, James P. Murphy, and Edwin M. Howey, executors of said Walter C. Howey, deceased Application April 13, 1950, Serial No. 155,633

2 Claims. (Cl. 101-4011) This invention relates to photoelectric engraving. It is an improvement in the method of photoelectric Celluloid half tone engraving such as described in U. S. Patent No. 2,179,002, to George Washington, Jr., in which the patentee saysIt is a principal object of my invention to provide an entirely new method for impressing the image on the print plate, said method consisting of destroying the material of which the print plate is composed, rather than cutting or compressing the same.

Because of the tool shown and described in the patent above referred to, it is impossible to make three dimensional relief half tone engravings because for this purpose it is necessary for the photograph to be reproduced by a graduated system of dotted and checkered spots in which the size of the spots is related to the three dimensional effect. For this purpose too, a tool having a square cross section must be used or at least a four sided section by means of which a pattern or marking of alternate squares mark the middle and highlight range of the system.

A further important feature of the present invention is the square printing dots which must be related to one another in such a manner that the diagonal lines through the squares are preferably at a 45 angle with the horizontal when the picture is viewed in an upright fashion. If these diagonals are made vertical or horizontal they destroy the illusion of the half tone. Further any dots but square have a tendency to show a moire or second image distortion. 7

According to the present invention, the image is impressed into the print plate by cutting, compressing and decomposition of material comprising the plate.

Further, heretofore, all shadow, middle tone and highlight elements of Celluloid half tone plates, although they differ in area, depth and separation have been engraved with a heated tool tapered at an obtuse angle.

Celluloid cuts so made are suitable for direct printing, but they collapse under high matrix pressure of stereotype printing. Middle tone and highlight four sided dots break down and render the plate useless.

My improved method engraves all printing dots with a four sided tool tapered at an acute angle. This may be made about 70 ending in a tip. The shape of the tip may be given any substantial angle. It may be made an obtuse angle or simply rounded over. This acutely tapered section engraves all ink accepting and printing dots which form the middle tone section and highlight section of the plate with an acute monolithic contour which will withstand matrix pressure and extend the usefulness of photoelectric Celluloid engraving to printing with plates stereotyped or electrotyped from matrices.

A feature therefore of the present invention is that all printing dots in the plate are formed with side walls spanning an acute angle.

In the present method all non-printing shallow shadow dots are preferably engraved by the blunt tip of the tool, but it is possible to continue the acute angled sides to a point, although in this case the tool must travel deeper into the plate for the larger dots of the middle tones and high lights which is sometimes a disadvantage. However the tool blunts over very quickly and these produce the shallow shadow or non-printing dots which are usually too small to be seen. The shape of the blunt tip therefore is of little consequence. If the tip is rounded the shadow dots will be rounded as in photoelectric engraving. The blunt end of the tool beyond the acute walled 2,699,720 Patented Jan. 18, 1955 shank may have an obtuse angle substantially larger than In the drawings:

Figure 1 shows in enlarged profile the obtuse angled engraving tool of photoelectric engraving machines now commonly in use.

Figure 2 shows an enlarged approximate profile of a novel type double angled and doubly profiled engraving tool used in my new invention.

Figure 3 shows a cross section profile of a plate having a dot structure made by half tone photoelectric engraving with the old style obtuse angled tapered tool in common use as shown in Figure 1.

Figure 4 shows an enlarged approximate cross section of a plate having a dot structure of a photoelectric engrgving made by the engraving tool as shown in Figure Figure 5 shows the round dot solid and shadow structure and the rectangular dot middle tone and highlight structure common both to photoengraving with the old tool and method and my new type photoelectric engraving system.

Figure 6 shows a cylindrical type photoelectric scanning and engraving machine as disclosed in my U. S. Patent No. 1,815,105, entitled Cylindrical Scanning, which may be used in carrying out this invention and which is commonly used in all photoelectric engraving machines now in commercial practice.

The preferred plate medium used in photoelectric engraving is a special mix of nitro-cellulose to which is attributed the toughest hardness characteristics of thermoplastic resins in common use.

The method of forming the plate is a combination of the photoengraving or dry point etching art, the embossing art, and manual engraving. This is shown somewhat diagrammatically in Figure 6 where the optical scanning system 7 scans a continuous tone photograph or other pictorial subject mounted on the scanning drum 9, either by transmitted light from the axis of the drum or by some known reflecting system. The variations or pulses from the scanning unit pass through the amplifier 8 and energize the engraving unit 11 for actuating the tool 1 which differs from 1 of Figure 1 as will later be explained. The engraving unit 11 and the scanning unit 7 are run in synchronism along the lead screw 12 which is turned by the motorized gear box 13 through the motor drive 16. The gear box 13 also drives the drums 9 and 10 on the same shaft or synchronously. The drum 10 carries the engraving plate against which the tool 1 acts. Tool 1 is actuated and forced at variable depth into the plate to be engraved.

Tool 1 may be given a reciprocating motion to engrave a dot structure by a tone generator, or oscillating shutter or other suitable alternative well known to the arts. The purpose of the oscillating member is to cause the tool to form evenly spaced raised and alternately depressed areas in the half tone plate after the manner that Levy screen half tones are photoengraved. The relative area and separation of the unetched dot structure left is a functional result of the depth at which the engraving tool becomes positioned into the plate when empowered by the photoelectric reflection of the relative light and shade of the picture.

The end or tip 2 of the tool 1 should be made blunt, that is, the conical or wall angles should be larger than 90 while 90 to are permissible in this respect, if the end 2 is made completely blunt, it will be rounded over in the tip rather than pointed. By making the end 2 obtuse, it is considerably shortened in height or length and therefore will make a more shallow impression than is possible with a sharp pointed end. As a matter of fact, as has been explained above, the rounded or blunt tip is chiefly responsible for the non-printing shallow shadow dots, whereas the acutely angled section 3 of the tool is responsible for the middle tone and high light structures in the printing plate.

As will be seen in Figure 2, the angle is indicated at 75 An acute angle from 70 to 80 or somewhat more is permissible for this section 3 of the tool. This section of the tool is at least twice as long or high as the section 2 of the-tool. The angleas indicated-in Figure 2is measured across from the edge of one face to the non-adjoining edge of the other face since the :lructure shown in Figure 2 for the section 13 .isa fourrsided rectangular truncated pyramid. The object of this arrangement of the wall structure of the tool is such as to provide additional strength iuswhich pillarsformedlin the, engraving plate'may serve .10t,. 11ly in. direct, printing. but. also. in making stereotype and other type plates which must be pressed from the master @Plate which, of course stands .up as ,embossing rather than as engraying.

I have found that by making the structure 3 to .have walls;.which standup from one another substantially less than 90, the .wall structure, particularly in thestereotype plate becomesextremely strong and will not crush, under the great pressure which maybe used in its formation. and use. .Inorder not to lengthen theworking end of: the tool, it is;.Pr.eferable as has beenexplained, .to have the end blunted over'fortheshallow clots and it is somewhat immaterial as to What angle the end 2 may have providing this; purpose .is accomplished.

,Inthearrangement indieatedin Figure 1, there is shown the tool ,1 generally used in the prior art. This tool is proyided with an obtuse angled truncated pyramid endZ in which the angle corresponding to the angleinthesection3 of Figure 2,is greater than90 Figure 3 shows, a plateA of a structure using the old type tool of Figure 1, in which theengraving dots5 ,are

of course at obtuse angles corresponding to the angle of the truncated end 2 of Figure 1.

In the arrangement indicated in Figure 4, the plate A, which'may beof Celluloid or other suitable thermo-plastic material is engraved or impressed with the recesses 5' whiehcorrespond to theend sections 2 and 3 of the tooll. In this case the bottom of the recesses. are roundedoyer or made at an obtuse angle, while the main .wall structure stands up rather sharply as indicated by the side profile17 of Figure 4. ,When a matrix or stereotype plate is taken from the engraved plate,;the thin wall structures will have considerable strength and will standup very well under the pressures used in cylindrical printingpresses and in other types of presses in which such platesare applied.

The method used in the present invention applies equally well for engraving materials otherthan Ce-lluloid withnnunheated tool although with a thermoplastic material for the plate a heated tool is commonly used.

-It is essential in thepresent invention that section 3 of the tool be four-sided so that a complete pin-point high light can be obtained when the tool is impressed to its maximum length or depth in engraving the plate. If this were not true it wouldinot be possible to obtain the full rangeof printing from deep shadow to-highlight. Ifthe tool section 3 were conical as indicated for the .section 2 in Figure 2, Whether ofobtuse or acute angle,it wouldnot be possible tov attain full highlight structure plate, since in that case the surface of the plate ,would have numerous spaced ridges where the circles made by the cone couldnot meet. Thestructure would besirnilar to that shown in Figure 5 of the George Washington, Jr., patent referred to above, particularly theextreme left set of four circles in --his -Figure-5. By making the-tool four sided in the main shank section 3 of the point, it is not necessary to stagger different rows of points and further the structure is built up very uniformly with highlight and middle tone sections of the plate formed with rectangularly spaced square dots and the shadow section filled circular dots made by the shallow impression of thebluntendof the tool.

WhatI claim is:

l. A method of forming a half tone relief printing plate comprising: embossinga blankby depressing therein a tool having an engraving head comprising a substantially conically shaped tip portion of circular cross-section with an obtuse apex angle, jo ined to a four sided truncated pyramid portion, the pyramid having an acute apex angle; said tool being depressedinto.saideblank within the limits of the substantially conical portion in the solid shadow sections of the plate and within the limits of the truncated pyramidport-ion .in the middletoneand highlightisections of the plate.

2. A method of forming a half tone. relief printing plate comprising: embossing ablank by-depress'ingthereina tool having an engraving head comprising a bluntly tapered tip portion of circular cross-section, joined to-.a fourside'dtruncated pyramid portion, the taperof the pyramidportionlbeing less than the taper ofssaidztip; said tool being depressed into. said blankwithin thetlimits of said bluntly tapered tip portion in the solid shadowsections of the plate andwithin-thelimits of the truncated pyramidportion in themiddletone. and. highlight. sections of the plate.

References Cited in'the file of this patent U I ED S A E LP TE 1921, Commercial Engraving Publishing C0,, vlndlanapolis. Copy ayailable 1:11 Div. 17. Only pages 243, 245 and 250, cited.

Clerc: Ilford Manual of, Process .Work, .4th ed., 19 46. Ilford Ltd.,1Lond,o n. Only pages 216 to 2 l9 ,madeof record. ,Copy available in Division 17.

Flader et al.: Modern Photoengraving, 1948. -M0dern Photoengraving Publishers, Chicago. Only pages :17 9 to 182 made of record. Copy available inDivision 17.

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