SCREEN PRINTING METHOD AND APPARATUS

Abstract: A direct screen printing method and apparatus includes one or a plurality of machines for printing indicia in single or multiple colors on a substrate, such as a cap (C) or a T-shirt. The method involves forcing ink (91) in the form of a viscous composition under constant gas pressure through a pattern in a screen (64) in contact with the substrate. The apparatus includes a holder (18) to support the substrate, height adjustable post (16) for providing the contact between the screen and the substrate, and pressure hose (80) for supplying gas to the ink (91) for a time and at a pressure appropriate to force the ink through the screen pattern to form a non-distorted detailed design on the substrate; in a preferred embodiment, the apparatus includes a screen print assembly including a replaceable screen holder (52), pressure hose (80) for introducing air under constant pressure to screen holder (52), and support members (84) on screen holder (52) for mounting a sensitized screen (64), especially a curved screen (64), upon which viscous ink (91) can be placed; and support (18) for mounting a substrate (C) for printing thereon by contacting screen (64) to the substrate (C) and introducing air under pressure to holder (52) to force said ink (91) through said sensitized screen (64) to print indicia on said substrate (C).

Description: SCREEN PRINTING METHOD AND APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a screen printing method and apparatus for applying indicia such as designs, letters, numbers and/or words on substrates. Particularly, the invention relates to a method and apparatus for directly printing indicia in the form of designs, letters, numbers and/or words, for example, on caps, hats, T-shirts and the like for identification, information, promotion, and/or aesthetic purposes but is not limited to any specific indicia or type of substrate. More particularly, the invention relates to printing such designs, letters and/or words on substrates with the use of a flat or curved screen and apparatus which incorporates a curved screen. In a preferred form of the apparatus, a screen print assembly incorporates a screen which is so constructed that it fits securely in the apparatus for cooperation with a cap mount assembly and is adapted to be tightened thereon. The securing means is a feature of the invention which permits the screen to be easily and quickly mounted and replaced, particularly a curved screen which must be properly secured in the screen assembly. In addition, the preferred direct screen printing apparatus according to the invention provides for mounting and replacement of a portion of the screen print assembly, namely the screen holder or can, such that a plurality of screen holders, each having a pre-sensitized screen, can be prepared for use in the screen printing apparatus which is closed by a cover so that, for example, different indicia can be printed on caps in a continuous assembly process and/ or different inks and/or colors of inks can be used for the printing. 2. Description of the Prior Art For many, many years indicia in the form of, for example, designs, letters, numbers and/or words have been applied to substrates for purposes of identification, information, promotion, or aesthetic purposes. Such substrates especially included hats, caps, T-shirts and other articles of clothing whereby the wearer could identify or be identified with a particular group, cause, club and the like. In addition, logos have been printed on caps or hats for purposes of advertising or information. Similarly, an infinite number of designs have been applied to articles of clothing for aesthetic, informational or other purposes. A number of patents have issued both in the United States and in countries foreign to the United States which disclose methods and apparatus for such printing. Early processes and apparatus for printing and dyeing fabrics are disclosed in U.S. Patents Nos. 576,623 and 798,528. Although the usual techniques for applying such indicia to substrates were somewhat elementary, for example, the use of stencils on containers or the like, or heat transfers for articles of clothing, the wide acceptance of indicia on clothing articles has prompted persons in the art to search for better methods and apparatus for applying indicia to clothing articles so that the detail of the designs is maintained and the design on the articles presents a professional appearance. Various techniques which have been used include the process and apparatus disclosed in U.S. Patent No. 3,745,970 wherein a " diaphragm ' carrying a pattern is forced by air into engagement with a plate for coating an article, and portable stenciling apparatus using a process as described in U.S. Patents Nos. 4,048,918 and 4,164,183. The attempt to obtain expert design in detail is complicated by the fact that some of the surfaces to be printed are curved or at least not perfectly planar. Special apparatus has been designed for printing such curved or irregular surfaces, such as that described in U.S. Patent No. 4,314,503. This is particularly true in the case of hats or caps where printing of the indicia on the head band is required after the hat is manufactured. A recent method and apparatus for printing curved surfaces described in U.S. Patent No. 4,381,706 comprise a frame having a curved printing screen. The device is designed for printing indicia on caps and hats using a squeegee. Although the method and apparatus described in the patent are said to overcome the difficulties of pattern distortion experienced in the art, there are still pattern distortions with the use of the patented method and apparatus. The present method and apparatus overcome these deficiencies and produce a non-distorted, detailed image on a substrate, either curved, planar or irregular, such as a cap, -hat, T-shirt or the like. Moreover, none of the prior apparatus includes means for quickly and easily replacing the entire screen holder in the screen print assembly forming a part of the apparatus nor do they disclose any means for quickly and easily replacing the screen in the screen print assembly, particularly a curved screen which must be properly secured. SUMMARY OF THE INVENTION The present invention is addressed to a method and apparatus for directly producing a printed indicia on a substrate by forcing ink through a predetermined pattern on a screen in contact with a surface of the substrate to be printed. The force is supplied by gas under pressure, preferably air at constant pressure. The ink is in the form of a substantially viscous composition and preferably in the form of a plastisol which is commercially available. The screen, which may also be commercially available, is supported by a screen frame such that the contour of the screen is substantially the same as the contour of the surface to be printed. A single color or multi-color design can be applied to the substrate using one or more frames mounted in substantial alignment with each other or mounted for indexing, preferably with means for drying the image after application being provided with the multiple applications. In a preferred aspect, the invention is directed to an apparatus for directly printing indicia on a substrate comprising a screen print assembly including a screen holder, a screen, means for mounting the screen to the screen holder, and a cap mount assembly for cooperation therewith. In a more preferred embodiment the screen print assembly and cap mount assembly are adapted to be used as one station of a multi¬ station printing apparatus and the screen holder is adapted to be removed from the assembly as a unit and replaced by another screen holder. By providing for replacement of one screen holder with another, a number of screen holders may be prepared, each having a pre-sensitized screen for use in a single screen print assembly. This permits the prepared screen holders to be provided with screens for printing different indicia using, for example, inks of different consistency depending upon the compositions of the substrate to be printed and/or inks of differing color. The invention also concerns an improved apparatus for mounting a screen on the screen holder such that one sdreen can be replaced with another quickly and easily. The screen may be flat or curved and is positively preregistered and located with respect to the screen holder and secured thereon by a mounting means which permits the screen to be secured such that the screen fabric is precisely taut for printing of an indicia on a substrate mounted on a mount assembly and in contact with the screen surface. The apparatus is particularly applicable to printing of indicia on substrates using a constant pressure compressed air as a fluid. The apparatus which includes a pivoted cover improves upon the efficiency of this method because it provides a screen holder which includes an improved fluid seal and screen mounting which insures reliable, consistent contact between the screen surface and the substrate to be printed. The latter apparatus is particularly adapted for use as one station of a multi-station printer such as the Hix Rotary Printer illustrated on page 28 of the publication entitled "Screenprinting" of March 1985 by the Signs of the Times Publishing Company, 407 Gilbert Avenue, Cincinnati, Ohio. By substituting the present apparatus for one or more of the six stations of the Hix Rotary Printer, a modular, continuous, direct cap printing apparatus is provided. The invention will be better understood from the following description of the invention taken in conjunction with the accompanying drawings wherein like numerals identify like elements. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Fig. 1 is an isometric view of a first and preferred embodiment of my screen printing apparatus in the form of one machine according to the invention for printing curved surfaces; Fig. 2 is a partial view showing a cap positioned on a mandrel of the device; Fig. 3 is a top view of the assembled air chamber housing and screen mount in the apparatus of Fig. 1; Fig. 4 is a cross-sectional view taken along lines IV-IV of Fig. 3; Fig. 5 is an end elevational view of the housing of Fig. 3; Fig. 6 is a detailed view showing the connection between the housing to the vertical part of the apparatus; Fig. 7 is a plan view of the screen frame and screen in an extended position; Fig. 8 is a side elevational view of the screen frame and screen of Fig. 7; Fig. 9 is a top plan view of the control unit for the apparatus; Fig. 10 is a front elevational view of the unit of Fig. 9; Fig. 11 is a side elevational view of the unit of Fig. 9; Fig. 12 is a rear view of the control unit of Fig. 9 with the rear panel removed taken along lines XII-XII of Fig. 11; Fig. 13 is a schematic view of a plurality of machines aligned to form a direct printing apparatus in accordance with the invention; Fig. 14 is a schematic view of a plurality of machines arranged in a circular fashion to form a direct printing apparatus in accordance with the invention; Fig. 15 is an isometric view of a second embodiment of the invention for printing planar or substantially planar surfaces; Fig. 16 is a top plan view of the housing for the apparatus shown in Fig. 15; Fig. 17 is a cross-sectional view of the housing taken along lines XVπ-XVπ of Fig. 16; Fig. 18 is an end elevational view of the housing shown in Fig. 16; Fig. 19 is a bottom plan view of the screen for the housing shown in Fig. 16; Fig. 20 is a top plan view of a third embodiment which is the preferred screen print assembly according to the present invention; Fig. 21 is a side elevation of the screen print assembly of Fig. 20 showing its position relative to the preferred form of cap mount assembly used in printing with the apparatus, the alternate positions of the cover and screen holder being shown in dashed lines; Fig. 22 is a side elevation view of the cap mount assembly taken at 90° to the elevation of Fig. 21; Fig. 23 is a bottom plan view of the cap mount assembly of Fig. 22; Fig. 24 is a top plan view of the cap mount assembly of Fig. 22; Fig. 25 is a top plan view of one end of a screen preferred for use with the screen print assembly of Fig. 20; Fig. 26 is a cross-sectional, enlarged view of one end of the screen print assembly in the circle XXVI showing the clip means for mounting a curved screen to the screen holder; Fig. 27 is a perspective view of the clip means of Fig. 26; and Fig. 28 is a cross-sectional, enlarged view of one end of a screen holder showing a clip means for mounting a flat screen to the screen holder. DESCRIPTION OF PRESENTLY ■ PREFERRED EMBODIMENTS OF THE INVENTION Figs. 1-5 illustrate the preferred apparatus comprising one machine M for directly printing indicia on caps according to the method of the invention. Referring to Figs. 1 and 2, the machine M includes a base 10 which may be constructed of a wide channel or table of suitable material and configuration. The base 10 is stationary relative to the rest of the machine. An aperture 12 is provided on one end of the base. A journal block 14 having an aperture therein aligned with aperture 12 in the base is secured to the lower surface of the base 10 by welding or the like. A. vertically adjustable standard or post 16 extends through the apertures in the block 14 and base 10 and supports a mandrel 18 at the upper end thereof. A fastener 20 extends through a side wall 22 of the block 14 into a vertical slot 24 in the post 16 and prevents rotation of the post 16 relative to the block 14 and the base 10. A curved upper surface 26 is provided on the mandrel 18 for supporting a cap C, as more particularly shown in Fig. 2, wherein the inner curved surface of the front head band 28 of the cap rests on the corresponding curved surface 26 of the mandrel 18. A cap hold down ring 30 in the form of a U-shaped member 32 having stops 34 at the outwardly extending ends is mounted on an upstanding hold down plate 36 fastened by Allen head screws 38 to a cap hold down base 40 mounted on the post 16. The plate 36 is adjustably secured to the post 16 by machine bolt 42 which secures the split ends of base 40 to the post 16. The member 32 of the cap hold down ring 30 is adjustably secured to the hold down plate 36 by a hold down knob 44 which threadably engages the member 32 through a slot 46 in the plate 36. Thus, once the position of the hold down base 40 is fixed on post 16 relative to the mandrel 18, the hold down ring 30 is vertically adjustable relative to the mandrel 18. After the cap C is positioned over the mandrel, the knob 44 is loosened, vertically lowering the hold down ring 30 to engage the back band 48 of a cap C, as shown in Fig. 2, to pull the front head band 28 tightly into engagement with the curved surface 26 of the mandrel 18. The stops 34 on the ring 30 prevent the back band 48 of the cap C from slipping off the member 32. Once the cap band is so engaged the knob 44 is tightened to engage member 32 against the plate 36 for printing of the cap C. Base 10 also supports the printing " head 50 including the housing 52 which is vertically aligned with the mandrel 18. The supporting means includes a block 54 fixed to the base 10 at the end opposite the aperture 12 for supporting a vertical post 56. A two-part lateral beam 58 having a circular cross section extends into and is supported by a block 60 at the upper end of post 56. One end of the • lateral beam 58 is secured in the block 60 by a fastener 62 as will be described in detail hereinafter with respect to Fig. 6. Housing 52 is secured to the opposite end of the lateral beam 58. Thus, the position of the housing 52 relative to the base 10 is fixed such that a cap C on the mandrel 18 which is secured to the post 16 can be brought into contact with a screen 64 secured to the lower part of the housing 52. To insure that the contact between the cap C and the screen 64 is substantially uniform across the screen the housing 52 may be moved inwardly and outwardly with respect to block 60 on beam 58 which extends through block 60 and is rotatable about beam 58. As shown in Fig. 6, the beam 58 is formed of two parts 58a and 58b which are connected to each other by fastener 65. At one end part 58a is welded to the rear side wall 66 of the housing 52; at the opposite end part 58b extends through block 60 and is retained by a fastener, such as set screw 62. As more particularly shown in Figs. 1-5, the housing 52 comprises a rectangular box-like structure having a pair of end walls 68 and a pair of side walls 66. The top of the structure is closed by a removable lid 70 which is secured by nuts 72 on threaded posts 74 welded to the end walls 68 of the housing 52. A threaded nipple 76 with a compression fitting nut 78 is placed in the lid 70 to provide an air passage into the structure. One end of a flexible hose 80, which may be made of plastic, rubber or other suitable conventional material, is affixed to the nipple. The opposite end of the hose may be connected to a source of air. A standard pressure relief valve 81 may be provided in the lid. The bottom wall 82 of the structure is open and is provided with a pair of laterally extending screen support members 84 having a curved inner surface to which a screen 64 having a frame 86 is secured by fasteners, such as screws 88. The screen 64 and screen frame 86 are shown in Figs. 7 and 8 and may be purchased. For example, a suitable screen and frame are available from Harco under its number HP-14F (frame only) or HP-14FS (frame with fabric screen). The screen mesh is preferably 300 line screen monofilament fabric, but any suitable mesh and fabric screen may be used. The screen is stretched tightly between the support members 84 and carries a pattern such as the "MHI" indicia shown at 90 in Fig. 7, which is desired to be printed onto the cap front head band 28 or the like. The preparation of the screen pattern 90 is conventional and well known to those skilled in the art. Essentially, the screen is coated with a photosensitive emulsion and a film positive sandwiched against it. The film is exposed to high intensity light to fix the non-image of non- pattern area which hardens to a greater extent than does the pattern area which remains relatively soft since it is opaque to the film positive. The screen is then washed out with water cleaning the soft, unexposed pattern to create the photosteneil image to be printed on the cap. Different screens and different patterns can be used as desired. Preparatory to printing with the device according to the invention, a mass, of ink 91 in the form of a viscous composition is placed on the upper surface of the screen 64 over the image or pattern area. The manner of charging the ink is incidental to the method and can be done by dipping ink from a container using a spatula or the like. The preferred ink is in the form of a plastisol such as Wilflex SSV-LF/H4 ink which is characterized by the manufacturer as a super opaque/non-bleeding vinyl plastisol screen printing ink, which is especially formulated for direct screen applications. Other suitable inks include Wilflex SSV-LF general purpose vinyl plastisol screen printing ink. Other inks are suitable provided they are in a relatively viscous state so that they will normally adhere to the upper surface of the screen. In addition to plastisols, water base inks and enamels, for example, can also be used provided they are adequately thickened, for example, using a thickener such as starch or the like. The consistency of other ink can be modified in other ways well known in the art for use in the method and apparatus of the invention. During printing, the ink mass is forced by compressed air introduced through a hose 80 into the air chamber formed by housing 52, through the screen pattern 90 and onto the fabric of the cap which is previously raised into contact with the lower surface of the -screen 64. The air pressure used to print is preferably about 6 psi but it may be more or less depending upon the type " and consistency of the ink, the screen fabric and mesh, the substrate fabric upon which the printing is to be done, the time for printing, and the detail desired in the final design. Air is provided from a conventional source such as an air compressor (not shown). The printing pressure is regulated in a control unit 92 such as that shown in Figs. 9-12. The control unit 92 comprises preferably a rectangular box 94 having an air inlet 96 through which air enters the unit at a pressure of about 30-40 psi. The air passes through tube 98 to an air regulator 100 having a pressue gauge 102, which , can be observed from the front of the unit, and then through an air flow valve 104 to an air outlet 106 to which an end of air hose 80 is attached. The regulator 100 is controlled by a knob 108 which also extends through the front of the box 94. The unit 92 is activated by a power on button control 110 and start button control 112 electrically connected to the valve 104 through the bus element 114 and fuse element 116, which are connected to a power source (not shown) through box receptacle 117. An emergency stop button control 118 is also provided in the electrical circuit and accessible from the front of the control unit 92. The details of the electrical circuit are well known and need not be described in further detail. To print an image, ink is forced under the regulated air pressure through a screen 64 for a specified predetermined time which is controEed by a timer 120 of the control unit 92. Preferably for a 6 psi air pressure, the printing time is approximately two seconds. Of course, the printing time also is dependent upon the air pressure, ink consistency and image detail required. — As shown in Figs. 9-11, the control unit 92 is self-contained and air pressure, time and regulator controls are both easily visible and accessible. Again, the unit 92 may have a different configuration from that illustrated so long as provision is made for regulating the time and pressure for admitting air into the housing 52 of the printing head 50 to force the ink through the pattern and onto the substrate, e.g. cap to be printed. Quick disconnect couplings or other connections, including threaded couplings, can be provided for the air lines or hoses. OPERATION The operation of a printing machine according to the invention illustrated in Figs. 1-14 is as follows: The lid 70 of the printing head or housing 52 is removed by removing the nuts 72 and a supply of viscous ink 91 is placed on the screen 64 so as to completely cover at least the image or pattern area. Of course, it may extend beyond that area. The lid 70 is replaced and the nuts 72 threaded and tightened on the posts 74. Wing nuts are preferable for the nuts 72 since they can be operated easily by hand. The mandrel 18 holding the cap C to be printed is raised such that the surface 26 is put into contact with the screen 64 and secured. The mandrel 18 can be raised by hand by grasping the cap hold ring 30 and lifting it or the post 16 carrying the mandrel 18 can be raised automatically using a hydraulic or pneumatic cylinder, operated for example by a conventional foot treadle control, to raise the mandrel and bring the surface of the cap front band 28 to be printed into contact with the lower edge of the screen. Of course, it is also within the scope of the invention to maintain the substrate in a stationary position relative to the floor and lower the printing head until the screen contacts the substrate. Air at approximately 6 psi constant pressure is then supplied to the printing head 50 by pressing start button control 112, forcing the ink through the screen 64 in the pattern area to print the desired image on the cap C. The mandrel 18 is then released and lowered and the printed cap is removed from the hold down ring 30 by turning knob 44 to permit the cap back band 48 to slide over the ends of the U-shaped ring member 32. The image produced on the cap has excellent detail without any distortion since all pressure is applied vertically, as distinguished from prior methods which utilize a squeegee which causes image distortion due to the movement of the screen surface and/or surface of the fabric being printed. The direct printing machine is used to produce an image in a single color or a portion of an image of multiple colors. For multi-colored printing, a plurality of machines M, each constructed in accordance with the description of the single machine set forth above are provided to form a direct printing apparatus. In one aspect of the invention schematically shown in Fig. 13, a series of machines are aligned in a substantially straight line and the substrate, i.e. a cap to be printed, is moved from machine to machine, i.e. from station to station. At each station a different color image or portion thereof is printed on the substrate. Preferably, conventional dryers, such as spot dryers D, are positioned between the machines to completely dry or cure the ink of the design previously applied before additional ink is printed on the substrate. In another aspect of multi-colored printing according to the invention, a plurality of printing machines M, such as shown in Fig. 1, may be positioned in a circular fashion to form a direct printing apparatus. For example, a rotatable table T as shown in Fig. 14 may be provided and adapted to be indexed to permit a single operator to load the substrate • to be printed on the machine, print multiple colored images or portions thereof automatically, and remove them at the same or a different station. Again, spot dryers D or the like may be provided between the individual machines M to cure the printed ink before printing additional designs or portions thereof. As in the case of the single machine, the multi-machine apparatus is controlled automatically with respect to the amount of air pressure and time required depending upon the screen mesh or meshes utilized, the print pattern or patterns, and ink or inks used. Since different screens and patterns are used, each station in the multi-color machine apparatus preferably has separate controls including an adjust¬ able pressure regulator and gauge, electrically operated three-way valve, and electrically operated timer or equivalent. Of course, all of the controls can - be physically housed in a single control unit for the convenience of the operator. Where a single or multiple-color apparatus is used for printing caps, it is desirable to provide a supply of ink which is adequate to print at least 50 caps before reloading is required. Of course, a greater or lesser ink supply may be provided. By way of example and not by way of limitation, three examples of direct cap printing according to the invention wiE be described. EXAMPLE I A 10096 polyester smooth front banded baseball cap C is to be printed with an indicia such as the "MHI" indicia shown in Fig. 7. A 290 line monofilament fabric screen 64 is secured in the printing head housing 52. A mass of Wilflex SSV-LF/H4 plastisol ink is placed on the inside surface of the screen over the pattern area. The cap band on a mandrel 18 is moved into contact with the lower edge of the screen. Air under 6 psi pressure is forced against the ink for 1 1/2 seconds and then the cap band is separated from contact with the screen. The resulting image printed on the cap band has excellent detail with no distortion or fuzzy edges. EXAMPLE II For a bold, letter design on a substrate, in the form of a cap, a coarser mesh screen, for example, of 110 line monofilament fabric is used since extremely fine detail is not required. Dark colored ink of the same type as in Example I is used. Air pressure at 6 psi is applied for approximately 1 1/2 seconds, resulting in a bold letter design of good detail, but not as good as in Example I. EXAMPLE III The same screen mesh and ink composition are used to print a bold letter design in light colored ink on a substrate in the form of a cap. Air under 8 psi pressure is applied for approximately 2 1/2 seconds. The resulting image is of substantially the same detail as in Example II, but not as good as in Example I. There is no distortion. It will be understood by those in the art that if the substrate is composed of multi-filament fabric, that is, if it is cabled, the pressure applied to the ink mass and the time of application should be increased since it will require more force to push the ink through the cabled screen and onto the substrate. Furthermore, an advantage of the present invention in which the ink is forced substantially vertically under constant pressure through the screen onto a substrate which is positioned directly vertically below the screen pattern is that any residual ink on the screen from a previous printing is placed in precisely the same intended position on the subsequently printed substrate. In other words, so-called "ghost images" are overprinted so that they are not easily visible to the naked eye. The application of air under constant pressure in a vertical direction over the entire image area or pattern results in substantially no image distortion since there is no movement or so-called "chatter" of the screen and/or substrate materials with respect to one another. A second embodiment of the invention is shown in Figs. 15-19. A direct printing apparatus A for - printing an image on a substantially planar substrate, for example, an article of wearing apparel such as a T- shirt, comprises a substantially rectangular housing 122 with a plate 123 secured to a bracket 124 supported on a vertical post 125 secured in a sleeve 126 welded to a channel 128 forming a table or the like at a fixed distance from the floor. The housing 122, which is vertically adjustable on post 125 by screws 129, includes means for introducing air in the form of a hose 130 from a compressor into the housing through nipple 132 and a planar screen frame 134 with a screen 136 having an image such as "MHI" to be directly printed on the substrate. The housing includes a plurality of interlocked longitudinal and lateral reinforcing ribs 138 for strength. A pressure relief valve may also be provided in the housing. The screen frame 134 is removably attached to the housing 122 by fasteners 140 along the edges of the screen frame for replacement and for charging ink onto the screen for direct printing. A vertically adjustable plate or platen 142 is mounted on a post 144 which extends through a collar 146 having radial fins 148 welded to the channel 128 and is adapted to be raised or lowered by hand or automatically to bring an article of clothing on the platen into contact with the bottom surface of the screen 136 for direct printing of an image on the article. Although the platen 142 is rectangular, it may be any suitable shape. The article can be retained temporarily on the platen for printing by adhesive or by vacuum or other mechanical means, if desired. The source and control of the air pressure in this second embodiment may be the same as earlier described with respect to the embodiments of Figs. 1-12. Similarly, the viscous ink composition and supply may be identical to that used for printing caps. The essential difference between the two embodiments lies in the configuration of the substrate and printing screen which, in the ease of a flat or planar substrate, requires a flat or planar screen. For example, the Newman Roller Frame is suitable for printing flat articles, for example, T-shirts or the like. As described earlier herein, direct screen printing without the use of a squeegee is carried out by using compressed air under pressure to force ink from a viscous ink supply on one surface of a prepared screen through the screen fabric the opposite surface of. which is in contact with a substrate, such as a cap, and " onto the substrate. The pressure of the air is constant and is applied via a sealed screen holder or can for a predetermined time at predetermined pressure to provide a quality printed image on the substrate. In a further aspect of the present invention, an improved apparatus for practicing the aforementioned printing method is disclosed providing, inter alia, quick and facile replacement of one screen holder by another, better sealing of the compressed air in the screen holder and more secure mounting of the screen. In addition, the preferred apparatus shown in Figs. 20-28 of the drawings hereof and described hereinafter is adapted for use as a module on the basic structure of the Hix Rotary Printer previously identified. Referring to Figs. 20 and 21, the preferred and third embodi¬ ment of the screen printing apparatus includes two basic assemblies, a screen print assembly 210 and a cap or hat mount assembly 212. The screen print assembly 210 preferably includes a plate * 214- for mounting the assembly 210 to the T-bolts provided at each station of the Hix Rotary Printer although the plate may be mounted independently, for example on a standard or post 56 or the like. When used on the Hix Rotary Printer machine, the T-bolts extend through the holes 216 in the plate for mounting of the plate on an operating arm attached to the upper spindle disk of the machine. It will be noted that the end of the plate is preferably offset, such that, when in position, the screen holder 218 with screen 219 mounted thereon included in the screen print assem¬ bly 210 will extend vertically over platen 220 of the hat mount assembly 212 when the assembly 212 is mounted on one of the rectangular cross-section bars 222 which extend radially from the lower spindle disk in the center of the Hix Rotary Printer (see Fig. 22). If the plate 214 does not include an offset portion, the platen 220 is mounted over a bar 222 so that the screen holder is positioned above the platen for printing. The plate 214 includes a substantially rectangular opening 224 of a size slightly larger than the outer perimeter of wall 225 of the screen holder 218, such that the screen holder is adapted- to fit closely within the opening 224 when the screen holder is placed therein. The top of the opening 224 is increased to form an extended opening 226 which provides a shoμlder 227. around ' the opening 224. A flange or lip 228 extending around the upper portion of the wall 225 is adapted to be seated on shoulder 227 such that the screen holder is supported in the plate 214 of the screen print assembly 210. The top surface 229 of the flange or lip 228 is either flush with or below the top surface 230 of the plate 214 to permit the top of the screen holder to be sealed by a cover 232. The cover is pivotally mounted on one end by a bolt 233 which extends through the end and through hinges 234 on plate 214 and adapted to be locked in position by a wing nut 235 threaded to a bolt 236 fixed to plate 214 on the opposite end of the cover. An O-ring 237 extends around the inside of the cover opposite the extended opening 226 to seal the entire assembly against air leakage when the cover is locked in position by the wing nut. The cover 232 includes an opening 238 for communication with a source of compressed air, not shown, for introduction of air to the inside of the screen holder. As shown in Fig. 21, the cover 232 is adapted to be pivoted into the position shown in dashed lines to permit a screen holder 218' (also shown in dashed lines) with its screen 219' to be lifted from the plate 214 and replaced by another screen holder with screen mounted therein. In a prior embodiment, the screen print assembly was secured to a standard or post 56 and a hat mount assembly carrying a cap to be printed was raised so that the surface of the cap contacted the bottom of the screen for printing. Although the screen print assembly 210 and hat mount assembly 212 of the present embodiment may be mounted for operation in the same manner, the preferred mode is for the hat mount assembly 212 to be fixed relative to the screen print assembly 210 which is raised and lowered in accordance with the operation of the operating arm of the Hix Rotary Printer apparatus. According to the structure and operation of that machine, which is not part of the present invention per se, the screen print assembly is mounted such that it moves in the manner of an A-frame in the direction of the cap mount assembly and in approximately the last two inches of travel the screen print assembly 210 is adapted to move substantially vertically to provide contact between the screen surface and the substrate mounted on the fixed cap mount assembly 212 in order to produce a definitive image or indicia on the substrate. The preferred cap mount assembly, as shown in Figs. 21-24 includes a U-shaped channel member 240 which is adapted to be secured in position on a bar, such as radially extending bar 222 of the Hix Rotary Printer, by bolts 242 across plate 243. A platen 220, either flat or, as shown in the drawings, curved to conform with the curvature of the screen used, is mounted on an extending member 246 by bolt 248. The height of the platen is adjustable using a conventional hand adjustment means controlled- by a knob 250. The position of the platen on the member 246 may be precisely controlled by adjustment of the member which includes a slot 251 through which bolt 248 extends. As previously mentioned, the screen and platen may be flat or curved depending upon the configuration of the substrate to be printed. To provide a predetermined indicia on a substrate, the screen may be pre- sensitized in accordance with well-known techniques as previously described and then mounted on a screen holder, such as the screen holder of the present apparatus. To permit quick, easy and accurate installation of a screen on a screen holder, an improved means for preregistered mounting of the screen has been provided which is applicable to flat and curved screens. The mounting means insures that a substantial seal is provided between the screen frame and the depending or bottom wall edges of the screen holder. In the case of a curved screen, the mounting means also provides the screen with additional tautness which removes any inconsistencies in the screen fabric surface which would adversely affect the quality of the printed image upon contact of the fabric surface and the surface of the substrate by permitting ink to flow horizontally between the two surfaces rather than directly onto the substrate being printed. Fig. 25 shows a portion of a rectangular screen 252 adapted for use as either a flat or a curved screen. The screen fabric 253 is conventional and is stretched on a frame consisting of two sides 254 and two ends 255. Each end includes, at or near the center thereof, a slot 256 for locating the screen in a screen holder. When used as a curved screen in a holder as shown in Figs. 21 and 26, the screen 252 is mounted at each end on the bottom edges of the screen holder 218 by a U-shaped clip 258 (see Fig. 27), one leg section of which carries an upstanding pin 260 which is adapted to engage in slot 256 of the screen. The clip is mounted on the screen holder 218 by means of fasteners, such as screws 262, which extend through holes 264 in one of the other two leg sections of the clip and are threaded into corresponding threaded holes in the ends of the screen holder. By tightening the screws 262, the pin carried by the clip is forced tightly into the slot 256 forcing the screen 252 to assume the precise curvature of the bottom edges of the screen holder 218 to provide a tight seal between the sides and ends of the screen frame and the bottom edges of the screen holder. In the case of a flat screen, an L-shaped clip 265 is used, as shown in Fig. 28, which performs the same function by means of screws 266 which are threaded into the depending wall 267 of screen holder 268 such that pin 269 engages tightly in slot 256 of the screen frame 270. The end of the screen frame is retained between the flange or lip 272 of wall 267 and the leg 274 of clip 265. Although the improved clip means for mounting the screen is not essential for the enjoyment of the features of the improved printing apparatus described herein, it is preferable to those mounting means presently used since it facilitates sealing of the screen holder, replace¬ ment of screens for sensitizing and cleaning and proper registration of the screen on the screen holder. The present invention provides improved direct screen printing of substrates using compressed air at constant pressure for forcing ink onto a substrate in accordance with the teachings of the method of the invention. Air at constant pressure is applied for a predetermined time to the ink in the screen holder and, without relief, forces ink through the screen onto the substrate. Using the method and the preferred apparatus disclosed herein, each cap is printed with a quality image at about 4 psi air pressure in about 1.3 seconds so the process is substantially continuous except for replacing printed caps with caps to be printed. Each cycle takes a total of about 6 seconds. From the foregoing it is evident that direct printing according to the method and apparatus of the invention can be done by forcing ink through a pattern in a screen under predetermined appropriate constant air pressure for a- suitable time. The configuration of the screen surface is designed to correspond to the configuration of the article to be printed. In other words, a curved screen is used to directly print a curved article such as a band of a hat or cap, ahd a flat screen is used to print an image on a substantially flat surface such as the front of a T-shirt. If it is desired to print an irregular surface, a correspondingly irregular con¬ figured screen can be used. By systematically controlling the pressure of the air to maintain it constant to provide a controlled direct transfer of the ink through the screen to the substrate, a non-distorted, detailed image can be provided on or into the substrate accordiing to the invention. The method and apparatus of the invention are not restricted to any given shape or type or composition of substrate or media. The machine and apparatus can be operated by hand, semi-automatically or automatically to produce an image of a single color or multi-color using a single machine or a group of machines in which the article to be printed is moved from station to station by hand or automatically through appropriate indexing. By using mandrels of different styles, i.e. flat, cylindrical or curved, different screen printing presses can be used or adapted to use the inventive method. Although the invention has been described in terms of vertical and horizontal planes for convenience of description, with appropriate modification of the elements, for example, consistency of the ink used, the machine and/or apparatus could be used to print horizontally or at any angle to the horizontal. The present invention eliminates the use of pads, squeegees or transfers for imaging an article with ink, eliminates distortion of the printed image and produces excellent detail in one color or a plurality of colors in a single design by direct printing. The method and apparatus employ constant air pressure for charging conventional inks through a conventional screen but does it in such a way as to achieve heretofore unrealized detail in the printing of images on substrates. Additionally, although the invention has been described in terms of printing articles of clothing, i.e. caps, hats, T-shirts, it is equally applicable to any substrate where a design, information, advertising or the like is desired, as for example, on containers, boxes, metal forms such as billets or blooms and machinery, although in such cases the detail of the image provided by the invention may be greater than needed. Having described presently preferred embodiments of the invention, it is to be understood that they may otherwise be embodied within the scope of the appended claims.

Claims: CLAIMS: 1. A method of printing indicia on a substrate comprising: a) providing a pattern on a screen corresponding to the indicia to be printed; b) contacting the substrate to be printed to the screen; and c) forcing ink in the form of a viscous composition under constant gas pressure for a predetermined time through said screen pattern and onto said substrate " to directly print said indicia on said substrate without relieving said constant pressure. 2. The method as set forth in Claim 1. wherein the ink is forced through the pattern under constant air pressure. 3. The method as set forth in Claim 1 or Claim 2 wherein the ink is in the form of a plastisol. 4. The method as set forth in .Claim 1 wherein a surface of the substrate is curved. 5. The method as set forth in Claim 4 wherein the screen is curved to correspond with the curved substrate. 6. The method as set forth in Claim 1 and separating said substrate from said screen for removal. 7. Apparatus for printing indicia on a substrate comprising at least one printing machine having: a) means for mounting the substrate to be printed; b) means for mounting a screen for contact of one surface of the screen by said substrate during printing; e) ink in the form of a viscous composition on the opposite surface of said screen; and d) means for forcing said ink under constant gas pressure for a predetermined time through a pattern in said screen and onto said substrate to directly print said indicia thereon without relieving said constant pressure. 8. Apparatus as set forth in Claim 7 wherein said substrate mounting means is adjustable relative to said screen. 9. Apparatus as set forth in Claim 7 and including a closed housing for mounting the screen. 10. Apparatus as set forth in Claim 9 wherein compressed air is introduced into said housing. 11. Apparatus as set forth in Claim 10 wherein said means for forcing the ink through the pattern comprises air which is passed from a compressor through a regulator into said housing. 12. Apparatus as set forth in Claim 7 wherein said ink is in the form of a plastisol. 13. Apparatus as set forth in Claim 7 wherein substrate mounting means includes a curved mandrel and said screen includes a corresponding curved surface. 14. Apparatus as set forth in Claim 7 wherein said substrate mounting means includes a substantially flat platen and said screen includes a corresponding flat surface. 15. Apparatus as set forth in Claim 7 wherein said apparatus includes a plurality of individual machines for printing indicia in separate colors. 16. Apparatus as set forth in Claim 15 wherein the machines are aligned substantially with each other and the substrate to be printed is moved from station to station. 17. Apparatus as set forth in Claim 15 wherein the machines are arranged with others in a substantially circular manner and the substrate to be printed is moved from station to station. 18. Apparatus as set forth in Claim 15 or Claim 16 or Claim 17 wherein means for drying the indicia previously applied to the substrate is interposed between at least two machines. 19. Apparatus as set forth in Claim 18 wherein means for drying the indicia previously applied to the substrate is interposed between each of the plurality of machines. 20. Apparatus as set forth in Claim 19 wherein said machines and means for drying are indexed to permit an operator to mount a substrate on at least one of the machines at a first station and index the device to a second station for printing of the indicia on a substrate. 21. Screen printing apparatus for directly printing indicia on a substrate comprising: a screen print assembly including a replaceable screen holder, means for introducing fluid under pressure to said screen holder, and means on said screen holder for mounting a sensitized screen upon which viscous ink can be placed; and means for mounting a substrate for printing thereon by contacting said screen to said substrate and introducing fluid under pressure to said holder to force said ink through said sensitized screen to print indicia on said substrate. 22. Screen printing apparatus as set forth in Claim 21 wherein said mounting means includes means for registering said screen on said screen holder. 23. Screen printing apparatus as set forth in Claim 21 or Claim 22 wherein said screen mounting means includes a clip for attaching each end of the screen to the holder, each end of the screen including a slot, and each clip including a pin for engagement in the slot to force said screen tightly against bottom edges of the screen holder. 24. Screen printing apparatus as set forth in Claim 21 wherein the screen print assembly includes means for closing the top of said screen holder. 25. Screen printing apparatus as set forth in Claim 24 wherein the closing means comprises a cover. 26. Screen printing apparatus as set forth in Claim 25 wherein the cover is pivotally mounted. 27. Screen printing apparatus as set forth in Claim 21 wherein said screen is curved and said substrate mounting means includes a curved platen for cooperation therewith. 28. Screen printing apparatus as set forth in Claim 21 wherein said screen is flat and said substrate mounting means includes a flat platen for cooperation therewith. 29. Screen printing apparatus as set forth in Claim 21 wherein said substrate means is adjustable to provide the cooperation between said screen and said platen during printing. 30. Screen printing apparatus as set forth in Claim 21 including means forming a part of the screen print assembly for attaching said apparatus to a printing machine. 31. Screen printing apparatus as set forth in Claim 30 wherein said attachment means comprises a plate having an offset portion. 32. A screen print assembly comprising: a replaceable screen holder; means for introducing fluid under pressure to said screen , holder; and means on said screen holder for mounting a sensitized screen upon which viscous ink can be placed for directly printing indicia on a substrate. 33. A screen print assembly as set forth in Claim 32 including means for closing the top of said screen holder. 34. A screen print assembly as set forth in Claim 33 wherein the closing means comprises a cover. 35. A screen print assembly as set forth in Claim 34 wherein the cover is pivotally mounted. 36. A screen print assembly as set forth in Claim 32 wherein said screen is curved. 37. A screen print assembly as set forth in Claim 32 wherein said screen is curved and said screen mounting means includes a clip attaching each end of the screen to the holder. 38. A screen print assembly as set forth in Claim 32 wherein said screen mounting means includes a clip attaching each end of the sereen to the holder, each end of the screen including a slot, and each clip including a pin for engagement in the slot to force said screen tightly against bottom edges of the screen holder. 39. A clip for mounting a framed screen in registration on bottom edges of a screen holder wherein each end of the screen frame includes a slot, said clip including means for attaching said clip to the sereen holder and a pin for engagement in the slot to force said screen into engagement with said bottom edges when said clip is attached to the screen holder. 40. A clip as set forth in Claim 39 wherein said clip is substantially U-shaped and includes three leg sections, two of which form an obtuse angle, the means for attaching the clip to the sereen holder being in one of the two leg sections and the pin extending from the third of the leg sections.

Inventors: ANDERSON RONALD C, ANDERSON, RONALD, C.
Applicants: ANDERSON RONALD C, ANDERSON, RONALD, C.
Application year: 1985
Main classification: B41F15
IPC codes: B41F15