Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M3/00—Printing processes to produce particular kinds of printed work, e.g. patterns
  • B41M3/16—Braille printing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M1/00—Inking and printing with a printer's forme
  • B41M1/12—Stencil printing; Silk-screen printing

Definitions

• This invention relates to a screen printing process, in which a screen printing forme is made using a photo- polymerizable material.
• Oth ar Zeman in an article in "Der Siebdruck", Vol. 27, January 1981, pp. 24 ff., describes the manufacture of sensitized screen printing materials, and indicated in particular how a thicker layer of sensitizing material can be obtained, in order that prints with a larger thickness may be made.
• the impregnated screen may be further laminated to a thickness of at most 0.3 mm above the screen level.
• a larger thickness (0.3-2 mm) is required, use is made of a liquid photo- polymerizable mass, which is solidified by the image-wise exposure, and at the same time attaches itself to the screen material, i.e., is anchored in the gauze or fabric.
• the two techniques described above are very cumber ⁇ some, require great skill to be correctly carried out, and have the inherent disadvantage that the screens, which are relatively expensive, can only be used once.
• Dutch patent application 7607224 discloses making braille script by screen printing, in which a normal screen printing forme is used, i.e. one that has not been made thicker, and a printing ink is used which contains a swelling agent.
• the printed pattern applied, or paste deposited, is then expanded by a heat treatment.
• This method has the disadvantages that the degree of swelling, i.e. the thickness of the printed pattern, cannot be accurately controlled, that its implementation requires a large amount of energy, and that many materials are not resistant to the high temperature of the heat treatment (180 C) .
• the surface of the dry printed pattern is not smooth and even rather rough, which is unpleasant to "read".
• the invention provides a screen printing process in which a screen printing forme is made using a photopolymerizable material, characterized in that the photo-
• OMPI polymerizable material is used in the form of a sheet which before or after exposure and development is firmly secured to the screen, the thickness of the sheet, the nature of the screen and the nature of the printing ink being selected so that the resulting printed pattern, after drying, has a maximum thickness of at least 0.25 mm.
• the photopolymerizable sheet material can very easily be pressed down on the screen, or attached to the screen doctored with liquid photopolymerizable material, while the expensive screen can afterwards be easily and fully cleaned for re-use.
• the thickness of the printed pattern can be accurately controlled, drying does not require a large amount of energy and not a high temperature either, and the dry printed pattern consists of a hard, undeformable material with a smooth surface.
• Photopolymerizable materials which are solid-at normal temperatures, and can be provided in the form of a flexible sheet are known per se. Suitable materials of this kind are photo ⁇ sensitive compositions of the nylon type, soluble in water, in dilute acid or in alcohols.
• a photosensitive resin composition comprises, for example, as essential components a polymer containing a basic nitrogen atom in the main chain or in a side chain, a photopolymerizable unsaturated monomer, and a photosensitizer.
• TJS patent 4,145,222 for detailed information about such a photosensitive composition, reference is made to TJS patent 4,145,222.
• Photopolymerizable sheet materials suitable for use in accordance with the present invention are commercially available in various thicknesses from about 0.2 to about 1.2 mm under the names of Toyobo Printight (made by Toyobo Company, Ltd., Japan) and Miraclon and Rigilon (made by Tokyo Yoko Ono, Japan) .
• the photopolymerizable sheet, to which a protective peel-off cover foil is applied on one side, is fixedly connected on the other side to a polyester or metal backing, by means of an adhesive layer which may also have an anti- halo effect.
• This fixed connection with a backing is of importance, because the material is intended for making printing plates, in particular relief printing plates.
• the fixed backing in the above-described commercial products it is sufficient for the fixed backing in the above-described commercial products to be made temporary or of the peel-off type, which can be effected in a simple manner by just omitting the adhesive layer.
• a photopolyjierizable sheet 0.2-0.7 mm thick as generally speaking, this gives the best results in producing the contemplated relatively thick printed pattern.
• the sheet thickness to be selected in a specific case is dictated in part by the nature, and in particular the thickness, of the printed . pattern, but also depends on the thickness of the gauze of the screen.
• a thin gauze comprising a large number of threads per running centimeter, to produce an equally thick printed pattern with the same printing ink, must be combined with a thicker photopolymerizable sheet than a thick gauze which contains a relatively small number of threads per running cm.
• the cover foil or the backing is removed in products as described above, and the photopolymerizable sheet is exposed through a positive original.
• Any suitable light source (point light or tubular lamps) radiating in the UV-range may be used for the exposure, such as a high-pressure or low-pressure mercury vapour lamp, a metal halide lamp, a xenon lamp, or a carbon-arc lamp. Care should be taken that this exposure is not too intensive, and in any case less than required to effect complete photopolymerization.
• the entire surface of the sheet should be treated with the water jets as uniformly as possible to ensure complete development.
• development will take approximately 3-15 minutes, depending on conditions.
• the sheet which, as a result of the development, has a soft and slightly sticky feel, is then pressed against the screen for it to adhere firmly to the screen threads. This operation may be carried out, for example, in a vacuum frame.
• the covered screen is dried, for example, in a drying stand or with a stream of hot air at approximately 30-60 C, and subjected to after- exposure with TV radiation, as described before, to complete the photopolymerization or cure the photopolymerizable material.
• the backing or cover foil still present is stripped off, whereafter the screen printing forme is ready for use.
• the screen is first doctored with photopolymerizable material in the liquid form, as for example marketed by the above- mentioned Toyobo firm. Subsequently, the screen thus pre-treated is pressed against the free surface of a photopolymerizable sheet, for example by means of a squeegee, which sheet is on its other side provided with a strippable backing or cover foil as described above. The resulting laminate is then dried for some time, for example, 20-40 min.
• a great many screen materials may be used for carrying out the present screen printing process, such as, among other materials, nylon, polyester, metallized polyester and steel. It is of importance for the screen to contain not too few and also not too many threads per running cm. Fewer than 15 threads per running cm is generally insufficient for a firm adherence of the developed photo ⁇ polymerizable sheet, especially in areas with little photopolymerized material only, whereas with more than 73 threads per running cm its permeability to the printing ink to be used is insufficient for the screen to be completely filled in one or a few squeegee passes only. Preferably, screensare used containing 24-51 threads per running cm. For printing, the screen ready for printing is
• the gap varies depending on the thickness of the screen printing forme, the printing ink used, the nature and desired thickness of the printed pattern, and the type of article being printed. Commonly, the gap is between approximately 2 and 6 mm
• the printing operation proper can be effected in the manner conventional for screen printing processes, namely, by applying the printing ink to the screen and pressing it through the screen meshes and depositing it on the article being printed using, for example, a squeegee of rubber or synthetic plastics material.
• the present invention contemplates producing a relatively thick printed pattern, namely, one in which the maximum thickness of the individual characters, after drying, is at least 0.25 mm.
• the thickness of the photo ⁇ polymerizable sheet in combination with the nature of the screen, in particular the thickness of the gauze, are of importance, as described hereinbefore.
• a further important item is the nature of the printing ink. As a matter of fact, it should have a high solid content, and is allowed to exhibit, at most, only a slight degree of secondary flow.
• the solid content of the printing ink used is preferably at least 80%.
• Suitable printing inks of this type are the known per se IR-curable inks.
• Particularly suitable for use according to the present invention are the (also known per se) UV-curable printing inks having a solid content of substantially 100%, and which immediately after printing can be dried throughout by UV-irradiation in.a short period of tim , for example in 10 seconds to 1 minute,, whereby secondary flow and loss of height of the printed image are minimized.
• the fast drying or curing of the printing inks last-mentioned is based on a UV-initiated polymerization, which need not be discussed in more detail herein, as both the principle and countless practical implementations thereof are described extensively in the literature.
• UV-curable printing inks are marketed, for example, by Advance-excello, Chicago, United States of America, under the name of Solex.
• the present screen printing process has numerous applications, such as for braille printing, decorative relief printing, • and printing for electronic purposes.
• the most widely divergent flat materials may be printed,
• OM such as paper, synthetic plastics material ,metal, textile, glass, ceramics, etc. and all sorts of additives may be incorporated in the printing ink to suit requirements, such as colorants, pigments, electrically conducting or insulating substances, magnetizable particles, etc.
• braille can be printed on both sides of the paper, because, unlike classical braille, no deformation of material takes place.
• the screen can be easily liberated from all the material present thereon for it to be re-used.
• the screen printing form can be treated with a suitable solvent for, in particular, the photo- polymerized material present.
• suitable solvents are ethanol, bleaching water, fairly concentrated formic acid or acetic acid, or combinations thereof. Owing to the action of the solvent the photopolymerized material begins to swell and becomes soft, where ⁇ after the screen may be sprayed clean for example with a high- pressure sprayer. Subsequently, the screen may be degreased, for example, by means of a soda solution or the like, and then be dried, whereafter it may be used for performing a next screen printing cycle.
• the starting point was a sheet of Toyobo Printight type EF-70, size A3 (Toyobo Co.,. Ltd., Japan), which was modified in that the anti-halo adhesive layer had been omitted between, the 0.55 mm thick, water-washable photopolymerizable layer and the polyester backing thereof.
• the protective cover foil on the other side of the photopolymerizable layer was removed, and subsequently this layer was exposed in a screen printing vacuum copying frame through a positive braille original with a carbon arc lamp of 60 A, 220 V, 16.7 k at a distance of 80 cm. for 75 sec.
• the material was then developed by spraying the exposed layer uniformly and vigorously with hot water having temperature of 60-80 C for 10 min. Excess water was carefully removed with a cloth, whereafter the rather soft developed layer, whose surface was somewhat sticky as a result of the development, was contacted with a screen printing frame spanned with a polyester gauze of 40 threads per running cm, and was firmly secured to the screen threads by applying vigorous suction (90% of absolute vacuum) in a screen printing vacuum copying frame for 5 min. Subsequently the coated screen printing frame was dried for 20 min. in a drying stand at 30-40 C, and subjected to after-exposure for a further 5 min.
• the screen printing forme was then placed in a screen printer with its coated side facing downwards and so as to leave a gap of 4 mm between it and a sheet of paper to be printed.
• Printing was effected using a UV-curable printing ink produced by mixing Solex HUG-UV-9119 in a 75/25 ratio with Solex HUB 9050 halftone base (both being products of Advance-excello, Chicago, U.S.A.) .
• the printing ink was applied to the screen printing forme and pressed through the meshes and deposited on the sheet of paper to be printed by means of a squeegee of synthetic plastics material.
• the resulting o assembly was dried at 22-25 C for 30 min. , whereafter the polyester backing was removed.
• the screen printing forme was then ready for use.

Landscapes

• Photosensitive Polymer And Photoresist Processing (AREA)
• Printing Methods (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Non-Metallic Protective Coatings For Printed Circuits (AREA)
• Printing Plates And Materials Therefor (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=19838556

Family Applications (1)

Country Status (5)

Families Citing this family (8)

Family Cites Families (9)

• 1981
  • 1981-12-15 NL NL8105657A patent/NL8105657A/nl not_active Application Discontinuation
• 1982
  • 1982-12-15 JP JP58500134A patent/JPS58502111A/ja active Pending
  • 1982-12-15 IT IT24752/82A patent/IT1155378B/it active
  • 1982-12-15 EP EP83900069A patent/EP0096687A1/en not_active Withdrawn
  • 1982-12-15 WO PCT/NL1982/000045 patent/WO1983002176A1/en not_active Ceased

Non-Patent Citations (1)

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