JPH0473708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to printing technology and printing equipment, particularly for use in printing processes by novel techniques involving thermally induced chemical changes in offset masters or negative layers. Concerning the production of offset masters and negatives.

BACKGROUND OF THE INVENTION Both resistive ribbon thermal transfer printing and electroetching printing are known techniques for providing high resolution, good quality printing, particularly of the type used in computer terminals and typewriters. Resistive ribbon thermal transfer printing is a type of thermal transfer printing in which thin ribbons are used. That ribbon is generally a supporting layer, (like paper)
It consists of three to four layers, including a layer of meltable ink that is transferred in contact with the receiving medium, and a layer of electrically resistive material. A variation of this is to make the resistive layer thick enough to be a support layer, thereby eliminating the need for a separate support layer. A thin conductive layer is also optionally provided for current return.

To transfer ink from the soluble ink layer to the receiving medium, the ink layer is brought into contact with the receiving medium surface. The ribbon is also brought into contact with a power supply and the receiving surface (paper) one wishes to print on.
selectively brought into contact with a fine printing needle at a point opposite the . When a current is applied from the thin printing needle, the current flows through the resistive layer and locally generates resistive heat, which melts a small amount of ink in the meltable ink layer. This molten ink is then transferred to a receiving medium to perform printing. Resistive ribbon thermal transfer printing is U.S. Patent No. 3744611, U.S. Patent No. 4309117
No. 4400100, No. 4491431, and No. 4491431.
Described in No. 4491432.

The materials used in resistive printing ribbons are well known in the art. For example, the resistive layer is usually a carbon or graphite filled polymer, such as polycarbonate. A thin current return layer of metal, eg Al. Thermally meltable inks consist of various resins with colorants therein and typically melt at about 100°C. Currently commercially available printers, such as IBM
In those sold under the name QUIETWRITER®, printing currents of approximately 20-30 mA are used.

Electroerosion printing is also described in U.S. Pat.
4339758 and 4086853, which are well known in the art. Electroerosion printing is known as a suitable technique for producing direct-print offset masters and direct-print negatives. Electroerodible recording media generally consist of a support layer and a thin conductive layer. The support layer may be made of paper, for example.
It can be a polyester such as Mylar®. On the other hand, the thin conductive layer is a metal such as Al. To print, part of the thin Al layer is removed with an electric arc. To carry it out, a printing head consisting of multiple needles, typically 0.3-0.5 mm diameter tungsten wire needles, is used while maintaining good electrical contact between the needle tips and the aluminum layer. Then, the electron passes across the erodible medium. When an area is to be printed, a pulse is applied to the appropriate needle at a precise time;
An arc is created between the energized needle and the Al layer. This arc is hot enough to cause partial removal of the aluminum by decomposition, such as vaporization.

Practical electroetching media not only require a base layer between the support substrate and the thin metal layer, but also an overlayer on the thin metal layer. Hose and cover layers are used to protect the aluminum layer in areas where the arc is not applied and to minimize wear and fouling of the head. Typically, the base layer is a hard layer consisting of hard particles embedded in a suitable binder, such as silica in a crosslinked cellulosic binder. The overlayer is typically a lubricating and protective overlayer consisting of a polymer containing a solid lubricant, such as graphite, in a cellulosic binder.

Depending on the nature of the various layers in the electroetching medium, direct printing offset masters and direct printing negatives can be formed. For example, a direct printing negative may be constructed from a transparent polymer support layer and a thin aluminum layer deposited directly onto the support layer. After electrolytic etching writing, the Al layer becomes patterned. This is because the Al layer is light reflective, while the substrate is transparent, so electrolytic writing will create the light opaque and light transparent areas needed to create the negative. Electroetched negatives can be used in plate making equipment of the type used to make "masters", such as those used in offset optical lithography. The master may be produced by contact printing using electro-etched negatives.

Direct printing masters can easily be made by galvanic etching to simplify the way masters or plates are manufactured in a suitable offset plate printing shop. In such a structure, the electrolytic recording medium consists of a support layer, a base layer that is hydrophobic, an Al
It typically consists of a layer and an optional covering layer. When the Al layer is galvanically etched and the cover layer is removed, areas of the Al layer (non-written area) and base layer (written area) are exposed. Since the Al layer is hydrophilic, non-written areas with Al attract water but repel organic ink. The writing area of the recording medium consists of a hydrophobic base layer and will therefore repel water and accept organic ink. Direct printing masters are produced in that way, since the information to be printed is better drawn onto the master by virtue of the surface's affinity for water and ink.

If there were no problems of damage to the Al layer in undesired areas, the substrate-Al layer combination could itself be used as a direct printing master and a direct printing negative. For direct printing negatives, a transparent polymer sheet, typically polyester, can be used as the substrate. This is transparent to light, while
Since Al is reflective, direct printing negatives will be obtained. Also, since Al is hydrophilic and the polyester substrate is hydrophobic, a direct printing master could also be produced in principle.

Traditionally, galvanic etching has been used in the production of lithographic printing masters. However, in actual use, these masters have shown that their lifespans have been significantly reduced compared to conventional printing plates or masters produced using various chemical treatments to produce photosensitized plates. And it's not long. One of the technologies for directly manufacturing offset masters is the U.S. Patent No.
No. 4,081,572, which uses a light beam to change selected regions of a hydrophilic polymer layer to a hydrophobic state, thereby forming ink-receptive and ink-repellent regions. be. However, such technology is not directly usable in standard commercial methods;
They are expensive and generally require large amounts of power.
The overall energy efficiency of this type of system is very low, since a considerable amount of power is required for the operation of the laser. The system also requires additional sophisticated optics to focus and direct the light beam and a mask that must be positioned to define the pattern of the polymer layer exposed to the light beam. .

Printing techniques such as facsimile printing often incorporate dyes that can locally change color where the current discharge occurs. An example of this is described in U.S. Pat. No. 3,113,512, in which electrically induced color changes are grouped together within a sheet.
The original image scanned by the transmitting means is thus reproduced.

In general, the prior art does not provide techniques for producing offset masters or direct printing negatives using equipment that is energy efficient and suitable for processes using commercially available equipment. moreover,
Color changes of the type known in the art using dyes and electrochromic materials do not provide sheets that are very stable over a range of all normal environmental parameters of temperature and light. In the prior art, it was desired to write with as low a current as possible and as fast as possible. For that reason, many of the chemical changes used in printing were of the type that occur at low temperatures (typically 100 degrees Celsius or less). However, the use of such materials is disadvantageous.
This is because ambient conditions often include very high temperatures and/or light (such as ultraviolet light). This causes a gradual color change in the sheet.

It is also desirable to provide a system that economically supplies and very efficiently distributes the energy required to produce a localized change to the recording medium in which that change must be produced. desired. This reduces the overall power required,
making the system more commercially applicable. Additionally, it would be advantageous if a system could be provided that would match or exceed the resolution and print quality obtained with commercial techniques such as resistive ribbon printing and electroetching printing. The prior art does not offer a technology with inherent stability against environmental factors, and two highly efficient printing technologies, resistive ribbon, are particularly suited for computer output terminals and typewriter-style operation. It is not beyond the capabilities of either printing or galvanic etching.

It is therefore an object of the present invention to provide an improved technique and apparatus for producing offset masters or direct printing negatives in which electrical energy is applied directly to the recording medium to effect the required changes within the recording medium. This is the first purpose of

It is an object of this invention to provide a printing device that utilizes multi-needle recording heads of the type used in resistive ribbon printing and electroetching printing to produce local changes in a layer to influence its properties. Another object of the invention.

It is another aspect of this invention to provide an improved printing technique for directly influencing a resistive layer in a recording medium using low levels of electrical energy, wherein the resistive layer is stable at temperatures up to at least 150°C. This is the purpose of

Provides an improved technique for the production of negative and offset masters, in which the recording medium consists of a resistive layer whose properties are locally varied in good resolution in order to change its color and/or its ink retention capacity. This is another object of this invention.

It is another object of this invention to provide a printing technique and apparatus applicable to resistive ribbon transfer printing.

Commercially available printing devices produce prints and/or chemical changes by passing electrical current through localized areas of a highly stable resistive layer without the need for any wet chemical changes. It is another object of the present invention to provide an improved printing technique and apparatus that allows it to be used for producing masters or masters.

DISCLOSURE OF THE INVENTION In this invention, a multineedle printing head, of the type used in resistive ribbon printing or electroerosion printing, is used to apply localized electrical current to a resistive layer of a recording medium. The recording medium consists of a resistive layer, a thin conductive layer such as metal, and a supporting substrate. If the thin conductive layer is to be transparent, InSno can be used with a substrate that is optically transparent. Areas of the resistive layer through which high density current flows from the recording stylus undergo chemical changes that change the ink holding capacity and/or color of these areas.
For example, a hydrophilic resistive layer changes to a hydrophobic state in localized regions upon resistive heating by passing a high density electrical current therethrough, making those regions ink-attractive (oleophilic). The remaining portion of the resistive layer maintains its hydrophilic nature, thus forming ink retention and repellent regions. In this way, a master used for printing is manufactured.

The resistive layer is typically a polymeric layer that can be manufactured to have a resistance comparable to that in the resistive layer of a resistive printing ribbon. The thickness of the resistive layer will vary depending on the desired life of the master and the resolution to be obtained. Typically, the resistive layer is about 0.5 to 2 mm thick. If the recording medium is to be used only for printing purposes, rather than as a printing master, the thickness of the resistive layer may be thinner, for example less than 5 microns.

In this technique, the resolution obtained depends on the diameter of the recording stylus and the thickness of the resistive layer. The same or better resolution and printing accuracy of resistive ribbon printing and electroetching printing is easily obtained with the present invention. Additionally, current and power requirements are less than that in traditional resistive ribbon printing, typically 14-20 mA at 10-12V.

These and other objects, features, and advantages will become apparent from the more detailed description of the preferred embodiments that follows.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention uses high density electrical current to generate strong resistive heating and locally change the chemical behavior of a resistive layer in a recording medium. This approach allows printing to locally vary the ink holding capacity and/or color of the resistive layer and eliminates the need for wet chemical processing, galvanic etching of thin metal layers or meltable ink layers. Negatives and masters can be manufactured without any problems.

FIG. 1 shows an apparatus for carrying out the invention. In the figure, a recording medium 10 is a substrate or a support layer 1
2, a thin conductive layer 14, and a resistive layer 16. A multineedle head of the type used in resistive ribbon printing or electroetching printing is provided to direct the current to the resistive layer 16. This type of head is well known and consists of a plurality of printing needles 18 and a large contact (ground) electrode 20. When the selected pattern of printing needles 18 is energized, a current, indicated by arrow 22, flows through the resistive layer and returns through the conductive layer 14 to the ground electrode 20, as indicated by arrow 24. If the current density is high enough in the resistive layer in the vicinity of the printing needles 18, strong resistive heating will occur and the small areas 26 of the resistive layer 16 will change their properties and/or color. In particular, resistance layer 1
If 6 is initially hydrophilic, region 26 can become lipophilic by passing a high density current therethrough.

The apparatus of Figure 1 is nearly identical to the apparatus used in resistive ribbon printing, except that there is no fusible ink layer. Resistive layer 16 has a resistance of about 200, typically about 200
It has a resistance equivalent to ~1200 ohms/square. The thickness of the resistive layer 16 will vary depending on the required printing resolution and the plate life of the recording medium 10 if it is used as a master. When used for printing, ie if it is not to be used as a master, the ink holding capacity of the resistive layer should not be altered and the resistive layer can be up to 5 microns thick. When the recording medium 10 has a modified ink retention capacity and is used as a plate in offset lithography, the thickness of the layer 16 is typically about
It is 0.2 to 2 mil. The conductive layer 14 is made of Al, Ni,
Made of any type of metal, including Cr, Cu, stainless steel, etc. Its thickness is typically about 1000 angstroms.

The substrate or support layer 12 is made of Mylar®.
It can be a commonly used material such as polyethylene terephthalate), Teflon®, polytetrafluoroethylene, polyester, etc.
Its thickness is generally about 1 micron.

The resistive layer consists of a polymer with limited electrical conductivity and is initially hydrophilic. When the temperature of the polymer locally increases to a sufficient temperature range above about 150°C, it undergoes a chemical change and is converted to a hydrophobic material. In the practice of this invention, a suitable resistant polymer for use as layer 16 is about 150
It does not undergo any chemical or physical changes at temperatures below °C. Preferably, it does not undergo chemical changes up to temperatures above 250°C, generally from 300 to 400°C. This is because these substances are very stable under normal ambient conditions;
It means that no color change and/or structural or chemical changes occur even when stored in an unfavorable environment for a long period of time.

One type of suitable resistive material for layer 16 is
It is a polymeric binder with conductive materials therein such as ZnO, TiO ₂ , CdS or graphite. Built-in mechanisms for visible changes can also be included in this resistive layer. The binder has structural features that cause heat-induced dehydration and hydrophilicity reduction within the image area when subjected to an electrical pulse.

An example of a suitable polymeric binder is polyamic acid, which undergoes thermal ring closure to form a polyimide precursor when an electrical pulse is applied.
It is.

Polyamic acid is hydrophilic, while polyimide precursors are hydrophobic. This conversion is as follows.

Other polymer systems with thermally labile pendant groups on the polymer chains can also be used for imaging when high density electrical current is passed through the resistive layer. Resistive layer 16 may be a coating applied to thin metal layer 14 from a polar solvent such as diglyme, glyme, THF (tetrahydrofuran), or NMP (n-metal pyrrolidone). The coating is then dried at about 100°C.

Polyamic acid films can be further improved by half containing silicon to increase their abrasion resistance and reduce their coefficient of friction. Such siloxane-modified polyamic acids are known and are commercially available from M and T. If desired, a visible change can occur when a current pulse is applied by including a color-forming material that changes color only when exposed to elevated temperatures. Such dyes are well known in imaging techniques and are typically very stable below about 150°C.

Other types of materials may be used to form resistive layers 16 for direct image formation upon application of pulses of electrical energy.
It can be used for. As mentioned, this can be used to create a long print offset master. This type of resistant polymer consists of ionic polymers that are hydrophilic and have good abrasion resistance. Conductive fillers such as ZnO, CdS, ZnI ₂ , MoO, etc. are added to improve the conductivity and wear resistance of these ionic polymers. Additionally, it can be integrated with dye-forming systems, including either Leuco or thermochromic dyes. The use of these dyes produces visible changes in the electrical image area.

When writing is performed by applying computer-driven electrical pulses to the recording head, the current causes the hydrophilic ionic polymer to undergo a cross-linking reaction, resulting in
This causes a loss of ionicity in the imaged area. The written area now becomes lipophilic, while the non-written area remains hydrophilic. The recording medium 10 can therefore be used directly as an offset master or as a photographic negative.

An example of an ionic polymer that can be converted to a nonionic polymer upon application of electrical energy is polyacrylic acid-polyamine complex, which is both hydrophilic and ionic. The conversion of this substance into a lipophilic state when electrical energy is applied is represented by the following scheme.

This concept also makes it applicable to techniques for separate polymer-to-metal mapping of written and non-written areas. That is, if the ionic polymer system is soluble in a water/alcohol solvent, the non-written areas can be removed with a solvent. The write area, on the other hand, remains intact because it has been rendered insoluble by the application of electrical energy during the write operation.

Another type of material suitable for resistive layer 16 is a thermally cross-linking, water-insoluble material. This type of material can be used to produce masters with a long press life that can print thousands of copies. The resistive layer is made of a hydrophilic, water-insoluble polymeric binder and materials such as ZnO, TiO ₂ , MoO, CdS, Sb ₂ O ₃ ,
Contains conductive materials such as ZnI ₂ , graphite, etc. The thermally crosslinkable binder changes from a hydrophilic state to a hydrophobic state when a sufficiently high density current is applied to the resistive layer from the printing needle 18. Non-written regions of the resistance layer (where no current is applied) remain hydrophilic. If desired, visible changes can also be produced by incorporating thermochromic dyes into the resistive layer.

Polymers suitable for use as thermally crosslinkable binders include combinations of low molecular weight novolac type resins (or phenol formaldehyde type resins) and polyacrylamides. When electrical energy is applied to the material, the novolac resin is converted to a highly crosslinked resol and the polyacrylamide is converted to a less basic imide or nitrile. Eventually, the electrically imaged regions of the resistive layer become hydrophobic, while the remainder of the resistive layer remains hydrophilic. An example of this transformation is as follows.

The polyacrylamide in this combination can also be replaced with high molecular weight polyamines, polyethers, polyoxyethylene aryl ethers, polyvinylpyrrolidone, and the like. Polyvinyl acetal resins can also be used as well as thermosetting resins, such as phenolic resins, epoxy resins, urea resins, melamine resins, diisocyanate resins.

Multifunctional monomers such as pentacrylslittal triacrylate can be included as additives in the polyvinyl alcohol, polyacrylamide or polyacrylate to effect heat-induced crosslinking of the writing area.

In addition to these substances, diazopolyacrylamide can be used. This is because this material is an ionic hydrophilic polymer. Upon heating, the diazo group is lost and a reactive intermediate is formed that causes crosslinking in the exposed areas. An example of this conversion is shown below.

Other diazo and diazonium photosensitizers include phenol formaldehyde resin, PVA, polyacrylamide, and polymethyl methacrylate.
It can be used in polymer matrices, such as methacrylic acid copolymers. These photosensitizers are used for crosslinking and curing.

FIG. 2 shows a recording medium 28 that can be used in combination with a multineedle head to produce a projection foil. Recording medium 28
is a transparent substrate 30 such as Mylar (registered trademark);
It consists of a transparent conductive layer 31, such as InSnO, and a resistive layer 31 that can be colored by a color change caused by passing an electric current through the layer. For this purpose, the multineedle head includes a printed electrode 34 and a wide contact (ground) electrode 36. The dense localized current from the printing needle is indicated by arrow 38. Arrow 40, on the other hand, indicates a low density current returning through ground electrode 36. The dense localized current from printed electrode 34 changes the color of area 42 to produce a colored foil.

The resistive layer 32 is imaged as a result of polymer cross-linking/structural changes and/or color development in the written areas when a current is localized in the layer. Resistance layer 3
2 is a polymeric binder with conductive fillers and color-defining substances therein, such as ZnO, ZnI ₂ , MoO, CdS, etc. Polymers that can be used for this purpose include cellulose acetate butyrate (CAB), CAB-urethanes, epoxy polymers, polyimides, polyorganosiloxanes, and polyether-urethane mixtures, polyacrylates (PMMA, glycidyl methacrylate, PMMA
-MA resin), and polyvinyl alcohol-diazoacrylamide. Thermochromic dyes can be used for color development or color change, as described below.

Commercially available multi-needle printing heads of the type used in resistive ribbon printing can be used for this type of resistive layer recording. The recording needle is approximately 10
It can be a tungsten needle with a diameter of ~150 microns. Depending on the diameter of the needle, a recording current of about 0.25-25 mA at about 10-12V can be used. For example, a needle with a diameter of approximately 20 microns
A current of 25 mA can be used. The electrical pulse width can be 0.1 to 2 msec. For sheet resistance as described, energies of about 0.05 to 5 J/ ^cm2 provide the necessary changes for localized imaging in the resistive layer.

In the practice of the present invention, a recording medium is provided in which a resistive layer therein locally changes its properties in response to an electric current from a multineedle recording head of the type used in resistive ribbon printing or electroerosion printing. It is a change of . This recording device is very efficient compared to those that require erosion of the conductive layer or transfer of a strictly fusible ink layer. I mean,
This is because electrical energy is converted into thermal energy in the layer where the change is to occur. The resolution and print quality obtained with resistive ribbon printing and electroerosion printing can also be obtained, and this new printing technology has the advantage that power and energy levels can be lower than those required by prior art techniques. .

Although the invention has been described in accordance with specific embodiments thereof, it will be obvious that various modifications may be made to the technology without departing from the spirit and scope of the invention.

[Brief explanation of drawings]

FIG. 1 shows the improved printing device of the present invention in which current from the printing needle flows through a resistive layer causing a change in the color and/or ink retention of the layer. FIG. 2 illustrates another apparatus for carrying out the invention, in which both the internal conductive layer and the substrate layer are transparent, and a color change occurs in the resistive layer through which the current passes and the printing operation is carried out. It will be done.

Claims (1)

[Claims] 1 A support layer, a thin conductive layer that serves as a current return path, and a hydrophilic resistance layer whose hydrophilicity can be locally changed by passing a current therethrough. a recording medium comprising said resistive layer which is hydrophilic at temperatures below about 150° C., wherein said resistive layer provides a pattern of electrical current through selected areas of said resistive layer, said electrical current contacting said needle being excited thereby; A recording device comprising a multi-needle recording head localized in said region of a resistive layer and sufficiently dense that the localized current changes the state of said localized region from hydrophilic to oleophilic. 2. The apparatus of claim 1, wherein the electrical current increases the temperature of the localized portion to at least about 200°C. 3. The device of claim 2, wherein the resistive layer is a polymeric binder having electrically conductive particles therein. 4. The device of claim 3, wherein the resistive layer further comprises a color former active at temperatures above about 200<0>C. 5. The device of claim 3, wherein the sheet resistance of said resistive layer is in the range of about 200-1200 ohms/area. 6. The device of claim 5, wherein the current is applied as current pulses of 0.25 to 25 mA. 7. The apparatus of claim 6, wherein the current is pulsed with a pulse width in the range of about 0.1 to 2 msec. 8. The device of claim 5, wherein said thin conductive layer is made of Al. 9. The device of claim 5, wherein the support layer and the thin conductive layer are transparent. 10. The device of claim 1, wherein said resistive layer comprises a polymer selected from the group consisting of hydrophilic polyamic acids and siloxane-modified polyamic acids having conductive particles therein. 11. The device of claim 10, wherein the polymer has thermally unstable pendant groups on its polymer chain. 12. The device of claim 1, wherein the resistive layer comprises an ionic polymer. 13. The device according to claim 12, wherein the ionic polymer is a polyacrylic acid-polyamide complex. 14. said resistive layer comprises a polymer having electrically conductive particles therein, said polymer selected from the group consisting of low molecular weight novolac-type resins and polyacrylamides to generate sufficient resistive thermal energy for crosslinking as described above; 2. The device of claim 1, wherein the device crosslinks when a current pulse of sufficient strength is applied to cause the crosslinking to occur. 15. said resistive layer comprises a polymer having conductive particles therein, said polymer selected from the group consisting of high molecular weight polyamines, polyethers, polyoxyethylene aryl ethers, polyvinylpyrrolidone and polyvinyl acetal resins, A device according to claim 1 for use with thermoset resins such as resins, epoxy resins, urea resins, melamine resins and diisocyanate resins. 16 The resistive layer consists of a polymer having electrically conductive particles therein, said polymer comprising a polyfunctional monomer such as pentaacryltrital triacrylate as an additive in polyvinyl alcohol, polyacrylamide or polyacrylate. mass,
and diazopolyacrylamide, which loses its diazo group and crosslinks when heated to a sufficient temperature. 17. The resistive layer comprises a polymeric binder having conductive particles therein, the polymeric binder comprising cellulose acetate butyrate (CAB), CAB-urethane, epoxy, polyimide, polyorganoloxane and polyether- urethane mixture,
The device of claim 1 selected from the group consisting of polyacrylates such as PMMA, glycidyl methacrylate, PFFA resins and polyvinyl alcohol-diazoacrylamide. 18 Coating a layer of electrically conductive material on top of the supporting substrate layer, having a sheet resistance on said layer of electrically conductive material in the range of about 200 to 1200 ohms/square, and having a hydrophilic property even at temperatures above about 150°C a multi-needle recorder coated with a hydrophilic resistive layer consisting of a polymeric binder having conductive particles therein, capable of delivering current pulses to selected ones of the recording needles above said recording medium; A head is placed in contact with the resistive layer and a current pulse is applied through a selected one of the recording needles to generate a high density local current in the region of the resistive layer in contact with the selected excitation needle. and resistive heating sufficient to irreversibly change the hydrophilicity of the region by the electric current to make the region oleophilic. 19. The method of claim 18, wherein said current has an intensity in the range of about 0.25-25 mA. 20. The method of claim 18, wherein the current pulse has a length of about 0.1 to 2 msec. 21. The method of claim 19, wherein the resistive layer has a thickness in the range of about 0.2 to 2 mils. 22. The method of claim 21, wherein the conductive layer is made of a metal and the support layer is made of an organic material. 23. Claim 18, wherein the resistance layer has a hydrophilicity that changes at a temperature of about 300 to 400°C.
The method described in section. 24. The method of claim 18, wherein the conductive material layer and the substrate layer are optically transparent.