JP6147485B2 - Variable lithography printing - Google Patents

Description

  The present disclosure relates to the use of certain solvents in fountain solutions used during variable lithographic printing. The present disclosure also relates to an apparatus that uses such a dampening solution and a method that uses such a dampening solution, for example, in variable lithographic printing applications.

  In various embodiments, fountain solutions, systems, and processes useful for variable lithographic printing are disclosed. Conventional offset lithographic systems use polar dampening fluid and non-polar ink to create an image. In the present disclosure, the fountain solution is relatively non-polar, and instead the ink is relatively polar. By selecting the appropriate reimageable imaging member chemistry, ink chemistry, and fountain solution chemistry, the system allows both ink and fountain solution to wet the surface of the rewritable imaging member. Even in that state, the fountain solution will energetically maintain the wettability of the surface in the presence of ink. Such a structure is reached by considering the surface wetting conditions for the surface tension and surface energy polar and dispersive components of all three components: imaging member surface, ink, dampening fluid. Among other benefits, this system actually allows a small amount of ink residue to be left by the dampening solution passing through the imaging member when a new layer of dampening solution is applied after each printing pass. Can be removed.

FIG. 1 shows a variable lithographic printing apparatus capable of using the dampening liquid of the present disclosure. FIG. 2 is a graph of α vs. β showing wetting conditions in the image area of the offset plate for conventional oil-based offset ink. FIG. 3 is a graph of α vs. β showing the wet condition of the conventional aqueous offset dampening solution in the non-image area of the offset plate. The dotted circle represents the wetting condition of the fountain solution in the presence of ink. FIG. 4 is an α vs β graph showing the wetting conditions obtained with the variable lithographic printing of the present disclosure, where both the ink and the dampening fluid can wet the surface of the imaging member simultaneously, The fountain solution wets the plate in the presence of ink (shown as a dotted circle). FIG. 5 is an illustration of a series of characters printed using 100% Novec ™ 7500 fountain solution. FIG. 6 is an illustration of the same series of characters printed with an aqueous fountain solution for comparison with FIG.

  FIG. 1 illustrates a system for variable lithography that can use the dampening fluid of the present disclosure. The system 10 includes an imaging member 12. The imaging member comprises a substrate 22 and a reimageable surface layer 20. The surface layer is the outermost layer of the imaging member, i.e. the layer of the imaging member furthest away from the substrate. As shown here, the substrate 22 is cylindrical, but the substrate may be in the form of a belt or the like. The surface layer 20 is typically silicone (eg, methyl silicone or fluorosilicone), and carbon black may be added to enhance the energy absorption of the surface layer.

  In the illustrated embodiment, the imaging member 12 rotates counterclockwise and begins with a clean surface. A fountain solution subsystem 30 is disposed at the first location to uniformly wet the surface of the fountain solution 32 and create a uniform and controlled thickness layer. Ideally, the fountain solution layer is about 0.15 micrometers to about 1.0 micrometers thick, uniform, and free of pinholes. As described further below, the fountain solution composition helps to flatten the layer and make the layer thickness uniform. Using a sensor 34, for example, an in-situ non-contact laser gloss sensor or contact laser sensor, the uniformity of the layer is confirmed. The dampening fluid subsystem 30 can be automated using such sensors.

  In the optical patterning subsystem 36, an energy source (eg, a laser) is applied to the layer of dampening liquid, energy is selectively applied to a portion of the layer, and the dampening liquid is evaporated to the shape of the image to receive the substrate. A “negative” latent image of the desired ink image to be printed on is created. An image area where ink is desired is created, and a non-image area where the dampening solution remains is created. An optional air knife 44 is also shown to maintain a clean dry air supply, control the temperature of the air, and reduce contamination with dust prior to ink application, thereby reducing the surface layer 20 Control the airflow above. The printing subsystem 46 is then used to apply ink to the imaging member. The printing subsystem 46 may comprise a “keyless” system that uses an anilox roller to meter offset ink on one or more forming rollers 46A, 46B. Ink is applied to the image area to create an ink image.

  The rheology control subsystem 50 partially cures or makes the ink image tacky. The curing source may be, for example, an ultraviolet light emitting diode (UV-LED) 52, and the optical element 54 can be used to focus the light if desired. Another mode of increasing cohesion and viscosity utilizes ink cooling. This could be done, for example, by blowing cold air onto the reimageable surface by jet 58 after applying the ink and before transferring the ink to the final substrate. Alternatively, a heating element 59 can be used near the printing subsystem 46 to maintain a first temperature, and a cooling element 57 can be used to maintain a near second nip near the nip 16. We were able to.

  The transfer subsystem 70 then transfers the ink image to the target substrate or receiving substrate 14. This is accomplished by passing a recording medium or receiving substrate 14 (eg, paper) through the nip 16 and between the impression roller 18 and the imaging member 12.

  Finally, the imaging member must cleanly remove any residual ink or fountain solution. The dampening liquid residue can be removed easily and quickly using an air knife 77 with sufficient airflow. The remaining ink can be removed by the cleaning subsystem 72.

  The role of the fountain solution is to provide selectivity when imaging and transferring the ink to the receiving substrate. When the ink donor roll of the ink source of FIG. 1 contacts the fountain solution layer, this layer is ink applied only to the dry (ie, uncovered) fountain of the imaging member. It is divided as follows.

  As mentioned above, water is usually the main component of the fountain solution (on a weight basis). Water itself has a high latent heat when it vaporizes and requires high energy at the imaging station.

  In addition, water has a high surface tension around 70 dynes / cm. This reduces the ability of the dampening solution to rapidly form a thin film on the imaging member surface. A conventional solvent that is sometimes added to reduce surface tension is isopropyl alcohol (ie, isopropanol). However, isopropanol is a volatile organic compound (VOC), and is typically required to have low discharge power due to environmental regulations. For example, California requires that the amount of isopropanol be less than 5%, or that the print production equipment be equipped with a solvent recycling system that captures the discharged isopropanol. With this concentration of isopropanol, the surface tension is still too high to obtain good performance.

  Thus, to further reduce the surface tension, typically a surfactant is added to the water to reduce the surface tension to approximately 20-30 dynes / cm. However, such surfactants are usually composed of copolymer molecules with a hydrophilic head and a hydrophobic tail, and the hydrophobic tail is sufficient to sufficiently wet the imaging member and the surface of the dampening fluid. It must be long and these copolymer molecules tend to have high boiling points above 200 ° C. As a result, these copolymer molecules may plate out unevenly as residues when water evaporates, causing variations in the printing process, peeling off the dampening fluid layer, and removing residues on the surface from the dampening fluid. Will have a slight effect on the thickness of the new layer. In order to accurately control the thickness of the fountain solution, a fountain solution is required that produces little or no residual surfactant residue.

In addition, water has a low kinematic viscosity of about 1 centistoke (1 mm ² / sec). In general, the fountain solution must have a positive diffusion coefficient so that it can sufficiently wet the surface of the imaging member when first placed. However, during the image forming process in which the dampening fluid is heated and evaporated to create a latent image, the adjacent dampening fluid is also partially heated. This partial heating further reduces the kinematic viscosity of the adjacent dampening liquid and further diffuses or retracts depending on the shape of the latent image being created. If there is a backward effect at the sharply protruding end of a character such as “W” or “V”, the protruding end of the ink will be rounded when printing. In a straight line with no curved portion, the fountain solution tends to diffuse and fill in the evaporated region, particularly in the case of a thick layer of fountain solution (thickness of about 2 μm). In milliseconds, the aqueous dampening solution spreads somewhat even if the surface of the imaging member has an appropriate surface roughness that makes it easier to fix the dampening solution in place. It will end up. To increase the viscosity of the fountain solution, gum arabic is sometimes added to the fountain solution. However, gum arabic has a high boiling point, and residues may remain.

  Note that the advantage of water based dampening solutions is that water has a highly polar component for surface tension (surface tension can be divided into two components, a polar component and a dispersive component). . This property helps the dampening liquid repel the ink, tends to have a low polar surface tension and a high dispersive surface tension. As a result, the surface energy at the interface between the ink and the fountain solution remains high and does not wet each other.

  As a result, the preferred solvent for the fountain solution must be a liquid with low heat of vaporization, low surface tension, and high kinematic viscosity. Unfortunately, liquids containing these three elements tend to have high dispersive surface tension components and low polar surface tension components. In conventional lithographic printing systems, these liquids tend to mix easily with polymer / oil-based inks that tend to have high dispersive surface tension and low polar surface tension. This will cause a background effect in non-image areas (where ink is not applied) and coloration in the image areas.

It should be noted that silicone or fluorosilicone is considered a desirable and useful material for the surface of the imaging material due to its low surface free energy and excellent pressure release nip ink release characteristics. Such materials typically have a siloxane backbone and have methyl (—CH ₃ ) or trifluoromethyl (—CF ₃ ) side chains. However, many liquids are well known to swell elastomeric materials. It would be preferable to use a liquid for the solvent of the fountain solution that does not act as a plasticizer, or a solvent that provides long surface life without wearing these rubber materials. Certain solvents have low molecular weights, which necessarily swell silicones and fluorosilicones to some extent, depending on the degree of fluoro substitution. In these swollen states, wear may proceed indirectly by causing separation of particles that absorb near-infrared laser energy on the imaging member surface (eg, carbon black). These particles then act as abrasive particles. Desirably, the dampening solution / solvent should have a low tendency to swell or penetrate the elastomer.

  If possible, it would be desirable to be able to easily recycle the fountain solution. This is useful for reducing total waste and lowering the overall system cost. If the fountain solution has a very different density compared to water, it may be beneficial to recondense the fountain solution because it can be separated more easily. Also, the fountain solution is desirably non-toxic, does not apply VOC regulations, has a low global warming potential, a low or zero ozone depletion potential, and is easily handled / transported.

  In a conventional offset printing system, the dampening liquid is mainly composed of water. The fountain solution and ink are designed to wet the non-image area and the image area of the static offset plate, respectively, and have a relationship of polarity and dispersibility. Surface energy models are often used to describe the mutual surface energy of imaging surfaces, inks, and fountain solutions. These surface energy models are useful for predicting the wettability of a liquid in the presence of another liquid on an ideal surface and are described in detail in many prior art references. Yes.

According to such a surface energy model, the surface tension of an arbitrary liquid or the surface energy of an image forming surface is mainly composed of a dispersive component and a polar component according to the relationship of formula (i). It can be expressed inside.
Where γ is the total surface energy (or surface tension of the liquid) in units of J / m ² , or more generally in dynes / cm. The total surface energy is composed of two orthogonal components, a dispersive component γ _d and a polar component γ _p , and acts largely independently. Polar and dispersive components of liquid surface tension or solid surface energy can be obtained from, for example, First Ten Angstroms, Inc (Portsmouth, VA), Diversified Enterprises (Claremont, NH), or Biolin Scientific Inc. (Linthicum Heights, MD) can be calculated from tensiometers or contact angle measurements known in the art using commercially available scientific equipment provided by several equipment vendors. Α and β in formula (i) are further defined according to formulas (ii) and (iii).

  α and β are useful for describing molecular surface interactions acting in the direction of molecular distance. The hydrogen bonding component of the liquid surface tension has a small effect, but should not be ignored when determining the chemical synthesis and miscibility of one fountain solution and the ink chemistry (diffusing one liquid into another) It should be noted that this is not possible and is usually not included in these models.

When measuring in reduced pressure or in dry air, the total surface energy γ of formula (i) is added to the surface. However, the measured value of the surface tension often changes when two kinds of liquids, or one kind of liquid and a solid surface contact each other. In general, the surface tension (in the absence of air) that occurs between any two components a and b is often referred to as γ _ab . Therefore, the surface tension between the ink (i) and the fountain solution (f) is often indicated by γ _if . Similarly, the surface tension between ink (i) and imaging surface (s) is often written as γ _is .

Experimentally and theoretically, it has been found that this interaction energy can be well estimated by the Fowke model for the interaction energy of equation (iv).

From these simple models, various diffusion coefficients can be calculated from Young's equation understanding the equilibrium behavior of liquids on the surface and the mechanical interactions associated with diffusion. The condition that the fountain solution (f) spreads energetically and uniformly on the image forming plate (s) in the non-image area is as follows. Given by the positive diffusivity S _f > 0 of the fountain solution,
Where the r term is an enhancement factor if the surface has a fine roughness or fine pattern that tends to increase the effective interfacial energy, and no air is trapped in the pattern.

Similarly, the condition that ink (i) uniformly wets the imaging plate (s) in the image area is the positive ink diffusion of the ink on the imaging surface in the presence of air, as shown in equation (vi). Given by the coefficient S _i > 0.

The condition that the dampening liquid (f) reliably wets the image forming plate (i) in the non-image area and the ink (i) is repelled in the non-image area (the ink roller exists on the dampening liquid layer). ), Given by the positive diffusion coefficient S _fi > 0 of the fountain solution in the presence of ink, as shown in equation (vii).

  Many plot the surface energy of ink, fountain solution, and printing surface in a graph of alpha parameter (y-axis) versus beta parameter (x-axis), which is useful for showing the wetting phenomenon. Referring now to FIGS. 2-4, in such a graph, for each component, a solution with a diffusion coefficient S equal to zero is shown in the graph as a circle, also known as a wet envelope. Yes. In the case of the diffusion coefficient of the liquid on the surface in the presence of air, these circles are centered at the origin. When considering the diffusion coefficient of a liquid in the presence of another liquid other than air, such a wet envelope is no longer centered at the origin. Liquids with α-β surface tension parameters inside these circles typically wet the surface and have a positive diffusion coefficient, while liquids with α-β parameters outside these circles Typically forms droplets that do not spread on the surface and have a wet contact angle given by the Young equation.

It is necessary that all these three diffusion conditions described above by conditions (v, vi, vii) are satisfactory for the image forming system in order to achieve good print quality, Not enough. In the past, these three types of diffusion conditions pattern the imaging plate to have two distinct regions: an image forming region with a surface energy of γ _s1 and a non-image region with a surface energy of γ _s2. Therefore, the conventional offset printing was satisfactory. These areas are preferentially accepted by either fountain solution or ink, but not by both. In other words, the plate has a hydrophilic / oleophobic non-image area and hydrophobic / hydrophobic properties with mutually exclusive wetting characteristics to apply different energies that simultaneously solve equations (v), (vi), (vii) Consists of lipophilic image areas. These conditions can be plotted on a graph with two separate αβ plots, as shown in FIGS. 2 and 3, corresponding to the image and non-image regions of the plate, respectively. For these plots, we have estimated that r is about 1, but the interpretation of these plots does not change even if r is a higher value.

Referring to FIG. 2, the solid circle represents the enclosed α-β region of the solution that appears to wet the image area of the plate. The position of the diamond shape above the circle corresponds to the surface energy of the image area of the plate (i.e., the α-β coordinate of the surface energy of the plate). Similarly, the surface tension of the ink is represented by a dotted circle and is inside the circle of the offset plate, indicating that the ink will wet the surface of the offset plate. Downward triangles (β about 7 and α about 4) represent water, and water alone does not wet the surface of the offset plate due to its high surface tension. However, when surfactant is added to water to create fountain solution (FS), the effective β component (ie, polarity) is significantly reduced, and the new location of the αβ plot in the circle showing surface wettability ( β approximately 3, α approximately 4). This new position is represented by an upward triangle. The broken circle connecting the diamond shape and the dotted circle represents a wet envelope, and in this portion, wetting occurs on the image area of the surface in the presence of ink (when conditions vii and S _fi = 0) ). The fact that the fountain solution is outside the dashed circle indicates that the surface of the image area is preferentially wetted by the ink.

  FIG. 3 in contrast shows the situation of the non-image areas of the board. Here, the surface energy of the plate has a considerably large polar component, and therefore the circle indicating the wettability represented by the solid circle is considerably large. At this time, the surface tension of the fountain solution (represented by a dotted circle) is in a solid circle wet envelope and a dashed circle wet envelope. At this time, the fountain solution is fairly closely related to the actual surface energy of the non-image area. The fact that the dotted circle falls within the dashed circle indicates that the surface is preferentially wet with dampening water in the presence of the print roller. In other words, the fountain solution will repel the ink strongly in the non-image areas because the fountain solution is in the dashed circle. The arrangement of these curves and points is merely illustrative and does not suggest the absence of other structures.

  Unlike conventional offset printing, all three types of diffusion conditions must be satisfied on one unique surface of a variable lithographic printing imaging member. Such a solution has not been developed in the past due to the fact that conventional offset plates have two separate surfaces, resulting in ink materials and chemistry, fountain solution, imaging surface Is not mathematically enforced. Thus, if a range of ink chemistry is used to provide a robust print quality, and variable lithographic printing uses only one imaging surface, it uses only one surface (ie, not two). It would be desirable to provide a fountain solution that can satisfy all three types of diffusion conditions (in one α-β graph).

  The present disclosure contemplates systems where the fountain solution is hydrophobic and the ink is somewhat hydrophilic (including a small amount of polar components). This system can be used primarily with imaging member surfaces with low dispersible surface energy. Thus, it can work with imaging members that are silicone, fluorosilicone or Viton®-based elastomers that provide robustness against high temperature wear against the laser energy used in variable lithographic printing. A representative ink / fountain / surface system of the present disclosure is shown in FIG. Here, the solid circle represents the wet condition of a completely smooth surface. However, when there is a fine pattern on the surface, the radius of the wetting condition on the surface can be effectively expanded in the αβ space, and the correct wettability circle is represented by a dotted circle. This is due to the fact that the effective fractal surface area of the surface is increased, i.e. the factor r is greater than 1, increasing the effective possible wetting energy space. This allows ink (represented by triangles) and dampening fluid (represented by squares) to enter the wet envelope of the surface pattern. Thus, the surface energy of the surface (represented by the diamond mold) no longer goes directly on top of its wet envelope (dotted circle). The dampening solution represented by the square is in the dotted circle created by the surface energy of the plate (diamond type) and the triangle (represented by the ink), even when ink is present Note that the surface is preferentially wetted by the fountain solution.

  When using an energy source (eg, a laser) to create a pattern of the dampening fluid layer, it is also desirable that the edges of the pattern remain stable for an extended period of time. A surface pattern that enhances the wettability of the ink also helps to fix the dampening fluid in place to maintain the pattern. In addition, by using the surface tension of the dampening solution in the range close to the smooth surface wetting curve, the diffusion coefficient is minimized tangentially (no roughness effect due to fine patterns), This reduces the tension that promotes diffusion or receding of the dampening solution. Therefore, careful selection and design of ink and fountain chemistry, reimageable surface energy and pattern can improve image quality in terms of both background coloration and image edge quality. it can.

  In such systems, the ink should have appreciable polar surface tension and low dispersive surface tension. For example, ultraviolet (UV) offset inks derived from acrylate oligomers and monomers have appreciable polar surface tension components and many other desirable properties. For example, due to environmental concerns and the low total cost of ownership, lithographic printing with UV was used in packaging and sheet-fed offset printing. The odor problem that exists with such UV offset inks has generally been eliminated by using monomers with high boiling points. In fact, one company has an approved list that includes UV offset inks because other inks (eg, cobalt curable inks or solvent-based inks) are sometimes considered to pose significant risks in the packaging industry. The polar component of the surface tension of the UV offset ink can be adjusted and controlled by selecting monomers and oligomers suitable for the ink and by adding a surface leveling agent to the ink. In other embodiments, the ink is an ester group (—COO—), an ether group (—O—), a carbonyl group (—CO—), an amino group (—NRR ′), a cyano group (—CN), or a hydroxyl group. A monomer containing a (—OH) group may be contained. Exemplary monomers that can be used in the UV offset ink envisioned by this disclosure include acrylates such as methyl methacrylate or t-butyl acrylate, acrylonitrile, acrylamide, vinyl alcohol, and the like.

  By choosing the appropriate chemistry, it is possible to devise a system where both ink and dampening fluid wet the imaging member surface, but the ink and dampening fluid do not wet each other. The system also includes a dampening liquid in the presence of ink residue to actually lift the ink residue from the imaging member surface by having a high affinity for surface wetting in the presence of ink. It can also be designed such that is more energetically favorable. In other words, the fountain solution will remove microscopic background defects (eg, less than 1 μm radius) that may remain in subsequent prints.

  Generally speaking, a variable lithographic system can be described as including an ink, a dampening liquid, and an imaging member surface, where the dampening liquid is an alpha of the surface energy of the ink and the surface energy of the imaging member surface. -It has the α-β coordinate of the surface energy in the circle connecting the β coordinate. In certain embodiments, the fountain solution has a total surface tension of greater than 15 dynes / cm and less than 30 dynes / cm, and the polar component is less than 5 dynes / cm. The imaging member surface may have a surface tension of less than 30 dynes / cm and a polar component of less than 2 dynes / cm. For example, the imaging member surface may be made from silicone, fluorosilicone or fluoroelastomer.

  The fountain solution of the present disclosure is useful to satisfy all the conditions of digital variable lithographic printing listed above. The fountain solution includes a solvent that is either a volatile hydrofluoroether (HFE) liquid or a volatile silicone liquid. Hydrofluoroethers and silicones are liquids at room temperature (ie, 25 ° C.).

In certain embodiments, the volatile hydrofluoroether liquid has the structure of formula (I):
In the formula, m and n are each independently an integer of 1 to about 9, and p and q are independently an integer of 0 to 19. As can be seen, in general, the two groups attached to the oxygen atom are fluoroalkyl groups.

  In certain embodiments, q is 0 and p is not 0. In these embodiments, the right hand side of the compound of formula (I) is a perfluoroalkyl group. In other embodiments, q is 0 and p has a value of 2m + 1. In these embodiments, the right hand side of the compound of formula (I) is a perfluoroalkyl group and the left hand side of the compound of formula (I) is an alkyl group. In still other embodiments, both p and q are at least 1.

  In this regard, the term “fluoroalkyl” as used herein is one in which one or more hydrogen atoms may be replaced with fluorine atoms (ie, not essential) and are fully saturated. A group consisting entirely of carbon and hydrogen atoms. The fluoroalkyl group may be linear, branched or cyclic.

The term “alkyl” as used herein refers to a group composed entirely of carbon and hydrogen atoms, fully saturated and having the formula —C _n H _{2n + 1} . The alkyl group may be linear, branched or cyclic. Note that alkyl groups are a subset of fluoroalkyl groups.

The term “perfluoroalkyl” as used herein refers to a group composed entirely of carbon and fluorine atoms, fully saturated and having the formula —C _n F _{2n + 1} . Perfluoroalkyl groups may be linear, branched or cyclic. Note that perfluoroalkyl groups are a subset of fluoroalkyl groups and cannot be considered alkyl groups.

In certain embodiments, the hydrofluoroether has a structure of any one of formulas (Ia) to (Ih).

  Among these formulas, the formulas (Ia), (Ib), (Id), (Ie), (If), (Ig), (Ih) are It has one alkyl group and one perfluoroalkyl group and may be either branched or straight chain. In some terminology, these are also called broken hydrofluoroethers. Formula (Ic) contains two fluoroalkyl groups and is not considered a split hydrofluoroether.

  Formula (I-a) is also known as 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4- (trifluoromethyl) pentane, CAS number 132182-92-4. It is commercially available as Novec ™ 7300.

  Formula (Ib) is also known as 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2- (trifluoromethyl) hexane. CAS number 297730-93-9. It is commercially available as Novec ™ 7500.

  Formula (Ic) is also known as 1,1,1,2,3,3-hexafluoro-4- (1,1,2,3,3,3-hexafluoropropoxy) pentane, CAS number 870778-34-0. It is commercially available as Novec ™ 7600.

  Formula (Id), also known as methyl nonafluoroisobutyl ether, has CAS number 163702-08-7. Formula (I-e), also known as methyl nonafluorobutyl ether, has CAS number 163702-07-6. A mixture of formula (Id) and (Ie) is commercially available as Novec ™ 7100. These two isomers are inseparable and have essentially the same properties.

  Formula (If) is also known as 1-methoxyheptafluoropropane or methyl perfluoropropyl ether and has CAS number 375-03-1. It is commercially available as Novec ™ 7000.

  Formula (I-g), also known as ethyl nonafluoroisobutyl ether, has CAS number 163702-05-4. Formula (Ih), also known as ethyl nonafluorobutyl ether, has CAS number 163702-06-5. Mixtures of formula (Ig) and (Ih) are commercially available as Novec ™ 7200 or Novec ™ 8200. These two isomers are inseparable and have essentially the same properties.

There is also the possibility that a similar structure with a cyclic aromatic skeleton with perfluoroalkyl side chains can be used. In particular, a compound of formula (A) is envisaged,
In the formula, Ar is an aryl group or a heteroaryl group, k is an integer of 1 to about 9, t represents the number of perfluoroalkyl side chains, and t is 1 to about 8.

  The term “aryl” refers to an aromatic group composed entirely of carbon and hydrogen atoms. When aryl is described in combination with a range of carbon atoms, it should not be construed as including substituted aromatic groups. For example, the phrase “aryl containing 6-10 carbon atoms” should be construed to refer only to a phenyl group (6 carbon atoms) or a naphthyl group (10 carbon atoms) and methylphenyl It should not be construed as containing the group (7 carbon atoms).

  The term “heteroaryl” refers to a cyclic group consisting of carbon atoms, hydrogen atoms, and heteroatoms in the ring of the group, and the cyclic group is aromatic. The heteroatom may be nitrogen, sulfur or oxygen. Exemplary heteroaryl groups include thienyl, pyridinyl, quinolinyl. When heteroaryl is described in combination with a numerical range of carbon atoms, it should not be construed as including substituted heteroaromatic groups. Note that heteroaryl groups are not a subset of aryl groups.

Hexafluoro-m-xylene (HFMX) and hexafluoro-p-xylene (HFPX) are specifically envisioned as useful compounds of formula (A) that can be used as low cost fountain solutions. HFMX and HFPX are shown below as formulas (Aa) and (Ab).
It should be noted that any co-solvent combination of the fluorinated fountain solution can be estimated to help suppress undesirable features such as low combustion temperatures.

Alternatively, the solvent of the fountain solution is a volatile silicone liquid. In certain embodiments, the volatile silicone fluid is a linear siloxane having the structure of formula (II):
In the formula, R _a , R _b , R _c , R _d , R _e and R _f are each independently hydrogen, alkyl or perfluoroalkyl, and a is an integer of 1 to about 5. In certain embodiments, R _a , R _b , R _c , R _d , R _e , R _f are all alkyl. In a more specific embodiment, these are all alkyls of the same length (ie, the same number of carbon atoms).

Exemplary compounds of formula (II) include hexamethyldisiloxane and octamethyltrisiloxane, which are shown below as formulas (II-a) and (II-b).

In other embodiments, the volatile silicone fluid is a cyclosiloxane having a structure of formula (III):
Wherein R _g and R _h are each independently hydrogen, alkyl or perfluoroalkyl, and b is an integer from 3 to about 8. In certain embodiments, the R _g and R _h groups are all alkyl. In a more specific embodiment, these are all alkyls of the same length (ie, the same number of carbon atoms).

Exemplary compounds of formula (III) include octamethylcyclotetrasiloxane (aka D4) and decamethylcyclopentasiloxane (aka D5), which are represented by formulas (III-a) and (III-b) As shown below.

In other embodiments, the volatile silicone fluid is a branched siloxane having the structure of formula (IV):
In the formula, R ₁ , R ₂ , R ₃ and R ₄ are independently alkyl or —OSiR ₁ R ₂ R ₃ .

An exemplary compound of formula (IV) is methyltrimethicone (also known as methyltris (trimethylsiloxy) silane), which is commercially available from Shin-Etsu as TMF-1.5 and has the formula (IV-a It is shown below using the structure of

  Any of the aforementioned hydrofluoroether / perfluorinated compounds are miscible with each other. Also, the optional silicones described above are miscible with each other. This allows the optimum printing performance or other characteristics (eg boiling point or combustion temperature) to be adjusted for the fountain solution. Combinations of these hydrofluoroethers and silicone fluids are specifically contemplated as being within the scope of this disclosure. It should also be noted that silicones of formula (II), (III), (IV) are not considered polymers, but rather are separate compounds from which the actual formula can be known.

  In certain embodiments, it is envisioned that the fountain solution includes a mixture of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). Most silicones are derived from D4 and D5, which are produced by hydrolysis of chlorosilanes produced by the Rochow process. The ratio of D4 and D5 distilled from the hydrolyzate reaction is generally 85% by weight of D4 to 15% by weight of D5, and this combination is an azeotrope.

  In certain embodiments, it is assumed that the dampening solution comprises a mixture of octamethylcyclotetrasiloxane (D4) and hexamethylcyclotrisiloxane (D3), where D3 is 30 of the total weight of D3 and D4. Present in amounts up to%. The effect of this mixture is to lower the effective boiling point of the thin layer of fountain solution.

The volatile hydrofluoroether liquid and volatile silicone liquid of the present disclosure have low heat of vaporization, low surface tension, and good kinematic viscosity. As a reference, Table 1 below compares these properties with those of water.

  The tests in Table 1 show that all of these liquid compounds have a much lower heat of vaporization, reducing the amount of energy that must be applied to the imaging station to create a latent image. In addition, liquid compounds have a much lower surface tension, and as a result may not require any additional surfactant. Also, many of these compounds are significantly different in density from water and are generally insoluble in water as well.

  In some embodiments, the liquid solvent used in the fountain solution has a heat of vaporization of less than 200 kJ / kg or less than 120 kJ / kg when measured at 1 atmosphere and 25 ° C.

  One result of using these liquids in the fountain solution is that the fountain solution can have a surface tension of about 15 to about 30 dynes / cm. This low surface tension helps the dampening fluid diffuse and wet the imaging member surface. In another specific embodiment, the dampening fluid has a kinematic viscosity at 25 ° C. of greater than 1 centistokes and a surface tension at 25 ° C. of less than 72 dynes / cm.

  Desirably, there are at least three conditions that are compatible with a robust digital offset imaging system. First, the fountain solution has a slightly positive diffusion coefficient so that the fountain solution wets the imaging member surface. In addition, it is often further necessary that the dampening system used to coat the imaging surface member be as uniform and reproducible as possible. First, the fountain solution quickly diffuses over the finely rough surface of the imaging member due to the positive diffusion coefficient. This would be considered a passive and natural “self-leveling” process. Second, the fountain solution maintains a diffusion coefficient in the presence of the ink, or in other words, the fountain solution has a surface energy value that is closer to the imaging member surface than the ink. As a result, the surface of the imaging member is wetted to a certain value by the dampening liquid compared to the ink, and the dampening liquid lifts up any ink residue, and the surface of the part where the ink has not removed the dampening liquid by the laser. Prevent from adhering to. Third, the ink should wet the imaging member surface with a roughness enhancing factor in the air (ie, when no dampening fluid is present on the surface). It should be noted that if the ink is applied with a thickness of 1-2 μm, the surface may have a thickness of less than 1 μm.

  In addition to these three conditions, it is desirable that the fountain solution does not wet the ink in the presence of air. In other words, the print nip should be missing at the exit, which is the interface between the ink and fountain solution and not inside the fountain solution. Thus, the fountain solution does not tend to remain on the imaging member surface after the ink has been transferred to the receiving substrate. In practice, this condition is difficult to achieve and requires a small amount of dampening liquid to be removed from the printing system with an air knife and to selectively evaporate the dampening liquid from the printing system. Or it would be acceptable to be able to establish a small balance of dampening liquid for emulsification in the printing subsystem.

  Finally, it is also desirable that the ink and fountain solution are not chemically mixed so that there may be simply an emulsified mixture. The ink and fountain solution may have α-β coordinates close to each other, but often reduce miscibility by increasing the difference in Hanson solubility parameters by selecting chemical components with different hydrogen bonding degrees. Can do.

  Other additives may also be present in the fountain solution. Such additives may include biocides, sequestering agents, corrosion inhibitors, and humectants.

  Biocides prevent or destroy the growth of fungi or microorganisms that may be present in the immersion liquid. Exemplary biocides include sodium benzoate, phenol or phenol derivatives, formalin, imidazole derivatives, sodium dehydroacetate, 4-isothiazolin-3-one derivatives, benzotriazole derivatives, amidine and guanidine derivatives, quaternary ammonium salts. , Pyridine, quinoline and guanidine derivatives, quinoline, diazine and triazole derivatives, oxazole and oxazine derivatives, bromonitropropanol, 1,1-dibromo-1-nitro-2-ethanol, 3-bromo-3-nitropentane- 2,4-diol is mentioned. The biocide can be used in an amount of about 0.001% to about 1% by weight of the fountain solution.

  A sequestering or chelating agent is used to chelate dissolved ions that may be present in the fountain solution and prevent, for example, reaction with other components in the ink. Exemplary sequestering agents include organic phosphonic acids and phosphonoalkanetricarboxylic acids such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, hydroxyethylethylenediaminetriacetic acid, nitrilotriacetic acid, 1 -Hydroxyethane-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), and salts thereof. The sequestering agent may be used in an amount of about 0.001% to about 1% by weight of the fountain solution.

  The corrosion inhibitor prevents corrosion of related components of the imaging member. Exemplary inhibitors include sodium nitrate, sodium phosphate, benzotriazole, 5-methylbenzotriazole, thiosalicylic acid, benzimidazole.

  The humectant prevents the dampening solution from drying too quickly, which can cause several problems that occur in the final printed product. Exemplary humectants include ethylene glycol, glycerin and propylene glycol.

  The fountain solution of the present disclosure is based on a nonpolar solvent. It is envisioned that the fountain solution is used in the system in combination with an ink containing a polar component.

  Some aspects of the present disclosure will be further understood by reference to the following examples. The examples are illustrative and are not intended to limit the embodiments.

  FIG. 5 is an illustration of a series of characters printed using 100% Novec ™ 7500 fountain solution. FIG. 6 is an illustration of the same series of letters printed with a dampening solution containing 90% by weight water, 8% by weight isopropanol, 2% by weight SILSURF surfactant. Don't forget that ink is placed after the fountain solution. Comparing the arrows (a) at the top of p in each figure, the edges are clear in FIG. 5 and not rounded in FIG. 6, indicating that there is almost no retraction of the dampening liquid in FIG. Show. Similarly, when comparing the arrow (b) on the upper left side of “a” in each figure, the edge is clear in FIG. 5 and rounded in FIG. 6, which is also the dampening solution in FIG. 5. It shows that there is almost no setback. The same effect is seen on the lower right side of “a” and is indicated by the arrow (c).

Claims (10)

A process for variable lithographic printing,
Applying a liquid containing a solvent that is a volatile hydrofluoroether liquid or a volatile silicone liquid to the imaging member surface;
Creating a latent image by evaporating the applied liquid from a selective position on the imaging member surface, creating a hydrophobic non-image area and a hydrophilic image area;
Developing the latent image by applying polar ink to the hydrophilic image area;
Transferring the developed latent image to a receiving substrate. The solvent is a volatile hydrofluoroether liquid having the structure of formula (I);

Wherein, m and n are independently integers of. 1 to 9, p and q are independently an integer of 0 to 19, The process of claim 1. Polar component of the surface tension of the ink is greater than the polar components of the surface tension of the liquid, The process of claim 1. The solvent is a volatile silicone liquid having the structure of formula (III);

Wherein, _{R g} and _{R h} are each independently hydrogen, alkyl or perfluoroalkyl, b is an integer of 3-8, the process according to claim 1. The liquid for use in the process of claim 1 comprising a solvent that is a volatile hydrofluoroether liquid or a volatile silicone liquid . The liquid according to claim 5 , wherein the solvent is a volatile hydrofluoroether liquid . The volatile hydrofluoroether liquid has the structure of formula (I);

Wherein, m and n are independently integers of. 1 to 9, p and q are independently an integer of 0 to 19, the liquid of claim 6. The liquid according to claim 7 , wherein q is 0 and p is not 0. It said volatile hydrofluoroether liquid, having any one of structures of formula (I-a) ~ (I -h), a liquid of claim 6.
A variable lithographic system comprising ink, the liquid of claim 5 and an imaging member surface, wherein the liquid has a surface energy that is less than the surface energy of the ink and the surface energy of the imaging member surface.