WO2005075209A1

WO2005075209A1 - Method of making an ink-jet receiver

Info

Publication number: WO2005075209A1
Application number: PCT/GB2005/000148
Authority: WO
Inventors: Julie Baker
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 2004-02-05
Filing date: 2005-01-17
Publication date: 2005-08-18
Anticipated expiration: 2006-08-05
Also published as: GB0402574D0

Abstract

A method of manufacturing an improved ink jet receiver having a foamed polymer ink-receiving layer involves coating onto a support a polymer solution, at least one blowing agent and, optionally, a surfactant, to form a coated support comprising at least one layer of a coated solution of a polymer, at least one blowing agent and, optionally, a surfactant; interacting with the coated solution to activate the at least one blowing agent to generate gas bubbles within the solution thereby causing foaming of the polymer; and drying the coated solution, which method further comprises at least two of A) selecting a surfactant which enables the size of the bubbles formed to be controlled depending on whether or not a first criterion is met, which first criterion is that the critical aggregation concentration of the surfactant is substantially the same as the concentration associated with the midpoint of the dynamic surface tension curve of the surfactant; and, on whether or not a second criterion is met, which second criterion is that the surfactant has a low static surface tension; B) reducing the pH of the polymer solution prior to the addition of the at least one blowing agent; and C) preventing activation of the at least one blowing agent until alter the coated solution is formed.

Description

METHOD OF MAKING AN INK-JET RECEIVER

FIELD OF THE INVENTION The present invention relates to the field of ink-jet printing. More specifically, it relates to a method of making an ink-jet receiver comprising a foamed polymer, ink-receiving layer, such ink-jet receivers and to a method of printing thereon.

BACKGROUND OF THE INVENTION Commercially available photo quality ink-jet receivers can generally be classified into one of two categories according to whether the principal component material forms an ink-receiving layer that is porous or non- porous in nature. Porous ink-jet receivers are typically formed from inorganic materials with a polymeric binder. When ink is applied to the receiver, it is quickly absorbed into the porous, layer by capillary action. However, the open nature of the porous layer can contribute to instability of printed images, particularly when exposed to environmental gases such as ozone. Ink-jet receivers having a non-porous layer are typically formed by the coating of one or more polymeric layers onto a support. When ink is applied to such receivers, the polymeric layers swell and absorb the applied ink. Due to limitations of the swelling mechanism, this type of media is slow to absorb the ink. Once dry, however, printed images tend to be relatively stable when subjected to light and ozone. Hybrid ink-jet receivers which provide the benefits of both the porous and non-porous receivers described above are being investigated as alternatives to porous and non-porous receivers. One example is that described in our European Patent Application Nos. 03015858.8 and 03015361.3, which comprises a foamed polymer layer prepared by activating blowing agents in a hydrophilic polymer layer coated onto an ink-jet support. The resulting foamed hydrophilic polymer layer provides the benefit of rapid uptake of ink usually associated with a porous receiver and the benefit of relative stability to light and ozone more normally associated with a non-porous receiver. Our European Patent Application No. 03078204.9 describes the use of a surfactant to control the size of bubbles formed in making such an ink-jet receiver and our European Patent Application No. 03025812.3 and our International Patent Application claiming priority from UK Patent Application No. 0303261.2 describe the effects on the manufacture of such foamed polymer materials of preventing blowing agent activation until after coating of a polymer solution onto a support and of adjusting the pH of the polymer solution prior to addition of blowing agent. Other methods of forming porous polymer layers are known, such as those described in US-A-6228476 and US-A-2001/0021726. Such methods rely on the use of curable polymers.

PROBLEM TO BE SOLVED BY THE INVENTION It would be desirable to provide an ink-jet receiver having the beneficial properties of both porous and non-porous receivers and which can be easily manufactured. It is still further desirable that relatively low temperatures can be used in manufacturing and that the manufacturing method provides beneficial surface properties and may be selected to provide suitable rates of ink absorbancy depending upon the whether dye or pigment based inks are utilized.

SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided a method of manufacturing an ink-jet receiver comprising a foamed polymer ink-receiving layer, said method comprising coating onto a support a polymer solution, at least one blowing agent and, optionally, a surfactant, to form a coated support comprising at least one layer of a coated solution of a polymer, at least one blowing agent and, optionally, a surfactant; interacting with the coated solution to activate the at least one blowing agent to generate gas bubbles within the solution thereby causing foaming of the polymer; and drying the coated solution, which method further comprises at least two of A) selecting a surfactant which enables the size of the bubbles formed to be controlled depending on whether or not a first criterion is met, which J - first criterion is that the critical aggregation concentration of the surfactant is substantially the same as the concentration associated with the midpoint of the dynamic surface tension curve of the surfactant; and, on whether or not a second criterion is met, which second criterion is that the surfactant has a low static surface tension; B) reducing the pH of the polymer solution prior to the addition of the at least one blowing agent; and C) preventing activation of the at least one blowing agent until after the coated solution is formed. In a second aspect of the invention, there is provided an ink-jet receiver obtainable by the above method. In a third aspect of the invention, there is provided a method of printing comprising Hie steps of loading an ink-jet printer with an ink-jet receiver obtainable by the above method, and printing an image onto the ink-jet receiver using said printer to generate a print. In a fourth aspect of the invention, there is provided an ink-jet print obtainable by the above method of printing.

ADVANTAGEOUS EFFECT OF THE INVENTION The present invention provides a method of making an ink-jet receiver comprising a foamed polymer ink-receiving layer, which can be formed without high processing temperatures and which provides beneficial properties of both porous and non-porous ink-jet receivers. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a graph of variation in log(concentration of a surfactant) against surface tension for a number of different surfactants; Figures 2 to 4 show scanning electron micrographs of sections through materials according to the present invention; Figures 5 to 7 show schematic representations of sections through three different materials made according to the method of the present invention; Figure 8 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer formed with coating A as described below; Figure 9 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer formed with coating B as described below; Figure 10 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer formed with coating C as described below; Figure 11 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer formed with coating E as described below; Figure 12 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer for ed with coating F as described below; Figure 13 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer formed with coating G as described below; Figure 14 is a scanning electron micrograph of a section through an ink-jet receiver showing the bubble formation in an ink-receiving layer formed with coating H as described below; Figure 15 shows a cross-section of an ink-jet receiver comprising a foamed hydrophilic polymer layer on a support; and, Figure 16 show a cross-section of an ink-jet receiver of Figure 15 following passage of the ink-jet receiver through a fuser device.

DETAILED DESCRIPTION OF THE INVENTION The method of manufacturing an ink-jet receiver according to the present invention, as set out above, comprises at least two of the steps of selecting a surfactant which enables the size of the bubbles formed^' to be controlled (step A, above), reducing the pH of the polymer solution prior to addition of the at least one blowing agent (step B, above) and preventing activation of the at least one blowing agent until after the coated solution is formed (step C, above). Preferably, the method comprises the step of selecting a surfactant which enables bubble size to be controlled (step A, above), more preferably a surfactant is selected in order to control bubble size, in combination with either the step of reducing the pH of the polymer solution prior to addition of the at least one blowing agent (step B, above) or the step of preventing activation of the at least one blowing agent until after the coated solution is formed (step C, above), or more preferably both. By choosing an appropriate surfactant, it has been found that the size of the bubbles in a polymer foam can be controlled. Accordingly, by selecting an alternative surfactant, the size of the bubbles in the polymer foam can be selectively adjusted. The present invention provides a method of manufacturing an ink- jet receiver comprising a foamed ink-receiving layer. A polymer solution and at least one blowing agent, and optionally a surfactant, are coated onto a support to form a coated support comprising at least one layer of a coated solution of a polymer, at least one blowing agent, and optionally a surfactant. The support may be, for example, a resin-coated paper, film base, acetate, polyethylene terephthalate (PET), a printing plate or other suitable support. Preferably, the polymer is a hydrophilic polymer, such as, for example, polyvinyl alcohol (PNA), polyethylene oxide (PEO), polyvinyl pyrrolidone (PNP) or gelatin. The polymer may be present in any suitable amount for the particular utility, which may depend on the amount and type of ink and on the absorbant properties of the particular polymer used. A laydown of polymer onto a support may be, for example, from 2-40 g/m², preferably 4-40 g/m², more preferably 6-20 g/m² and still more preferably 8-18 g/m , which may be coated as a single layer or in two or more layers. Such amounts would be useful, for example, if PNA was the polymer material. The at least one blowing agent may be added to the polymer solution prior to, during or after coating of the polymer solution onto the support. Where a bead coater comprising a standard slide hopper is utilised for coating the support, the at least one blowing agent may, typically, be added to the polymer solution prior to or during coating of the polymer solution onto the support. Where the blowing agent is added to the polymer solution prior to coating onto the support, the interaction with the polymer solution in order to activate the blowing agent may begin prior to the step of coating the support. In this case, the receiver is prepared by coating a support with a layer of foamed polymer solution in which bubbles are formed. The bubbles are formed, for example, in an aqueous solution of a hydrophilic polymer and blowing agent. The aqueous solution containing the bubbles is then coated onto a support. The foamed polymer solution is created by heating the solution prior to its application to the support, to promote the decomposition of the blowing agent to generate a gas. Preferably, however, the activation of the blowing agent is delayed until after coating of the support. Typically, the interaction with the coated solution is by heating of the coated support, for example during the drying process. The heat causes the blowing agent to decompose and create gas bubbles, thereby forming a polymer foam on the support. Alternatively, an acid may be added to the solution to react with the blowing agent again to generate a gas within the solution. In this alternative method, it is preferable that a compound, which on heating releases an acid, is added to the solution. When the solution is heated, acid is released which reacts with the blowing agent to cause decomposition of the blowing agent and the consequent generation of gas. When dry, the material is suitable for use as an ink- jet receiver. In a preferred embodiment, the blowing agent may be selected such that the heat provided to dry the coated support is sufficient to cause decomposition of the blowing agent and generation of the gas. The blowing agent used in the method of the present invention is selected in dependence on the temperature at which it reacts to generate gas. By selecting a blowing agent that reacts at a relatively low temperature, material may be formed without requiring high temperatures. Accordingly, blowing agents that react at a relatively low temperature, e.g. less than 200°C, more preferably in the rantge 50-120°C, are preferred. Examples of suitable blowing agents for use in the method of the present invention, include a mixture of sodium nitrite and ammonium chloride, metal carbonates and bicarbonates. Further examples of suitable blowing agents are described in, for example, the Handbook of Polymeric Foams and Foam Technology, Edited by Daniel Klempner and Kurt C. Frisch, Chapter 17: Blowing Agents for Polymer Foams, Section 3 Chemical Blowing Agents, (Chapter written by Dr. Fyodor A. Shutov). The preferred blowing agent is a combination of sodium nitrite and ammonium chloride. The amount of blowing agent in the polymer solution for use in generating the foamed polymer layer may, for example, be up to about 200% by weight as a proportion of blowing agent to polymer. Preferably, it would be in an amount of at least 5%, such as in an amount of from about 10% to about 60%, more preferably from about 30% to about 50%. Where more than one layer of a polymer solution for generating a foamed polymer material is coated onto a support, the proportion of blowing agent in each layer may vary, but is typically within the above ranges. Preferably, a surfactant is coated onto the support to form a coated solution of a polymer, at least one blowing agent and a surfactant, and most preferably is added to the polymer solution prior to coating. The amount of _r surfactant present in a polymer solution for use in generating a foamed polymer material is preferably in the range of from about O.O /o to about 2.0% by weight as a proportion of polymer present and more preferably about 0.05% to about 1.0%. Where more than one layer of polymer solution is applied to a support, the proportion of surfactant in each layer may vary, but is in each case preferably within the aforementioned ranges. Suitable surfactants for use in accordance with the present invention include, for example, Surfactant 1 (available as Lodyne™ SI 00), Surfactant 2 (which is described in US-A-2002/0155402, the content of which, describing Surfactant 2 and other surfactants that may be useful in the present invention, is incorporated herein by reference), Surfactant 3 (available as Olin™ 10G) and Surfactant 4 (available as Zonyl FSN), having the following structural formulae: Surfactant 1

where Rf is a range of fluorocarbon chain lengths based on the general structure C_nF2n₊ι, where typically n possesses the following series of values, 6, 8, 10, 12, and 14.

Surfactant 2

where the terminal group "T" is H.

Surfactant 3

where m+n=10 on average Surfactant 4

R_f-CH₂CH₂0(CH₂CH₂O)_yH

where y is 0-25 and Rf is a range of fluorocarbon chain lengths and is represented by the structure F(CF₂CF₂)χ, where x is 1-9.

Any suitable method of coating may be used to coat the solution onto the support. For example, curtain coating, bead coating, air knife coating or any other suitable method may be used. Typically, in bead coating, a set-up is used in which a multi-layer arrangement of liquids is applied to a moving web via a hopper. The ink-jet receiver formed may comprise one or more layers, for example, two or three layers, of foamed polymer material, which layers may be the same or different. Preferably, where more than one layer of foamed polymer material is present, the layers of foamed polymer material are adjacent one another and polymer is of the same type in each. In a most preferred embodiment, the polymer solution for use in generating the foamed polymer layer of the ink-jet receiver comprises PNA as a hydrophilic polymer with, for example, sodium nitrite and ammonium chloride as blowing agents, which may be dual coated onto the support, and the foamed polymer formed after coating. According to step A of the method of the present invention, selection of a surfactant for addition to the solution enables control of the size of bubbles formed in the material. Figure 1 shows a graph of variation in log(concentration of a surfactant) against both dynamic and static surface tension for three different surfactants, Surfactant 1, Surfactant 2, and Surfactant 3. Lines 2, 4 and 6 are the relationships between the variation in dynamic surface tension with changing logarithm of the concentration of surfactant for each of Surfactant 1, Surfactant 2 and Surfactant 3 respectively. Lines 8, 1.0 and 12 are the relationships between the variation in static surface tension with changing logarithm of the concentration of surfactant for each of Surfactant 1, Surfactant 2 and Surfactant 3 respectively. For each of the surfactants, two different parameters are determined based on the relationships shown by lines 2 to 12. Firstly, the logarithm corresponding to the critical aggregation concentration CAC of each surfactant is identified as follows. A straight line fit is applied to the region of maximum slope of the static surface tension (SST) curves 8,10 and 12. Another straight line fit is applied to the region of the SST curve where the surface tension has levelled out at or close to a minimum value. The point at which these two lines intersect represents a logarithm value of a corresponding concentration, the concentration being known as the critical aggregation concentration, or CAC. As explained above, Figure 1 shows a graph of variation in log(concentration of a surfactant) against both dynamic and static surface tension for three different surfactants. Accordingly, in this example, the CAC is represented by a log value. Secondly, the log of the concentration corresponding to the midpoint of the dynamic surface tension (DST) curve, log C^{m "DST}, is interpolated from the point on the DST curve 2, 4 and 6 where the surface tension is midway between that of the solvent i.e. the maximum dynamic surface tension and the value at the CAC i.e. minimum static surface tension. It can be seen from the Figure that the logarithm of the CAC of

Surfactant 1 is almost co-incident with the logarithm of the concentration corresponding to its c^mιd"DST. Surfactant 1 also gives a low static surface tension at the concentrations that these surfactants are commonly used at, i.e. log[conc(wt%)] = -0.5. From Table 1 below, it can also be seen that this surfactant produces the smallest bubbles. For Surfactant 2, it can be seen that the logarithm of its CAC is much lower than the logarithm of the concentration corresponding to its C™ ^" and that its static surface tension levels out at much higher values than Surfactant 1. The average bubble size produced by Surfactant 2 is significantly larger than that achieved with Surfactant 1. Although like Surfactant 1, the logarithm of the CAC of Surfactant 3 is almost co-incident with the logarithm of the concentration corresponding to its c^mld"DST, its static surface tension levels out at a relatively high value like Surfactant 2, and like Surfactant 2 results in much larger bubbles. From this data, it is demonstrated that to achieve smaller bubbles the logarithm of the CAC of a surfactant used, needs to be close in value to the logarithm of the concentration corresponding to c^mιd"DST for that surfactant and that a low static surface tension of the surfactant is also required. If the graph in Figure 1 was shown with a linear scale as opposed to a log scale, the condition would be that the CAC must be close in value to c^mιd"Dsτ. Typically, for a surfactant that satisfies this criterion, the logarithm of its CAC should be within 0.5 log units, preferably within 0.25 log units of the logarithm of the concentration corresponding to the c^mιd"Dsτ. A low static surface tension preferably means a value less than 28mN/m, preferably less than 24mN/m. If only one of these criteria is achieved, much larger bubbles are produced. In other words, for small bubbles to be formed in the foam and material two criteria have to be met: First, the CAC of the surfactant must be of similar concentration to that associated with the midpoint of its dynamic surface tension curve c ^ld"DST, which may be measured by a specified overflowing cylinder method; and secondly, the surfactant must also have a low static surface tension. If either the difference between the CAC and c^mιd"DST is too great, e.g. greater than 0.5 log units, or the static surface tension is too high, e.g. greater than 28mN/m, larger bubbles are formed. Preferably, for example, where an ink-jet receiver having small bubbles is desired, e.g. for use with a dye-based ink, a surfactant having a CAC of similar concentration to that associated with the midpoint of its dynamic surface tension curve c ^ιd"DST, e.g. within 0.5 log units, and a low static surface tension, e.g. less than 28 mN/m, may be utilised. In a further aspect of the invention, there is provided the use of one or more surfactants to control the size of bubbles in an ink-jet receiver made according to the method of the present invention wherein at least one of and preferably both of the steps B and C are comprised in the method. The bubble size may be controlled by selecting the surfactant or mixture of surfactants such that a desired bubble size is achieved. Without being bound by theory, it is believed that making use of certain properties of surfactants can allow bubble size to be controlled. In particular, it is believed that the CAC, SST and DST (as defined above) of the surfactants, and the inter-relationship between them can form the basis from which a surfactant may be chosen to enable a desired bubble size. Preferably, therefore, the surfactant may be chosen to control bubble size according to certain properties of the surfactant, and, in particular, the CAC, SSC and DST and their inter-relationship as discussed above. More preferably, the surfactant is chosen such that it meets certain predetermined criteria relating to the properties of the surfactant such that the desired size of bubbles is formed in the ink-j et receiver. Preferably, the surfactant is selected from Surfactant 1, Surfactant 2 and Surfactant 3, as defined above, according to the desired bubble size. A mixture of surfactants having appropriate properties may also be utilised. In accordance with step B of the method of the present invention, the pH of the polymer solution is preferably reduced to a value of less than pH 6 before addition of the blowing agents, since it has been found that if the pH of the solution is dropped, or maintained at a level of less than pH 6, before the blowing agents are added or the blowing agents are dual melted into a layer in which the pH has been reduced, the surface roughness of the final coating is significantly reduced. More preferably, the pH is reduced to a value of 5 or below, for example to about pH 2 or about pH 4 or to a pH in the range from 2 to 5. Still more preferably, the pH is reduced to a value of 4 or below, and most preferably to a pH value in the range 2 to 4. If the blowing agents are added to the coating solution prior to coating, in the manner described above, it is possible that gas bubbles can form prior to coating. Whether or not bubbles are formed depends on the temperature required for initiation of the decomposition of the blowing agent or agents. When gas bubbles are present in the coating solution it has been found that they can act as nucleation sites for other bubbles to form around when the blowing agents decompose vigorously in the drying section of the coating track. This results in quite rough surfaces on the ink-jet receiver. Coating quality can also be affected when the pre-formed bubbles pass down the hopper, causing lines, streaks and edge retraction. It has been found that if the blowing agents are dual melted into one of the layers at the hopper there is not enough time or heat available for the blowing agents to begin to decompose before the coating process begins.

Therefore no bubbles are pre-formed, the bubbles not beginning to form until the coating solution containing the blowing agents passes into the dryers where the heat can initiate the gas formation. As there are no pre-formed bubbles to act as nucleation sites for new bubbles to form around significantly smoother surfaces can be achieved on the ink-jet receiver. The coating quality is also improved due to there being no pre-formed bubbles in the coating solution. If two or more components are required for initiation of decomposition of the blowing agents the prevention of any pre-formed bubbles can also be achieved by adding one of the components to the coating solution prior to coating and dual melting the other one or more at the hopper. This method prevents the components being able to react until they all come together in the hopper. A further method of achieving prevention of initiation of decomposition is to add each component required to a separate layer, if two or more layers of coating solution are coated onto the support, of the coating. Once again, this method prevents the components being able to react until all the layers are coated together. Improved surface quality and coating quality can be achieved by preventing the initiation of the decomposition of the blowing agents prior to coating. Should it be desired to obtain to obtain an ink-jet receiver having small bubbles, which may be useful, for example, for use with_, a dye based ink, it is preferable to select a surfactant that can control the average bubble size to be less than 10 μm, preferably in the range 3-8 μm. A suitable such surfactant is, for example, Surfactant 1, defined above. Accordingly, in another aspect of the invention, there is provided an ink-jet receiver having an ink-receiving layer comprising a foamed hydrophilic polymer having an average pore size of less than 10 μm and preferably in the range 3 to 8 μm. Should, on the other hand, it be desired to obtain an ink-jet receiver having larger bubbles, which may be useful, for example, for use with a pigment based ink it is preferable to select a surfactant that can control the average bubble size to be at least 10 μm, preferably at least 11 μm and most preferably in the range 11-15 μm. A suitable such surfactant is, for example, Surfactant 2 or Surfactant 3, defined above. Accordingly, in another aspect of the invention, there is provided an ink-jet receiver having an ink-receiving layer comprising a foamed hydrophilic polymer having an average pore size of at least 10 μm and preferably in the range 11 to 15 μm. In a preferred embodiment of the method of printing according to the present invention, the method farther comprises applying pressure and/or heat to a print generated using an ink-jet printer on an ink-jet receiver comprising a foamed polymer ink-receiving layer, obtainable by the above described methods. Surface properties of the print that may be improved by the method of printing include surface roughness (i.e. generating a print with a smoother surface) and glossiness. Preferably, the method of printing comprises applying heat and pressure to the print. The heat and pressure may be applied to the print, for example by the use of a fusing device. In a preferred embodiment, the ink-jet print is treated by the application of heat and/or pressure using a belt fαser or a nip roller. In any case, it is preferable that the means for applying heat and/or pressure to the print, e.g. a fusing device, is integral to or associated with the ink- jet printer. Typical heat and pressure conditions applied using a belt fuser at a rate of ~25mm s (0.5 inches per second (IPS)) are a temperature of 150°C (300 ) and 1080 kg/m (60 lbs/inch) nip pressure. The treatment conditions may be varied depending on the degree of gloss, surface roughness, etc. desired, and of course on the properties of the particular foamed polymer material. On a more general application, the conditions for applying heat and/or pressure to the voided polymer receiver, especially a foamed polymer receiver, may range from 40-200°C, preferably in the range 60-160°C and up to 2100 kg/m (120 lbs/inch) nip pressure, preferably from 720-1800 kg/m (40-100 lbs/inch) nip pressure. The rate that the receiver is passed, for example through a fusing device, may range from 6.25 to 500 mm s, preferably from 10 to 250 mm/s. - Depending upon the amount of heat and/or pressure applied to the receiver, and on the specific properties of the voided polymer layer utilised in the invention, further benefits in image density, image stability and water fastness may be exhibited. Ink-jet inks for use according to the present invention may be any suitable inks, many such inks being known in the art, and are typically liquid compositions comprising a solvent or carrier liquid (such as water or aqueous alcohol solution), dyes and/or pigments, humectants, organic solvents, detergents, thickeners, preservatives and the like. The precise qualities of the foamed polymer receiver, such as a foamed polymer receiver, chosen may depend on the requirements of the type of printing and the type of ink and vice versa. ?Th.e invention is illustrated, without limitation, by the following Examples.

EXAMPLES Examples 1-3 were carried out to demonstrate the effect of surfactant on bubble size.

Example 1 A resin-coated paper support was coated on one side, simultaneously, using a standard slide hopper, with three layers. Each layer comprised of polyvinyl alcohol (PNA), blowing agents (a total of 50% by weight compared to the PNA laydown) and some of Surfactant 1, which has the formula: Surfactant 1

where Rf is a range of fluorocarbon chain lengths based on the general structure C_nF_2n+ι, where typically n possesses the following series of values, 6, 8, 10, 12, and 14.

The surfactant and the blowing agent were added to the PNA solution at a pH of 6 prior to coating the support. The layer coated nearest the support consisted of 6.1 g/m² of PNA, 1.72 g/m² of sodium nitrite, 1.33 g/m² of ammonium chloride and 0.106 g/m² of Surfactant 1. The middle layer consisted of 6.7 g/m² of PNA, 1.89 g/m² of sodium nitrite, 1.46 g/m² of ammonium chloride and 0.212 g/m² of Surfactant 1. The top layer consisted of 7.3 g/m² of PNA, 2.06 0 0 g/m of sodium nitrite, 1.59 g/m of ammonium chloride and 0.318 g/m of Surfactant 1. To initiate the blowing process, the dryers inside the coating track were set to 90°C through which the coating of this invention and the control were passed.

Example 2 The method according to Example 1 was repeated except that Surfactant 2, which has the following formula, was used in place of Surfactant 1. Surfactant 2

where the terminal group "T" is H.

Example 3 TThe method according to Example 1 was repeated except that Surfactant 3, which has the following formula, was used in place of Surfactant 1.

Surfactant 3

where m + n = 10 on average The scanning electron micrographs shown in Figures 2 to 4 are sections through the resultant materials formed using, respectively, Surfactant 1, Surfactant 2 and Surfactant 3 in Examples 1-3 above. The micrographs indicate that Surfactant 1 (Figure 2) produces bubbles that are considerably smaller than those produced by Surfactant 2 (Figure 3) and Surfactant 3 (Figure 4). ?The scanning electron micrographs are drawn schematically in Figures 5 to 7, corresponding respectively to Figures 2 to 4. In each of Figures 5 to 7, a support 14 is covered with a layer 16 of foamed polymer. It can be seen that the bubbles 18 are larger in the material formed using Surfactant 2 than those in the material formed using Surfactant 1. Similarly, the bubbles in the material formed using Surfactant 3 are larger than those in the material formed using Surfactant 1. Table 1 shows the average bubble size that is achieved when using each of the surfactants.

Table 1

The bubble size was measured by placing a randomly chosen area of each coating under the light microscope and a micrograph was then taken using image analysis software (Soft Imaging System, SiS). Prior to taking the micrograph, the software was set to the chosen magnification that had previously been accredited using accredited stage micrometer A818. The diameter often randomly chosen bubbles was then measured and the average size calculated. By measuring the static and dynamic surface tensions of solutions containing each surfactant at various concentrations and plotting the results as a function of log(concentration), the logarithms of the critical aggregation concentration and the midpoint of the dynamic surface tension curve can be identified. Any suitable method may be used to measure dynamic and static surface tension of liquids. In the present examples, the surface tensions of a range of concentrations of the test surfactant are measured in the trial coating composition under a standard set of conditions at 40°C. The concentration of the surfactant was usually varied from 0.001 to 1 wt% in log concentration intervals of ~0.5. Higher or intermediate concentrations were sometimes measured as necessary to improve estimates of critical aggregation concentration or the midpoint of the dynamic surface tension curve. Both the static surface tension SST and dynamic surface tension DST measurements were made using the Wilhelmy blade method as described by Padday, J F, 2^nd Int. Congress of Surface Activity, Butterworths, 1957, 1, 1. The DST measurements were made with an overflowing circular cylinder, having a diameter of 37.5 mm and a liquid overflow rate of ~9 ml/sec. The data was obtained by raising the surface of the flowing liquid until it just touched the Wilhelmy blade, momentarily dipping the blade by electromechanical means to induce wetting, and taking a final reading 60 seconds later. Other suitable methods of measuring dynamic surface tension would be any technique that offers similar dynamic time scales (surface age) i.e. of the order of 0.05 to 0.25 seconds. Examples include the maximum bubble pressure method and the falling curtain method. The SST measurements were not true equilibrium values, but values taken after a defined period. SST values were obtained by, stopping the flow in the dynamic cell, waiting 30 seconds, raising the surface of the liquid until it just touches the Wilhelmy blade, momentarily dipping the blade by electromechanical means to induce wetting, and taking a final reading 60 seconds later, i.e. 90 seconds after stopping the flow

Example 4 Example 4 was carried out to demonstrate the effect of preventing the activation of the blowing agents until after coating. A resin-coated paper support was coated on the front simultaneously, on a bead-coating machine using a standard slide hopper, with three ink-receiving layers to form two coatings - coating A (a control) and coating

B. Each layer comprised polyvinyl alcohol (PNA), blowing agents (a total of 50% by weight compared to the PNA laydown) and some of Surfactant 1 (defined above, and available as Lodyne™ SI 00). In both coatings A and B, the blowing agent was added to PNA solution having a pH of 6. Coating A was a control coating in which the blowing agents were added directly to the polymer solutions prior to coating. In coating A, the ink-receiving layer nearest the support consisted of 5.7 g/m² of PNA, 1.61 g/m² of sodium nitrite, 1.24 g/m² of ammonium chloride and 0.106 g/m of Surfactant 1. The middle ink-receiving layer consisted of 6.2 0 0 0 g/m of PNA, 1.75 g/m of sodium nitrite, 1.35 g/m of ammonium chloride and 9 O 0.212 g/m of Surfactant 1. The top ink-receiving layer consisted of 7.1 g/m of 9 9 ^*"

PNA, 2.00 g/m of sodium nitrite, 1.55 g/m of ammonium chloride and 0.318 g/m² of Surfactant 1. Therefore the total PNA laydown of the entire coating pack was 19.0 g/m² and the total laydown of the blowing agents was 9.5 g/m². Coating B was a coating where the blowing agents were dual melted into the top ink-receiving layer at the hopper. In coating B the ink-receiving layer nearest the support consisted of 9 9

6.4 g/m of PNA and 0.106 g/m of Surfactant 1. The middle ink-receiving layer consisted of 7.2 g/m² of PNA and 0.212 g/m² of Surfactant 1. The top ink- 9 9 receiving layer consisted of 5.4 g/m of PNA and 0.318 g/m of Surfactant 1. The blowing agents were dual melted into the top ink-receiving layer at the time of coating. The 40% sodium nitrite solution was dual melted using a laydown of 9 0

13.4 mls/m (which is equivalent to 5.35 g/m of sodium nitrite). The 20% ammonium chloride solution was dual melted using a laydown of 20.8 mls/m²

(which is equivalent to 4.15 g/m of ammonium chloride). Therefore the total PNA laydown of the entire coating pack was 19.0 g/m and the total laydown of the blowing agents was 9.5 g/m i.e. the same as for coating A. To initiate the blowing process, the dryers inside the coating track were set to 90 °C through which the coating according to the present invention, coating B, and the control coating, coating A, were passed. Figures 8 and 9 show scanning electron micrographs for coating A and coating B respectively. The figures indicate that bubble formation is unaffected by the method of addition of the blowing agents. This is important since the ink retention of the surface is therefore unaffected. Table 2 shows the surface roughness measurement from both coating A and coating B. The table shows how the method of addition of the blowing agent effects the surface roughness of the resulting ink receiving layer. Table 2

Rt = Maximum value from peak to valley Rz = Average peak to valley height Rpm = Average height

From the data in Table 2, it can be seen that significantly smoother surfaces are achieved when the blowing agents are dual melted (coating B) into one of the ink-receiving layers at the hopper (indicated by lower roughness figures), compared to adding the blowing agents to the PNA solutions prior to coating (coating A). It can thus be seen that the method of addition of the blowing agents can affect the surface characteristics and coating quality of a foamed polymeric inkjet reciever. Both improved surface quality and coating quality can be achieved by preventing the activation of the blowing agent(s) until after coating has taken place. Furthermore, the use of Surfactant 1 was also found to improve the surface smoothness of the ink-jet receiver. It will be understood by those skilled in the art that the invention is not limited to use with bead coating. Any conventional coating method may be used.

Example 5 A resin coated paper support was coated on the front with three ink-receiving layers. Each layer comprised polyvinyl alcohol (PNA) and some of Surfactant 1 (defined above and available as Lodyne™ SI 00). Blowing agents were either added to each layer at a rate of 50wt% with respect to the PNA laydown of that layer or dual melted into the top layer at the coating point at a rate of 50wt% compared to the total PNA laydown of the coating. In the first examples, (coating C and coating D), the ink-receiving 9 9 layer nearest the support consisted of 5.0 g/m of PNA, 1.41 g/m of sodium 9 9 nitrite, 1.09 g/m of ammonium chloride and 0.106 g/m of Surfactant 1. The 9 9 middle ink-receiving layer consisted of 5.7 g/m of PNA, 1.61 g/ of sodium nitrite, 1.24 g/m² of ammonium chloride and 0.212 g/m² of Surfactant 1. The top 9 9 ink-receiving layer consisted of 6.9 g/m of PNA, 1.94 g/ of sodium nitrite, 1.51 g/m² of ammonium chloride and 0.318 g/m² of Surfactant 1. Therefore the total PNA laydown of the entire coating pack was 17.6 g/m² and the total laydown of the blowing agents was 8.8 g/m . For coating C, the pH of the polymer solution was adjusted down to pH 4.0 with sulphuric acid before the sodium nitrite and ammonium chloride were added. For coating D, the pH of the polymer solution was left unadjusted at pH 6.0. Coating D is a control coating. In each case, the three layers were coated simultaneously on a bead-coating machine using a standard slide hopper. In the next examples, (coating H, coating E, coating F and coating G), the ink-receiving layer nearest the support consisted of 5.7 g/m of PNA and 0.106 g/m² of Surfactant 1. The middle ink-receiving layer consisted of 6.5 g/m² of PNA and 0.212 g/m of Surfactant 1. The top ink-receiving layer consisted of 5.4 g/m² of PNA and 0.318 g/m² of Surfactant 1. For coating H the pH of the polymer solution was adjusted to pH 2.0 using sulphuric acid. For coating E the pH of the polymer solution was adjusted to pH 4.0 using sulphuric acid. For coating F the pH of the polymer solution was adjusted to pH 5.0 using sulphuric acid. For coating G the pH of the polymer solution was left unadjusted at pH 6.0. For each coating the blowing agents were then dual melted into the top ink-receiving layer. The 40% sodium nitrite solution was dual melted using a laydown of 12.4 mls/m² (which is equivalent to 4.96 g/m² of sodium nitrite). The 20% ammonium chloride solution was dual melted using a laydown of 19.2 9 0 mls/m (which is equivalent to 3.84 g/m of ammonium chloride). Therefore the total PNA laydown of the entire coating pack was 17.6 g/m and the total laydown of the blowing agents was 8.8 g/m² i.e. the same as for coating A and coating B. Again, the three layers were coated simultaneously on a bead-coating machine using a standard slide hopper. To initiate the blowing process the dryers inside the coating track were set to 90°C. Each of the coatings passed through the dryers. Figures 10, 11, 12, 13 and 14 show that the bubble formation is unaffected by either the pH of the polymer solution or the method of addition of the blowing agent. Figure 10 shows coating C where the polymer solution pH was adjusted to pH 4 and the blowing agents were added directly to the solution. Figure 11 shows coating E where the polymer solution pH was adjusted to pH 4 and the blowing agents were dual melted into the top ink- receiving layer at the hopper. Figure 12 shows coating F where the polymer solution pH was adjusted to pH 5 and the blowing agents were dual melted into the top ink- receiving layer at the hopper. Figure 13 shows coating G where the polymer solution pH was left ^■unadjusted at pH 6 and the blowing agents were dual melted into the top ink- receiving layer at the hopper. Figure 14 shows coating H where the polymer solution pH was adjusted to pH 2 and the blowing agents were dual melted into the top ink- receiving layer at the hopper. Table 3 below shows the surface roughness measurements from all of the coatings.

Table 3

Rt = Maximum value from peak to valley ? 2; = Average peak to valley height Rpm = Average height

From the data in Table 3 above, it can be seen that the pH of the polymer solution has a significant effect on surface roughness. Irrespective of whether the blowing agents are added directly to the polymer solutions or dual melted into the top layer at the coating point, significantly smoother surfaces are achieved when the pH of the polymer solution is reduced from pH 6 down to pH 4. The data in the table also shows that at least where the blowing agents are dual melted into the top layer at the coating point, increasingly smooth surfaces are obtained by reducing the pH of the polymer solution to pH 5, to pH 4 and to pH 2

It will be understood by those skilled in the art that the invention is not limited to use with bead coating. Any conventional coating method may be used.

Example 6 An ink-jet receiver comprising a foamed polymer ink-receiving layer on a resin coated paper support was prepared. Three layers of a solution comprising polyvinyl alcohol (PNA) and Surfactant 1 (available as Lodyne™ SI 00), having a pH reduced to 4, were coated onto a resin coated paper support on a bead coating machine using a standard slide hopper. The layer nearest the support consisted of 5.7 g/m of PNA and 0.106 g/m² of Surfactant 1. The middle layer consisted of 6.5 g/m² of PNA and 0.212 g/m² of Surfactant 1. The top layer consisted of 5.4 g/m² of PNA and 0.636 g/m² of Surfactant 1. The blowing agents sodium nitrite and ammonium chloride were then dual melted into the top ink-receiving layer. The 40% sodium nitrite solution was dual melted using a laydown of 12.4 ml/m² (which is equivalent to 4.96 g/m² of sodium nitrite). The 20% ammonium chloride solution was dual melted using a 9 9 laydown of 19.2 ml/m (which is equivalent to 3.84 g/m of ammonium chloride). The total PNA laydown of the entire coating pack was 17.6 g/m and the total laydown of blowing agents was 8.8 g/m² (50% by weight as a proportion of the total PNA laydown). A control coating was prepared at the same time where the layers were identical to those described above, except the blowing agents (sodium nitrite and ammonium chloride) were omitted, i.e. this coating contained just PNA and Surfactant 1. To initiate the blowing process, the dryers inside the coating track were set to 90°C through which the coating used to demonstrate this invention and the control were passed. The coated support containing the PNA and the blowing agent resulted in a foamed receiver in which bubbles were formed throughout the three- layer pack. Figure 15 shows a cross-section of the foamed receiver. Both the foamed polymer coating and the PNA control were treated by applying heat and pressure by passing them through a belt fuser at 12.5 mm/s (0.5 inches per second (IPS)) at 150°C (300°F) and under 1080 kg/m (60 lbs/inch) nip pressure. . Both coatings were then compared to untreated samples for surface roughness and gloss, the results of which are presented in Table 4 and Table 5 respectively.

Table 4: The effect on surface roughness of applying heat and pressure treatment

Key. Rz = Average peak to valley height Rpm = Average height The data in Table 4 indicate that treating the foamed receiver by applying heat and pressure using a fusing device results in a large reduction in surface roughness, whereas it had no effect on the PNA control because that was already so smooth. Table 5: The effect on gloss of applying heat and pressure treatment

The data in Table 5 indicate that treating the foamed receiver by applying heat and pressure using a fusing device results in a large increase in gloss, whereas only marginally increases in gloss are seen when the PNA control is treated. The foamed polymer ink-jet receiver has gloss of 52.1 at 60°. It is considered that a gloss of greater than 40 at 60° is an acceptable level of gloss for an ink-jet print to be accepted by a consumer as a gloss print. From this example, it can be seen that treating the foamed receiver by applying heat and pressure using a fusing device results in large improvements in both surface roughness and gloss. These large improvements were not seen when a PNA coated support corresponding to a typical non-porous receiver control was treated.

Claims

CL IMS:

1. A method of manufacturing an ink-jet receiver comprising a foamed polymer ink-receiving layer, said method comprising coating onto a support a polymer solution, at least one blowing agent and, optionally, a surfactant, to form a coated support comprising at least one layer of a coated solution of a polymer, at least one blowing agent and, optionally, a surfactant; interacting with the coated solution to activate the at least one blowing agent to generate gas bubbles within the solution thereby causing foaming of the polymer; and drying the coated solution, which method further comprises at least two of

A) selecting a surfactant which enables the size of the bubbles formed to be controlled depending on whether or not a first criterion is met, which first criterion is that the critical aggregation concentration of the surfactant is substantially the same as the concentration associated with the midpoint of the dynamic surface tension curve of the surfactant; and, on whether or not a second criterion is met, which second criterion is that the surfactant has a low static surface tension; B) reducing the pH of the polymer solution prior to the addition of the at least one blowing agent; and

C) preventing activation of the at least one blowing agent until after the coated solution is formed.

2. A method as claimed in Claim 1, wherein, in step A, the second criterion is that the surfactant has a static surface tension of below 28 mN/m.

3. A method as claimed in Claim 2, wherein the second criterion is that the surfactant has a static surface tension of below 24 mN/m.

4. A method as claimed in any one of Claims 1 to 3, wherein, in step A, the first criterion is that the logarithm of the critical aggregation concentration of the surfactant is within about 0.5 log units of the logarithm of the concentration associated with the midpoint of the dynamic surface tension curve of the surfactant.

5. A method as claimed in any one of Claims 1 to 3, wherein, in step A, the first criterion is that the logarithm of the critical aggregation concentration of the surfactant is within about 0.25 log units of the logarithm of the concentration associated with the midpoint of the dynamic surface tension curve of the surfactant.

6. A method as claimed in any one of the preceding claims, wherein, in step A, the surfactant is selected in order to control the size of the bubbles formed.

7. A method as claimed in any one of the preceding claims, wherein, in step A, the critical aggregation concentration of the surfactant is substantially the same as the concentration associated with the midpoint of the dynamic surface tension curve of the surfactant; and, the surfactant has a low static surface tension.

8. A method as claimed in any one of the preceding claims, wherein the surfactant is a surfactant according to the formula

where Rf is a range of fluorocarbon chain lengths based on the general structure C_nF_2n+ι, where typically n possesses the following series of values, 6, 8, 10, 12, and 14. • ^' 9. A method as claimed in any one of the preceding claims, wherein, in step A, the surfactant is selected in order to provide an average bubble size of less than 10 μm.

10. A method as claimed in Claim 9, wherein, in step A, the surfactant is selected in order to provide an average bubble size in the range of 3 to 8 μm.

11. A method as claimed in any one of Claims 1 to 6, wherein, in step A, the first and/or the second criterion is not met.

12. A method as claimed in Claim 11 , wherein, in step A, tihe surfactant is selected in order to provide an average bubble size of at least 10 μm.

13. A method as claimed in Claim 12, wherein the surfactant is selected in order to provide an average bubble size in the range of 11 to 15 μm.

14. A method as claimed in any one of Claims 1 to 6, and 11 to 13, wherein the surfactant is a surfactant according to the formula

where the terminal group "T" is H.

15. A method as claimed in any one of Claims 1 to 6, and 11 to 13, wherein the surfactant is a surfactant according to the formula

wherein m + n = 10 on average.

16. A method as claimed in any one of the preceding claims, wherein the proportion by weight of surfactant to coated solution is from about 0.01% to about 2.0%.

17. A method as claimed in Claim 1, wherein the surfactant is a fluoro-surfactant.

18. A method as claimed in any one of the preceding claims, wherein, in step B, the pH of the polymer solution is reduced to a value of pH 5 or below.

19. A method as claimed in Claim 18, wherein the pH is reduced to a value of pH 4 or below.

20. A method as claimed in Claim 19, wherein the pH is reduced to a value in the range of pH2 to pH 4.

21. A method as claimed in any one of Claims 18 to 20, wherein the pH value is reduced by the addition of acid.

22. A method as claimed in any one of the preceding claims, wherein, in step C, the blowing agent is dual melted into a layer of polymer solution in the coating apparatus prior to coating of the polymer solution onto the support.

23. A method as claimed in any one of Claims 1 to 21 , wherein, in step C, the blowing agent comprises a first component and a second component and wherein the first component is added to the polymer solution prior to coating the polymer solution onto the support and the second component is added to the polymer solution either simultaneously or after coating the polymer solution onto the support.

24. A method as claimed in any one of Claims 1 to 21 , wherein, in step C, the blowing agent comprises a first component and a second component and wherein the first component is added to a first polymer solution for coating as a first layer and the second component is added to a second polymer solution for coating as a second layer, said first and second layers to be coated simultaneously.

25. A method as claimed in any one of the preceding claims, wherein heat is applied to the coated solution.

26. A method as claimed in Claim 25, wherein heat is applied to the coated solution during the drying step.

27. A method as claimed in any one of the preceding claims, wherein the polymer is a hydrophilic polymer.

28. A method as claimed in Claim 27, wherein the hydrophilic polymer is selected from the group consisting of polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone and gelatin.

29. A method as claimed in any one of the preceding claims, wherein the proportion by weight of blowing agent to polymer in the coated solution is up to about 200%.

30. A method as claimed in Claim 29, wherein the proportion by weight of blowing agent to polymer in the coated solution is from 5% to 60%.

31. A method as claimed in Claim 30, wherein the proportion by weight of blowing agent to polymer in the coated solution is from 30% to 50%.

32. A method as claimed in any one of the preceding claims, which comprises steps A and B.

33. A method as claimed in any one of the Claims 1 to 31, which comprises steps A and C.

34. A method as claimed in any one of Claims 1 to 31, which comprises steps B and C.

35. A method as claimed in any one of the preceding claims, which comprises steps A, B and C.

36. An ink-j et receiver obtainable by the method of any one of

Claims 1 to 35.

37. A method of printing comprising the steps of loading an ink-jet printer with an ink-jet receiver as claimed in Claim 36; and printing an image onto the ink-jet receiver using said printer to generate a print.

38. A method of printing as claimed in Claim 37, which further comprises applying pressure and/or heat to the print thereby improving the surface properties.

39. A method as claimed in Claim 38, wherein the application of pressure and/or heat to the print reduces the roughness and increases the gloss of the surface of the print.

40. A method as claimed in Claim 38 or Claim 39, wherein the application of pressure and/or heat to the print is carried out using a fusing device.

41. An ink-jet print obtainable by the method of any one of Claims 37 to 40.