Ink composition for inkjet printing

Abstract

To provide an ink formulation that enables an, optionally non-pigmented, ink composition that dries opaque, e.g. opaque white.SOLUTION: There is disclosed an improved inkjet ink composition comprising: a cellulosic polymer for forming a porous network structure; a blend of a nonsolvent for the cellulosic polymer and a solvent for the cellulosic polymer, wherein the solvent is more volatile than the nonsolvent; a film forming binder with high polarity, wherein the film forming binder is separately soluble in both the nonsolvent and the blend. Evaporation of the solvent blend leaves behind a structure comprising a first solid phase of cellulosic polymer and a second solid phase of binder, which exhibits good opacity and improved abrasion resistance.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] It is known that white can be formed by precipitating organically soluble celluloses (e.g., ethyl cellulose) from a mixture of rapidly evaporating organic solvents and water, such as acetone and water. After the acetone evaporates, the cellulose phase separates from the water, forming a polymer network with water droplets intermixed throughout the solid phase. After the water evaporates, pores remain where the water droplets previously were, and air enters them. The difference in refractive index between the cellulose structure and air results in sufficient light scattering to produce an observable white color. Due to the heterogeneous nature of the opaque cellulose film, its structural strength, and therefore its abrasion resistance, is insufficient, and it can be easily removed with a single, gentle rub with a finger.

[0002] US Pat. No. 4,389,503 describes a solution to improve abrasion resistance by including a co-binder, i.e., a further binder in addition to the cellulose ester binder, but this has a significant adverse effect on the opacity of the deposited ink. Summary of the Invention [Problem to be solved by the invention]

[0003] The present invention has been made to improve this problem. [Means for solving the problem]

[0004] According to one aspect of the present invention, there is provided an inkjet ink composition comprising a cellulosic polymer for forming a porous network structure, a blend of a non-solvent for the cellulosic polymer and a solvent for the cellulosic polymer that is more volatile than the non-solvent, and a film-forming binder that is substantially insoluble in acetone alone and separately soluble in both the non-solvent and the blend.

[0005] When the ink composition is deposited on a substrate, the more volatile solvent evaporates first. The resulting increase in the concentration of the nonsolvent in the blend leads to the precipitation of the cellulosic polymer, which forms a network structure containing pores or voids. The high polarity of the film-forming binder, which makes it essentially insoluble in acetone but soluble in the nonsolvent, allows the film-forming binder to remain in the liquid nonsolvent while the cellulosic polymer phase separates from the nonsolvent, thereby preventing the film-forming binder from coalescing into the porous network structure. As a result, once all the solvent blend has evaporated, a heterogeneous structure exhibiting two glass transition temperatures is obtained, consisting of a highly scattering porous cellulosic polymer layer as the first solid phase and a coherent film of the binder as the second solid phase.

[0006] Thus, the film-forming binder of the claimed composition provides improved adhesion of the print deposit to the substrate while maintaining the highly scattering open structure of the cellulosic polymer film that imparts good opacity.

[0007] Thus, the ink formulations of the present invention allow for opaque, eg, opaque white, drying, optionally non-pigmented ink compositions.

[0008] This contrasts with the co-binders of U.S. Patent No. 4,389,503, which, due to their compatibility with cellulose, tend to coalesce with the cellulose to form a single solid membrane, a combination that inhibits the formation of a network structure and light-reflecting pores.

[0009] The non-solvent preferably comprises water.Water is generally the preferred non-solvent because it is cheap, non-toxic, and many preferred cellulose-based polymers are insoluble in water.Nevertheless, depending on the selected cellulose-based polymer, certain non-aqueous non-solvents may be used instead or in combination with water, for example, ethylene glycol and / or propylene glycol.

[0010] Preferably, the non-solvent is present at greater than 10 weight percent before evaporation of the blend. Higher non-solvent percentages result in more non-solvent droplets in the deposited layer, leading to more voids in the resulting ink, which in turn leads to a larger film thickness, resulting in a more opaque ink.

[0011] When the non-solvent comprises water, the cellulosic polymer may comprise one or more of a cellulose ester and a cellulose ether. When an aqueous solvent and a non-aqueous non-solvent are used, alternative cellulosic polymers may be used, including, for example, one or more of methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, or nanocellulose.

[0012] Cellulose esters are generally preferred as they provide better abrasion resistance compared to cellulose ethers.

[0013] More preferably, the cellulosic polymer may include one or more of cellulose acetate propionate and cellulose acetate butyrate, both of which have high solubility in organic solvents, with acetone and blends of acetone and ethanol being the preferred solvents.

[0014] The lower limit of the cellulosic polymer content depends on the acceptable level of opacity required for the resulting film deposit. Increasing the cellulosic polymer content increases the opacity and also increases the viscosity of the liquid ink. The upper limit of the acceptable cellulosic polymer content is typically limited by the maximum acceptable viscosity of the ink. In certain applications, the composition may contain 3 to 10 weight percent cellulosic polymer before evaporation of the blend.

[0015] Because most suitable cellulosic polymers are highly insoluble in water, the solvent for the cellulosic polymer is typically an organic solvent or a blend of organic solvents. Examples of suitable solvents include one or more of acetone, methanol, ethanol, and n-propanol.

[0016] The solvent preferably comprises one or more of acetone and ethanol. The optimized composition may include a mixture containing both acetone and ethanol, which, due to their different volatilities, allows for fine tuning of the evaporation rate and / or solubility of the cellulosic polymer.

[0017] The film-forming binder may comprise a polymer, oligomer, or organic molecule that is insoluble in acetone without the presence of a protic cosolvent, such as water or ethanol.

[0018] The highly light-scattering properties of the cellulose layer also make it structurally very weak, so there are potentially many film-forming binders that can form films with greater strength than the highly scattering cellulose layer, thus improving the abrasion resistance of the deposit. The selection of a preferred film-forming binder can be made by considering the relative affinity of the cellulose-based polymer and film-forming binder for the substrate, such as glass, metal, or plastic, onto which the deposit will be printed.

[0019] The film-forming binder may include an ionic polymer and a corresponding non-polymeric counterion. The non-polymeric counterion is volatile so that the film-forming binder in the heterogeneous structure includes the non-ionic polymer. The ionic polymer can be formed by neutralizing an acidic or basic polymer. Generally, film-forming binders containing ionic polymers are preferred because they produce a water-insensitive (i.e., water-insoluble) deposit after evaporation of the neutralized non-polymeric counterion.

[0020] An additional advantage of using an ionic film-forming binder is that it is electrically conductive. This allows for the creation of conductive inks without the need for additional conductive agents. Thus, the water and film-forming binder may be present in the composition in an amount sufficient to provide a conductivity of at least 400 microsiemens per centimeter, with or without additional conductive agents.

[0021] Examples of suitable film-forming binders, including nonionic polymers, include one or more of polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyethylene glycol, polyethyloxazoline, polyhydroxyethyl acrylate, polydimethylaminoacrylate, polyhydroxyethyl methacrylate, polydimethylamino methacrylate, polyvinyl alcohol, and nanocellulose. Experiments have shown that polyvinylpyrrolidone is effective. Other compounds are likely to be effective because they are soluble in water, allowing them to form films from the aqueous phase while also being soluble in blends of organic solvents and water.

[0022] Examples of suitable film-forming binders comprising ionic polymers include one or more of amine / ammonia-neutralized acrylic polymers, copolymers comprising amine- and / or ammonia-neutralized acrylic polymers and amine- and / or ammonia-neutralized methacrylic polymers, copolymers comprising amine / ammonia-neutralized methacrylic polymers, amine / ammonia-neutralized rosin, and amine / ammonia-neutralized rosin-maleic acid modified rosin, amine / ammonia-neutralized styrene maleic anhydride, copolymers comprising amine / ammonia-neutralized styrene maleic anhydride and carboxylic acid-neutralized polydimethylaminoacrylate, carboxylic acid-neutralized polydimethylamino methacrylate, amine- and / or ammonia-neutralized carboxymethylcellulose, and amine- and / or ammonia-neutralized carboxymethylcellulose acetate butyrate.

[0023] Among these, amine- and ammonia-neutralized acrylic polymers, amine- and ammonia-neutralized methacrylic polymers, amine-neutralized rosin, and maleic acid-modified rosin have been proven effective through experiments by the present inventors.

[0024] Others are soluble in water, which is considered reasonable in view of the fact that they are expected to be soluble in blends of organic solvents and water, allowing them to form films from an aqueous phase.

[0025] More preferably, the film-forming binder comprises an acrylic resin neutralized with an amine and / or ammonia.

[0026] Generally, the abrasion resistance of the dried, deposited ink increases with increasing weight percent of the film-forming binder. Preferably, the film-forming binder is present in an amount sufficient to form a separate, bonded film layer upon evaporation of the solvent blend for bonding the light-scattering cellulose layer to the substrate, although any amount that provides improved abrasion resistance compared to the cellulose film alone is advantageous. Experiments have shown that compositions containing a nonionic film-forming binder present at 2 weight percent provide good abrasion resistance. For ionic film-forming binders, the 2% figure refers to the free acid or free base component (e.g., polymer component) of the film-forming binder. Weight percentages below 2% have not been tested, but are expected to be at least partially effective.

[0027] The amount of film-forming binder present is limited by the reduction in opacity of the resulting print deposit. Experiments have shown that compositions containing weight percent ratios of cellulosic polymer to film-forming binder polymer between 4:1 and 1:1 provide acceptable opacity, i.e., 80% or greater. Deposits formed using a 1:2 ratio were transparent. This is speculated to be a result of the binder polymer filling voids in the cellulosic web, inhibiting light scattering. Ratios between 1:1 and 1:2 have not yet been tested.

[0028] According to another aspect of the present invention, there is provided a print deposit comprising a light-scattering layer having a porous network structure comprising a cellulosic polymer and a binder layer, the binder layer being at least partially between the light-scattering layer and a substrate on which the print deposit is located, and binding the light-scattering layer to the substrate. [Brief explanation of the drawings]

[0029] [Figure 1] 1 illustrates the stages in the formation of an opaque, non-uniform print deposit containing a highly scattering layer. [Figure 2] Scanning electron microscope image of a printed deposit of highly scattering cellulose film without a binder layer (Figure 2). [Figure 3] 1 is a scanning electron microscope image of a print deposit with a heterogeneous structure including a highly scattering cellulose film and a distinct binder layer. [Figure 4] 1 is a scanning electron microscope image of a print deposit of a prior art formulation in which cellulose and binder are combined. DETAILED DESCRIPTION OF THE INVENTION

[0030] Example of a compound Codes composed of droplets of each of the following non-limiting liquid ink formulations were deposited onto a glass substrate using a Domino® 60 μm Ax series continuous inkjet printer in an air-conditioned laboratory with a room temperature of approximately 21 degrees Celsius and humidity below 40%, although this was not strictly controlled.

[0031] The abrasion resistance of the dried deposits was measured using a Taber Linear Abrasion Tester - Model 5750, using a CS-5 Calibrase felt tip and an applied force of 350 g. Each of the following formulations provided satisfactory results that were considered to require at least 20 rubs to show signs of damage to the printed code.

[0032] The opacity of the dried droplets was measured using an X-Rite eXact spectrophotometer on films hand drawn onto glass substrates using a 76 μm K bar. Each of the following formulations provided satisfactory results of at least 80% opacity.

[0033] [Table 1]

[0034] Cellulose acetate propionate was used as the cellulosic polymer. Water was used as the non-solvent for the cellulosic polymer. A blend of acetone and ethanol was used as the solvent for the cellulosic polymer. A carboxylic acid-functional acrylic resin containing aminomethylpropanol was used as the film-forming binder. The aminomethylpropanol neutralizes the acrylic, making it ionic and water-soluble. As a result of its ionic nature, the formulation does not require a separate conductive agent to enable deposition by continuous inkjet printing.

[0035] [Table 2]

[0036] [Table 3]

[0037] [Table 4]

[0038] [Table 5]

[0039] [Table 6]

[0040] [Table 7]

[0041] Lithium nitrate is used as the conductive agent in Example 7. As PVP is a non-ionic material, it does not impart conductivity and therefore a separate ionic material is required to make the formulation printable by continuous inkjet.

[0042] FIG. 1 illustrates the stages in the formation of a heterogeneous print deposit formed from an inkjet ink composition such as those exemplified above. Ink droplets 10, containing a cellulosic polymer, a film-forming binder, and a blend of solvent and water, are deposited onto a substrate 11 by an inkjet printing process.

[0101] One or more of the more volatile organic solvents preferentially evaporate, leaving behind a fluid containing a higher proportion of water. This causes phase separation within the droplet, resulting in a cellulose phase and an aqueous phase.

[0102] The film-forming binder is present substantially exclusively in the aqueous phase. As the water evaporates, the evaporated droplets leave behind a porous cellulose network structure with numerous voids that impart high light-scattering properties to the deposit. When all the water has evaporated, a heterogeneous structure consisting of a highly light-scattering cellulosic web layer 12

[0103] and a binder layer 13, consisting primarily of the film-forming binder, located between the cellulosic web layer and the substrate and essentially binding the cellulosic polymer to the substrate, is left. As a result of the non-uniform structure, the print deposit exhibits two Tg values, one associated with the cellulosic web layer 12 and the other associated with the binder polymer layer 13 .

[0043] Figures 2, 3, and 4 are scanning electron microscope images, where Figure 2 provides a comparison of a deposit of a highly scattering cellulose film without a binder layer, Figure 3 provides a heterogeneous structure comprising a highly scattering cellulose film with a binder layer formed using one of the exemplary ink formulations described above, and Figure 4 provides a cellulose film with a compatible binder similar to that used in U.S. Patent No. 4,389,503. It can be seen that the deposit in Figure 3 preserves the light-scattering porous structure to a significantly greater extent than that shown in Figure 4, and therefore the deposit in Figure 3 has improved opacity over the deposit in Figure 4.

Claims

1. 1. An ink-jet ink composition comprising: a cellulose-based polymer for forming a porous network structure; a blend of a non-solvent for the cellulosic polymer and a solvent for the cellulosic polymer, the solvent being more volatile than the non-solvent; a film-forming binder that is substantially insoluble in acetone alone and is separately soluble in both said non-solvent and said blend; 1. An ink-jet ink composition comprising:

2. The composition of claim 1 , wherein the non-solvent comprises water.

3. The composition of claim 2 , wherein the cellulosic polymer comprises one or more of a cellulose ester and a cellulose ether.

4. The composition of claim 3 , wherein the cellulosic polymer comprises one or more of cellulose acetate propionate and cellulose acetate butyrate.

5. 10. The composition of any preceding claim, wherein the solvent comprises one or more of acetone, methanol, ethanol and propanol.

6. The composition of claim 5 , wherein the solvent comprises acetone and ethanol.

7. 10. The composition of any preceding claim, wherein the film-forming binder comprises an ionic polymer and a corresponding non-polymeric counterion.

8. 10. The composition of any preceding claim, wherein the film-forming binder comprises a carboxylic acid functional acrylic neutralized with a volatile amine and / or ammonia.

9. The composition of any preceding claim, wherein the film-forming binder comprises polyvinylpyrrolidone.

10. 2. The composition of any preceding claim, wherein the non-solvent is present in greater than 10 weight percent.

11. The composition of claims 2 and 7, and optionally any of claims 3-6 and 8-10, wherein the water and film forming binder are present in an amount sufficient to impart to the composition a conductivity of at least 400 microSiemens / centimeter, regardless of the presence of additional conductive agents.

12. A printer ink cartridge containing the ink-jet ink composition according to any one of claims 1 to 11.

13. A print deposit comprising a light scattering layer having a porous network structure comprising a cellulose-based polymer and a binder layer, the binder layer being between the light scattering layer and a substrate on which the print deposit resides, bonding the light scattering layer to the substrate.

14. 12. A method of printing comprising providing a composition according to any one of claims 1 to 11, depositing said ink composition on a substrate, and optionally drying said deposited composition.

15. An article marked with a print deposit using the method of claim 14.

16. 1. An ink-jet ink composition comprising: A cellulosic polymer; a non-solvent for the cellulosic polymer; a solvent for the cellulosic polymer, the solvent being more volatile than the non-solvent; a film-forming binder that is separately soluble in both the non-solvent and the solvent blend of the solvent and the non-solvent; Including, an ink-jet ink composition, characterized in that the cellulosic polymer and the film-forming binder are incompatible, and upon evaporation of both the solvent and non-solvent, the cellulosic polymer and the film-forming binder form a heterogeneous structure exhibiting two glass transition temperatures.

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