EP1960213A1

EP1960213A1 - Recording materials for ink-jet printing

Info

Publication number: EP1960213A1
Application number: EP06830212A
Authority: EP
Inventors: Volker Schädler; Chrystelle Egger; Roland Ettl; Wolfgang Schmidt; Frank Konietzni
Original assignee: BASF SE; Felix Schoeller Jr Foto und Spezialpapiere GmbH
Current assignee: BASF SE; Felix Schoeller Jr Foto und Spezialpapiere GmbH
Priority date: 2005-12-09
Filing date: 2006-11-30
Publication date: 2008-08-27
Also published as: US8017189B2; US20110244146A1; JP5339917B2; DE102005059321A1; US8329266B2; JP2009518201A; US20080305286A1; WO2007065841A1

Abstract

The invention relates to a method for producing recording materials that can be printed using an ink-jet printer, said materials having a gel layer and the method being characterised by the following steps: a) a supporting material is coated with a dispersion or solution of an organic gelatinising agent, which can be chemically cross-linked by polycondensation or polyadduct formation; b) the gel is then formed by polycondensation or polyadduct formation; and c) finally the gel is dried.

Description

RECORDING MATERIALS FOR INK-JET

The invention relates to a process for the production of recording materials which can be printed with a color jet printer (ink-jet) and which have a gel layer, characterized in that a) a support with a dispersion or solution of an organic gel former, rather by polycondensation or polyadduct formation is chemically crosslinkable, is coated,

b) subsequently causing gel formation by polycondensation or polyadduct formation and

c) the gel is finally dried.

The invention further relates to the substrates obtainable by this process, in particular papers, for ink-jet printing.

With ink-jet printing, ink is applied from a storage container to the substrate to be printed; With the "drop on demand" process, the storage vessel moves and the paint is applied at the desired location, with the "continuous drop" process, a continuous color jet is applied on the way to the substrate e.g. distracted by electrostatic charge, so that the mark appears on the substrate in the desired position in the desired shape and color.

Papers for ink-jet printing are generally made up of several layers. There is a barrier layer on the base paper to prevent color from diffusing into the base paper. The color receiving layer follows the barrier layer. The ink receiving layer alone absorbs the printing ink. As much color as possible must be able to be taken for a high image quality. At the same time, the printing process and the subsequent drying should only take as short a time as possible.

The quality of the image and also the duration of the printing process are therefore essentially determined by the properties of the color receiving layer. So far, the ink-receiving layer has usually contained inorganic pigments for receiving the printing ink. In Journal of SoI-GeI Science and Technology 13, 147-152 (1998), e.g. B. color receiving layers of colloidal silicates or aluminates are described. The pigments are combined with polyvinyl alcohol as a binder and solidified into a porous three-dimensional structure (gel layer).

Papers for ink-jet printing are relatively expensive due to their complicated layer structure and especially due to the high content of inorganic pigments. Such papers could be significantly cheaper if the inorganic pigments were replaced by cheaper raw materials. However, the properties of the papers should not be impaired if possible. Even without inorganic pigments, the printability, in particular also the printing and drying speed, and the image quality should therefore meet high requirements.

Color-receiving layers made from organic polymers have also already been described. According to US Pat. No. 6,265,059, emulsion polymers are coagulated to form the ink-receiving layer. EP-A 191 645 describes the complex formation from an acidic and basic polymer to form the color receiving layer.

EP-A 1 020 300 describes a mixture of two polymers that dries to a gel. According to abstract, JP -A 708121 1 relates to the production of a color receiving layer by irradiation of a water-soluble polymer, e.g. a polyacrylic acid or polyacrylamide.

The color-receiving layers which have hitherto been obtainable with organic polymers have not yet reached a satisfactory level of properties.

The object of the present invention was a process for the production of recording materials for ink-jet printing, in which the content of inorganic pigments in the ink-receiving layer can be reduced or such pigments can be dispensed with entirely, the good application properties of the papers being retained as far as possible.

The method defined at the outset was accordingly found. The recording materials obtainable by this process and the use of the recording materials for ink-jet printing were also found.

Process step a)

Any substrate can be used as the carrier, preferably it is a cellulose-containing substrate, in particular a base paper, particularly preferably base paper, which has at least on the side to be coated with a barrier layer, for. B. is made of polyethylene. The barrier layer is intended to prevent color from penetrating the base paper. The base paper is particularly preferably provided with a barrier layer on both sides. The gelling agent is dissolved or dispersed in a solvent. Suitable solvents are water or organic solvents, especially those with a boiling point below 250 ° C. at 1 bar. Water, water-miscible organic solvents and mixtures of water with these solvents in any ratio are preferred. Water is particularly preferred. Aqueous solutions of the gel former are very particularly preferred.

A gel consists of a spatial network and a liquid that at least partially fills the interstices of the network. An essential feature of the invention is that this spatial network is formed from the organic gel formers by polycondensation and / or poly addition.

The liquid is preferably the above solvent, especially water (hydrogel).

Organic compounds which can be chemically crosslinked by polyaddition or polycondensation are considered as gel formers.

Polycondensation is understood to mean a chemical reaction in which water is split off. When an adduct is formed, the reactants react without elimination of water or another compound.

Examples of polyadduct formation are polyisocyanate polyadducts, in particular polyurethanes, which are obtained by reacting polyisocyanates with compounds containing hydroxyl or amino groups in a suitable organic solvent (solvogels).

Suitable polyisocyanate polyadducts are e.g. known from DE 10 2005 025 970.7 and the prior art cited therein. To form a three-dimensional network, the functionality of the polyisocyanates (ie average number of isocyanate groups per molecule) or the functionality of the compounds reactive with isocyanate (ie average number of hydroxyl and amino groups per molecule) should be greater than 2, preferably greater than 2.3, particularly preferably be greater than 2.8. In the context of the present invention, gels which are formed by polycondensation are preferred.

In particular, the organic gelling agent is a compound made from aromatic hydroxyl compounds and an aldehyde (phenol-aldehyde resin) or from amino compounds and an aldehyde (amino-aldehyde resin). The phenol-aldehyde resins are preferably reaction products of a low molecular weight aldehyde (molecular weight preferably less than 200 g / mol, in particular less than 100 g / mol) with a low molecular weight aromatic hydroxyl compound composed preferably of only one aromatic ring, which has at least one hydroxyl group and is optionally substituted by alkyl groups (molecular weight preferably less than 200, in particular less than 150 g / mol). The aldehyde is preferably formaldehyde, acetaldehyde or furfural, particularly preferably formaldehyde. The aromatic hydroxyl compound is preferably phenol or cresol.

The amino aldehyde resins are preferably reaction products of a low molecular weight aldehyde (molecular weight preferably less than 200 g / mol, in particular less than 100 g / mol) with a low molecular weight amino compound which contains at least two primary amino groups (molecular weight preferably less than 200, in particular less than 150 g / mol). The aldehyde is preferably formaldehyde, acetaldehyde or furfural, particularly preferably formaldehyde. The amino compound is preferably urea or melamine.

The phenol-aldehyde resins and amino-aldehyde resins are preferably solutions, in particular aqueous solutions. The reaction products from the above compounds are therefore not yet crosslinked or only to such an extent that the reaction products are still soluble in water (at 20 ° C., 1 bar).

Amino aldehyde resins are very particularly preferred. The molar ratio of aldehyde group to the reactive hydrogen atoms of the amino groups (primary amino groups have two reactive H atoms) is preferably 0.08 to 2 mol of aldehyde, preferably formaldehyde, to 1 mol of amino group.

The resins can be reacted with other compounds. Alcohols with which the methylol groups formed in the reaction with formaldehyde can be etherified are particularly suitable. In the later networking, i.e. further conversion of the methylol groups or etherified methylol groups, these alcohols are then split off. Suitable amino-formaldehyde resins are e.g. B. available from BASF as Kaurite®, Kauramine® and Luwipale®.

The solids content of the resin solution or dispersion is preferably between 2 and 50% by weight, the viscosity of the solution or dispersion being less than 5000 mPas, in particular less than 1000 mPas). The dispersion or solution of the gel former may contain other additives in addition to the gel former itself. For example, wetting agents are suitable which can bring about a better distribution and uniform coating of the gel former on the support. Examples include fluorosurfactants that reduce the surface tension on the substrate. The amount of wetting agent is preferably 0.1 to 3 parts by weight per 100 parts by weight of gelling agent (dry, without solvent). Additives which influence the subsequent pore size of the dried coating are also suitable. In particular, latex particles, organic or inorganic pigments, organic solvents, ionic and non-ionic surfactants, etc. may be mentioned. Catalysts which initiate or accelerate the gel formation which follows in process step b) are also particularly suitable. Information on the type of catalysts can be found in the following section.

On process step b)

The gel formation is then brought about by chemical crosslinking. The chemical crosslinking to the gel can be brought about by increasing the temperature, by irradiating with high-energy light, by changing the pH or by adding a catalyst or by a combination of these measures.

In the case of polyisocyanate polyaddition products, the addition reaction can be catalyzed by tin or organotitanium compounds. Method according to one of claims 1 to 9, characterized in that the chemical crosslinking is brought about by increasing the temperature, adding a catalyst or by increasing the temperature and adding a catalyst.

In the case of amino aldehyde resins, the crosslinking, i.e. the further reaction of the methyl groups or etherified methylol groups with one another or with amino groups, e.g. catalyzed by sulfuric acid or formic acid. Crosslinking is preferably carried out at temperatures from 30 to 100 ° C.

In order to form a suitable gel structure, it should be avoided that excessive drying takes place simultaneously with the crosslinking. Drying out of the gel during the crosslinking reaction can be prevented by high air humidity. The chemical crosslinking is therefore preferably carried out at least in part, in particular towards the end of the crosslinking reaction, under a relative atmospheric humidity of at least 50%, particularly preferably of at least 70%.

A two-stage process is particularly advantageous, in which the chemical crosslinking is carried out in a first stage only to the extent that after this first stage the partially crosslinked polymer is still present in solution or dispersion and the viscosity is preferably less than 5000 mPa ^* s. The second crosslinking stage (final crosslinking) is then preferably carried out at the relative air humidity indicated above. In particular, the coating obtained after crosslinking the gelling agent should contain at least 10% by weight of solvent, particularly preferably at least 20% by weight of solvent, based on the total weight of crosslinked gelling agent (gel) and solvent, before the final drying under atmospheric humidity; Process step c)

After crosslinking and the associated formation of the gel, drying can take place. The usual drying methods for removing the solvent, in particular water, can be used. Thermal or infrared technology processes are preferably used.

Suitable drying temperatures are e.g. B. between 30 and 100 ° C.

When drying, the solvent (water) is generally completely or to a residual content of less than 3% by weight, in particular less than 0.5% by weight, particularly preferably less than 0.1% by weight, based on the total weight removed from gel and any residual solvent.

The gel finally obtained preferably has pores. Small pores with a diameter of less than 10 μm are particularly important for use as a printable substrate. The diameter of these small pores is in particular in the range from 10 nm to 1 μm.

The proportion of these small pores is preferably at least 10% by volume (at 20 ° C.), particularly preferably at least 20% by volume, but the proportion is generally less than 70% by volume. The vol% refers to the total volume of the porous gel or the porous gel layer after drying.

The size and volume fraction of the pores is determined using the mercury intrusion method in accordance with DIN 66133. Mercury is pressed into a sample of the gel. Small pores require a higher pressure to be filled with Hg than large pores, and a pore size distribution can be determined from the corresponding pressure / volume diagram. The density of the gel is preferably 500 g / dm3 to 1200 g / dm ³ (20 ° C) The thickness of the dried gel layer is preferably between 1 to 50 μm.

In addition to the crosslinked gel former, the gel layer can contain further constituents (see above). A content of pigments, in particular inorganic pigments, is however not necessary in the context of this invention in order to achieve satisfactory or good performance properties. A pigment content is therefore in particular less than 40% by weight, particularly preferably less than 20% by weight, in particular less than 10% by weight, based on the sum of all components of the gel layer (dry). The pigment content is very particularly preferably less than 5% by weight, in particular less than 2% by weight, based on the sum of all components of the gel layer (dry). In a particularly preferred embodiment, pigments are completely dispensed with in the gel layer.

The gel layer (dry) consists in particular of more than 50% by weight, particularly preferably more than 70% by weight, very particularly preferably more than 90% by weight or more than 95% by weight from the crosslinked gel former, preferably from the gel former crosslinked by polyaddition or polycondensation, these being in particular the phenol-aldehyde resins or amino-aldehyde resins defined above.

For use

The recording materials obtainable by the process according to the invention are printable, in particular they can be printed using a color jet printer (inkjet printing). The above gel layer particularly preferably serves as a color receiving layer in these recording materials.

The ink-receiving layer is particularly preferably formed from a gel crosslinked by polycondensation or polyaddition.

The ink-receiving layer is very particularly preferably formed from a crosslinked phenol-aldehyde resin or amino-aldehyde resin.

Recording materials, in particular for color jet printing, preferably have the following layer structure, the order of the layers from a) to f) corresponding to the spatial arrangement: a) optionally a barrier layer, for example made of polyethylene (back of the base paper) b) base paper c) a barrier layer, for example made of polyethylene (front side of the base paper) d) gel layer according to the invention as ink receiving layer e) optionally further non-porous or porous layers for fixing the dye, as adhesive layers, intermediate layers f) optionally a porous cover layer to protect the layers against soiling , Scratching, abrasion, etc., to adjust the surface gloss, sliding properties, to improve the adhesion of pigmented inks, etc.

The recording materials are particularly suitable for printing by color jet printers (ink-jet printers). With the gel layer according to the invention, inorganic pigments can be largely or completely dispensed with in these substrates; at the same time, very good print quality is achieved.

Examples

example 1

In a 1000 ml beaker, a solution of a melamine-formaldehyde condensate with a molar ratio of melamine / formaldehyde = 1/1.5 with bidistilled water was prepared as a 39.9% by weight low-viscosity solution. 30 ml of this solution were mixed with 8.2 g of 37% by weight HCl and 10 μl of Zonyl® (fluorosurfactant from DuPont) and mixed vigorously. The reactive solution was then heated to 60 ° C. in a water bath for about 15 minutes and applied to a PE-coated base paper with a hand knife at a layer thickness of 100 μm when a honey-like viscosity was reached. Immediately after doctoring, the gel-coated paper was aged for 180 minutes at about 60 ° and 60% humidity. The paper was then placed in a drying cabinet and dried at 85 ° C. for 120 minutes. The paper coated in this way was printed with a Canon printer (print setting: photo paper, best print quality) and showed good color pick-up and good print image.

Example 2

In a 1000 ml glass beaker, a solution of a melamine-formaldehyde condensate with a molar ratio of melamine / formaldehyde = 1/1.5 with bidistilled water was prepared as a 36% by weight, low-viscosity solution. 30 ml of this solution 3 g of formic acid and 10 μl of Zonyl® (fluorosurfactant from DuPont) were added and the mixture was mixed vigorously. The reactive solution was then heated to 80 ° C. in a water bath for 100 min and then applied to a PE-coated base paper with a hand knife at a layer thickness of 100 μm. Immediately after doctoring, the gel-coated paper was at about 50 ° C and 75% humidity for 10 minutes. aged. The paper was then placed at room temperature and dried. The paper coated in this way was printed with an inkjet printer from Hewlett Packer (HP2300) (print setting: photo paper, best print quality) and showed good color absorption and good print image in comparison to a conventional photo paper based on a silicate coating (see column “reference Paper").

The following values describe the print image:

Volume fraction of pores

The volume fraction of pores was determined with the mercury intrusion according to DIN 66133. In contrast to the uncoated base paper, the paper coated according to the invention obtained according to Example 2 contains a high volume fraction of pores with a diameter of less than 1 μm.

Claims

1. Process for the production of recording materials which can be printed with an ink jet printer and which have a gel layer for this purpose, characterized in that a) a support with a dispersion or solution of an organic gel former which is chemically formed by polycondensation or polyadduct formation can be cross-linked, is coated,

c) the gel is finally dried.

2. The method according to claim 1, characterized in that the gel former is a compound which can be crosslinked by polycondensation

3. The method according to claim 1 or 2, characterized in that it is in the organic gelling agent is a compound of aromatic hydroxyl compounds and an aldehyde (phenol-aldehyde resin) or from amino compounds and an aldehyde (amino-aldehyde resin).

4. The method according to any one of claims 1 to 3, characterized in that the gel former is an amino-formaldehyde resin, in particular a urea-formaldehyde resin or a melamine-formaldehyde resin.

5. The method according to any one of claims 1 to 4, characterized in that the amino-formaldehyde resin has a formaldehyde content of 0.08 to 2 moles of formaldehyde per mole of amino group.

6. The method according to any one of claims 1 to 5, characterized in that the dispersion or solution of the gel former contains water, water-miscible organic solvents or mixtures thereof as solvents.

7. The method according to any one of claims 1 to 6, characterized in that the dispersion or solution further additives, e.g. Contains wetting agents or additives that affect the subsequent pore size of the dried coating.

8. The method according to any one of claims 1 to 7, characterized in that the carrier is a cellulose-containing carrier material, pre- preferably around a paper that is covered with a barrier layer, e.g. B. of polyethylene is coated.

9. The method according to any one of claims 1 to 8, characterized in that the chemical crosslinking is brought about by increasing the temperature, by irradiating with high-energy light, by changing the pH or by adding a catalyst or by a combination of these measures.

10. The method according to any one of claims 1 to 9, characterized in that the chemical crosslinking at least in part at temperatures from 30 to

100 ° C and a relative humidity of at least 50%.

1 1. The method according to any one of claims 1 to 10, characterized in that the chemical crosslinking is carried out in two steps, the gel former in the dispersion or solution being first crosslinked and the final crosslinking taking place at a relative atmospheric humidity of at least 50% .

12. The method according to any one of claims 1 to 1 1, characterized in that the coating obtained after crosslinking the gelling agent before the final drying still at least 10 wt.% Solvent (eg water), based on the total weight of crosslinked gelling agent (gel ) and contains solvents.

13. The method according to any one of claims 1 to 12, characterized in that the gel after drying contains at least 10% by volume pores with a diameter of less than 10 μm, based on the total volume of the gel layer.

14. The method according to any one of claims 1 to 13, characterized in that the thickness of the dried gel layer is 1 to 50 microns.

15. Recording materials obtainable by a process according to one of claims 1 to 14.

16. Recording materials for color jet printing, which have a gel layer obtainable as a color receiving layer by a process according to one of claims 1 to 14.

17. Recording materials for color jet printing which have a gel crosslinked by polycondensation or polyaddition as the ink receiving layer.

18. Recording materials for color jet printing, which have a crosslinked phenol-aldehyde resin or amino-aldehyde resin as the ink-receiving layer.

19. Recording materials for color jet printing, characterized in that they are structured as follows (the order of the layers from a) to f) corresponds to the spatial arrangement): a) if appropriate, a barrier layer, e.g. made of polyethylene (back of the base paper) b) base paper as a carrier material c) a barrier layer, e.g. made of polyethylene (front of the base paper) d) gel layer obtainable according to a method of claims 1 to 14 as a color receiving layer or color receiving layer according to claim 17 or 18 e) optionally further non-porous or porous layers for fixing the dye, as adhesive layers, intermediate layers f) optionally one porous cover layer to protect the layers against

Soiling, scratching, abrasion, etc., to adjust the surface gloss, sliding properties, to improve the adhesion of pigmented inks, etc.

20. Use of the recording materials according to one of claims 1 to 19 for color jet printing.

21. A method for printing on recording materials with a color jet printer, characterized in that a recording material according to one of claims 1 to 19 is used.