EP1273975A1 - Method for printing substrates by digital offset printing using toner - Google Patents

Abstract

Digital offset printing of a substrate with a toner comprising pigment-polymer particles in a hydrocarbon liquid comprises providing the substrate, before printing, with a coating comprising at least 25% of a copolymer of ethylene and an acrylic monomer (I). Digital offset printing of a substrate with a toner comprising pigment-polymer particles in a hydrocarbon liquid comprises providing the substrate, before printing, with a coating comprising at least 25% of a copolymer of ethylene and an acrylic monomer of formula (I). CH2=CR<1>-COOR<2> (I) R<1> = H or Me; R<2> = H or 1-6C alkyl. Independent claims are also included for: (1) a substrate for printing with a toner as above, having a coating comprising (parts) a copolymer as above (75), polyurethane (0-25), silica gel (0-20) and optionally conventional additives; (2) a coating as above.

Description

The present invention relates to a method for printing substrates by means of digital offset printing, a toner consisting of pigment polymer particles in a hydrocarbon carrier liquid is used, as well as the substrates and their coating.

A variety of different printing processes are known in the prior art. For printing on substrates based on colored templates, this is lithographic Offset printing process as fast and particularly high quality prints generating process estimated. For single templates or small ones However, the conventional offset method is not suitable for the number of runs, because relatively high costs for the production of the lithographic printing template. A more suitable method for such individual prints is xerography, at a dry toner for each individual printed substrate is applied. The costs per print are therefore independent of the Circulation figure. Another method suitable for single prints for digital The laser and inkjet printers represent templates, as do laser printers print xerographically. The disadvantage of xerography is that the Using solid toner particles the achievable resolution is limited.

The process of digital offset printing combines the flexibility of Xerography with the high resolution and color brilliance of offset printing. in this connection the digital template is transformed directly into an electrostatic image on the photo image plate implemented, transferred to the printing roller and then printed on the substrate. Since no print template has to be created, in principle, just like with the Xerography a new motif can be printed with each printing process. The toner However, like in lithographic offset printing, it is an ink or paste, so that the limitation of the resolution at the Xerography in digital offset printing is avoided. The desired high Dissolution requires a special toner made up of pigment polymer particles a hydrocarbon carrier liquid. Printing presses and corresponding toners are commercially available from Indigo N.V., the Netherlands available. These toners are described, inter alia, in U.S. Patents 6,146,803 and 5,935,754.

It has been shown that these toners are not sufficient on many substrates stick, so that on the one hand the print quality suffers and on the other hand the Transfer of pressure from the platen to the substrate is unsatisfactory.

For paper is a coating with a dispersion of 10% polyamide in Propanol has been proposed. However, this ages over time and is too not optimal because of the use of an organic solvent.

For plastic substrates, WO 01/22172 A1 describes coating the substrates to be printed with a coating which contains at least 25% SiO ₂ . Coatings made from UV-curable acrylic esters, acrylic copolymers, styrene-acrylic copolymers, polyvinyl alcohols, diamine-terminated poly (propylene oxide) and polyethylene terephthalates are mentioned. However, the applicability of such a coating is limited.

The present invention is therefore based on the object of a method for To provide printing on substrates with which the advantageous properties of digital offset printing can be fully used.

Surprisingly, it has now been found that a coating consists of a Ethylene-acrylic acid copolymer printing on a wide variety of substrates the special toner in digital offset printing.

The object is accordingly achieved by a method for printing on substrates by means of digital offset printing with a toner which contains pigment polymer particles in a hydrocarbon carrier liquid, the substrate being provided with a coating prior to printing which comprises at least 25% of a copolymer Ethylene and an acrylic acid of formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 C atoms, and optionally contains further polymers and auxiliaries.

Statistical and block copolymers of ethylene and (meth) acrylic acid and (meth) acrylic acid alkyl esters are suitable as ethylene-acrylic acid copolymer. The alkyl ester group optionally has 1 to 6 C atoms, in particular 1 to 3 C atoms, ie R ² preferably represents methyl, ethyl, propyl, butyl, pentyl or hexyl and in particular CH ₃ , C ₂ H ₅ or C. ₃ H ₇ . (Meth) acrylic acid means methacrylic acid, acrylic acid or mixtures thereof. According to the invention, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer and mixtures of two or more thereof are particularly suitable. Ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer, in particular ethylene-acrylic acid copolymer, are particularly preferred.

It is also believed that propylene and other polyolefin copolymers can be used instead of ethylene copolymers, but this is not preferred from the point of view of cost.

Copolymers of ethylene and acrylic acids of the formula I have been known for a long time and commercially available. The average molecular weight is typically Range from 100,000 to 1,000,000. Usually more than 50 mol%, preferably contain more than 80 mol% of ethylene monomers. The copolymers are used according to the invention as an aqueous dispersion. The dispersions can usual additives such as emulsifiers, dispersants, stabilizers etc. contain.

The invention is based on ethylene-acrylic acid copolymer for the sake of simplicity described, it goes without saying that all the others above mentioned copolymers can be used equally.

Up to 75%, preferably up to 50% and in particular up to 25%, other polymers, in particular polyurethanes, can be mixed into the ethylene-acrylic acid copolymer. Furthermore, up to 20%, preferably up to 15%, of silica gel can be added to the coating. The weight per unit area of the coating is 1 to 30 g / m ² , preferably approximately 2 to 3 g / m ² .

Unless otherwise stated, percentages relate to the weight.

In addition to paper and cardboard, the substrate also includes plastics, ceramics and glass and metal into consideration.

In particular, it is possible to print so-called transfer papers, in which the print is then transferred to another object, for example a t-shirt or a cup. According to a preferred embodiment, the invention therefore relates to a method for printing transfer papers for textiles, a release paper having a release layer of silicone or wax and a coating of 75 parts of a copolymer of ethylene and an acrylic acid of the formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 carbon atoms, 0 to 25 parts of a polyurethane and 0 to 20 parts of silica gel and, if appropriate, other customary auxiliaries are provided.

The release paper typically has a basis weight of 80 to 150 g / m ² , preferably 90 to 100 g / m ² . The release layer usually has a basis weight of about 2 g / m ² for silicone and about 20 g / m ² for wax.

The coating is advantageously applied by applying an aqueous dispersion of the constituents, for example by means of a doctor knife, and has a weight per unit area in the range from 10 to 30 g / m ² . Dispersions with solids contents in the range from 5 to 40% work well.

The transfer paper coated and printed according to the invention is then in is known to be placed on the textile and by the action of heat and print transfer the representation to the textile.

In a further preferred embodiment, the invention relates to a method for printing transfer papers for colored or black textiles. in this connection it is important that the print is particularly well received, as the printed layer side not like the light and white textiles on the Textile comes to rest. There is an adhesive layer on dark surfaces on a release paper. A white layer is applied to this the print is then also visible against a dark background and colourfast remains. After printing, the printed layer must be covered with a second one Release paper covered and the print after peeling the first one Release paper with the adhesive layer are applied to the textile. Thereby the printed layer side comes to lie on the surface where it is special is claimed.

An adhesive layer composed of a mixture of ethylene-acrylic acid copolymer, polyurethane and ethylene-vinyl acetate copolymer with a basis weight of 10 to 20 g / m ² is advantageously used on a release paper as described above.

The white layer consists of a white pigment such as TiO ₂ , BaSO ₄ or CaCO ₃ in a binder consisting of 75 parts of a copolymer of ethylene and an acrylic acid of the formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 carbon atoms and 0 to 25 parts of a polyurethane and, if appropriate, other customary auxiliaries. The weight per unit area is advantageously about 20 to 30 g / m ² , the white pigment content 5 to 25% by weight. The coating to be printed is preferably applied over the white layer. This contains 75 parts of a copolymer of ethylene and an acrylic acid of the formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 carbon atoms, 0 to 25 parts of a polyurethane and 0 to 20 parts of silica gel and, if appropriate, other customary auxiliaries and has a weight per unit area of 10 to 20 g / m ² .

In a further preferred embodiment, the invention relates to a method for printing in particular hard surfaces by means of transfer papers. Transfer papers for this purpose are described in German Patent Application No. 197 03 731.3. The transfer paper then has a separating layer made of a polyolefin or polyolefin copolymer with a melt index according to ASTM-D-1238 (MFI) of 3.5 to 22/10 min on a commercial paper suitable for xerography. at 2.16 kg / 190 ° C with a basis weight of 20 to 50 g / m ² . Since the toner for digital offset printing does not adhere sufficiently to these known papers, a coating of 75 parts of a copolymer of ethylene and an acrylic acid of the formula I is used according to the invention CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 carbon atoms, and 0 to 25 parts of a polyurethane and, if appropriate, other customary auxiliaries with a weight per unit area of 2 to 10, preferably 2 to 3 g / m ² applied.

These transfer papers are particularly suitable for the transfer of prints to metal, Suitable for ceramic and plastic surfaces. For this, the coated and printed transfer paper on the hard surface made of metal, ceramic, plastic etc. hung up and transferred the representation by means of pressure and heat. ever after whether the release paper is warm or after cooling subtracted, you either get a transfer of the pressure with a part the plastic layer or just a transfer of the pressure. The latter is Particularly desirable for metal surfaces, so that the metallic shine the parts of the surface that are not filled in by the representation are preserved. mostly will not be a square, corresponding to the size of the transfer paper Transfer presentation.

The following examples are intended to illustrate the invention.

example 1

A plain paper with a basis weight of 90 g / m ² was coated with a 25% aqueous dispersion of an ethylene-acrylic acid copolymer by means of a doctor blade. After drying, the coating was 2-3 g / m ² thick. This paper was printed in a digital offset printing machine (Indigo NV, the Netherlands) with Elektrolnk ® (Indigo NV, the Netherlands). The print quality was excellent. No aging of the paper could be observed in a period of 3 years. Even after repeated heating and cooling, no observable post-hardening occurs.

Example 2

A commercially available release paper was first provided with a release coating made of silicone, which was dried to a basis weight of 2 g / m ² . A dispersion of 75 parts of an ethylene-acrylic acid copolymer (25% by weight in water), 25 parts of a polyurethane (40% by weight in water) and 20 parts of silica gel (40% by weight in Water) and other usual auxiliaries applied. After drying, the coating had a basis weight of 20 g / m ² . A color representation was printed on this transfer paper in a digital offset printing machine (Indigo NV, The Netherlands) with Elektrolnk ® (Indigo NV, The Netherlands). The transfer paper was then placed on a T-shirt, the T-shirt placed in an ironing press and the pressure was transferred to the textile at a temperature of between about 180 to 200 ° C. in about 10 to 20 seconds. After cooling, the release paper was removed. The print quality on the textile was excellent and was not affected by several washes at 40 ° C.

Example 3

A commercially available release paper was first provided with an adhesive coating composed of a mixture of EEA, PU and EVA, which was dried to a basis weight of 15 g / m ² . A dispersion of 75 parts of an ethylene-acrylic acid copolymer (25% by weight in water), 25 parts of a polyurethane (40% by weight in water) and 20 parts of TiO ₂ as a white pigment (40% by weight) was then applied using a doctor blade. -% applied in water) as well as other usual auxiliaries. After drying, the coating had a weight per unit area of 25 g / m ² . Finally, a coating of 75 parts of an ethylene-acrylic acid copolymer, 25 parts of a polyurethane and 20 parts of silica gel and other customary auxiliaries with a basis weight of 15 g / m ^{2 was applied} in the same way. A color representation was printed on this transfer paper in a digital offset printing machine (Indigo NV, The Netherlands) with Elektrolnk ® (Indigo NV, The Netherlands). The transfer paper was then placed on a black T-shirt, the T-shirt was placed in an ironing press and the pressure was transferred to the textile at a temperature of around 220 ° C in about 10 to 20 seconds. After cooling, the release paper was removed. The print quality on the textile was excellent and was not affected by several washes at 40 ° C.

Example 4

A commercially available normal paper was first provided with a separating layer made of an ethylene-vinyl acetate copolymer with 7 to 18% by weight of vinyl acetate groups, which was dried to a basis weight of 40 g / m ² . A dispersion of 75 parts of an ethylene-acrylic acid copolymer (25% by weight in water) and 25 parts of a polyurethane (40% by weight in water) and other customary auxiliaries was applied by means of a doctor knife. After drying, the coating had a basis weight of 2 g / m ² . A color representation was printed on this transfer paper in a digital offset printing machine (Indigo NV, The Netherlands) with Elektrolnk ® (Indigo NV, The Netherlands). The transfer paper was then placed on a cup and transferred by the action of heat in a device known per se. After cooling, the release paper was removed. The print quality was excellent.

Claims (8)

Process for printing substrates by means of digital offset printing with a toner which contains pigment-polymer particles in a hydrocarbon carrier liquid,
characterized in that
the substrate before printing with a coating of at least 25% of a copolymer of ethylene and an acrylic acid of the formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 C atoms, and optionally further polymers and customary auxiliaries are provided. A method according to claim 1, characterized in that the coating consists of 75 parts of the ethylene-acrylic acid copolymer, 0 to 25 parts of a polyurethane and 0 to 20 parts of silica gel and optionally other conventional auxiliaries. A method according to claim 2, characterized in that the coating consists of ethylene-acrylic acid copolymer and optionally other auxiliaries. A method according to claim 2 or 3, characterized in that R ^{1 is} H or CH ₃ , in particular H, and R ^{2 is} H. Method according to one of claims 1 to 4, characterized in that the coating is applied by applying the components in the form of an aqueous dispersion. A substrate for printing with a toner comprising pigment polymer particles in a hydrocarbon carrier liquid,
characterized in that
there is a coating of 75 parts of a copolymer of ethylene and an acrylic acid of the formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 carbon atoms, has 0 to 25 parts of a polyurethane and 0 to 20 parts of silica gel and, if appropriate, other customary auxiliaries. Substrate according to claim 6, characterized in that the substrate is a transfer paper for transferring the print onto an object. Coating for substrates that are printable with a toner comprising pigment-polymer particles in a hydrocarbon carrier liquid
characterized in that
the coating of 75 parts of a copolymer of ethylene and an acrylic acid of the formula I. CH ₂ = CR ¹ -COOR ² in which R ^{1 is} H or CH ₃ and R ^{2 is} H or an alkyl radical having 1 to 6 carbon atoms, 0 to 25 parts of a polyurethane and 0 to 20 parts of silica gel and optionally other customary auxiliaries.