EP1434915A1

EP1434915A1 - Novel coating color composition

Info

Publication number: EP1434915A1
Application number: EP02764904A
Authority: EP
Inventors: Anna-Liisa Tammi; Päivi MIETTINEN
Original assignee: Raisio Chemicals Oy
Current assignee: BASF SE
Priority date: 2001-10-03
Filing date: 2002-10-02
Publication date: 2004-07-07
Also published as: WO2003029560A1; FI20011932A0; FI20011932A; FI118091B

Abstract

The invention relates to coating of paper and paperboard and is especially directed towards a novel pigment coating composition for coating of paper and paperboard. The novel coating composition contains pigment, latex, optionally a polymer made of hydrophobic monomers in the presence of starch and/or plain starch, if necessary, known additives used in coating compositions, and in addition styrene maleic imide.

Description

Novel coating color composition

The present invention relates to coating of paper and paperboard and is especially directed towards a novel pigment coating composition for coating of paper and pa- perboard. The novel coating composition comprises pigment, latex, optionally a polymer which is made of hydrophobic monomers in the presence of starch, optionally also other binders and, if necessary, known additives used in coating compositions, and it is characterized in that it comprises styrene maleic imide. The invention is also directed towards paper or paperboard coated with the novel coating composition and by all coating methods.

The purpose of coating is to improve the surface properties of paper or paperboard, such as gloss, printability and print quality. The most commonly used surface treatment is pigment coating, wherein color, in other words pigment-binder mix- ture, is applied on the surface of base material at a coating unit or at a separate coating machine. The thickness of the coating layer is adjusted, and finally the coating is dried. A usual pigment coating mixture comprises pigment agents, of which there may be one or several present, binder or binders, water, and optionally additives, such as hardeners, viscosity and water retention regulating agents and lubricants. The ratios of the coating mixture components can vary rather widely, depending on the purpose of use and the quality requirements of the end product, the coating method and the quality of the base paper.

As coating pigments in pigment coating mixtures la. kaolin, calcinated kaolin, cal- cium carbonate (both grown and precipitated), titanium dioxide, satine white, talc, gypsum, chalk, aluminium hydroxide, barium sulphate, and sodium aluminium silicate are used, of which the most commonly used are kaolin, calcinated kaolin, talc and calcium carbonate. Soluble binders, such as starch, casein, soya protein, car- boxy methyl cellulose and polyvinyl alcohol, or latexes, such as styrene butadiene (SB), acrylate and polyvinyl acetate latexes, or starch-stabilized latex can be used as binders. Small amounts of various additives are added to pigment coating mixtures to improve the use properties of the mixture or to provide it with certain special features. Such known additives are la. dispersants, agents which change flow properties, defoamers and foaming inhibition agents, preservatives, lubricants, hardeners, and optical brighteners.

In US patent no. 2,577,624, a water-soluble salt of styrene maleic anhydride co- polymer is used as a binder in a coating color. In WO publication 99/51815, a kao- lin pigment, which is suitable for coating compositions and has a certain particle form is disclosed, and styrene maleic anhydride is mentioned as an optional hydro- philic additive. In the abstract of JP patent 62258732, the use of a copolymer of styrene and maleic acid and/or maleic anhydride as a dispersing agent in water solutions of calcium carbonate is mentioned.

DE 43 42 147 discloses dispersions for use in paper-sizing compositions, said dispersions containing styrene maleic anhydride imidized to at least 90% as one component. WO publication 99/45039 describes a polymer dispersion for use in paper- sizing compositions, wherein at most 75% of the maleic anhydride monomer units of the dispersions have been imidized. In the publications US 3 ,444, 151 and WO

00/78818 polymer dispersions are prepared, wherein styrene maleic anhy- dride/imide is included during preparation. The dispersions obtained according to what is mentioned above are used in floor polishing compositions or in the sizing of paper and paperboard, respectively.

According to the invention it has now been found that the printability and print quality of coated paper are substantially improved if the coating color composition comprises styrene maleic imide. Styrene maleic imide is an imidized styrene maleic anhydride copolymer, which in turn is a copolymer of styrene and maleic acid an- hydride. In the composition according to the invention, partly or folly imidized styrene maleic anhydride copolymer can be used. Styrene maleic imide, when mixed in a paper coating color, clearly improves the surface energy of paper by remarkably lowering the polar component. Styrene maleic imide is especially suitable for coating systems, where talc, kaolin and/or 5 calcium carbonate are used as pigments. Styrene maleic imide helps to bind pigment particles, especially talc and kaolin particles, more tightly than mere SB latex and it can also act as a dispersing agent. Styrene maleic imide makes the paper surface hydrophobic, which means that in a printing situation the surface is not deeply wetted and dries easily when the small amount of moisturizing water vaporizes 0 quickly. Styrene maleic imide can be added to the color separately or mixed with some other component, for example pigment (pigment slurry) or latex. If desired, styrene maleic imide can also be included in latex during latex preparation.

Styrene maleic imide improves the surface strengths and offset printability of pa- 5 per, also when it is used as a co-binder with a calcium-containing pigment or dispersed directly into the pigment. For example, the particle structure of precipitated calcium carbonate is crystalline, for which reason the pore structure of the surface of a paper coated with a precipitated calcium carbonate containing color can be rough (large pores). With the coating composition according to the invention, a o consistent coating and a surface with good printability is obtained also when a carbonate pigment is used.

Consequently, the present invention is directed towards a novel coating color composition, which comprises as its components a) pigment, b) latex, c) optionally a 5 polymer made of hydrophobic monomers in the presence of starch, in other words starch-stabilized latex and/or plain starch, d) if necessary, known additives used in coating compositions, and further, e) styrene maleic imide.

The coating color composition according to the invention may comprise 0.1 - 5 o parts of styrene maleic imide, preferably 0.1 - 3 parts, and more preferably 0.5 - 2 parts. Instead of styrene maleic imide, the composition according to the invention may comprise partly imidized styrene maleic anhydride. Partly imidized styrene maleic anhydride means for example imidization to 50 - 100%, preferably to over 75% but below 90%.

When the compositions of coating mixtures are given, the proportions of the components are usually calculated so that the total amount of pigments is marked as 100 and the amounts of the other components are given as relative to the amount of the total pigment. The proportions of all components are given as dry parts. In this disclosure the amounts of the components of the coating composition according to the invention are given as described above.

Suitable pigments for a coating color composition according to the invention are coating pigments known in the art, such as kaolin, calcinated kaolin, gypsum, chalk, ground and precipitated calcium carbonate, titanium dioxide, satine white, talc, aluminium hydroxide, barium sulphate and sodium aluminium silicate. Especially suitable for a coating color composition according to the invention are calcium-containing pigments, such as kaolin, calcinated kaolin, gypsum and ground or precipitated calcium carbonate, and talc, as well as mixtures of the above, especially a mixture of talc and kaolin or carbonate and kaolin.

Suitable binders are latexes known in the art, such as styrene butadiene latexes (SB), acrylate latexes and polyvinyl acetate latexes (PVAc), especially SB latexes. A coating color composition according to the invention may contain in addition to latex also starch-stabilized latex and/or plain starch as a co-binder. In addition to these, other binders, such as CMC, can be used.

By starch-stabilized latex is meant a copolymer, which is formed when hydrophobic vinyl monomers are polymerized in the presence of native or modified starch. Modified starch can mean for example degraded (for example oxidized), anionized, cationized, and/or amphoteric starch. Starch may be any of the known starches, such as potato, corn, waxy corn, barley, wheat, or tapioca starch, preferably potato starch. Instead of starch also any other polysaccharide, which contains a free hy- droxyl group, such as amylose, amylopectine, carrageen, cellulose, chitosan, chitin, dextrines, guar gum (guarane), and other galactomannans, arabic gum, hemicellu- lose components, and pullulan, can be used, but starch is the most preferred poly- saccharide for the purposes of the invention. Processes for the preparation of starch-polymer dispersions have been disclosed for example in the publications US 4,301,017, US 5,003,022 and WO 00/46264. Monomers used in the preparation of a suitable polymer that is optionally included in the coating composition according to the invention, are hydrophobic monomers, such as for example styrene, alpha-metyl styrene, acrylates, acrylonitrile, etc.

A preferred coating color composition according to the invention comprises a) 100 parts of pigment, b) 5 - 18 parts of latex, c) 0 - 5 parts of starch-stabilized latex or plain starch, d) 0 - 3 parts of known additives, and e) 0.1 - 5 parts of styrene maleic imide. More preferably the amount of latex is 6 - 15 parts, even more preferably 8 - 14 parts and most preferably 9 - 12 parts. The amount of known additives is preferably 0.2 - 2.5 parts, more preferably 0.2 - 2.0 parts, for example about 1.5 parts.

If a polymer made of hydrophobic monomers in the presence of starch, in other words starch-stabilized latex, is desired to be used, its amount in a coating color composition according to the invention is 0.1 - 5 parts, more preferably 0.2 - 4 parts, even more preferably 0.3 - 3 parts and most preferably about 0.5 - 1.5 parts.

If plain starch is desired to be used in the composition according to the invention, its amount is preferably 0.5 - 5 parts, more preferably 1 - 3 parts and most preferably 1.5 - 2.5 parts, for example about 2 parts.

When both starch-stabilized latex and starch are desired to be used in the composi- tion according to the invention as a co-binder, their total amount is preferably 1 - 5 parts and more preferably 2.5 - 4 parts. A preferred coating color composition according to the invention, which contains plain starch as a co-binder, comprises a) 100 parts of pigment, of which 70 parts are talc and 30 parts kaolin, b) 10 parts of latex, c) 3 parts of starch, d) optionally known additives, and e) 3 parts of styrene maleic imide.

Another preferred coating color composition according to the invention comprises a) 100 parts of pigment, of which 40 parts are talc and 60 parts kaolin, b) 10 parts of latex, c) 3 parts of starch, d) optionally known additives, and e) 3 parts of styrene maleic imide.

An especially preferred coating color composition according to the invention which contains calcium carbonate pigment, comprises a) 100 parts of ground calcium carbonate (GCC), b) 11 parts of latex, c) 0.75 parts of starch-stabilized latex and 2 parts of plain starch, d) if necessary, known additives, and e) 0.75 parts of styrene maleic imide.

Another preferred coating color composition according to the invention comprises a) 100 parts of ground calcium carbonate (GCC), b) 12 parts of latex, c) 0.5 parts of starch-stabilized latex, d) if necessary, known additives, and e) 1 part of styrene maleic imide.

One preferred coating color composition according to the invention which contains calcium carbonate pigment comprises a) 100 parts of precipitated calcium carbon- ate (PCC), b) 10 parts of latex, c) 2 parts of plain starch, d) if necessary, known additives, and e) 2 parts of styrene maleic imide.

Another preferred coating color composition according to the invention comprises a) 100 parts of ground calcium carbonate (GCC), b) 9 parts of latex, c) 3 parts of plain starch and 1 part of starch-stabilized latex, d) if necessary, known additives, and e) 1 part of styrene maleic imide. The dry solids content of a ready-for-use coating color composition according to the invention is usually over 50%, for example 50 to 65%, preferably about 60%, depending on the pigments used in the composition.

The invention is also directed to paper or paperboard that has been coated with a coating color composition according to the invention, as well as to the use of styrene maleic imide in coating color compositions for use in coating of paper or paperboard.

Due to the coating color composition according to the invention, the surface strength, printability and thus the print quality of a paper or paperboard coated with the said color are substantially improved, especially in the novel offset printing process which is faster than before. The product according to the invention changes the pore structure of paper surface so that it becomes more dense, and gives hydro- phobicity. As the polar component is clearly decreased, the surface of paper is favourable for offset printing. Using the coating color composition according to the invention is also environmentally advantageous, as faster-drying inks and shorter drying times can be used in offset-printing, thus making remarkable energy savings possible. Smaller amount of solvents can be used with colouring agents, and no isopropanol is needed in the printing. In offset-printing isopropanol has commonly been used in the fountain solution. Isopropanol is a slightly detrimental solvent, and its use has been tried to be decreased.

The following examples illustrate the invention. Examples 1 to 6 disclose different coating color compositions, of which the compositions in examples 2 to 6 are compositions according to the invention. All the colors according to examples 1 to 6 further contain ordinary color additives. Examples 6 to 7 present the test results obtained. Example 1 (Reference color)

70 parts of talc 30 parts of kaolin 10 parts of SB latex 3 parts of starch

The basic color was prepared by mixing latex and boiled starch into pigment slurry.

Example 2

70 parts of talc 30 parts of kaolin 10 parts of SB latex

3 parts of starch 3 parts of styrene maleic imide

Styrene maleic imide was also slurried with the basic color. Otherwise the prepara- tion was in accordance with Example 1.

Example 3

40 parts of talc 60 parts of kaolin

10 parts of SB latex 3 parts of starch 3 parts of styrene maleic imide

The color according to the invention was prepared by first mixing the basic color as in Example 1. Styrene maleic imide was slurried with the basic color. Example 4

100 parts of ground calcium carbonate 5 11 parts of SB latex

2 parts of starch

0.75 parts of starch-stabilized latex 0.75 parts of styrene maleic imide

0 The color according to the invention was prepared by first mixing styrene maleic imide into the pigment slurry and then the other components.

Example 5

5 100 parts of ground calcium carbonate

12 parts of SB latex 0.5 parts of starch-stabilized latex

1 part of styrene maleic imide

o The color according to the invention was prepared by mixing the other agents into the pigment slurry.

Example 6

5 100 parts of precipitated calcium carbonate

10 parts of SB latex

2 parts of starch

2 parts of styrene maleic imide

0 The color according to the invention was prepared by first mixing styrene maleic imide into the pigment slurry and then the boiled starch. Example 7. The improvement of printability when talc-kaolin pigment is used

The colors in Examples 1 and 2 were used. The colors are otherwise identical ex- cept that the color in example 2 contains styrene maleic imide according to the invention. In addition, both colors similarly contained ordinary color additives.

The base paper was coated with the colors on a pilot-scale coating apparatus 10 g/m on both sides of the paper. The papers were printed in laboratory scale. Results from paper analyses are presented in tables 1 and 2.

Table 1. Improvement in printability when talc-kaolin pigment is used

From the results it is noticed that when styrene maleic imide is used, the properties of paper are clearly favourable for printing. The paper coated with a color according to the invention is clearly hydrophobic, which is shown by the high wet repulsion value. Furthermore, quickly drying inks could be used, which is advantageous in terms of energy technology.

Example 8. Improvement of printability when calcium carbonate pigment is used

Common SB latex was compared to a mixture wherein part of the binder has been replaced with styrene maleic imide, starch-stabilized latex and/or plain starch. Ground calcium carbonate (GCC) or precipitated calcium carbonate (PCC) was used as pigment. In addition, ordinary additives, which were the same at all test points were used in the colors. The base paper was a basic LWC paper. The papers were printed in laboratory scale with a Briifbau apparatus.

Table 2. 100 parts of ground calcium carbonate (GCC) as pigment

Reference color: 13 parts of SB latex

Color A: 12 parts of SB latex, 1 part of starch-stabilized latex, 0.5 parts of styrene maleic imide

Color B: 12 parts of SB latex, 0.5 parts of starch-stabilized latex, 1 part of styrene maleic imide

Color C: 11 parts of SB-latex, 2 parts of starch, 0.75 parts of starch-stabilized latex, 0.75 parts of styrene maleic imide Table 3. 100 parts of precipitated calcium carbonate (PCC) as pigment

Reference color: 13 parts of SB latex

Color A: 11 parts of SB latex, 2 parts of styrene maleic imide

Color B: 10 parts of SB latex, 2 parts of starch, 2 parts of styrene maleic imide

Color C: 11 parts of SB latex, 2 parts of styrene maleic anhydride

With both calcium carbonates, when the compositions according to the invention were used, the ink settled properly on the surface, whereby a clear printing image and better surface gloss were obtained.

Claims

1. A coating color composition which comprises as its components a) pigment, b) latex, c) optionally a polymer prepared of hydrophobic monomers in the presence

5 of starch, in other words starch-stabilized latex, and/or plain starch, d) if necessary, known additives used in coating compositions, characterized in that it further comprises e) styrene maleic imide.

2. The coating color composition according to claim 1, characterized in that it com- 0 prises 0.1 — 5 parts, preferably 0.1 - 3 parts, and even more preferably 0.5 - 2 parts of styrene maleic imide.

3. The coating color composition according to claim 1, which contains as its components a) 100 parts of pigment, b) 5 - 18 parts of latex, c) 0 - 5 parts of starch- 5 stabilized latex or plain starch, d) 0 - 3 parts of known additives, and e) 0.1 - 5 parts of styrene maleic imide.

4. The coating color composition according to claim 1, which contains as its components a) 100 parts of pigment, b) 6 - 15 parts of latex, c) 0.2 - 4 parts of starch- 0 stabilized latex or 1 - 3 parts of starch, d) 0.2 - 2.5 parts of known additives, and e) 0.1 - 3 parts of styrene maleic imide.

5. The coating color composition according to claim 1, which contains as its com- - ponents a) 100 parts of pigment, b) 9 - 12 parts of latex, c) 0.3 - 3 parts of starch- 5 stabilized latex or 1.5 - 2.5 parts of starch, d) 0.2 - 2 parts of known additives, and e) 0.5 - 2 parts of styrene maleic imide.

6. The coating color composition according to claim 1, which contains as its components a) 100 parts of pigment, b) 6 - 15 parts of latex, c) altogether 1 - 5 parts of o starch-stabilized latex and starch, d) if necessary, known additives, and e) 0.1 - 3 parts of styrene maleic imide.

7. The coating color composition according to claim 1, which contains as its components a) 100 parts of a mixture of talc and kaolin, b) 10 parts of latex, c) 3 parts of starch, d) if necessary, known additives, and e) 3 parts of styrene maleic imide.

8. The coating color composition according to claim 1, which contains as its components a) 100 parts of ground calcium carbonate, b) 11 parts of latex, c) 0.75 parts of starch-stabilized latex and 2 parts of plain starch, d) if necessary, known additives, and e) 0.75 parts of styrene maleic imide.

9. The coating color composition according to any one of claims 1 to 8, characterized in that styrene maleic imide is totally or partly imidized styrene maleic anhydride.

10. The coating color composition according to any one of claims 1 to 8, characterized in that the pigment is kaolin, gypsum, ground or precipitated calcium carbonate, talc or a mixture of some of these.

11. The coating color composition according to claim 10, characterized in that the pigment is grown or precipitated calcium carbonate or a mixture of talc and kaolin.

12. The coating color composition according to any one of claims 1 to 8, characterized in that the latex is styrene butadiene latex.

13. Paper or paperboard, characterized in that it has been coated with a coating color composition according to any one of claims 1 to 8.

14. The use of styrene maleic imide in coating color compositions for use in coating of paper or paperboard.