Dispersant

Abstract: The invention relates to a polymer suitable as a dispersant, built up from A) 0-80 mol % of one or more monomers having the formula in which R₁, R₂, R₃ and R₄ may be the same or different and represent H or alkyl, B) 0-70 mol % of one or more monomers having the formula in which R₅, R₆ and R₇ may be the same or different and represent H or alkyl and R₈ is alkyl or substituted alkyl, and the alkyl group R₈ may also be interrupted by - O - groups, C) 5-50 mol % of one or more monomers containing a heterocyclic group having at least one basic ring nitrogen atom, or to which such a heterocyclic group is attached following polymerization, D) 0-10 mol % of one or more monomers containing one or more groups reactive to cross-linking or coupling, and E) 0-20 mol % of one or more monomers not falling within the groups A-D, the amount of monomers from group A together with monomers containing an acrylate group being at least 20 mol %, as well as organic salts thereof, and also to the use thereof.

Description: The present invention relates to a solution of a polymer, or organic salts thereof, suitable as dispersants, which polymers contain heterocyclic groups having at least one basic ring nitrogen. The invention also relates to the use of such polymer solutions for the production of coatings and printing inks, pigment dispersions as well as powdered solids coated with the dispersant according to the invention. The introduction of solids into liquid media requires high mechanical forces. This depends substantially on the wettability of the solid by the surrounding medium and on the affinity to this medium. For the purposes of reducing these dispersing forces it is conventional to use dispersants facilitating the dispersion. These are mostly surfactants or tensides having an anionic, cationic or a non ionic structure. These agents are directly applied to the solid or added to the dispersing medium in relatively small amounts. It is further known that these solids tend to flocculate following the dispersion, which nullifies the work earlier done and leads to serious problems. These problems have been accounted for by the London/van der Waal's forces by which the solids attract each other. For the purposes of counteracting these attractive forces absorption layers must be applied to the solid. This is done by using such tensides. During and following the dispersion there is an interaction between the surrounding medium and the solid particle, resulting in a desorption of the tenside by exchange for the surrounding medium present in a higher concentration. This medium, however, is not capable in most cases of building up such stable absorption layers, resulting in a crash of the whole system. This becomes apparent by the increase in viscosity in liquid systems, losses of gloss and color shifts in lacquers and coatings as well as insufficient color force development in pigmented synthetics. To solve this problem, e.g., EP-A 154.678, EP-A 74080, US-A 4.032,698 and DE-A 24 38 414 propose dispersants. These dispersants, however, only lead to a partial solution, particularly with respect to the miscibility without flocculation of different pigments with each other, such as organic pigments and inorganic pigments. Moreover, the pigment pastes prepared by the methods defined tend to interact with the surrounding medium, e.g., after use in lacquers. Consequently, it can be assumed that the absorption layers built up only have insufficient stability against desorption. A number of dispersants proposed in these publications further have the drawback that the storage stability is too poor, which leads to precipitation, phase separation, crystallization, etc. This results in that such products are inhomogeneous and useless in practice after a relatively short time. GB-A 883.750 is directed to a stable aqueous copolymer emulsion comprising a specific quaternary vinyl pyridinium monomer copolymerized in water with styrene, methylacrylate or other monomers, said copolymer containing from 0.2 to 5% of quaternary nitrogen. US-A 2,721,852 relates to quaternary interpolymers containing vinyl pyridine or vinylquinoline. The object of the present invention is to find dispersants which do not show the above described drawbacks or in which these drawbacks have been considerably reduced. The second object is to find a dispersant having excellent compatibility with a wide range of different binders, especially binders on a polyacrylate basis and air drying alkyd resins. It is also an object of the invention to find a dispersant capable of being used in the production of binder-free pigment dispersions without further binder additives during the dispersing process. These objects are attained according to the invention by a polymer solution in organic solvent suitable as dispersant, as defined in claim 1. The solutions of the polymers have excellent compatibility with all kinds of binders for coatings and printing inks, more in particular with binders on a polyacrylate basis and on an alkyd basis. Pigment dispersions stabilized with the polymers are distinguished by a high resistance to flocculation. good rheological properties as well as a proper strength of color and a high gloss. The solution according to the invention can be added in relatively small amounts, to the material to be ground for the dispersing process. The optimum activity of the polymer compound according to the invention is obtained at concentrations of preferably 1 mg to 10 mg, based on 1 m 2 BET surface of the pigment. The solution according to the invention can also be used without further binder additives during the dispersing process. The polymer present in the solution then adopts the function of a dispersing resin. Thus binder-free pigment dispersions are obtained which, in the further applications thereof in coatings and printing inks. have excellent compatibility and do not entrain unnecessary, disturbing dispersing resins. Optimum results are obtained at a polymer solution/pigment weight ratio of 1 : 1.5 to 1 : 3 with organic pigments and 1 : 4 to 1 : 8 with inorganic pigments. The products according to the invention consist of a polymer chain having attached thereto the heterocyclic groups with basic nitrogen atoms. Such a chain can be obtained by polymerizing-in vinylimidale. Preferred are compounds with basic nitrogen groups having a pKa value of 2 to 14, more in particular 5 to 14 and most preferably 5 to 12. These pKa values relate to the measurement thereof at 25°C in a 0.01 molar concentration in water. These basic groups impart to the dispersants according to the invention a basicity as is also known in this technical field. These basic groups allow the dispersants to form organic salts too. The dispersants can therefore be used in the form of such salts. These salts are obtained by neutralization of the polymer with organic acids, e.g., aromatic acids having not more than 25 C atoms or aliphatic and cycloaliphatic acids having not more than 22 C atoms. Preference is given to salts of the polvmer with organic monocarboxylic acids. The content of vinyl-imidazole ranges between 5 and 50 mol %, preferably between 25 and 40 mol %. Vinylimidazole is used, because in the first place it is easiest with this compound to prepare the polymers and in the second place the dispersants prepared therewith have excellent properties. The other components of the polymer chain aim at providing optimum compatibility with binders and/or solvents as conventional for coatings and printing inks. The polymer chain can advantageously comprise at least one monomer of the acrylate type. Suitable monomers are the esters of acrylic acid and methacrylic acid as well as reaction products of ethylene oxide and/or propylene oxide therewith. In this respect it is observed that such reaction products may be both OH- and alkyl-terminated. It is intended in this connection that these reaction products be either alkyl-terminated or, if they are OH-terminated, so little reactive that they do not give rise to further reactions. If these alkoxylated products are reactive, they should be comprised by groups C or D. Monomers that can be suitably used are, e.g., methyl methacrylate, ethyl methacrylate. n-butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, 2-ethyl hexyl methacrylate. dimethyl aminoethyl methacrylate, cyclohexyl methacrylate, methylacrylate, isobornyl methacrylate, ethyl acrylate, butyl acrylate. 2-ethyl hexyl acrylate, cetyl methacrylate, stearyl methacrylate. behenyl methacrylate, polypropylene glycol monomethacrylate, polyethylene glycol monomethacrylate and EO-PO-monomethacrylate. The selection of the monomers is determined by the compatibility of the polymer chain with binder/solvent. One of the monomers preferred is methyl methacrylate, since this monomer provides good compatibility and good film properties. Monomer mixtures can also be used. The amount of monomer of the acrylate type ranges between 0 and 70 mol %, the amount being determined by inter alia the molecular weight of the monomers. In case of a higher molecular weight, e.g., monomers with an EO-PO chain, a smaller amount is used on a molar base. A group of monomers that is present concerns the vinylaromatic monomers, such as styrene, α-methyl styrene, vinyl toluene, etc. In general, this group can be defined by the formula in which R 1 , R 2 and R 3 may be H or (C 1 -C 4 ) alkyl. The nucleus substitution R 4 may be absent (R 4 = H) or consist of methyl or higher alkyl (such as C 2 -C 18 ). This group of monomers affects the compatibility with the binders and solvents. Monomers from this group can be used in amounts of 5 to 80 mol%. Preferred are amounts up to 25 mol%, more in particular 5-15 mol%. According to the present invention the monomers from this group of vinylaromatic compounds and the monomers of the acrylate type are both present. The amount of monomers from group A together with monomers containing acrylate groups are at least 20 mol%. A next group of monomers is the group used for intercoupling two or more substantially linear polymer chains. In specific cases it may be advantageous, e.g., from the viewpoint of preparation, to prepare relatively low molecular polymers and to interconnect them by means of reactive monomers. For this purpose, in principle the same monomers can be used as described above for attaching heterocyclic groups to the polymer chain. In general, these monomers are used only in those cases in which a crosslinking or coupling is to be obtained. It is of course possible to combine the monomer groups C and D and to use excess monomer relative to the heterocyclic groups. Thus it is preferably possible first to attach the heterocyclic groups and then to carry out the coupling process. The amount of monomers from group D depends on the desired molecular weight. In general, not more than about 2-4 reactive groups are required per polymer chain. The coupling can be effected by reaction of the polymerized-in monomers with each other or by using a di- or trifunctional compound as described in relation to the attachment of the heterocyclic group to the chain. The last group of monomers present only in relatively small amounts, i.e. 0-20 mol %, preferably 0-10 mol %, more in particular 0-5 mol %, preferably 0 mol %, comprises the monomers that are not comprised by groups A-D, such as acrylamide, methacrylamide, vinyl ester, vinyl ether, acrylonitrile. etc. These monomers can be used for finely adjusting the dispersant properties. The polymers can be prepared in the conventional manner, e.g., by mass or solution polymerization. The polymerization in a solvent is preferred in view of the controllability of the polymerization and the viscosity of the final product. Suitable solvents are DMSO, THF, DMF, ethyl, propyl, butyl, acetate, benzene, toluene, xylene, N-butanol, isobutanol, isopropanol, MEK, MIBK, and acetone. The monomers are preferably polymerized using a radical reaction, by addition of peroxides, optionally in the presence of redox systems. The polymerization time depends on the temperature and the desired final product properties but is preferably within the range of from 0.5 to 10 hours at temperatures ranging from 50 to 190°C. The polymerization can be carried out continuously, discontinuously or semicontinuously. If it is preferred to obtain a polymer chain having random distribution of monomers, all of the monomers together will be preferably added to the reaction mixture. This may be done in one portion or in the course of time. On the basis of the reactivity of the monomers, which is known, a skilled worker can control the polymerization so as to obtain the desired distribution. The present solution of polymers suitable as dispersants have an excellent dispersing effect. The compatibility with all types of binders for coatings and printing inks is excellent. By suitably selecting monomers a substantially universal dispersant is obtained. The solutions according to the invention can be used for the production of aqueous and non-aqueous coatings, such as paints and printing inks. They are not water-soluble but may have a self-emulsifying effect in water, so that these are suitable for use in aqueous coatings and printing inks too. In this connection aqueous coatings and printing inks, as used herein, also refer to those products which partially comprise organic cosolvents. The dispersant, is surprisingly superior to known agents built up on the basis of isocyanate, although rather simple raw materials have been used. With the dispersants pigments that are hard to stabilize can be stabilized without any problems. Also pigment mixtures can be stabilized without causing problems. Following stabilization with the dispersants according to the invention the pigments show a very high resistance to flocculation and impart to a lacquer film containing the pigments an excellent gloss. Pigments used in this field are the organic and inorganic pigments insoluble in the employed liquid, e.g., soot, polycyclic pigments, iron oxides, etc. The invention also relates to pigment dispersions, i.e., mixtures of pigment, solution according to the invention and water and/or non-aqueous liquid. These dispersions are sometimes also referred to as binder-free pigment dispersions or pigment slurries. As non-aqueous liquids, use is made of the organic solvents conventional in the field of coatings and printing inks. The amounts of pigment range between 10 and 70 % by weight, and the amounts of solution range between 1 and 10 % by weight. EXAMPLE 1 A polymerization of 12.0 g methyl methacrylate, 32.76 g cyclohexyl methacrylate, 35.84 g butylacrylate, 18.82 g vinyl imidazole and 2.0 g tertiary butyl perbenzoate was effected in 50.71 g xylene and 16.91 g n-butanol. The solid content was adjusted to 40 % by weight with butyl acetate. EXAMPLE 2 In 15.67 g secondary butanol and 47.0 g butyl acetate were polymerized 29.97 g isobornyl methacrylate, 9.36 g styrene, 38.71 g 2-ethyl hexyl acrylate, 14.12 g vinyl imidazole, 0.62 g tertiary butyl-per-2-ethyl hexoate and 1.23 g tertiary butyl perbenzoate. At the end of the polymerization the solid content was adjusted to 50 % by weight by means of butyl acetate. EXAMPLE 3 In 45.08 g xylene and 22.54 g n-butanol, 12.00 g methyl methacrylate, 32.76 g cyclohexyl methacrylate, 35.84 g butyl acrylate, 18.82 g vinyl imidazole and 2.0 g tertiary butyl perbenzoate were polymerized. At the end of the polymerization the solid content was adjusted to 50 % by weight by adding 33.80 g xylene. EXAMPLE 4 In 47.00 g toluene and 15.67 g n-butanol, 29.97 g isobornyl methacrylate, 9.36 g styrene, 38.71 g 2-ethyl hexyl acrylate, 14.12 g vinyl imidazole and 11.85 g tertiary butyl perbenzoate were polymerized. At the end of the polymerization a polymer solution was obtained having a solid content of 60% by weight. EXAMPLE 5 In 43.75 g xylene and 14.59 g n-butanol, 23.31 g isobornyl methacrylate, 31.35 g butyl acrylate, 10.92 g styrene, 3.71 g acrylonitrile, 16.47 g vinyl imidazole and 1.72 g tertiary butyl perbenzoate were polymerized. At the end of the polymerization the solid content of the polymer solution was adjusted to 50% by weight by adding xylene. EXAMPLE 6 19.98 g isobornyl methacrylate, 10.62 g vinyl toluene, 30.42 g 2-ethyl hexyl acrylate, 6.75 g polyethylene glycol monomethacrylate, 16.38 g cyclohexyl methacrylate, 15.53 g vinyl imidazole, 0.67 g tertiary butyl peroctoate and 1.34 g tertiary butyl perbenzoate were polymerized in 50.85 g butyl acetate and 16.95 g secondary butanol. At the end of the polymerization the solid content of the polymer solution was adjusted to 50% by weight with butyl acetate. EXAMPLE 7 In 98.67 g butyl acetate and 19.74 g n-butanol the following substances were polymerized in the manner described in Example 1: 19.98 g isobornyl methacrylate, 10.92 g cyclohexyl methacrylate, 10.62 g vinyl toluene, 15.0 g methyl methacrylate, 6.75 g polyethylene glycol monomethacrylate, 14.12 g vinyl imidazole and 1.56 g tertiary butyl perbenzoate. At the end of the polymerization the solid content of the solution was adjusted to 40% by weight by adding butyl acetate. To evaluate the behaviour of the dispersants according to the invention, these were used in three different lacquer systems, while also comparing with the dispersant according to Example 14 of EP-A-154,678. The compositions of the three lacquer systems are listed in the following Table 1. By using these three lacquer systems as well as four pigments that are known to be hardly dispersible, a number of pigmented lacquers were prepared using a dispersant according to the present invention, while also comparing with a dispersant according to the state of the art. The results are listed in Table 2, in the last two columns of which the stability of the pigmented lacquer systems is indicated by a scale of 1-6. A visual evaluation of the behaviour of the lacquer when placed on a glass sheet is given in the column "behaviour film". A visual evaluation of the behaviour of the liquid lacquer is given in the column "behaviour lacquer". To evaluate the compatibility of the dispersants according to the invention, it was determined to what extent the dispersants could be diluted with a number of types of test benzines ("white spirit"). In the following Table 3 it is indicated how many parts of the different test benzines can be added to the dispersant according to Example 6 without the occurrence of precipitation or flocculation. Example 6 Test benzine K 21 7 Test benzine K 30 5 Test benzine K 60 3 For the purposes of comparison it may be indicated that the product used in Table 2 for comparative purposes was hardly soluble in these substances, since precipitation already occurred when adding less than 1 part by weight of test benzine to 1 part by weight of the binder. To determine the compatibility with oil-modified alkyl resins 1 part of dispersant (solid) was added to 10 parts by weight (solid) of two different binders. The compatibility of the dispersant according to the invention with two oil-modified alkyd resins is indicated in Table 4. Example 6 comparative example ALFTALAT AM 649 m, 60 % Hoechst AG ALKYDAL M 48,55 % Bayer AG. To determine the storage stability at room temperature of the binders according to the invention, the binder according to Example 6 and the binder according to Example 14 of European patent application 154,678 were stored at room temperature. After 8 days, 30 days and 150 days the condition of the binders was evaluated. The binder according to Example 6 was still clear and liquid after 8, 30 and 150 days. The comparative example showed turbidity after 8 days, turbidity and thickening after 30 days, and turbidity and solidification after 150 days. It is apparent from the above tests that the dispersants according to the invention show a clearly improved dispersing effect as well as an improved compatibility with oil-modified alkyd resins, improved solubility in aliphatic hydrocarbons and an improved storage stability.

Claims: A solution of a polymer in an organic solvent, said polymer comprising A) 5-80 mol% of one or more monomers having the formula in which R1, R2, R3 and R4 may be the same or different and represent H or alkyl, B) up to 70 mol% of one or more monomers having the formula in which R5, R6 and R7 may be the same or different and represent H or alkyl and R8 is alkyl or substituted alkyl, and the alkyl group R8 may also be interrupted by - O - groups, C) 5-50 mol % of vinylimidazole, D) 0-10 mol % of one or more monomers containing one or more groups reactive to cross-linking or coupling, and E) 0-20 mol % of one or more monomers not falling within the groups A-D, wherein the amount of A and B together, must be at least 20 mol % and A and B are both present, as well as organic salts thereof. A solution as claimed in claim 1, in which the amount of monomers from group B is at least 20 mol %. A solution as claimed in claim 1 or 2, wherein the polymer consists of: 5-15 mol % monomers from group A, 25-70 mol % monomers from group B, 25-40 mol % monomers from group C, 0-5 mol % monomers from group D, and 0-5 mol % monomers from group E. A solution as claimed in claims 1-3, in which the monomers from group A are selected from vinyl toluene, styrene and α-methyl styrene. A solution as claimed in claims 1-4, in which the monomers from group B are selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, 2-ethyl hexyl methacrylate, dimethyl aminoethyl methacrylate, cyclohexyl methacrylate, methylacrylate, isobornyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate, cetyl methacrylate, stearyl methacrylate, behenyl methacrylate, polypropylene glycol monomethylacrylate, polyethylene glycol monomethacrylate and EP-PO monomethacrylate. A solution as claimed in claims 1-5, in which the content of monomers from group D is greater than 0 mol % and the monomers are selected from 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, acrylic acid, methacrylic acid and alkoxylated OH-functional reaction products of said compounds. The use of the solution as claimed in claims 1-6 in the production of coatings and printing inks. The use as claimed in claim 7, using 1-10 mg polymer per m2 pigment surface (BET). Powdered solids to be incorporated in liquid systems, coated with the polymer as described in claims 1-6. Solids as claimed in claim 9, in which the content of polymer ranges between 1 and 10 mg per m 2 pigment surface. Pigment dispersions consisting mainly of one or more pigments, a polymer as described in claims 1-6 and water and/or non-aqueous liquid. A pigment dispersion as claimed in claim 11, consisting mainly of 10-70 % by weight of pigment, 1-10 % by weight of said polymer and 20-89% by weight of water and/or non-aqueous liquid.

Inventors: QUEDNAU PETER HERMANN, WULFF WALTER ANDREAS, QUEDNAU, PETER HERMANN, WULFF, WALTER ANDREAS
Applicants: BUERO W WULFF ING, EFKA CHEMICALS BV, EFKA-CHEMICALS B.V., ING. BUERO W. WULFF
Application year: 1988
Main classification: C08F226
IPC codes: C08F26, C08F220, C08F212, B01F17, C09D17, C09C3, C09D11, C09B67, C08F226, C09D7