WO2000055224A1

WO2000055224A1 - Polymer dispersion and method for producing the same

Info

Publication number: WO2000055224A1
Application number: PCT/EP2000/002322
Authority: WO
Inventors: Hans-Jürgen ADLER; Axel Henke; Thomas Schmidt-Hansberg
Original assignee: Chemetall Gmbh
Priority date: 1999-03-17
Filing date: 2000-03-16
Publication date: 2000-09-21
Also published as: AU3812200A; DE19911842A1

Abstract

The invention relates to an aqueous polymer dispersion which is produced by means of a two-step emulsion polymerisation process and which consists essentially of 5 to 50 wt.% of a copolymer and 0.1 to 3 wt.% of an emulsifier with the remainder being water or/and an organic solvent. Said copolymer has a spherical or/and essentially spherical particulate form and a particle diameter of 10 to 500 nm or a coil structure and consists of 95 to 0 wt.% of at least one monomeric vinyl compound and 5 to 100 wt.% of at least one monomeric phosphoric acid ester containing a vinylidene group.

Description

Polymer dispersion and process for its preparation

description

The invention relates to an aqueous polymer dispersion and a process for its preparation. Aqueous polymer dispersions with different compositions are widely used today for the application of protective layers to metallic surfaces.

From DE-A 19 42 423 an aqueous emulsion is known which consists of a polymerized acrylic resin, at least one emulsifier, a mercaptan and a water-soluble colloid, the acrylic resin at least 20% by weight of acrylic acid ester or methacrylic acid ester and the colloid one or more carboxylic acid groups contains. The acrylic acid resin may also contain styrene, methyl styrene or vinyl toluene. In addition, 1 to 5% by weight of a polymerizable acid, in particular itaconic acid, methacrylic acid or acrylic acid, can be present in the acrylic resin. The emulsifier used contains phosphate, phosphonate, sulfate or sulfonate groups. The mercaptan is used in an amount of up to 4 parts by weight per 100 parts by weight of total monomer, and alkyl mercaptans having at least 6 carbon atoms are used as mercaptans. The emulsion can also contain a pigment, in particular a corrosion-inhibiting pigment, and is used as a base coat for steel.

DE-A 25 33 043 discloses a process for emulsion polymerization in which a vinyl halide or a mixture of a vinyl halide and a vinyl ester or an ester of an unsaturated carboxylic acid is polymerized in an aqueous medium in the presence of a surface-active agent and an initiator, wherein a phosphate ester is used as the surface-active agent, which has one or two alkyl groups each having 8 to 10 carbon atoms. After this

CONFIRMATION COPY Processes can be used to produce stable emulsions which are suitable for producing color-stable films.

DE-C 27 43 764 describes an aqueous plastic dispersion which contains a vinyl polymer and an emulsifier, the emulsifier being a water-soluble salt of an alkanephosphonic acid or an alkanephosphonic acid monoalkyl ester or a mixture of these salts. The dispersion is produced in the presence of the emulsifier by polymerizing at least one vinyl monomer.

EP-B 0 208 194 discloses binders for aqueous anticorrosion paints, which are emulsions which are a copolymer consisting of styrene and a methacrylic acid ester and 0.5 to 4% by weight of a monoalkyl phosphate and 0.1 to 3% by weight. 5% by weight of an ethoxylated alkylphenol and / or an ethoxylated C ₈ to C ₈ fatty alcohol, these two additives acting as an emulsifier system, the amount of the two additives being based on the amount of copolymer and the copolymer having an average particle diameter of 0 , 01 to 0.5 μm.

EP-A 0 305 850 discloses an aqueous dispersion for paints which, by copolymerization of 25 to 98% by weight of acrylic and / or methacrylic acid esters, 1 to 10% by weight of acrylic and / or methacrylic acid, 1 to 8% by weight a compound of the general formula

O

CH ₂ = CY - C - O - Z - O - p - OY

¹¹ I

O OH

Y = H and / or Ci - to C ₈ - hydrocarbon radical Z = Ci - to C ₈ - alkyl radical and 0 to 60% by weight of a further copolymerizable olefinic compound in an organic solvent, neutralization of the copolymer solution and dilution with water and optionally distilling off the solvent. Vinylaromatics (styrene and vinyltoluene), vinyl ethers, vinyl esters, (meth) acrylamide or (meth) acrylonitrile can be used as the copolymerizable olefinic compound. The copolymer solution can be neutralized with aqueous ammonia solution. The known aqueous dispersion can be used for the production of paints and as a coating agent for coating metals. The polymer content of the known dispersion is 40 to 60% by weight and the pH of the dispersion is between 6.8 and 10. A disadvantage of the dispersion known from EP-A 0 305 850 is seen in the fact that it is used to prepare it Solvent, preferably butanol, isobutanol, propanol, ethanol, methyl isobutyl ketone, toluene or xylene, must be used, which is separated from the dispersions by distillation, a quantitative separation of the solvent should hardly be possible.

The invention has for its object to provide an aqueous polymer dispersion which is solvent-free and the polymer particles have a spherical particle shape and a particle diameter <200 nm. The invention is also based on the object of providing a method for producing an aqueous polymer dispersion which does not use organic solvents and avoids neutralization of the polymer dispersion.

The object on which the invention is based is achieved by a polymer dispersion comprising water and / or organic solvent, which is characterized in that it consists essentially of 5 to 50% by weight, preferably 5 to 30% by weight, of a copolymer, 1 to 3% by weight, preferably 0.3 to 3% by weight, of an emulsifier and the remainder water and / or organic solvent, the copolymer having a spherical or / and essentially spherical particle shape and a particle diameter of 10 to 500 nm, preferably up to 400 or particularly preferably up to 200 nm, or has a coil structure and from 95 to 0% by weight, preferably 90 to 40% by weight, at least one monomeric vinyl compound and 5 to 100% by weight, preferably 10 to 60% by weight, of at least one monomeric phosphoric acid ester containing a vinylidene group, and that it is composed by two-stage emulsion polymerization in water or / and Organic solvent is produced, wherein the monomeric vinyl compound was introduced in whole or in part in the first stage and wherein in the second stage the monomeric phosphoric acid ester and optionally the rest of the monomeric vinyl compound was added to the polymerization product of the first stage.

In addition, the object is achieved by creating an aqueous polymer dispersion which consists essentially of 5 to 30% by weight of a copolymer, 0.3 to 3% by weight of an emulsifier and the rest of water, the copolymer having a spherical particle shape and a Has particle diameter of 10 to 200 nm and is made up of 95 to 60% by weight of at least one monomeric vinyl compound and 5 to 40% by weight of at least one monomeric phosphoric acid ester containing a vinylidene group. The amounts given in% by weight relate to the fact that the aqueous polymer dispersion or the copolymer are each 100% by weight. Monomeric vinyl compounds are unsaturated organic compounds which contain the very polymerizable groups CH ₂ = CH- (vinyl group) and CH ₂ = CR- (vinylidene group). According to this definition, the acrylic and methacrylic compounds and styrene also belong to the monomeric vinyl compounds (see Römpps Chemie-Lexikon, 8th edition, 1988, keyword: vinyl monomers). The particle size is determined by known methods, e.g. B. with the light scattering method (photon correlation spectroscopy), the laser diffraction method, the single counting method (Coulter measuring principle), the covalence method or with a chromatographic method or with another fractionation method such as the flow-field-flow fractionation Method. The particle shape is determined by means of electron microscopy (scanning or transmission electron microscopy) or solid-state NMR spectroscopy or from light scatter measurements. The pH of the polymer dispersion according to the invention is in the weakly acidic range from about 2 to 4, and according to the invention, the neutralization of the polymer dispersion or its conversion into the alkaline range is deliberately avoided, since it was found that the Copolymer particles in the weakly acidic pH range are more stable than in the neutral or alkaline pH range and that the phosphoric acid ester groups in the weakly acidic pH range adsorb better on the aluminum than their salts, which are above pH 7 in the copolymer Particles are present. It was also found that the pH should not fall below 2, since phosphoric acid esters lose stability in the strongly acidic range, because they are partially hydrolytically cleaved under these conditions.

The fact that the aqueous polymer dispersion according to the invention has a content of 5 to 50% by weight, preferably 5 to 30% by weight, of the copolymer means that the dispersion has a relatively low viscosity and therefore has the form of thin layers a metallic or metal oxide substrate can be applied, the spherical particles being spontaneously adsorbed on the substrate surface and forming thin layers. The advantageous interaction of the emulsifier and the copolymer constructed according to the invention ensures that the aqueous polymer dispersion is stable over a long period of time, ie that the particle shape and size are constant over a long period of time and that the discrete individual particles during the Do not agglomerate storage time. While the monomeric vinyl compounds used determine the hardness and elasticity of the individual copolymer particles and thus also the hardness and elasticity of the thin layer consisting of the copolymer, the phosphoric acid ester contained in the copolymer is particularly responsible for the binding of the thin copolymer layer to a metallic or metal oxide substrate .

According to the invention it is further provided that the copolymer contains 2 to 5% by weight of a crosslinking agent (copolymer = 100% by weight). By the invention Crosslinking of the copolymer gives dimensionally stable copolymer particles which can also be processed into films.

According to the invention, the copolymer contains, as monomeric vinyl compound, styrene, vinyl acetate, a vinyl ether, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, an acrylic acid ester, a methacrylic acid ester, an amide of acrylic acid and / or an amide of methacrylic acid, the alcohol residue of the ether and the esters Has 1 to 8 carbon atoms and one or more carbon atoms of the ester or the ethers can be substituted by an alkyl or aryl radical which has 1 to 8 carbon atoms. According to the invention, the copolymer contains as monomeric phosphoric acid esters of formula I or II

II

or a mixture of the compounds I and II, where R — is hydrogen or an alkyl radical having 1 to 4 carbon atoms, in particular a methyl radical, and wherein R _{2 is} an alkoxy, alkyl or aryl group having 2 to 12 carbon atoms is and can be linear or branched. The use of the aforementioned monomeric vinyl compounds and monomeric phosphoric acid esters results in aqueous polymer dispersions with good performance properties, in which the discrete copolymer particles are present as dimensionally stable microgels.

According to the invention, it has proven to be particularly advantageous if the aqueous polymer dispersion contains an anionic or nonionic surfactant, preferably a sodium alkylbenzenesulfonate or sodium dodecyl sulfate, as emulsifier. The use of these emulsifiers ensures that the dispersion is stable for at least 12 months and that the copolymer particles do not agglomerate during this time.

According to the invention, the copolymer contains as crosslinker p-divinylbenzene, a bis-acrylic acid ester or a bis-methacrylic acid ester, the alcohol group of the esters having 1 to 8 carbon atoms. The use of these crosslinkers advantageously ensures that the discrete copolymer particles are dimensionally stable.

In addition, the polymer dispersion according to the invention can contain small amounts e.g. a fungicide, a UV stabilizer, a film-forming aid or a plasticizer.

The aqueous polymer dispersion according to the invention has particularly advantageous performance properties if it has a pH of 2 to 3 and consists of 20% by weight of a copolymer, 0.5 to 0.75% by weight of the emulsifier sodium dodecyl sulfate and the rest water, where the copolymer has a particle diameter of 50 to 100 nm and consists of 2% by weight of p-divinylbenzene as a crosslinking agent, 45 to 46% by weight of styrene and 45 to 46% by weight of n-butyl acrylate as a vinyl compound and 6 to 8% by weight of a mixture of 2-methacryloyloxyethyl phosphate and bis-2-methacryloyloxyethyl phosphate in a ratio of 1: 1 is built up as a phosphoric acid ester. This dispersion forms very thin layers on substrates.

The object on which the invention is based is further achieved by a process for the preparation of the aqueous polymer dispersion, in which a two-stage emulsion polymerization is carried out at 50 to 90 ° C., an aqueous solution of the emulsifier being prepared in the first stage, then into the aqueous emulsifier solution all or part of the monomeric vinyl compound is introduced and a radical generator is added to this mixture, and in the second stage the polymerization product of the first stage of the monomeric phosphoric acid esters and optionally the rest of the monomeric vinyl compound is added and a radical generator is added.

By means of the two-stage emulsion polymerization according to the invention it is advantageously achieved that the monomeric phosphoric acid ester is polymerized into the outer shell of the copolymer particles and that this component is therefore available almost quantitatively for the binding of the copolymer particles to a substrate, while the core of the copolymer particles consists entirely of the monomeric vinyl compounds is built up, which are responsible in particular for the hardness and elasticity of the copolymer particles. The fact that the monomeric phosphoric acid ester is polymerized in varying amounts into the outer shell of the copolymer particles means that the swelling of the copolymer particles caused by water can be influenced, since the swelling of the particles increases with increasing phosphoric acid ester content.

According to the invention it is further provided that 60 to 100% by weight and in the second step 40 to 0% by weight of the monomeric vinyl compounds are introduced and polymerized (total amount of vinyl compounds = 100% by weight). This weight ratio ensures that the outer shell of the copolymer particles has a sufficiently large number of groups that are required to bind the copolymer to the substrate.

In a further embodiment of the invention it is provided that at least one peroxy compound, preferably ammonium peroxide sulfate, is added as the radical generator. Water-soluble peroxy compounds are used as radical formers, 0.5 to 3 g radical formers / kg monomers being used in the first and second stages. The water-soluble radical formers are used in the form of highly diluted solutions.

Finally, it is provided according to the invention that a part of the crosslinking agent is introduced into each of the first and second stages, it being expedient has proven if 70 to 90% by weight of the crosslinker is introduced in the first stage and 30 to 10% by weight in the second stage.

It is not necessary to neutralize the aqueous polymer dispersions prepared by the process according to the invention before their further use, since their pH is generally between 2 and 3. The process according to the invention avoids the use of organic solvents and therefore provides products which are solvent-free. The aqueous polymer dispersions according to the invention can be used in particular to apply thin polymer layers to different metallic and metal oxide substrates.

The polymer dispersions according to the invention can be used to coat workpieces with surfaces of metals, alloys, glass, ceramics, etc. be used. In particular, those of iron, steel, zinc, titanium, magnesium, aluminum and their alloys can be coated as surfaces. The coatings serve in particular to protect against corrosion and have proven themselves extremely well for pretreatment before painting or other coating with an organic layer. They can also be used on non-metallic-inorganic surfaces or on surfaces of titanium alloys as coatings for implants. You can also form an adhesive layer on which e.g. subsequently adhesive layers are to be applied.

The subject matter of the invention is explained in more detail below using an exemplary embodiment.

At 75 ° C the emulsifier sodium dodecyl sulfate is dissolved in water. Styrene, n-butyl acrylate and divinylbenzene are added dropwise to the emulsifier solution at 75 ° C. At the same time, the mixture of the radical formers ammonium peroxide sulfate in the form of a 1% aqueous solution is added dropwise. In the first stage of the emulsion polymerization, the monomeric compounds are polymerized at 75 ° C. with stirring up to about 90%. In this intermediate product, styrene, n-butyl acrylate and a mixture of 2-methacryloyloxyethyl phosphate and bis-2-methacryloyloxyethyl phosphate in a ratio of 1: 1 and a 1% strength aqueous solution of the radical generator ammonium peroxide sulfate are then added dropwise at 75 ° C introduced with stirring.

After all the substances have been added, the mixture is stirred at 75 to 70 ° C. until the polymerization reaction has ended. The table below shows the amounts of raw material introduced in the two stages of the emulsion polymerization.

The aqueous polymer dispersion produced by two-stage emulsion polymerization has a solids content of 20% by weight and its pH is 2.5 to 2.6. The aqueous dispersion can be applied directly to a metallic or metal oxide substrate without neutralization and, if necessary after drying, forms a thin polymer layer.

Claims

claims

1. water or / and organic solvent-containing polymer dispersion, characterized in that it consists essentially of 5 to 50% by weight of a copolymer, 0.1 to 3% by weight of an emulsifier and the remainder water and / or organic solvent, wherein the copolymer has a spherical and / or substantially spherical particle shape and a particle diameter of 10 to 500 nm or has a coil structure and from 95 to 0% by weight of at least one monomeric vinyl compound and from 5 to 100% by weight of at least one vinylidene group containing monomeric phosphoric acid ester, and that it by two-stage

Emulsion polymerization is prepared in water and / or organic solvent, the monomeric vinyl compound being introduced in whole or in part in the first stage and in the second stage the monomeric phosphoric acid esters and optionally the remainder of the monomeric vinyl compound being added to the polymerization product in the first stage.

2. Aqueous polymer dispersion, characterized in that it consists essentially of 5 to 30% by weight of a copolymer, 0.3 to 3% by weight of an emulsifier and the rest of water, the copolymer having a spherical particle shape and a particle diameter of 10 up to 200 nm and from 95 to 60% by weight of at least one monomeric vinyl compound and from 5 to

40% by weight of at least one monomeric phosphoric acid ester containing a vinylidene group, and that it is prepared by two-stage emulsion polymerization in water or / and organic solvent, the monomeric vinyl compound being introduced in whole or in part in the first stage and in the second stage the Polymerization product of the first stage of the monomeric phosphoric acid ester and optionally the rest of the monomeric vinyl compound was added. Aqueous polymer dispersion according to Claim 1 or 2, characterized in that the copolymer contains 2 to 5% by weight of a crosslinking agent.

Aqueous polymer dispersion according to claim 1 or 2, characterized in that the copolymer as monomeric vinyl compound styrene, vinyl acetate, a vinyl ether, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, an acyl ester, a methacrylic ester, an amide of acrylic acid and / or an amide Contains methacrylic acid, where the alcohol radical of the ether and the ester has 1 to 8 carbon atoms and where one or more carbon atoms of the ether or ester can be substituted by a radical which has 1 to 8 carbon atoms.

5. Aqueous polymer dispersion according to claim 1 or 2, characterized in that the copolymer as monomeric phosphoric acid compounds of formula I or II

II

or contains a mixture of compounds I and II, where R _{1 is} hydrogen or an alkyl radical having 1 to 4 carbon atoms, in particular a methyl radical, and wherein R _{2 is} an alkoxy, alkyl or aryl group having 2 to 12 carbon atoms is.

6. Aqueous polymer dispersion according to claim 1 or 2, characterized in that it contains an anionic or nonionic surfactant, preferably a sodium alkylbenzenesulfonate or sodium dodecyl sulfate, as emulsifier.

7. Aqueous polymer dispersion according to claim 3, characterized in that the copolymer contains as crosslinking agent p-divinylbenzene, a bis-acrylic acid ester or a bis-methacrylic acid ester, the alcohol group of the esters having 1 to 8 carbon atoms.

8. Aqueous polymer dispersion according to claims 1 to 7, characterized in that it has a pH of 2 to 3 and from 20% by weight of a copolymer, 0.5 to 0.75% by weight of the emulsifier, sodium dodecyl sulfate and The remainder consists of water, the copolymer having a particle diameter of 50 to 100 nm and consisting of 2% by weight of p-divinylbenzene as a crosslinking agent, 45 to 46% by weight of styrene and 45 to 46% by weight of n-butyl acrylate as the vinyl compound and 6 to 8 % By weight of a mixture of 2-methacryloyloxyethyl phosphate and bis-2-methacryloyloxyethyl phosphate is built up in a ratio of 1: 1 as the phosphoric acid ester.

9. A process for the preparation of an aqueous polymer dispersion according to claims 1 to 8, characterized in that a two-stage emulsion polymerization is carried out at temperatures of 50 to 98 ° C, preferably to 90 ° C, wherein in the first stage a water or / and organic

Solvent-containing solution of the emulsifier is prepared, then all or part of the monomeric vinyl compound is introduced into the aqueous emulsifier solution and a radical generator is added to this mixture and

10. wherein in the second stage the polymerization product of the first stage of the monomeric phosphoric acid esters and optionally the rest of the monomers

Vinyl compound is added and a radical generator is added.

11. The method according to claim 9, characterized in that in the first stage 60 to 100 wt.% And in the second stage 40 to 0 wt.% Of the monomeric vinyl compound are introduced and polymerized.

12. The method according to claim 9, characterized in that at least one water-soluble peroxy compound, preferably ammonium peroxydisulfate, is added as the radical generator.

13. The method according to claim 9, characterized in that in each case part of the crosslinker is introduced into the first and second stages.