DE2918067C2 - Water-dilutable thermosetting coatings - Google Patents

Description

AT 3 25 741 and AT 3 25 740 describe heat-curing coating agents based on specific polymer dispersions which, when mixed with water-soluble or water-dispersible amino resins, produce highly elastic, scratch-resistant, weather-resistant, well-adhering and crater-free coatings. In addition to the claimed copolymer dispersions, which are predominantly made up of acrylic monomers, and the amino resin, the coating agents have a pigment paste as an essential component, through which the corresponding pigment and filler content is introduced into the paint.

According to the patents mentioned, the dispersant contained in this pigment paste can be, among other things, a water-dilutable solution polymer of the acrylic type.

However, it has been shown that in order to achieve optimum properties of the paint, particularly with regard to flow and application without boiling bubbles at higher layer thicknesses, it is not enough to keep the type and amount of the monomers that make up the dispersion within relatively narrow limits, but that the dispersing medium in the pigment paste is of essential importance. It has been shown that using a suitable dispersing medium gives significantly greater freedom in selecting the monomers that make up the dispersion. This in turn makes it much easier to adapt the coating composition to the respective requirements.

It has now been found that binder compositions of polymer dispersions and water-soluble solution polymers, as well as amino resins and optionally pigments and/or fillers which contain specially selected solution polymers, allow the formulation of coating agents which meet all practical requirements.

• a) einer verträglichen Kombination von
  • (1) 40-85 Gew.-% einer durch Emulsionspolymerisation erhaltenen Polymerisatdispersion mit der Monomerenzusammensetzung
    • 22-89 Gew.-% Acryl- und/oder Methacrylsäureester mit Monoalkoholen mit 1 bis 18 C-Atomen,
    • 0-50 Gew.-% Styrol und/oder alkylsubstituiertes Styrol,
    • 1-3 Gew.-% Acryl- und/oder Methacrylsäure,
    • 10-25 Gew.-% Acryl- und/oder Methacrylsäuremonoester mit Glykolen oder Polyalkylenglykolen,
  • (2) 5-40 Gew.-% eines wasserlöslichen und/oder wasserdispergierbaren Amino-Formaldehyd-Kondensationsproduktes, dessen Methylolgruppen teilweise oder vollständig mit Monoalkoholen veräthert sind,
  • (3) 10-40 Gew.-% eines nach Neutralisation mit Basen wasserlöslichen Lösungspolymerisats aus
    • 10-80 Gew.-%, vorzugsweise 25-35 Gew.-% Hydroxyalkyl(meth)acrylaten, deren Homopolymerisate eine Glasübergangstemperatur von unter -25°C, vorzugsweise unter -40°C aufweisen,
    • 8-86 Gew.-%, vorzugsweise 60-70 Gew.-%, (Meth) acrylsäurealkylestern, deren Homopolymerisate eine Glasübergangstemperatur von unter -40°C, vorzugsweise unter -55°C aufweisen und
    • 4-12 Gew.-%, vorzugsweise 6-7 Gew.-%, (Meth) acrylsäure sowie gegebenenfalls
    • bis zu 30 Gew.-% alkylsubstituierten vinylaromatischen Monomeren, deren Homopolymerisate eine Glasübergangstemperatur von unter -40°C aufweisen und/oder Diestern der Malein- oder Fumgarsäure mit C&sub4;-C&sub1;&sub0;- Monoalkoholen,
• wobei die Summe der Komponenten (1) bis (3) 100 ergeben muß, sowie
• b) 0-100 Gew.-% (bezogen auf die Bindemittel-Kombination) eines oder mehrerer Pigmente und/oder Füllstoffe und weiters die üblichen Hilfslösungsmittel und Additive.

The present invention therefore relates to improved water-dilutable, heat-curing coating compositions based on binder combinations of aqueous polymer dispersions, water-soluble solution polymers and amino resins, which optionally further contain pigments, fillers and lacquer auxiliaries, consisting of

• (a) a compatible combination of
  • (1) 40-85 wt.% of a polymer dispersion obtained by emulsion polymerization with the monomer composition
    • 22-89 wt.% acrylic and/or methacrylic acid esters with monoalcohols with 1 to 18 C atoms,
    • 0-50 wt.% styrene and/or alkyl-substituted styrene,
    • 1-3 wt.% acrylic and/or methacrylic acid,
    • 10-25 wt.% acrylic and/or methacrylic acid monoesters with glycols or polyalkylene glycols,
  • (2) 5-40% by weight of a water-soluble and/or water-dispersible amino-formaldehyde condensation product whose methylol groups are partially or completely etherified with monoalcohols,
  • (3) 10-40 wt.% of a solution polymer which is water-soluble after neutralization with bases and
    • 10-80% by weight, preferably 25-35% by weight of hydroxyalkyl (meth)acrylates, the homopolymers of which have a glass transition temperature of below -25°C, preferably below -40°C,
    • 8-86% by weight, preferably 60-70% by weight, of (meth)acrylic acid alkyl esters, the homopolymers of which have a glass transition temperature of below -40°C, preferably below -55°C and
    • 4-12 wt.%, preferably 6-7 wt.%, (meth)acrylic acid and optionally
    • up to 30% by weight of alkyl-substituted vinylaromatic monomers whose homopolymers have a glass transition temperature of below -40°C and/or diesters of maleic or fumaric acid with C₄-C₁₀ monoalcohols,
• where the sum of components (1) to (3) must be 100, and
• b) 0-100 wt.% (based on the binder combination) of one or more pigments and/or fillers and furthermore the usual auxiliary solvents and additives.

In a particular embodiment, component (3) can be present in the coating agent as a partially still soluble reaction product with 20-60 wt.% of component (2) used in the coating agent.

Compatibility within the meaning of the invention is understood to mean the property that a clear varnish prepared from the specified components in the specified proportions produces a homogeneous and perfectly clear film when baked.

Compared to the coating agents according to AT 3 25 741 or AT 3 25 740, the coating agents according to the invention which contain the selected component (3) show further improved flow properties and in particular allow the achievement of high layer thicknesses when sprayed on, which can be baked without boiling bubbles and pinholes if the usual flash-off times are observed. While in the products of the patents mentioned the film thickness reaches a critical limit in this regard at around 45 µm, when using the selected component (3) or the partial reaction product with the amino-formaldehyde condensation product, film thicknesses of more than 60 µm can also be obtained without defects. The coating agents according to the invention also show a much lower dependence on the ambient air humidity during application than the usual paints based on aqueous polymer dispersions.

It was also not foreseeable for the person skilled in the art that when using a polymer resin which has an extremely low glass transition temperature, the boiling tendency of paints based on polymer dispersions can be influenced to this extent.

The polymer dispersions (component 1) are produced in a known manner by emulsion polymerization in the presence of anionic and optionally non-ionic emulsifiers and radical initiators. Suitable anionic emulsifiers are hydrocarbon sulfonates such as dodecylbenzenesulfonate, sodium lauryl sulfate, sodium tridecyl sulfate or the sulfates of ethoxylated fatty alcohols such as sodium lauryl ethoxylate sulfate or an octylphenol reacted with ethylene oxide and then sulfated. Non-ionic emulsifiers of the ethoxylated alkylphenol type are also advantageously used in a mixture with the anionic emulsifiers. To increase storage stability, further emulsifiers can be added after the end of the polymerization.

Suitable monomers which make up the polymer dispersions are in particular the esters of acrylic or methacrylic acid with straight-chain or branched monoalkanols with 1 to 18 carbon atoms, such as methyl, ethyl, propyl, butyl, etc. acrylate or methacrylate. In addition to the intended proportion of acrylic or methacrylic acid, the polymer dispersions contain proportions of esters of acrylic or methacrylic acid with glycols, such as ethylene glycol (ethanediol), propylene glycol (propanediol), etc., or polyalkylene glycols, such as di-, tri- or polyethylene glycol or the corresponding propylene glycols.

The dispersions can contain styrene or alkyl-substituted styrenes, such as vinyltoluene, α -methylstyrene, tert-butylstyrene, etc., as additional monomer building blocks.

The amino resins (component 9) used are the amino-aldehyde condensates based on aminotriazines such as melamine, benzoguanamine, etc., as well as urea, etc., which are commonly used in the paint industry as cross-linking components. The largely or completely etherified types, which may be present in their monomeric or oligomeric form, are preferred, e.g. hexamethoxymethylmelamine.

The component (3) used according to the invention is a solution polymer with an acid number of at least 26 mg KOH/g, which is water-soluble after at least partial neutralization of the carboxyl groups present with inorganic or organic bases. Due to their composition, these polymers have extremely low glass transition temperatures.

• 1. Hydroxyalkylester der (Meth)acrylsäure, deren Homopolymerisate eine Glasübergangstemperatur von unter -25°C aufweisen:
  Acrylsäurehydroxyäthylester (-30°C)
  Acrylsäure-(2)-hydroxypropylester (-49°C)
  Acrylsäure-(4)-hydroxybutylester (-64°C)
  Polyäthylenglykolmonomethacrylate mit einem Molekulargewicht von ca. 220-240 (<-25°C)
  Polypropylenglykolmonomethylacrylat mit einem Molekulargewicht von ca. 260-550 (<-25°C)
  2. Ester der (Meth)acrylsäure, deren Homopolymerisate eine Glasübergangstemperatur von unter -40°C aufweisen:
  n-Propylacrylat (-45°C)
  n-Butylacrylat (-56°C)
  Isobutylacrylat (-40°C)
  2-Äthyl-hexylacrylat (-70°C)
  n-Octylacrylat (-80°C)
  n-Decylmethacrylat (-60°C)
  n-Dodecylmethacrylat (-65°C)
  Isobornylmethacrylat (-114°C)
  
• 3. Alkylsubstituierte vinylaromatische Monomere, deren Homopolymerisate eine Glasübergangstemperatur unter -40°C aufweisen, wie z. B. n-Octylstyrol (-45°C), n-Nonylstyrol (-53°C), n-Decylstyrol (-65°C), n-Dodecylstyrol (-52°C) bzw. die entsprechenden substituierten Methylstyrole.
• 4. Maleinsäure- und Fumarsäurediester, von Monoalkoholen mit 4- 10 Kohlenstoffatomen, wie z. B. Dibutylmaleinat, Dibutylfumarat, Di-Äthylhexylmaleinat und Dioctylfumarat.

Suitable monomers whose homopolymers have the required glass transition temperatures are, for example:

• 1. Hydroxyalkyl esters of (meth)acrylic acid, whose homopolymers have a glass transition temperature below -25°C:
  Acrylic acid hydroxyethyl ester (-30°C)
  Acrylic acid (2)-hydroxypropyl ester (-49°C)
  Acrylic acid-(4)-hydroxybutyl ester (-64°C)
  Polyethylene glycol monomethacrylate with a molecular weight of approx. 220-240 (<-25°C)
  Polypropylene glycol monomethyl acrylate with a molecular weight of approx. 260-550 (<-25°C)
  2. Esters of (meth)acrylic acid whose homopolymers have a glass transition temperature below -40°C:
  n-propyl acrylate (-45°C)
  n-Butyl acrylate (-56°C)
  Isobutyl acrylate (-40°C)
  2-Ethyl-hexyl acrylate (-70°C)
  n-Octyl acrylate (-80°C)
  n-Decyl methacrylate (-60°C)
  n-Dodecyl methacrylate (-65°C)
  Isobornyl methacrylate (-114°C)
  
• 3. Alkyl-substituted vinylaromatic monomers whose homopolymers have a glass transition temperature below -40°C, such as n-octylstyrene (-45°C), n-nonylstyrene (-53°C), n-decylstyrene (-65°C), n-dodecylstyrene (-52°C) or the corresponding substituted methylstyrenes.
• 4. Maleic acid and fumaric acid diesters of monoalcohols with 4-10 carbon atoms, such as dibutyl maleate, dibutyl fumarate, diethylhexyl maleate and dioctyl fumarate.

The solution polymers are produced by radical polymerization in inert organic solvents such as ethyl acetate, ethyl glycol acetate, butanol, glycol ether, especially diethylene glycol monobutyl ether. The solvent is preferably placed in a suitable reaction vessel and the monomer mixture and the initiator are added at the reaction temperature. It is also possible to place part of the total mixture in the reaction vessel and add the rest during the course of the reaction. To convert the polymers into the water-soluble form, the carboxyl groups of the solution polymers are completely or partially neutralized with amines, preferably tertiary alkyl or alkanolamines. To produce solvent-free solution polymers, the solvent can be removed from the dilute aqueous solution by distillation, optionally using the azeotropic process and/or in a vacuum.

All products commonly used in the paint industry can be used as pigments or fillers. The proportions to be used for the various purposes and colors are known to those skilled in the art. To produce pigmented paints, the pigments are dispersed with component (3) on the usual grinding units and mixed into the dispersion. Of course, the usual paint additives such as antifoam agents, flow agents, corrosion inhibitors, slip agents, etc. can also be added to the paint or one of the components, provided the additive is compatible with the binder or the binder solution.

The following examples illustrate the invention without limiting its scope. Parts are by weight.

1. Preparation of polymer dispersions (component 1)

The polymer dispersions used according to the invention are prepared in a known manner by the emulsion polymerization process. The dispersions used in the examples have the following composition (in parts by weight): °=c:230&udf54;&udf53;vu10&udf54;&udf53;vz22&udf54;&udf53;vu10&udf54;

2. Preparation of solvent polymers

• HEA Hydroxyäthylacrylat
  HPA 2-Hydroxypropylacrylat
  HBA 4-Hydroxybutylacrylat
  PAMA Polyalkylenglykolmonomethacrylat
  • (a) Polypropylenglykolmonomethacrylat (MG: 376-434)
    (b) Polyäthylenglykolmonomethacrylat (MG: 394-438)
• BAC n-Butylacrylat
  EHA 2-Äthyl-hexylacrylat
  DMA Dodecylmethacrylat (Laurylmethacrylat)
  ACS Acrylsäure
  MACS Methacrylsäure
  OST n-Octylstyrol
  DBF Dibutylfumarat
  BDG Diäthylenglykolmonobutyläther
  EGA Äthylenglykolmonoäthylätheracetat
  BU Butanol

The solvent is placed in a stirrer equipped with a reflux condenser, addition vessel, thermometer and inert gas supply line. The mixture of the monomers and the initiator, preferably azodiisobutyronitrile and optionally regulator, is prepared in the addition vessel. This mixture is added to the solvent heated to approx. 80°C over a period of 6 hours, while maintaining the reaction temperature of 80°C. After the addition has been completed, further initiator (approx. 1-3 parts) is added to the mixture and the temperature is kept at 80°C for a further 2 hours. The mixture is then kept at 100°C for a further hour. The solids content of the resins according to the composition given in Table I is between 45 and 50% by weight.
Explanation of abbreviations in Table 1

• HEA Hydroxyethyl Acrylate
  HPA 2-hydroxypropyl acrylate
  HBA 4-hydroxybutyl acrylate
  PAMA polyalkylene glycol monomethacrylate
  • (a) Polypropylene glycol monomethacrylate (MW: 376-434)
    (b) Polyethylene glycol monomethacrylate (MG: 394-438)
• BAC n-butyl acrylate
  EHA 2-ethyl-hexyl acrylate
  DMA dodecyl methacrylate (lauryl methacrylate)
  ACS Acrylic Acid
  MACS Methacrylic acid
  OST n-octylstyrene
  DBF Dibutyl fumarate
  BDG Diethylene glycol monobutyl ether
  EGA Ethylene glycol monoethyl ether acetate
  BU Butanol

Example 1-5

Using solution polymers C, J and K and dispersions I and II, paints were produced according to the following recipe:

Dimethylethanolamine was added to the solution polymer (component 3) until a sample mixed 1:1 with distilled water had a pH of approx. 9. 50 parts of the anhydrous, neutralized resin solution were ground with 80 parts of TiO₂ rutile on a three-roller and mixed with 25 parts of hexamethoxymethylmelamine. This mixture was slowly added with intensive stirring to the dispersion adjusted to approx. pH 7 with dimethylethanolamine, diluting it with deionized water if necessary. After thorough mixing Table 1 Composition of the solution polymers used according to the invention (component 3) &udf53;vu10&udf54;&udf53;vz23&udf54;&udf53;vu10&udf54;3 parts of a 10% aqueous solution of p-toluenesulfonic acid neutralized with dimethylethanolamine and 0.3 parts of corrosion inhibitor were added. Finally, the paint mixture was adjusted to a spray viscosity of 20 s (according to DIN 53 211) using deionized water. The paint was applied by spraying onto cleaned, non-pretreated sheet steel and baked for 30 minutes at 160°C.

Table 2 shows the composition of the paint formulations 1 to 5. The test results are summarized in Table 3. Table 2 Composition of the paints according to examples 1-5 &udf53;vu10&udf54;&udf53;vz19&udf54;&udf53;vu10&udf54; Table 3 &udf53;vu10&udf54;&udf53;vz21&udf54;

Example 6

734 parts of solution polymer A were diluted with 1006 parts of deionized water, adjusted to a pH of about 8.5 with dimethylethanolamine and the butanol present was distilled off as far as possible with part of the water. A 30% resin solution was obtained, the pH of which was adjusted to 9 with dimethylethanolamine.

83 parts of the resin solution were ground with 80 parts of TiO₂ rutile and 25 parts of diethylene glycol monobutyl ether on a three-roll mill and mixed with 25 parts of a largely methylolated melamine condensate etherified with methanol. The mixture was slowly added with intensive stirring to 111 parts of dispersion I adjusted to pH 7-7.5 with dimethylethanolamine, with deionized water being added at the same time if necessary. After thorough mixing, 3 parts of a 10% aqueous solution of p-toluenesulfonic acid neutralized with dimethylethanolamine and 0.3 parts of corrosion inhibitor were added.

The paint mixture was adjusted to a spray viscosity of 20 s (according to DIN 53 211) with deionized water, applied by spraying onto cleaned steel sheet and baked for 30 min at 160°C.

The test results are shown in Table 4.

Example 7

The solution polymer J was mixed with 80 parts of hexamethoxymethylmelamine and heated to 150°C for 5 hours with stirring, during which small amounts of water and solvent escaped. The resin thus obtained was mixed with dimethylethanolamine until a sample mixed 1:1 with distilled water had a pH of about 9. 50 parts of the anhydrous, neutralized resin solution were ground with 80 parts of TiO₂ rutile on a three-roller and mixed with 11.8 parts of hexamethoxymethylmelamine.

This mixture was slowly added with intensive stirring into 111 parts of dispersion I adjusted to pH 7-7.5 with dimethylethanolamine, and if necessary, simultaneously diluted with deionized water.

The paint is processed analogously to Example 6. The results of the paint test are summarized in Table 4. Table 4 &udf53;vu10&udf54;&udf53;vz10&udf54;&udf53;vu10&udf54;

Claims (2)

1. Water-dilutable, heat-curing coating agents based on binder combinations of aqueous polymer dispersions, water-soluble solution polymers and amino resins, which may also contain pigments, fillers and paint additives, consisting of
(a) a compatible combination of (1) 40-85 wt.% of a polymer dispersion obtained by emulsion polymerization with the monomer composition 22-89 wt.% acrylic and/or methacrylic acid esters with monoalcohols with 1 to 18 C atoms, 0-50 wt.% styrene and/or alkyl-substituted styrene, 1-3 wt.% acrylic and/or methacrylic acid, 10-25 wt.% acrylic and/or methacrylic acid monoesters with glycols or polyalkylene glycols, (2) 5-40% by weight of a water-soluble and/or water-dispersible amino-formaldehyde condensation product whose methylol groups are partially or completely etherified with monoalcohols, (3) 10-40 wt.% of a solution polymer which is water-soluble after neutralization with bases and 10-80% by weight, preferably 25-35% by weight of hydroxyalkyl (meth)acrylates, the homopolymers of which have a glass transition temperature of below -25°C, preferably below -40°C, 8-86% by weight, preferably 60-70% by weight of (meth)acrylic acid alkyl esters, the homopolymers of which have a glass transition temperature of below -40°C, preferably below -55°C and 4-12 wt.%, preferably 6-7 wt.%, (meth)acrylic acid and optionally up to 30% by weight of alkyl-substituted vinylaromatic monomers whose homopolymers have a glass transition temperature of below -40°C and/or diesters of maleic or fumaric acid with C₄-C₁₀ monoalcohols, where the sum of components (1) to (3) must be 100, and (b) 0-100 wt.% (based on the binder combination) of one or more pigments and/or fillers and furthermore the usual auxiliary solvents and additives.
2. Coating agent according to claim 1, characterized in that the component (3) is present in the coating agent as a partial, still soluble reaction product with 20-60 wt.% of the intended amount of component (2).