HK1070094B - Coating composition and process for its preparation - Google Patents

Description

Coating composition and method for preparing the same

The present invention relates to novel coating compositions having improved open time and methods for their preparation.

Aqueous polymer dispersions are commonly used to prepare coating compositions.

One particularly important property associated with treating coating materials is open time. In the case of physically drying the coating, open time refers to the period of time during which a second coating can be applied to the still-wet coating and no visible "cracks" will occur after drying.

The open time required in the particular case is generally set by the addition of glycols or high-boiling solvents, according to the state of the art. In many cases the desired open time can be achieved by simply adding the appropriate coalescent. For coatings that do not contain emissions and solvents, no solvent can generally be added. Therefore, the setting of the open time may become problematic in this case.

An open time of around 10 minutes is considered optimal for the coating material, since adjustments can still be made during this time. The long open time has the disadvantage of being susceptible to contamination.

In addition to the above methods, the prior art also discloses other methods of influencing the open time of the coating material.

US-A-6,303,189 describes A process for extending the open time of aqueous coating compositions using an aqueous polyurethane dispersion and A coalescent agent. The comparative examples show a significant reduction in the open time of aqueous coating compositions based on acrylate dispersions without polyurethane dispersions.

EP-A-593,151 describes ｃA process for increasing the open time using emulsions containing mutually reactive groups and modifiers.

WO-A-02/32,980 discloses aqueous polyurethane coating materials comprising aqueous polyurethane oligomer dispersions having an open time of at least 20 minutes.

EP-A-62,106 describes ｃA process for preparing copolymers having ｃA higher water resistance by emulsion polymerization in the presence of polyvinyl alcohol as protective colloid.

EP-A-538,571 discloses ｃA process for preparing emulsifier-free aqueous dispersions, in which selected monomers are reacted in the monomer feed process in the presence of selected polyvinyl alcohols.

In prior art methods for increasing open time, a modifier (typically a selected polymer) is added to the coating composition.

The object of the present invention is to provide a novel coating composition whose open time can be varied in a simple manner without the addition of special auxiliaries.

It is another object of the present invention to provide a new method for precisely adjusting the open time of a coating composition.

The present invention provides an aqueous coating composition comprising:

a) (meth) acrylate homopolymer and/or (meth) acrylate copolymer-based polymer dispersions prepared by emulsion polymerization in the presence of protective colloids,

b) if desired, pigments and/or fillers, having a Pigment Volume Concentration (PVC) of from 0 to 30%,

c) if desired, a homogenizing aid,

d) if desired, the coalescing agent(s),

e) if desired, a polymeric thickener, and

f) if desired, other conventional additives.

The polymer dispersions to be used according to the invention are prepared by emulsion polymerization in which the monomers are metered in continuously or discontinuously.

The polymer dispersions to be used according to the invention are characterized in that their preparation is carried out in the presence of the selected stabilizer or stabilizer mixture which acts as a protective colloid.

Conventional polymeric substances which act as protective colloids can be used for the stabilizers. Examples thereof are cellulose ethers, polyethylene oxides, starch derivatives or, in particular, polyvinyl alcohols.

In addition to the protective colloids, other stabilizers, for example low molecular weight emulsifiers, which may be based, for example, on sulfates, sulfonic acids, carboxylic acids or polyethylene oxides, may be used in the emulsion polymerization.

Preferred are polymer dispersions prepared in the absence of emulsifiers.

The invention is characterized by the presence of protective colloids during the actual emulsion polymerization. If desired, protective colloids and/or emulsifiers may also be added after the end of the polymerization.

Particular preference is given to using polyvinyl alcohol as protective colloid.

The number-average molecular weight of a typical polyvinyl alcohol used according to the invention is 14000-205000 (determined by Gel Permeation Chromatography (GPC) at 20 ℃ C.) (corresponds to a 4% strength aqueous solution having a viscosity of 2-70 mPas at 20 ℃ C.; determined by means of a falling ball viscometer in accordance with H ö pper, DIN 53015).

Polyvinyl alcohols are generally prepared by hydrolysis of polyvinyl acetate.

Particularly suitable polyvinyl alcohols preferably have a degree of hydrolysis of from 70 to 100 mol% and an aqueous solution viscosity of from 2 to 70 mPas at 20 ℃.

Other suitable polyvinyl alcohols may be hydrophilically or hydrophobically modified in any manner.

An example of a hydrophobically modified polyvinyl alcohol containing water-soluble monomer units in its backbone is Exceval from Kuraray^®Ethylene-containing polyvinyl alcohol.

Another possibility is to modify the polyvinyl alcohol by grafting onto the alcohol radical, for example by partial acetalization of the alcohol radical of the polyvinyl alcohol, for example in such a way that the polyvinyl alcohol has any desired groups, which may be hydrophobic or hydrophilic, for example Mowiflex from Kuraray^®Polyvinyl alcohol type.

The polyvinyl alcohol used according to the invention is preferably dissolved at the beginning of the polymerization (usually in water at least 90 ℃ in 2 to 3 hours) and fed in before the polymerization.

The total amount of protective colloid used before and during the emulsion polymerization is generally from 1 to 20% by weight, preferably from 2 to 12% by weight, more preferably from 3 to 11% by weight, based on the total amount of monomers used.

All stabilizers and emulsifiers, if appropriate, can be fed in appropriately at the beginning of the emulsion polymerization; alternatively and preferably, part of the stabilizer and emulsifier is fed in at the beginning, if appropriate, and the remainder is added continuously or in one or more stages after the start of the polymerization. This addition may be carried out separately or together with other components, such as monomers and/or initiators.

The (meth) acrylate-based polymer dispersions used according to the invention are derived from acrylates and/or methacrylates, if desired together with further monomers copolymerizable therewith, in particular ethylenically unsaturated hydrocarbons and/or small amounts of ethylenically unsaturated ionic comonomers, and can be obtained by free-radical emulsion polymerization.

The acrylic esters are generally esters of acrylic acid with alcohols, preferably alkanols having 1 to 12, preferably 1 to 8, in particular 1 to 4, carbon atoms, such as, in particular, methanol, ethanol, n-butanol, isobutanol or 2-ethylhexanol.

Preferred monomers of this type are methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate. It is preferable that

The methacrylic esters are generally esters of methacrylic acid with alcohols, preferably alkanols having 1 to 12, preferably 1 to 8, in particular 1 to 4, carbon atoms, such as, in particular, methanol, ethanol, n-butanol, isobutanol or 2-ethylhexanol.

Preferred monomers of this type are methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and 2-ethylhexyl methacrylate.

The polymer dispersion used according to the invention can be chosen from homopolymers or copolymers derived from esters of acrylic acid with aliphatic monoalcohols having 1 to 10 carbon atoms, homopolymers or copolymers derived from esters of methacrylic acid with aliphatic monoalcohols having 1 to 10 carbon atoms.

In addition to these acrylates and methacrylates, the polymer dispersions used in the present invention may also be derived from additional α, β -monoethylenically unsaturated monocarboxylic and dicarboxylic acid esters, such as, for example, the maleic and itaconic esters formed with the above-mentioned alcohols.

Furthermore, the polymer dispersions used according to the invention may contain small amounts of units derived from ethylenically unsaturated ionic comonomers: for example from alpha, beta-monoethylenically unsaturated monocarboxylic and dicarboxylic acids, for example from acrylic acid, methacrylic acid, maleic acid and itaconic acid and their water-soluble salts.

This fraction is generally less than 2% by weight, based on the total monomer fraction, of units derived from the ethylenically unsaturated ionic comonomer.

In addition to these (meth) acrylates, the polymer dispersions used according to the invention preferably comprise further units which originate from ethylenically unsaturated hydrocarbons. The polymer dispersion used according to the invention can be chosen from copolymers derived from esters of acrylic and/or methacrylic acid with aliphatic monoalcohols having 1 to 10 carbon atoms and ethylenically unsaturated hydrocarbons, in particular ethylene and/or styrene.

These ethylenically unsaturated hydrocarbons are generally aromatic or aliphatic α, β -unsaturated, optionally halogenated hydrocarbons, such as ethylene, propylene, 1-butene, 2-butene, vinyl chloride, 1-dichloroethylene, styrene, α -methylstyrene and o-chlorostyrene, preference being given to ethylene and styrene.

It is also possible to use esters of vinyl alcohol with monocarboxylic acids having from 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate, vinyl stearate and vinyl Versatic acid.

Nitriles of α, β -monoethylenically unsaturated carboxylic acids, such as acrylonitrile; and/or conjugated dienes having from 4 to 8 carbon atoms, such as 1, 3-butadiene and isoprene.

The (meth) acrylate and the ethylenically unsaturated hydrocarbon generally constitute the principal monomers, and they generally represent a percentage of more than 50% by weight, based on the total amount of monomers to be polymerized by the free radical aqueous emulsion polymerization process.

These monomers typically have only moderate to low levels of solubility in water under standard conditions (25 ℃,1 atm).

Of course, other comonomers which modify these properties in a specific manner can be added. These monomers are usually copolymerized only as modifying monomers in amounts of less than 50% by weight, generally from 0.5 to 20% by weight, preferably from 1 to 10% by weight, based on the total amount of monomers to be polymerized.

The monomers typically used to increase the internal strength of films formed from aqueous polymer dispersions typically contain at least one epoxy, hydroxyl, N-methylol or carbonyl group, or at least two nonconjugated ethylenically unsaturated double bonds.

Examples thereof are N-alkylolamides of alpha, beta-monoethylenically unsaturated carboxylic acids having 3 to 10 carbon atoms, of which N-methylolacrylamide and N-methylolmethacrylamide are particularly preferred, as well as esters of the carboxylic acids with alkanols having 1 to 4 carbon atoms. Also suitable are monomers comprising two vinyl groups, monomers comprising two vinylidene groups and monomers comprising two alkenyl groups.

Particularly advantageous in the context of the present invention are diesters of dihydric alcohols with α, β -monoethylenically unsaturated monocarboxylic acids, preferably acrylic acid and methacrylic acid.

Examples of such monomers containing two nonconjugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates, such as ethylene glycol diacrylate, 1, 2-propylene glycol diacrylate, 1, 3-butylene glycol diacrylate, 1, 4-butylene glycol diacrylate and ethylene glycol dimethacrylate, 1, 2-propylene glycol dimethacrylate, 1, 3-butylene glycol dimethacrylate, 1, 4-butylene glycol dimethacrylate, and also divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, diallyl acrylate, diallyl fumarate, methylenebisacrylamide, Cyclopentadienyl acrylate or triallyl cyanurate.

Of particular importance in the context of the present invention are also methacrylic acid C₁-C₉Hydroxyalkyl esters and acrylic acid C₁-C₉Hydroxyalkyl esters, such as n-hydroxyethyl acrylate, n-hydroxypropyl acrylate or n-hydroxybutyl acrylate and n-hydroxyethyl methacrylate, n-hydroxypropyl methacrylate or n-hydroxybutyl methacrylate, and also compounds such as diacetoneacrylamide and acetoacetoxyethyl acrylate and acetoacetoxyethyl methacrylate.

In addition, compounds of the formula R³Si(CH₃)_0-2(OR⁴)_3-1The organosilicon monomer of (1), wherein R³Is defined as CH₂＝CR⁴-(CH₂)_0-1Or CH₂＝CR⁵CO₂-(CH₂)_1-3；R⁵An unbranched or branched, optionally substituted alkyl radical having from 3 to 12 carbon atoms, which may, if desired, be interrupted by ether groups; and R⁴Is H or CH₃。

Examples thereof are vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinylmethyldi-n-propoxysilane, vinylmethyldiisopropyloxysilane, vinylmethyldi-n-butoxysilane, vinylmethyldi-sec-butoxysilane, vinylmethyldi-tert-butoxysilane, vinylmethyldi (2-methoxyisopropoxy) silane and vinylmethyldioctyloxysilane.

The aforementioned monomers are usually copolymerized in an amount of 0.2 to 10% by weight, based on the total amount of the monomers to be polymerized.

The preparation of aqueous Polymer dispersions has been described several times before, and is therefore known to the person skilled in the art [ see, for example, Encyclopedia of Polymer science and Engineering, Vol.8, p.659 ff (1987) ].

The dispersions are prepared by emulsion polymerization of at least one (meth) acrylate and, if desired, other ethylenically unsaturated monomers in the presence of preferably water-soluble polymerization initiators and in the presence of protective colloids, emulsifiers, if appropriate, and further customary additives.

In this case, the monomer is generally added by means of a continuous feed.

The polymerization of the ethylenically unsaturated monomers is carried out in the presence of at least one initiator for the free-radical polymerization of the ethylenically unsaturated monomers.

Suitable free radical polymerization initiators for initiating and continuing the polymerization during the preparation of the dispersion include all known initiators capable of initiating a free radical aqueous emulsion polymerization.

These initiators may be peroxides (for example alkali metal peroxodisulfates) or azo compounds.

As polymerization initiators it is also possible to use the so-called redox initiators which consist of at least one organic and/or inorganic reducing agent and at least one peroxide and/or hydroperoxide, for example tert-butyl hydroperoxide and sulfur-containing compounds (for example sodium hydroxymethanesulfinate, sodium sulfite, sodium metabisulfite, sodium thiosulfate and acetonosulfite adducts), or hydrogen peroxide and ascorbic acid; reducing sugars can also be used in respect of other reducing agents which can form free radicals with peroxides.

It is also possible to use combination systems which comprise small amounts of metal compounds which are soluble in the polymerization medium and whose metal components can be present in a plurality of valence states, for example ascorbic acid/iron (II) sulfate/hydrogen peroxide, where ascorbic acid is frequently also replaced by sodium hydroxymethanesulfinate, acetone-bisulfite adduct, sodium sulfite, or sodium bisulfite, and hydrogen peroxide is frequently replaced by organic peroxides, for example by tert-butyl hydroperoxide or alkali metal peroxodisulfates and/or ammonium peroxodisulfate. Instead of the acetone bisulfite adduct mentioned, it is also possible to use other bisulfite adducts known to the person skilled in the art, such as those described in EP-A-778,290 and the references cited therein.

Other preferred initiators are peroxodisulfates, for example sodium peroxodisulfate.

The amount of initiator or initiator composition used for the emulsion polymerization is within the conventional amounts used for aqueous emulsion polymerization. The amount of initiator used is generally not more than 5% by weight, based on the total amount of monomers to be polymerized.

The initiators are preferably used in amounts of from 0.05 to 2.0% by weight, based on the total amount of monomers to be polymerized.

The entire amount of initiator can be fed in at the beginning of the emulsion polymerization or, preferably, a portion of the initiator is fed in at the beginning of the polymerization and the remainder is added continuously or in one or more stages after the polymerization has started. This addition can be carried out separately or together with other components, for example monomers and/or stabilizers.

The molecular weight of the emulsion polymer in the aqueous polymer dispersion can be adjusted by adding small amounts of one or more molecular weight-adjusting substances. These regulators are generally used in amounts of up to 2% by weight, based on the monomers to be polymerized. As regulators can be used all substances known to the person skilled in the art. Preference is given to, for example, organic thio compounds, silanes, allyl alcohols and aldehydes.

The aqueous polymer dispersion may also contain a range of additional substances, such as plasticizers, preservatives, pH regulators and/or defoamers.

The polymerization temperature is generally from 20 to 150 ℃ and preferably from 60 to 120 ℃. If desired, the polymerization is carried out under superatmospheric pressure.

After the polymerization has been completed completely, it is desirable and/or necessary to liberate odoriferous substances (such as residual monomers and other volatile organic components) in large amounts from the resulting aqueous polymer dispersion. This can be done in a manner known per se, for example physically by distillative removal (in particular steam distillation) or by stripping with inert gas. Furthermore, it is possible to reduce the residual monomer content chemically, by means of free-radical postpolymerization, in particular under the action of a redox initiator system, as described, for example, in DE-A-4,435,423. Preference is given to postpolymerization using redox initiator systems comprising at least one organic peroxide and one organic and/or inorganic sulfite.

Particularly preferred is a combination of physical and chemical processes, wherein after the residual monomer content has been reduced by chemical post-polymerization it is further reduced by physical processes to preferably less than 1000ppm, more preferably less than 500ppm, in particular less than 100 ppm.

The monomer component can be fed in at the beginning or advantageously at a constant rate or according to a metering profile during the polymerization.

The emulsion polymerization is generally carried out at a pH of less than or equal to 9. For adjusting the pH of the polymer dispersion, it is in principle possible to use buffer systems such as sodium acetate.

It is preferred that the pH is advantageously from 2 to 9; preferably the pH is 3-8.

The solids content in the polymer dispersions having component a) used according to the invention is generally from 40 to 80% by weight, preferably from 50 to 75% by weight, more preferably from 50 to 70% by weight. The weight data in this case are based on the total mass of the dispersion.

As component b) it is possible to use pigments and/or fillers known per se for use in coating compositions. They are solids of organic and/or inorganic matrix and are preferably used in powder form. For the purposes of this specification the pigment is a solid having a refractive index of greater than or equal to 1.75. For the purposes of this specification the filler is a solid having a refractive index of less than 1.75.

Examples of pigments are metal oxides, in particular titanium dioxide.

Examples of fillers are alkaline earth metal oxides and/or sulfates, in particular calcium carbonate or barium sulfate.

The Pigment Volume Concentration (PVC) of pigments and/or fillers, if present, in the coating composition of the present invention may be up to 30%. This corresponds to a maximum volume of 30 parts per 100 parts of dry coating.

Particularly preferred are coating compositions comprising pigments and/or fillers having the following characteristics: which is finely divided exclusively and has an average particle size D₅₀Less than or equal to 0.4. mu.m, preferably from 0.1 to 0.4. mu.m, very preferably from 0.2 to 0.3. mu.m.

As component c) it is possible to use homogenizing aids known per se. These homogenization aids are water-miscible organic solvents, preferably water-miscible polyols, in which part of the alcohol groups may be etherified. Preference is given to using 1, 2-propanediol, methyldiglycol and butyldiglycol.

By "water-miscible" in the sense of the present description is meant that the homogenization aid is miscible with water in any proportion at 20 ℃.

As component d) it is possible to use the coalescing agents known per se. These coalescents are organic solvents which are immiscible or have low miscibility with water, preferably polyols which are (partially) esterified and/or (partially) etherified which are immiscible or have low miscibility with water. They may be diesters, ester alcohols, diethers, ether alcohols or alcohol ether esters derived from polyhydric alcohols. Examples include 2, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate, ethylene glycol 2-ethylhexyl ether, ethylene glycol butyl ether, ethylene glycol propyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, butyl diglycol acetate, diisobutyl adipate, diisobutyl glutarate, diisobutyl succinate or a mixture of two or more of these compounds. The term "low miscibility with water" or "low water miscibility" for the purposes of this specification means miscibility with water of less than 10 wt.% at 20 ℃, preferably less than 6.5 wt.% at 20 ℃.

As component e) it is possible to use polymeric thickeners known per se. These thickeners are hydrophobically modified polyurethane or polyacrylate dispersions, for example the product Mowilith^®LDM7002 or Mowilith^®VDM 7000。

Suitable further additives f) include dispersing agents, wetting agents, defoamers or buffers.

In a preferred embodiment, the coating composition of the invention comprises at least one pigment, in particular at least one white pigment, for example titanium dioxide.

To prepare the aqueous coating compositions of the invention, components a) and b) (if desired) and/or c) (if desired) and/or d) (if desired) and/or e) (if desired) and/or f) (if desired) may be mixed in a conventional manner.

Component d) (coalescent) is preferably employed when the coating composition without coalescent has a minimum film-forming temperature (MFFT) above room temperature.

The present invention also provides a process for preparing an aqueous coating composition as defined above, which comprises the following measures:

i) emulsion polymerization of acrylic and/or methacrylic esters in the presence of protective colloids in aqueous phase, with or without ethylenically unsaturated hydrocarbons, and

ii) if desired, pigments and/or fillers, and/or homogenization aids and/or coalescents, and/or polymeric thickeners and/or additives are added to the aqueous emulsion polymer.

The invention also provides the use of (meth) acrylate dispersions prepared in the presence of protective colloids to extend the open time of coating compositions.

The coating composition of the present invention is particularly suitable for various types of surface coatings. They are particularly useful as paints or food coatings.

The following examples illustrate the invention but are not intended to limit the invention.

Example 1

7 parts of PVA (polyvinyl alcohol, in the form of a 20% strength aqueous solution), 13 parts of water, 0.14 part of dodecanethiol, 0.05 part of tert-butyl hydroperoxide and 0.04 part of ascorbic acid are introduced into a polymerization reactor equipped with metering apparatus and temperature regulating device. A mixture of 4.7 parts of PVA (in the form of a 20% strength aqueous solution), 0.6 part of acrylic acid, 23.3 parts of MMA (methyl methacrylate), 23.3 parts of BuA (butyl acrylate) and 21 parts of water is metered in at 70 ℃ over 3 hours. At the same time, a solution of 0.2 part of tert-butyl hydroperoxide in 1.4 parts of water and a solution of 0.15 part of ascorbic acid in 1.7 parts of water are metered in. 30 minutes after the end of the metering, a solution of 0.03 parts of ascorbic acid in 0.37 parts of water is metered in over 30 minutes. After a total postpolymerization time of 1.5 hours, 0.05 part of tert-butyl hydroperoxide in 0.35 part of water and 0.07 part of sodium formaldehyde sulfoxylate in 0.66 part of water were added at 60 ℃. Neutralization was carried out at < 30 ℃ using 1.26 parts of sodium hydroxide (in the form of a 10% strength aqueous solution).

The pure acrylate dispersion stabilized with polyvinyl alcohol alone had a solids content of 50.2% and a glass transition temperature T_gThe temperature was 16.6 ℃.

The particle size distribution shows its mean diameter d_wIs 278nm, d_w/d_nThe value was 1.89.

Where d is_nThe value is the number average (number length average), d_wThe values are weight means (DeBroucker mean). These values have been described in the literature (for example NF X11-632-2 and NF ISO 9276-2 at 6/1/2000).

D in the description_nAnd d_wValues were determined by Ar laser aerosol spectroscopy. Such asMethods have been described, for example, in J.P.Fischer and E.N ö lken in prod.colloid&Polymer Sci, 77, 180 (1988).

Example 2

The process is as in example 1 except that the initial feed is 13 parts water, 0.05 part dodecanethiol, 0.05 part t-butyl hydroperoxide and 0.04 part ascorbic acid. A mixture of 11.7 parts of PVA (in the form of a 20% strength aqueous solution), 0.6 part of acrylic acid, 24.1 parts of styrene, 23.1 parts of BuA (butyl acrylate) and 23.6 parts of water is metered in at 70 ℃ over 3 hours.

The styrene/acrylate dispersion stabilized with polyvinyl alcohol alone has a solids content of 50.2% and a glass transition temperature T_gAnd the minimum film-forming temperature MFT was 23.2 ℃ each.

The particle size distribution shows that_wA value of 336nm, d_w/d_nThe value was 2.335.

Example 3

24.6 parts of water and 0.02 part of APS (ammonium peroxodisulfate) are introduced into a polymerization reactor equipped with metering device and temperature regulation. A mixture of 1.3 parts of tri-tert-butylphenyl ether sulfate, 1.3 parts of methacrylic acid, 22.6 parts of MMA (methyl methacrylate), 21.3 parts of BuA (butyl acrylate) and 25.5 parts of water is metered in at 80 ℃ over 3.5 hours. 30 minutes after the end of the metering, the reaction mixture is neutralized hot with 0.9 part of aqueous ammonia. After a total postpolymerization time of 1 hour, the neutralization was repeated and this time to a pH of 8.5 to 9 after cooling down with 0.9 part of aqueous ammonia (in the form of a 12.5% strength aqueous solution). The pure acrylate dispersion stabilized with emulsifier alone had a solids content of 46% and a glass transition temperature of 27 ℃. Particle size up to d_w361nm, and d_w/d_n＝2.900。

Example 4

The process is as in example 1 except that the initial charge is 19.6 parts water, 0.3 part tri-tert-butylphenyl ether sulfate (as a 12.5% strength aqueous solution)Form) and 0.02 part of APS (ammonium peroxodisulfate). A mixture of 0.9 part of tri-tert-butylphenyl ether sulfate (in the form of a 50% strength aqueous solution), 1.3 parts of methacrylic acid, 22 parts of MMA (methyl methacrylate), 20.7 parts of BuA and 21.3 parts of water is metered in at 80 ℃ over 3.5 hours. 30 minutes after the end of the metering, neutralization was carried out with 0.9 part of aqueous ammonia (in the form of a 12.5% strength aqueous solution) while hot. After a total postpolymerization time of 1 hour, the neutralization was repeated and this time cooled down with 0.9 part of aqueous ammonia (in the form of a 12.5% strength aqueous solution) and then neutralized to a pH of 8.5 to 9, 10.7 parts of PVA (in the form of a 20% strength aqueous solution) being added as a postaddition. The pure acrylate dispersion had a solids content of 48% and a glass transition temperature of 28 ℃. Particle size up to d_w119nm, and d_w/d_n＝1.076。

Example 5

The process is as in example 1 except that the initial feeds are 19.6 parts water, 0.3 parts tri-tert-butylphenyl ether sulfate and 0.02 parts ammonium peroxodisulfate. A mixture of 0.9 part of tri-tert-butylphenyl ether sulfate (50% strength), 1.3 part of methacrylic acid, 22 parts of methyl methacrylate, 20.7 parts of butyl acrylate and 21.3 parts of water is metered in at 80 ℃ over 3.5 hours. 30 minutes after the end of the metering, neutralization was carried out with 0.9 part of aqueous ammonia (12.5% strength) while hot. After a total postpolymerization time of 1 hour, neutralization was carried out again and this time after cooling down with 0.9 part of aqueous ammonia (12.5% strength) was carried out to a pH of 8.5 to 9. The pure acrylate dispersion stabilized with emulsifier alone had a solids content of 46% and a glass transition temperature of 28 ℃. Measuring the particle size to d by using a laser aerosol method_w110nm, distribution d_w/d_n＝1.093。

Example 6

The procedure is as in example 1 except that the initial feeds are 19.7 parts water, 1.2 parts nonylphenol polyethylene glycol ether containing 30 EO units (20% strength), 0.3 parts ethylene oxide-propylene oxide block polymer sulfate containing 20 EO units (50% strength) and 0.027 parts ammonium peroxodisulfate. In 8A mixture of 24.3 parts of styrene, 20.7 parts of 2-ethylhexyl acrylate, 1.9 parts of methacrylic acid, 1.1 parts of methacrylamide in 17.5 parts of water and 6 parts of nonylphenol polyethylene glycol ether having 30 EO units (20% strength), 1.4 parts of sulfuric ester of an ethylene oxide-propylene oxide block polymer having 20 EO units (50% strength) and 0.05 part of APS is metered in over 4 hours at 0 ℃. At 15 minutes after the end of the metering of the monomers, 0.2 part of ammonium peroxodisulfate in 1.1 parts of water and 0.067 part of sodium hydrogensulfite in 1.2 parts of water were metered in. After a total postpolymerization time of 1 hour, neutralization was carried out with 1.8 parts of aqueous ammonia (12.5% strength) and the mixture was cooled. The styrene/acrylate dispersion stabilized with emulsifier alone had a solids content of 50% and a glass transition temperature of 19 ℃. Measuring the particle size to d by using a laser aerosol method_w129nm, distribution d_w/d_n＝1.041。

Performance testing

The dispersions prepared by the above process were processed with the gloss paint formulation described below and tested for properties.

The gloss paint formulation used is a formulation for dispersion coatings having similar paint properties (according to the definition of DIN 55945, 1999-07). The Pigment Volume Concentration (PVC) in the formulation is less than 20%.

Glossy emulsion coatings were prepared as follows (ppw parts by weight): will be provided with

242ppw of water

242ppw 1, 2-propanediol

52ppw Dispex GA 40 (commercially available from Ciba Specialty Chemicals; dispersant containing ammonium salt of acrylic copolymer)

10ppw AMP 90 (2-amino-2-methyl-1-propanol)

20ppw antifoam BYK 022

20ppw fungicide Mergal K7

Mixing was carried out by feeding 2079ppw of titanium dioxide Kronos 2190 with stirring and then dispersing the mixture for 20 minutes with a dissolver having a toothed disc with a peripheral speed of at least 14 m/s. After the pigment dispersion is cooled, it is stirred and mixed

185ppw adhesive Dispersion

80ppw of pigment dispersion.

While continuing to stir at moderate speed, add

1.8ppw Ammonia (25% strength)

18.6ppw 1, 2-propanediol

4.6ppw Texanol (commercial Eastman Chemicals; solvent containing 2, 2, 2-trimethyl-1, 3-pentanediol monoisobutyrate) and finally thickener mixture 10.1ppw Mowilith LDM7002 (concentration in water is about 18%).

The resulting coating composition is shelf stable and its positive effects on open time and anti-blocking properties are surprising.

The open time of the paint film edge (wet edge open time) was tested according to the following method.

The test coating was applied to a non-absorbent substrate using a 100 μm box-type coating bar. The stopwatch was then started immediately. The substrate was held vertically and after three minutes the substrate was coated horizontally 12 times with a brush saturated with paint, gently from left to right.

This operation was repeated every three minutes until the coating film was dried.

The end of the open time is reached as soon as the "crack" is clearly visible at the inward painted edge.

Blocking resistance or adhesion is a measure of the surface tackiness of two films of paint that are pressed against each other (e.g., the squeeze that occurs between a window and a window frame).

The blocking resistance was determined as follows.

Test coatings were applied to the control using a 50 μm spiral coating rodCard (Leneta)^®) The above. The coated control card was then dried under standard conditions (23 ℃, 50% relative humidity) for 24 hours. The dried control cards were cut into strips and the strips were placed crosswise with the coated sides facing each other to form a limited contact area of the coating film. These contact zones were loaded with a 2kg weight at room temperature for 1 hour.

Adhesion is measured as the weight force (grams per square inch, equivalent to grams per 6.76 square centimeters) required to subsequently separate the coated film. The smaller the value, the better the anti-blocking property.

The example dispersions in the selected gloss coating formulation had an open time 2-3 times that of the standard dispersion and the bonding effect was halved. The results are shown in the following table.

Watch (A)

Example number	Monomers and stabilizers	Open time (min)	Adhesion (g/6.76 cm)2)
				I	Having PVA1)，2)Acrylic acid esters of	13	1100
C-I	Having an emulsifier3)Acrylic acid esters of	4	3000
				II	Having PVA1)，4)Styrene/acrylic acid ester of (A)	10	1600
C-II	Having an emulsifier5)Styrene/acrylic acid ester of (A)	4	2500

¹⁾PVA ═ polyvinyl alcohol

²⁾PVA-stabilized pure acrylate Dispersion example 1

³⁾Pure acrylate dispersions stabilized with emulsifiers according to example 3

⁴⁾PVA-stabilized styrene/acrylate Dispersion example 2

⁵⁾Styrene/acrylate dispersions stabilised with emulsifiers according to example 6

The following experiment illustrates the effect of various stabilizer systems on open time and bonding behavior.

For examples C to III, finely divided pure acrylate dispersions stabilized with emulsifiers according to example 5 were used, d of which_wThe value was 110 nm.

For examples C to IV, the emulsifier-stabilized coarsely dispersed pure acrylate dispersions according to example 3 were used, d of which_wThe value was 350 nm.

For examples C to V, stabilization was carried out using protective colloids according to example 4Of finely divided pure acrylate dispersions of_wThe value is 120nm and wherein the protective colloid is added after the preparation of the dispersion.

For example III, a protective colloid-stabilized pure acrylate dispersion according to example 1, d_wThe value was 270nm and wherein the protective colloid was added during the preparation of the dispersion.

Open time and adhesion behavior were determined as described above.

Gloss coatings were tested using the test methods described above.

The results are shown in the following table.

Watch (A)

Example number	Monomers and stabilizers	Open time (min)	Adhesion (g/6.76 cm)2)
				C-III	Having an emulsifier1)Acrylic acid esters of	3	548
C-IV	Having an emulsifier2)Acrylic acid esters of	4	188
				C-V	PVA with post-addition3)，4)Acrylic acid esters of	3	772
III	Having PVA3)，5)Acrylic acid esters of	7	342

¹⁾Pure acrylate dispersions stabilized with emulsifiers

²⁾Pure acrylate dispersions stabilized with emulsifiers, which are distributed more broadly than C-III

³⁾PVA ═ polyvinyl alcohol

⁴⁾PVA stable neat acrylate dispersions; dispersion as in example 3

⁵⁾PVA-stabilized pure acrylate dispersions

Claims (24)

1. Use of a (meth) acrylate dispersion prepared in the presence of a protective colloid for extending the open time of a coating composition, wherein the coating composition is an aqueous coating composition comprising

a) (meth) acrylate homopolymer and/or (meth) acrylate copolymer-based polymer dispersions prepared by emulsion polymerization in the presence of protective colloids,

b) if desired, pigments and/or fillers, having a Pigment Volume Concentration (PVC) of from 0 to 30%,

c) if desired, a homogenizing aid,

d) if desired, the coalescing agent(s),

e) if desired, a polymeric thickener, and

f) if desired, other conventional additives.

2. Use according to claim 1, wherein component a) of the aqueous coating composition is selected from the group consisting of homopolymers or copolymers derived from esters of acrylic acid with aliphatic monohydric alcohols having 1 to 10 carbon atoms, homopolymers or copolymers derived from esters of methacrylic acid with aliphatic monohydric alcohols having 1 to 10 carbon atoms and copolymers derived from esters of acrylic acid and/or methacrylic acid with aliphatic monohydric alcohols having 1 to 10 carbon atoms and ethylenically unsaturated hydrocarbons.

3. Use according to claim 2, wherein the ethylenically unsaturated hydrocarbon is ethylene and/or styrene.

4. Use according to claim 1, wherein the protective colloid used for preparing component a) is polyvinyl alcohol.

5. Use according to claim 1, wherein the aqueous coating composition comprises as component c) a water-miscible polyol.

6. Use according to claim 5, wherein component c) is 1, 2-propanediol.

7. Use according to claim 1, wherein the aqueous coating composition comprises as component d) an organic solvent which is immiscible or poorly miscible with water and which can lower the minimum film-forming temperature.

8. Use according to claim 7, wherein component d) is a polyol which is (partially) esterified and/or (partially) etherified.

9. Use according to claim 1, wherein the aqueous coating composition comprises as component e) a hydrophobically modified polyurethane and/or a hydrophobically modified polyacrylate.

10. Use according to claim 1, wherein the aqueous coating composition further comprises as component b) at least one pigment and/or at least one filler.

11. Use according to claim 10, comprising only pigments and/or fillers having an average particle size D50 of less than or equal to 0.4 μm.

12. Use according to any one of claims 1 to 11, wherein said aqueous coating composition is prepared according to a process comprising the steps of:

i) emulsion polymerization of acrylic and/or methacrylic esters in the presence of protective colloids in aqueous phase, with or without ethylenically unsaturated hydrocarbons, and

ii) if desired, pigments and/or fillers, and/or homogenization aids and/or coalescents, and/or polymeric thickeners and/or additives are added to the aqueous emulsion polymer.

13. Use of a (meth) acrylate dispersion prepared in the presence of a protective colloid as a coating for foodstuffs, wherein the coating is an aqueous coating composition comprising

a) (meth) acrylate homopolymer and/or (meth) acrylate copolymer-based polymer dispersions prepared by emulsion polymerization in the presence of protective colloids,

b) if desired, pigments and/or fillers, having a Pigment Volume Concentration (PVC) of from 0 to 30%,

c) if desired, a homogenizing aid,

d) if desired, the coalescing agent(s),

e) if desired, a polymeric thickener, and

f) if desired, other conventional additives.

14. Use according to claim 13, wherein component a) of the aqueous coating composition is selected from the group consisting of homopolymers or copolymers derived from esters of acrylic acid with aliphatic monohydric alcohols having 1 to 10 carbon atoms, homopolymers or copolymers derived from esters of methacrylic acid with aliphatic monohydric alcohols having 1 to 10 carbon atoms and copolymers derived from esters of acrylic acid and/or methacrylic acid with aliphatic monohydric alcohols having 1 to 10 carbon atoms and ethylenically unsaturated hydrocarbons.

15. Use according to claim 14, wherein the ethylenically unsaturated hydrocarbon is ethylene and/or styrene.

16. Use according to claim 13, wherein the protective colloid used for the preparation of component a) is polyvinyl alcohol.

17. Use according to claim 13, wherein the aqueous coating composition comprises as component c) a water-miscible polyol.

18. Use according to claim 17, wherein component c) is 1, 2-propanediol.

19. Use according to claim 13, wherein the aqueous coating composition comprises as component d) an organic solvent which is immiscible or poorly miscible with water and which can lower the minimum film-forming temperature.

20. Use according to claim 19, wherein component d) is a polyol which is (partially) esterified and/or (partially) etherified.

21. Use according to claim 13, wherein the aqueous coating composition comprises as component e) a hydrophobically modified polyurethane and/or a hydrophobically modified polyacrylate.

22. Use according to claim 13, wherein the aqueous coating composition further comprises as component b) at least one pigment and/or at least one filler.

23. Use according to claim 22, comprising only pigments and/or fillers having an average particle size D50 of less than or equal to 0.4 μm.

24. Use according to any one of claims 13 to 23, wherein said aqueous coating composition is prepared by a process comprising the steps of:

i) emulsion polymerization of acrylic and/or methacrylic esters in the presence of protective colloids in aqueous phase, with or without ethylenically unsaturated hydrocarbons, and

ii) if desired, pigments and/or fillers, and/or homogenization aids and/or coalescents, and/or polymeric thickeners and/or additives are added to the aqueous emulsion polymer.