EP3083864A1

EP3083864A1 - Method for applying dispersion adhesives

Info

Publication number: EP3083864A1
Application number: EP14821109.7A
Authority: EP
Inventors: Muhammad Babar; Gerhard KÖGLER; Hans-Peter Weitzel
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2013-12-16
Filing date: 2014-12-15
Publication date: 2016-10-26
Also published as: WO2015091375A1; CN105793379B; US10047253B2; DE102013226113A1; CN105793379A; US20160312083A1

Abstract

The invention relates to a method for applying dispersion adhesives containing one or more polyvinyl esters and optionally one or more additives, characterized in that one or more polyvinyl esters are produced by radical-initiated, continuous emulsion polymerization of a) one or more vinyl esters and, optionally, b) one or more additional ethylenically unsaturated monomers, and the dispersion adhesives are applied to a substrate by way of mechanical application methods.

Description

Process for applying dispersion adhesives

The invention relates to dispersion adhesives and methods for applying dispersion adhesives based on polyvinyl esters by means of a mechanical application process, in particular ^¬ re pipeline method, such as nozzle or roll coating method.

Dispersion adhesives based on polyvinyl esters are used widely, for example for the bonding of paper or cardboard box making, Envelope ^¬ proposals, brochures or cigarettes. Such products are usually produced on an industrial scale by assembly line production. The dispersion adhesives are hereby sheet usually by means of mechanical application methods, such nozzle applicator systems or rolling technologies, on the substrate ^¬ appli. In these application methods lead to contamination by adhesive, which caused by imprecise or uncontrolled adhesive application, also referred to as so-called "spraying", causing problems in manufacturing. If adhesive gets on the conveyor belt, this can lead to buildup of the finished material, which leads to downtime of the machine and time-consuming cleaning. During the application of the nozzle, often peg-shaped deposits form at the exit point of the nozzle, whereby the adhesive jet emerging from the nozzle is deflected. This is detrimental to an accurate control of the adhesive application and can also lead to pollution and eventually to a standstill of the system. In nozzle application systems, the dispersion adhesives are pumped through piping systems to a nozzle with a fast-opening and closing valve, for example at switching frequencies of up to 1000 / sec. Such high clock frequencies of the nozzle valves set the dispersion adhesives inside the nozzle extremely high shear forces. Suitable Dis- Accordingly, adhesive adhesives must be very shear-stable.

The application of dispersion adhesives by means of mechanical processes is described for example in EP-A 1889890 or EP-A 1887018. The polyvinyl esters used for this purpose were prepared by emulsion polymerization by Baten or semi-batch process. However, there is still a need for dispersion adhesives with which the requirements of mechanical application processes are even better met.

Against this background, the object was to provide new measures for applying dispersion adhesives based on polyvinyl esters by means of mechanical application methods with which one or more of the abovementioned problems can be avoided or reduced.

Surprisingly, this object was achieved by the polyvinyl esters contained in the dispersion adhesives were prepared by continuous, free-radically initiated emulsion polymerization.

The invention relates to methods for applying dispersion adhesives containing one or more polyvinyl ter and optionally one or more additives, characterized in that

the polyvinyl esters are prepared by means of free-radically initiated, continuous emulsion polymerization of a) one or more vinyl esters and optionally b) one or more further ethylenically unsaturated monomers and the dispersion adhesives are applied to a substrate by means of a mechanical coating process. Another object of the invention are dispersion adhesives containing one or more polyvinyl esters, one or more additives and water, characterized in that

the polyvinyl esters are obtainable by free-radically initiated, continuous emulsion polymerization of a) one or more vinyl esters and, if appropriate, b) one or more further ethylenically unsaturated monomers in the absence of emulsifiers, and

the polyvinyl esters have a polydispersity PD of at least 21 and

the proportion of the polyvinyl ester to the dispersion adhesives 40 to 99 wt .-%, based on the dry weight of the Dis ^¬ persionsklebstoffe.

Such dispersion adhesives are particularly suitable for the process according to the invention and for achieving the object according to the invention.

Suitable vinyl esters a) are, for example, those of carboxylic acids having 1 to 22 C atoms, in particular 1 to 12 C atoms. Preference is given to vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of α-branched monocarboxylic acids having 9 to 11 C atoms, for example VeoVa9R or VeoValOR (trade names of Momentive) , Vinyl acetate is particularly preferred.

The vinyl esters a) are used in an amount of preferably 50 to 100% by weight, more preferably 70 to 95% by weight and most preferably 75 to 90% by weight, based in each case on the total weight of the monomers ,

As a further ethylenically unsaturated monomers bl) are in particular ^¬ sondere one or more olefins, such as propylene or ethylene, preferably selected. The monomers b1) are copolymerized in an amount of preferably from 5 to 40% by weight, more preferably from 5 to 30% by weight and most preferably from 10 to 25% by weight, based in each case on the total weight of the monomers.

As further ethylenically unsaturated monomers b2), optionally in combination with one or more olefins, such as ethylene, one or more ethylenically unsaturated monomers can be selected from the group comprising (meth) acrylic esters, vinylaromatics, 1,3-dienes and vinyl halides ,

Suitable monomers from the group of esters of acrylic acid or methacrylic acid are, for example, esters of unbranched or branched alcohols having 1 to 15 C atoms. Preferred methacrylic esters or acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate. Particularly preferred are methyl acrylate, methyl methacrylate, n-butyl acrylate and 2-ethylhexyl acrylate.

Preferred vinyl aromatic compounds are styrene, methylstyrene and vinyltoluene. Preferred vinyl halide is vinyl chloride. The ^¬ be vorzugten dienes are 1,3-butadiene and isoprene. The monomers b2) in an amount of preferably 0 to 45 wt .-% and particularly preferably 10 to 30 wt .-%, in each ^¬ be subjected to the total weight of the monomers. Most preferably, no monomers b2) are copolymerized. If appropriate, from 0 to 10% by weight, in particular from 0.05 to 10% by weight, based on the total weight of the monomer mixture, of auxiliary monomers can be copolymerized. Most preferably, however, no auxiliary monomers are copolymerized. Examples of auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid,

Fumaric acid and maleic acid; ethylenically unsaturated carboxylic acid amides and nitriles, preferably acrylamide and acrylonitrile; Mono- and diesters of fumaric acid and maleic acid, such as diethyl and diisopropyl esters and maleic anhydride, ethylenically unsaturated sulfonic acids or salts thereof, preferably vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid. WEI tere examples are precrosslinking comonomers such as multiply ethylenically unsaturated comonomers, for example Divinyladi- pat, diallyl maleate, allyl methacrylate, triallyl isocyanurate or triallyl cyanurate, or postcrosslinking comonomers, Example ^¬ example acrylamidoglycolic acid (AGA), Methylacrylamidoglykolsäu- methyl ester (MAGME), N-methylolacrylamide (NMA ), N-methylol methacrylamide, N-methylolallyl carbamate, alkyl ethers such as the isobutoxy ether or esters of N-methylolacrylamide, of N-methylolmethacrylamide and of N-methylolallyl carbamate. Also suitable are epoxide-functional comonomers such as glycidyl methacrylate and glycidyl acrylate. Further examples are silicon funktionel ^¬ le comonomers such as acryloxypropyltri (alkoxy) - and methacryloxy propyltri (alkoxy) silanes, vinyltrialkoxysilanes and vinylmethyl dialkoxysilanes, whereby, for example, ethoxy and ethoxypropylene glycol ether radicals can be present as alkoxy groups. Nannt overall are also monomers having hydroxy or CO groups, tylacetoxyethylacrylat at ^¬ game as methacrylates and acrylates such as hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate and also compounds such as diacetoneacrylamide and acetone or methacrylate.

Preference is given to one or more polyvinyl esters selected from the group comprising vinyl ester homopolymers, vinyl ester copolymers, especially vinyl ester-ethylene copolymers, vinyl ester copolymers containing one or more vinyl ester units and one or more further monomer units from the group comprising vinylaromatics, Vinyl halides, acrylic acid esters, methacrylic acid esters and optionally ethylene. Examples of preferred vinyl ester copolymers are based on 50 to 90 wt .-% of one or more vinyl esters, 10 to 25 wt .-% of ethylene and optionally 1 to 40 wt .-% of a or more other monomers based on the total weight of the monomers.

Also preferred are comonomer mixtures of vinyl acetate with 10 to 25 wt .-% of ethylene; and comonomer mixtures of vinyl acetate with 10 to 25 wt .-% of ethylene and 1 to 40 wt .-% of one or more other comonomers from the group of vinyl esters having 1 to 12 carbon atoms in the carboxylic acid radical such as vinyl propionate, vinyl laurate, vinyl esters of alpha-branched 9- to 11-carbon carboxylic acids such as VeoVa9, VeoValO, VeoVall; and mixtures of vinyl acetate, 10 to 25 wt .-% of ethylene and preferably 1 to 40 wt .-% acrylic acid esters of unbranched or branched alcohols having 1 to 15 carbon atoms, in particular n-butyl acrylate or 2-ethylhexyl acrylate; and mixtures with 30 to 75 wt .-% vinyl acetate, 1 to 30 wt .-% of vinyl laurate or Vinylester an alpha-branched carboxylic acid having 9 to 11 carbon atoms, and 1 to 30 wt .-% acrylate of unbranched or verzweig ^¬ th Alcohols having 1 to 15 carbon atoms, in particular n-butyl acrylate or 2-ethylhexyl acrylate, which still contain 10 to 25 wt .-% of ethylene; and mixtures with vinyl acetate, 10 to 25% by weight of ethylene and 1 to 60% by weight of vinyl chloride; wherein the ^{mixtures can} still contain the said auxiliary monomers in the stated amounts, and the data in% by weight add up to in each case 100% by weight.

The polyvinyl have weight average particle diameter Dw of preferably 500 nm to 15 pm, more preferably from 1 pm to 12 pm, and most preferably 2 pm to 9 pm (determined static with ^¬ means of light scattering with the meter LS 13320 of the company Beckman Coulter).

The polyvinyl esters have a polydispersity PD of preferably 21, more preferably 21 to 100, more preferably 25 to 90, even more preferably 30 to 80, and most preferably 40 to 80. The polydispersity PD is known to be the ratio of weight average particle diameter Dw to the number average particle diameter Dn, PD = Dw / Dn (determination by means of static light scattering with the measuring instrument LS 13320 of the Company BeckmanCoulter). The polyvinyl esters are preferably bimodal or multimodal.

The polyvinyl esters, in the form of aqueous dispersions having a solids content of 50%, have a Brookfield viscosity of preferably 8000 mPas, more preferably 2000 to 6000 mPas, and most preferably 3000 to 5000 mPas (determined with a Brookfield viscometer, at 23 ° C and 20 rpm, using the spindle usually used for the respective viscosity range).

The polyvinyl esters have glass transition temperatures Tg of preferably -20 ° C to + 40 ° C, more preferably -10 ° C to + 30 ° C, more preferably from 0 ° C to +15 ° C, and most preferably from + 1 ° C up to + 10 ° C. The monomer selection or the selection of the proportions by weight of the comonomers takes place in such a way that the aforementioned glass transition temperatures Tg result. The glass transition temperature Tg of the polymers is determined by means of the DSC dynamic differential calorimeter from Mettler-Toledo in an open crucible at a heating rate of 10 K / min. The center of the glass transition during the 2nd heating cycle is evaluated. The Tg can also be approximated by the Fox equation. After Fox TG, Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1 / Tg = x ^ / Tgi + 2 Tg2 + ■■■ + ^ n ^^ nr where x _{n is} the mass fraction (% by weight / 100) of the monomer n , and Tg _{n is} the glass transition temperature in Kelvin of the homopolymer of the monomer n. Tg values for homopolymers are listed in Polymer Handbook 2nd Edition, J. iley & Sons, New York (1975).

The polymers are prepared by the emulsion polymerization process. The emulsion polymerization is usually carried out in an aqueous medium, ie usually in the absence of organic solvents. In the copolymerization of gaseous comonomers such as ethylene, 1,3-butadiene or vinyl chloride, it is also possible to work under pressure, generally between 5 bar and 100 bar, preferably between 65 and 80 bar. The polymerization temperature is generally 40 ° C to 100 ° C, preferably 50 ° C to 80 ° C, and more preferably 55 to 70 ° C. Polymerization at such temperatures gives polyvinyl ester dispersions with particularly advantageous rheological properties and high setting rates.

The initiation of the polymerization is preferably carried out with the customary for the emulsion polymerization redox initiator combinations. Examples of suitable oxidation initiators are the sodium, potassium and ammonium salts of peroxodisulfuric acid, hydrogen peroxide, t-butyl peroxide, t-butyl hydroperoxide, potassium peroxodiphosphate, tert. Butyl peroxypivalate, cumene hydroperoxide, isopropylbenzene monohydroperoxide, azobisisobutyronitrile. Preference is given to the sodium, potassium and ammonium salts of peroxodisulfuric acid and hydrogen peroxide. The initiators mentioned are generally used in an amount of 0.01 to 2.0 wt .-%, based on the total weight of the monomers.

The mentioned oxidizing agents, in particular the salts of peroxydisulphuric acid, can also be used alone as thermal initiators.

Suitable reducing agents the sulfites and bisulfites are for example the alkali metals and of ammonium, such as sodium sulfite, the derivatives of sulfoxylic acid such as zinc or Alkalifor- maldehydsulfoxylate, for example Natriumhydroxymethansulfi- nat (Brüggolit), (iso) ascorbic acid or salts thereof, and Gemi ^¬ specific of Salts of 2-hydroxy-2-sulfinato-acetic acid and 2-hydroxy-2-sulfonato-acetic acid with sodium sulfite (FF6). Preference is given to sodium sulfite, sodium bisulfite and in particular (iso) ascorbic acid or their (alkaline) alkali metal salts and FF6. The amount of reducing agent is preferably 0.015 to 3 wt .-%, based on the total weight of the monomers. The polymerization is usually carried out at pH values of 9 9, preferably 2 to 9 and more preferably 3 to 4.5. The adjustment of the pH can be carried out with the usual measures, such as acids, bases or buffers, such as sodium acetate or phosphates.

For controlling the molecular weight, regulating substances can be used during the polymerization. If regulators are used, they are usually used in amounts of from 0.01 to 5.0% by weight, based on the total weight of the monomers to be polymerized, and are metered in separately or else premixed with reaction components. Examples of such substances are n-dodecyl mercaptan, tert. Dodecylmercaptan, mercaptopropionic acid, methyl mercaptopropionate, isopro panol and acetaldehyde. Preferably, no regulatory substances are used.

The emulsion polymerization is preferably carried out in the presence of one or more protective colloids. Examples of protective colloids are polyvinyl alcohols; polyvinylpyrrolidones;

Polysaccharides in water-soluble form such as starches (amylose and amylopectin), celluloses and their carboxymethyl, methyl, hydroxyethyl, hydroxypropyl derivatives; Proteins such as casein or caseinate, soy protein, gelatin; Lignosulfonates; synthetic polymers such as poly (meth) acrylic acid, copolymers of (meth) acrylates with carboxyl-functional comonomer units, poly (meth) acrylamide, polyvinylsulfonic acids and their water-soluble copolymers; Melamine formaldehyde sulfonates, naphthalene formaldehyde sulfonates, styrene maleic acid and vinyl ether maleic acid copolymers.

Preferred protective colloids are polyvinyl alcohols. Apart from polyvinyl alcohols, particular preference is given to using no further protective colloids. Preferred dispersion adhesives contain no further protective colloids in addition to polyvinyl alcohols.

The polyvinyl alcohols may be partially saponified or fully saponified. Preference is given to partially hydrolyzed polyvinyl alcohols. The hydraulic The degree of hydrolysis of the polyvinyl alcohols is preferably from 80 to 95 mol%, more preferably from 83 to 92 mol%, and most preferably from 85 to 90 mol%. The polyvinyl alcohols are preferably composed exclusively of vinyl alcohol units and vinyl acetate units. However, it is also possible to use partially hydrolyzed, hydrophobically modified polyvinyl alcohols. Examples include partially hydrolyzed copolymers of vinyl acetate with hydrophobic comonomers such as isopropenyl acetate, vinyl pivalate, vinyl ethyl hexanoate, vinyl esters of saturated alpha-branched monocarboxylic acids having 5 or 9 to 11 carbon atoms, dialkyl maleates and dialkyl fumarates such as diisopropyl maleate and diisopropyl fumarate, vinyl chloride, Vinyl alkyl ethers such as vinyl butyl ether, olefins such as ethene and decene. The proportion of the hydrophobic units is preferably 0.1 to 10 wt .-%, based on the total weight of the partially hydrolyzed polyvinyl alcohol. It is also possible to use mixtures of the stated polyvinyl alcohols. Further preferred polyvinyl alcohols are partially hydrolyzed, hydrophobized polyvinyl alcohols which are obtained by polymer-analogous reaction, for example

Acetalization of vinyl alcohol units with Ci ~ to Cj-aldehydes as the butyraldehyde are obtained. The proportion of the hydrophobic units is preferably 0.1 to 10 wt .-%, based on the total weight of the partially hydrolyzed polyvinyl acetate. It is particularly preferred to dispense with hydrophobically modified polyvinyl alcohols.

The protective colloids are generally used in a total amount of 0.5 to 20 wt .-%, preferably 0.5 to 10 wt .-%, and particularly preferably 1 to 7 wt .-%, based on the weight of the ethylenically unsaturated ^¬ Gesamtge Monomers added in the emulsion polymerization.

The viscosity of the polyvinyl alcohols is preferably 1 to 60 mPas. These as well as the following information on the viscosities of polyvinyl alcohols refer to the Höppler viscous each determined at 20 ° C according to DIN 53015 in 4% aqueous solution.

Particularly preferred are medium-viscosity polyvinyl alcohols. Mid-viscosity polyvinyl alcohols have viscosities of preferably 19 to 39 mPas, more preferably 20 to 35 mPas, more preferably 21 to 30 mPas and most preferably 23 to 27 mPas.

The proportion of the medium-viscosity polyvinyl alcohols is preferably 0.5 to 6.0% by weight, more preferably 1.0 to 5.0

Wt .-%, particularly preferably 2.0 to 4.5 wt .-% and most preferably 3.0 to 4.5 wt .-%, each based on the dry weight of the polyvinyl esters. In a preferred embodiment, the emulsion polymerization is carried out in the presence of at least two polyvinyl alcohols, wherein at least one polyvinyl alcohol is a medium-viscosity polyvinyl alcohol. Particularly preferably, the emulsion polymerization is carried out in the presence of at least one medium-viscosity polyvinyl alcohol and at least one polyvinyl alcohol having a viscosity of 40 to 60 mPas (highly viscous polyvinyl alcohol).

The high-viscosity polyvinyl alcohol has a viscosity of preferably 40 to 60 mPas and more preferably 45 to 55 mPas. The proportion of the high viscosity ^'polyvinyl alcohols is preferably 0.01 to 2.5 wt .-%, more preferably 0.1 to 2 wt .-%, particularly preferably 0.2 to 1.5 wt .-% and most preferably 0 , 3 to 1.0 wt .-%, each based on the dry weight of the polyvinyl esters.

The total amount of high-viscosity polyvinyl alcohols and medium-viscosity polyvinyl alcohols is preferably 0.6 to 6.1 wt .-%, more preferably 1.1 to 5.5 wt .-%, particularly preferably 2.2 to 4.5 wt .-% and most preferably 3.0 to 4.0% by weight, based in each case on the dry weight of the polyvinyl esters. Optionally, the emulsion polymerization may be carried out in the presence of one or more low viscosity polyvinyl alcohols, preferably in combination with one or more medium viscosity polyvinyl alcohols and / or one or more high viscosity polyvinyl alcohols. Low viscosity polyvinyl alcohols have viscosities of preferably from 1 to 18 mPas, more preferably from 1 to 15 mPas, more preferably from 1 to 10 mPas, and most preferably from 2 to 8 mPas. The proportion of the low-viscosity polyvinyl alcohols is preferably from 0.01 to 5.0 wt .-%, more preferably 0.1 to 3.0 wt .-%, particularly preferably 1.0 to 2.5 wt .-% and am Most preferably 1.0 to 2.0 wt .-%, each based on the dry weight of the polyvinyl esters. The use of polyvinyl alcohols invention is particularly advantageous for the wet grip appliqued dispersion ^¬ adhesives.

The stated polyvinyl alcohols are accessible by means of methods known to the person skilled in the art.

In the emulsion polymerization process, it is also possible to polymerize in the presence of emulsifiers. Preferred amounts of emulsifiers are 0 to 7% by weight, in particular 1 to 7% by weight, based on the total weight of the monomers. The emulsion polymerization is preferably carried out in the absence of emulsifiers. Preferred dispersion adhesives are free of emulsifiers.

Examples of emulsifiers are anionic, cationic or nonionic emulsifiers. Examples of anionic emulsifiers are alkyl sulfates having a chain length of 8 to 18 C atoms, alkyl or alkylaryl ether sulfates having 8 to 18 C atoms in the hydrophobic radical and up to 40 ethylene or propylene oxide units, alkyl or alkylaryl sulfonates having 8 to 18 C atoms, esters and half esters of sulfosubstituted acid with monohydric ^alcohols or alkylphenols. Examples of nonionic emulsifiers ren are alkyl polyglycol ethers or alkylaryl polyglycol ethers having 8 to 40 ethylene oxide units.

Essential for the present invention is that the emulsion polymerization is carried out in a continuous procedure. Continuous polymerization is usually understood as meaning a polymerization process in which educts, such as monomers a) and / or optionally monomers b), optionally protective colloids and optionally initiators, are fed to the polymerization reactor or a reactor cascade, and polymerization mixture or polymerization product is taken off to the same extent ; that is, the resulting from the continuous process flow is equal to the sum of all the process continuously supplied partial streams.

Essential to the invention is thus the preparation of the polyvinyl esters by means of aqueous, free-radically initiated, continuous emulsion polymerization, preferably in a stirred tank cascade with at least two pressure reactors connected in series and subsequently at least one low pressure reactor.

The polymerization is preferably carried out in at least two pressure reactors connected in series and subsequently continued in at least one low-pressure reactor. As pressure reactors and low-pressure reactors, the conventional, correspondingly dimensioned steel reactors with Rührein ^¬ direction, heating / cooling system and lines for supplying the reactants or removal of the products can be used. The preferred plant configuration consists of two pressure reactors connected in series and one or two subsequent low-pressure reactors. If several low-pressure reactors are used, they can be operated both alternately (in parallel) and one behind the other (in series). Higher cascades with more than two pressure reactors can be used but due to the associated strongly increasing complex ^¬ complexity of the system is not always desirable.

The process is generally conducted so that in all pressure reactors, the sum of the incoming mass flows is equal to the sum of the exiting mass flows. The low pressure reactors are preferably operated side by side and used alternately. The pressure in the pressurized reactors arranged in series is adjusted, in general, that to the last of the series-connected motors Druckreak ^¬ a decreasing pressure gradient results from the ER most, which guarantees the mass flow in the pressure reactor cascade. The mass transport from the last pressure reactor into the downstream low-pressure reactor can take place for example by means of pressure-controlled valves or by means of a pump to the extent that the mass flows are fed into the upstream pressure reactors.

Before the start of polymerization, the pressure reactors in All- be common to 50 to 80% of the volume filled with a polymer dispersion, which is preferably the final product of polymerisation ^¬ tion with respect to copolymer composition, type and amount of surface active compound (s) (emulsifiers and Schutzkollo- which especially polyvinyl alcohols) as well as particle size and solids content. This can be done so that in the

Pressure Reactors this dispersion is prepared by batch polymerization, or the pressure reactors are filled with a separately prepared dispersion. If ethylene is copolymerized, then in a preferred Äusführungsform then the pressure reactors are subjected to ethylene. Ethylene pressure is generally regulated to result in a decreasing pressure gradient from the first to the last of the downstream pressure reactors. Preferably, the pressure difference between two consecutive the switched pressure reactors 2 to 40 bar.

Preferably 50 to 100 wt .-%, particularly preferably 60 to 95 wt .-% and most preferably 75 to 90 wt .-% vinyl ester a), based on the total weight of all vinyl esters a), are charged or added in the first pressure reactor and the remainder added to the subsequent pressure reactors. Monomer bl), in particular ethylene, is preferably added to at least 50 wt .-% and most preferably completely in the first pressurized reactor and submitted to any residual in the following Druckreak ^¬ factors or metered. The addition of the monomers b2) can be carried out so that it takes place partially or completely in the first pressure reactor or partially or completely in one of the further pressure reactors. Some of the monomers b2) can also be metered in the low-pressure reactor. The addition of the said auxiliary monomers can be wholly or partly carried out both in the first and in one of the subsequent pressure reactors or in the low-pressure reactor. Preferably, the auxiliary monomers are completely metered into the first pressure reactor.

The polyvinyl alcohols, ie in particular the medium-Po ^¬ lyvinylalkohol, where appropriate, the high-viscosity polyvinyl alcohol and optionally the low-viscosity polyvinyl alcohol, may be added completely in the first pressurized reactor or partly added in the first pressurized reactor and the remainder in another pressure reactors and / or the subsequent low-pressure reactors be added.

The polyvinyl alcohols are preferably initially introduced or added to at least 50% by weight and, in a preferred embodiment, completely into the first pressure reactor and the remainder is initially introduced or metered into the subsequent pressure reactors. Particularly preferably, the polyvinyl alcohols are completely introduced into the first pressure reactor or, in particular, metered in. The medium-viscosity polyvinyl alcohol is particularly preferably completely charged or metered into the first pressure reactor. For example, from 50 to 100% by weight, in particular from 90 to 100% by weight and particularly preferably 100% by weight, of the medium-viscosity polyvinyl alcohol, based on the total weight of the medium-viscosity polyvinyl alcohol used, may be initially charged or metered into the first pressure reactor and the remainder Submitted in the subsequent pressure reactors o- or metered.

It is also preferred to introduce the highly viscous polyvinyl alcohol into the first pressure reactor at 50 to 100% by weight, in particular 90 to 100% by weight and more preferably 100% by weight, based on the total weight of the high-viscosity polyvinyl alcohol used to dose and to submit the remaining balance in the subsequent pressure reactors or metering.

The polymerization is preferably initiated with a redox system of oxidation and reduction components, with preference ^¬ both components are dosed in all pressure reactors. The monomer conversion is controlled with the initiator feed. The initiators are added in total so that a continuous polymerization is ensured, and the polymerization in the first pressure reactor to a conversion of preferably at least 30 wt .-% and in the last pressure reactor of ^¬ preferably at least 90 wt .-% is performed , in each case based on the total weight of the monomers used in the process. The mean solids content in the first pressure reactor is preferably 15 to 40 wt .-% and particularly preferably 20 to 30

Wt .-%. The average solids content in the last of the series-connected pressure reactors is preferably 30 to 75 wt .-% and particularly preferably 40 to 60 wt .-%. These solids distributions can also be used to calculate the viscosities of the be influenced lyvinylesterdispersionen.

Overall, the metering rates of the educts are adjusted so that mean residence times in the pressure reactor cascade of preferably total 60 to 240 minutes result.

After completion of the polymerization in the pressure reactor cascade can be postpolymerized for residual monomer removal using known methods in the low pressure reactor, generally by redox catalyst initiated postpolymerization. In the low pressure reactor is preferably polymerized at atmospheric pressure or lower, that is, at a pressure of <1 bar abs and at a temperature of 30 ° C to 60 ° C. The polymerization is preferably continued up to a conversion of at least 99% by weight, based on the total weight of the monomers used in the process, particularly preferably up to a free monomer content of <1000 ppm.

Any volatile residual monomers can then be removed by distillation, preferably under reduced pressure, and optionally by passing or passing inert inert gases such as air, nitrogen or steam.

The aqueous dispersions or dispersion adhesives according to the invention have a solids content of preferably 30 to 75% by weight, particularly preferably 50 to 60% by weight. In the ver ^¬ remaining shares it is preferably water. The amounts of solid and water total add up to 100 wt -.%.

The dispersion adhesives preferably contain at least 40 weight percent, more preferably at least 50 weight percent, and most preferably 60 weight percent polyvinyl ester. The dispersion adhesives preferably contain at most 99% by weight and more preferably at most 95% by weight polyvinyl ester. The data in% by weight refer in each case to the dry weight of the dispersion adhesives.

Optionally, the dispersion adhesives contain one or more additives, for example plasticizers, such as phthalates, benzoates or adipates, film-forming aids, such as triazetin or glycols, in particular butylglycol, butyldiglycol, butyldipropylene glycol and butyltripropylene glycol, wetting agents, generally surfactants, thickeners, such as polyacrylates, polyurethanes , Cellulose ethers or polyvinyl alcohols, defoamers, tackifiers or other customary for the formulation of adhesives additives. The proportion of these additives may for example be up to 40 wt .-%, preferably 0 to 25 wt .-%, more preferably 1 to 15 wt .-%, particularly preferably 1 to 10 wt .-% and most preferably 1 to 5 wt .-%, depending on the dry weight of the dispersion adhesives.

The preparation of the dispersion adhesives can be carried out by the customary methods, generally by mixing the aforementioned components. The mixing can be done in conventional mixers, such as agitators or dissolvers. The mixing is preferably carried out at temperatures of 5 to 50 ° C, more preferably 15 to 40 ° C and most preferably 20 to 30 ° C.

The dispersion adhesives according to the invention can be used in the conventional machine application methods for dispersion adhesives, such as, for example, in the die or roll application methods. The dispersion adhesives are applied to substrates. The order can be continuous, line-shaped or punctiform. In this case, the dispersion adhesives of the invention are suitable for the bonding of different substrates, preferably paper, cardboard, wood, fiber materials, coated cardboard and for bonding cellulosic materials with plastics such as polymer films, for example, polyethylene, polyvinyl chloride, polyamide, polyester or polystyrene films. The dispersion adhesives find particular use as paper adhesives, packaging adhesives, wood adhesives and adhesives for woven and nonwoven fibrous materials. Particularly suitable are the dispersion adhesives for the bonding of cellulosic substrates, in particular paper, cardboard or cotton fabric, each with plastic films, or for the bonding of plastic films together (film / foil bonding).

The dispersion adhesives according to the invention are ideally suited for application by means of a mechanical application process. Thus, the occurrence of undesirable adhesive deposits on the application nozzle or uncontrolled "splashes" with the dispersion adhesives according to the invention can be avoided to the desired extent The dispersion adhesives exhibit advantageous rheological properties, such as low shear thinning It was also surprising that in the procedure according to the invention it is possible to dispense with the addition of emulsifiers to the dispersion adhesives or polyvinyl ester dispersions, and nevertheless the desired performance properties can be achieved.

The following examples serve to further illustrate the invention: Example 1: continuous polymerization

In a reactor cascade consisting of the two pressure reactors Rl (first reactor, volume: 18 liters) and R2 (second reactor, volume: 18 liters) and the pressureless reactor R3 (volume: 47 liters), each equipped with a heating jacket, stirrer and dosing ments, a continuous emulsion polymeriza- tion performed. The three reactors are connected by pipelines. The mass flow runs the reactor cascade starting in the first pressure reactor Rl, then through the second pressure reactor R2 and finally through the pressure-less reactor R3. Starting materials are fed continuously and the end product is continuously withdrawn from the pressureless reactor R3. 9.9 kg of an aqueous polymer dispersion which corresponded to the end product with regard to the monomer composition, the type and amount of protective colloid and the particle size and solids content were initially charged in the pressure reactor R1. The pressure reactor R2 was completely filled with the aforementioned polymer dispersion. The polymer dispersion had been prepared according to known methods by emulsion polymerization in batch mode.

In addition, 2.7 kg of vinyl acetate, 1.4 kg of a 10.3% strength aqueous solution of the polyvinyl alcohol C523 (degree of hydrolysis: 88 mol%, Höppler viscosity (determined at 20 ° C. in accordance with DIN 53015) were additionally introduced into the first pressure reactor R1 , in 4% aqueous solution): 23 mPas), 1 g of a 10% aqueous solution of ammonium iron (II) sulfate and 2.0 kg of water. The pH was adjusted to 3.8 with formic acid. The reactor R1 was heated to 60 ° C and the reactor R2 was heated to 65 ° C. The first reactor Rl was charged with ethylene, so that in the first reactor Rl a pressure of 60 bar and in the second reactor R2 a pressure of 55 bar was established, controlled by pressure valves. These pressures were maintained during the emulsion polymerization by further ethylene feed.

Subsequently, potassium persulphate (3% strength aqueous solution) at a metering rate of 90 g / h and sodium formaldehyde sulphoxylate (1.5% aqueous solution) at a metering rate of 90 g / h were metered into the reactor R1.

With the start of the polymerization reaction, recognizable by the temperature increase, the following components were metered into the reactor R1 at the following metering rates:

3.5 kg / h vinyl acetate,

900 g / h of ethylene and 3.7 kg / h of an aqueous mixture containing 4.2% by weight of polyvinyl alcohol C523 and 30 ppm of ammonium iron (II) sulphate with a pH of 3.8, adjusted with formic acid.

Simultaneously with the beginning of metering into the reactor Rl, the following components were metered into the reactor R2 at the following metering rates:

612 g / h vinyl acetate,

450 g / h potassium persulfate (3% aqueous solution) and

450 g / h of sodium formaldehyde sulfoxylate (1.5% strength aqueous solution) The following components are added continuously to the pressure-free reactor R3 at the following metering rates:

70 g / h tert-butyl hydroperoxide (10% aqueous solution), 120 g / h sodium formaldehyde sulfoxylate (5% aqueous solution) The process was carried out continuously for 24 hours. Additional information on the polymer dispersion obtained in this way is given in Table 1. The properties of the polymer dispersion are listed in Table 2.

Table 1: Composition of the polymer dispersions:

a) polyvinyl alcohol having a degree of hydrolysis of 88 mol% and a Höppler viscosity of 23 mPas (determined at 20 ° C according to DIN 53015, in 4% aqueous solution);

b) Data in wt .-% based on the total weight of the monomers.

Comparative Example 2: Batch Polymerization

The following components were placed in a pressure reactor with a volume of 600 liters:

140 kg of water,

70 kg of a 10% aqueous solution of the partially hydrolyzed polyvinylidene nylalcohol C523,

240 g of 98% formic acid,

140 g of iron (II) ammonium sulfate solution (10% in water).

The pressure reactor was evacuated and then 197 kg of vinyl acetate were added to the original. Thereafter, the reactor was heated to 50 ° C and subjected to an ethylene pressure of 43 bar (corresponding to a quantity of 42 kg of ethylene).

The polymerization was started by starting the metering of a 3% aqueous hydrogen peroxide solution at a rate of 350 g / h and a 10% aqueous Na-hydroxymethanesulfinate solution

(Brüggolit) started at a rate of 480 g / h. With the start of polymerization, the temperature was increased from 50 ° C to 70 ° C. 60 minutes after the start of the polymerization, vinyl acetate was metered in at a rate of 23 kg / h for 1.5. After the end of the vinyl acetate metering, the doses of the hydrogen peroxide solution and the Na hydroxymethanesulfinate solution were continued for a further 60 minutes. The total polymerization time was 3.5 hours. The polymer dispersion thus obtained was then transferred to a pressureless reactor. The pressure-free reactor was pressurized to 0.7 mbar. Into the pressure-less reactor, 880 g of a 10% aqueous tert-butyl hydroperoxide solution and 580 kg of a 10% Na-hydroxymethanesulfinate aqueous solution (Brüggolit) were added, followed by postpolymerization. The pH was adjusted to 4.5 by addition of aqueous sodium hydroxide solution (10% strength). Finally, the batch was filtered with a sieve with a mesh size of 150 μηα.

Additional information on the polymer dispersion obtained in this way is given in Table 1. The properties of the polymer dispersion are listed in Table 2.

Nozzle application method: Construction:

The dispersion adhesives were applied by means of nozzle application on a rotating stainless steel roller. The stainless steel roll had a circumference of 80 cm and rotated at a speed of 100, 120 or 140 revolutions / min about its own axis.

The dispersion adhesives were applied with an HHS application system with valves of the type GKD4-114-2m and nozzles of the type LVK-4 ap ^¬ . The nozzles were mounted at a distance of 4 mm vertically above the roll surface. The dispersion adhesives were adjusted by diluting with water to a viscosity of 800 mPas and was fed via hose lines using egg ner piston pump using a pressure of 9 bar to SI ^¬ sen. The application of the dispersion adhesives through the nozzles to the stainless steel roller was pulsed by the nozzles were opened at a constant rhythm and closed again. A cycle of once opening and closing the nozzle is called a pulse. There were set 18 pulses per nozzle To ^¬ rotation of the steel roll. From the stainless steel roller, the dispersion adhesives were immediately scraped off with a plastic squeegee.

The test was carried out under standard conditions at 23 ° C and a relative humidity of 50%.

120 minutes after the start of the nozzle application, the size of the peg-shaped structure was measured at the nozzle. The results of the testing are shown in Table 2. Spray obtained with roller application:

The test was carried out on a roll mill in standard atmosphere at 23 ° C and a relative humidity of 50%. The first roll had a diameter of 8 cm and dipped in a ^¬ Dis persionsklebstoff bath. The axis of a second roll was parallel to the axis of the first roll and mounted vertically above the first roll. The second roll also had a diameter of 8 cm. The two rollers rotated in opposite directions, each with a rotational speed of 60 U / min. Over the width of the gap between the two rolls, the amount of dispersion adhesive is set, the from the first roll on the second roller is transferred. The gap width was 0.4 mm.

An application disk was placed 0.2 mm above the second roller. The order disk had one

Diameter of 12 cm and a width of 2 cm.

At a distance of 5 cm from the roll mill, plexiglass sheets were applied.

Starting from an initial speed of 300 rpm, the speed of rotation of the application disk was increased incrementally by a further 100 rpm every minute until, for the first time, a drop of the dispersion adhesive removed from the application disk impinged on a Plexiglas disk. The corresponding rotational speed is specified for the respective dispersion adhesive ^¬ in Table 2 below.

Determination of polydispersity PD and weight-average particle diameter Dw:

The determination was carried out by means of static light scattering with the measuring device LS 13320 from BeckmanCoulter.

The dispersion adhesive of Example 1 shows good rheological properties, such as for machine application methods ge ^¬ wishes and leads in the application to the desired, fast setting rates and good mechanical properties.

In addition, the application characteristics of Example 1 of the invention is significantly advantageous over Comparative Example 2, as was shown, for example, when applied with the Wal ^¬ zenstuhl. In comparison example 2, spraying starts at 500 revolutions per minute, which leads to an imprecise adhesive application in the application. On the other hand, example 1 shows an advantageously low propensity to spatter, since spraying only starts at 1000 revolutions per minute. Roll ^¬ order process can be operated significantly faster and more precise. Table 2: Properties of the polymer dispersions and their A test results:

In the nozzle Application Example 1 shows less Nei ^¬ supply to build up on the nozzle. The 120-minute test was run smoothly at all speeds, the construction at the nozzle reaches a maximum of 3 mm. In Comparative Example 2, however, the test must be stopped after less than 120 min at the higher speeds (120 rpm and 140 rpm), since the structure exceeds 4 mm. The dispersion adhesive of Comparative Example 2 is therefore also insufficient for machine application methods.

Claims

Claims:

1. A method for applying dispersion adhesives containing one or more polyvinyl esters and optionally one or more additives, characterized in that

one or more polyvinyl esters are prepared by free-radically initiated, continuous emulsion polymerization of a) one or more vinyl esters and, if appropriate, b) one or more further ethylenically unsaturated monomers, and

the dispersion adhesives are applied to a substrate by means of a mechanical application process.

2. A process for applying dispersion adhesives according to claim 1, characterized in that one or more polyvinyl esters to 50 to 90 wt .-% of one or more vinyl esters, 10 to 25 wt .-% of ethylene and optionally 1 to 40 wt .-% based on one or more further ethylenically unsaturated monomers, based on the total weight of the monomers.

3. A method for applying dispersion adhesives according to claim 1 or 2, characterized in that the poly ^¬ vinylester a polydispersity PD of ^ have 21, wherein the polydispersity PD calculated from the ratio of the weight average particle diameter Dw to the number average particle diameter Dn, PD = Dw / Dn, results (determination with the Beckmann Coulter® LS according to ISO 13320).

4. A method for applying dispersion adhesives according to claim 1 to 3, characterized in that the emulsion polymerization is carried out at a temperature between 40 ° C to 100 ° C. Process for the application of dispersion adhesives according to Claims 1 to 4, characterized in that 0.5 to 6.0% by weight of one or more polyvinyl alcohols having viscosities of 19 to 39 mPas are used for the emulsion polymerization (determination of the viscosity by the method according to Hoppler, in accordance with DIN 53015, at 20 ° C., in 4% aqueous solution).

A process for applying dispersion adhesives according to claim 1 to 5, characterized in that the dispersion adhesives are free of emulsifiers.

A method for applying dispersion adhesives according to claim 1 to 6, characterized in that), optionally polyvinyl alcohols and, optionally, initiators are continuously fed in the continuous emulsion polymerization of a polymerization reactor or a reactor cascade Vinylester a) and / or optionally ethylenically unsaturated monomers b and chem in sliding ^¬ Measures continuously taken polymerization mixture.

Process for the application of dispersion adhesives according to claim 7, characterized in that the average residence times in the polymerization reactor or in the pressure reactor cascade amount to 60 to 240 minutes.

A method for applying dispersion adhesives according to claim 1 to 8, characterized in that the Maschi ^¬ order application methods are selected from the group comprising nozzle application method and roll application method.

Process for the application of dispersion adhesives according to Claims 1 to 9, characterized in that the sub- strat is selected from the group comprising paper and plastics.

1. dispersion adhesives containing one or more polyvinyl nylester, one or more additives and water, characterized in that

one or more polyvinyl esters are obtainable by means of free-radically initiated, continuous emulsion polymerization of a) one or more vinyl esters and optionally b) one or more further ethylenically unsaturated monomers in the absence of emulsifiers and the polyvinyl esters have a polydispersity PD of at least 21 (determination with the measuring instrument Beckmann Coulter® LS according to ISO 13320) and

the proportion of the polyvinyl ester to the Dispersionsklebstof ^¬ fen 40 to 99 wt .-%, based on the dry weight of the dispersion adhesives.