DE2035919A1 - Coating agents - Google Patents

Description

Coating agents

The present invention relates to aqueous coating agents, in particular those for coatings permeable substrates, such as paper, cardboard, fabric and Nonwovens.

It is customary to coat paper and cardboard with an aqueous dispersion of a pigment bound with a pigment binder. While casein and starch were used as conventional pigment binders in the past, more recently, film-forming organic polymers combined with casein or starch have been used as pigment binders. Due to the thermoplastic properties of the organic polymer, it would be conceivable to obtain a coating with a better appearance if the binder consisted only of the organic polymer. This has hitherto proven to be impossible, since the conventional organic polymers used in admixture with the pigment do not have a coating composition with a sufficiently high water retention capacity or a sufficiently high viscosity

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if they are used as the sole binder.

It is the object of the invention to provide a coating agent provide in which the film-forming ingredient is a synthetic organic polymer and in which one. without the conventional pigment binders such as starch and Casein, get by.

To solve this problem, the present invention provides an aqueous coating agent containing a latex mixture of 80 to 99%, preferably 88 % of a copolymer A and 1 to 20, preferably 3 to 12% of a copolymer B, where copolymer A is a film-forming polymer of 45% to 70 fo styrene and / or methyl methacrylate, 0 to 5 ° i ethylenically unsaturated carboxylic acid, the remainder being butadiene, which in an aqueous alkaline _solution; at pH 10 and 20 ⁰ C insoluble and essentially not ^, swellable and wherein copolymer B is a crosslinked copolymer of 35 to 50 $ butadiene-1,3 and 50 to 65 ^ of an ethylenically unsaturated carboxylic acid, which a _: essentially swellable and to at least $ 50 ■ - _; is insoluble in aqueous alkaline solution at pH 10 and 20 C.

The degree of crosslinking of the copolymer B is sufficient to to bring about the desired insolubility in aqueous alkaline solution, but it is not so great as to the To hinder swelling of the copolymer in aqueous alkaline solution.

In a further embodiment, the invention relates Coating agents with pigments dispersed therein. Such coating mixtures preferably exist from 5 to 25 parts by weight of a latex mixture of

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Copolymer A and Copolymer B per 100 parts by weight of pigment. Such coating mixtures are used to coat permeable substrates such as paper, cardboard, fabric or nonwovens.

Both for use as a coating agent and when the copolymer latex is used as a pigment binder it is desirable to adjust the viscosity up to the stage of preparation of the pigmented mixture for reasons easier handling and portability to keep low. The initial viscosity is expediently below approx. 200 cps. At a pH of about 7, the viscosity of the copolymer latex should preferably be kept low, since at this pH the latexes are more stable to treatment and transport. When applying the coating material to the substrate, the Viscosity can be increased to get the right coating properties to achieve. Many soluble thickeners are known which give a spread mix the desired Viscosity, e.g., sodium or ammonium salts of polyacrylic acid and its copolymers. But if you put this in the latex of a copolymer, -that If you want to use it as a pigment binder, the viscosity of the latex increases so much that it does not even have to to be processed at pH values below 7.

Dispersions of alkali-soluble copolymers, e.g. from im Commercially available polyacrylic acid copolymers that have a have low viscosity at pH 3, increase in viscosity rapidly as the pH value increases to 6 or 7 and are therefore not suitable for modifying the viscosity properties of common paper coating latices.

The copolymers B of the coating composition according to the invention since they are largely insoluble in alkali, have no significant effect on the viscosity of the copolymer mixture

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or the spreadable manure, Ms reaches a pH value above ■ 7 becomes »This becomes expedient by adding an alkali Thus brought about by aqueous ammonium hydroxide is with these inventive coating compositions The viscosity required for spreading purposes can be achieved in a simple manner by adding alkali, which makes it economical Use of butadiene copolymers as the sole binder for the pigment becomes possible »

The latices of the coating composition according to the invention are expediently produced in a manner known per se in the emulsion polymerization process. Herein, the mixture of monomers is polymerized while they are continuously dispersed in an aqueous, an emulsifying agent containing phase "In the conventional emulsion polymerization processes are usually from 1.5 to 5 wt. Fo emulsifier, based on the weight of the monomer mixture present" However, it is advantageous

- especially in the case of copolymer A _5, which forms the main part of the copolymer mixture, - use less than 1 percent by weight of emulsifying agent, based on the weight of the monomer mixture Degree of foaming during the application of the coating material, i.e. when the coating composition according to the invention is mixed and applied to the substrate and a reducing agent is used. Also in emulsion polymerization it is common to use a polymerization modifier, usually

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a mercaptan to increase the molecular weight of the polymer check. Even if one of the monomeric components of the polymerization formulation is a carboxylic acid, it is necessary "to polymerize at a pH below 7, usually at a pH of about 2-3.

If carboxylic acid is contained in copolymer A, this can be any ethylenically unsaturated carboxylic acid which is copolymerizable with the other monomeric constituents of the copolymer. Examples of such copolymerizable carboxylic acids are acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid and citraconic acid . In the case of dicarboxylic acids, the monoesters of these acids can also be used. The presence of carboxylic acid in copolymer A tends to have the effect that the copolymer becomes swellable in an alkaline medium. However, compared with that of Copolymer B, the effect is not significant. This property can be modified by changing the molecular weight of the copolymer, for example the swellability in an alkaline medium is reduced by increasing the molecular weight. Copolymer A can be a paper coating latex of an organic polymer of the conventional type. The proportion of copolymer A in a mixture according to the invention of copolymer A and copolymer B should preferably be 88 to 97 grains.

The proportion of copolymer B which is required in order to achieve the desired effect in terms of water retention capacity and viscosity in the coating composition depends, among other things, on its acid content. Copolymer B also has little binding effect on pigments, so that from this point of view it is advisable to keep the concentration of copolymer B as low as possible. To use copolymer B is most effective, it should advantageously not less than 50 $ ethylenically unsaturated carboxylic acid

contain. "_ _Λ ■ _Λ,. _c

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Copolymer B can be produced with any ethylenically unsaturated carboxylic acid, provided it is with butadiene »Monoethylenically unsaturated ones can be copolymerized Carboxylic acids copolymerize easily with butadiene. Dicarboxylic acids, on the other hand, polymerize slowly and it is generally not so easy to use copolymer B exclusively with a ©! carboxylic acid “normally will be hence Mono-Ethyle. unsaturated carboxylic acids, such as Methacrylic or acrylic acid, as the acid component of the copolymer B preferred.

The relatively low solubility of copolymer B in an alkaline medium is achieved by crosslinking the copolymer. As has often been mentioned, "so that the optimum effect of copolymer B on the properties of the coating is achieved with regard to viscosity and water retention capacity, the latex particles of copolymer" B must not be so densely crosslinked that they hinder the swelling of the particles under alkaline conditions . ₉ nor the molecular weight may be small and be present as low crosslinking that the copolymer is ..weitgehend soluble in aqueous alkali. The molecular weight and the degree of crosslinking can be controlled by the amount of a polymerisation modifier, for example mercaptan, used in the preparation of the copolymer.

For the preparation of pigmented coating slips, the finely divided pigments customary in paper spreading are used. These are normally mineral pigments, such as China Glay _s titanium dioxide, satin white, blanc fixe and calcium carbonate.

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Although the coating agent of the present invention for. The coating of permeable substrates without the Presence of conventional pigment binders such as casein, and When starch is provided, it can also contain small amounts of these conventional substances.

The preparation of the pigmented mixtures of the invention Coating agent and the application of the coating slips to the permeable substrates are carried out according to the Customary paper coating process.

The required ratio of copolymer A to copolymer B in a paper coating mixture depends on the total proportion of pigment binder (A + B) in the mixture. For coated printing papers of gravure printing quality, because of the low tackiness of the printing ink, a low content of pigment binder is sufficient, ie 8 to 10% binder in the pigment is sufficient for satisfactory printability. For coated offset printing papers, on the other hand, a higher content of pigment binder, around $ 12 to $ 16, is required, since the ink used in this printing process has a high tack. In order to achieve the same application viscosity in both cases with coating compounds for gravure printing grades and for offset litho grades of coated printing papers, the proportion of copolymer B present in the latex mixture of copolymer A and copolymer B for the gravure printing quality should therefore be higher than for the offset litho quality.

The coating compositions according to the invention are used with great advantage as the sole pigment binder in paper coating slips used. In addition, the filler-reinforced coating compositions according to the invention can be applied to the The back of a carpet fabric or upholstery fabric can be applied to anchor the pile to the carrier fabric and to give it the desired properties.

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The coating agent can also be used to an additional layer of the carrier material on the back to bind the carpet structure »Furthermore, with the agent according to the invention the viscosity of paints, which contain styrene-butadies-oopolymers., modified will. Furthermore, the agent according to the invention can be used to reduce the viscosity of latex dispersions which are used as · ■ Impregnating agent for rag felt carpets or as coatings for films, e.g. made of cellulose, polyester or Polyolefins are used to regulate au »Likewise, the Viscosity of pigmented leather finishes «that form a film contain organic polymer. Finally, the agent according to the invention can be used for modification the viscosity of a mixture based on pigment and film-forming organic polymer, as it is during manufacture used by solid foams.

The invention is illustrated by the following examples. All parts are listed here as parts by weight.

example 1

A copolymer (Copolymer A) in latex form was obtained by aqueous emulsion polymerization at 37% monomer content from 38 parts of butadiene, 60 parts of methyl methacrylate and 2 parts of itaconic acid prepared in the presence of 0.1 part of an emulsifier and 0.05 part of sodium hexamethaphosphate, The polymerization process was carried out until the conversion was essentially complete. The copolymer was found to be insoluble and essentially resistant to swelling when treated with an aqueous solution of ammonium hydroxide.

■ A copolymer (Copolymer B) in latex form was made into one Stirring autoclave prepared «The following components were put into the autoclave:

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Water 1 70 Parts Il Methacrylic acid 55 Il Sodium dodecyrbenzene
sulfonate 2 , 2 Il Tert .dodecylvercaptan Ό , 2 Il Ammonium peroxide
sulfate 0 , 4 Il Disodium salt of
Ethylene diamine tetra
acetic acid 0 , 5

The autoclave was then sealed, flushed with nitrogen and evacuated. Bs & wi s then 45 parts of butadiene charged, and the autoclave at 5O ⁰ G heated, Ms, the entire Monomerinhalt had substantially reacted in Oopolymer. The copolymer consisted of an acidic latex with a solid content of 37 °. This copolymer was not noticeably soluble in aqueous ammonium hydroxide solution at a pH of 9 and above, but gave a translucent suspension of a gelatinous mass.

A mixture of 92 parts was then made Oopolymer A with 8 parts of copolymer B. The viscosity of this mixture increased almost not at all than that Adjust pH to approx. β with aqueous ammonium hydroxide solution was increased. This mixture was used to prepare the following spread mix;

China clay 100 parts dry weight

"Dispex" 115 N.

Ha-salt of a polycarboxylic acid low molecular weight 0.3 ""

Latex mix 7 ""

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China, elay was made in water in a high speed mixer dispersed in the presence of the "Dispex" 115 1, the resulting Mixture, the late2cm mixture added and the solids content adjusted to 60 # «, * the pH value was finally adjusted to 9 Ms with aqueous ammonia.

The mixture prepared in this way has satisfactory flow and water resistance properties for the squeegee coating process. The properties of the coated paper meet the requirements for rotogravure printing. A similar mixture on the basis of a eggs alone of Copolymer A sufeereitetsn latex could not be successfully processed on a Rakelstreiehmaschine because viscosity Imoe water retention capacity was too low.

Example 2

A latexx form copolymer (copolymer A) was made from The following components are manufactured in a stirred autoclave were given

Water 150 parts

Stjrrol. 4-7 " Itaeonsamre 5 "

Sodium dodecyl sulfonate 1.6 ^M.

Am coadeasation product VG'ifi, los ^ rlphenol and ethylene oxide (haaäelsüloliches aichtionlBohes emulsifying agent) 3jO ⁿ "

Potash sulphate 0.8 ⁿ

Potassium sulfate 0.15 "

Sodium lexamethaphosphate 0.05 "

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The autoclave was flushed, closed and evacuated with nitrogen and 48 parts of 1,3-butadiene poured in «The Dispersion was kept at a temperature of 65 ° C, to substantially all of the monomer. Contents had been converted into Oopolymeres and an acidic one Yielded latex of about 40 # solids. This Copolymer was found when treated with an aqueous Solution of ammonium hydroxide as insoluble and essentially resistant to swelling.

An emulsion copolymer (copolymer B) in latex form (content 37 '$> solids) at 5O ⁰ C in a stirred autoclave made of 40 parts of butadiene and 60 parts of methacrylic acid in the presence of 2.4 parts Natriumdodezylbenzolsulfonat as an emulsifier and 0, 2 parts of tertiary dodecyl mercaptan as a polymerization modifier. When the resulting acidic, milky white latex was treated with an aqueous ammonium hydroxide solution, the pH being 9 or above, the copolymer did not dissolve into a clear solution, but instead formed a translucent suspension of strongly swollen gelatinous particles.

Corresponding amounts of the two latices were made into a mixture of 97 parts of copolymer A with 3 parts of copolymer B. processed. The pH of this latex mixture was raised to 6 by the addition of aqueous ammonia, without any noticeable increase in viscosity occurred.

This latex mixture was used for the preparation of the following Coating used:

China clay 100 parts dry weight

"Dispex" 115 N (sodium salt of a polycarboxylic acid with low molecular weight) 0.3 ""

Latex mix 14 ""

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China clay was dispersed in water in a high-speed mixer in the presence of "Dispex" 115 N as a dispersant for China clay, the latex mixture was added to the resulting mixture and the pesticide content was adjusted to $ 60. After the pH of the mixture had been increased to 9 to 10 by adding aqueous ammonia, the mixture had the corresponding pleating and water retention properties required for the order

them on paper using a high-speed squeegee coater made suitable. A similar paint mix made with just a latex of Copolymer A alone on the other hand, had too low * viscosity and insufficient Water retention to with a knife coater to be applied. After applying the coating material to the paper under Using a high speed squeegee coater and after drying and calendering the paper had one for offset litho printing suitable, satisfactory pick resistance and high gloss.

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Claims (2)

-13- claims . Aqueous coating agent containing a latex mixture of 80 to 99 #, preferably 88 to 97 # of a copolymer A and 1 to 20, preferably 3 to 12 percent of a copolymer B, where copolymer A is a film-forming polymer of 45 to 70% styrene and / or methyl methacrylate , 0 to 5 i * ethylenically unsaturated carboxylic acid, fiest is butadiene, which is insoluble and essentially not swellable in aqueous alkaline solution at pH 10 and 20 ° C, and where copolymer B is a crosslinked copolymer of 35 to 50 % butadiene-1 , 3 and 50 to 65 ί> an ethylenically unsaturated carboxylic acid, which is essentially swellable and at least 50 io insoluble in aqueous alkaline solution at pH 10 and 20 ° C, 2) Aqueous coating agent according to claim 1, characterized in that the copolymer A contains less than 1 $> of an Eanilgators, based on the monomer mixture used to produce the copolymer A. 1098U / 2086