CS254586B1 - Process for preparing self-cross linking of thermoreactive acrylate dispersions - Google Patents

Abstract

Self-crosslinking thermoreactive dispersion emulsion polymerization is produced by acrylic or methacrylamide, methyl methacrylate, or mixtures thereof, with acid esters acrylic containing 1-8 carbon atoms in the alkyl atoms, acrylonitrile and acid acrylic, in the presence of a crosslinker a comonomer which is N-methyloacryl- or methacrylamide. The polymerization is initiated exclusively by reducing agents such as aqueous solutions of bisulfites or formaldehyde sulfoxylates alkali metal or. \ t their ammonium salts. This allows you to process emulsion with sufficient operational certainty a monomer mixture containing as a crosslinker highly reactive N-hydroxyalkyl derivatives acrylic or methacrylamide.

Description

The present invention relates to a process for the preparation of self-crosslinking thermoreactive acrylate copolyraeric dispersions containing acrylic or methacrylamide, methyl methacrylate, acrylic acid or its esters with alcohols of 1-8 carbon atoms per molecule and crosslinking comonomer, especially N-methylolmethacryl or acrylamide, emulsion polymer .

The self-sieving thermoreactive types of acrylate copolymer dispersions find application in a wide variety of industries, e.g. in the leather industry, as film-forming binders for the manufacture of leather surface finishes, textile, where they are used in the production of nonwovens, or furniture, for the lamination of surface materials.

The most effective crosslinking comonomers include hydroxyalkyl derivatives of acrylic and methacrylamide. However, their high reactivity, which, while increasing the performance of the dispersion as well as the use of the products, desirably, may cause technological difficulties in the preparation of the binder itself. Especially in large-scale production using a conventional redox initiation system. The emulsions of the selected comonomers prepared in the first stage of manufacture become unstable upon addition of the cross-linking component, depending on its quality, and thus unusable products can be formed under polymerization conditions. In a marginal situation, the course of the reaction may become uncontrollable. However, even with relatively reliable technologies, the final binders, especially in cases where N-methylolmethacrylamide was used in the manufacture, show poor storage stability.

Large-scale manufacturers are therefore preferable to those types which contain less reactive alkoxy derivatives of N-alkyl acrylic or methacrylamide as crosslinkers such as e.g. N-isobutoxymethylacrylic or methacrylamide. Such treatment of copolymers generally increases the operational reliability of the dispersion production, but at the same time it can negatively affect its utility properties. The resistance of the binder film to organic solvents deteriorates, which is undesirable in most application areas. The manufacturing cost of the user is increased due to the higher energy consumption, since the crosslinking of the modified binder films occurs only at temperatures of 140 ° C. Crosslinking of polymer films containing non-etherified hydroxyalkyl derivatives occurs at temperatures about 20 ° C lower.

Considerable efforts have therefore been made to increase the reliability of the more reactive binder technology. One way is to reduce the dry matter content of the final product, which is obviously uneconomical for both manufacturers and consumers of binders. British Patent No. 997,921 suggests adjusting the acidity of the emulsions prior to polymerization by partially neutralizing the carboxyl groups present. This in turn leads to undesirable effects on the dispersion's utility properties due to the possibility of a mixture of homopolymeric polycarboxylate with a copolymer which is depleted by the corresponding amount of carboxyl groups.

USSR Pat. No. 1,035,033 deals with the storage stability of the binders in question. It is proposed to carry out the polymerization in the presence of 5-15 wt. 2-ethylhexyl acrylate (based on polymer composition) or styrene. This method of conducting the polymerization, however, again entails a penetrating intervention in the binder composition with corresponding negative impacts on the application area.

PV 06855-84 eliminates the negative effect of a highly reactive crosslinking component on the operational reliability of the technology by using their aqueous solutions prepared immediately prior to being put into emulsion according to AO No. 223 435 or 234 742. However, even in this case it is not &Gt; 45 wt. and guarantee a mean particle size of the dispersion < 0.1 µm.

More recently, it has been found that to achieve the desired goal, it is possible to produce aqueous dispersions of the initially specified copolymers by polymerizing the emulsion in the absence of a peroxy compound, which otherwise forms an essential part of a commonly used redox initiation system.

As polymerization initiators, solutions of reducing agents such as disulphites, formaldehyde sulphoxylates and optionally also alkali metal sulphites or hydrogen sulphites can be used in concentrations of 0.1-0.5 and the active ingredient, based on the total weight of the monomers to be treated. The binder can thus be produced with a dry matter content of: »50 wt. while keeping the mean particle size of the dispersion at ζ0.1 yum. The storage stability of the binder prepared by the process of the invention exceeds with certainty 6 months from the date of manufacture even when N-methylolmethacrylamide was used as the crosslinking comonomer.

The proposed principle of conducting polymerization has so far been described only for the polymerization of conjugated dienes according to USP No. 2,383,055.

Example 1

250 g of methacrylamide are poured into 250 g of a 60% aqueous solution of N-methylolmethacrylamide prepared according to AO 234 742 and the resulting suspension is stirred for 60 minutes. It is then poured with stirring into an emulsion of 2360 g of ethyl acrylate and 2260 g of methyl methacrylate in 3800 ml of distilled water, to which 355 g of anionic surfactant (Disponil SUS 87) was added.

After about 20 minutes of homogenization, start the emulsion in a stirred reactor maintained under an inert nitrogen atmosphere, in which 950 ml of distilled water and another 150 g of Disponil SUS 87 were preheated to 80 ° C and a pre-dispense of 50 ml of 5% aqueous sodium metabisulphite was started. The emulsion is dosed at a rate of 3.5-4 l / h and at the same time a further portion of the bisulfite solution is introduced into the reactor at a rate of 90 ml / h.

It maintains the polymerization temperature in the range of 80-83 ° C. The total emulsion drip time is 150-180 ml. Add the initiator solution for another 10 minutes after the emulsion is dispensed. The reactor contents are then allowed to cool spontaneously over a period of 2-2.5 hours and after reaching a temperature of 35-40 ° C, the dispersion is filtered through a sieve with a mesh diameter of 0.3-0.5 mm.

We obtain 10.2-10.5 kg of mechanically stable dispersion containing 48-51 wt. dry matter, practically free of coagulate. The dynamic viscosity of the product does not exceed 100 mPa · s and the mean particle size of the dispersion is 0.1 µm.

Example 2

To 1.82 kg of technical formalin, add 55 ml of a 20% aqueous NaOH solution while stirring,

0.4 g NaNO ₂ and 1.82 kg methacrylamide. After stirring for 60 minutes, dilute the reaction mixture with 2 L of distilled water and add 4.1 kg of methacrylamide. The resulting suspension is poured after an additional 2 hours into an emulsifier containing an emulsion prepared by mixing 39 kg of ethyl acrylate and 37 kg of methyl methacrylate in 38 L of distilled water to which 5 kg of Disponil SUS 87 has been added.

The emulsion is then dispensed within 150 minutes (i.e. at a rate of 55 l / h) to a reactor in which a heated solution of 3.8 kg Disponil SUS 87 in 38 l distilled water was introduced at 80 ° C and a pre-dispense of 115% aqueous sodium metabisulphite started. . Its next proportion is dosed during polymerization at a rate of 1.5 l / h. The temperature mode of the operation and its conduction are identical to Example 1.

Yield: 172-175 kg of dispersion.

Example 3

Emulsion prepared by mixing 2,740 g of ethyl acrylate, 2,615 g of methyl methacrylate, 290 g of methacrylamide and 275 g of a 60% aqueous solution of N-methylolacrylamide in 3.75 l of distilled water to which 408 g of Disponil SUS 87 was added together with 5% aqueous solution sodium bisulfite into a reactor in which 0.9 Ί of distilled water and 175 g of Disponil SUS 87 were introduced, under the conditions specified in the example;

Yield: 11.7-11.9 kg dispersion

Example 4

Emulsion prepared by mixing 2,700 g of methyl methacrylate, 2,440 g of butyl acrylate,

105 g of acrylic acid and 55 g of methacrylamide in 3.6 l of distilled water, to which 400 g of Disponil AES 60 was added, are charged together with a 5% aqueous sodium metabisulphite solution under the conditions specified in Example 1 to a reactor in which 1 , 1 l of distilled water and 45 g of Disponil AES 60.

Yield: 10.4-10.8 kg dispersion

Example 5

The emulsion prepared by mixing 3,380 g of butyl acrylate, 548 g of methacrylamide, 548 g of acrylonitrile and 260 g of Fenopone EP 110 in 3 l of distilled water is charged together with a 7% aqueous sodium metabisulphite solution into a reactor containing 1.1 l of distilled water and 100 g of Fenopon EP 110.

Yield: 8.8-9.0 kg dispersion

Claims (1)

Process for preparing self-crosslinking thermoreactive acrylate dispersions by emulsion copolymerization of acrylic or methacrylamide, methyl methacrylate or a mixture thereof with acrylic esters containing 1-8 carbon atoms in alkyl, acrylonitrile, acrylic acid and a crosslinking comonomer such as N-methylolacryl or N-methylol characterized in that exclusively reducing agents, such as aqueous solutions of alkali metal sulfites or formaldehyde sulfoxylates or their ammonium salts, are used as polymerization initiators.