EP0084810A2 - Process for strengthening fibre products with aqueous plastics dispersions - Google Patents

Abstract

For the consolidation of fiber structures, formaldehyde- and acrylonitrile-free acrylic resin dispersions are applied, the resin component of which consists of at least 40% by weight alkyl acrylates or / and methacrylates with at least 4 C atoms in the alkyl radical, optionally up to 57% by weight alkyl acrylates or methacrylates with a maximum of 3 carbon atoms in the alkyl radical or styrene, less than 1% by weight of acrylic or methacrylic acid and 3 to 15% by weight of hydroxyalkyl esters of unsaturated carboxylic acids and optionally other monoethylenically unsaturated monomers. The solidified fiber structures are characterized by low binder cooking losses and high wet strength.

Description

Field of the Invention

The invention relates to the solidification of fiber structures by applying aqueous acrylic resin dispersions which are free of formaldehyde and acrylonitrile and of formaldehyde-releasing substances. The invention further relates to the fiber structures solidified with these dispersions.

Aqueous acrylic resin dispersions whose plastic content contained self-crosslinking amide methylol groups and optionally nitrile groups have hitherto been used to solidify fiber structures which are notable for wet strength, water and wash liquor resistance and low water absorption. When the treated fiber material dries, small amounts of formaldehyde or acrylonitrile could be released, whereas health concerns have recently arisen. We are therefore looking for ways to solidify fiber structures with acrylic resin dispersions that do not give off acrylonitrile or formaldehyde when heated, but that achieve comparable performance properties as the previously used dispersions.

State of the art

Solidified fiber structures are described in EP A 12 032 and 12 033, for the production of which formaldehyde-free and acrylonitrile-free acrylic resin dispersions have been used. If the fiber structure is predominantly composed of hydrophilic fibers, in particular cellulosic fibers, an acrylic resin dispersion is used, the plastic content of which is predominantly composed of C ₄ -C ₈ -alkyl esters of acrylic or methacrylic acid, furthermore of methyl methacrylate or styrene and 0.5-10% is built up from an unsaturated dicarboxylic acid or a mixture thereof with an unsaturated monocarboxylic acid. In addition, up to 10% by weight of amides or hydroxyalkyl esters of acrylic or methacrylic acid in acrylic or methacrylic acid can be involved in the synthesis of the plastic portion, but these comonomers are not believed to have any influence on the performance properties of the dispersion. For the consolidation of fiber structures, which consist predominantly of hydrophobic fibers, very similar dispersions are proposed, in whose structure unsaturated monocarboxylic acids can also be involved as a component containing carboxyl groups. The minimum content of unsaturated carboxylic acids is 1% by weight, however 2-4% by weight is preferred. The wash resistance of the fiber structures finished with these dispersions is unsatisfactory. This may be due to the content of acid groups, but these groups are essential in order to achieve a satisfactory wet adhesion or wet strength in the absence of crosslinking comonomers, such as n-methylolacrylamide.

Task and solution

In the consolidation of fiber structures by applying aqueous, acrylonitrile and formaldehyde-free acrylic resin dispersions, products with reduced water absorption, good wet adhesion or wet strength and low binder loss in the case of hot laundry and alkali treatment are to be obtained. The object is achieved by the solidified fiber structures and the process for their production in accordance with the patent claims.

Industrial applicability

For the purposes of the invention, fiber structures made from hydrophilic or hydrophobic fibers or from mixtures of such fibers can be solidified. Preference is given to the consolidation of fiber structures composed predominantly of hydrophobic fibers. The most important types of fibers include polyester, polyamide and polypropylene fibers. Polyester fibers are preferred. In addition to wool and silk, the hydrophilic fibers include, above all, native or regenerated cellulosic fibers such as cotton, rayon and rayon. An interesting field of application of the invention is the consolidation of mineral fiber structures.

Among the fiber structures to be consolidated, nonwovens occupy the most important position. The solidification according to the invention gives you the strength required for the application. When strengthening fabrics, knitted fabrics or knitted fabrics, the focus is on improving the sliding resistance or knot strength.

The beneficial effects

are illustrated below on consolidated polyester fiber nonwovens with a basis weight of 18 g / m ² and a binder layer of 14-16%.

It must be described as surprising that with a reduction in the proportion of the unsaturated carboxylic acid a high wet strength, low water absorption and, above all, a substantial reduction in the loss of binder in the hot wash could be achieved by incorporating hydroxyalkyl esters in the acrylic resin. The hydroxyalkyl esters of the unsaturated carboxylic acids are extremely hydrophilic and mostly result in water-soluble homopolymers. The same also applies to the amides of acrylic or methacrylic acid. While the latter, as expected, significantly reduce the resistance to hot washing of the solidified fiber structures if they are involved in the construction of the acrylic resin, the hydroxyesters mentioned surprisingly have the opposite effect. However, this only applies if the acrylic resin contains very little or no carboxyl groups.

The fiber structures solidified according to the invention are notable for a particularly low loss of strength in the wet state compared to the dry state. The level of dry strength values can be adjusted in a known manner by controlling the film hardness according to the requirements. The aim of maintaining this level of strength largely in the wet state is achieved by the invention in a satisfactory manner.

Structure of the acrylic resin dispersion

In order for them to be sufficiently wash-resistant even without crosslinking, the acrylic resins must be relatively hydrophobic. For this reason, they contain as component A at least 40% by weight of units of alkyl esters of acrylic or / and methacrylic acid with at least 4 carbon atoms in the alkyl radical. Alkyl radicals with 4 to 8 carbon atoms are preferred. The n-butyl esters are particularly preferred. The proportion of this hydrophobic ester component is preferably 50 to 80% by weight of the acrylic resin.

Depending on the intended purpose of the solidified fiber structure, the acrylic resin can be soft and self-adhesive to hard and non-tacky. These properties are determined in a manner known per se by coordinating the quantitative ratio between hardening and softening monomer components. Since the hydrophobic higher alkyl esters of component A are mostly plasticizing at the same time, alkyl esters of acrylic and / or methacrylic acid with a maximum of 3 carbon atoms in the alkyl radical and / or styrene may be involved in the formation of the acrylic resins in order to set a greater hardness than component B. The hardness of the acrylic resin can also be increased by increasing the proportion of methacrylic acid esters in component A at the expense of the proportion of acrylic acid esters.

It is not necessary for the acrylic resin to contain carboxyl groups for reasons of the application properties of the consolidated fiber structures. Because of the improved Stability of the aqueous dispersion can, however, be advantageous if acrylic or methacrylic acid is involved in the build-up of the acrylic resin as component C in an amount of at least 0.1% by weight. If the proportion of acrylic or methacrylic acid is increased by more than 1%, the resistance to hot water in the solidified fiber structures decreases considerably. The proportion of these acids should therefore be less than 1.%, preferably not more than 0.5% by weight.

Hydroxyalkyl esters of α, β-unsaturated polymerizable mono- or dicarboxylic acids form an essential component (D) of the emulsion polymer. The hydroxyalkyl esters are preferably derived from acrylic or methacrylic acid, in particular from the former. As a rule, they contain a hydroxyl group which is bonded to an alkyl radical with 2 to 4 carbon atoms. Hydroxyethyl acrylate and methacrylate, 2-hydroxypropyl acrylate and methacrylate and 4-hydroxybutyl acrylate and methacrylate are preferred. The acrylic resin preferably contains 4 or more% by weight of units of these hydroxyalkyl esters. Shares above 10% by weight generally no longer have any advantages, so that this limit is preferably not exceeded.

Other monoethylenically unsaturated comonomers other than components A to D can optionally be involved in the construction of the acrylic resin. Polyunsaturated, crosslinking monomers should not be involved. Such monomers, e.g. Ethylene glycol dimethacrylate are occasionally contained as an impurity in the hydroxyalkyl esters to be used as component D. The content of such polyunsaturated monomers should not exceed 0.1% by weight of the acrylic resin.

Since no formaldehyde is to be released when the fiber structures equipped with the acrylic resin dispersion are dried, no monomers which contain formaldehyde in a capped, cleavable form may be involved in the construction of the acrylic resin. These include, above all, N-methylolamides of unsaturated polymerizable carboxylic acids and derivatives thereof which can be converted into the N-methylolamides mentioned by hydrolysis. These are e.g. the corresponding N-methylol alkyl ethers or Marmich bases. Likewise, the dispersions should not contain any formaldehyde condensation resins. Acrylonitrile and methacrylonitrile are also preferably not involved in the build-up of the acrylic resins, because residues of these monomers remain in the aqueous phase and could be released when the finished fiber structure dries. Examples of comonomers which can be involved in the construction of the acrylic resins as component E are vinyl esters, in particular vinyl acetate, vinyl chloride, vinylidene chloride, N-vinylpyrrolidone, and butadiene, ethylene or propylene. Their proportion is usually less than 20% by weight. If amides of acrylic or methacrylic acid are involved in the structure of the polymer, their proportion in the polymer should be less than 4% by weight.

The acrylic resin dispersions can be prepared by all common methods of emulsion polymerization. They can contain anionic, cationic or nonionic emulsifiers or compatible mixtures thereof. They are expediently produced with solids contents of 50 to 70% by weight.

Solidification of fiber structures

The preparation of the dispersion for the consolidation of fiber structures depends on the application process and the requirements placed on the end product. The additives used in these processes, such as wetting agents, foam suppressants, thermosensitizers, plasticizers and smoothing agents, antistatic agents, antimicrobiotics, dyes, fillers, flame retardants, fragrances, etc., can also be used. In general, the dispersions are diluted with water to a binder content of 10 to 40% by weight. The viscosity of the diluted dispersion can range from 10 to 10,000 mPa.s. An approximately 15 to 25% liquor is sprayed on to consolidate wadding, for example made of polyester, polyamide or polyacrylonitrile fibers. Compact nonwovens and needle felts can be solidified well by impregnation with 10 to 40% liquors and subsequent squeezing and drying. Light fiber fleeces can also be consolidated by foam impregnation; To do this, add Schäimsnittel and foam stabilizers to the approximately 10 to 25% dispersion and foam with air up to a liter weight of 100 to 300 g. The impregnation is expediently carried out on the horizontal foulard. Very light non-woven fabrics can be partially solidified by printing with pastes that contain 20 to 40% binder and are adjusted to a viscosity of 4000 to 8000 mPa.s. Needle felts for high-quality floor and wall coverings are preferably splashed with thickened, possibly foamed liquors. Finally, nonwoven bonding is also possible by brushing.

The solidified fiber structures generally contain between 5 and 100%, based on the fiber weight, of binder. The preferred binder content is between 10 and 30% by weight. The fiber structures equipped according to the invention obtain their favorable application-technical properties only by drying at dryer temperatures above 110 ° to about 200 °, preferably in the range between 120 and 160 ° C.

If additional resistance of the solidified fiber structure to organic solvents is required, a crosslinking agent, for example glyoxal, can be added to the dispersion.

Examples A) Production of the plastic dispersions

In a 1 liter round-bottom flask equipped with a stirrer and contact thermometer, 155 parts of completely demineralized water were heated to 80 ° C. with stirring and 0.16 part of a 90% sulfonated ethoxylated alkyl-arylol-maleic acid, dissolved in 5 parts of a monomer, namely at

Examples 1,2,4 to 8 butyl methacrylate

Examples 3 and 1.2 butyl acrylate

Examples up to 11 ethyl acrylate

and mixed with 5 parts of a 4% ammonium peroxodisulfate solution. Then after a pause of 4 minutes within 4 hours at 80 ° C an emulsion of

240 parts of deionized water

1 "of the emulsifier mentioned above

0.9 "ammonium peroxodisulfate

395 "of a monomer mixture according to the attached table

dripped. The temperature was then kept at 80 ° C. for a further 2 hours. The mixture was then cooled to room temperature and the pH was adjusted to 2.2 using phosphoric acid. Stable, coagulate-free dispersions were obtained.

B) Solidification of fiber structures and application test

Polyester fabric that has been removed from any existing conditions (sizing, finishing agents) is impregnated with the approx. 50% plastic dispersion, and excess dispersion is squeezed off to a liquor absorption of 80-100% using a padder. The fabric strip is dried in a forced-air drying cabinet at 80 ° C. for 5 minutes, after cooling the resin layer is determined. The sample piece of 18 x 18 ca in 125 ml of a solution containing 3 g of Marseille soap and 2 g of calcined soda per liter is then washed in a laboratory washing machine (Linitest® device) at 40 ° C. for 10 minutes. After rinsing in hot and then in cold water, drying is carried out at 90 ° C. for 30 minutes, and the resin coating is determined again after cooling. The binder cooking wash loss (BKV) is given in the table in part C as a percentage of the resin coating.

To determine the breaking resistance, thermally pre-consolidated polyester fleece with a basis weight of approx. 18 g per m ^{2 is} impregnated with the plastic dispersion diluted to approx. 25% dry substance, excess dispersion is squeezed out with the padding so that a resin coating of approx. 15% is achieved. The damp fleece is dried in the stenter at 140 ° C for 5 minutes. The breaking resistance is determined according to DIN 53 857, Part 2 on dry fleece (F) and on wet fleece (F _n ) after a 1-hour water storage using a tensile testing machine that corresponds to DIN 51 221. The results are shown in the table in part C.

C) Tabular overview of the polymer compositions and the results of the application test

Examples 1 to 8 illustrate the invention. Examples 9 to 12 are comparative experiments with dispersions which are not based on the teaching of the invention.

Claims (4)

1. Process for solidifying a fiber structure by applying an aqueous acrylic resin dispersion, the resin component of A) at least 40% by weight of alkyl esters of acrylic and / or methacrylic acid with at least 4 C atoms in the alkyl radical, B) optionally up to 57% by weight of alkyl esters of acrylic or / and methacrylic acid with a maximum of 3 carbon atoms in the alkyl radical or / and styrene, C) optionally acrylic and / or methacrylic acid D) Hydroxyalkyl esters of a, β-unsaturated polymerizable carboxylic acids E) optionally further monoethylenically unsaturated comonomers which differ from A to D and which contain no amide-ethiol groups or derivatives thereof and no carboxyl groups,
is built up, and drying the treated fiber structure at an ambient temperature above 110 ° C.,
characterized,
that the proportion C of acrylic or methacrylic acid units makes up less than 1% by weight and the proportion D of the hydroxyalkyl esters makes up 3 to 15% by weight of the acrylic resin. 2. Solidified fiber structures containing an emulsion polymer as a binder A) at least 40% by weight of alkyl esters of acrylic or / and methacrylic acid with at least 4 C atoms in the alkyl radical, B) optionally up to 57% by weight of alkyl esters of acrylic or / and methacrylic acid with a maximum of 3 carbon atoms in the alkyl radical or / and styrene, C) optionally acrylic or methacrylic acid D) Hydroxyalkyl esters of a, β-unsaturated polymerizable carboxylic acids E) optionally further monoethylenically unsaturated comonomers which differ from A to D and which contain no amide methylol groups or derivatives thereof and no carboxyl groups,
, characterized in that the proportion C of acrylic or methacrylic acid units makes up less than 1% by weight and the proportion D of the hydroxyalkyl esters makes up 3 to 15% by weight of the acrylic resin. 3. Solidified fiber structure according to claim 2, characterized in that the fiber portion consists predominantly of polyester fibers. 4. Solidified fiber structure according to claims 2 or 3, characterized in that the fiber structure is a non-woven fleece.