EP0807704B1 - Recovery of fibres from bonded nonwovens - Google Patents

Abstract

A method for removing a polymer binder containing carboxylate groups cross-linked via alkaline earth metal ions from impregnated nonwovens comprises: (1) the nonwoven is treated with an aqueous alkali salt solution so that the alkali salt anions combine with the alkaline earth metal cations to form a poorly soluble salt or chelate; and (2) the binder-free fibres are separated. Preferably a phase transfer catalyst, preferably an alkyl phenol ethoxylate, fatty alcohol ethoxylate, oxo alcohol ethoxylate or quat. organic ammonium salt, is used in the alkali salt solution. Calcium ions are the cations present. The binder comprises a radical-polymerised polymer containing 0.1-30 wt.% carboxylate groups, of which 50-100 wt.% are present as salts containing alkaline earth metal cations. The alkali salt solution has a temperature of 10-100 degrees C. The nonwoven is added to the alkali salt solution, which is then optionally stirred before separating the fibres 1-60 minutes later.

Description

The invention relates to a method for the recovery of Nonwoven fibers. Nonwoven fabrics can be coated or impregnation with a binder.

Basically there is a desire for recyclable nonwovens, where the fibers are recovered after use can be. To do this, the binder must be solidified Nonwoven can be detached. Accordingly, according to JP 5 384 189 and the unpublished German patent application P 19 535 792.3 (0050/46241) for strengthening nonwovens uncrosslinked binders, which are obtained by transferring Carboxyl groups in carboxylate groups are soluble in water and so can be separated from the fibers.

In order to obtain nonwovens with good strength, binders are used used that crosslink after application to the nonwoven. For crosslinking, the binders can contain several monomers ethylenically unsaturated groups or monomers with other reactive Groups, e.g. Methylol groups. A networking over metal salt groups, e.g. crosslinking via Ca carboxylate groups is e.g. known from EP 442 370. It is also desirable to have fibers to be recovered from nonwovens bound with crosslinked binders.

The object of the present invention was therefore a method for Recovery of fibers from crosslinked binders or consolidated nonwovens.

• die Faservliese mit einem Polymerbindemittel mit Carboxylatgruppen gebunden sind, wobei die Carboxylatgruppen über Erdalkalikationen vernetzt sind
• die Faservliese mit einer wäßrigen Lösung eines Alkalisalzes behandelt werden, wobei das Anion des Alkalisalzes mit den Erdalkalikationen ein schwerlösliches Salz oder Komplex bildet und anschließend
• die vom Bindemittel befreiten Fasern abgetrennt werden.

The object was achieved by a method for detaching binders from nonwoven fabrics bound with these binders, characterized in that

• the nonwoven fabrics are bound with a polymer binder with carboxylate groups, the carboxylate groups being crosslinked via alkaline earth metal cations
• the nonwoven fabrics are treated with an aqueous solution of an alkali salt, the anion of the alkali salt forming a poorly soluble salt or complex with the alkaline earth metal cations and then
• the fibers freed from the binder are separated.

For the method according to the invention, nonwovens can be made from the most varied Fibers are used.

For example, synthetic fibers such as viscose, polyester, Polyamide, polypropylene, polyacrylonitrile, carbon fibers or fibers of homo- and copolymers of vinyl chloride or Tetrafluoroethylene or fibers of natural origin such as Cellulose, cellulose, cellulose, cotton or wood fibers or also glass, ceramic, or mineral fibers or mixtures of this.

The fibers are folded into non-woven fabrics and then with solidified a binder, for which purpose the binder in known Way e.g. by impregnation, spraying, cracking, dipping or printing on the fibers. Then follows generally drying to remove the solvent, in general water. In this way, known to those skilled in the art a bound, i.e. get consolidated nonwoven.

The nonwoven fabrics thus produced find e.g. Application as Base materials for roofing membranes or floor coverings. As a binder are generally used polymers, which build up from ethylenically unsaturated monomers.

The polymers contain carboxylate groups which are alkaline earth metal are networked, i.e. they are cross-linked with metal salts.

The polymers preferably contain 0.1 to 30% by weight, particularly preferably 0.5 to 25% by weight and very particularly preferably 5 to 20 % By weight of carboxylate groups, based on the weight of the polymer (weight of alkaline earth cations not included).

The carboxylate groups are preferably 50 to 100, especially preferably 80 to 100% as a salt with alkaline earth metal ions.

Preferred alkaline earth metal cations are Ca ²⁺ and Ba ²⁺ , Mg ²⁺ . Ca ²⁺ is particularly preferred.

The metal salt crosslinked polymers are e.g. based on polymers available with carboxylic acid or carboxylic anhydride groups by adding an alkaline earth salt, e.g. an oxide, hydroxide, Carbonates or bicarbonates e.g. for aqueous dispersion or solution of the polymer as described in EP-A-442 370 is.

The metal salt crosslinked polymer is preferably from the following Monomers A), B) and C) built up:

Monomers A)

Monomers A) are monomers with at least one carboxylic acid or Carboxylic anhydride group, which converts to the metal salt groups can be. Particularly noteworthy are acrylic acid, Methacrylic acid, itaconic acid, maleic acid, maleic anhydride.

The amount of these monomers is determined by the desired one Content of carboxylate groups cross-linked with alkaline earth metal cations.

Monomers B)

Main monomers B) selected from C ₁ -C ₂₀ alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides are of particular technical importance. Vinyl ethers of alcohols containing 1 to 10 carbon atoms, aliphatic hydrocarbons with 2 to 8 carbon atoms and 1 or 2 double bonds or mixtures of these monomers.

Examples include (meth) acrylic acid alkyl esters with a C ₁ -C ₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

In particular, mixtures of the (meth) acrylic acid alkyl esters suitable.

Vinyl esters of carboxylic acids with 1 to 20 C atoms are e.g. Vinyl laurate, stearate, vinyl propionate, vinyl versatic acid and vinyl acetate.

Suitable vinyl aromatic compounds are vinyl toluene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of nitriles are Acrylonitrile and methacrylonitrile.

The vinyl halides are substituted with chlorine, fluorine or bromine ethylenically unsaturated compounds, preferably vinyl chloride and Vinylidene chloride.

Examples of vinyl ethers include Vinyl methyl ether or vinyl isobutyl ether. Vinyl ether of 1 to 4 carbon atoms is preferred containing alcohols.

As hydrocarbons with 2 to 8 carbon atoms and two olefinic Double bonds are butadiene, isoprene and chloroprene.

Monomers C)

In addition to these main monomers, other monomers C), for example monomers containing hydroxyl groups, in particular C ₁ -C ₁₀ -hydroxyalkyl (meth) acrylates or (meth) acrylamide, can be used in the polymer.

Customary polymers generally consist of at least 40, preferably at least 60, particularly preferably at least 80% by weight of the above main monomers B).

The polymerization can be carried out by customary polymerization processes take place, e.g. by substance, emulsion, suspension, Dispersion, precipitation and solution polymerization. With the above Polymerization is preferred to exclude worked by oxygen, preferably in a stream of nitrogen. The usual equipment for all polymerization methods used, e.g. Stirred tanks, stirred tank cascades, autoclaves, tubular reactors and kneader. Preference is given to the Solution, emulsion, precipitation or suspension polymerization worked. The methods of solution are particularly preferred and especially emulsion polymerization. The polymerization can in solvents or diluents, e.g. Toluene, o-xylene, p-xylene, Cumene, chlorobenzene, ethylbenzene, technical mixtures of alkyl aromatics, cyclohexane, technical aliphatic mixtures, Acetone, cyclohexanone, tetrahydrofuran, dioxane, glycols and glycol derivatives, Polyalkylene glycols and their derivatives, diethyl ether, tert-butyl methyl ether, methyl acetate, isopropanol, Ethanol, water or mixtures such as Isopropanol / water mixtures be carried out. Preferably, as Solvent or diluent water, if necessary, with proportions up to 60 wt .-% of alcohols or glycols used. Especially water is preferably used.

The metal-crosslinked polymers are generally in the form their aqueous solution or dispersion applied to the nonwovens. After drying, the nonwovens are bound, i.e. solidified. The non-woven fabrics then generally contain 1 to 40 parts by weight, preferably 5 to 30 parts by weight, of the metal-crosslinked Binder, based on 100 parts by weight of fibers.

After the later use of the bonded non-woven fabrics can the fibers are recovered according to the method of the invention by removing the binder from the nonwoven, i.e. of the Fibers is separated.

For this, the nonwoven fabric is washed with an aqueous solution of a salt, (hereinafter referred to as "soluble salt), whose anion with the Alkaline earth formation forms a salt that is sparingly soluble in water.

The soluble salt can be inorganic or organic Trade salt.

In particular, it is an alkali metal salt.

The anion of the soluble salt can e.g. around oxalate or carbonate, which e.g. with the calcium cation form sparingly soluble salt.

The anion of the soluble salt can also be, for example, an organic anion which forms a poorly soluble complex with the alkaline earth metal, for example Ca ²⁺ . EDTA is particularly worth mentioning here.

The soluble salt contained in the aqueous solution has preferably a solubility of at least 10 g / l water 23 ° C.

The aqueous solution preferably contains the salt in amounts of 0.02 to 15 parts by weight, particularly preferably in amounts of 0.1 to 10 parts by weight, very particularly preferably from 0.5 to 2.5 parts by weight, based on 100 parts by weight of water.

The solubility of the formed during treatment of the nonwoven sparingly soluble alkaline earth metal salt, however, is preferably smaller than 0.5 g / l water at 23 ° C.

In addition to the soluble salt, the aqueous solution preferably contains another phase transfer catalyst.

Suitable phase transfer catalysts are e.g. in Chimia 34 (1980) No. 1, pages 12 to 20. As phase transfer catalysts may be mentioned e.g. Polyalkylene glycols which e.g. is commercially available under the name Pluriol® or quaternary, organic Ammonium salts, e.g. commercially available under the name Lutensit are.

genannt, worin R¹-R⁴ unabhängig voneinander für einen organischen Rest, bevorzugt einen Kohlenwasserstoffrest mit 1 bis 12 C-Atomen, bevorzugt 1 bis 6 C-Atomen stehen und X^⊖ für ein Anion, bevorzugt ein anorganisches Anion z.B. Cl^-, Br^⊖ steht.Quaternary organic ammonium salts include, in particular, those of the formula I.

mentioned, wherein R ¹ -R ⁴ independently of one another are an organic radical, preferably a hydrocarbon radical having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms and X ^{⊖ is} an anion, preferably an inorganic anion, for example Cl ^- , Br ^⊖ stands.

Particularly preferred phase transfer catalysts are those with Alkoxy groups, preferably with 2 to 20 alkoxy groups, e.g. Alkylphenol ethoxylates (e.g. Lutensole® AP, emulsifier 825 fatty alcohol ethoxylates (e.g. Lutensol A8) and oxo alcohol ethoxylates (e.g. Lutensol AO7, Lutensol ON80).

By alkoxylation of alkylphenols, fatty alcohols or Contain oxo alcohols with alkylene oxides, preferably ethylene oxide these phase transfer catalysts alkoxy groups.

The content of the phase transfer catalyst in the aqueous solution is preferably 0.01 to 1 part by weight, particularly preferably 0.08 to 0.5 part by weight, based on 100 parts by weight of water.

In addition, e.g. still bases, especially Sodium hydroxide solution is added to the proportion of alkali cations to increase.

The temperature of the aqueous solution can e.g. 10 to 100 ° C, in particular 15 to 80 ° C and particularly preferably 20 to 50 ° C. Temperatures above 30, in particular above, are advantageous 40 ° C, for an even better and, above all, faster replacement of the To reach binder from the nonwoven.

The nonwoven fabric can be used as a whole or in shredded form method according to the invention are supplied.

The nonwoven fabric is preferably divided into parts with an edge length of Crushed 1 to 10 cm.

For treatment with the aqueous solution, the nonwoven fabric is preferred added to the aqueous solution. The amount of nonwoven is preferably 1 to 200 g, particularly preferably 5 up to 150 g and very particularly preferably 10 to 80 g per liter Solution. The duration of treatment can be shortened by intensive stirring become. Generally, the time required is 5 minutes up to 1 hour. With strong stirring, however, are less sufficient than 30 minutes, in particular less than 20 minutes to detach at least 80% by weight of the binder from the fiber and recover the fibers.

Examples

Polyester spunbonded fabrics from Hoechst, Bobingen, were impregnated with Acronal® DS 2324x (binder application of 20% by weight ± 2 (solid / solid). Acronal DS 2324X is an aqueous dispersion of a metal salt-crosslinked polymer (crosslinking of the carboxylate groups of the polymer with Ca ²⁺ cations) on an acrylate basis, the drying was carried out at 5 minutes at 200 ° C. in a Mathis laboratory dryer, after which the approximately A-4 sized fleece sheets were cut into pieces of about 1 cm ² .

A cold saturated sodium oxalate solution (approx. 3% by weight) and in each case a 10% by weight solution of soda or Na ₄ EDTA (Trilon B) in water were prepared. In each 250 g of the solution obtained, the amounts of the phase transfer catalyst indicated in the table and optionally sodium hydroxide solution were added.

For the recovery of binder-free fibers from the nonwovens pieces of the shredded nonwoven (see above) were in Given 250 g of the solution. The temperature of the solution and the amount of the nonwoven is shown in the table.

The fleece pieces were cleaned after about 24 hours using a laboratory stirrer Stirred at 2000 rpm for 15 min.

The fibers were then filtered through a 60 μ sieve, 2 h dried at 130 ° C and weighed.

The degree of recycling R given in the table is calculated in accordance with R = Nonwoven before recycling in g - weighed fibers in g Binder content in the nonwoven before recycling in g 100%

In the event that the weighed fibers are completely free of binders, the degree of recycling is 100%. Values above 100% in the table can be explained by the fact that when the fibers were filtered off, very fine fibers were possibly not retained by the sieve and the weight of the fibers after recycling was too low.

Claims (7)

1. A process for dissolving a binder off a fiber web bonded therewith, which comprises

   treating the fiber web, which is bonded with a polymeric binder having carboxylate groups crosslinked via alkaline earth metal cations, with an aqueous solution of an alkali metal salt to form a sparingly soluble salt or complex between the anion of the alkali metal salt and the alkaline earth metal cations, and then

   removing the fiber freed of the binder.
2. A process as claimed in claim 1, wherein the aqueous solution further comprises a phase transfer catalyst.
3. A process as claimed in claim 1 or 2, wherein the phase transfer catalyst is selected from the group consisting of the alkylphenol ethoxylates, fatty alcohol ethoxylates, oxo alcohol ethoxylates and quaternary organic ammonium salts.
4. A process as claimed in any of claims 1 to 3, wherein the alkaline earth metal cations are Ca²⁺.
5. A process as claimed in any of claims 1 to 4, wherein the polymeric binder bonding the fiber web is a free-radically polymerized polymer having a carboxylate group content of from 0.1 to 30% by weight, based on the polymer, and from 50 to 100% by weight of the carboxylate groups are present as a salt with an alkaline earth metal cation.
6. A process as claimed in any of claims 1 to 5, wherein the aqueous solution of the alkali metal salt has a temperature of from 10 to 100°C.
7. A process as claimed in any of claims 1 to 6, wherein the fiber web is introduced into the aqueous solution of the alkali metal salt, the aqueous solution is stirred if necessary, and the fiber freed of the binder is separated off after from 1 to 60 minutes.