Method for coagulating polymer dispersions using expandable microspheres

Abstract

Method for coagulating an aqueous polymer dispersion, where the aqueous polymer dispersion comprises at least one polymer in dispersion in aqueous phase, and also comprises thermally expandable, thermoplastic microspheres, the polymer dispersion is coagulated by energy input, and the coagulated composition is delivered via an outlet aperture, preferably in the form of a nozzle.

Claims

1. A method for coagulating an aqueous polymer dispersion, the method comprising: coagulating the aqueous polymer dispersion comprising thermally expandable, thermoplastic microspheres and a polymer in dispersion in an aqueous phase by energy input, thereby obtaining a coagulated composition, wherein the coagulation takes place thermally by heating or the coagulation takes place thermally by heating and simultaneously by shearing; and delivering the coagulated composition via an outlet aperture.

2. The method of claim 1, wherein the energy for said coagulating is input thermally.

3. The method of claim 1, wherein the polymer in dispersion is an emulsion polymer or a polyurethane.

4. The method of claim 1, wherein the polymer in dispersion comprises more than 40 wt % of C.sub.1-C.sub.20 alkyl (meth)acrylates.

5. The method of claim 1, wherein the polymer in dispersion has a glass transition temperature of less than or equal to 0 C.

6. The method of claim 1, wherein the aqueous polymer dispersion is an adhesive.

7. The method of claim 1, wherein the aqueous polymer dispersion comprises a tackifier.

8. The method of claim 1, wherein an amount of the polymer in dispersion in the aqueous polymer dispersion is from 20 to 75 wt %, and an amount of the microspheres in the aqueous polymer dispersion is from 0.1 to 20 wt %.

9. The method of claim 1, wherein the microspheres have a shell of a thermoplastic polymer with a blowing agent enclosed therein, and the microspheres in the unexpanded state have a particle size with a volume median D(0.5) of from 5 to 40 m.

10. The method of claim 9, wherein the shell of the microspheres is formed from a copolymer of ethylenically unsaturated monomers comprising at least one monomer selected from the group consisting of a (meth)acrylic ester monomer, a vinylidene halide monomer, acrylonitrile, and a vinyl ether monomer.

11. The method of claim 9, wherein the shell of the microspheres is formed from a copolymer of monomers comprising alkyl (meth)acrylate, vinylidene chloride, and acrylonitrile, or of monomers comprising a vinyl ether monomer and acrylonitrile.

12. The method of claim 1, wherein the microspheres have an expansion start temperature T.sub.start of from 40 to 140 C. and a maximum expansion temperature T.sub.max which is higher than T.sub.start and is from 80 to 200 C.

13. The method of claim 2, wherein said coagulating takes place thermally by heating to a temperature of from 50 to 150 C., or said coagulating takes place thermally by heating to a temperature of from 50 to 150 C. and simultaneously by shearing with a shear rate of from 100 to 500 000 1/s.

14. The method of claim 1, wherein the coagulated composition is applied to at least one substrate.

15. The method of claim 14, wherein the aqueous polymer dispersion is an adhesive dispersion which is applied in a coagulated form to at least one substrate selected from the group consisting of paper, board, and card.

16. The method of claim 14, wherein the aqueous polymer dispersion is an adhesive dispersion which is applied in a coagulated form to a sealable region of a cardboard pack and the cardboard pack is sealed via the adhesive dispersion.

17. The method of claim 8, wherein a total solids content of the aqueous polymer dispersion is from 30 to 80 wt %.

18. The method of claim 1, wherein the energy for said coagulating is input thermally and by shearing.

Description

EXAMPLES

Ingredients

(1) PD 1: Aqueous dispersion of an acrylic ester copolymer, prepared by two-stage emulsion polymerization, with polymerization first of 80 parts by weight of a monomer emulsion 1 and then of 20 parts by weight of a monomer emulsion 2. Monomer emulsion 1: consisting of 90 parts by weight n-butyl acrylate, 2 parts by weight hydroxypropyl acrylate, 6.4 parts by weight methyl methacrylate, and 1.6 parts by weight acrylic acid Monomer emulsion 2: consisting of 86.5 parts by weight n-butyl acrylate, 2 parts by weight hydroxypropyl acrylate, 3.6 parts by weight glycidyl methacrylate, 6.3 parts by weight methyl methacrylate, and 1.6 parts by weight acrylic acid Solids content=61.9%, Tg=35 C. Polymer 1: acResin 3500; carboxyl-containing poly(n-butyl acrylate), K value about 11-16, solids content=100% Expancel 031 DU 40 dry, unexpanded, expandable microspheres, particle size D(0.5) 10-16 m; Tstart 80-95 C.; Tmax 120-135 C.

(2) Mixtures are prepared from the aqueous polymer dispersions and the expandable microparticles. The mixtures are subjected to simultaneous heating and shearing by being passed through a heatable capillary. Heating is to a maximum of 120 C. The capillary has a diameter of 1 mm and a length of 175 mm. The shear rate is 150 1/s.

(3) The dispersion undergoes coagulation, as is evident from the formation of an extrudable strand. Particularly advantageous is the formation of a strand (in linear bead form) which, in spite of the residual water that remains, develops not only adhesion to paper and card but also an inner cohesion, thereby counteracting the restorative forces during carton sealing.

(4) Adhesive bonding test: with strand delivery, application takes place to a test paper, against which a further piece of paper is pressed at about 10 N/cm.sup.2. After about 3-5 seconds, the bond is parted. If adhesion is good and the inner cohesion is developed rapidly, tearing of the paper is observed.

(5) The results are summarized in the table below.

(6) TABLE-US-00001 TABLE 1 Test results of polymer dispersions Temperature at Example Composition the capillary Result 1 PD1 117 C. no coagulation (comparative) 0 wt % no strand formed microspheres 2 PD1 104 C. coagulation, strand 1 wt % formed, some microspheres tearing into paper 3 PD1 91 C. coagulation, strand 1 wt % formed, tearing microspheres into paper 10 wt % polymer 1

(7) The results show that inventive examples 2 and 3 allow strand delivery and also that the strand produced is able to develop bond strength, thereby enabling the bonding of paper. In contrast, noninventive example 1 does not coagulate and does not produce a strand.