THERMALLY EXPANDABLE COMPOSITIONS

Abstract

The present invention relates to a thermally expandable composition comprising at least one peroxidically crosslinking polymer which does not contain glycidyl (meth) acrylate as a monomer in copolymerized form; at least one polymer, which is polymerized with glycidyl (meth) acrylate as a monomer present in a proportion of from 2 to 20% by weight, based on the respective polymer; at least one peroxide; and at least one endothermic chemical propellant, moldings containing this composition, and a method for sealing and filling cavities in components, for reinforcing or stiffening components, in particular hollow components, and for bonding movable components using such molded bodies.

Claims

1. A thermally expandable composition, containing a) at least one peroxidically crosslinking polymer that does not contain glycidyl (meth)acrylate as a monomer in copolymerized form, b) at least one polymer that contains glycidyl (meth)acrylate as a monomer in copolymerized form in a proportion from 2 to 20 wt % with respect to the respective polymer, c) at least one peroxide, and d) at least one endothermic chemical propellant.

2. The thermally expandable composition as set forth in claim 1, wherein the at least one peroxidically crosslinking polymer a) is selected from among ethylene vinyl acetate copolymers, functionalized ethylene vinyl acetate copolymers, functionalized ethylene butyl acrylate copolymers, ethylene propylene diene copolymers, styrene butadiene block copolymers, styrene isoprene block copolymers, ethylene methyl acrylate copolymers, ethylene ethyl acrylate copolymers, ethylene butyl acrylate copolymers, ethylene (meth)acrylic acid copolymers and mixtures thereof.

3. The thermally expandable composition as set forth in claim 2, wherein the at least one peroxidically crosslinking polymer a) is selected from among ethylene vinyl acetate copolymers and functionalized ethylene vinyl acetate copolymers.

4. The thermally expandable composition as set forth in claim 1, wherein the at least one polymer b) is a terpolymer which, in addition to the glycidyl (meth)acrylate as a unit, contains monomers selected from the group of ethylene, propylene, acrylic acid esters, styrene, vinyl acetate and combinations thereof.

5. The thermally expandable composition as set forth in claim 4, wherein the terpolymer contains acrylic acid ester monomers selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate and combinations thereof.

6. The thermally expandable composition as set forth in claim 1, wherein the proportion of glycidyl (meth)acrylate in the polymer b) is 6 to 10 wt. %, with respect to the total mass of the copolymer.

7. The thermally expandable composition as set forth in claim 1, wherein the endothermic chemical propellant is selected from among: bicarbonates; solid, optionally functionalized, polycarboxylic acids; salts of, optionally functionalized, polycarboxylic acids; and mixtures thereof.

8. The thermally expandable composition as set forth in claim 7, wherein the endothermic chemical propellant comprises a mixture of sodium hydrogen carbonate and citric acid in a ratio of sodium hydrogen carbonate to citric acid of 1:2 to 1:10.

9. The thermally expandable composition as set forth in claim 1, wherein the composition contains, with respect to the total weight of the composition, no more than 70 wt % of at least one peroxidically crosslinking polymer a) that does not contain glycidyl (meth)acrylate as a monomer in copolymerized form, and/or no more than 20 wt % of at least one polymer b) that contains glycidyl (meth)acrylate as a monomer in copolymerized form in a proportion from 2 to 20 wt % with respect to the respective polymer.

10. The thermally expandable composition as set forth in clam 1 wherein the composition contains less than 3 wt. % of ADCA (azodicarbonamide) or OBSH (4,4′-oxybis(benzenesulfonyl hydrazide)).

11. The thermally expandable composition as set forth in clam 10 containing 30-80 wt. % of a); 2 to 40 wt. % of b); at least one peroxide, and 1 to 35 wt. % of at least one endothermic chemical propellant.

12. The thermally expandable composition as set forth in clam 11 wherein the at least one polymer of b) comprises two different terpolymers selected such that each has a melt mass-flow rate in a range of 0.5 to 45 g/10 min and contains glycidyl methacrylate as a monomer in copolymerized form.

13. The thermally expandable composition as set forth in clam 12 wherein the two different terpolymers are ethylene/methyl (meth)acrylate/glycidyl methacrylate and ethylene/butyl (meth)acrylate/glycidyl methacrylate.

14. The thermally expandable composition as set forth in clam 11 wherein a) comprises at least one ethylene vinyl acetate copolymer with a vinyl acetate content of 10 to 25 wt. %, with respect to a total mass of the copolymer, selected such that the copolymer has a melt mass-flow rate in a range of 1.5 to 25 g/10 min.

15. A molded body, wherein the molded body has a thermally expandable composition as set forth in claim 1.

16. A method for sealing and/or filling cavities in components, for reinforcing and/or stiffening components, or for adhering movable components which comprises utilizing the thermally expandable composition as set forth in claim 1.

17. A method for sealing and/or filling cavities in components and/or for reinforcing and/or stiffening components comprising steps of: providing a component with the thermally expandable composition as set forth in claim 1; and then heating to a temperature above 110° C., such that the thermally expandable composition expands and seals, fills, reinforces or stiffens the component.

18. A method of using the molded body as set forth in claim 10 to acoustically seal cavities in components, to seal cavities in components against water or moisture; and/or to reinforce or stiffen components, comprising steps of: a) inserting the molded body into a cavity of a component or fixing the molded body to a component; and b) heating the molded body to a temperature above 110° C., such that the thermally expandable composition of the molded body expands and hardens thereby sealing, reinforcing and/or stiffening the cavity and/or the component.

Description

EXEMPLARY EMBODIMENTS

General Test Procedure/Production of the Formulations:

[0089] To prepare the thermally expandable preparations according to the invention, the contained polymers were processed into a homogeneous mass at room temperature in the kneader or, if necessary, under heating to up to 150° C. with fillers. The other, non-reactive components such as fillers, soot, stabilizers, and softening agents, if present, were then added one after the other and kneading was continued until the formulation was smooth.

[0090] At below 70° C., all of the reactive components such as, for example, accelerators, peroxides, activators and catalysts, zinc oxide, calcium oxide, and propellant were then added and kneaded together slowly until the adhesive was homogeneously mixed. The propellants were then used as a master batch in part.

Determination of the Expansion

[0091] To determine the expansion, test specimens having the approximate dimensions 20 mm×20 mm×3 mm were cut out of the manufactured sheets of the exemplary formulations, these were placed into a convection oven, which was heated to the temperatures named in the tables (heating-up time about 7 to 10 minutes), and the test specimens were then left at this temperature for the time period indicated in the tables (including the heating-up time). The expansion at 175° C. corresponds to the ideal conditions that are achieved during curing in automotive engineering. The expansion at 160° C. simulates underbaking conditions, and the expansion at 200° C. simulates overbaking conditions.

[0092] The extent of the expansion [%] was determined using the water displacement method according to the formula

[00001]$\mathrm{Expansion}=\frac{\left(m.Math..Math.2-m.Math..Math.1\right)}{m.Math..Math.1}\times 100$ [0093] m1=mass of the test specimen in the original state in deionized water [0094] m2=mass of the test specimen after annealing in deionized water.

Determination of Water Absorption

[0095] To determine the water absorption, test specimens having approximate dimensions 20 mm×20 mm×3 mm were prepared in a manner analogous to those for determining the expansion and expanded and hardened in the convection oven at predefined temperatures analogously to the method for determining expansion, as indicated in the tables. The test specimens expanded in this way were then conditioned for 24 hours in a standard atmosphere (23° C., 50% relative humidity); the mass m was determined immediately after conditioning.

[0096] For storage in the water bath, the test specimens were kept in a container filled with water about 5-10 cm below the water surface for 24 hours at 23° C. After removal, the test specimens were drained, superficially dried using an absorbent cloth, and weighed again mo. The test specimens were then stored again for 24 hours in a standard atmosphere (23° C., 50% relative humidity) and weighed again m.sup.24.

[0097] The water absorption [wt %] was calculated according to the following equation:

[00002]$\mathrm{Water}.Math..Math.\mathrm{absorption}=\frac{m_i-m}{m}\times 100$ [0098] m: Mass of the test specimen before storage in water in the immersion bath [0099] m.sub.i: Mass of the test specimen after storage in water in the immersion bath after time i [0100] i=0: Measurement immediately after removal [0101] i=24: Measurement after 24 hours in the standard atmosphere (23° C., 50% relative humidity)

Exemplary Formulation (EVA-Based, Peroxide-Crosslinking)

[0102]

TABLE-US-00001 Substance name/group Comparative Comparative Inventive Inventive Inventive (generic names) formulation 1 formulation 2 formulation 1 formulation 2 formulation 3 EVA polymer 1 63.45 67.2 43.7 53.7 51.70 Terpolymer 15.00 10.00 10.00 Terpolymer 2 2.00 Citric acid 17.50 15.00 20.00 17.50 17.50 NaHCO.sub.3 3.50 3.00 4.00 3.50 3.50 Talcum 5.25 4.50 6.00 5.25 5.25 EVA polymer 2 8.75 7.50 10.00 8.75 8.75 Peroxide 1 Peroxide 2 1.25 2.5 1.00 1.00 1.00 Antioxidant 0.3 0.3 0.3 0.3 0.30 Process oil Co-crosslinker TOTAL 100 100 100 100 100 Expansion 20 min, 160° C. 278 416 554 666 511 25 min, 175° C. 510 487 659 676 656 40 min, 200° C. 380 325 928 938 962 Water absorption immediately after removal in % 20 min, 160° C. 9.8 11.6 4.9 4.9 6.0 25 min, 175° C. 7.6 9.2 5.0 5.0 4.5 Water absorption after 24 hours in % 20 min, 160° C. 0.8 0.7 0.3 0.1 0.0 25 min, 175° C. 1.1 1.2 0.2 0.0 0.0

Exemplary Formulation (EVA-Based, Peroxide-Crosslinking)

[0103]

TABLE-US-00002 Substance name/group Inventive Inventive Inventive Inventive Inventive (generic names) formulation 4 formulation 5 formulation 6 formulation 7 formulation 8 EVA polymer 1 51.20 48.70 46.20 49.70 51.90 Terpolymer 10.00 10.00 10.00 9.50 10.00 Terpolymer 2 2.00 2.50 5.00 7.50 2.00 Citric acid 17.50 17.50 17.50 17.50 17.50 NaHCO.sub.3 3.50 3.50 3.50 3.50 3.50 Talcum 5.25 5.25 5.25 5.25 5.25 EVA polymer 2 8.75 8.75 8.75 8.75 8.75 Peroxide 0.20 Peroxide 1.00 1.00 1.00 1.00 0.60 Antioxidant 0.30 0.30 0.30 0.30 0.30 Process oil 1.00 Co-crosslinker 1.50 TOTAL 100 100 100 100 100 Expansion 20 min, 160° C. 529 488 497 474 527 25 min, 175° C. 668 646 634 632 667 40 min, 200° C. 981 989 945 932 990 Water absorption immediately after removal in % 20 min, 160° C. 3.6 4.7 4.1 4.1 4.8 25 min, 175° C. 3.9 2.7 5.1 4.1 4.0 Water absorption after 24 hours in % 20 min, 160° C. 0.0 0.0 0.3 0.1 0.0 25 min, 175° C. 0.0 0.0 0.0 0.4 0.0

Components Used:

[0104]

TABLE-US-00003 EVA polymer 1 EVA, 16.5-19.5% VA content, melting point 82-90° C., MFI 1.5-6 g/10 min (190° C., 2.16 kg)) Terpolymer Terpolymer (GMA/EBA), reactive ethylene terpolymer, 9 wt % Glycidyl methacrylate, 20 wt % Butyl acrylate, melting point 72° C., MFI 8 g/10 min (190° C., 2.16 kg)) Terpolymer 2 Ethylene acrylic acid ester glycidyl methacrylate terpolymer, methyl acrylate content 24 wt %, glycidyl methacrylate content 8 wt %, melting point 65° C., MFI 6 g/10 min (190° C., 2.16 kg) Master batch Citric acid Citric acid, dissociation temperature >150° C. (TGA measurement) NaHCO.sub.3 NaHCO.sub.3, dissociation temperature >120° C. (TGA measurement) Talcum Talcum EVA polymer EVA, 17-19% VA, melting point 85-89° C., MFI about 1.5-4 2 g/10 min (190° C., 2.16 kg)) Peroxide 1 Di-(2-tert.-butyl-peroxyisopropyl)-benzene, 95% peroxide, 8.98% active oxygen content, half-life temperature 1 h = 146° C., t90 = 175° C. (rheometer t90 about 12 min) Peroxide 2 2,5-dimethyl-2,5-di-(tert.-butylperoxy)-hexane, 45% peroxide, powder with chalk, 4.96% active oxygen content, half-life emperature 1 h = 147° C., t90 = 175° C. (rheometer t90 about 12 min) Antioxidant Bis[3,3-bis-(4′-hydroxy-3′-tert-butylphenyl)butanoicacid]-glycol ester, molecular weight 794 g/mol, melting point 167-171° C. Process oil Paraffin process oil, pour point 18° C., kinematic viscosity, 3000 mm.sup.2/s at 40° C. Co-crosslinker Trimethylol propane trimethacrylate, TMPTMA,

[0105] The tests according to the invention show low water absorption, particularly the examples with two terpolymers. At the same time, the results with respect to the expansion behavior were able to be improved.