Microfine adhesive powders and process
View Patent ↗Microfine powder adhesive blends are provided. The powders are comprised of a polyolefin base resin component and acid or acid derivative functionalized polyolefin component with one or more optional components. The microfine powders are produced from melt blended adhesive products using a dispersion process and have median particle sizes from 5 to 250 micrometers.
1. A process for producing microfine adhesive blend powders comprising:
(a) combining a particulate melt blended adhesive blend composition comprised of 40 to 99 weight percent polyolefin base resin selected from the group consisting of ethylene homopolymers, propylene homopolymers, copolymers of ethylene and propylene, copolymers of ethylene and C 4-8 α-olefins and ethylene-vinyl acetate copolymers and 1 to 60 weight percent maleic anhydride grafted polyolefin selected from the group consisting of ethylene homopolymers, copolymers of ethylene and C 3-8 α-olefins, propylene homopolymers and propylene-ethylene copolymers with a nonionic surfactant and polar liquid medium containing at least 50 weight percent water;
(b) heating the mixture above the melting points of the blend components;
(c) agitating the mixture to disperse the blend in the polar liquid medium;
(d) cooling the dispersion below the melting points of the blend components; and
(e) recovering the adhesive powder blend.
2. The process of claim 1 wherein the weight ratio of polar liquid medium to melt blended adhesive composition is from 1:1 to 9:1, the nonionic surfactant is a block copolymer of ethylene oxide and propylene oxide and the weight ratio of nonionic surfactant to melt blend is from 0.05:1 to 5:1.
3. The process of claim 2 wherein the maleic anhydride grafted polyolefin is high density polyethylene grafted with from 0.3 to 4 weight percent maleic anhydride.
4. The process of claim 2 wherein the nonionic surfactant contains at least 50 percent ethylene oxide and has a molecular weight greater than 3500.
5. The process of claim 4 wherein the nonionic surfactant contains about 80 percent ethylene oxide and 20 percent propylene oxide and has a molecular weight from about 11250 to about 16250.
6. The process of claim 4 wherein the nonionic surfactant contains about 50 percent ethylene oxide and 50 percent propylene oxide and has a molecular weight of about 4500.
7. The process of claim 2 wherein the mixture is heated to 90° C. to 250° C. and the agitator tip speed is from 500 to 3,500 ft/mm.
8. The process of claim 1 wherein the melt blended adhesive composition additionally contains up to 30 weight percent elastomeric component.
9. The process of claim 1 wherein the particulate melt blended adhesive composition is pelletized.
10. A microfine adhesive blend powder produced by the process of claim 1 .
11. The microfine adhesive blend powder of claim 10 having a median particle size from 5 to 250 micrometers wherein the particles are spherical or substantially spherical.
12. The microfine adhesive blend powder of claim 11 wherein the a maleic anhydride grafted polyolefin is high density polyethylene grafted with from 0.3 to 4 weight percent maleic anhydride.