Melt in place binders for binding particulate fillers to substrates
View Patent ↗The invention relates to the use of a melt-in-place acrylic binder that is applied to a substrate in the form of a powder, followed by a fusing together of the binder powder by heat or radiation. Particulate filler is present either on the substrate, mixed with the binder powder, or admixed into the binder powder prior to fusion. The fused binder helps adhere the particulate fillers to the substrate, and may or may not cover the particulate filler.
1. A process for forming a melt-in-place acrylic coating on a substrate comprising:
a. forming a powder/particulate blend fused composition comprising admixing:
1) 1-50 weight percent of thermoplastic acrylic polymer powder particles, wherein said acrylic polymer is a homopolymer or copolymer comprising 30 to 100 weight percent of methylmethacrylate monomer units, has a weight average molecular weight of from 40,000 to 200,000 g/mol, and has an average particle size of from 1 to 1000 microns; and
2) 50 to 99 weight percent of particulate filler, wherein said particulate filler is a material in the form of separate particles or divided fragments selected from the group consisting of pellets, beads, powders, granules and chips;
b. fusing the acrylic powder particles to the particulate filler to form a fused acrylic polymer powder- particulate filler composite;
c. placing said fused acrylic polymer powder- particulate filler composite onto the substrate;
d. melting said acrylic polymer powder of the fused acrylic polymer-particulate filler composite above the Tg of the acrylic polymer for a predetermined time to allow the acrylic polymer powder to melt and flow into a continuous, non- continuous or semi-continuous coating, wherein said acrylic polymer powder has a Tg of from 40 to 100° C.; and
e. cooling the substrate, acrylic polymer coating and particulate filler below the Tg of the acrylic polymer, to fuse the acrylic polymer powder and form a coated substrate.
2. The process of claim 1 , wherein said acrylic polymer powder particles are spherical.
3. The process of claim 1 , wherein said acrylic polymer powder particles are granular and irregular.
4. The process of claim 1 , wherein said acrylic polymer powder contains latent functionality capable of crosslinking.
5. The process of claim 1 , wherein said composition placed on the substrate further comprises 5 to 50 weight percent impact modifiers, based on the weight of the acrylic polymer powder.
6. The process of claim 1 , wherein said composition placed on the substrate further comprises a dye or pigment.
7. The process of claim 1 , wherein said substrate comprises a polymer.
8. The process of claim 1 , wherein said substrate comprises a bituminous material.
9. The process of claim 1 , wherein the average particle size of said acrylic polymer powder particles are less than the average size of said particulate filler particles.
10. The process of claim 1 , wherein said acrylic polymer powder has an average particle size of from 50 to 500 microns.
11. The process of claim 1 , wherein said melting of said acrylic polymer powder is caused by heating or irradiation of said acrylic polymer.