Stable aqueous dispersions of hydrophilic phenolic resins having low xylenol and bisphenol-A content
View Patent ↗Storage stable aqueous dispersions of a heat-reactive hydrophilic phenolic resin (e.g., phenol/formaldehyde) are disclosed. The dispersions comprise a base resin that is the reaction product of an aromatic alcohol and an aldehyde, and an etherified resin component selected from the group consisting of an etherified phenol/aldehyde resin, an etherified cresol/aldehyde resin, and mixtures thereof. The dispersions further comprise a protective colloid (e.g., polyvinyl alcohol). The addition of the etherified resin component in an amount of at least about 20% by weight of the base resin provides storage stability, but does not adversely affect the desirable physical and chemical characteristics (e.g., chemical resistance) of end products made from such dispersions. Moreover, the dispersions of the present invention can avoid the use of etherified resin components derived from bisphenol-A and/or xylenols, which present heath concerns in food coating applications.
1. A storage stable aqueous dispersion of a phenolic resin, said dispersion comprising:
(a) a heat-reactive, non-etherified hydrophilic phenolic base resin that is the reaction product of phenol and formaldehyde reacted in a molar ratio of formaldehyde to phenol from about 1:1 to about 2:1;
(b) an etherified resin component selected from the group consisting of an etherified phenol/aldehyde resin, an etherified cresol/aldehyde resin, an etherified phenol/cresol/aldehyde resin and mixtures thereof, wherein said etherified resin component is present in an amount of at least about 20% by weight of said base resin; and
(c) a protective colloid,
wherein said dispersion remains visually homogeneous by not exhibiting any separation, settling, foaming, coalescence or agglomeration of a dispersed phase for at least about 3 months.
2. The dispersion of claim 1 , wherein said etherified resin component is blended with said base resin at a blending temperature from about 25° C. to about 60° C.
3. The dispersion of claim 1 wherein the etherified resin component comprises 60% to 80% by weight of the phenolic base resin.
4. The dispersion of claim 1 , wherein said etherified resin component comprises an etherified phenol/formaldehyde resin.
5. The dispersion of claim 4 , wherein said etherified resin component comprises an etherified phenol/cresol/formaldehyde resin.
6. The dispersion of claim 1 , wherein said dispersion has a bisphenol-A content of less than about 0.1% by weight and a xylenol content of less than about 0.1% by weight.
7. The dispersion of claim 1 , wherein said protective colloid comprises polyvinyl alcohol.
8. The dispersion of claim 6 , wherein said protective colloid is present in an amount representing from about 5% to about 15% of the combined weight of aromatic alcohol and aldehyde reacted to form said base resin.
9. The dispersion of claim 1 , wherein said etherified resin component is present in an amount from about 30% to about 80% by weight of said base resin.
10. The dispersion of claim 1 , wherein said dispersion has a solids content of at least about 35% by weight.
11. The dispersion of claim 10 , wherein said solids content is from about 40% to about 80% by weight.
12. The dispersion of claim 1 , wherein said dispersion is storage stable for at least about 6 months.
13. A method for making a storage stable aqueous dispersion of a phenolic resin, said method comprising blending, at a blending temperature of less than about 60° C., (a) a heat-reactive, non-etherified hydrophilic phenolic base resin that is the reaction product of phenol and formaldehyde, and (b) an etherified resin component selected from the group consisting of an etherified phenol/aldehyde resin, an etherified cresol/aldehyde resin, an etherified phenol/cresol/aldehyde resin, and mixtures thereof, wherein said etherified resin component is present in an amount of at least about 20% by weight of said base resin, to form a resin mixture and forming the storage stable aqueous dispersion by mixing the resin mixture with (c) a protective colloid, so that the aqueous dispersion remains visually homogeneous by not exhibiting any separation, settling, foaming, coalescence or agglomeration of a dispersed phase for at least about 3 months.
14. The method of claim 13 , wherein said etherified resin component is formed from reacting n-butanol with a phenol/cresol/aldehyde adduct having a functionality from about 1.5 to about 2.75.
15. The method of claim 13 , wherein said blending temperature is from about 25° C. to about 60° C.
16. The method of claim 13 , wherein said base resin is in an aqueous solution.
17. The method of claim 13 , wherein said etherified resin component has a solids content of at least about 35% by weight.
18. The method of claim 17 , wherein said solids content is from about 50% to about 75% by weight.
19. A storage stable aqueous dispersion made according to the method of claim 13 , wherein said dispersion is storage stable for at least about 3 months.