Starch Suspension for Adhesive Coatings

Abstract

This specification discloses suspensions and method for making the suspensions. The suspension comprises a suspension medium and is loaded with an insoluble solid. The suspension medium is an aqueous solution made at least one soluble polymer and at least one thixotropic gum. The suspension medium can be loaded with high levels of solids (more than 15% by weight of the medium). The resulting suspension is highly stable and has low viscosity. In embodiments the suspension exhibits no significant sedimentation for at least 3 months, and has a viscosity of less than about 20,000 cP. In an illustrative embodiment, the suspensions may be used to improve the properties of corrugating adhesives by adding to a corrugating adhesive a suspension that has suspension medium comprising polyvinyl alcohol and gellan and that suspends unmodified high amylose starch.

Claims

1. A composition comprising: water; a soluble polymer; a thixotropic gum; and an insoluble solid; wherein the water, polymer and gum are mixed to form a suspension medium; wherein the starch is dispersed in the suspension medium to form a suspension having a viscosity of less than 20,000 cP; and wherein the suspension is stable for at least 3 months.

2. The composition of claim 1 wherein the polymer is selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, alginates, polyacrylic acid and mixtures thereof.

3. The composition of claim 1 wherein the gum is selected from the group consisting of gellan, xanthan gum, locust bean gum, carrageenan, guar, alginate, carboxymethylcellulose, hydroxyethylcellulose, hemicellulose, gum Arabic and agar, and mixtures thereof.

4. The composition of claim 1 wherein the gum is selected from the group consisting of gellan or carrageenan, and mixtures thereof.

5. The composition of claim 1 wherein the insoluble solid is a modified or unmodified base starch, and the base starch is selected from the group consisting of corn, rice, pea or other pulse, wheat, tapioca, sorghum, arrowroot, oats, sago, potato, including high amylose and low amylose variants.

6. The composition of claim 1 wherein the insoluble solid is high amylose corn starch.

7. The composition of claim 1 wherein the suspension medium comprises between 2% and 40% polymer (by weight of the medium).

8. The composition of claim 1 wherein the suspension comprises greater than 15% starch (by weight of the suspension medium).

9. The composition of claim 1 wherein the suspension medium comprises between 10% and 15% polymer (by weight of the medium), the polymer being polyvinyl alcohol; and between 0.001% and 1% gum (by weight of the medium), the gum being gellan gum; and the suspension comprises between 1.5% and 50% starch (by weight of the medium), the starch being unmodified high amylose corn starch.

10. A method of making a suspension comprising: mixing water; a soluble polymer; and a thixotropic gum at between 75 and 99 C. for between 5 and 60 minutes to form a suspension medium; allowing the medium to cool to between 25 and 50 C.; and adding starch to the medium to form a suspension.

11. The method of claim 10 wherein the polymer is selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, alginates, polyacrylic acid, and mixtures thereof.

12. The method of claim 10 wherein the gum is selected from the group consisting of gellan, xanthan. gum, locust bean gum, carrageenan, guar, alginate, carboxymethylcellulose, hydroxyethylcellulose, hemicellulose, gum Arabic and agar, and mixtures thereof.

13. The method of claim 10 wherein the gum is selected from the group consisting of gellan or carrageenan, and mixtures thereof.

14. The method of claim 10 wherein the suspension medium comprises between 2% and 40% polymer (by weight of the medium).

15. The method of claim 10 wherein the suspension comprises at least 15% starch (by weight of the medium).

16. The method of claim 10 wherein the suspension medium comprises between 10% and 15% polymer (by weight of the medium), the polymer being polyvinyl alcohol; and between 0.001% and 1% (by weight of the medium) gum, the gum being gellan gum; and the suspension comprises between 15% and 50% starch (by weight of the medium), the starch being unmodified high amylose corn starch.

17. A method of delivering an unmodified starch component during paper making comprising: providing a suspension during paper making, the suspension comprising water; a soluble polymer; a thixotropic gum; and a starch; wherein the water, polymer and gum are mixed to form a suspension medium; wherein the starch is dispersed in the suspension medium; and wherein the suspension has a viscosity of less than 20,000 cPs (at least 15% starch solids by weight of the medium)

18. The method of claim 17 wherein the suspension is provided as part of a corrugating adhesive; wherein the corrugating adhesive comprises unmodified corn starch; boric acid or a boric acid salt, a basic agent, and the suspension; and wherein the suspension comprises between 15% and 50% starch (by weight of a suspension medium); the starch being unmodified high amylose corn starch and wherein the suspension medium comprises between 10% and 15% polymer (by weight), the polymer being polyvinyl alcohol; and between 0.001% and 1% gum (by weight) gum, the gum being gellan gum.

19. The method of making a corrugating adhesive comprising: mixing water; an unmodified starch; a basic agent; and boric acid or a boric acid salt for sufficient time to make a corrugating adhesive; and adding to the adhesive a suspension comprising between 15% and 50% unmodified high amylose corn starch (by weight of a suspension medium); and wherein the medium. comprises between 10% and 15% polyvinyl alcohol (by weight); and between 0.001% and 1% gellan gum (by weight).

20. A corrugating adhesive comprising: a first starch; boric acid or a boric acid salt; a basic agent; polyvinyl alcohol; gellan gum; and a second starch being an unmodified high amylose corn starch.

Description

EXAMPLE 1

Illustrative Suspension

[0043] Suspension A: Sixty grams of Celvol 203 polyvinyl alcohol is stirred into 400 grams of water. The solution is heated to 90 C. with continuous stirring. One-half gram of gellan gum is added to the stirred solution; the combine solution is stirred for 10 minutes. The solution is then cooled to 30 C. and 150 grams Hylon VII high amylose corn starch is stirred into the mixture. The solution is further cooled to room temperature and then treated with 1% by weight ACTICIDE biocide. The resulting suspension is stable for up to 6 months without significant sedimentation.

[0044] Suspension B: One-half gram of gellan gum was added to 250 grams of water with continuous stirring during heating to 90 C. The mixture is held at this temperature for 10 minutes. This solution was then blended with 200 grams a polyvinyl alcohol solution (30% by weight). The combined solution is cooled to 30 C. and 150 grams of Hylon VII is then added with stirring. This suspension is likewise treated with biocide and has similar stability.

EXAMPLE 2

Corrugating Adhesive

[0045] Slurry of 170 g water, 35 g NaOH and 2 liters of water is mixed in a container and heated with stirring to about 40 C. (105 F.). The mixture is mixed at 3000 rpm for 90 seconds. Twenty-five grams of borax (10 mol) is added with an additional 3 minutes of mixing, Two-and-one-half liters of water (about 27 C. (80 F.)) are added, followed by 1.5 kg of unmodified starch. The mixture is then mixed for 2 minutes. One kilogram of this adhesive is mixed with 25 grams of Suspension A. The resulting adhesive exhibits superior green bond (wet tack) when applied to liner and medium grade papers used to make corrugated packaging board. Upon heating of adhesive and board in a commercial corrugating process, the adhesive demonstrates superior bond strength than the same adhesive without the additive.