PROCESS FOR PREPARING A BONDING RESIN FOR USE IN A COATING

Abstract

The present invention relates to a process for preparing a bonding resin suitable for use in coatings. The invention is directed to a method for preparing a bonding resin for use in a coating, wherein a solution of lignin in an organic solvent is mixed with polyglycerol polyglycidyl ether and optionally one or more additives.

Claims

1. A method for preparing a bonding resin for use in a coating, the method comprising: mixing a solution of lignin in an organic solvent with polyglycerol polyglycidyl ether to provide a bonding resin.

2. The method according to claim 1, wherein the bonding resin contains less than 1 wt-% solvent other than an organic solvent.

3. The method according to claim 1, wherein the solution of lignin in the organic solvent comprises at least 5% by weight of lignin.

4. The method according to claim 1, wherein a weight ratio between lignin, calculated on a basis of dry lignin, and a total amount of polyglycerol polyglycidyl ether is from 0.1:10 to 10:0.1.

5. The method according to claim 1, wherein an additive is mixed with the solution of lignin, wherein the additive is selected from a group consisting of urea, tannin, surfactant, a solvent, a dispersing agent, a filler, and combinations thereof.

6. The method according to claim 1, wherein the lignin is modified by glyoxylation, etherification, esterification or any other method where lignin hydroxyl content or amine content or thiol content is increased.

7. The method according to claim 1, wherein the lignin is not chemically modified before being used in the method.

8. The method according to claim 1, wherein the organic solvent is selected from a group consisting of ketones, esters, alcohols, hydrocarbons, ethers, dihydrolevoglucosenone, and mixtures thereof.

9. A bonding resin obtained by the method of claim 1.

10. The method of claim 1 further comprising: providing the bonding resin and preparing a coating with the bonding resin.

11. A paper, wood, or metal coated with the bonding resin according to claim 9.

12. The method according to claim 1, wherein an additive is mixed with the solution of lignin.

Description

DETAILED DESCRIPTION

[0014] It is intended throughout the present description that the expression lignin embraces any kind of lignin, e.g. lignin originated from hardwood, softwood or annular plants. Preferably the lignin is an alkaline lignin generated in e.g. the Kraft process. Preferably, the lignin has been purified or isolated before being used in the process according to the present invention. The lignin may be isolated from black liquor and optionally be further purified before being used in the process according to the present invention. The purification is typically such that the purity of the lignin is at least 90%, preferably at least 95%. Thus, the lignin used according to the method of the present invention preferably contains less than 10%, preferably less than 5% impurities. The lignin may then be separated from the black liquor by using the process disclosed in WO2006031175. The lignin may then be separated from the black liquor by using the process referred to as the LignoBoost process. The lignin may be provided in the form of particles, such as particles having an average particle size of from 50 micrometers to 500 micrometers.

[0015] Typically, the bonding resin according to the present invention is applied to the surface of a substrate to be coated. The cross-linking in the bonding resin then takes place, resulting in a coating.

[0016] The weight ratio between lignin (dry weight) and the total amount of polyglycerol polyglycidyl ether is preferably in the range of from 0.1:10 to 10:0.1, such as from 1:10 to 10:0.3, such as from 5:10 to 5:0.3, such as from 1:10 to 10:1. The amount of lignin in the bonding resin is preferably from 5 wt-% to 50 wt-%, calculated as the dry weight of lignin and the total weight of the bonding resin.

[0017] As used herein, the term organic solvent means a carbon-based substance that is used to dissolve another substance or substances. Since the organic solvent is carbon-based, it has at least one carbon atom in its structure. The organic solvent also has at least one hydrogen atom. As used herein, the organic solvent is a liquid at 25 C.

[0018] Preferably, the organic solvent is selected from ketones (such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl amyl ketone (MAK), Isophrone), esters (butyl acetate, ethyl acetate, methoxy propyl acetate (MPA), butylglycol acetate), alcohols (butanol, isopropanol), glycol ethers (ethylene glycol monobutyl ether, butyl glycol ether etc.), or hydrocarbons (naphtha, xylene etc.) or ethers or bio-based solvents (dihydrolevoglucosenone, cyrene etc.) mixture thereof.

[0019] According to the present invention, the solution of lignin in organic solvent is prepared before mixing the solution of lignin in organic solvent with the polyglycerol polyglycidyl ether.

[0020] The solution of lignin in organic solvent is preferably mixed with the polyglycerol polyglycidyl ether at room temperature, such as at a temperature of from 15 C. to 30 C. The mixing is preferably carried out for about 5 seconds to 2 hours. Preferably, the viscosity of the mixture is monitored during mixing, either continuously or by taking samples and determining the viscosity thereof.

[0021] The method for preparation of the bonding resin according to the present invention does not involve radical polymerization. Further, no radical initiator is used in the method for preparation of the bonding resin according to the present invention.

[0022] The bonding resin may also comprise 1-20 wt-% additives, such as urea, tannin, solvents, surfactants, dispersing agents and fillers. The bonding resin may also comprise coupling agent. Coupling agents are for example silane-based coupling agents.

[0023] The bonding resin according to the present invention contains less than 1 wt-% of solvent other than organic solvents, preferably less than 0.5 wt-%, more preferably 0 wt-%.

[0024] The amount of urea in the bonding resin can be 0-40% preferably 5-20% calculated as the dry weight of urea and the total weight of the bonding resin.

[0025] A filler and/or hardener can also be added to the bonding resin. Examples of such fillers and/or hardeners include limestone, cellulose, sodium carbonate, and starch.

[0026] The reactivity of the lignin with the polyglycerol polyglycidyl ether can be increased by modifying the lignin by glyoxylation, etherification, esterification or any other method where lignin hydroxyl content or carboxylic content or amine content or thiol content is increased. Preferably, the lignin used according to the present invention is not modified chemically.

[0027] The coating compositions can be applied to substrates in any manner known to those skilled in the art. In some embodiments, the coating composition comprising the bonding resin according to the present invention is sprayed or roll coated onto the substrate. The bonding resins may be pigmented and/or opacified with known pigments and opacifiers. Thus, for non-limiting example, spraying, rolling, dipping, and flow coating application methods can be used for both clear and pigmented coating. In some embodiments, after application onto a substrate, the coating may be cured thermally at temperatures in the range from about 130 C. to about 250 C., and alternatively higher for time sufficient to effect complete curing as well as volatilizing of any fugitive component therein.

[0028] For substrates intended as coil coatings, the coating compositions may be applied at a rate in the range from about 0.5 to about 15 milligrams of polymer coating per square inch of exposed substrate surface. In some embodiments, the water-dispersible coating is applied at a thickness between about 1 and about 25 microns.

EXAMPLES

Example 1

[0029] Lignin solution was prepared first by adding 63.2 g of powder lignin (solid content 95%) and 140 g of ethylene glycol monobutyl ether (EGME) were added to a 500 mL glass reactor at ambient temperature and were stirred for 120 minutes to make sure that the lignin was completely dissolved.

Example 2

[0030] Coating formulation was prepared by weighing 50 g of the lignin solution from the example 1, 15 g of polyglycerol polyglycidyl ether weighing into a 250 ml plastic container and stirred with a wooden stick for 2 minutes. Coating formulation was applied on an aluminum metal sheet using a film applicator. Then, the metal sheet was baked in an oven at 200 C. for 10 minutes. The cured coating was able to withstand 30 MEK double rubs, it had 100% adhesion (by cross hatch tape off method), a 2H pencil hardness and no cracking from bending the metal sheet at 0 T. The coated panel was bent back on itself with the coating side out. If there was no crack at the edge, the result was reported as 0 T. After 1 hour in boiling water, the film was not blushed.

Example 3

[0031] Coating formulation was prepared by weighing 50 g of the lignin solution from the example 1, 5 g of polyglycerol polyglycidyl ether weighing into a 250 ml plastic container and stirred with a wooden stick for 2 minutes. Coating formulation was applied on an aluminum metal sheet using a film applicator. Then, the metal sheet was baked in an oven at 200 C. for 10 minutes. The cured coating was able to withstand 30 MEK double rubs, it had 100% adhesion (by cross hatch tape off method), a 2H pencil hardness and no cracking from bending the metal sheet at 0 T. After 1 hour in boiling water, the film was not blushed.

Example 4

[0032] Lignin solution was prepared first by adding 84.2 g of powder lignin (solid content 95%) and 120 g of diacetone alcohol (DAA) were added to a 500 mL glass reactor at ambient temperature and were stirred for 120 minutes to make sure that the lignin was completely dissolved.

Example 5

[0033] Coating formulation was prepared by weighing 50 g of the lignin solution from the example 4, 20 g of polyglycerol polyglycidyl ether weighing into a 250 ml plastic container and stirred with a wooden stick for 2 minutes. Coating formulation was applied on an aluminum metal sheet using a film applicator. Then, the metal sheet was baked in an oven at 200 C. for 10 minutes. The cured coating was able to withstand 30 MEK double rubs, it had 100% adhesion (by cross hatch tape off method), an HB pencil hardness and no cracking from bending the metal sheet at 0 T. After 1 hour in boiling water, the film was not blushed.

[0034] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.