WO1999019376A1

WO1999019376A1 - Continuous process for producing rheology modifiers

Info

Publication number: WO1999019376A1
Application number: PCT/US1998/021329
Authority: WO
Inventors: Robert A. Sutton; Steven V. Barancyk; Timothy B. Syput; Frederick A. Bralski
Original assignee: Ppg Industries, Inc.
Priority date: 1997-10-14
Filing date: 1998-10-09
Publication date: 1999-04-22
Also published as: AU9691898A

Abstract

An improved process for dispersing a rheology modifier in a resinous material in which the rheology modifier comprises the reaction product of an amine and an isocyanate. The improvement comprises the process being conducted in a continous manner by: (a) simultaneously metering the amine, the isocyanate or the reaction product thereof and the resinous material into a first high shear mixer to form a mixture as said mixture flows through the high shear mixer; (b) continously flowing the mixture of (a) into and through a low shear mixing stage; (c) continuously flowing the mixture of (b) into and through a second high shear mixer. Steps (a, b and c) thus resulting in the dispersion of the rheology modifier in the resinous material.

Description

CONTINUOUS PROCESS FOR PRODUCING RHEOLOGY MODIFIERS

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing rheology modifiers useful in coatings compositions. More particularly, the present invention relates to a continuous process for producing rheology modifiers.

Rheology modifiers, which are sometimes referred to as sag control agents, can be an important component of a coating composition. By controlling flow and sag of the coating, the rheology modifiers allow for the deposition of coating with sufficient thickness to impart the necessary corrosion protection while maintaining the desired appearance, i.e., gloss, distinctness of image (DOI), and smoothness.

Rheology modifiers are described in U.S. Patent Nos. 4,311,622, 4,677,028, and 4,851,294 and are the reaction products of a diisocyanate and an amine, optionally reacted in the presence of a binder or resin. These rheology modifiers are generally crystalline in nature and their effectiveness is dependent on size of the crystals as well as the concentration of the modifiers in the coating composition. Typically the rheology modifiers are incorporated into the binder via a batch process which results in differences in crystal growth and average crystal size from batch to batch leading to inconsistent coating properties.

It would be desirable to have a process for producing rheology modifiers in coating binders in a continuous manner resulting in coatings with consistent and controllable properties.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an improved process for dispersing a rheology modifier in a resinous material in which the rheology modifier comprises the reaction product of an amine and an isocyanate. The improvement comprises the process being conducted in a continuous manner by:

(a) Simultaneously metering the amine, the isocyanate or the reaction product thereof and the resinous material into a first high shear mixer to form a mixture as said mixture flows through the high shear mixer.

(b) Continuously flowing the mixture of (a) into and through a low shear mixing stage. (c) Continuously flowing the mixture of (b) into and through a second high shear mixer. Steps (a), (b) and (c) thus resulting in the dispersion of the rheology modifier in the resinous material.

In a preferred embodiment of the invention, the amine and the resinous material and optionally a solvent are premixed and the mixture metered to the first high speed mixer. The isocyanate, usually diluted with a solvent, is separately and simultaneously metered to the first high shear mixer.

In another preferred embodiment of the invention, the amine, the resinous material, and the isocyanate are separately and simultaneously metered to the first high shear mixer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a continuous process for dispersing rheology modifiers in resinous materials that are useful in controlling the flow and sag of coating compositions. The resinous materials are those which are typically used as binders in coating compositions and include oligomers and polymers which are reactive with aminoplast curing agents such as polyols. Specific examples include acrylic polyols, polyester polyols, including alkyds, and polyurethane polyols. Examples of suitable resinous materials are described in U.S. Patent No. 4,311 ,622. Examples of other suitable resinous materials are carbamate group containing polymers and amide group containing polymers. Suitable aminoplast resins are based on the addition products of an aldehyde such as formaldehyde, with an amine or an amide such as melamine, urea or benzoguanamine. The aminoplast may optionally be alkylated, typically with a C, to C₄ alcohol. However, condensation products of other amines and amides can also be employed, for example, aldehyde condensates of triazines, diazines, triazoles, guanadines, guanamines and alkyl- and aryl-substituted melamines. Some examples of such compounds are N,N'-dimethyl urea, benzourea, dicyandiamide, formoguanamine, acetoguanamine, glycoluril, 2-chloro-4,6-diamino-l,3,5-triazine, and the like.

The rheology modifier used in the continuous process of this invention is a reaction product of an amine and an isocyanate. The amine may contain one or more amino groups, but preferably the amine is a monoamine and more preferably a monoprimary amine. Suitable monoamines include benzylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, methylbutylamine, ethylpropylamine, and ethylbutylamine. Additionally, hydroxy containing monoamines may be used such as 2-aminoethanol, 1- aminoethanol, 2-aminopropanol, 3-aminopropanol, l-amino-2-propanol, 2-amino-2- methylpropanol, 2-aminobutanol, 2-amino-2-methyl-l,3-propanediol, and 2-amino-2-ethyl- 1,3-propanediol. Preferably the monoamine is benzylamine or hexylamine. Examples of suitable amines are described in U.S. Patent Nos. 4,31 1,622 and 4,677,028.

The isocyanate is preferably a polyfunctional monomeric isocyanate, more preferably a di or tri functional isocyanate. The polyisocyanate can be an aliphatic, cycloaliphatic or aromatic polyisocyanate, or mixtures thereof. Diisocyanates are preferred, although higher polyisocyanates such as triisocyanates can be used either in place of or in combination with diisocyanates. Examples of the aliphatic isocyanates are trimethylene, tetramethylene, tetramethylxylylene, pentamethylene, hexamethylene, 1 ,2-propylene, 1,2-butylene, 2,3-butylene, and 1,3-butylene diisocyanates. Also suitable are cycloaliphatic isocyanates such as 1,3-cyclopentane and isophorone diisocyanates; aromatic isocyanates such as m-phenylene, p-phenylene and diphenylmethane-4,4-diisocyanate; aliphatic-aromatic isocyanates such as 2,4- or 2,6-tolulene diisocyanates and 1,4-xylylene diisocyanate; nuclear-substituted aromatic isocyanates such as dianisidine diisocyanate and 4,4-diphenylether diisocyanate; triphenylmethane-4,4,4-triisocyanate, and 1,3,5-triisocyanatobenzene; and dimers and trimers of polyisocyanates such as the isocyanurate of tolulene diisocyanate and hexamethylene diisocyanate. Isothiocyanates corresponding to the above-described isocyanates, where they exist, can be employed as well as mixtures of materials containing both isocyanate and isothiocyanate groups. Isocyanates are commercially available from Bayer USA, Inc. under the trademarks MONDUR and DESMODUR. Preferably the polyfunctional monomeric isocyanate is 1 ,6-hexamethylene diisocyanate. Examples of suitable isocyanates are described in U.S. Patent Nos. 4,311,622 and 4,677,028. The equivalent ratio of amine to isocyanate ranges from 0.7 to 1.5:1, preferably 1 :1, with the primary amine being considered monofunctional. For optimum sag control, the amine isocyanate reaction product is crystalline.

The rheology modifier may be formed by reacting the amine with the polyfunctional isocyanate in a suitable reaction vessel generally at a temperature between about 20°C to about 80°C, preferably from about 40°C to about 60°C in the presence of solvent. In carrying out the reaction, it is preferred that the isocyanate be added to the amine in the reaction vessel. The reaction product, preferably dissolved in solvent, may then be added to the resinous material in accordance with the present invention.

In a preferred embodiment of the present invention, the sag control agent is formed in the presence of the resinous material during the continuous process. The polyfunctional isocyanate and optionally a solvent forms one component. Typically the amine is combined with the resinous material and optionally a solvent to form a second component. This may be accomplished by mixing the amine and the resinous material in any suitable vessel prior to metering into the first high shear mixer of the continuous process of this invention. Alternatively, the amine and the resinous material may each be metered simultaneously through a mixer, either a static or a dynamic inline mixer, to form the second component and then this mixture is continuously metered into the first high shear mixer of the continuous process. Typically, the first component generally contains from about 5 to about 40 weight percent of isocyanate with the remainder being solvent. Typically, the percent by weight of amine in the second component is about 0.2 to about 5 percent based on weight of amine and resinous material. Solvent may be present in the second component in amounts of about 20 to about 50 percent by weight based on the total weight. In the first stage of the continuous process, the two components are continuously metered into the first high shear mixer. The ratio of the two components is adjusted to produce the desired equivalent ratio of amine to isocyanate. In the first high shear mixer the components of the rheology modifier are mixed together under high shear conditions allowing for the intimate and complete mixing of the amine and the polyfunctional isocyanate and to initiate crystallization.

The two components are simultaneously metered into the first high shear mixer by any means that will produce a constant continuous flow of the materials. Preferably fluid metering pumps are used. Metering pumps are commercially available from Bran and Luebbe, Milton Roy, SCI Log, or Pulsafeeder.

The two components may optionally be heated as they are metered into or before they are metered into the first high shear mixer. When heated, the temperature will range from about 30°C to about 50°C, preferably from about 30°C to about 40°C.

In another embodiment of the invention the polyfunctional isocyanate, the amine and the resinous material are each separately and simultaneously metered into the first high shear mixer. Optionally a solvent may also be present in any or all of the three separate feeds into the first high shear mixer. Suitable solvents for use in the process include aliphatic solvents such as hexane, heptane, naphtha, and mineral spirits; aromatic solvents such as toluene, xylene, and SOLVESSO 100; alcohols such as ethyl, methyl, n-propyl, isopropyl, n-butyl, isobutyl and amyl alcohol, and m-pyrol; glycols such as ethylene glycol and propylene glycol; esters such as ethyl acetate, n-butyl acetate, isobutyl acetate, isobutyl isobutyrate, and oxohexyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, methyl n-amyl ketone, and isophorone. Additional solvents include glycol ethers and glycol ether esters such as ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether acetate. The high shear mixers used in the continuous process may be any commercially available high shear mixer. Preferably the high shear mixers are rotor-stator type mixers. Rotor-stator type mixers are commercially available from Charles Ross & Son Company, Hauppauge, New York as Ross Mixer Emulsifiers. These high shear mixers contain a high speed rotor operating at close clearance to a stationary stator. As the rotor turns it draws material in and accelerates the material towards the rotor blade periphery where the material is expelled through openings in the stationary stator producing a high shearing action on the material. The stator head may have a number of different opening configurations. The most common are round openings, vertical rectangular slot openings, and a round hole screen combined with an outer retaining head with larger openings. The operating speed or the speed of the tip of the rotor in feet per minute is another determining factor of the amount of shear imparted on the material passing through the mixer. For purposes of this invention the rotor operates at a tip speed of from about 1000 to about 12,000 feet per minute (305 to 3658 meters per minute), preferably 1000 to about 6000 feet per minute (305 to 1829 meters per minute). A typical measurement of operating speed of a rotor is revolutions per minute, but this measurement does not give an accurate measurement of the velocity of the material and thus the shear imparted on the material at the tip of the rotor where the material is expelled through the stator openings. A rotor at a given diameter will have a higher tip speed than a rotor with a smaller diameter when they are turning at identical revolutions per minute. The higher tip speed translates into higher material velocity and thus higher shear for the mixer with the larger diameter rotor, thus rotor tip speed is a more closely related to the shear imparted on the material than a measurement of revolutions per minute. Another factor that effects the amount of shear imparted on the material passing through the mixers is the residence time in the mixer of the various materials. The longer the time, the greater the shearing action on the material. Typically mixing time in the first and in the second high shear mixers of the claimed continuous process ranges from about 0.1 to about 10 minutes, preferably from about 0.1 minutes to about 5 minutes.

After exiting the first high shear mixer, the mixture is continuously flowed into the low shear mixing stage of the continuous process of the present invention. This stage furthers the reaction resulting in crystal growth or propagation. The low shear mixing may be by any means; however, preferably the low shear mixing is achieved by flowing the material through a length of tubing, preferably coiled. The tubing may be jacketed to allow for heating or cooling of the mixture as it flows through this stage of the process. By controlling the temperature during this stage of the reaction controls the crystal growth. If the crystals are too small, the effectiveness of the rheology modifier will be adversely effected, and if the crystals are too large, the appearance of the coating composition in which the rheology modifier is used may be adversely effected. Typically the temperature is maintained between about 20°C to about 80°C, preferably from about 40°C to about 60°C, during this stage of the process. Generally the residence time of the rheology modifier in the low shear stage of the claimed continuous process is between about 0.5 to about 15 minutes, preferably between about 0.5 to about 10 minutes. The total residence time in the first high shear mixer, the low shear mixing stage and the second high shear mixer added together is about 3 to about 20 minutes.

In another embodiment of the claimed invention, a stir tank is used for the low shear stage of the continuous process. The mixture flows from the first high shear mixer into one end or side of the stir tank which is equipped with a means of low shear agitation, usually a stirrer or mixer, and then flows out another end or side of the stir tank. The tank may be equipped with baffles to facilitate mixing, and may be jacketed to facilitate temperature control.

After exiting the low shear stage of the process, the rheology modifier flows into a second high shear mixer. The second high shear mixer ensures the complete dispersion of the crystallized rheology modifier into the resinous material and breaks up any agglomerates that may have formed during the low shear stage of the process. The presence of agglomerates in the rheology modifier can have a detrimental effect on appearance and sag resistance.

Total flow velocities of the mixture through the continuous process of the present invention varies according to mixer sizes and tubing diameters, but typically the flow velocity of the mixture through the process is between about 50 centimeters per minute to about 450 centimeters per minute.

The resinous material containing the dispersed rheology modifier produced by the continuous process typically has a percent total solids of between about 50 to about 70 weight percent, and generally contains about 1 to about 10 weight percent of rheology modifier based on total solids.

The resinous material produced by the continuous process is useful in modifying the flow characteristics of coating compositions. The rheology modifier is typically used as a sag control agent to control the sag properties of a coating composition. The resinous material containing the dispersed rheology modifier can then be combined with other ingredients contained in the coating composition such as curing agents, pigments, adjuvant resins, additives such as UN light absorbers, antioxidants and the like. The coating compositions will use between about 0.5 to about 5 weight percent, preferably about 0.5 to about 3 weight percent of the rheology modifier produced by the continuous process of the present invention, with the percentages based on total resin solids of the coating composition. The invention will be further described by reference to the following example which is presented for the purpose of illustration only and is not intended to limit the scope of the invention.

EXAMPLE A rheology modifier was dispersed in resinous material using the continuous process of the present invention in the following manner:

COMPONENT A Chemical Weight in parts

Acrylic resinl 13500.0 Benzylamine 283.3

AROMATIC 1002 2358.5 COMPONENT B

Chemical Weight in parts 1 ,6-hexamethylene diisocyanate 221.5

AROMATIC 100 1725.8

1 Acrylic resin comprised of 23% butyl acrylate, 23% butyl methacrylate, 30% hydroxyethyl acrylate, 22.5% styrene, and 1.5% methacrylic acid, with the percentages based on total weight of monomers, and having a number average molecular weight of approximately 1800 and a weight average molecular weight of 4000, and 74% weight solids in AROMATIC 100 solvent (commercially available from Exxon Chemicals America).

2 Mixed aromatics solvent, available from Exxon Chemicals America.

Components A and B were simultaneously, continuously and individually metered by an Accupump, commercially available from SCI Log Corporation, to a rotor-stator type high shear mixer, a Series 400 Inline Model Ross Mixer Emulsifier commercially available from Charles Ross & Son Company. Components A and B were intimately mixed at a rotor rate of 5000 rpm resulting in a rotor tip speed of 1800 feet per minute (549 meters per minute). The flow rate of the Component A feed was 90 milliliters per minute, and the flow rate of the Component B feed was 12.45 milliliters per minute. Component A was heated to 35°C by a heat tape surrounding the feed line prior to being fed to the mixer. The residence time in the mixer was approximately 1 minute. The temperature of the material 9 inches downstream of the mixer ranged from 40°C to 55°C; however, during most of the run this temperature ranged between 50°C and 53°C. After the high shear mixer, the mixture of Components A and B were passed into the low shear stage of the process. The low shear stage consisted of a coiled stainless steel tube surrounded by a copper jacket. Water at a temperature of approximately 50°C was circulated from a controlled temperature water bath through the jacket. The length of the tube was 20 feet, resulting in a material residence time of approximately 4.5 minutes in the coiled tube. The material was then passed through a second rotor-stator type high shear mixer, a Series 400 Inline Model Ross Mixer Emulsifier, operating at a rotor rate of 7667 rpm and a rotor tip speed of 2760 feet per minute (841 meters per minute). The residence time in this mixer was also approximately 1 minute. The material was then collected upon exiting the second high shear mixer. Approximately 40 kg of resinous material containing the dispersed rheology modifier was produced. The resinous material had a total solids of 62.5 percent by weight determined at 110°C for 1 hour, and contained 5 percent by weight of the rheology modifier based on total solids.

Claims

WHAT IS CLAIMED IS:

1. An improved process for dispersing a rheology modifier in a resinous material in which the rheology modifier comprises the reaction product of an amine and an isocyanate, the improvement comprising conducting the process on a continuous basis by:

(a) simultaneously metering the amine, isocyanate or reaction product thereof and the resinous material into a first high shear mixer to form a mixture as said mixture flows through said high shear mixer;

(b) continuously flowing the mixture of (a) into and through a low shear mixing stage;

(c) continuously flowing the mixture of (b) into and through a second high shear mixer; steps (a), (b) and (c) resulting in the dispersion of the rheology modifier in the resinous material.

2. The process of claim 1 in which the isocyanate is a monomeric polyisocyanate.

3. The process of claim 2 wherein the monomeric polyisocyanate is selected from the group consisting of 1 ,6-hexamethylene diisocyanate and the isocyanurate of hexamethylene diisocyanate.

4. The process of claim 1 wherein the amine is a monoprimary amine.

5. The process of claim 1 wherein the monoprimary amine is selected from the group consisting of benzylamine and hexylamine.

6. The process of claim 5 wherein the monoprimary amine is benzylamine.

7. The process of claim 1 wherein the resinous material comprises polymeric or oligomeric materials which are reactive with an aminoplast.

8. The process of claim 1 in which the isocyanate and the amine are separately metered to the first high speed mixer.

9. The process of claim 8 in which the amine and resinous material are premixed and the mixture metered to the first high speed mixer.

10. The process of claim 1 in which the isocyanate, the amine, and the resinous material are separately metered to the first high speed mixer.

11. The process of claim 1 in which the equivalent ratio of amine to isocyanate ranges from 0.7 to 1.5:1.

12. The process of claim 1 wherein the first and second high shear mixers are rotor-stator type mixers and the first high shear mixer is operated at a rotor tip speed of about 1000 to 6000 feet per minute (305 to 1829 meters per minute); the second high shear mixer is operated at a rotor tip speed of about 1000 to 6000 feet per minute.

13. The process of claim 1 wherein the residence time of the materials in the first and second high shear mixers is from 0.1 to 5 minutes and in the low shear mixing stage is from 0.5 to 10 minutes, such that the total residence time in the first high shear mixer, the low shear mixing stage and the second high shear mixer added together is from about 3 to 20 minutes.

14. The process of claim 1 wherein the rheology modifier is present in the resinous material in amounts of about 1 to 10 percent by weight based on total solids.

15. The process of claim 1 wherein the temperature of the mixture flowing through the low shear mixing stage is between about 20┬░C to 80┬░C.

16. The process of claim 1 wherein the temperature of the mixture flowing through the low shear mixing stage is between about 40┬░C to 60┬░C.