WO2014028376A1

WO2014028376A1 - Rust preventive coating composition

Info

Publication number: WO2014028376A1
Application number: PCT/US2013/054513
Authority: WO
Inventors: Mukesh K. MADHUP
Original assignee: 3M Innovative Properties Company
Priority date: 2012-08-16
Filing date: 2013-08-12
Publication date: 2014-02-20

Abstract

The present invention relates to a single pack epoxy resin based rust preventive coating composition having dual nature comprising a high molecular weight modified diglycidyl ether bisphenol A epoxy resin, a butylated urea formaldehyde resin, a low molecular weight unmodified diglycidyl ether bisphenol A based epoxy resin and a solvent, behaving as thermoplastic or thermosetting depending on different temperature exposure condition during application and use. This composition is useful in temporary metal surface protection.

Description

RUST PREVENTIVE COATING COMPOSITION

FIELD OF THE INVENTION

The present invention relates to a single pack epoxy resin based rust preventive coating composition having dual nature, behaving as thermoplastic or thermosetting depending on different temperature exposure condition during application and use. This composition is useful in temporary metal surface protection from corrosion.

BACKGROUND OF THE INVENTION

Rust preventive temporary corrosion prevention coating materials currently in market are based on (used at very low dry film thickness) alkyd, oils etc usually semidrying or air drying systems. Rust preventive coatings are used for temporary protection of metallic surface followed by stripping of the coating and application of actual system.

Epoxy based chemistries are being used in the applications such as adhesives, sealants, paints, etc. for various properties like chemical & solvent resistance, high bond strengths and good corrosion protections, etc.

Epoxy resins are an important class of polymeric materials, characterized by the presence of more than one three-membered ring known as the epoxy, epoxide, oxirane, or ethoxyline group. By strict definition, epoxy resins refer only to uncross-linked monomers or oligomers containing epoxy groups. However, in practice, the term epoxy resin is loosely used to include cured epoxy systems.

There are two main categories of epoxy resins, namely the glycidyl epoxy, and non-glycidyl epoxy resins. The glycidyl epoxies are further classified as glycidyl-ether, glycidyl-ester and glycidyl-amine. Glycidyl epoxies are prepared via a condensation reaction of appropriate dihydroxy compound, dibasic acid or a diamine and epichlorohydrin.

Commercial uses of epoxy resins can be generally divided into two major categories:

protective coatings and structural application. The excellent corrosion, abrasion, and chemical resistance properties of these epoxy coatings allow their dominant position as protective coatings in the markets. The largest single use is in coatings.

The majority of epoxy coatings are based on Diglycidyl ether of bisphenol-A (DGEBA) or modifications of DGEBA.

DGEBA is a typical commercial epoxy resin and is synthesised by reacting bisphenol-A with epichlorohydrin in presence of a basic catalyst. By varying the relationship between bisphenol A and epichlorohydrin, various molecular weights are obtained for the completed epoxy resin. Structure of DGEBA is shown below.

The outstanding performance characteristics of these resins are conveyed by the Bisphenol-A moiety, the ether linkages and the hydroxyl and epoxy groups.

Further, liquid epoxy resins (LERs) and low molecular weight solid epoxy resins (SERs) based on bisphenol A and bisphenol F epoxies are commonly used.

Almost all the epoxy based coating materials used in these markets are made of two components viz. epoxy resin in base part and amine/amides in curative part applied and cured at ambient conditions. Usually curing reaction goes on immediately after mixing and hence these materials have a limited 'pot life' before which the mixed coating must be applied. Moreover, they have poor or low fracture energy, high shrinkage, and show brittle behavior and also the solvent based epoxy systems contributes to volatile organic content.

Single pack epoxies are also used which include different kind of modification of the epoxy including formation of air drying epoxy ester.

US Patent US 6,444,272 Bl, 3 Sept. 2002 (Kansai Paint Co.), discloses a single packaged epoxy coating with composition of (a) an epoxy resin, (b) a ketimine compound having at least two primary amino group blocked with carbonyl compound, (c) a dehydrating compound and (d) an organic solvent.

The currently available epoxy based coating materials are either thermosetting or thermoplastic depending on their chemical composition. None of them exhibit a dual nature, behaving as thermoplastic or thermosetting depending on different temperature exposure.

Therefore, there is a requirement to provide solution for temporary metal surface protection with enhanced corrosion protection, having fast drying characteristics, excellent adhesion and at lower dry film thickness and strippability and a dual nature, behaving as thermoplastic or thermosetting depending on different temperature exposure condition during application and use. SUMMARY OF THE INVENTION

An objective of the present invention is to provide a single pack, temporary, superior rust preventive epoxy resin coating composition having a dual way of action wherein it acts as both thermoplastic and thermosetting according to the requirement. The composition of the present invention has excellent adhesion over unprepared substrates including that the removal of mill scale from the metallic pipes/structures is not a prerequisite.

The present invention provides a solution for temporary metal surface protection with enhanced corrosion protection, having fast drying characteristics and at lower dry film thickness and having strippability. The single coating composition disclosed here provides two kinds of behavior, (1) thermoplastic when air dried and (2) thermosetting when heated above 120°C.

Accordingly, one embodiment of the present invention is related to a coating composition comprising modified diglycidyl ether bisphenol A based high molecular weight epoxy resin, a butylated urea formaldehyde resin, an unmodified diglycidyl ether bisphenol A based epoxy resin and a solvent.

In a further aspect, the instant coating composition comprises the individual components in the following concentration:

• components of the base

o modified epoxy resin in an amount of 20% to 60%,

o unmodified epoxy resin in an amount of 3% to 18%.

• urea formaldehyde resin in an amount of 2% to 15% as curing agent

The solvent forms the rest of the weight of the composition.

In another aspect of the present invention, it optionally comprises a suitable organic or inorganic pigment for desired shade development and a suitable solid or liquid rheology additive.

This invention also relates to a process for preparing the rust preventive composition wherein the process comprises mixing of modified and unmodified epoxy resins and solvent or solvent mixture and urea resin in a variable speed disc dispenser and adding ground pigment/color concentrate as per desired shade and optionally adding additives and stirring at a slow speed.

In another aspect of the present invention, a process for applying the composition comprising one of the following three methods:

• Spray application: conventional or airless gun application in single coat or multiple coat (Dry film thickness in the range of 10 to 30 microns, typical 25 microns)

• Application by Brush: a general purpose paint brush can be used for application of the

coating over the substrate, desired dry film thickness can be achieved in single or multiple coats.

• Application by Dipping: the substrate or component to be coated can be dipped inside the coating and taken out for drying or heat curing.

The present invention possesses at least the following advantages:

• Single pack epoxy coating

• Dual nature of application ( as thermoplastic & thermosetting) according to requirement

• Temporary coating

• Economical Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, because various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

The components of the coating composition interact synergistically to confer a unique combination of the physical and chemical properties to the resultant composition which make it superior to the state of the art compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of assisting in the explanation of the invention, there are shown in the drawings embodiments which are presently preferred and considered illustrative. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein.

Figure 1 : Shows abrasion resistance test showing very high abrasion resistance

observed > 50 mg at CS - 17 wheel, 1000 Cycles

Figure 2: Shows scratch resistance test where the coating passes > 2 Kg of load.

Figure 3(a) & (b): Shows salt spray test which passes 150 hours.

Figure 4: Shows flexibility test and

Figure 5: Shows final product applied on the pipe.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification are to be understood as being modified in all instances by the term "about". It is noted that, unless otherwise stated, all percentages given in this specification and appended claims refer to percentages by weight of the total composition.

Thus, before describing the present invention in detail, it is to be understood that this invention is not limited to particularly exemplified systems or process parameters that may of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only, and is not intended to limit the scope of the invention in any manner. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the case of conflict, the present document, including definitions will control.

It must be noted that, as used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a "solvent" may include two or more such solvents.

The terms "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

As used herein, the terms "comprising" "including," "having," "containing," "involving," and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains.

The present invention is a single pack epoxy resin for anti corrosive coating purpose having dual nature. This single composition performs as a thermosetting resin coating as well as thermoplastic resin coating depending on the requirement.

A thermoplastic, also known as a thermo softening plastic, is a polymer that becomes pliable or moldable above a specific temperature, and returns to a solid state upon cooling. Most thermoplastics have a high molecular weight, whose chains associate through intermolecular forces; this property allows thermoplastics to be remolded because the intermolecular interactions spontaneously reform upon cooling.

A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 200°C (392°F)), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in

semiconductors and integrated circuits (IC). Once hardened a thermoset resin cannot be reheated and melted back to a liquid form. The thermoset bonds break down upon melting and do not reform upon cooling. Further the present composition is a single pack consisting of a high molecular weight modified DGEBA epoxy resin, a low molecular weight un modified DGEBA epoxy resin, a butylated urea formaldehyde, solvents and optional pigments and additives.

The coating composition of the present invention is a solvent based modified DGEBA epoxy resin composition comprising 2 bases and a curing agent, wherein the bases comprises high molecular weight(HMW) modified DGEBA epoxy resin, a low molecular weight (LMW) unmodified DGEBA epoxy resin and other optional additives; while the curing agent consists essentially of butylated urea formaldehyde.

Epoxy resin with a mean molecular weight of over 700 is called high molecular, and epoxy resin with a mean molecular weight of under 700 low molecular. The low molecular can be handled without solvent additives, which evaporates and are therefore used for casting, thick coatings, gap- filling glues, etc

The DGEBA epoxy resin is modified basically for adhesion improvement on different kind of substrates. The high molecular weight modified DGEBA epoxy resin possessing high viscosity remains uncured at normal and at a temperature of 120°C which contributes to the thermoplastic nature of the single pack. The low molecular weight unmodified DGEBA epoxy resin reacts in the presence of urea formaldehyde at a temperature of 120°C and thus contributes to the thermosetting property of the present single pack. The high molecular epoxy resins must as a rule be dissolved in organic solvents to be manageable and hence the present pack consist of solvents selected from the organic solvent groups such as aromatic hydrocarbons, ketonic or esters and solvents for handling urea formaldehyde and un modified epoxy resin.

Optionally, the mixture also consist of organic or inorganic pigments and solid or liquid rheology additive based on bentonite clay or modified urea etc.

Thus this invention leads to a new composition and technology introduction in terms of a single product behaving thermoplastic (if dried at room temperature) and thermosetting (if cured at elevated temperature at >120°C). Faster drying product compared with oil based or alkyd based existing products.

This may prove to be a future focused technology if superior short term rust prevention is required with flexibility of air drying or heating the coated component for faster cycle time. A huge business potential is involved in case of consumer's up gradation from oil based rust preventive to the instant single pack epoxy based rust preventive composition behaving as thermoplastic and thermosetting coating thus achieving superior temporary corrosion protection as disclosed in the current invention.

Hereinafter, the present invention will be described in detail with reference to the following examples. The following examples are set forth to assist in understanding the invention and should not, of course, be construed as specifically limiting the invention described and claimed herein. Experimental Details

General Information and Materials: All the ingredients of the present composition were procured from the commercial suppliers in India (Butyrated urea resin), epoxy resin produced in Japan (Mitsui chemicals) and Thailand (Aditya Birla chemicals).

EXAMPLE 1

In a preferred embodiment of the present invention, the standard rust preventive coating composition of the invention has the following composition. The composition comprises (A) Base components and (B) a curing agent

The components of the composition are shown in Table 1

Table 1

The instant composition was prepared by blending of the raw materials by variable speed disc disperser. The machine consists of a shaft with a circular saw tooth type or fan type mixing blade at the end of the shaft. A clean vessel was kept under variable speed disc disperser/mixer. Weighed amount of both epoxy resins were put into the clean vessel. It was stirred with slow speed (tip speed approx 2ft/s) mix for 5-10 minutes. Weighed amount of solvent or solvent mixture was slowly added into the vessel and stirred (tip speed approx 5-15 ft/s) for 15-20 minutes. Later urea resin was added into the mixture and stirred for 10-15 minutes (tip speed approx 5-15ft/s). Finally, ground pigment/color concentrate as per desired shade were added along with additives and stirred for 10-15 minutes at slow speed.

EXAMPLE 2

The product as obtained by Example 1 was subjected to tests for various performance parameters such as physical properties, chemical resistance, humidity resistance, flexibility, abrasion resistance, salt spray resistance etc., at the 3M India Ltd, Ahmedabad, India.

The following tables show the test and results conducted with the present rust preventive coating for the parameters mentioned above:

Physical properties:

Table 2

EXAMPLE 3

Chemical resistance Test:

Chemical resistance tests were performed as per ISO 15741-2001 [Conditioning of Test Panel as per Cycle B of ISO 15741; 4.3.2] Substrate: steel; condition at 18°C to 25°C and relative humidity < 80% until the coating is at least tack-free; dry for 30 minutes in a circulating-air oven at 150+/- 2°C; condition for a minimum of 30 minutes at 18°C to 25°C and relative humidity < 80% before testing.

Coating was done as below:

The panels which are 150 cm x 50 cm milled steel, surface free from oil and dirt (wiped by acetone) were coated with the present composition at 25 Microns DFT (Dry Film Thickness) x 2 coats (Total 50 microns). The 2nd coating was done after the surface was completely dried with the 1st coat. After the second coat was flashed off , the coated panel was heat cured for 30 minutes at 150°C (as per ISO 15741 Method described above).

After the curing is completed the panels were conditioned for 30 minutes at 18°C to 25°C and relative humidity < 80%) before testing and exposed to the chemicals listed in Table 3 and were observed at an interval of 24 Hrs.

The data obtained is listed in Table 3. Table 3:

EXAMPLE 4

Humidity resistance Test:

A test panel of 150 cm x 50 cm was coated with the claimed composition of the present invention at 25 microns DFT.

After drying for 7 days at ambient temperature (30°C +/-2°C) air drying or curing (heating 5+ Minutes at > 80°C) of the coating the coated panel it is subjected in humidity resistance chamber having 97% relative humidity and 50°C temperatures. Periodical observation were taken.

It was found that coating passes 800 Hrs of the test without any blistering or other defect. The data obtained is as illustrated in Table 4.

Table 4:

EXAMPLE 5

Abrasion resistance Test:

Abrasion resistance tests were conducted as per ASTM D 4060-10. This is a test method to determine resistance of organic coating to abrasion produced by Taber abraser to coating applied on a plane rigid surface. Briefly, abrasion resistance is calculated as loss in weight at a specified number of abrasion cycles, as loss in weight per cycle, or as number of cycles required to remove a unit amount of coating thickness. Abrasion of coating depends on abrasive type (CS-10, CS-17, H- 10 etc.), load applied and number of cycles abraded on the coating. For example, a coating can be tested by CS-17 wheel, 1 Kg of load and for 1000 cycles. Initial weight and final weight of the panel is taken calculated for loss of coating. RPM are kept as per electric supply either 72 +/- 2 r/min for 110v/60Hz or 60 +/- 2 r/min for 230v/50Hz.

For conducting the experiment a circular metallic disc of 100 mm diameter, 2 mm thickness was coated with the present composition at 25 microns DFT with spray application of the current composition of rust preventive coating.

The coated disc was cured at 120°C for 5 minutes.

The coating was tested for abrasion resistance after conditioning for minimum 30 minutes by keeping at 23 +/- 2°C.

Abrasion resistance testing was done at CS - 17 wheel, 1000 Cycles at 1 Kg Load. (Fig-1) Very high abrasion resistance observed > 50mg at CS - 17 wheel, 1000 Cycles. (Table 5)

Table 5:

EXAMPLE 6

Scratch resistance Test

A 50 x 150 mm panel taken from a 150 cm x 50 cm panel comprising milled steel, surface free from oil and dirt (wiped by acetone) was coated with present rust preventive coating by spray application method.

The coated panel was cured at room temperature of 23 +/- 2°C.

The cured panel was tested for scratch resistance after 7 days drying.

The coating passes > 2 Kg of load when tested for scratch resistance. (Fig-2)

EXAMPLE 7

Salt Spray resistance Test

Salt spray test was performed as per test method ASTM B 117. This practice (ASTM B 117) provides a controlled corrosive environment which has been utilized to produce relative corrosion resistance information for specimens of metals and coated metals exposed in a given test chamber (a salt fog chamber of 5% NaCl solution at 35°C).

It is an accelerated test method of evaluation of coating for corrosion resistance. A panel, which is a 150 cm x 50 cm milled steel, surface free from oil and dirt (wiped by acetone) is coated with the claimed rust preventive composition.

The coated cured/dried panel was subjected into a test chamber which remains at 35°C, with continuous salt fog of 5% Solution of Pure NaCl in distilled water.

The results obtained are tabulated in Table 6.

No corrosion observed up to 168 Hrs of the exposure in salt spray. (Fig-3 (a) & 3(b)).

Table 6:

EXAMPLE 8

Flexibility Test: As per ASTM D 522 -93a.

This test method covers the determination of the resistance to cracking (flexibility) of attached organic coatings on substrates of sheet metal or rubber-type materials.

The coating materials under test are applied at uniform thickness to panels of sheet metal or rubber-type materials. After drying or curing the coated panels are bent over a mandrel and the resistance to cracking of the coating is determined. There are two test methods under this, Test method 1, where the coated panels are bent over a conical mandrel and Test method 2, where the coated panels are bent over cylindrical mandrels of various diameters. Substrate of the test remains

0.8 mm cold rolled steel panel size as 100 mm x 150 mm.

The current coating composition passes at flexibility test (Test method 1 - cylindrical mandrel) when 7 days dried (23+/2°C), where the panel is subjected to this test at (0°C) as well as at room temperature (23+/2°C).

The above example clearly shows that the various components of the coating composition synergistically interact to give rise to a coating composition with the desired superior properties and most importantly the dual nature of behaving thermoplastic and thermosetting depending on different temperature exposure condition during application and use. The field trails proves the better stability and desired protective anti rust property of the composition.

Claims

We Claim:

1. A coating composition comprising a modified epoxy resin, a urea formaldehyde resin, an unmodified epoxy resin and a solvent.

2. The composition as claimed in claim 1 wherein the modified epoxy resin is present in an amount of 20% to 60%, a urea formaldehyde resin in an amount of 2% to 15%, an unmodified epoxy resin in an amount of 3% to 18%).

3. The composition as claimed in claims 1 and 2, wherein, the epoxy resin has a dual nature, behaving as thermoplastic or thermosetting depending upon the temperature exposures.

4. The composition as claimed in claims 1 to 3 wherein the modified epoxy resin is Diglycidyl ether Bisphenol A (DGEBA) based high molecular weight epoxy resin.

5. The composition as claimed in claims 1 to 4 wherein the modified epoxy resin has a molecular weight of about 15,000 to about 30,000.

6. The composition as claimed in claims 1 to 5 wherein the modified epoxy resin is soluble in solvents.

7. The composition as claimed in claim 6 wherein the solvents are selected from groups comprising aromatic hydrocarbons or ketonic or esters.

8. The composition as claimed in claim 1 wherein the unmodified epoxy resin is Diglycidyl ether Bisphenol A (DGEBA) based low molecular weight epoxy resin.

9. The composition as claimed in claims 1 to 8 wherein the unmodified epoxy resin is soluble in the solvents selected from aromatic hydrocarbons, alcohols, esters or ketones.

10. The composition as claimed in claims 1 to 9 wherein the butylated urea formaldehyde resin is soluble in solvents.

1 1. The composition as claimed in claim 10 wherein the solvents are selected from alcohols, esters, ketones, glycol ethers, aromatic hydrocarbons or chlorinated hydrocarbons.

12. The composition as claimed in claims 1 to 1 1 wherein it optionally comprises pigments or rheology additives.

13. The composition as claimed in claim 1 wherein the rheology additives is based on bentonite clay or modified urea.

14. A process for preparing the composition claimed in claim 1, wherein the process comprises: mixing of modified and unmodified epoxy resins and solvent or solvent mixture and urea resin in a variable speed disc dispenser and

adding ground pigment/color concentrate as per desired shade and optionally adding additives and stirring at a slow speed.

15. A process for preparing the composition as claimed in claim 14 wherein the process comprises mixing of:

weighed amount of modified and unmodified epoxy resins at a tip speed of about 2ft/s for 5- 10 minutes,

mixing weighed amount of solvent or solvent mixture at a tip speed of about 5-15 ft/s, stirring for 15-20 minutes,

adding urea resin at a tip speed of about 5-15ft/s,

mixing for 10-15 minutes in a variable speed disc dispenser,

adding ground pigment/color concentrate of desired shade along with optional additives, and stirring for 10-15 minutes at slow speed.

16. A process for applying the composition claimed in claim 1 comprising one of spray application, application by brush, and application by dipping.

17. An article coated with the composition as claimed in claim 1.