MXPA98009570A - Uretane healing agent, solid, finished in ether de vin - Google Patents

Abstract

The present invention relates to solid curing agents, vinyl enamel finishes, for powder coatings, can be prepared by the reaction of an aliphatic diisocyanate with a polyol and then with hydroxyvinyl ether, or by the reaction of an aliphatic polyisocyanate with hydroxy-vinyl jelly. Powder coatings, based on the curing agents, thus prepared, are extremely useful for coating substrates sensitive to heat, for exposure to ultraviolet light, heat, or ambient

Description

URETANE HEALING AGENT, SOLID, FINISHED IN VINYL ETHER Field of the Invention This invention relates to urethane curing agents, terminated in vinyl ether. More particularly, this invention relates to urethane curing agents, terminated in vinyl ether, which are derived from safe, non-hazardous materials, and which are non-crystalline solids at room temperature, to make possible their use in powder coatings. .

BACKGROUND OF THE INVENTION Vinyl ether-terminated urethane resins are extremely reactive prepolymers, which are known to undergo rapid polymerization when exposed to radiation. These compounds are particularly useful as curing agents in applications that require a high speed cure of a resin formulation, such as radiation curable coatings. Another disadvantage related to the use of these functionalized vinyl ether urethanes is that their commercial availability is relatively limited. In general, the available prepolymers constitute liquid or septisolids materials (with a glass transition temperature, Tg, extremely low). The patent of E. U. A., No. 4,751,273 (Lapin, et al.), Provides specific examples of such urethane resins, terminated in vinyl ether, liquid and semi-solid. These curing agents, while extremely useful in liquid coatings, radiation curable, have only limited use in powder coatings. Typically, due to their liquid or semi-solid state, they can not be used beyond a few percentages (< 5%) in powder coatings. Higher amounts typically cause the powder to form blocks or sinter during storage, which makes the powder non-sprayable during electrostatic coating operations. Solid urethane curing agents, terminated in vinyl ether, which are more conductive for use in powder coatings, radiation curable, have been proposed. For example, EP-A-0 636 669 (DSM, N.V.) provides an example of a vinyl ether functionalized crystalline curing agent which remains solid at room temperature (melting range 90-108se). This curing agent arises from the reaction of the hydroxybutyl vinyl ether (HBVE) with the hexamethylene diisocyanate monomer (HDI) in a molar ratio of 1: 1 (stoichiometric) of hydroxy to isocyanate groups. The reaction product is a crystalline, short chain urethane oligomer (HBVE-HDI-HBVE).

Another disadvantage with the use of a crystalline curing agent in powder coatings is that it makes the manufacture of powders extremely difficult. The powders, based on crystalline materials, take a long time to recrystallize, after the extrusion of the melt, making the grinding and subsequent handling very disordered and difficult. Another disadvantage with the use of this duration agent is that HDI is known to be unsafe to handle, due to its high toxicity. Thus, the presence of residual monomeric HDI (unreacted) in the curing agent will expose the end user to serious health hazards. For example, the HDI monomer has been known to cause skin sensitization, which can lead to serious respiratory diseases for workers, including asthma and permanent lung function decline. Likewise, the HDI monomer easily becomes airborne, due to its vapor pressure at room temperature which, in turn, increases the risk of inhaling its vapors or mists. It will be convenient to provide a urethane curing agent, finished in vinyl ether, which is solid at room temperature, easier to process in a melt, much safer to handle and effective in curing powder coatings.

Compendium of the Invention ThereforeIt is an object of this invention to provide a urethane curing agent, terminated in vinyl ether, which does not have the above drawbacks. It is another object of this invention to provide a urethane curing agent, terminated in vinyl ether, which is derived from safe and less hazardous monomers. Still another object of this invention is to provide a urethane curing agent, terminated in vinyl ether, which remains solid at room temperature. And yet another object of this invention is to provide a method for preparing urethane curing agents, terminated in vinyl ether, of the aforementioned character. Another object of this invention is to provide a urethane curing agent, finished in vinyl ether, which can be effectively incorporated in powder coatings, without degrading the stability and capacity of electrostatic spraying of the powder. Still another object of this invention is to provide a urethane curing agent, finished in vinyl ether, which is a non-crystalline material, obtain powder coatings based thereon, easier in its melt process and handling, during the manufacture of the powder. And yet another object of this invention is to provide a vinyl ether-terminated urethane curing agent that is extremely useful in curing powder coatings, particularly powder coatings that can be cured by exposure to radiation, heat, or both, and especially those that can be used to coat heat-sensitive substrates, such as wood and plastic, without causing permanent thermal damage to the substrate during cure. The various objects, features and advantages of this invention will become more apparent from the following description and the appended claims. Detailed Description of the Preferred Modes of the Invention This invention provides urethane prepolymers, terminated in vinyl ether, which are prepared from safer and less hazardous materials and which are non-crystalline solids at room temperature, to enable them They are extremely useful as curing agents in powder coatings. This invention also provides a method for the preparation thereof. Exposed broadly, the desired vinyl ether-terminated urethane curing agents of this invention can be prepared by reacting an aliphatic diisocyanate monomer with a polyol and then reacting the product obtained with a hydroxy-vinyl ether, or reacting -doing an aliphatic polyisocyanate with a hydroxy-vinyl ether. In this invention, the reagents are selected particularly from materials that are relatively safe and less dangerous to handle. Also, the reaction product which is obtained by any of the above preparation methods, will comprise vinyl ether-terminated urethane prepolymers, which are non-crystalline solids at room temperature or higher. In the first embodiment of the invention, the desired product is prepared by the two-step reaction sequence, in which the non-crystalline aliphatic diisocyanate monomer (with relatively low vapor pressure) is first reacted with a polyol that crystallizes or not , the resulting material is an adduct of the isocyanate with the polyol, and then this adduct, thus obtained, is further reacted with a hydroxy-vinyl ether for the terminal finishing of the adduct with a hydroxy-vinyl ether, the resulting material is a urethane prepolymer, solid, non-crystalline, finished in vinyl ether. The first reaction between the aliphatic diisocyanate monomer and the polyol can be seen as an addition reaction, where a diisocyanate adduct is formed with a polyol. The reaction conditions will be chosen in order to form a urethane oligomer, terminated in isocyanate, with the virtual exclusion of poly-alcohol-terminated materials.

The aliphatic diisocyanate monomers, which can be used in the first reaction, include those selected from materials that do not crystallize, have a vapor pressure lower than that of monomeric hexa-methylene diisocyanate (HDI) at room temperature (i.e. less than 0.011 mm Hg, at 252C), and preferably containing isocyanates with different reactivities. The inventors have thus identified only one material that meets the above criteria, which is the isophorone diieo cyanate (IPDI). Thus, in the preferred embodiment of the invention, isophorone diisocyanate (vapor pressure of 0.00048 mm Hg, at 252C) is employed in the first reaction. The polyols, which can be subjected to the first reaction include those selected from polyols that crystallize or not, although polyols that do not crystallize are preferred. Examples of suitable diols, useful herein, include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylethyl propanediol, neopentyl glycol ( 2, 2'-dimethyl-1,3-propanediol), 2-butyl-2-ethyl-1,3-propanediol (BEPD), 2-methyl-1,3-propanediol (MP diol), 1,2 -butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,3-isobutanediol, 1,2-isobutanediol, 2,3-butanediol, 2-butanediol (1,4), 2, 2, 4-trimethyl-1,3-pentane-diol, 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,4-cyclopentanediol, 1,6-hexanediol, 1,4-dimethoxy-cyclohexane, 1, 2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4'-methylene-bis (cyclohexanol), 4,4'-isopropylidene-bis (cyclohexanol), (bisphenol A hydro -genated), 1,4-bis (hydroxymethyl) cyclohexane, 1,3-bis (hydroxyethyl) -cciohexane, 1,3-bis (hydroxypropyl) cyclohexane, 1,3-bis (hydroxyisopropyl) cyclohexane, dodecanediol, xylene glycol , 4,4'-isopropylidene-diphenol (bisf enol A), adducts of bisphenol A / propylene oxide, adducts of hydroquinone / propylene oxide and adducts of hydroquinone / ethylene oxide. In the above embodiment of the invention, neopentyl glycol (NPG) is used in the first reaction. Reaction conditions that can be employed in the first reaction include temperatures in the approximate range of 75 to lOOsc. Care must be taken to control the exothermic reaction of the urethane. The reaction is also usually carried out in a moisture-free atmosphere, such as in a nitrogen atmosphere. It is also preferred that the reaction be carried out in the presence of a catalyst. A particularly preferred catalyst is that which contains tin, for example dibutyltin dilaurate. In the reaction, a stoichiometric amount in excess of the aliphatic diisocyanate is employed. In general, reagents are present in about 2: 1 to 2: 1.5 molar of the isocyanate to hydroxy groups. However, in the preferred embodiment of the invention, the reactants are present in a molar ratio of 2: 1 of the isocyanate to hydroxy groups. The first reaction can be illustrated by the following equation, in which the preferred reactants are reacted in the preferred molar equivalent proportions: The product obtained by the first reaction, which comprises the end-capped or isocyanate-terminated urethane oligomer, will subsequently be reacted in the second reaction with a hydroxy-vinyl ether for the end cap of the product, with ether groups. of vinyl and forms the desired non-crystalline solid vinyl ether-terminated urethane prepolymer. The hydroxy vinyl ethers that can be used to obtain the desired product include those prepared by any of the methods well known to those of ordinary skill in the art. The hydroxy vinyl ethers are usually prepared by the reaction of acetylene with polyols, at elevated temperatures, in the presence of a basic catalyst. Examples of hydroxyvinyl ethers that are commercially available and are useful here, include hydroxybutyl vinyl ether and hydroxyethyl vinyl ether. It will be understood that other hydroxy vinyl ethers can be used, such as, for example, those of the general formula CH 2 = CH-O-R-OH, where R is selected from the group of alkyl, aryl, alkaryl, aralkyl radicals , cycloalkyl and alkyl oxide, although n-butyl is preferred. Thus, in the preferred embodiment of the invention, the hydroxybutyl vinyl ether (HBVE), particularly the 4-hydroxybutyl vinyl ether, is used in the second reaction. The reaction conditions that can be employed in the second reaction are generally the same as those of the first reaction. Usually, this reaction will immediately follow the completion of the first reaction in the same reaction vessel. Care must be taken here to control the exothermic reaction well. In the preferred embodiment of the invention, the reagents are employed in equivalent stoichiometric amounts. Thus, the reagents are present in approximately a molar ratio of 1: 1 of the isocyanate to hydroxy groups, to ensure complete polymerization. The second reaction can be illustrated by the following equation, in which the preferred reactants are reacted in the preferred molar equivalent proportions: HO (CH,) 4 -0-CH = CH2 (II) The product obtained by the second reaction will be the final product of the solid urethane prepolymer, non-crystalline, terminated in vinyl ether, containing more than one diisocyanate in the polymer chain. This product can be semi-crystalline or amorphous, but more likely an amorphous, non-crystalline prepolymer is formed. As can be seen from the above equations I and II, the first reaction with the polyol serves to extend the chain of the final prepolymer product, since each hydroxy group available in the polyol will react with an isocyanate group and form a reactant finished in isocyanate of a higher molecular weight, for the second reaction. This urethane oligomer, terminated in higher molecular isocyanate, in turn, serves to form the higher molecular weight vinyl ether finished urethane product, which may remain solid at room temperature or higher. The desired product generally has a Tg greater than 202C and typically in the range of about 25 to 452C or more. Also, the use of the isocyanate-terminated urethane oligomer as a reactant in the second reaction, instead of a monomeric diisocyanate, reduces the amount of the residual diisocyanate monomer contained in the final product. While it is still probable that the reaction product obtained contains a certain amount of residual (unreacted) aliphatic diisocyanate monomer, the curing agent will still be relatively safe to handle and will present much lower health risks, since the monomeric diisocyanate material it is particularly selected for its relatively low vapor pressure at room temperature. The resulting vinyl ether-terminated urethane resins are, therefore, relatively safe, non-crystalline, solid at room temperature and are particularly suitable for curing powder coatings. In the second embodiment of the invention, the desired product is prepared by a final stage reaction reaction sequence of one stage, where an aliphatic, non-crystalline polyisocyanate (with relatively low vapor pressure) is reacted with a hydroxy-vinyl ether . The aliphatic polyisocyanates that can be used in the one-step reaction are selected from materials that do not crystallize and have a lower vapor pressure than monomeric HDI at room temperature. Examples of aliphatic polyisocyanates that meet the above criteria include functionalized polymers derived from IPDI, such as isocyanurates and uretdiones. In the preferred embodiment of the invention, the isocyanurate of isophorone diisocyanate (IPDI trimer) is employed in the reaction. The hydroxy vinyl ethers that can be used to obtain the desired product of the second embodiment include those mentioned above.

The reaction conditions that can be employed in the one-step reaction include temperatures not exceeding 110se. Care must be taken to control the exothermic reaction equally. The reaction is also usually carried out in a moisture-free atmosphere, such as a nitrogen atmosphere. It is preferred that the reaction be carried out in the presence of a catalyst, such as an organic tin catalyst, for example dibutyltin dilaurate. In the reaction, a stoichiometric equivalent amount of the reactants is employed. Thus, the reactants are present in a molar ratio of 1: 1 of the isocyanate to hydroxy groups, to ensure complete polymerization. The reaction of a stage can be illustrated by the following equation, in which the preferred reactants are reacted in the preferred proportions of the molar equivalents: (lll) The product obtained by this reaction will be the final product of the desired urethane, solid, non-crystalline, finished in vinyl ether prepolymer. This prepolymer can be semi-crystalline or amorphous, but more likely an amorphous prepolymer is formed.

The use of a polyisocyanate presents even lower risks to the end user, since the vapor pressure is lower than its monomeric counterpart. The resulting vinyl ether-terminated urethane resins are, therefore, relatively safe, as are non-crystalline, solid at room temperature t and are particularly suitable for curing powder coatings. The desired product generally has a Tg greater than 20 c and typically in the range of 30 to 50 C or greater. Powdered, clear or pigmented, non-sintered coatings, based on the aforementioned curing agents of this invention, can be easily prepared in a conventional process of melt extrusion and grinding. These powders can be formulated to cure, by any method known in the art. For example, powder coatings can comprise resins that form films, which can be entangled with solid vinyl ether urethane curing agents, when exposed to heat (eg, infrared or convection), radiation (e.g. of electron beams or ultraviolet), or both, depending on the type of healing initiator contained in the powder formulation. Particularly useful crosslinkable resins herein are those based on unsaturated polymers, such as unsaturated poly-esters and unsaturated poly (meth) acrylates.

Powder coatings, based on the curing agents of this invention, which include the healing aspect of both heat (e.g., the peroxide initiator) and radiation (e.g., photoinitiator) have been found especially suitable for coating substrates. sensitive to heat, since they can be completely cured at extraordinarily low temperatures, so as not to cause thermal damage to the substrate. Heat-sensitive substrates, coated with powder coatings, typically include hardwood, laminated bamboo, wood composites, such as particle board, electrically conductive particle board, fiber board, medium density fibreboard, Masonite boards and other substrates that contain a significant amount of wood, all of which are usually scorched, warped, gas-purified, or otherwise degraded, when coated and cured with traditional heat-curable powders, and also plastics , such as ABS, PPO, SMC, polyolefins, acrylics, nylons and other copolymers that will usually buckle or purge the gas, when coated and heat-cured with traditional heat-curable powders, like paper, cardboard and compounds and components with a heat sensitive appearance and the like. Heat-resistant substrates can also be coated with such powders, which include steel or other alloys in sheet metal form, reinforcing bars, pipe lines, cold spiral springs, and steel strips, as well as glass, ceramics, such as ceramic slabs, coal, graphite and the like. Also, powder coatings employing the curing agents of this invention surprisingly exhibit improved flexibility and adhesion to substrates after curing. It is believed that the polymeric nature of the curing agent serves to provide this advantageous effect. The invention will be further clarified by the consideration of the following non-limiting examples, which are intended to be purely exemplary of the invention.

EXAMPLE 1 Preparation of the Solid Urethane Prepolymer, Finished in Vinyl Ether The following ingredients were reacted in the given proportions, using a two-step reaction method (described in detail below) to form the solid ether-terminated urethane prepolymer. vinyl of this example.

The IPDI was charged in a 0.5 liter reaction vessel, equipped with stirrer, addition funnel, thermal torque controller and nitrogen spray inlet. Heating and stirring were initiated with the flow of nitrogen at the rate of 30-50 ml / min. , in the presence of the tin catalyst. When the temperature reached 75 ° C, a portion of the NPG (~ 25% by weight) was added to the pellet. A strong exothermic reaction took place, indicating the start of the urethane reaction. Care must be taken to control the exothermic reaction below 100C. After the exothermic reaction declined, the second, third and fourth portions of the NPG were added in several hours, while controlling the exothermic reaction after each addition. The adduct had a free isocyanate content (% NCO) of 15.6% (15.3% of the theory). At this point the HBVE was slowly added through the addition funnel at the rate of 3-5 ml (min) During the addition, a strong exothermic reaction took place, care must be taken to prevent the exothermic reaction from exceeding 100 seconds. After the addition was complete, the mixing was continued until the percent of the free NCO was below 0.3% Finally, the resin was discharged, cooled, milled and then packed.The coated product comprised a non-crystalline amorphous material, the which is solid at room temperature and had a Tg of about 252c and a molecular weight of 800 g / mol (theoretical).

Example 2 Preparation of the Double Healing Powder Coating The following ingredients were mixed together in a given manner, to form a pigmented powder coating, which can be cured by exposure to combined heat and UV radiation, and which was found particularly suitable for coating heat sensitive substrates.

The unsaturated polyester XP 3125 is an unsaturated, solid-functional, semi-crystalline, acid-functional polyester resin based on fumaric acid, terephthalic acid and 1,6-hexanediol sold by DSM Resins. The photoinitiator Lucerin TPO is a photoinicer based on 2,4,5-trimethyl-benzoyldiphenyl-phosphine oxide sold by BASF. The Irgacure 184 photoinitiator is an aryl ketone, based on 1-hydroxycyclohexyl-phenol-ketone, sold by Ciba Additives. The peroxide initiator Lupersol 231XL is a peroxy-ketal thermal initiator based on 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane sold by Elf Atochem. Resiflow P-67 is an acrylic flow aid, sold by Estron Chemical. TiPure R-902 is a white titanium dioxide pigment, sold by Du Pont.

The powder coating was electrostatically cured with a triboelectric gun on a 1.27 cm thick medium density fibreboard (MDF), which was preheated with quartz infrared (IR) lamps at about 93-1212C. The coated board was heated then with quartz IR lamps at about 2042C for about 40 seconds, to melt and flow the powder into a molten film to initiate thermal curing. Immediately after the flow to the outside, the molten film was passed under two ultraviolet (UV) lamps of 600 watts V / H, at 6.1 meters / minute, for about a total of 1 second, to initiate UV curing. The cured powder coating exhibited the following properties in the MDF.

MEC = methyl ethyl ketone Example 3 Preparation of the solid urethane prepolymer, terminated in vinyl ether The following ingredients were reacted in the given proportions, using a one-step reaction method (described in detail below) to form the prepolymer of solid urethane, finished in vinyl ether, of this example. 1 The IPDI trimer, T-1890, is a trimer of isophorone diisocyanate, sold by Hiils.

The HBVE was charged to a 0.5 liter reaction vessel, equipped with agitator, addition funnel, thermal torque controller and nitrogen spray inlet. The IPDI trimer was added slowly with gentle stirring. After the addition, the stirring was continued with moderate heat application (the maximum temperature does not exceed 60se) until all the IPDI trimer was dissolved. After dissolution, the temperature rose slowly to 100 ° C. The reaction mixture was then allowed to react for 2-3 hours. At this time, the temperature decreased to 70-75se and 0.075 g (0.02% by weight) of the dibutyltin dilaurate catalyst was added to the reaction mixture. Care must be taken to control the exothermic reaction below 110se. The mixture was continued until the percentage of free NCO was below 0.5%. Finally, the resin was discharged, cooled, ground and then packed. The recovered product comprised a non-crystalline amorphous material, which was solid at room temperature and had a Tg in the approximate range of 30-352C and a Tg of about 50-552C. From the foregoing, it will be seen that this invention is well adapted to obtain all the purposes and objects indicated above, together with the other advantages that will be evident and inherent. Since many possible variations of the invention can be made, without departing from its scope, the invention does not intend to be limited to the disclosed embodiments and examples, which are considered to be purely exemplary. Therefore, reference should be made to the appended claims to assess the true spirit and scope of the invention, in which exclusive rights are claimed.

Claims (22)

1. CLAIMS 1. A urethane prepolymer composition, solid, non-crystalline, terminated in vinyl ether, which has the chemical formula:
2. 2 . The composition of claim 1, having an amorphous microstructure.
3. 3. The composition of claim 1, which has a glass transition temperature (Tg) in the approximate range of 25 to 45 ° C.
4. 4. A solid, non-crystalline urethane prepolymer composition, terminated in vinyl ether, comprising the reaction product of a hydroxy vinyl ether with an adduct obtained by the reaction of a non-crystalline aliphatic diisocyanate monomer, with a crystalline polyol or not crystalline.
5. 5. The composition of claim 4, wherein the aliphatic diisocyanate has a vapor pressure less than about 0.011 mm Hg, at 25 c.
6. 6. The composition of claim 4, wherein the aliphatic diisocyanate comprises the isophorone diisocyanate.
7. 7. The composition of claim 6, wherein the hydroxy vinyl ether comprises the hydroxybutyl vinyl ether.
8. 8. The composition of claim 7, wherein the polyol is a non-crystalline polyol.
9. 9. The composition of claim 8, wherein the polyol comprises neopentyl glycol.
10. 10. The composition of claim 9. wherein the aliphatic diisocyanate, polyol and hydroxy-butyl-vinyl ether is reacted in an amount of about 2: 1: 1 molar equivalents.
11. 11. A method for the preparation of a solid, non-crystalline, vinyl ether-terminated urethane prepolymer, comprising reacting about 2 molar equivalents of a non-crystalline aliphatic diisocyanate monomer, having a vapor pressure of less than about 0.011 mm of Hg, at 252C, with about 1-1.5 molar equivalents of a crystalline or non-crystalline polyol, and then reacting the obtained product with about 1 molar equivalent of a hydroxyvinyl ether, and recovering the urethane prepolymer, solid , not crystalline, finished in vinyl ether.
12. 12. The method of claim 9, wherein the aliphatic diisocyanate comprises the isophorone diisocyanate, the polyol comprises the non-crystalline neopentyl glycol and the hydroxy vinyl ether comprises the hydroxybutyl vinyl ether.
13. 13. A solid, non-crystalline urethane prepolymer composition, terminated in vinyl ether, having the chemical formula:
14. 14. The composition of claim 13, which has an amorphous microstructure.
15. 15. The composition of claim 13, which has a glass transition temperature in the approximate range of 30 to 50se.
16. 16. A solid, non-crystalline urethane prepolymer composition, terminated in vinyl ether, comprising the reaction product of a hydroxy-vinyl ether with a non-crystalline aliphatic polyisocyanate.
17. 17. The composition of claim 16, wherein the aliphatic polyisocyanate has a vapor pressure less than about 0.011 mm Hg, at 252C.
18. 18. The composition of claim 16, wherein the aliphatic polyisocyanate comprises a trimer of isophorone diisocyanate.
19. 19. The composition of claim 17, wherein the hydroxy vinyl ether comprises the hydroxybutyl vinyl ether.
20. 20. The composition of claim 19, wherein the aliphatic polyisocyanate and the hydroxybutyl vinyl ether are reacted in equivalent stoichiometric amounts.
21. 21. A method for the preparation of a solid, non-crystalline, vinyl ether-terminated urethane prepolymer, which comprises reacting stoichiometric equivalent amounts of a non-crystalline aliphatic polyisocyanate, having a vapor pressure of less than about 0.011 mm Hg, a 252C, with a hydroxy-vinyl ether, and recover the resulting solid, non-crystalline, vinyl ether-terminated urethane prepolymer.
22. 22. The method of claim 21, wherein the aliphatic polyisocyanate comprises a trimer of isophorone diisocyanate and the hydroxyvinyl ether comprises the hydroxybutyl vinyl ether.