WO2019068531A1

WO2019068531A1 - Method and composition for rotational casting of polyurethane coating layer

Info

Publication number: WO2019068531A1
Application number: PCT/EP2018/076088
Authority: WO
Inventors: Gerald King; Enrico FRESCHI; Cesare Santucci; Stefania Nardin
Original assignee: Lanxess Solution Italia S.R.L.
Priority date: 2017-10-02
Filing date: 2018-09-26
Publication date: 2019-04-11
Also published as: IT201700109802A1

Abstract

The addition of a small amount of a diaminocyclohexane to a polyurethane prepolymer curing composition or a curative composition used in preparing the polyurethane prepolymer curing composition creates a polyurethane reaction mixture with properties, e.g., thixotropic properties that that are surprisingly beneficial for coating substrates using rotational casting processes.

Description

Method and Composition for Rotational Casting of Polyurethane Coating Layer

The present invention provides a polyurethane prepolymer curing composition that allows for thicker polyurethane layers to be produced during a single pass when using a rotational casting process to coat a substrate, e.g., a cylindrical substrate, an improved process for rotational casting of thick polyurethane coating layers during a single coating pass, a curative composition useful in the process, a polyurethane layer produced thereby, and an article coated by the inventive composition.

BACKGROUND

Methods for coating various substrates are known, e.g., conventional casting techniques, spray techniques, drawdowns, etc. Rotational casting techniques have been employed for coating polyurethane elastomer compositions onto substrates, typically cylindrical substrates. Several advantages are associated with this method over other known coating methods, for example, the rotational casting method requires shorter production time, no mold is needed and in general no mold is used, and the loss of materials by, e.g., overspraying, is avoided.

Ruprecht et al., "Roll Covering by Rotational Casting with Fast-reacting PUR Systems", Polyurethanes World Congress 1991 (Sep. 24-26) pp. 478-481 , describes rotational casting techniques useful for producing roll coverings using fast-reacting polyurethane elastomer systems. In these systems, the polyurethane reaction mixture is metered through a movable mixing head which travels at constant speed in the axial direction along a rotating roll core a short distance above its surface. The polyurethane reaction mixture solidifies very quickly (in a matter of seconds), to produce a polyurethane coating with a thickness buildup of 4 to 5 mm. Additional layers of the polyurethane reaction mixture are applied until the desired thickness of polyurethane coating is achieved.

Rotational casting reduces the number of steps involved in roll coating, and methods and equipment have been reported that are said to allow for the application of thicker coating layers, e.g., US Pat. 5,601 ,881 , which discloses the use of a sheet die, and US Pat Pub 2004/0091617, which discloses a die that divides a coating inlet stream into a plurality of outlet streams. However, even with these newer methods and apparatus, there are still rigorous demands on the coating composition used. For example, if a polyurethane reaction mixture gels too slowly, the polyurethane coating will drip off the roll. If the polyurethane reaction mixture is formulated l to gel quicker, the polyurethane can gel in the head of the mixer or cause ridges or other imperfections in the coating layer. Such problems can cause the process to be shut down while the equipment is cleaned, which can lead to other surface problems and increase the cost of the operation.

US Pat. 5,895,806, incorporated herein by reference, discloses a polyurethane prepolymer composition containing dual thixotropic agents and US Pat. 5,895,609, also incorporated herein by reference, discloses a rotational casting method for coating a cylindrical object employing the polyurethane prepolymer composition of the '806 patent. Using the composition containing dual thixotropic agents, a thicker coating was achieved per each pass without any dripping or ridging. These polyurethane coating compositions have found wide commercial use on rigid substrates, e.g., metals, plastics and composites, in areas such as, for example, paper and steel mill rolls, industrial rolls and graphic art printing rolls.

US Pat 6,747,1 17, incorporated herein by reference, discloses a composition useful for rotationally casting cylindrical parts comprising an isocyanate-terminated polyurethane prepolymer and a curative agent comprising a polyaspartic ester, typically as part of a co- curative system along with compounds selected from aromatic diamines and diols.

US Pat. 5,601 ,881 , incorporated herein by reference, discloses the use of a sheet die that is disposed parallel to the axis of rotation of the substrate at a selected angle, whereby the rate of reaction of the reaction mixture and the relative movement are synchronized with the circumferential speed of the rotating body in such a way that the successive convolutions overlay in the form of scales and connect together seamlessly to allow for the application of thicker coating layers. However, problems are associated with the use of a sheet die. For example, differences in flow rate across the outlet can arise from channeling of flow in various areas caused by partial plugging, or viscosity increase in one area of the die, resulting in the lower viscosity, fresher material taking the path of least resistance around this area. As a result, flow becomes less even and production must eventually be stopped to clean the die.

US Pat Pub 2004/0091617, incorporated herein by reference, discloses a rotational casting method and device for producing thicker layers that makes use of a die having an applicator surface and an internal network of branched channels for dividing the stream of polymeric reaction mixture into multiple streams that are conveyed through a plurality of respective outlet channels to the applicator surface. This process using a plurality of smaller outlet streams can overcome many challenges found in the use of the wider outlet stream of a sheet die, but challenges still remain in finding a polyurethane coating composition meeting all the required viscosity and cure parameters.

US Pub Pat Appl. 20140213741 , i.e., co-pending Appl No. 14/107,044, discloses polyurethane prepolymer curing compositions comprising MDI prepolymers with low free MDI content and curatives of known rotational casting formulations that provide polyurethane resins and products with improved mechanical properties when used in rotational casting.

Improvements in rotational casting polyurethane coating compositions are still needed in order to consistently form a thicker, high quality polyurethane elastomer layer, e.g., greater than 5 mm or 10 mm thick, in a single rotational casting pass. Despite the many rotational casting methods and compositions available, new compositions and methods are needed to improve the speed and quality of the polyurethane coatings obtained. For example, the ability to consistently prepare thicker polyurethane films in a single pass, without having to stop, e.g., to clean out the ejection ports, would reduce time and costs in manufacturing. Thus, rotational casting method and/or composition that would allow for producing layers as thick as possible that can make use of known rotational casting apparatus are highly desirable.

It has been found that adding a small amount of a diaminocyclohexane, e.g., 1 ,2- diaminocyclohexane to a polyurethane reaction mixture provides exceptional and unexpected advantages for compositions used in rotational casting processes. While diaminocyclohexanes are known in the art, compositions of the invention comprising e.g., 1 ,2-diaminocyclohexane have not been used in the preparation of thick polyurethane elastomer layers, e.g., 20, 30, 40 mm thick or greater, using a single pass rotational casting process.

SUMMARY OF THE INVENTION

The present invention provides a method for coating a substrate, including but not limited to a cylindrical substrate, with one or more polyurethane layers, which method makes use of known rotational casting techniques, typically without the use of a mold, and a polyurethane reaction mixture comprising an isocyanate terminated prepolymer, more than one prepolymer may be used, and a particular curative composition that comprises a polyol and a cyclical diamine, e.g., a diaminocyclohexane, in particular 1 , 2-diaminocyclohexane, the use of which allows for the formation of thicker polyurethane layers from a single rotational casting pass. In the present discussion, the curative composition is generally described as a discreet entity which is added as such to a prepolymer composition. In many embodiments this is in fact true, as it is a very efficient way to blend the components of the polyurethane reaction mixture when using one of the many known rotational casting apparatus. However, in other embodiments of the invention, any of the various components of the polyurethane reaction mixture can be added as a single component or as a part of a mixture comprising one or more of the other components of the polyurethane reaction mixture

Rotational casting apparatus of various types are known in the art and many of these can be used in the present method. In general, rotational casting comprises rotating a substrate about an axis at a selected rotational speed, applying a polymeric reaction mixture to a surface of the rotating substrate by ejecting the polymeric reaction mixture through an outlet, e.g., an ejection port in a die, at a selected flow rate, and effecting relative linear movement between the rotating substrate and the outlet in a direction parallel to the axis of rotation of the substrate. In general no mold is required and in present invention no mold is required and generally not used.

The polyurethane reaction mixture comprises:

A) an isocyanate terminated prepolymer prepared by reacting a polyol, typically a diol, with a polyisocyanate, typically a di-isocyanate, and

B) a mixture comprising one or more polyols, a diaminocyclohexane, optionally one or more polyamines e.g., aromatic polyamines, and optionally a catalyst, and in some embodiments, other components common in the art may also be present.

In many embodiments of the invention, B) comprises two or more polyols, e.g., B) often comprises a first polyol and a second polyol different from the first polyol, wherein the first polyol has a Mn of 250 or greater and the second polyol has a Mn of less than 400. For example, the first polyol may have a MN of 400 or greater, often 600 or greater and the second polyol has a Mn of less than 400 and often less than 250.

Component B) represents the elements of the curative composition. The ratio of component A) to the total amount of the mixture of component B) will vary depending on the desired characteristics of the polyurethane being produced and the exact materials being used, which ratio can be determined by means well known in the art in light of the present disclosure. In general, the total active hydrogen content of the curative is equal to about 80-1 15%, e.g., 95 to 105%, of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer.

For example, in one embodiment the curative composition comprises, based on the combined weight of i), ii), iii) and iv) :

i) 35 wt% to about 97 wt%, e.g., 50 to 97wt% of one or more polyols, typically two or more polyols, typically a first polyol having a number average MW (Mn) of 250 or greater, e.g., 400 or greater or600 or greater, and a second polyol different from the first polyol having anMN ofless thamn 400, e.g., less than 250,

ii) 0 to 60 wt%, e.g., 0.5 to 60 wt% or 0.5 to 45 wt% of one or more aromatic polyamines, typically wherein at least one aromatic polyamine is a diamine,

iii) 0.5 to 10 wt%, e.g., 1 to 7 wt%, of a diaminocyclohexane, e.g., 1 , 2-diaminocyclohexane, and iv) 0 t o1 wt%, e.g., 0.001 to 0.5 wt% of a catalyst.

Given that the elements of component B), i.e., curative composition, is blended with a significant amount of prepolymer in the preparation of the polyurethane reaction mixture, the amount of 1 , 2-diaminocyclohexane in the polyurethane reaction mixture is generally from about 0.1 to about 5 wt%, typically from about 0.25 to about 3.5 wt%, and often from about 0.3 to about 1 .5 wt%, based on the total weight of the prepolymer, polyol, diaminocyclohexane, aromatic amine and catalyst present in the polyurethane reaction mixture.

The present method using the curative of the invention can be used to prepare a polyurethane layer of greater than 5 mm or 10 mm or more, e.g., 15, mm, 20mm, 25 mm, 30 mm or more, in a single rotational casting pass, and in some embodiments polyurethane layers up to 40 mm, 50 mm or greater are prepared.

In addition to the rotational casting coating method of the invention, embodiments include the curative composition, the polyurethane reaction mixture, the polyurethane layer produced according to the method, and a substrate coated with a polyurethane layer according to the invention.

In the present application, the indefinite article "a" or "an" refers to one or more than one unless otherwise noted. DESCRIPTION OF THE INVENTION

In the present invention, the components of the polyurethane reaction mixture, e.g., the isocyanate terminated prepolymer and the curative composition, are mixed shortly before application to the substrate. This typically occurs in a mixing head, e.g., a metered mixing head, after which the mixture is sent as a stream under pressure to an inlet of the die comprising the outlet port or ports through which the polyurethane reaction mixture is ejected onto the substrate.

As the reaction mixture is applied to the rotating substrate, a relative linear movement between the rotating substrate and the outlet is effected in a direction parallel to the axis of rotation of the substrate. Therefore, each turn of the substrate produces a helical convolution of the reaction mixture, i.e., coating composition, that is slightly offset but typically in overlapping contact with the previous convolution. In this manner, the coating can be advanced linearly along the surface of the substrate as the relative translational movement of the die progresses. In the present disclosure, a "rotational casting pass" or "coating pass" is one complete linear transversal of the rotating substrate by the die or coating outlet in a direction parallel to the axis of rotation. The polyurethane reaction mixture is selected and mixed so as to have a reaction rate slow enough so that successive convolutions of applied coating material meld together seamlessly, but fast enough so that the coating hardens soon thereafter.

The polyurethane reaction mixture can begin reacting immediately upon mixing, which is expected to cause the viscosity of the polyurethane reaction mixture to rise. The reaction mixture needs to be discharged from the die while the viscosity is relatively low and the mixture flows well, e.g., a viscosity (Brookfield) ranging from about 100 centipoise (cps) to about 5,000 cps. A liquid reaction mixture with this low viscosity typically allows for only a relatively low thickness (such as the 4-5 mm disclosed in Ruprecht et al.) to be applied without dripping. Rapid curing of the reaction mixture will cause rapid thickening of the mixture and possibly allow for thicker layers, but this can also lead to clogging of the ejection ports. The multi-port die of US Pat Pub 2004/0091617 is designed to allow for a flow viscosity of the reaction mixture ranging from about 5,000 cps to about 500,000 cps, but not all the difficulties in preparing rotationally cast layers over 10, 20 or 30 mm thick are overcome by using these apparatus while also using existing polyurethane reaction mixtures.

The present method makes use of the discovery that adding a small amount of a diaminocyclohexane, in particular 1 ,2-diaminocyclohexane, to the polyurethane reaction mixture or curative composition used in rotational casting formulations not only overcomes many of the difficulties regarding viscosity, cure rate, etc., without encountering problems associated with overly fast curing, overly slow curing, control of the coating composition flow rate, etc., but also allows one to prepare thicker polyurethane coating layers without adversely effecting surface characteristics or obstructing the ejection outlet of the apparatus via clogging, etc. The composition is particularly useful in the production of thicker layers, e.g., 20mm, 30 mm, 40 mm or thicker, the production of which is typically facilitated by using rotational casting apparatus comprising a sheet die, such as described in US Pat. 5,601 ,881 , or a multi-outlet die, such as described in US Pat Pub 2004/0091617.

The presence of 0.5 to 10 wt%, often from 0.5 to 3.0 wt%, of 1 ,2-diaminocyclohexane in a curative composition, based on the weight of the total curative composition, provides a curative and a polyurethane reaction mixture composition that are extremely well suited for use in rotational casting methods due to the unexpectedly large and highly beneficial thixotropic effects. That is, while under physical stress, e.g., shear in the mixing head and die, the polyurethane reaction mixture prepared according to the invention by, e.g., mixing the curative composition with a prepolymer, maintains a low viscosity and acceptable flow rate, but when ejected onto the surface of the substrate to be coated, the viscosity increases dramatically. This change in viscosity is greater than seen with other known thixotropic amines and allows for thicker films to be prepared in a single rotational casting pass. In many embodiments of the invention, a single polyurethane layer, produced in a single pass, is thick enough to serve as the final coating product without the addition of additional layers. It has also been noted that the temperature of the composition formed by mixing the curative composition with the prepolymer does not rise as quickly inside the mixing head and die as is seen with compositions lacking the diaminocyclohexane.

One general embodiment of the invention provides a rotational casting method for coating a substrate with one or more layers of polyurethane elastomer, comprising mixing an isocyanate terminated prepolymer with a curative composition of the invention comprising a polyol and 1 ,2- diaminocyclohexane to form a polyurethane reaction mixture; ejecting the polymeric reaction mixture as an outlet stream through an outlet, e.g., one or more outlet port in a die, at a selected flow rate onto a substrate rotating about an axis at a selected rotational speed; and effecting relative linear movement between the rotating substrate and the outlet in a direction parallel to the axis of rotation of the substrate. The relative linear movement and the rate of reaction of the reaction mixture are typically synchronized with the circumferential speed of the rotating body in such a way that successive convolutions of the outlet streams of the polymeric reaction mixture overlap and meld together seamlessly.

For example:

A method for coating a substrate comprising:

I) rotating the substrate about an axis at a selected rotational speed; II) applying a polyurethane reaction mixture to a surface of the rotating substrate by ejecting the polymeric reaction mixture through a die comprising one or more ejection ports at a selected flow rate, wherein the polyurethane reaction mixture comprises

A) an isocyanate terminated prepolymer prepared by reacting a polyol with a polyisocyanate; and

B) a mixture comprising, based on the total weight of components i, ii, iii and iv:

i) from about 35 wt% to about 97 wt%, of two or more polyols, comprising a first polyol and a second polyol different from the first polyol, wherein the first polyol has a Mn of 250 or greater the second polyol has a Mn of less than 400,

ii) from 0 to about 60 wt%, e.g., about 0.5 to about 60 wt% of one or more aromatic polyamines, wherein at least one aromatic polyamine is a diamine, iii) from about 0.5 to about 10 wt.% of a diaminocyclohexane, and

iv) 0 to about 1 wt%, e.g., about 0.01 to about 0.5 wt% of a catalyst, wherein A and B are present in amounts so that the mixture of B has a total active hydrogen content that is equal to about 80-1 15% of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer of A; and

III) effecting relative linear movement between the rotating substrate and the die in a direction parallel to the axis of rotation at a selected relative linear speed, wherein the reaction mixture flow rate, the relative linear speed and the rotational speed are synchronized in such a way that successive convolutions of the outlet streams of the polymeric reaction mixture overlap and meld together seamlessly.

The process of the invention can provide in a single coating pass, i.e., one complete linear transversal of the rotating substrate in a direction parallel to the axis of rotation, a polyurethane layer of from 1 to 100 mm thick, e.g., 2 to 80 mm, 2 to 50 mm, 5 to 45 or 50 mm, or 10 to 45 mm thick, with excellent physical and surface characteristics onto the rotating substrate, although multiple layers can be applied to the substrate by consecutive coating passes as known in the art. No mold is required in the process and in general no mold is used.

In one embodiment the polyurethane reaction mixture is ejected through a sheet die having an outlet in the form of a slit so that the reaction mixture is expelled in the form of a sheet-like stream, which slit may have a length to width ratio of 10 to 300, e.g., 100 to 250.

In one embodiment the polyurethane reaction mixture is ejected through a die that divides the polyurethane reaction mixture into a plurality of outlet streams, e.g., 2 to 32 streams often from 3 to 16 streams, that are ejected onto the substrate through a plurality of outlet ports that are spaced apart from each other such that the outlet streams flow together seamlessly after application to the substrate.

Each step of the process occurs at temperatures from 10 to 120°C, however, different temperatures may be employed for each individual processing step. Elevated temperatures may be needed in order to feed the polyol or curative into the mixing head, the reaction to form the polyurethane may produce heat and raise the temperature of the reaction mixture before or after application to the substrate. In the present invention, use of the invention curative often allows the curative and prepolymer to be mixed and transported through the outlet without a significant increase in temperature.

Particular embodiments of the invention relate to particular curative compositions and polyurethane reaction mixtures comprising an isocyanate terminated prepolymer and the curative composition. In certain particular embodiments the curative composition comprises, based on the total weight of components i, ii, iii and iv:

i) from about 35 wt% to about 97 wt%, of two or more polyols, comprising a first

polyol and a second polyol different from the first polyol, wherein the first polyol

has a Mn of 250 or greater the second polyol has a Mn of less than 400,

ii) from 0.5 to about 60 wt% of one or more aromatic polyamines, wherein at least one aromatic polyamine is a diamine,

iii) from about 0.5 to about 10 wt.% of a diaminocyclohexane, and

iv) 0 to about 1 wt% of a catalyst,

For example, the curative composition above wherein the first polyol has a Mn of 400 or greater or a Mn of 600 or greater, or the curative wherein the first polyol has a Mn of 250 or greater, 400 or greater or 600 or greater and the second polyol has a MN of less than 250.

In some embodiments the curative comprises:

i) from about 50 wt% to about 97 wt% of the two or more polyols,

ii) from 0.5 to about 45 wt% of the one or more aromatic polyamines,

iii) from about 1 to about 5 wt.% of 1 , 2-diaminocyclohexane, and

iv) from about 0.01 to about 0.5 wt% of the catalyst.

Other optional materials may also be present in the curative composition, e.g., other amines such as aliphatic polyamines, thixotropic colloidal additives such as fumed silica, clay, bentonite, and talc. When used to prepare layers that are over 5 mm thick, e.g., 10mm, or 20 mm thick or greater, fillers and reinforcing agents such as particles, microspheres and fibers such as glass microspheres, hollow glass microspheres, glass fibers coarse-meshed fabric tapes, glass-fiber rovings, wires and the like may be incorporated into the polyurethane reaction mixture, e.g., by adding them to the polyol or the curative composition.

The diaminocyclohexane of the curative composition is typically 1 , 2-diaminocyclohexane and in general, the benefit of adding 1 , 2-diaminocyclohexane levels off at levels above 5 wt%, often above 3 wt%. That is, while more 1 , 2-diaminocyclohexane can be added, the beneficial thixotropic effect above 5 wt%, and often above 3 wt%, is not significantly greater than that observed at 5 wt% or 3 wt%. A benefit can be observed upon addition of a small amount of 1 , 2- diaminocyclohexane, however, in general, at least 0.5 wt% of 1 ,2-diaminocyclohexane is used in order to provide an effect large enough to be valuable in the present invention. In certain embodiments, 1 , 2-diaminocyclohexane is present at 1 wt% or more, e.g.,1 .5 wt% or more, 1 .75 wt% or more, and in various embodiments, ranges of from 1 .0 to 5 wt%, 1 .5 to 5 wt%, 1 .75 to 5wt% of , 1 , 2-diaminocyclohexane are employed, e.g., 1 .5 to 3 wt%, 1 .75 to 3 wt%, 2 to 5wt% or 2 to 3 wt%.

Polyols useful in the curative include a variety of diols, triols and tetrols including:

alkyl or alkenyl diols, triols and tetrols, such as ethane diol, propane diol, butane diol, cyclohexane dimethanol, neopentyl glycol, trimethylol propane, pentaerythritol and the like;

amine containing diols and triols, such as diethanolamine, triethanolamine, dipropanolamine, tripropanolamine, di-isopropanolamine, tri-isopropanolamine, dibutanolamine, and the like;

ether diols such as diethylene glycol, dipropylene glycol, dibutylene glycol, triethylene glycol, hydroquinone-bis-hydroxyethyl ether;

polymeric polyols, including polyols often used to prepared prepolymers, such as polyethylene glycols, polypropylene glycols, polytetramethylene glycols, polyester glycols, polycaprolactone glycols, polycarbonate glycols, co-polyester glycols, and the like.

Polyols of the curative composition having a Mn of 400 or greater or 600 or greater are often selected from the polymeric polyols above and in certain embodiments, polyether polyols such as, polyethylene glycols, polypropylene glycols, polytetramethylene glycols etc.

In many embodiments the polyol comprises a higher Mn polyol, e.g., Mn of 400, 600 or greater, and a lower Mn polyol, e.g., Mn of 400, 300, 250 or less. In many embodiments the higher Mn polyols are diols, while the lower Mn polyols may comprise diols, triols and/or tetrols. In some embodiments, the lower Mn polyol comprises a triol or a tetrol, e.g., triols or tetrols having a Mn of less than 250, such as neopentyl glycol, trimethylol propane, pentaerythritol, triethanolamine, tripropanolamine, tri-isopropanolamine, and the like. In general, the majority, i.e., more than 50 wt%, of all polyols in the curative composition are diols, often 75, 80, 85, 90, 95 wt% or more are diols.

For example, in certain embodiments, the one or more polyol of the curative comprises:

a polyether diol having a Mn of 250 or greater and a diol, triol or tetrol having a Mn of less than 250; a polyether diol having a Mn of 400 or greater and a diol, triol or tetrol having a Mn of less than 400, such as 250 or less; or

a polyether diol having a Mn of 600 or greater and a diol, triol or tetrol having a Mn of less than 400, such as 250 or less.

In many such embodiments, the diol, triol or tetrol having a Mn of less than 400, or 250 or less, comprises a triol or tetrol, often a triol.

In many embodiments the curative composition of the invention comprises one or more aromatic polyamines, typically aromatic diamines such as methylenedianiline, phenylene diamines, 4,4'- methylene-bis(3-chloroaniline), 4,4'-methylene-bis(3-chloro-2,6-diethylaniline), diethyl toluene diamine (DETDA), tertiary butyl toluene diamine (TBTDA), dimethylthio-toluene diamine, trimethylene glycol di-p-aminobenzoate, 1 ,2-bis(2-aminophenylthio)ethane, 4,4'-methylene bis(2- chloroaniline), 2,2',5-trichloro-4,4'-methylene-diamine, naphthalene-1 ,5-diamine, , toluene-2,4- diamine, dichlorobenzidine, diphenylether-4,4'-diamine, e.g., methylenedianiline, 4,4'-methylene- bis(3-chloroaniline), 4,4'-methylene-bis(3-chloro-2,6-diethylaniline), diethyl toluene diamine (DETDA), tertiary butyl toluene diamine (TBTDA), dimethylthio-toluene diamine, 1 ,2-bis(2- aminophenylthio)ethane or toluene-2,4-diamine. In certain embodiments the curative composition comprises diethyl toluene diamine (DETDA) and/or dimethylthio-toluene diamine.

Typically a catalyst is present in the curative compositions at typical catalysts levels. The catalyst may be any known in the art for catalyzing the reaction of isocyanate terminated prepolymers with polyols or polyamines.

For example, in certain particular embodiments the curative composition comprises:

i) from about 35 wt% to about 97 wt%, e.g., from about 45 to about 97wt%, based on the total weight of the curative mixture, of two or more polyols wherein at least one polyol has a number average MW (Mn) of 400 or greater or 600 or greater, e.g., PTMEG, and at least one polyol has a number average MW (Mn) of less than 250 or less, e.g., trimethylol propane or tri-isopropyl amine, ii) from 0.5 to 60 wt%, e.g., from 0.5 to 45 wt%, of one or more aromatic diamines,

iii) from 1 to 5 wt% e.g., from 1 .5 or 1 .75 to 3 wt%, of 1 ,2-diaminocyclohexane, and

iv) from 0 to 1 wt%, e.g., from 0.001 to 0.5 wt% of a catalyst. The prepolymer of the invention is prepared by reaction of a stoichiometric excess of a polyisocyanate monomer, typically a diisocyanate, with a polyol, typically a diol. For example, a 1 .1 :1 to 15:1 excess of polyisocyanate monomer relative to polyol is used, in many embodiments ratios ranging from 1 .5 or 2:1 to 8:1 , 10:1 or 12:1 isocyanate monomer may be used, e.g., the ratio is often at least 3:1 , at least 4:1 or at least 5:1 of isocyanate monomer to polyol. More than one polyol may be used and more than one polyisocyanate may be used. Excess isocyanate monomer is often removed after the prepolymer reaction is complete, and in some embodiments of the invention, the prepolymer comprises 1 wt% or less free isocyanate monomer, e.g., 0.5 wt% or less or 0.1 wt% or less.

It is well understood in the art that a polyurethane prepolymer generally contains, in addition to any particular prepolymer compound, other compounds, typically in small amounts. Thus, there should be no confusion when the "prepolymer" is said to contain more than a single prepolymer molecule, such as other analogous prepolymers, unreacted starting materials, side products, solvents, etc.

Polyols used in the preparation of the prepolymers may be selected from any such polyol known in the art, for example, polyether polyols, polyester polyols, polycaprolactone polyols, polycarbonate polyols, co-polyester polyols, alkane polyols, or mixtures thereof. In many embodiments the polyol used in the preparation of the prepolymers will have a number average molecular weight from about 200, 250 or 400 to about 6000 or 10,000 Daltons, in some embodiments a lower molecular weight polyol may also be present. In many embodiments, diols are preferred over triols and polyols having a larger number of hydroxyl groups.

It should be recognized that polyols useful in the preparation of the prepolymer may also be employed in the curative composition.

Despite "ester" being a general term often used to encompass acyclic and cyclic esters, and sometimes even "carbonates", one skilled in the art recognizes that materials sold as polyester polyols, polycaprolactone polyols, and polycarbonate polyols have, and generally impart to the prepolymer and polyurethane, different characteristics, and are marketed as different materials. In the present application the terms "polyester polyol", "polycaprolactone polyol", and "polycarbonate polyol" are used to refer to three separate materials. "Polyester polyol" as used herein refers to a polyol having a backbone derived mainly from a polycarboxylate and a poly alcohol, e.g., a majority of the ester linkages in the backbone are derived from a polycarboxylate and a polyol, such as found in poly(ethylene adipate) glycol:

"Polylactone polyol" as used herein refers to a polyol having a backbone derived mainly from a hydroxycarboxylic acid or lactone, as opposed to being derived from a polycarboxylate and a polyol, as found in poly caprolactone:

"Polycarbonate polyol" as used herein refers to a polyol having a backbone comprising mainly carbonate linkages, -0(CO)-0-, as opposed to carboxylate linkages, -0(CO)-R wherein R is a hydrogen or an organic radical bound to the carbonyl by a C-C bond.

"Co-polyester polyols", as used herein refers to a polyol wherein a portion of the backbone is derived from a polycarboxylate and a poly alcohol as described above, and a portion of the backbone is derived from a hydroxyacid or lactone, or which also incorporates carbonate linkages.

For example, useful polyols may include polyesters of adipic acid or other dicarboxylic acids; polyethers of ethylene oxide, propylene oxide, 1 ,3-propanediol, tetrahydrofuran, etc.; polycaprolactone (PCL), polycarbonate, and copolymers and terpolymers formed from the above, and mixtures thereof. In various optional embodiments, the polyol comprises glycols or triols having molecular weights ranging, for example, from 60 to 400, e.g., from 80 to 300 or from 100 to 200, for example, such glycols or triols may include ethylene glycol, isomers of propylene glycol, isomers of butane diol, isomers of pentanediol, isomers of hexanediol, trimethylolpropane, pentaerythritol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, etc., and mixtures thereof.

Often, the polyether polyol is a polyalkylene ether polyol represented by the general formula HO(RO)nH, wherein R is an alkylene radical and n is an integer large enough that the polyether polyol has a number average molecular weight of at least 250. These polyalkylene ether polyols are well-known components of polyurethane products and can be prepared by the polymerization of cyclic ethers such as alkylene oxides and glycols, dihydroxyethers, and the like by known methods. Representative polyols include polyethylene glycols, polypropylene glycols (PPG), copolymers from propylene oxide and ethylene oxide (PPG-EO glycol), poly(tetramethylene ether) glycol PTMEG or PTMG, and the like. The polyester polyols are typically prepared by reaction of dibasic acids, e.g., adipic, glutaric, succinic, azelaic, sebacic, or phthalic acid or derivatives thereof, with diols such as ethylene glycol, 1 ,2-propylene glycol, 1 ,4-butylene glycol, 1 ,6-hexylene glycol, and alkylene ether polyols such as diethylene glycol, polyethylene glycol, polypropylene glycols, polytetramethylene ether glycol and the like. Polyols such as glycerol, trimethylol propane, pentaerthythritol, sorbitol, and the like may be used if chain branching or ultimate cross-linking is sought. Examples of polyester polyols include poly(adipate) glycol, poly(hexamethylene adipate) glycol, poly(ethylene adipate) glycol, poly(diethylene adipate) glycol, poly(ethylene/propylene adipate) glycol, poly(trimethylolpropane/hexamethylene adipate) glycol, poly(ethylene/butylene adipate) glycol, poly(butylene adipate) glycol, poly(hexamethylene/neopentyl adipate) glycol, poly(butylene/hexamethylene adipate) glycol (PBHAG), poly(neopentyl adipate) glycol, and the like including copolymers and terpolymers thereof.

Polylactone polyols include those made by polycondensation of, e.g., a caprolatone such as ε- caprolactone, and the like, often initiated by a small polyol such as ethylene glycol.

Hydrocarbon polyols can be prepared from ethylenically unsaturated monomers such ethylene, isobutylene, and 1 ,3-butadiene, e.g., polybutadiene polyols and the like.

Polycarbonate polyols can also be used in forming the prepolymers of the invention and can be prepared by reaction of glycols, e.g., 1 ,6-hexylene glycol and the like, with organic carbonates, e.g., diphenyl carbonate, diethyl carbonate, or ethylene carbonate and the like.

Co-polyester polyols include those wherein the backbone comprises polyester portions and portions comprising caprolactone or polycaprolatone.

In many embodiments if the invention, the polyol used in forming the prepolymers comprises a diol, and in some embodiments, the majority or all of the polyols used in to form the prepolymer are diols. In various embodiments of the invention, the polyol used in forming the prepolymers comprises a polyether diol, a polyester diol, a polylactone diol and/or a co-polyester diol, and in some embodiments the polyol used in forming the prepolymers comprises a polyether diol. In certain embodiments, the polyurethane reaction mixture comprises a prepolymer prepared using a polyol comprising a polyether or co-polyether diol, such as a polyethylene glycol, polypropylene glycol, or polytetramethylene ether glycol, e.g., a polytetramethylene ether glycol. As with the polyol, almost any polyisocyanate monomer known in the art may be used to prepare the prepolymer, including, e.g., paraphenylene diisocyanate (PPDI), toluidine diisocyanate (TODI), isophorone diisocyanate (IPDI), 2,4- and /or 4,4'-methylene bis (phenylisocyanate) (MDI), toluene- 2,4-diisocyanate (2,4-TD I), toluene-2,6-diisocyanate (2,6-TD I), naphthalene-1 ,5-diisocyanate (NDI), diphenyl-4,4'-diisocyanate, dibenzyl-4,4'-diisocyanate, stilbene-4,4'-diisocyanate, benzophenone- 4,4'diisocyanate, 1 ,3- and 1 ,4-xylene diisocyanates, 1 ,6-hexamethylene diisocyanate, 1 ,3- cyclohexyl diisocyanate, 1 ,4-cyclohexyl diisocyanate (CHDI), the three geometric isomers of 1 ,1 '- methylene-bis(4-isocyanatocyclohexane) (abbreviated collectively as Hi₂ MD I), and mixtures thereof.

In certain embodiments the polyisocyanate monomer component used in preparing the prepolymers comprises paraphenylene diisocyanate, 4,4'-methylene bis (phenylisocyanate) and/or a toluenediisocyanate.

Processes for combining and reacting the components of the prepolymer composition of the invention are well known in the art and need not be discussed here.

Many of the prepolymers, polyols, isocyanates, polyamines, catalysts, etc., used in the invention are known in the art and many are commercially available.

Depending on the polyol and curatives used, polyurethane layers of a variety of hardnesses can be prepare, in some embodiments for example, from Shore 60 A to 1 00A or from 70A to 95A, but higher and lower hardnesses can also be prepared according to the invention. The method of the invention is particularly well suited to coating of rolls, pipes, wheels, belts, die cutting devices and a variety of other substrates, especially other cylindrical substrates. The substrates can be fabricated from metal, plastic, ceramic, glass, or any other suitable material. This includes substrates that have the same diameter across the length of the cylinder, as well as those that have differing diameters at various positions along the cylinder. It can also be used to make tubes or coat the inside of pipes. It is also well suited to the use of reinforcing fabric or cord during the production of the covering.

EXAMPLES

The method of the invention was used to coat steel rollers, in a single pass, with a 40 mm thick layer of a polyurethane prepared from a TMEG / MD I prepolymer with %NCO of from 1 1 to 1 1 .5 using a multi-port die which divided the polyurethane reaction mixture into eight streams and ejected the streams through 8 corresponding ejection ports. The polyurethane reaction compositions were prepared according to standard procedures in a metered mixing head connected to the multi-port die using the following curative compositions.

The curatives were mixed with the prepolymer in the following approximate ratios to prepare rotationally cast polyurethane elastomers with the designated hardness.

Claims

1 . A method for coating a substrate comprising:

I) rotating the substrate about an axis at a selected rotational speed;

II) applying a polyurethane reaction mixture to a surface of the rotating substrate by ejecting the polymeric reaction mixture through a die comprising one or more ejection ports at a selected flow rate, wherein the polyurethane reaction mixture comprises

ii) from 0 to about 60 wt% of one or more aromatic polyamines, wherein at least one aromatic polyamine is a diamine,

iii) from about 0.5 to about 10 wt.% of a diaminocyclohexane, and

iv) 0 to about 1 wt% of a catalyst,

wherein A and B are present in amounts so that the mixture of B has a total active hydrogen content that is equal to about 80-1 15% of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer of A; and

2. The method according to claim 1 wherein B) is a mixture comprising, based on the total weight of components i, ii, iii and iv:

i) from about 35 wt% to about 97 wt%, of the two or more polyols,

ii) from 0.5 to about 60 wt% the one or more aromatic polyamines, wherein at least one aromatic polyamine is a diamine,

iii) from about 0.5 to about 10 wt.% of 1 , 2-diaminocyclohexane, and

iv) 0 to about 1 wt% of a catalyst.

3. The method according to claim 1 , wherein in B) the first polyol has a Mn of 400 or greater.

4. The method according to claim 3, wherein the first polyol has a Mn of 600 or greater.

5. The method according to claim 1 wherein the second polyol has a Mn of less than 250.

6. The method according to claim 5, wherein B) is a mixture comprising:

i) from about 50 wt% to about 97 wt% of the two or more polyols,

ii) from 0.5 to about 45 wt% of the one or more aromatic polyamines,

iii) from about 1 to about 5 wt.% of 1 , 2-diaminocyclohexane, and

iv) from about 0.01 to about 0.5 wt% of the catalyst.

7. The method according to any proceeding claim wherein 75 wt% of the two or more polyols in B comprise diols.

8. The method according to claim 7 wherein the two or more polyols of B also comprise a triol or tetrol.

9. The method according to claim 1 wherein the polyurethane reaction mixture is ejected through a sheet die having an outlet in the form of a slit.

10. The method according to claim 9 wherein the outlet in the form of a slit has a length to width ratio of 10 to 300.

1 1 . The method according to claim 1 wherein the polyurethane reaction mixture is ejected through a die that divides the polyurethane reaction mixture into a plurality of outlet streams, which streams are ejected onto the substrate through a plurality of outlet ports that are spaced apart from each other such that the outlet streams flow together seamlessly after application to the substrate.

12. The method according to claim 1 1 where the number of outlet streams that the polymeric reaction mixture is divided into ranges from 2 to about 32 streams.

13. A polyurethane reaction mixture comprising:

i) from about 35 wt% to about 97 wt%, of two or more polyols, comprising a first polyol and a second polyol different from the first polyol, wherein the first polyol has a Mn of 250 or greater the second polyol has a Mn of less than 400, ii) from 0.5 to about 60 wt% of one or more aromatic polyamines, wherein at least one aromatic polyamine is a diamine,

iii) from about 0.5 to about 10 wt.% of a diaminocyclohexane, and

iv) 0 to about 1 wt% of a catalyst,

wherein A and B are present in amounts so that the mixture of B has a total active hydrogen content that is equal to about 80-1 15% of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer of A.

14. The polyurethane reaction mixture according to claim 13, wherein in B) the first polyol has a Mn of 400 or greater.

15. The polyurethane reaction mixture according to claim 14, wherein the first polyol has a Mn of 600 or greater.

16. The polyurethane reaction mixture according to claim 13, wherein the second polyol has a Mn of less than 250.

17. The polyurethane reaction mixture according to claim 16, wherein B) is a mixture comprising: i) from about 50 wt% to about 97 wt% of the two or more polyols,

ii) from 0.5 to about 45 wt% of the one or more aromatic polyamines,

iii) from about 1 to about 5 wt.% of 1 , 2-diaminocyclohexane, and

iv) from about 0.01 to about 0.5 wt% of the catalyst.

18. A curative composition comprising, based on the total weight of components i, ii, iii and iv: i) from about 35 wt% to about 97 wt%, of two or more polyols, comprising a first

has a Mn of 250 or greater the second polyol has a Mn of less than 400,

iii) from about 0.5 to about 10 wt.% of a diaminocyclohexane, and

iv) 0 to about 1 wt% of a catalyst.

19. The curative composition according to claim 18, wherein the first polyol has a Mn of 400 or greater.

20. The curative composition according to claim 19, wherein the first polyol has a Mn of 600 or greater.

21 . The curative composition according to claim 18, wherein the second polyol has a Mn of less than 250.

22. The curative composition according to claim 21 comprising:

i) from about 50 wt% to about 97 wt% of the two or more polyols,

ii) from 0.5 to about 45 wt% of the one or more aromatic polyamines,

iii) from about 1 to about 5 wt.% of 1 , 2-diaminocyclohexane, and

iv) from about 0.01 to about 0.5 wt% of the catalyst.

23. The curative composition according to claim 21 wherein the one or more aromatic polyamines comprises one or more compounds selected from the group consisting of diethyl toluene diamine, tertiary butyl toluene diamine, dimethylthio-toluene diamine, 1 ,2-bis(2-aminophenylthio)ethane and toluene-2,4-diamine.

24. A polyurethane elastomer obtained according to the method of claim 1 wherein the polyurethane elastomer is in the form of a layer that is 10 mm thick or greater and was prepared in a single coating pass.

25. The polyurethane elastomer according to claim 24, wherein the polyurethane elastomer is in the form of a layer that is 20 mm thick or greater.

26. A substrate coated with a polyurethane layer obtained according to the method of claim 1 .