Patent Application
20120157620
The invention relates to amine epoxy adducts and to their use for preparing polyurea and polyurethane coatings.
More specifically, the invention relates to polymeric amine-epoxy adducts and adduct blends having symmetric and asymmetric structures, and to their application for sprayable, solvent-free (VOC-free) polyurea (PU) and polyurea-polyurethane (PU-PUR) coatings.
Sprayable VOC-free PU and PU-PUR hybrid systems are widely used for the coating of different substrates, such as metals, polymers, concrete, etc. One of the advantageous features of such coatings is that the coating hardens relatively quickly.
However, the state-of-the-art, two-component, hot sprayed PU coatings show moderate adhesion to metal surfaces. Therefore, in most cases, first an epoxy primer layer is applied onto the metal, and the coating is applied after its hardening. Epoxy primer, however, sets usually rather slowly. Under 10° C. the process will even not occur without the heating of the substrate to be coated. This way fast curing, one of the main advantages of PU systems, will be lost or considerably diminished.
Further problems are that setting time of PU coatings cannot be regulated freely, most known primary di- and polyamines react with isocyanates too quickly, and that these compounds usually contain also considerable amounts of aromatic diamine chain extenders being harmful to the natural environment, and also to the workers. These substances belong to the materials of medium to high risk. (Manufacturing and application of some of those, e.g. the ones with N50/53 classification will be strongly limited by the new European regulation on chemical substances [(REACH]).
U.S. Pat. No. 6,723,821 suggests the use of certain polyamine-epoxide adducts for improving the adhesion of polyurea coatings. According to the description, these adducts are formed by reacting a polyamine with a compound containing an epoxy group while the epoxy ring opens. Among the epoxy compounds primarily Bisphenol A, Bisphenol F and epoxy novolac based products are mentioned, which are excellent film forming materials per se, and are successfully applied in lacquer industry. Among the amine components almost the full commercial product assortment is listed, but in the examples only aliphatic and aromatic primary diamines are shown. This way, the prepared adduct contains always at least two primary amino groups.
On concrete surface better adhesion is achieved than with the polyurea containing no adduct, but the product has not been tested on other surfaces.
According to our own examinations, coatings prepared with adducts according to the above mentioned document do not show satisfactory adhesion to metal surface. (See later in Table 6/4.)
The object of the invention is to provide liquid polymer amine-epoxy adducts, which are suitable to prepare sprayable, solvent-free polyurea and polyurea-polyurethane coatings with excellent adhesion, and with adjustable pot life, i.e. with reactivity with isocyanates that can be regulated at will in a wide range.
It is a further object of the invention to provide amine-epoxy adducts wherein the amount of especially hazardous starting amines remains under 0.1% m/m.
The invention relates to amine-epoxy adducts and adduct blends with a maximum viscosity of 300 mPas at 70° C., and with an average molecular mass (
The adducts according to the invention can be used for the preparation of sprayable PU and PU-PUR coatings. Thus the invention relates to the use of amine-epoxy adducts according to the invention in the preparation of PU and PU-PUR coatings, and also to the coatings prepared.
By the use of the adducts according to the invention the pot life of PU and PU-PUR coatings can be regulated in wide range, and the properties of the coatings prepared this way, such as adhesive strength on metal surface and corrosion resistance are better than those of the known coatings.
Adducts and adduct blends according to the invention are applied for preparing PU or PU-PUR adducts as follows: the amine-epoxy adduct or adduct blend according to the invention are partly or fully substituted for one or more components of the amine blends i.e. of their “A” components.
The invention also relates to the preparation of hot sprayed PU primer, wherein one or more amine epoxy adduct according to the invention having a viscosity of less than 100 mPas at 70° C. is substituted for a part of the amine components of the PU.
The invention relates on the one hand to amine-epoxy adducts and adduct blends. By the suitable choice of the starting amines and epoxy compounds we are able to prepare adducts having various structures and properties. The average molecular mass of the amine-epoxy adducts according to the invention is between 300 and 8000, preferably between 300 and 6000. Amine-epoxy adducts according to the invention contain at least one, preferably more than one alcoholic hydroxyl groups which are formed during the amine-epoxy addition. Amine-epoxy adducts according to the invention are characterized by the following:
Amines useful for preparing the amine-epoxy adducts according to the invention may be primary or secondary aliphatic, cycloaliphatic, araliphatic, aromatic, mono-, di- and triamines. Some preferred starting amines are listed in Table 1.
n
According to the invention, polyoxylalkileneamines i.e. polyetheramines are preferred, which contain homogenous or mixed polyether chains built up from ethylene oxide, propylene oxide or polytetrahydrofuran (PTHF), such as for example, the products of Huntsman belonging to the Jeffamine series: M: monoamine, D: diamine, T: triamine, SD: secondary diamine etc., and the numbers following the letters are values referring to the average molecular mass of the product.
Beyond those, for example, the following amines can also be used:
Also preferred starting amines are the already mentioned aromatic and cycloaromatic amines used in PU and/or PUR manufacturing as chain extenders, which are, however, hazardous for the environment (toxic, carcinogenic), such as for example:
Cheap adducts containing aromatic secondary amines or, combined with diamine, adducts containing secondary and primary amines, characterized by asymmetric structure and providing advantageous properties can be prepared by using monomines which would be very dangerous by themselves, such as:
(For classification data and further parameters see e.g. the actual volume of TCI Laboratory Chemicals, 2008-2009, www.tcieurope.eu).
Mixtures of the above listed amines may also be used for easier regulation of the reaction time with isocyanates during the preparation of the coating. For example, it is preferred to apply amine combination where at least 50% of the amino groups in the obtained adduct are secondary.
For the preparation of adducts reacting slowly with isocyanates some aliphatic, cycloaliphatic, araliphatic and aromatic primary monoamines are especially preferable due to their steric hindrance, such as e.g.: 2-ethylaniline, 2-methyl-cyclohexylamine, tert-octylamine and similar ones. Bis-aspartate type secondary amines (e.g. Desmophen products of Bayer) are also preferable to regulate the isocyanate reactivity due to their various structures.
For adducts according to the invention epoxy compounds listed in Table 2 are preferred as epoxy components.
n
Further epoxy compounds which can be used beyond the ones listed in the Table are, for example:
From monoepoxy compounds:
From active diluents, the following di- and polyepoxy compounds:
According to the invention, the low viscosity mono-, di- and polyepoxy compounds i.e. active diluents, their mixture, as well as epoxy resins and resin mixtures containing active diluents are especially advantageous as starting epoxy compounds.
For example, active diluents of the type AH-3, AH-5, AH-7, AH-14, AH-17, AH-18, AH-P61, Epilox M985 are preferred.
For the preparation of adducts according to the invention numerous combinations of the above listed amines and epoxy compounds can be used. For example, primary mono-, di- and triamines or their mixtures can be reacted with mono-, di-, tri- and tetraepoxy compounds, and with their mixtures in various ratios. For better overview, such combinations are shown in Table 3 and Table 4.
Among adducts prepared by the combinations, the following ones fall outside the scope of the present invention:
Consequently, adducts containing only tertiary amino groups are outside the scope of the invention.
It can be seen in Table 4 that, starting with purely secondary amines, there is only one case when we can obtain adducts according to the invention. Also in this case a tertiary amino group can be formed in the molecule, which may cause problems both for preparation and application. Consequently, the use of secondary amines alone has only ignorable importance for the invention. Secondary amines, combined with primary amines may only be important as so-called active diluents.
Our goal is to prepare adducts which are polymers according to the REACH classification. Therefore, we preferably choose such combination of raw materials wherein at least one of them is classified as being polymeric. It means, the average number of monomer units is more than 3, and none of the homologues represents more mass than 50% of the whole raw material. See Guidance for monomers and polymers, European Chemicals Agency, 2008. http://guidance.echa.europa.eu/docs/guidance_document/polymers_en.pdf; or Gyula Körtvélyessy: About REACH in another way: monomers-polymers (in Hungarian), http://www.kortvelyessy.extra.hu/REACH/polimerek_monomerek.pdf)
When, according to the invention, one or both raw materials are polymers according to said classification, then the obtained adduct is not pure material, but a blend of adduct molecules.
The invention further relates to a process for preparing adducts and adduct-blends according to the invention. In the course of the, process one or more amino and epoxy raw materials are mixed in a suitable ratio and heated. The process may be carried out in one or more steps. If the process is carried out in more, preferably in two steps, it comprises the following steps:
a) in the first step a di- or polyepoxy compound is reacted with monoamine, and the obtained product is reacted with another mono- or diamine, or
b) in the first step, a primary di- or polyamine is reacted with a monoepoxy compound, and the obtained product is reacted with another mono- or diepoxy compound.
If the starting amines are especially hazardous, then the number of steps may be three or even more, in order to fulfill the REACH requirements.
The progression of the reaction is monitored by measuring the amine and epoxy numbers. Amine and epoxy compound are usually applied in equimolar amount. In certain cases maximum 50 mol %, preferably maximum 30 mol % amine excess is applied. Instead of excess primary amine, so-called active diluent may also be used, which is of secondary diamine character: of this, also maximum 50 mol %, preferably maximum 30 mol % is used.
Such amine excess is preferably applied when the starting materials are primary diamine and diepoxy compounds.
If the starting materials are the above mentioned hazardous ones being harmful to human health, the reaction will be continued so long and at so high temperature (if necessary, applying also special catalysts) till the ratio of the remaining starting amine(s) decreases below 0.1 mass % related on the final amine-epoxy adduct. (So that we do not exceed the REACH limit value).
Another feasible way is that the hazardous amine is first reacted with a low (5 to 10 mol %) epoxy excess, and then we bind the free epoxy groups by adding another amine having more favorable properties. It is preferred that the ratio of adduct(s) from the hazardous amine(s) is over 90% in the obtained adduct mixture.
According to the invention we can advantageously prepare asymmetric adducts, usually in two steps. For example, first a primary monoamine is reacted with an epoxy group of a diepoxy compound, and the so obtained semi-adduct is reacted with another amine. It is also feasible that in the first step a di- or triamine is reacted with a monoepoxy compound, and in the second step another mono- or diepoxy compound is applied.
During the adduct preparation, especially in industrial scale, dosage and/or mixing irregularities may cause local variations in concentration. Due to the further reaction of the formed secondary amines and —OH groups side reactions may start, and this way more or less oligomer molecules may be formed. For example, when reacting three molecules of diamines and two molecules of diepoxy compounds the average molecular mass of adducts will be higher. Since their viscosity grows proportionally with the amount and molecular mass of the oligomers, it is suggested to apply amine excess, or to use so-called active diluent.
Viscosity of adducts according to the invention is maximum 300 mPas at 70° C., preferably maximum 200 mPas, and especially preferably under 100 mPas. Adducts or mixtures having so low viscosity can be used to prepare primers. Such primers are also within the scope of the invention.
The invention relates also to the use of adducts and adduct blends according to the invention as amine and/or polyol blend components of polyurea (PU) systems, polyurea-polyurethane (PU-PUR), or polyurethane-polyurea (PUR-PU) hybrid systems.
In the amine blends (in the so-called “A” component) instead of 5-100 mass %, preferably 10-50 mass % of the traditional amine, adducts according to the invention are used. Asymmetric adducts are advantageously used: 0-100%, preferably 20-50% of the applied adducts are of asymmetric structure.
Amine epoxy adducts belonging to the scope of the invention can be used together with all di- and polyisocyanates and their mixtures (irrespectively if they belong to the aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates), which have already been used for preparing PU or PUR coatings. For example, especially preferable are the different MDI-based modified isocyanates, MDI based prepolymers, trimerized HDI products, etc.
Adhesive strength of the coatings prepared with adducts according to the invention is better than that of the known coatings: as we show in the examples below, it reaches, even exceeds 15 MPa, preferably 18 MPa, and especially preferably 20 MPa.
Corrosion resistance of the coating systems according to the invention is also excellent, as it will be proven by measurements later.
In the following, the invention will be illustrated by examples, which however, do not limit the scope of invention. We have prepared the samples partly in laboratory (L) scale, partly in large laboratory scale, i.e. in autoclave (A). Adducts with the same composition but made in different scale are assigned different-ly, since the scale-up means different reaction conditions (dosing time, heat transfer, mixing conditions), therefore, the prepared adducts and adduct blends have more or less different properties.
In a traditional open metal can of 700 ml used in lacquer industry with an upper filling hole of 80 mm diameter, 116 g MPMD and 214 g AH-17 are weighed. Under continuous stirring, it is heated up to 60±2° C. by an electric basket heater. At this temperature the conversion reached 81% in 1.5 hours, and then, 98.5% conversion has been reached after two more hours at 90±1° C. Reactivity and the consumption of the epoxy groups were monitored by determining amine and epoxy numbers. Average viscosity of the prepared full adduct was 350±20 mPa·s at 20° C., 44±10 mPa·s at 50° C. and 17±5 mPa·s. at 70° C.
The experiment has been repeated with the same parameters, but using a four-neck sulphurizing flask, using the laboratory technique described in Example 2. Viscosity parameters of the adduct have been the same as above within the error limits.
Adduct Nr. 1 does not belong to the scope of the invention, but we prepared and tested if for comparison. This adduct reacts still too quickly with the isocyanates we actually use, similarly to the starting amine, therefore, we did not deal with its polymer variants either.
120 g Jeffamine D230 aliphatic polyether diamine is weighed into a 500 ml four-neck sulphurizing flask equipped with dropping funnel and thermometer, and it is heated to 70±2.5° C. by an electric basket heater under intensive, continuous stirring. While keeping the substance, and later the reaction mixture at this temperature for two hours, 222 g 2-etylhexyl glycidyleter is added slowly into the flask within 2 hours under continuous and intensive stirring. Depending on the epoxy content of the reaction mixture it is kept at the prescribed 70±2.5° C. for further 1.5 hours, and at 90±25° C. for further 1.5 hours. Reactivity and the consumption of epoxy groups are monitored by determining the amine and epoxy numbers, and after the full consumption of the starting epoxy groups the reaction mixture is cooled down intensively to room temperature. Average viscosity of the prepared full adduct is 770±20 mPa·s at 20° C., 80±10 mPa·s at 50° C., 30±5 mPa·s at 70° C., amine number: 164±5, epoxy number: 0,0.
1 mol AH-P61+1 mol Ethacure 100+1 mol AH-17
In the first step, 164 g AH-P61, 60 g Ethacure 100 and 2.5% triethanoleamine (as catalyst) are weighed into the 700 ml metal can. Under continuous stirring it is heated up to 135±2° C. by an electric basket heater in 1 hour, and it is kept at this temperature for 2.5 hours till the starting epoxy groups are almost completely consumed, i.e. the conversion calculated for the semi-adduct reaches 97%. Reactivity and the decrease of epoxy groups are monitored by determining the amine and epoxy numbers.
To the semi-adduct prepared this way, we added 80 g AH-17 (instead of the necessary 76 g, 5.27% more) to secure that by the end of the reaction Ethacure 100 will react fully. Mixing and heating has been continued at the same temperature for 9 hours. Monitoring of the conversion was he same as for the semiadduct.
Excess epoxy groups were consumed fully, the amount of residual Ethacure 100 decreased under the required limit, to 0.08%, i.e. related to Ethacure we exceeded the 99.9% conversion. Measured viscosity of the prepared full adduct was 1820±20 mPa·s at 20° C., 195±10 mPa·s at 50° C. and 69±5 mPa·s at 70° C.
27 g Ethacure 100, 4.4 g i.e. 2.5% triethanolamine (catalyst) and 150 g AH-P61 are weighed into a 700 ml metal can. Under continuous stirring it is heated up to 115±5° C. in 1 hour by an electric basket heater. After five hours the conversion was 83.5%. After that, the covered can has been placed into a drying chamber and kept there overnight without mixing. By morning it reached 99.4% conversion. Reactivity and the decrease of epoxy groups are monitored by determining the amine and epoxy numbers.
Viscosity of the prepared full adduct was 835±20 mPa·s at 20° C., 124±10 mPa·s at 50° C. and 49±5 mPa·s at 70° C.
Starting Components:
497 g Jeffamin D2000 and 103 g AH-17 are weighed in a 700 ml metal can. Under continuous stirring, by an electric basket heater it is heated up to 110±5° C. in 1 hour, and then it is kept at this temperature for 2 hours. At this stage, conversion reached 43%. Raising the temperature to 140±5° C., mixing was continued for further 3.5 hours, till the starting epoxy groups are almost completely consumed, i.e. we reached the 98.7% conversion. Reactivity and the consumption of epoxy groups are monitored by determining the amine and epoxy numbers. Measured viscosity of the prepared full adduct was 884±20 mPa·s at 20° C., 161±10 mPa·s at 50° C. and 73±5 mPa·s at 70° C.
Mixing equipment of stainless construction material with 42 l total volume, with dosing equipment, reflux and submerging cooler and collecting can. Equipment can be heated and cooled.
3. Operation steps
When preparing the adducts in Examples 1-6. and in Tables 5/1-5/4. the exact weighing has not been carried out on the basis of the theoretical molecular masses but on the actual amine numbers and epoxy equivalents of the used substances.
Typical parameters of the adducts prepared as in Examples 1-6 or similarly are shown in Tables 5/1.-5/4. For comparison, there are some adducts in the Tables which do not belong to the scope of our invention, because according to the REACH rules they cannot be classified as polymers, and/or their viscosity is more than 300 mPas at 70° C.
Table 5/1. shows the properties of adducts prepared from different primary, di- and triamines with monoepoxy compounds. At the upper part of Table 5/1 there are only non-polymer classified, and lower mainly polymer-classified adducts are shown, the latter ones belong to the present invention.
Table 5/2 shows the viscosity of some adducts and adduct blends prepared from primary monoamines with the same diepoxy active diluents (AH3=butandiol-bisglycidylether) at 50 and 70° C., as well as their REACH classification, and that whether they fall within the scope of the invention. It can be seen that product “MA-01” is outside the scope of the invention for two reasons: first, it is not polymer according to REACH, second, its viscosity is much more that 300 mPas at 70° C. The situation is similar for adducts MA02 and MA-07, too. Viscosities of MA-09 and MA-15 are still preferable, but since they are not polymers, they are outside the scope. At the bottom part of the Table, the viscosity of “PA” adducts is preferable both by laboratory and autoclave scales, and since they are polymer classified, they are within the scope of the invention.
+Theoretical mol mass of adduct Nr. 1. is 302 g/mol, in the practice, due to AH-17 it is usually over 310 g/mol.
+Average mol mass of adduct Nr. 68. is ~6.338 g/mol, the highest among the examples.
Adducts being printed with gray background in Tables 5/1, 5/2, 5/3 and 5/4 have been prepared in autoclave. We have sprayed PU coatings with these adducts: their composition and the obtained results are shown in Tables 6/1-6/4. In the formulations in Tables 6/1-6/4. the adducts according to the invention served as substitutes for a part=(10-70 mass %) of the amine blend in the “A” (“POLY”) component of the PU systems.
In the upper part of Tables 6.1-6.4 the traditional, commercially available amine components of the “A” components (amine blends) are given in bold. Below them, the new amine-epoxy adducts according to the invention, then one or more of the isocyanate components, used as “B” (i.e. “ISO”) component are listed. Furthermore, the gel times of the homogenized A+B components, and the mechanical strength properties of the coatings are shown.
The solvent-free gel time given here is not identical with gel time in industrial practice, which is usually measured on a vertical surface with a coating material sprayed on one single spot for some seconds, measuring the fluid period by stopwatch. This gel time has been obtained according to the Polinvent (PI) internal standard, defining a new laboratory gel time measuring method worked out by the inventors. Laboratory gel time shown in Tables 6. is measured as follows:
Solvent Test:
Solvent-Free Test:
If the system with 66 m/m % solvent content produces gel slowly, then the measurement of PU gel time is carried out without adding solvents, the result is given in seconds [sec].
Finally, at the bottom of Tables 6. the adhesive strength values of the coatings are given, using metal sheets with identical surface roughness.
As reference values for the spray tests, we applied the suggested formulations in the product description of the raw material producer Huntsman (HRef. 1. and HRef. 2.), as well as a DRef. 1 formulation which can be considered as a PU-PUR copolymer system (most raw materials of that are produced by Dow).
For the spray tests we applied a GlasCraft Guardian A6-6000 type PU reactor from Graco, with 3 and 6 m hoses, 1:1 mass ratio, by the original 23940-XX Probler P2 Elite Dispense Gun type spraying gun, preparing 1.5 mm thick coatings in average, on thoroughly cleaned steel plates with a size of 0.5×20×40 cm. Since the spray process needs at least 10 litres of POLY and ISO components each, the large laboratory scale adducts have been used for the spray tests. The pre-treatment of the steel plates has been carried out by CLEMCO BNP 720 DS machine and tip 6, operated by compressed air (5 bar pressure). Immediately before the grit blasting procedure we filled F40 designated corundum grains (354-500 μm grain size) into the machine. On the round table serving as working surface of the grit blasting chamber we placed 4 steel plates simultaneously. After grit blasting, we measured the surface roughness at 3 spots each on the steel plates by a Taylor-Hobson Surtronic 10 type roughness measurement device, and registered the values in the protocol.
After the PU spraying the adhesion strength has been measured on these steel plates, while most of the mechanical properties have been measured on specimens being cut out from PU coatings applied to polypropylene sheets, and removed later on.
+Dref-1, industrial product, see: www.dow.com/hyperlast/product/hyperkote/index.htm
++USA-C = POLY and ISO components of the sprayed PU system were made similarily to Example 6 (Control) of U.S. Pat. No. 6,723,821.
+++PU-C = Like USA-C, but in the ISO component, S2054 type isocyanate is substituted also for PC, i.e. it does not contain PC.
In Table 6.1 the formulations Href 1 and Href 2 differ in their isocyanate components only. The tensile strength values of these reference coatings are nearly the same, their ultimate elongations are, however, very different, because the S 2067 type (Suprasec 2067® brand name) isocyanate provides more dense network. Mainly due to its lower ultimate elongation, this coating has about twice as much adhesive strength as Href 1.
Comparing the data in Tables 6/1-6/4 it can be seen that this tendency always prevails for both coatings with different isocyanates but otherwise identical “POLY” compositions. It is also shown that coatings prepared with many adducts exhibit considerably higher adhesion than the reference compositions, especially if they are applied in a ratio over 10%. Another important advantage is that we are able to regulate (i.e. increase) both the solvent and solvent-free gel time in a wide range.
The adducts described in U.S. Pat. No. 6,723,821 aimed at improving the PU coatings which are suitable to protect concrete surfaces. In the introduction partwe mentioned already that these coatings do not adhere to metal surfaces satisfactorily. As it can be seen in Table 6/4, columns USA-C and USA-2A, if the coatings of the cited US document are prepared on the same way as the other coatings according to the present invention (i.e. the same roughening, same steel plates, sprayed with the same reactor and same gun), the adhesion of the reference (control) coating was 5 N/mm2, and the coating containing the adduct according to Examle 2 of the cited document has a somewhat better, 6.1 N/mm2 adhesion strength. Both are lagging behind the usually expected 8 N/mm2. The most important reason of this result was that the ISO component contained 12.5% of PC, i.e. propylene carbonate as diluent. The PC molecules which will remain back to a great extent unreacted in the coating will worsen the adhesion, decrease the tensile strength, and increase the ultimate elongation, i.e. they act as plasticizers.
If we use the the isocyanate component instead of the PC (see PU-C and PU-2A columns in Table 6/4) adhesion and other mechanical properties are much more favorable. However, it can also be seen that the coating which contains a large amount of the adduct according to Example 2 (there are 33% in the POLY component) do not provide higher adhesion on steel surface than the adduct-free (and PC-free) PU-C, i.e. control coating. Its reason is presumably that for the preparation of the adduct according to Example 2, a considerable excess of Ethacure 100 was used, more specifically: instead of the equimolar ratio of 2:1, a ratio of 6.3:1 was used. Consequently, the actual adduct concentration in the “POLY” component was only 16.1%, instead of 33%.
We do not wish to bind the explanation of the above results to any theory, but we do think that the increase in adhesive strength which can be achieved by the amine-epoxy adducts according to the invention can be attributed mainly to the hydrogen bridges. Such bridges are formed by the hydroxyl groups with different surfaces, including the metal surfaces. One way for the hydroxyl groups to get into the molecules is that they are already there in certain epoxy resins. On the other hand, in the course of the addition reaction between the epoxy compound and the amino compound the epoxy group opens up and an alcoholic hydroxyl group is formed. Furthermore, hydroxyl groups can be brought in by amino-alcohols as well. It is known from the works: Flexible Polyurethane Foams, 2. edition, ed. R. Herrington and K. Hock, Dow Chemical Company, Midland, Mich., USA (1977) and W. D. Vilar, Chemistry and Technology of Polyurethanes, 3. edition, Vilar Poliuretanos Ltd., Lugoa, Rio de Janeiro (2002), that amino groups are willing to react with isocyanate groups by orders of magnitude quicker than hydroxyl groups are. Therefore, in PU systems, in the course of the reaction with the isocyanates (chain growth and polymerization) a high ratio of the hydroxyl groups remains back unreacted, and this way they are able to create hydrogen bridges.
Based on the U.S. Pat. No. 6,723,821 description which was already referred to, one would expect that the more hydroxyl groups are present, the higher adhesion strength can be achieved. In contrast to that, we surprizingly observed that it was not worth attempting to reach a maximum of hydroxyl number. Our explanation for that is that the substituted urea bonds which are created in the reaction with the isocyanate group, are also able to form hydrogen bridges in the necessary amount and quality. When reaching the best adhesion values, presumably complex and chelate bonds are formed being related to the simultaneous presence of hydroxyl and substituted urea groups.
We note that the lower hydroxyl group number compared to the adducts made of the usual lacquer industry epoxy resins plays, in the case of metal coatings, a role (by improving the adhesive strength and by decreasing water absorption) also in the excellent corrosion resistance of the coatings according to the invention.
Testing of Corrosion Resistance
Corrosion protection of cast iron and steel pipes of different diameter is an especially demanding task. The DIN EN 10290 standard contains the test methods for their external coatings. One of these tests is the cathodic disbondment test. The results of such tests are given in Table 7.
The data in Table 7 show that the tested coatings more than fulfilled the standard requirements in all cases (suitable under 8 mm). The relatively quick measurements at 60° C. showed somewhat more favorable picture, they are suitable for quick control, but they correlate well with the room temperature tests which are more time consuming.
The data in series 3 show that, when we sprayed a primer layer first, and then applied the tradition HRef 2. thick coating, the corrosion resistance became especially good.
Table 8 shows that, using the so-called solvent laboratory gel time measurement, we can simply characterize the differences in reactivities of different adducts and amines which have been commercially available already, we can set the order of those. Using this method, the efficiency of designing formulations, the so-called formulating can be considerably improved.
1immediately = full or at least 50 v/v % gel forming at the moment of pouring together
2p. opal = immediately opal after pouring together
3h. opal = at pouring together still clear, but becomes opal during homogenization.
Summarizing, it can be stated that by using the new adducts:
| Number | Date | Country | Kind |
|---|---|---|---|
| P0900532 | Aug 2009 | HU | national |
| P1000390 | Jul 2010 | HU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/HU2010/000090 | 8/24/2010 | WO | 00 | 2/13/2012 |
