CS259883B2 - Method of dried coating preparation - Google Patents

Abstract

Hydrated catalyst complexes and a process for accelerating the polymerisation of isocyanate terminated prepolymers by facilitating the introduction of water into these systems by way of the hydrated catalyst complexes in the vapour phase.

Description

The present invention relates to the drying of paints, coatings and the like. The invention provides an improved process (and the resulting product) in that drying is performed more efficiently than hitherto.

Two-component systems, with their continuously variable formulation options and above-average dry coating properties, served well the purpose of introducing the VAPOCUR (Trade Mark) process in the field of industrial painting. The term " VAPOCURE procedure " is used to generally refer to procedures for rapidly curing polymer coatings with a vapor phase curing agent.

Unfortunately, the main drawback of these systems, namely the limited processability, is that they are not suitable for applications that use large volumes of paint daily. In such cases, there is no time to mix, dilute, and stabilize the two-component systems, because in the color preparation workplace that is always used in such cases, a large amount of color (which normally comes with a viscosity suitable for use) is continuously recirculated colors and application site.

Such a paint, as defined below, must be of the one-component type and have viscosity and other rheological properties that remain permanently stable when used in a pressurized recirculation system. Often the paint remains in the pipeline during prolonged production interruptions, for example due to a breakdown in operation or on holiday, and yet must flow freely whenever the equipment is started up. A two-component system with limited processability, constantly changing viscosity characteristics and pressure sensitivity is apparently unsuitable under such conditions.

Water and catalyst must be present in the oven if moisture-curing, single-component, one-component coating systems are to be dry-cured. The amount of water per gram of ink used for coupling with prepolymer molecules can be accurately calculated and, for example, the two-component VAPOCURE (trade mark) system empirically determined, one catalyst molecule for every six reaction positions, also applies to one-component systems, The optimum ratio of water to catalyst can be calculated for the composition.

When all these circumstances are taken into account and the drying conditions are maximized, the one-component coating system rapidly polymerizes and provides dried coatings with initial hardness and chemical stability that push the established level achieved with the two-component compositions into the background.

This is possible because the average molecular weight of the reactants in the one-component system is much lower, allowing a high solids content with the same viscosity to be used, while a higher percentage of NCO groups gives a higher crosslinking density, helping to eliminate both catalyst and the solvents while continuing to dry.

While the two-component system contains all the components needed to form the polymer in the applied coating, the one-component system requires the presence of some water to fully polymerize. The water and catalyst enter the coating in a gaseous state from the air surrounding the object to be coated. There must be a concentration gradient for this water and also for the catalyst.

The purpose of the present invention is to provide a hydrated catalyst complex and a method for its use in drying one-component coatings and substantially overcoming or ameliorating the problems associated with drying such coatings.

The problem was solved by a process for preparing a dried coating by applying a one-component binder containing free isocyanate groups to the substrate. It is based on the fact that a binder with a polyisocyanurate, urethane, urea, biuret or allophonate structure is dried by the action of a hydratreated vapor phase catalytic complex consisting of an amine, a tertiary amine, an alkanolamine, an organometallic or organic metal salt in a mass concentration of 100 to 3,000 ppm in an atmosphere with a relative humidity of 40 to 80% and at a temperature of 10 to 40 ° C.

The invention is applicable to the drying of paints, varnishes, varnishes, printing binders and printing inks, liquid adhesives, surface coatings, sealants and the like.

In addition, an explanation of the basic terms used in the description, subject matter, and reference of the invention is given.

The term "coating" for the purposes of the present invention means the same as the term "coating" or the like.

The term "drying" or "drying" includes "curing" and means that the coating is either non-sticky (non-greasy), insoluble in solvent and has a high degree of integrity, or is able to overcome acceptable abrasion or pressure without damage.

The term "substrate" includes any surface to which a binder can be adhered and adheres to when the drying agent acts. .

The term "binder" includes all paints, varnishes and similar substances containing free isocyanate groups.

The term "drying agent" means a composition which causes drying of a coated binder and which is multicomponent and consists of water as the first component, together with at least one other component selected from the group consisting of an amine or other hydratable compound such as an organometallic or inorganic metal salt which accelerates the desired reaction when combined with water.

Although structural analysis has not yet been performed, it is believed that water and the other desiccant component (s) react in the vapor phase to form a hydrated catalyst complex which unexpectedly and very vigorously speeds up the binder drying rate. However, it should be understood that this description in no way supports here. or other drying theory.

The term "free isocyanate groups" or "free NCO groups" includes any compound that has potentially free such groups, i.e., the prepolymer contains isocyanate groups that may be released or are accessible for reaction with water molecules (to polymer growth and / or or coating) and includes not only polyisocyanates with urethane and urea structures, but also polyisocyanates with polyisocyanurate, biuret and allophonate structures.

The term "amine" includes tertiary amines and alkanolamines, which may be either (a) polyfunctional, (b) aromatic, (c) aliphatic, or cycloaliphatic in nature. Particular examples are triethylamine and dimethylethanolamine (DMEA) and di-tertiary amines such as N, N, N ', N'-tetramethylethylenediamine (TMEDA) and N, N, N, N, 2-pentamethyl-1,2- propandiamm (PMT) and all combinations of such amines in the desired ratio, wherein the synergistic effects of such a combination may be advantageously utilized.

The term "atmosphere" refers to the gaseous environment in the oven.

Examples of organ metal are dibutyl methilaurate, tetraethyl lead. titanium acetylacetonate, dimethyl tin dichloride and tin and zinc octoates.

Examples of inorganic metal salts are bismuth nitrate and ferric chloride.

Preferably, the drying agent acts in the vapor phase. The term "vapor phase" indicates that the agent is in gaseous, vapor form, or otherwise airborne form (for example, as a dispersion, mist, or aerosol) in which it is accessible for reaction. This phase is achieved by atomizing a predetermined amount of water and a further selected component. The concentration level (water and other component (s)) may vary according to local requirements. However, there appears to be a relationship between the extent of hydrated complex formation and the acceleration of drying.

Typically, the substrate covered with a binder is subjected to an atmosphere comprising water atomized to such an extent that a relative humidity level in the range of 40 to 80 ° / o is obtained, depending on the temperature, which may be in the range of 10 to 40 ^ C.

The other component (or components) is normally present in the order of ppm and varies depending on the component selected. For example, a dimethylethanolamine-containing atmosphere may contain from 500 to 5,000 ppm of this substance, N, N, N ', N'-tetramethylethylenediamine may contain from 250 to 2,500 ppm of this substance and and N, N, N, N, N, N, N-pentamethyl-1. -propanediamine may contain 200 to 2000 ppm; of this substance.

The present invention is particularly suitable for drying commercially available one-component binders. It is well known that one-component systems traditionally require an extended period to achieve a fully enhanced dry state ro. It is found that accelerating the curing by increasing the temperature has an adverse effect on productivity, as this temperature increase causes a reduction in the availability of water at the reaction sites. Previously, one-component systems requiring moisture to cure were unsuccessful on an industrial scale.

However, the present invention not only facilitates the introduction of moisture, but also so accelerates the crosslinking reaction that fully dried coatings can be achieved, for example, from 3 to 4 minutes. For example, exposing a standard test panel coated with a single component paint of up to 100 microns in thickness to the drying agent of the present invention may result in a liquid-to-solid transition being effected in a shorter time as described above.

This led to the inevitable conclusion that both water and catalyst molecules should be present at the site of the reaction at the same time. The best theory to explain this phenomenon is that the catalyst molecule undergoes a complexing reaction with the available water molecules, and this hydrated catalyst complex permeates the wet coating coating in proportion to the vapor pressure concentration gradient. The existence of this hydrated catalyst complex is supported by the experimental data set forth below, which have been utilized using special apparatus to determine the relative combustion temperature of various chemical compounds.

A kombustimeter is an instrument that utilizes the variation in resistivity between the reference and active fibers generated by the heat from combustion of any organic compound in the vapor phase, and converts it into an output signal, measured in millivolts. The achieved stress in millivolts is then proportional to the heat of combustion of the test compound and its concentration. The following tables and the attached graphs show the results obtained when certain amounts of five different chemical compounds were tested at constant concentrations and varying relative humidity levels. The original output voltage achieved on the instrument is set to zero and is independent of the relative humidity of 0 to 100%.

The concentration of each material in the vapor phase is selected to match the optimum output voltages in the range of interest.

Five compounds (dimethylethanolamine, N, N, N ‘, N‘-tetramethylethylenediamine and N, N, N‘, N ‘, 2-pentamethyl259183) were tested as evidence that a hydrated catalyst complex exists.

8

-1,2-propanediamine, solventn-afta 100 and ethanol to determine if their combustion heat (burning temperature measured by output voltage) has changed with relative humidity changes. The results are shown in Table 1.

Table I

Catalyst: dimethylethanolaniin Temperature - 25 ° C, concentration = 2055 ppm.

Relative humidity (%) Voltage (mV) 0 23.94 10 22.80 14 21.04 45 14.25 60 10.26 75 7, '98 81 5.70

Catalyst: N, N, N, N-tetramethylethylenedlamine

Temperature = 25 ° C, concentration = 776 ppm.

Relative humidity ( %) Voltage (mV) 0 18.25 15 Dec 17.10 45 14.25 62 12.83 88 10.26

Catalyst: N, N, N ‘, N‘ 2-pentamethyl-1,2-propanediamine

Temperature = 25 ^σ ΰ, concentration = 775 ppm.

Relative humidity (%) Voltage (mV) 4 17.10 16 17.10 45 14.25 62 12.54 80 11.40

Solventnafta 100

Temperature = 25 ° G, concentration = 6578 ppm.

Relative humidity i (%) Voltage (®1V) Ю 14.25 16 14.25 45 14.25 65 14.25 85 14.25

Ethanol

Temperature = 25 ° C, concentration = 1770 ppm.

Relative humidity ('%) Voltage - (mV?) 16 14.25 24 14.82 45 14.82 80 14.82

The results of Table I are summarized in the accompanying Fig. 1, with the vertical axis у plotted in millivolts -a and the horizontal axis k plotted relative humidity in percent at 25 ° C.

The graphical information is explained as follows: dtoethylethanolamm represents line A,

N ^ N / N ^ N ^ tetramefhylethylenediamine represents line B,

N, N, N, N-pentamethyl-1H-propanediamine represents line C, solvent naphtha 100 represents line D, and ethanol is represented by line E.

In Figure 1, the results are plotted as the output voltage versus relative humidity. Three compounds were affected by relative humidity changes, while two compounds were not affected by relative humidity changes. The three affected compounds are in all cases tertiary amines, of which alkanolamine (dimethylethanolamine) shows particularly promising variations. The other two compounds showed no dependence on relative humidity, exhibiting a constant output voltage of 14 and 14.5 mV over the entire relative humidity range of 0 to 100%. One of the unaffected compounds is ethanol, which would normally form very strong hydrogen-water bonds in the liquid phase. The fact that no deviations have been found for ethanol further supports the assumption that the complex with water occurs at the target, the amino terminus of the dimethylethanolamine molecule, which also contains a hydroxyscape in its structure.

The graph for dmethyiethanolamine shows a linear dependence on relative humidity, suggesting that the formation of complexes with water molecules is proportional to the concentrations of these two compounds, and that the heat of combustion of the formed complex has actually changed. lethanola minu.

As can be seen from the foregoing, for single-component systems it is important that certain parameters be kept above the minimum level in order for the VAPOCURE chamber to achieve the correct cure response. Since the applied coating weight, catalyst concentration and injection rate are either fixed or controllable under the conditions of today's devices, only then remains to be determined that the humidification and temperature control is preferably performed as desired.

The invention will be further described with reference to the following specific examples. Again, it is to be understood that the following description is intended only as an illustration of the invention.

Comparative Example 1

Two standard, rectangular, test coating panels (substrate) were sprayed with a one-component white paint that had previously been mixed with the calculated amount of water necessary for effective and complete crosslinking. The first panel was used as a control and allowed to air dry, the second panel being used as a test and processed as follows:

The test panel was placed in a closed oven, where an atmosphere containing dimethylethanolamine (DMEA) at a concentration of 1250 ppm was created by injecting precisely metered doses of the compound. The temperature was maintained at 25 ° C and the relative humidity at 40%. This medium was recirculated at a rate of 1.5 meters per second for 2 minutes, and then a three minute cleaning cycle began. After the cleaning cycle had removed the dimethylethanoliamine from the oven and replaced it with clean air, the test panel could be safely removed.

The test panel had traces of surface _{from the} shell, while the lower parts remained completely wet. It took 3 to 4 hours for the test panel to reach a curing degree of 3 to 4 (as defined below). The control panel needed 8 to 10 hours to reach the same degree of cure.

Comparative Example 2

In this experiment, two panels were sprayed with a one-component white paint which had previously been mixed with 0.5% by weight of dimethylethanolamine to catalyze the cure reaction. One panel was again used as a control for air drying, while the other test panel was processed as follows:

The test pan was placed in a sealed oven, where an atmosphere of water was created by injecting accurately metered portions of water to achieve a relative humidity of 65% at 25 ° C. This environment was recirculated at a rate of 1.5 meters per second for 2 minutes, and then a three minute cleaning cycle restored normal conditions and the test panel could be removed.

The test panel showed a slight increase in tack but at 4 hours reached a cure degree of 3 to 4 (see explanation below). The control panel needed 6 hours to achieve the same degree of cure and a much longer time than the resistance to solvent rubbing.

Even if the transfer of the dimethylethanolamine molecule to the coated coating was a concentration gradient supported by the spray rate, it would be easy to detect and understand. The transfer of water molecules appears to be less clear. A well-accepted hypothesis, however, is that the catalyst, which is very hydrophilic, forms a complex with the available water molecules and thus permits transfer to the wet coating coating. In the vicinity of the NCO group, the water molecules react rapidly and thus perhaps allow the entrained catalyst molecules to be removed from the coating.

Relying on ambient conditions to deliver the necessary amount of water to the curing tunnel throughout the year could be somewhat risky, especially in areas that suffer from low relative humidity at certain times of the year. For this reason, it is necessary to moisten the curing zone in each VAPOCURE device when using single-component VAPOCURE systems.

Table II shows the interaction between water and the catalyst as formed by gravimetric addition to the one-component VAPOCURE paint in the mass and not in the vapor phase.

Table II

Influence of Moisture and Catalyst on VAPOCURE One Component System

Additive 2% Time to Time for thickening of gelatinization by weight

H2O 2 hours 12 hours

H2O: DMEA 3.5 minutes 5 minutes (1: 1)

DMEA 25 minutes none - minutes Unlimited stability in closed containers no

Example 1

In this experiment, two standard paint panels were coated with a one-component white paint as a substrate in an unmodified stable form. One panel was again air dried as a control, while the other panel was tested as follows:

The test panel was placed in a closed oven, where an atmosphere containing 1250 ppm of dimethylethanolamine was formed at a relative humidity of 65% at 25 ° C by accurately injecting accurately measured portions of dimethylethanolamine -and water. This environment was recirculated for 2 minutes and then a 3 minute cleaning cycle restored to normal conditions and the test panel was removed. The test panel had a degree of cure of 1 to 2 (see explanation below), showing only a few minutes later a minimal effect when subjected to twenty double rubs with methyl ethyl ketone (MEK). The control panel was still completely wet, and also after 24 hours the coating was soluble on contact with methyl ethyl ketone.

Example 2

In this experiment, two standard paint panels were coated with a one component white paint as a substrate in an unmodified stable form. One panel was air dried as a control, while the other panel was tested as follows:

The test panel was placed in a sealed oven to create an atmosphere containing 600 ppm of N, N, N ', N'-tetramethylethylenediamine at 65% relative humidity and at 25 ° C by injecting metered doses of N, N, N' together. , N'-tetramethylethylenediamine and water. This environment was then recirculated for 2 minutes, after which the three minute cleaning cycle resumed normal conditions and the test panel was removed. The test panel was found to be fully cured, and a few minutes later had full resistance to contact with methyl ethyl ketone. The control panel was completely wet and the test the next day showed that the coating still showed some solubility of v-methyl ethyl ketone.

Example 3

In this experiment, two standard paint panels were coated with a one-component white paint as a substrate in an unmodified stable form. One panel was air dried as an o-control and the other was tested as follows:

The test panel was placed in a sealed oven, where an atmosphere containing 500 ppm of N, N, N, N, N-N-2-pentamethyl-1,2-propane diamine was created at 65% relative humidity at 25 ° C by injecting measured accurately doses of N, N, N ', N', 2-pentamethyl-1,2-propanediamine and water. This medium was then recirculated for 2 minutes and then a 3 minute cleaning cycle restored to normal oven conditions and the test panel removed.

Again, it was found that the test panel was fully cured at this point and a few minutes later showed full resistance to contact with methyl ethyl ketone. The control panel was wet and the next day showed that it had some solubility in methyl ethyl ketone.

Other variable parameters that affect the cure rate of single component systems are catalyst concentration, temperature, coating weight and spray rate.

Since the catalyst concentration and coating weight should be kept constant, only other variables, temperature, relative humidity and spray velocity, have to be considered.

Since temperature prescribes the air capacity to carry water, it is important that this variable parameter does not fall below a predetermined level. Also, the rate of any reaction is temperature dependent, which implies that very low temperatures have a double harmful effect by reducing atmospheric humidity and slowing the reaction rates.

The spray rate of the recirculated air stream helps by providing the necessary concentration gradient of the water / catalyst mixture to penetrate it into the wet coating coating. Speeds should be as high as possible, although a speed of 1.0 meter per second can be allowed.

Giant. Figures 2 to 4 show the effect of these variable parameters on the cure level of a one-component system.

In these Figures 2 to 4, the vertical axis θ indicates the degree of cure (see the explanation below), while in Fig. 2: the horizontal x axis indicates the temperature in degrees Celsius. For this case, the spray rate was maintained at 1.4 meters per second, the relative humidity was 6П percent and the dimethylethanolamine had a concentration of 1250 ppm, Fig. 3: the horizontal x-axis indicates the relative humidity in percent. For this case, the spray rate was maintained at 1.4 meters per second, the temperature was maintained at 25 degrees Celsius and the dimethylethanolamine had a concentration of 1250 ppm, Figure 4: the horizontal x-axis indicates the spray rate in meters per second. For this case, the relative humidity was maintained at 60%, the temperature was 25 ° C and the dimethylethanolamine concentration was 1250 ppm.

The degree of cure is directly correlated with the following hardness scale:

239Э & 3

Curing grade Hardness pencil hardness "H" pencil hardness "3B" or better pencil hardness "6B" or better imprint weak adhesion sticky coating moving layer thick liquid liquid unchanged

Table III serves to illustrate how the degree of cure of a particularly selected one-component system is influenced by these critical variables described previously.

Table III

Panel no. DMEA ppm Relative humidity % Temperature ° C Spray speed m / s Degree of cure Critical factor 1 650 61 20 May 3.5 9 Low catalyst concentration 2 800 64 16 3.5 4 Low catalyst concentration, low temperatures 3 1 250 30 32 1.4 4 Low relative humidity 4 1 350 55 31 0.8 3 Low spray rate 5 1 250 66 20 May 1.4 1 The right conditions 6 1000 60 25 1.4 1 The right conditions

The conditions to be maintained for the successful drying of one-component paint systems for dimethylethanolamine are as follows:

A. oven:

1. a temperature of 25 to 30 ° C;

2. a relative humidity of 60 to 65% maximum,

3. Spray speed not less than 1,0 m / s;

4. A catalyst concentration of 1100 to 1,250 ppm.

B. post-drying treatment chamber:

1. a temperature of approximately 25 ° C;

2. A spraying rate not less than 1,0 meter per second.

Further experiments in which the water and catalyst concentration levels were variable showed that certain concentration ratios had a maximum effect on the curing effect and that this ratio was tied to the formation of a certain hydrated catalyst complex in the air solution, facilitating the introduction of water into the hydrophobic paint. coating.

In summary, the invention provides a method for accelerating the polymerization of isocyanate-terminated prepolymers by facilitating the entry of water into these systems by forming hydrated catalyst complexes in the vapor phase.

Claims (2)

A process for preparing a dried coating by applying a one-component binder containing free isocyanate groups to a substrate, characterized in that the binder with a polyisocyanurate, urethane, urea, biuret or allophoneate structure is dried by treatment with a hydrated vapor phase catalytic complex consisting of an amine, tertiary amine , organometallic or organic metal salts at a concentration of 100-3000 ppm by weight in an atmosphere having a relative humidity of 40 to 80% and at a temperature of from 10 to 40 ° C. 2. Process according to claim 1, characterized in that the binder ^{1 is} dried at a temperature of 25 [deg.] C. and a relative humidity of 65%.