DE19724236B4 - Method for polarizing hydrophobic surfaces - Google Patents

Abstract

method for polarizing the hydrophobic surfaces of a workpiece, thereby characterized in that surfaces be treated with a polarizing agent or the polarizing agent added to an agent used to form the hydrophobic surfaces is, wherein the polarizing agent is obtainable by reacting a Diisocyanate with a first polyalkylene glycol, wherein the first Polyalkylene glycol derived from a monool, diol or polyol is and an average molecular weight in the range of 400 to 30,000 has, and subsequent Reacting the prepolymer thus formed with a second polyalkylene glycol, wherein the second polyalkylene glycol is derived from a monool and has an average molecular weight in the range of 400 to 24,000, and wherein to form the prepolymer 0.8 to 1.2 moles of diisocyanate per mole of free hydroxyl groups of the first polyalkylene glycol and to form the polarizing agent 0.8 to 1.2 moles of the second polyalkylene glycol be used per mole of diisocyanate.

Description

The The invention relates to a method for polarizing the hydrophobic surfaces a workpiece, and in particular a method for polarizing the hydrophobic surfaces of sized and / or coated papers.

Workpieces with hydrophobic surfaces be for numerous applications needed. The hydrophobic character of the workpiece surfaces is based either on the Selection of a suitable workpiece material, such as. Teflon, or is targeted in the manufacture of the workpiece by adding or applying hydrophobing agents, e.g. Paraffin, produced. A provided in this way with a hydrophobic surface workpiece is little or no wettable with water and has in the Generally, a low water absorption capacity. A further processing of workpieces with such hydrophobic surfaces using aqueous systems, such as. However, printing with water-based inks is only possible, if the surface previously treated with so-called wetting agents. These wetting agents but reduce the desired Hydrophobicity of the workpiece and allow such an undesirable Absorption of water. For this reason compromises had to be made in Buy be taken where either largely on the processing ability or waived the hydrophobicity of the workpiece surfaces.

From the DE 195 26 278 A1 coating compositions are known which contain at least one water-dispersible polyisocyanate and which are suitable for the production of coated papers and cardboard. The water-dispersible polyisocyanates are obtainable by reacting unmodified polyisocyanates having an average NCO functionality of 1.8 to 4.2 and mono- or polyhydric, preferably having from 5 to 70 ethylene oxide units, optionally containing ester groups Polyalkylenoxidpolyetheralkoholen. The coating composition is intended to ensure the bleeding fastness of visually brightened coating colors.

The DE 42 03 217 A1 teaches a process for making coatings on any water-resistant substrates using an aqueous coating agent whose binder consists essentially of a hydrophilically modified, water-compatible polyisocyanate having free isocyanate groups. The hydrophilically modified polyisocyanates are prepared by reacting suitable starting polyisocyanates with substoichiometric quantities of monohydric or polyhydric polyether alcohols whose polyether chains consist of at least 70 mol% of ethylene oxide units.

It There is therefore a need for a method for polarizing the hydrophobic surfaces of workpieces, on the one hand the Weiterverarbeitbarkeit the workpieces with aqueous systems allows on the other hand, the desired hydrophobic properties, in particular the resistance to a Absorption or penetration of water, not deteriorated.

According to the invention Therefore, a method is provided for polarizing the hydrophobic surfaces of a workpiece, which is characterized in that the surfaces with a polarizing agent or the polarizing agent, possibly already during the production of the workpiece, added to an agent used to form the hydrophobic surfaces is, wherein the polarizing agent is obtainable by reacting a Diisocyanate with a first polyalkylene glycol, wherein the first Polyalkylene glycol derived from a monool, diol or polyol is and has a mean molecular weight in the range of about 400 to about 30,000, and then reacting the prepolymer so formed with a second polyalkylene glycol, wherein the second polyalkylene glycol derived from a monool and has an average molecular weight in the range of about 400 to about 24,000, and wherein the Formation of the prepolymer about 0.8 to 1.2 moles of diisocyanate per mole free hydroxyl groups of the first polyalkylene glycol and for formation of the polarizing agent about 0.8 to 1.2 moles of the second polyalkylene glycol each Mol diisocyanate can be used.

The diisocyanate and the first and the second polyalkylene glycol are preferably used in stoichiometric amounts. More preferably, about 1 mole of diisocyanate per mole of free hydroxyl groups of the first polyalkylene glycol is used to form the prepolymer, and about 1 mole of the second polyalkylene glycol per mole of diisocyanate is used to form the polarizing agent. The average molecular weight of the first polyalkylene glycol is preferably in the range between about 4,500 and 9,000, while the average molecular weight of the second polyalkylene glycol is preferably between about 2,600 and 4,800.

The in the method according to the invention used workpiece can be made of glass, natural and artificial stone, rubber, paper, cardboard, Ceramics, leather, textiles, metal, plastic and wood existing Group selected become. According to one particularly preferred embodiment becomes as a workpiece used a sized paper. The polarizing agent is in in this case the sizing agent (i.e., the water repellent) added and, optionally, in a known manner with the aid of a Applied size press. According to one another embodiment of the invention is a coated paper as the workpiece used and the polarizing agent added to the coating color. The coating color is in a known manner in a coating machine applied.

The to form the prepolymer by reacting with a diisocyanate used first polyalkylene glycol is preferably an addition product of ethylene oxide and / or propylene oxide to a monool, diol or polyol. That as a starter molecule monool, diol or polyol used is preferably glycerin, sorbitol, sucrose or trimethylolpropane. The polyalkylene glycol may be a block copolymer or a polymer having random distribution of the ethylene oxide and Be propylene oxide units. The number of alkylene oxide units preferably varies between 8 and 600, more preferably between 100 and 150.

The diisocyanate used for reaction with the first polyalkylene glycol is preferably an aromatic diisocyanate, more preferred Toluene diisocyanate.

The used for reaction with the prepolymer second polyalkylene glycol is preferably an addition product of ethylene oxide and / or propylene oxide to a monool, wherein as monool preferably methanol or butanol be used. The polyalkylene glycol may be a block copolymer or a polymer having random distribution of the ethylene oxide and Be propylene oxide units. The number of alkylene oxide units is preferably in the range of 8 to 400, here preferably between 60 and 80. Particularly preferably, the second polyalkylene glycol about 70 ethylene oxide and / or propylene oxide units.

The Polarizing agent may be used alone or in combination with the Formation of hydrophobic surfaces used, for example paraffins, synthetic sizing agents, Polymers or starch, be used. Preferably, the polarizing agent becomes this to form the hydrophobic surfaces used in in an amount of 0.05 to 1.0 percent by weight, more preferably in an amount of 0.1 to 0.3 percent by weight, respectively on the solids content of the mixture added.

The inventive method results in workpieces with polarized hydrophobic surfaces opposite to the Ingress of water extraordinarily resistant are, at the same time but further processed using aqueous systems can be. For example, by the addition of the polarizing agent to a sizing agent a vollgeleimtes paper are produced, the almost no water absorbs its surface compared to conventional vollgeleimten papers but is much better wettable. Of the same effect can be synonymous by adding the polarizing agent to a coating color.

The with the aid of the method according to the invention achieved polarization of the hydrophobic surfaces can be determined by a determination the interface energy the treated with the polarizing agent or with the addition of the Polarizing means formed hydrophobic surface detected become. But since the workpieces are solids, a direct measurement of the interfacial energy is not possible. The Determination of the interfacial energy must therefore over indirect Methods are carried out, e.g. a contact angle measurement with liquids known surface tension.

The contact angle of a liquid drop applied to a solid is determined by the equilibrium of forces in the three-phase contact solid / liquid / gaseous. From this equilibrium follows the equation introduced by Young: γ s = γ l cosΘ + y sl y _{s is} the interfacial energy of the solid, y _{l is} the surface tension of the liquid used for the measurement, y _{sl is} the interfacial energy at the phase transition solid / liquid and Θ is the contact or contact angle.

In the case of a contact angle Θ <90 °, the solid is wetted by the liquid. A contact angle Θ> 90 ° indicates that the solid is not or only partially wetted by the liquid.

In In practice, there are a number of factors that affect the value of Randwinkel Θ additionally influence can. Which includes Among other things, the macroscopic roughness of the solid, the chemical heterogeneity the solid surface and the Resolution of the wetting liquid and any chemical reactions that may occur when the liquid longer Time acts on the solid surface.

These factors can be eliminated in many cases by measuring the so-called static advance edge angle Θ _a , which can be obtained, for example, with the aid of the dynamic edge angle method (DRM). In this method, the solid sample to be examined is placed on a movable measuring table, with the aid of a control, a syringe containing the desired liquid selected and applied via a cannula, a drop of liquid on the solid surface. Using a video camera, an image of the liquid drop is taken and evaluated in real time using a personal computer. Among other things, this apparatus enables the measurement of the static advancing edge angle Θ _a , to the determination of which the drop is continuously increased, so that it constantly wets a fresh solid surface. The measurement of the contact angle is made in this case only when the movement of the liquid drop is stopped, that is, the fluid pressure in the cannula is zero.

To determine the interfacial energy γ _{s of} a solid, it is necessary to measure the contact angle with several liquids of known surface tension. In order to obtain meaningful values, the interfacial energy γ _{s is} separated into a dispersive (hydrophobic) and a polar component according to the method of Owens-Wendt-Rabel-Kaelble: γ = γ d + γ p

The dispersive component γ ^d interface energy is based almost exclusively on London van der Waals forces. By contrast, the polar fraction γ ^{p of} the interfacial energy is determined, for example, by dipole-dipole, inductive and acid-base forces and hydrogen bonds.

worin γ_l und γ_s die oben angegebenen Bedeutungen besitzen und die hochgestellten Indizees d und p den dispersiven bzw. polaren Anteil von γ_l bzw. γ_s bezeichnen. Durch Messung des Randwinkels Θ_a unter Verwendung mehrerer Flüssigkeiten mit bekannten Werten für γ_l, γ_l ^d und γ_l ^p lassen sich aus dieser Gleichung durch lineare Regression die unbekannten Größen der Festkörperoberfläche γ_s ^d und γ_s ^p bestimmen.Based on theoretical considerations, the following evaluation equation results considering Young's equation above:

wherein γ _l and γ _{s have} the meanings given above and the superscript indices d and p denote the dispersive or polar fraction of γ _l and γ _s , respectively. By measuring the contact angle Θ _a using several liquids with known values for γ ₁ , γ ₁ ^d and γ ₁ ^p , the unknown quantities of the solid surface γ _s ^d and γ _s ^p can be determined from this equation by linear regression.

Further Features and advantages of the invention will be apparent to those skilled in the art from the following description of preferred embodiments.

Example 1: Preparation of the polarizing agent

to Preparation of a usable in the process according to the invention Polarizing agent was toluene diisocyanate with a first polyalkylene glycol reacted at room temperature. The first polyalkylene glycol was a Addition product of ethylene oxide with glycerol with a middle Molecular weight of about 6,000. The ethylene oxide content was about 130 units. Per mole of free hydroxyl groups of the polyalkylene glycol was about 1 mole of toluene diisocyanate used. The one obtained in this way Prepolymer was subsequently reacted with a second polyalkylene glycol. The second polyalkylene glycol was an addition product of ethylene oxide to butanol with a middle one Molecular weight of about 3,500. The ethylene oxide content was about 80 units. For the reaction with the prepolymer was the second Polyalkylenglykol preferably used in excess, so that after the Reaction no reactive diisocyanate remained.

The polarizing agent thus obtained is in water to form a colorless, clear to green Lich yellow, cloudy solution soluble and has a pH of between 6 and 8 on.

Example 2: Polarization the surface a glued paper

• Anmerkung: A = Polarisierungsmittel aus Beispiel 1

Using an alkyl ketene dimer with urea and paraffin additives as sizing agent, a sized paper having a basis weight of 40 g / m ^{2 was} prepared. The sizing was carried out in a known manner by adding the sizing agent to the mass. The dried, sized paper was then subjected to surface sizing in another size press. The sizing agent used here was a 6% starch liquor with different additives of the polarizing agent obtained according to Example 1. The composition of sizing agents used for surface sizing is shown in Table 1 below. Table 1: Composition of sizing agent used for surface sizing

• Note: A = polarizing agent from example 1

In Table 1 designates Sample No. 2-1 with the alkyl ketene dimer glued paper, which can be used without the use of a sizing agent Surface sizing was driven through the size press. Sample No. 2-2 denotes the paper sized using the alkylketene dimer, without further Surface treatment. Sample No. 2-3 refers to this using an alkyl ketene dimer sized paper, its surface treated in a size press with a 6% starch liquor. Samples Nos. 2-4 to 2-6 correspond to the pattern No. 3, wherein the 6% starch fleet but different weights of the polarizing agent, each based on the solids content of the starch solution were added.

Using the dynamic edge angle method described above, the static advance edge angles Θ _a and the interfacial energies of the samples thus obtained were determined. The measuring liquids used were water, glycerol, formamide and ethylene glycol. In addition, the Cobb values were determined according to the international standard ISO 535 (DIN EN 20535), which is a measure of the water absorption capacity of papers. The Cobb 60 "value is the calculated mass of water that is absorbed in 60 seconds by 1 m ² paper or paperboard under the conditions specified in the standard. The results obtained are shown below in Tables 2 and 3.

Table 2: Results of the contact angle measurements

Table 3: Interfacial energies and Cobb 60 '' values of the sized papers

Of the Table 2 above it can be seen that the using Water measured contact angle by the addition of the polarizing agent decreases significantly, that is, with the addition of the polarizing agent to the for the surface sizing used starch fleet preserved paper surface is much better wettable. This result correlates with the from Table 3 to be taken significant increase in the polar Proportion of interfacial energy due to the addition of polarizing agent. Stay at the same time but the Cobb 60 "values are almost unchanged. Of the Addition of the polarizing agent thus causes better wettability of the sized paper with water, without the resistance of the paper to one Penetration of water or the water absorbency in disadvantageous Way to change.

Example 3: Polarization a coated paper

In the same manner as described in Example 2, a paper sized with an alkyl ketene dimer was obtained. The paper had a basis weight of 80 g / m ² . The sized paper was then treated in a coater with a coating color having a pigment content of 100% chalk at a solids content of 59.3% and a pH of 9.0. In further experiments, different amounts of the polarizing agent obtained according to Example 1 were added to this coating color. Table 4 below shows the compositions of the coating color, the respective proportions of polarizing agent, based in each case on the solids content of the coating color, and the amount of coating applied to the sized paper.

Table 4: Composition of the coating color

With the aid of the dynamic edge angle method described above, the interfacial energies γ _{s of} the samples thus obtained were determined. The measurements of the static advancing edge angles were carried out on both uncalanded and calendered samples to compensate for the influence of surface roughness of the examined samples on the measurement result. In addition, as described in Example 2, the Cobb 60 "values for water absorbency were determined. The results obtained are shown below in Tables 5 and 6.

Table 5: Results of the contact angle measurements

Table 6: Interfacial energies and Cobb 60 "values of coated papers

It can be seen from the results given in Tables 5 and 6 that the addition of the polarizing agent to the coating color markedly increases the polar fraction of the interfacial energy γ _s ^p compared to the conventional coating color. The decrease of the values obtained for the contact angle with water of 101.8 ° for the coating color without addition of polarizing agent to 66.9 ° at a polarizing agent content of 1% up to 45.7 ° at a polarizing agent content of 5% also indicate that only the Polarizer addition to the coating color ensures a wettability of the coated paper. However, this increased wettability does not result in an undesirable increase in water absorbency. Due to the increased wettability, the addition of polarizing agent thus results in significantly better processibility with aqueous systems while at the same time retaining the desired hydrophobic properties of the coated paper.

Example 4: Polarization a coated paper

In the same way as described in Example 3, the glued Paper from Example 2 treated with a coating color. The composition the coating color, as well as the added amounts of polarizing agent are given in Table 7 below. The percentages on Polarizing agents each refer to the solids content the coating color.

Table 7: Composition of the coating color

With the aid of the dynamic edge angle method described above, the interfacial energies γ _{s of} the samples thus obtained were determined. In addition, as described in Example 2, the Cobb 60 "values for water absorbency were determined. The results obtained are shown in Tables 8 and 9 below.

Table 8: Results of the contact angle measurements

Table 9: Interfacial energies and Cobb 60 '' values of the coated paper

The result given in Tables 8 and 9 correlates with the results obtained above with respect to the use of a 100% chalk paint. The polarizing agent addition causes a significant increase in the polar portion of the interfacial energy γs ^p as compared to the conventional coating color. At the same time, the contact angle obtained with water decreases. The Cobb 60 "values remain substantially constant despite the improved wettability.

Comparative example

Of the Experiment from Example 4 was performed using the in this example standard coating color repeated, the 1.0 wt .-%, based on the solids content of the coating color, a commercial Wetting agent (Silastan C2, available from the Schill & Seilacher GmbH & Co., Böblingen, Germany) were added. The ones obtained for this coating color Results of the contact angle measurements are shown in Table 10 below specified.

Table 10: Static advance edge angles Θ _a

at the measurement of interfacial energies and the Cobb 60 "values of the thus obtained coated paper were as shown in Table 11 below Results obtained.

Table 11: Interfacial energies

Of the Comparison of the commercial Wetting agent Silastan C2 with the results obtained for sample No. 4-3 From Tables 8 and 9 clearly shows that the conventional wetting agent, although expected, the wettability of the coated paper increases, however at the same time the water absorption capacity increased by more than 25%. This undesirable Effect does not occur when using the polarizing agent according to the invention one.

Claims (27)

A method of polarizing the hydrophobic surfaces of a workpiece, characterized in that the surfaces are treated with a polarizing agent or the polarizing agent is added to an agent used to form the hydrophobic surfaces, the polarizing agent being obtainable by reacting a diisocyanate with a first polyalkylene glycol, wherein the first polyalkylene glycol is derived from a monool, diol or polyol and has an average molecular weight in the range of 400 to 30,000, and then reacting the thus-formed prepolymer with a second polyalkylene glycol, wherein the second polyalkylene glycol is derived from a monool and has an average molecular weight in the range from 400 to 24,000, and wherein for forming the prepolymer 0.8 to 1.2 moles of diisocyanate per mole of free hydroxyl groups of the first polyalkylene glycol and to form the polarizing agent 0.8 to 1.2 moles of the second polyalk Ylenglykols be used per mole of diisocyanate. Method according to claim 1, characterized in that that this Diisocyanate and the first and the second polyalkylene glycol in stoichiometric Quantities are used. Method according to claim 1 or 2, characterized that to Formation of the prepolymer 1 mole of diisocyanate per mole of free hydroxyl groups of the first polyalkylene glycol and to form the polarizing agent 1 mole of the second polyalkylene glycol per mole of diisocyanate used become. Method according to one of the preceding claims, characterized characterized in that Workpiece off made of glass, natural and artificial stone, rubber, paper, cardboard, ceramics, Leather, textiles, metal, plastic and wood existing group selected becomes. Method according to claim 4, characterized in that that as the workpiece a glued paper is used and the polarizing agent one Sizing agent is added. Method according to claim 4, characterized in that that as the workpiece used a coated paper and the polarizing agent of Coating color is added. Method according to one of claims 1 to 6, characterized that as the first polyalkylene glycol is an addition product of ethylene oxide and / or propylene oxide is used on the monool, diol or polyol. Method according to claim 7, characterized in that that this first polyalkylene glycol an ethylene oxide and / or propylene oxide from 8 to 600 units. Method according to claim 8, characterized in that that the Ethylene oxide and / or Propylene oxide in the range between 100 and 150 units. Method according to claim 7, characterized in that that as the first polyalkylene glycol is a block copolymer. Method according to claim 7, characterized in that that as the first polyalkylene glycol is a random distribution copolymer the ethylene oxide and propylene oxide units is used. Method according to one of claims 1 to 11, characterized that this average molecular weight of the first polyalkylene glycol in the range between 4,500 and 9,000. Method according to one of the preceding claims, characterized characterized in that as the first polyalkylene glycol of glycerine, sorbitol, sucrose or trimethylolpropane-derived polyalkylene glycol used becomes. Method according to one of the preceding claims, characterized characterized in that second polyalkylene glycol has an average molecular weight in the range from 2,600 to 4,800. Method according to one of the preceding claims, characterized characterized in that as the second polyalkylene glycol is an addition product of ethylene oxide and / or propylene oxide is used on the monool. Method according to claim 15, characterized in that that as the second polyalkylene glycol is a block copolymer. Method according to claim 15, characterized in that that as the second polyalkylene glycol is a random distribution copolymer the ethylene oxide and Propylene oxide units is used. Method according to claim 15, characterized in that that the Ethylene oxide and / or propylene oxide in the range between 60 and 80 units lies. Method according to claim 18, characterized that the Ethylene oxide and / or propylene oxide is about 70 units. Method according to one of the preceding claims, characterized characterized in that as the second polyalkylene glycol is a derivative of methanol or butanol Polyalkylene glycol is used. Method according to one of the preceding claims, characterized characterized in that as the diisocyanate is an aromatic diisocyanate. Method according to one of the preceding claims, characterized characterized in that as the diisocyanate toluene diisocyanate is used. Method according to one of the preceding claims, characterized characterized in that Polarizing agent used to form the hydrophobic surface In an amount of 0.05 to 5.0 wt .-%, based on the Solids content is added. Method according to claim 23, characterized that to Formation of the hydrophobic surface Sizing agent used and the polarizing agent in an amount from 0.1 to 0.3 wt .-% is added. Method according to claim 23, characterized that to Formation of the hydrophobic surface a Coating color is used and the polarizing agent in an amount from 1 to 5 wt .-% is added. Use of a polarizing agent for polarization hydrophobic surfaces a workpiece, wherein the polarizing agent is obtainable by reacting a Diisocyanate with a first polyalkylene glycol, wherein the first Polyalkylene glycol derived from a monool, diol or polyol is and an average molecular weight in the range of 400 to 30,000 has, and subsequent Reacting the prepolymer thus formed with a second polyalkylene glycol, wherein the second polyalkylene glycol is derived from a monool and an average molecular weight in the range of 400 to 24,000 and wherein to form the prepolymer 0.8 to 1.2 mol Diisocyanate per mole of free hydroxyl groups of the first polyalkylene glycol and to form the polarizing agent 0.8 to 1.2 moles of the second Polyalkylene glycol per mole of diisocyanate can be used. Use according to claim 26, characterized that this Polarizing agent available is more stoichiometric by reacting Amounts of the diisocyanate and the first and second polyalkylene glycol.