Use of polyvinyl isoacetals in printing ink formulas

The present invention relates to the use of polyvinyl isoacetalen obtained by the reaction of polyvinyl alcohol with a branched aliphatic aldehyde in a formulation for printing ink.

The use of polyvinyl acetals, especially polyvinyl butyral, as binders in printing ink formulations has long been known.

For this reason, polyvinyl acetals are often used (eg, as a binder in flexographic printing inks), which have the lowest possible viscosity in the dissolved state. Therefore, at the same time, it is possible to realize a high pigment ratio and a binder ratio in the printing ink, which leads to a higher desired ink strength.

In the production of such polyvinyl acetals, a correspondingly less viscous polyvinyl alcohol is generally selected as the raw material, which is then usually acetalized with n-butyraldehyde. The disadvantages of this procedure are that the conversion rate tends to decrease, and that the low glass transition temperature with low molecular weight and the associated increased stickiness make it difficult to produce the product. .. At that time, the low Tg (<65 ° C) inherent in the low-viscosity polyvinyl acetal also poses difficulties in the final application, for example, when printing ink.

Many chemically different polyvinyl acetals have already been proposed for use in printing inks. For example, it is known to use a copolymer of a tertiary vinyl ester and vinyl acetate as a raw material for producing polyavinyl acetal, and the copolymer is further used as an impurity as a tertiary ester functional group. Is contained in the molecule. Moreover, in addition to butyraldehyde, long chain aldehydes with 5-10 carbon atoms are known to be used for acetalization. Similarly, after acetalization of polyvinyl alcohol or during acetalization, long chain molecules such as sugars or oligoglycols can react with the polymer chains and also act as impurities.

The disadvantages of these methods are their high complexity and their apparently higher cost compared to the large-scale industrially established acetalization of polyvinyl alcohol with butyraldehyde.

<p num="0007"> Therefore, what is desirable for printing ink formulations is polyvinyl, which at the same time has high Tg and low viscosity, but is not significantly different from known polyvinyl butyral in terms of its properties, especially in terms of polarity and manufacturing method. Use acetal.</p><p num="0008"> Butyraldehyde used for the industrial production of polyvinyl butyral consists exclusively of n-butyraldehyde. This is presumably due to its large-scale industrial production by hydrocarbonylation of propene (oxo method), which provides thermodynamically controlled and almost exclusively n-butanol.</p><p num="0009"> Polyvinyl butyral produced by acetalization of polyvinyl alcohol with isobutyraldehyde is a known compound (eg, Fitzhugh, Crozier, J. Pol. Sci. Vol. VIII, No. 2, p. 225-241 or Nakamura, Suzuki, J. . Pol. Sci, Vol. 34, p. 3319-3328 (1996)), but with technical significance based on the poor industrial availability of isobutyraldehyde compared to n-butyraldehyde. Does not have.</p><p num="0010"> Surprisingly, isobutyraldehyde-based polyvinyl butyral has the required properties such as high glass transition temperature and low viscosity, but at the same time does not show significant changes in polarity and therefore favorably. It has been found that it wets the pigment and is therefore well suited for use in printing inks. Regardless of the validity of this theory, this can be explained by the branching of molecules.</p>

<p num="0011"> By using, for example, isobutyraldehyde instead of the conventional n-butyraldehyde for acetalization of polyvinyl alcohol, lower viscosity and lower viscosity and compared to comparative products of the same chemical composition based on n-butyraldehyde A polyvinyl acetal showing a higher glass transition temperature is obtained. These compounds are hereinafter referred to as polyvinyl isoacetals.</p><p num="0012"> The object of the present invention is the use of polyvinyl isoacetal as a binder in a printing ink formulation, wherein the acetal group of the polyvinyl isoacetal has at least one branch at the α or β position with respect to the keto group. It results from one or more aliphatic keto compounds having 4 to 10 carbon atoms.</p><p num="0013"> The use of polyvinyl isoacetals according to the present invention in the application of printing inks provides the advantage of lower viscosity with the same binder content than the use of polyvinyl acetals with n-acetal groups. In the printing ink / printing ink concentrate, the pigments and binders are present in a certain ratio (often 1: 1.2), so for a given final viscosity of the printing inks, the amount of pigments and binders is optionally high. It doesn't become. Then, if a binder with a relatively low viscosity is provided, the degree to which it contributes to the overall viscosity is also relatively low initially. Therefore, the proportion of pigment can be increased. At the same time, a slightly higher binder must be added. The overall viscosity, however, does not exceed a predetermined maximum. However, the system has more pigments and binders, which results in higher ink strength.</p><p num="0014"> A further advantage is the enhanced Tg of polyvinyl isoacetal compared to the conventional n-acetal. This is important in that respect for printing inks. This is because higher temperature stability means lower stickiness and slower softening of the printing ink on the surface. Premature softening can, in some cases, lead to delamination of the complex in laminated printing inks (Laminationsdruckfarben). Even in the case of surface printing (beverage paper container), the softening of the printing ink earlier than planned is a drawback. Beverage paper containers may adhere to each other or the ink may fail.</p><p num="0015"> Polyvinyl isoacetals according to the present invention are advantageously composed of polyvinyl alcohol and one or more aliphatic aldehydes having 4 to 10 carbon atoms having at least one branch at the α- or β-position with respect to the aldehyde group. Obtained by reaction with.</p><p num="0016"> Within the scope of the present invention, the acetal group is advantageously one or more aliphatic aldehydes or isobutyl aldehydes, isobarrel aldehydes, (α) -isobarrel aldehydes [2-methylbutanal], (β)-. Polyvinyl acetals resulting from keto compounds in the group of isobarrel aldehyde [3-methylbutanal] and pivalin aldehyde [2,2-dimethylpropanol] are used.</p><p num="0017"> Alternatively, polyvinyl isoacetals can be combined with polyvinyl alcohol. a) One or more aliphatic keto compounds having 3 to 10 carbon atoms and having at least one branch at the α or β position with respect to the keto group. b) One or more additional aliphatic keto compounds with 2-10 carbon atoms It can be caused by a parallel reaction with.</p><p num="0018"> The proportion of acetal groups in polyvinylisoacetals from aliphatic keto compounds having 4-10 carbon atoms with at least one branch at the α- or β-position relative to the keto group is 2-10 carbon atoms. It may be 20-95 mol%, preferably 50-90 mol%, based on the acetal group of the polyvinyl acetal from the additional aliphatic keto compound having.</p><p num="0019"> Advantageously, acetaldehyde and / or n-butyraldehyde is used as additional aliphatic keto compounds.</p><p num="0020"> The polyvinyl isoacetals used according to the present invention advantageously have a viscosity at least 10% lower than the corresponding polyvinyl (n) acetals. For this comparison, of course, other chemically identical polyvinyl isoacetals and polyvinyl (n) acetals must be considered, except for the n / iso-acetal group. Viscosity measurements are made according to the methods given in the examples.</p><p num="0021"> In addition to the polymeric binder, the commonly used components of the printing ink formulation are solvents and optionally additives such as waxes, co-binders (ketone resins, urethanes, etc.), and dispersion aids and adhesion promoters. According to the present invention, polyvinyl isoacetal is used in a proportion of 1 to 30% by mass with respect to the printing ink formulation.</p><p num="0022"> Within the scope of the present invention, it is also possible to use a mixture of polyvinyl isoacetal and polyvinyl acetal having an n-acetal group known from the prior art as a binder for printing ink.</p><p num="0023"> Therefore, a further object of the present invention is the use of a mixture of polyvinyl isoacetal and at least one additional polyvinyl acetal as a binder in a printing ink formulation, wherein the acetal group of the polyvinyl isoacetal is keto. The at least one additional polyvinyl acetal, which results from one or more aliphatic keto compounds having 4-10 carbon atoms and having at least one branch at the α or β position with respect to the group, is composed of polyvinyl alcohol and It is obtained by reaction with one or more additional aliphatic keto compounds having 2-10 carbon atoms.</p><p num="0024"> The special embodiments described for the use of polyvinyl isoacetals also apply to use in mixtures with conventional polyvinyl acetals as well.</p><p num="0025"> Advantageously, additional polyvinyl acetals are obtained, for example, by reaction of acetaldehyde and / or n-butyraldehyde with polyvinyl alcohol. The reaction conditions correspond to those of polyvinyl isoacetal. In particular, a mixture of polyvinyl isoacetal obtained by the reaction of polyvinyl alcohol and isobutyraldehyde and polyvinyl acetal obtained by the reaction of polyvinyl alcohol and n-butyraldehyde is used.</p><p num="0026"> Advantageously, the mixture used according to the invention contains 10 to 90% by weight of polyvinyl isoacetal and 90 to 10% by weight of additional polyvinyl acetal, especially 50% by weight each.</p><p num="0027"> The method for producing a polyvinyl isoacetal is essentially the same as that of a polyvinyl acetal having an n-acetal group. The polyvinyl isoacetal used in the present invention is obtained by reaction of at least one polyvinyl alcohol with at least one of the above-mentioned keto compounds under acid catalysis. This reaction is known to those of skill in the art and can be read, for example, from WO2009 / 132987A1 or EP09175666.8.</p><p num="0028"> Generally, in the production of polyvinyl acetal, polyvinyl alcohol is first dissolved in water under heating and charged into a reaction vessel at a temperature of about 0 to 20 ° C. For this reason, in the first process modification, the acid (HCl, HNO)₃Or H₂SO₄) Is added, or in a further variant, one or more keto compounds or aldehydes are added. As the keto compound or aldehyde, preferably isobutyraldehyde is used under the acquisition of polyvinyl butyral.</p><p num="0029"> According to the process modifications, at the temperatures described above, the desired keto compound is added to form a mixture of polyvinyl alcohol and acid, or the acid is added to form a mixture of polyvinyl alcohol and keto compound. Each addition is carried out until the desired degree of acetalization of the polyvinyl acetal is reached, which precipitates from the reaction mixture as a solid. Method The addition of the acid or keto compound in step a) can be carried out at various dispensing times and / or with a dispensing interruption.</p><p num="0030"> To complete the reaction, the reaction mixture is heated to 30-90 ° C, preferably 35-80 ° C in method step b) and held at this temperature for a period of time. .. In the case of so-called heat denaturation, in addition to perfecting the acetalization reaction, the intramolecular acetal exchange reaction can also be carried out under the formation of the acetal domain and the alcohol domain.</p><p num="0031"> Advantageously, the polyvinyl isoacetals used according to the present invention have a residual alcohol content of 10 to 30%, particularly preferably 15% to 25% and / or 62% to 89.5%, particularly preferably 67% to. It has a degree of acetalization of 84.5%.</p><p num="0032"> Measurement method: a) Measurement of polyvinyl acetate content The polyvinyl acetate content is understood to be the weight percent percentage of acetyl groups resulting from the amount of caustic potash solution used to saponify 1 g of the substance. Measurement method (based on EN ISO 3681): Approximately 2 g of the substance to be tested is precisely weighed into a round bottom flask up to 1 mg and dissolved in 90 ml ethanol and 10 ml benzyl alcohol under reflux. After cooling, the solution is adjusted to neutral to phenolphthalein with 0.01 N NaOH. Subsequently, add 25.0 ml of 0.1 N KOH and heat under reflux for 1.5 hours. The flask is sealed and cooled, and the excess amount of alkaline solution is back titrated with 0.1 N hydrochloric acid to phenolphthalein as an indicator until the discoloration does not disappear. Similarly, the blank sample is processed. The PV-acetate content is calculated as follows: PV-acetate content [%] = (ba) * 86 / E, where a = 0.1 N KOH used for the sample (ml) , B = 0.1 N KOH usage (ml) for blank test and E = net weight (g) of the substance to be tested in dry condition.</p><p num="0033"> b) Measurement of polyvinyl alcohol group content The polyvinyl alcohol group content (polyvinyl alcohol content) is the proportion of hydroxyl groups, which can be detected by later acetylating acetic anhydride. Measurement method (based on DIN 53240): Exactly weigh about 1 g of Mobital into 300 ml of ground-Erlenmeyer flask to 1 mg, add 10.0 ml of acetic anhydride-pyridine-mixture (23:77 V / V), and 15-20 hours, 50 ° C. Heat to. After cooling, add 17 ml of 1,2-dichloroethane and shake temporarily. Subsequently, add 8 ml of water with stirring, seal the flask with a stopper, and stir for 10 minutes. Rinse the neck and stopper of the flask with 50 ml of deionized water, cover with a layer of 5 ml of n-butanol, and titrate free acetic acid against phenolphthalein with 1N caustic soda solution. Similarly, the blank sample is processed. The polyvinyl alcohol content is calculated as follows: polyvinyl alcohol content [%] = (ba) * 440 / E, where a = 1N NaOH used for the sample (ml), b = Amount of 1N NaOH used for blank testing (ml) and E = net weight (g) of the substance to be tested in the dry state.</p><p num="0034"> c) Viscosity measurement The viscosity of the polyvinyl acetal used is measured with a hepler viscometer at 20 ° C. using a solution in ethanol, n-butanol or MEK (methyl ethyl ketone) according to DIN 53015.</p>

<figref num="1">The figure which shows the solution viscosity of polyvinyl isobutyraldehyde acetal dissolved in ethanol</figref>

Pure and mixed polyvinyl isoacetals and polyvinyl acetals are produced by reaction of isobutylaldehyde or n-butyraldehyde and a mixture of aldehydes with isobutylaldehyde / acetaldehyde or n-butylaldehyde / acetaldehyde under the same polyvinyl alcohol under acid catalytic action. And their use in printing ink formulations was investigated.

Example 1 540 g of polyvinyl alcohol with a viscosity of 3.06 mPas (4% in water) and a degree of hydrolysis of 96.5 mol% is dissolved in 6660 mL of water. After adding 340 g of isobutyraldehyde, the reaction is initiated at 4 ° C under a metered supply of 870 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 36 ° C for 2 hours and maintained at this temperature for an additional 2 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 20 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Comparative example 1 540 g of polyvinyl alcohol with a viscosity of 3.06 mPas (4% in water) and a degree of hydrolysis of 96.5 mol% is dissolved in 6660 mL of water. After adding 340 g of n-butyraldehyde, the reaction is initiated at 4 ° C under a metered supply of 870 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 36 ° C for 2 hours and maintained at this temperature for an additional 2 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 20 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Example 2 684 g of polyvinyl alcohol with a viscosity of 4.60 mPas (4% in water) and a degree of hydrolysis of 98.5 mol% is dissolved in 6516 mL of water. After adding 394 g of isobutyraldehyde, the reaction is initiated at 4 ° C under a metered supply of 820 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 44 ° C for 2 hours and maintained at this temperature for an additional 1.5 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 20 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Comparative example 2 684 g of polyvinyl alcohol with a viscosity of 4.06 mPas (4% in water) and a degree of hydrolysis of 98.5 mol% is dissolved in 6516 mL of water. After adding 394 g of n-butyraldehyde, the reaction is initiated at 4 ° C under a metered supply of 820 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 44 ° C for 2 hours and maintained at this temperature for an additional 1.5 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 20 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Example 3 648 g of polyvinyl alcohol with a viscosity of 9.94 mPas (4% in water) and a degree of hydrolysis of 98.4 mol% is dissolved in 6552 mL of water. After adding 400 g of isobutyraldehyde, the reaction is started at 4 ° C under a metered supply of 780 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 48 ° C for 2 hours and maintained at this temperature for an additional 2 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 20 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Comparative example 3 648 g of polyvinyl alcohol with a viscosity of 9.94 mPas (4% in water) and a degree of hydrolysis of 98.4 mol% is dissolved in 6552 mL of water. After adding 400 g of n-butyraldehyde, the reaction is initiated at 4 ° C under a metered supply of 780 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 48 ° C for 2 hours and maintained at this temperature for an additional 2 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 20 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Example 4 (Mixed Acetal from Iso-BuA + AcA) 720 g of polyvinyl alcohol with a viscosity of 3.06 mPas (4% in water) and a degree of hydrolysis of 96.5 mol% is dissolved in 6480 mL of water. After adding 152.2 g of acetaldehyde and 204.2 g of isobutyraldehyde, the reaction is initiated at 8 ° C under a metered supply of 1330 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 36 ° C for 2 hours and maintained at this temperature for an additional 2 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 40 mL of 10% caustic soda solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Comparative Example 4 (Mixed Acetal from n-BuA + AcA) 720 g of polyvinyl alcohol with a viscosity of 3.06 mPas (4% in water) and a degree of hydrolysis of 96.5 mol% is dissolved in 6480 mL of water. After adding 152.2 g of acetaldehyde and 204.2 g of n-butyraldehyde, the reaction is initiated at 8 ° C under a metered supply of 1330 mL of 20% hydrochloric acid solution. After terminating the hydrochloric acid supply, the reaction solution is warmed to 36 ° C for 2 hours and maintained at this temperature for an additional 2 hours. The precipitated solid is filtered off and washed thoroughly with water. For neutralization or alkalinization, mix 40 mL of 10% caustic alkaline solution with the product suspension and warm again slightly. Excess alkaline solution is removed by washing with water. Subsequently, the product is dried.

Solutions were prepared from the products obtained from Examples / Comparative Examples 1-4 and these were examined for their viscosities. Moreover, these products were analytically characterized. The results are shown in Table 1.

The products from Example 1 and Comparative Example 1 were tested for printing ink application. The results are listed in Tables 2 and 3.

It can be seen that all polyvinyl isoacetals have lower viscosities than polyvinyl acetals, which allows higher solid proportions of pigments and binders to be reached in the printing ink formulation at a given maximum viscosity. As a result, higher ink strength can be obtained. Depending on the results obtained, all polyvinyl isoacetals have a higher glass transition temperature (Tg) than polyvinyl acetals. This results in an undesired apparent reduction in stickiness in the final application.

As shown in FIG. 1, the polyvinyl isobutyraldehyde acetal dissolved in ethanol has a clearly lower solution viscosity at the solid concentration (&gt; 20%) commonly used for the production of printing ink concentrates. There is. This allows the use of more binders and pigments at a given viscosity of the ink concentrate or printing ink. Thereby, higher ink strength can be obtained at the same printing viscosity. These higher ink intensities also allow the application of higher printing speeds, which leads to higher throughput and thus time savings in the printing process.

<tables num="1"><img id="000002" he="229" wi="158" file="JP5773785B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

<tables num="2"><img id="000003" he="69" wi="158" file="JP5773785B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

<tables num="3"><img id="000004" he="59" wi="158" file="JP5773785B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

<tables num="4"><img id="000005" he="229" wi="158" file="JP5773785B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>