DE102004054568A1 - High shear thinning polyvinyl acetals - Google Patents

Abstract

The invention relates to highly shear-thinning polyvinyl acetals, characterized in that their solution viscosity in 30 wt .-% - solution in methyl ethyl ketone in a shear rate range of 1 to 100 s · -1 · decreases by at least 30%. The invention further provides a process for the preparation of highly shear-thinning polyvinyl acetals by acetalization of partially saponified or fully hydrolyzed vinyl ester polymers having> = 50 mol% of vinyl alcohol units with one or more aldehydes, optionally in the form of their hydrates, hemiacetals or full acetals. characterized in that the aldehyde is completely added within a maximum of 15 minutes.

Description

The This invention relates to high shear thinning polyvinyl acetals, process for the preparation of high shear thinning polyvinyl acetals, as well as their use.

The Preparation of polyvinyl acetals derived from the corresponding polyvinyl alcohols by polymer-analogous reaction with the corresponding aldehydes to be obtained, has been known since 1924, being in the aftermath a variety of aldehydes for the preparation of the corresponding polyvinyl acetals have been used. Polyvinyl acetals are used in a 3-stage process (polyvinyl acetate -> polyvinyl alcohol -> polyvinylacetal) producing products resulting in addition to vinyl acetal groups still contain vinyl alcohol and vinyl acetate units. commercial Polyvinylformal, Polyvinylacetacetal and Polyvinyl butyral (PVB) obtained.

Under other due to their good pigment binding power are polyvinyl butyrals also used as a binder in paints and especially in printing inks. When used in the coating area is applied by spraying made the requirement that the coating agent at high Shear rate is low on application, to be coated quickly and easily. After the application should the viscosity but again rise rapidly, to run and run to prevent.

The EP 535643 A1 relates to a process for the preparation of polyvinyl acetals having improved melt viscosity by means of acetalization of vinyl alcohol copolymers having a proportion of polyethylenically unsaturated comonomers. For the purpose of acetalization, polyvinyl alcohol and aldehyde are introduced and the acid is metered in continuously. From JP-A 2001-288215 a process for the preparation of polyvinyl acetal resins is known in which polyvinyl alcohol and aldehyde are each partially charged, and the remaining portions are added in portions after cooling the reaction mixture. In JP-A 2000-159831, the main portion of the polyvinyl alcohol is initially charged for the preparation of polyvinyl acetal, acid catalyst and aldehyde are added and the remainder is added to polyvinyl alcohol. In the process of JP-A 10-158328, the acetalization is optimized by adding already acetalated polyvinyl alcohol. WO 03/066690 relates to a process for the preparation of polyvinyl acetals with lower metal contents, wherein the acetalization of polyvinyl alcohol takes place in two reactors connected in series.

It The object was to provide polyvinyl acetals, which in particular in organic solvents, almost independent from the polymer composition and concentration, at high shear stress (Shear rate) a pronounced shear thinning show, that is which are highly pseudoplastic.

The invention relates to highly shear-thinning polyvinyl acetals, characterized in that their solution viscosity in 30 wt .-% - solution in methyl ethyl ketone in a shear rate range of 1 to 100 s ^-1 by at least 30% decreases.

One Another object of the invention is a process for the preparation of high shear thinning polyvinyl acetals by acetalization of partially hydrolyzed or fully hydrolyzed vinyl ester polymers with ≥ 50 mol% Vinyl alcohol units containing one or more aldehydes, optionally in the form of their hydrates, half or full acetals, characterized that the aldehyde content is completely added within a maximum of 15 minutes becomes.

suitable conduct partially hydrolyzed or fully saponified vinyl ester polymers from polymers which contain 50 to 100 mol% of vinyl ester units contain. Suitable vinyl esters are vinyl esters of unbranched or branched carboxylic acids with 1 to 15 carbon atoms. Preferred vinyl esters are vinyl acetate, vinyl propionate, Vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate (Isopropenyl acetate), vinyl pivalate and vinyl ester of α-branched Monocarboxylic acids with 5 to 11 carbon atoms, for example VeoVa9R or VeoVa10R (trade names the company Shell). Particularly preferred is vinyl acetate.

In addition to the vinyl ester units, it is also possible if appropriate to copolymerize one or more monomers from the group comprising methacrylic acid esters and acrylic esters of alcohols having 1 to 15 carbon atoms, olefins, dienes, vinylaromatics and vinyl halides. Suitable monomers from the group of the Es ter of acrylic acid or methacrylic acid are esters of unbranched or branched alcohols having 1 to 15 carbon atoms. Preferred methacrylic esters or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-, iso- and t-butyl acrylate, n-, iso- and t-butyl methacrylate, 2-ethylhexyl acrylate, norbornyl acrylate. Particularly preferred are methyl acrylate, methyl methacrylate, n-, iso- and t-butyl acrylate, 2-ethylhexyl acrylate and norbornyl acrylate. Suitable dienes are 1,3-butadiene and isoprene. Examples of polymerizable olefins are ethene and propene. As vinyl aromatic styrene and vinyl toluene can be polymerized. Of the group of vinyl halides usually vinyl chloride, vinylidene chloride or vinyl fluoride, preferably vinyl chloride, are used. The proportion of these comonomers is calculated so that the proportion of vinyl ester monomer is ≥ 50 mol% in the vinyl ester polymer.

Possibly can even more comonomers in a proportion of preferably 0.02 to 20 wt .-%, based on the total weight of the vinyl ester polymer be included. examples for such comonomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably crotonic, Itaconic acid, fumaric acid and maleic acid; further ethylenically unsaturated carboxamides and -nitriles, preferably N-vinylformamide; also cyclic amides, the nitrogen on the unsaturated Carry group, such as N-vinylpyrrolidone; Mono- and diesters of fumaric acid and maleic such as the diethyl and diisopropyl esters and maleic anhydride, ethylenically unsaturated sulfonic acids or their salts, preferably vinylsulfonic acid. Suitable as comonomers are also cationic monomers such as diallyldimethylammonium chloride (DADMAC), 3-trimethylammoniumpropyl (meth) acrylamide chloride (MAPTAC) and 2-trimethylammoniumethyl (meth) acrylate chloride. Furthermore, as Auxiliary monomers suitable for vinyl ethers and vinyl ketones.

suitable Comonomers are also polymerizable silanes or mercaptosilanes. Preferred are γ-acrylic or γ-methacryloxypropyltri (alkoxy) silanes, α-methacryloxymethyltri (alkoxy) silanes, γ-methacryloxypropylmethyldi (alkoxy) silanes, Vinylalkyldi (alkoxy) silanes and vinyltri (alkoxy) silanes, where as Alkoxy groups, for example methoxy, ethoxy, methoxyethylene, Ethoxyethylene, Methoxypropylenglykolether- or Ethoxypropylenglykolether residues can be used. Examples of this are vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, Vinyltriisopropoxysilane, vinyltris (1-methoxy) isopropoxysilane, vinyltributoxysilane, Vinyltriacetoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, methacryloxymethyltrimethoxysilane, 3-methacryloxypropyltris (2-methoxyethoxy) silane, vinyltrichlorosilane, Vinylmethyldichlorosilane, vinyltris (2-methoxyethoxy) silane, trisacetoxyvinylsilane, 3- (triethoxysilyl) propylbernsteinsäureanhydridsilan. Prefers are also 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane and 3-mercaptopropylmethyldimethoxysilane.

Further Examples are precrosslinking comonomers such as multiply ethylenic unsaturated Comonomers, for example divinyl adipate, diallyl maleate, allyl methacrylate, Butanediol diacrylate or triallyl cyanurate, or post-crosslinking comonomers, for example, acrylamidoglycolic acid (AGA), Methylacrylamidoglykolsäuremethylester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylolallyl carbamate, alkyl ethers such as the isobutoxy ether or ester of N-methylolacrylamide, the N-methylolmethacrylamide and N-methylolallyl carbamate.

These Vinyl ester polymers are commercially available or can be used in known manner be prepared by polymerization; preferably by bulk polymerization, suspension polymerization or by Polymerization in organic solvents, especially preferred in alcoholic solution. Suitable solvents and regulators are, for example, methanol, ethanol, propanol, isopropanol. The polymerization is refluxed at Temperature of 40 ° C up to 100 ° C carried out and by adding more common Initiators initiated radically. Examples of common initiators are percarbonates such as cyclohexyl peroxydicarbonate, azo initiators or peresters such as t-butyl perneodecanoate or t-butyl perpivalate. The adjustment of the molecular weight can in a known manner by addition of regulator, by the solvent content, by varying the initiator concentration and by varying the Temperature done. After completion of the polymerization, the solvent and optionally excess monomer and distilled off regulator.

The saponification of the vinyl ester polymers is carried out in a manner known per se, for example by the belt or kneader process, in the alkaline or acidic state with the addition of acid or base. Preferably, the vinyl ester solid resin is taken up in alcohol, for example, methanol, to adjust a solid content of 15 to 70% by weight. The hydrolysis is preferably carried out in the basic, for example by adding NaOH, KOH or NaOCH ₃ . The base is generally used in an amount of 1 to 5 mol% per mole of ester units. The hydrolysis is carried out at temperatures of 20 ° C to 70 ° C. After completion of the hydrolysis, the solvent is distilled off and the polyvinyl alcohol is obtained as a powder. However, the polyvinyl alcohol can also be obtained by successively adding water while distilling off the solvent as an aqueous solution.

When Fully hydrolyzed vinyl ester polymers are referred to as such Polymers whose degree of hydrolysis> 96 Is mol%. Partially hydrolyzed polyvinyl esters are to be understood as meaning with a degree of hydrolysis ≥ 50 mol% and ≤ 96 Mol%. The partially or fully hydrolyzed vinyl ester polymers have preferably a degree of hydrolysis of from 50 mole% to 99.9 mole%, especially preferably from 70 mole% to 99.9 mole%, most preferably from 90 mole% to 99.9 mole%. The viscosity of the polyvinyl alcohol (DIN 53015, Höppler method; 4% solution in water) 1 to 30 mPas, preferably 1 to 10 mPas, and serves as a measure of the molecular weight and for the degree of polymerization of partially or fully hydrolyzed vinyl ester polymers. The degree of polymerization of the polyvinyl alcohol used is at least 130th

preferred Aldehydes are aliphatic and aromatic aldehydes of 1 to 15 C atoms and their mixtures. Particularly preferred aldehydes the group of aliphatic aldehydes having 1 to 15 carbon atoms Formaldehyde, acetaldehyde, propionaldehyde, and most preferred Butyraldehyde, or a mixture of butyraldehyde and acetaldehyde. As aromatic aldehydes can For example, benzaldehyde or its derivatives can be used. The aldehydes can also in the form of their half or full acetals or their aldehyde hydrates be used. The amount of aldehyde added depends on this after the desired Acetalization. Because the acetalization with almost complete sales expires the amount of addition can be determined by simple stoichiometric calculation become.

to Acetalization become the partially or fully saponified polyvinyl esters preferably in aqueous Medium recorded. Usually becomes a solid content of the aqueous solution adjusted from 4 to 30 wt .-%. The acetalization takes place in the presence of acid catalysts such as hydrochloric acid, sulfuric acid, nitric acid or Phosphoric acid.

To Addition of the catalyst, the solution is cooled to preferably -10 ° C to + 30 ° C. Where: The lower the molecular weight of the modified used Polyvinyl alcohol, the lower the precipitation temperature is selected. The Acetalization reaction is by adding the aldehyde, respectively Half or full acetal started.

Preferably the aldehyde or hemiacetal or acetal component is within of a maximum of 10 minutes, more preferably within a maximum 5 minutes in total. In this case, the addition of the aldehyde within this time, for example, continuously, or in the form of a Gradients, that is in different dosing rates, or in blocks. The addition the aldehyde component can in this time in one step or also in several steps, that is in the form of intervals, be made. Preferably, the impact addition of the aldehyde is in a step.

The Acetalization is carried out after completion of the addition of the aldehyde Heat of the batch at 20 ° C up to 60 ° C and several hours Stir, preferably 1 to 6 hours completed, and the powdered reaction product isolated by filtration and subsequent washing step. to Stabilization can further Alkalis are added. While the precipitation and post-treatment can be done with emulsifiers to the aqueous suspension of the polyvinyl acetal.

With this approach, high-shear-thinning polyvinyl acetals are accessible, which are characterized by a very pronounced structural viscosity in organic solvents. By high shear thinning is meant that the solution viscosity of a 30% solution of the respective polyvinyl acetal in methyl ethyl ketone, in a shear rate range of 1 to 100 s ^-1 , decreases by at least 30% and more. The solution viscosity is determined in a manner known to those skilled in the art using commercial rheometers, for example a cone-plate measuring system. For example, the measuring method for viscosity measurement described in the examples can be used.

The high shear thinning Polyvinyl acetals are particularly suitable for use as binders in printing inks. Suitable ink formulations are those skilled in the art known and generally contain 5 to 50 wt .-% pigment content, for example, disazo or phthalocyanine pigments, 4 to 25 wt .-% Polyvinyl acetal binders and solvents, for example Alcohols such as ethanol or esters such as ethyl acetate. Possibly can Other additives such as retarders, adhesion promoters, plasticizers and contain other additives such as fillers or waxes be.

Also for laminated safety glass and glass composites, high-security glass or disc foils are the high shear thinning Polyvinyl acetals very well suited.

The highly shear thinning polyvinyl acetals can also be used as binders in paints on aqueous Base or based on organic solvents find advantageous use, for example as a binder for the inner coating of cans. Further fields of use of the high shear thinning polyvinyl acetals are the use as binders in corrosion inhibitors. Furthermore, the highly shear thinning polyvinyl acetals are also suitable as binders in the ceramics industry, especially as binders for ceramic green bodies. To mention is also the use as a binder for ceramic powder and metal powder in the injection molding (powder injection molding).

The high shear thinning Polyvinyl acetals can as a binder for use photographic films. Profitable they leave especially as a binder for photothermographic materials deploy.

The The following examples serve to further illustrate the invention, without to restrict these in some way:

Example 1:

In A 6 liter glass reactor was distilled 2715 ml. Water, 500 ml 35 % nitric acid and 1172 ml of a 20.0% aqueous solution of a fully saponified polyvinyl alcohol of the type 03/20, viscosity 3.4 mPas (DIN 53015; Höppler method; 4-point aqueous Solution), submitted. The original was stirred within one hour to -2 ° C (precipitation temperature) cooled. Subsequently In a period of 7 minutes, 200.5 g of butyraldehyde, pre-cooled to -4 ° C, were added. The internal temperature rose briefly to 0 ° C. About three to five minutes after the addition of butyraldehyde, the initially clear approach was milky cloudy, and already eight minutes later the product fell out. After 40 minutes reaction time at -2 ° C, the Temperature over a period of 3.5 hours increased to 25 ° C and this temperature for more Held for 2.5 hours. Then the product was aspirated and while washed with distilled water until the filtrate is neutral responded. Subsequently Drying was carried out up to a solids content of at least 98 %, first at 22 ° C, then at 35 ° C in a vacuum.

It became a white, powdery Polyvinyl butyral obtained with 12.7 wt .-% of vinyl alcohol units. The vinyl acetate content was below 2.0 wt .-%. The viscosity (10%) in EtOH) amounted to 25.4 mPas.

Example 2:

In A 6 liter glass reactor was distilled 1200 ml. Water, 500 ml 35 % nitric acid and 2400 ml of 10.0% aqueous solution a mixture of two fully saponified, commercially available Polyvinyl alcohols (blend Clariant Mowiol 4-98 (20%) and Clariant Mowiol 6-98 (80 %), Viscosity 5.4 mPas (DIN 53015, Höppler method, 4% aqueous solution). The original was stirred within 1 hour at 1 ° C (Precipitation) cooled. Subsequently were added over a period of 3 minutes 216.5 g of butyraldehyde, pre-cooled to -4 ° C. The internal temperature rose briefly to 3 ° C. About two to four minutes after the addition of butyraldehyde, the initially clear approach was milky cloudy, and already seven minutes later the product fell out. After 40 minutes reaction time at 1 ° C, the Temperature over a period of 3.5 hours increased to 26 ° C and this temperature for more Held for 2.5 hours. Then the product was aspirated and while washed with distilled water until the filtrate is neutral responded. Subsequently Drying was carried out up to a solids content of at least 98 %, first at 22 ° C, then at 35 ° C in a vacuum.

It became a white, powdery Polyvinyl butyral obtained with 11.2 wt .-% of vinyl alcohol units. The vinyl acetate content was below 2.0 wt .-%.

Example 3:

It The procedure was analogous to Example 2 with the difference that 184.5 g of butyraldehyde were used for the acetalization.

It became a white, powdery Polyvinyl butyral obtained with 13.6 wt .-% of vinyl alcohol units. The vinyl acetate content was below 2.0 wt .-%.

Comparative Example 4

One commercial Polyvinyl butyral with analog molecular weight and comparable OH number (% by weight of vinyl alcohol units) as in the polyvinyl butyrals of Examples 2 and 3.

Determination Methods:

1. Determination of dynamic viscosity a solution of polyvinyl acetals:

90.00 + 0.01 g ethanol and 10.00 + 0.01 g polyvinyl acetal were in one 250 ml Erlenmeyer flask weighed with ground stopper and at 50 ° C in the shaker Completely dissolved. Subsequently was at 20 ° C chilled and the dynamic viscosity (DIN 53 015, method according to Höppler) at 20 ° C with a suitable ball, e.g. the ball 2 or 3, determined.

2. Determination of the vinyl alcohol content

Of the Content of vinyl alcohol groups in the polyvinyl acetals was by the acetylation of the hydroxyl groups with acetic anhydride in the presence of Pyridine and 4-dimethylaminopyridine determined.

To 1 g + 0.001 g polyvinyl acetal in 24 mL pyridine and 0.04 g 4-dimethylaminopyridine at 50 ° C solved within 2 hours. The at 25 ° C cooled solution was mixed with 10 ml of a mixture of pyridine and acetic anhydride (87/13 parts by volume) and thoroughly mixed for 1 hour. Thereafter, 30 ml of a mixture of pyridine / water (5/1 parts by volume) were added. added and shaken for an additional hour. Subsequently was titrated to pH 7 with methanolic 0.5 N KOH.

3. Determination of the viscosity of the polyvinyl alcohol solutions:

The Determination of viscosity the partially or completely saponified solid resins used as starting materials was carried out analogously to the determination of the dynamic viscosity of the polyvinyl acetals; it was only 4% aqueous solutions used.

Application testing:

a) Preparation of organic solutions with Polyvinyl acetal (30% solution in methyl ethyl ketone):

75 g Polyvinylactal were in 175 g of methyl ethyl ketone (MEK) in a lockable Glass jar with volume 500 ml at 23 ° C solved and with the help of a dissolver (mechanical stirrer with 3000 rpm) intensively at least Stirred for 15 minutes. Subsequently the vessel was closed and with a magnetic stirrer stirred for a further 3 h 45 min. After 4 hours, the polyvinyl acetal was completely and homogeneously dissolved in MEK. The solution was then rheologically characterized (see b)).

b) Measurement of solution viscosity:

The 30% solution of the polyvinyl acetal in MEK (prepared according to a) was measured with a Bohlin rheometer CVO 120 HR with a cone-plate measuring system (CP 4/40) at 20 ° C. To avoid evaporation, the measuring system was covered with a solvent trap. For measurement, about 4 g of the solution were added to the measuring system within 1.5 min. After these 1.5 minutes, the solution was continuously advanced for 90 seconds at a constant shear rate of 10 s ^-1 . After that, it was waited 60 s and then a pre-set measuring program was started, which starts at a shear rate of 0.3 s ^-1 and ends at 500 s ^-1 and then goes back to a shear rate of 0.3 s ^-1 . Within this shear rate range from 0.3 s ^-1 to 500 s ^-1 , 40 measurement points were recorded for the viscosity, the respective corresponding shear rate being kept constant for a short time (constant rate test). The viscosity was evaluated at a shear rate of 1 s ^-1 and 100 s ^-1 .

table 1 shows the results of the rheological measurement according to b) at 30% solutions of polyvinyl acetal in MEK.

Table 1:

As can be seen from the table, the preparation process according to the invention leads to polyvinyl acetals which show strongly pseudoplastic rheology behavior in solution, ie the viscosity of these solutions drops dramatically in the shear rate range of 1 to 100 s ^-1 . This is demonstrated by Examples 1 to 3, where the decrease in viscosity at 100 s ^-1, based on the value at 1 s ^-1, amounts to more than 30%. In example 3, the decrease is even more than 50%. Commercially available polyvinyl acetals do not show this pronounced pseudoplastic behavior. Here, the decrease in the viscosity at the shear rate of 100 s ^-1 relative to the value at the shear rate of 1 s ^-1 only amounts to 26.6% (Comparative Example 4).

Out The examples also show that the intrinsic viscosity of the polyvinyl acetals of the invention in organic solvents the bigger, the faster the aldehyde addition was made in the synthesis (Comparison Example 1 with 7 minutes Aldehyde addition with Examples 2 and 3 with 3 minutes Aldehyde addition). A rapid acetalization obviously leads to one Polyvinyl acetal with inhomogeneously distributed acetal groups, this have particular rheological behavior.

Claims (10)

High shear thinning polyvinyl acetals, characterized in that their solution viscosity in 30 wt .-% solution in methyl ethyl ketone in a shear rate range of 1 to 100 s ^-1 by at least 30% decreases. Process for the preparation of high shear thinning Polyvinyl acetates according to claim 1, by acetalization of partially saponified or fully saponified vinyl ester polymers having ≥50 mol% Vinyl alcohol units with one or more aldehydes, optionally in the form of their hydrates, half or full acetals, characterized that the aldehyde content is completely added within a maximum of 15 minutes becomes. Process for the preparation of high shear thinning Polyvinyl acetals according to Claims 1 to 2, characterized that comprising one or more aldehydes from the group aliphatic and aromatic aldehydes acetalated with 1 to 15 carbon atoms becomes. Process for the preparation of high shear thinning Polyvinyl acetals according to Claims 1 to 3, characterized that the aldehyde content is completely added within a maximum of 10 minutes becomes. Process for the preparation of high shear thinning Polyvinyl acetals according to claim 4, characterized in that the aldehyde content is completely added within a maximum of 5 minutes becomes. Use of high shear thinning polyvinyl acetals according to Claim 1 as a binder in printing inks. Use of high shear thinning polyvinyl acetals according to Claim 1 as a binder in paints and corrosion inhibitors. Use of high shear thinning polyvinyl acetals according to Claim 1 as a binder for ceramic green bodies, ceramic powder and metal powder. Use of high shear thinning polyvinyl acetals according to Claim 1 as a binder for photographic films. Use of high shear thinning polyvinyl acetals according to claim 1 as a binder for pho tothermographic materials.