WO2006053621A1

WO2006053621A1 - Highly shear-thinning polyvinyl acetals

Info

Publication number: WO2006053621A1
Application number: PCT/EP2005/011299
Authority: WO
Inventors: Kurt Stark
Original assignee: Wacker Polymer Systems Gmbh & Co. Kg
Priority date: 2004-11-11
Filing date: 2005-10-20
Publication date: 2006-05-26
Also published as: DE102004054568A1; TW200624453A

Abstract

The invention relates to highly shear-thinning polyvinyl acetals, characterized in that their solution viscosity decreases by at least 30 % in a 30 % by weight solution in methyl ethyl ketone with a shearing rate ranging from 1 to 100 s-1. The invention also relates to a method for producing highly shear-thinning polyvinyl acetals by acetalizing partially saponified or completely saponified vinyl ester polymers with ≥ 50 mol % vinyl alcohol units with one or more aldehydes, optionally in the form of their hydrates, hemiacetals or full acetals, characterized in that the aldehyde portion is completely added by metering within a period of no longer than 15 minutes.

Description

High shear thinning polyvinyl acetals

The invention relates to high-shear-thinning polyvinyl acetals, to processes for the preparation of highly shear-thinning polyvinyl acetals, and to their use.

The preparation of polyvinyl acetals which are obtained from the corresponding polyvinyl alcohols by polymer-analogous reaction with the corresponding aldehydes has been known since 1924, with a large number of aldehydes being used subsequently to prepare the corresponding polyvinyl acetals. Polyvinyl acetals are produced in a 3-stage process (polyvinyl acetate -> polyvinyl alcohol -> polyvinyl acetal), resulting in products which, in addition to vinyl acetal groups, also contain vinyl alcohol and vinyl acetate units. Polyvinyl formal, polyvinyl acetoacetal and polyvinyl butyral (PVB) have in particular achieved commercial significance.

Due in part to their good pigment binding power, polyvinyl butyrals are also used as binders in paints and especially in printing inks. When used in the coating area, when applied by spraying, the requirement is made that the coating agent be thin at high shear rate during application, so that it can be coated quickly and without problems. After application, however, the viscosity should again increase rapidly in order to prevent bleeding and runoff.

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 each partially be submitted, and the remaining portions in each case be metered in portions after cooling the reaction mixture. In JP-A 2000-159831, the main portion of the polyvinyl alcohol is prepared for the production of polyvinyl acetal, acid catalyst and aldehyde are added, and the remainder is added to polyvinyl alcohol. In the method of JP-A 10-

158328, the acetalization is optimized by adding an ace- talised polyvinyl alcohol. WO 03/066690 relates to a process for the preparation of polyvinyl acetals having lower metal contents, the acetalization of polyvinyl alcohol being carried out in two reactors connected in series.

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

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

Another object of the invention is a method for

Production of highly shear-thinning polyvinyl acetals by acetalization of partially hydrolyzed or fully hydrolyzed vinyl ester polymers containing> 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 content within of a maximum of 15 minutes is completely added.

Suitable partially hydrolyzed or fully hydrolyzed vinyl ester polymers are derived from polymers containing from 50 to 100 mol% of vinyl ester units. Suitable vinyl esters are vinyl esters of unbranched or branched Carbonsäu¬ Ren having 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 esters of α-branched monocarboxylic acids having 5 to 11 carbon atoms, for example VeoVa9R or VeoValOR (trade names of Shell ). Vinyl acetate is particularly preferred.

In addition to the vinyl ester units, it is also possible where appropriate to use one or more monomers from the group comprising methacrylic acid esters and acrylic esters of alcohols having from 1 to 15 carbon atoms.

Atoms, olefins, dienes, vinyl aromatics and vinyl halides are co-polymerized. Suitable monomers from the group of esters of acrylic acid or methacrylic acid are esters of unbranched or branched alcohols having 1 to 15 C 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 vinylaromatics, styrene and vinyltoluene can be copolymerized. Of the group of vinyl halides, vinyl chloride, vinylidene chloride or vinyl fluoride, preferably vinyl chloride, are usually used. The An¬ part of these comonomers is such that the proportion of vinyl ester monomer> 50 mol% in the vinyl ester polymer be¬ contributes.

If appropriate, further comonomers may be present in a proportion of preferably 0.02 to 20% by weight, based on the total weight of the vinyl ester polymer. Examples of such comonomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably crotonic acid, itaconic acid, fumaric acid and maleic acid; further ethylenically unsaturated carboxylic acid amides and nitrites, preferably N-vinylformamide; also cyclic amides which on the nitrogen an unsaturated group such as N-vinylpyrrolidone; Mono- and diesters of fumaric acid and maleic acid, such as diethyl and diisopropyl esters and maleic anhydride, ethylenically unsaturated sulfonic acids or salts thereof, preferably vinylsulfonic acid. Also suitable as comonomers are cationic monomers such as diallyldimethylammonium chloride (DADMAC), 3-trimethylammoniumpropyl (meth) acrylamide chloride (MAPTAC) and 2-trimethylammoniumethyl (meth) acrylate chloride. Further suitable as Hilfsmonomere vinyl ethers and vinyl ketones.

Suitable comonomers are also polymerizable silanes or mercaptosilanes. Preference is given to γ-acryl or γ-methacryloxypropyltri (alkoxy) silanes, α-methacryloxymethyltri (alkoxy) silanes, γ-methacrylox, ypropylmethyldi (alkoxy) silanes, vinylalkyldi- (alkoxy) silanes and vinyltri (alkoxy) silanes, where as alkoxy groups, for example, methoxy, ethoxy, Methoxyethy.len, ethoxyethylene, Methoxypropylenglykolether- or ethoxypropylene glycol ether radicals can be used. Examples of these are vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriopropoxysilane, 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) propylsuccinic anhydride silane. Also preferred are 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane and 3-mercaptopropylmethyldimethoxysilane.

Further examples are precrosslinking comonomers such as multiply ethylenically unsaturated comonomers, for example divinyl adipate, diallyl maleate, allyl methacrylate, butanediol diacrylate or triallyl cyanurate, or postcrosslinking comonomers, for example acrylamidoglycolic acid (AGA), Methylacrylamido- glykolsäuremethylester ^'(MAGME), N-methylolacrylamide (NMA) , N-methylol methacrylamide, N-methylolallyl carbamate, alkyl ethers such as the isobutoxy ether or ester of N-methylolacrylamide, N-methylolmethacrylamide and N-methylolallylcarbamate.

These vinyl ester polymers are commercially available or can be prepared in a known manner by means of polymerization; preferably by bulk polymerization, suspension polymerization or by polymerization in organic solvents, particularly preferably in alcoholic solution. Suitable solvents and regulators are, for example, methanol, ethanol, propanol, isopropanol. The polymerization is carried out under reflux at a temperature of 40 ° C to 100 ° C and initiated by addition of conventional initiators radically. Examples of common initiators are percarbonates such as cyclohexyl peroxydicarbonate, azo initiators or peresters such as t-butylperneodecanoate or t-butyl perpivalate. The adjustment of the molecular weight can be carried out in a known manner by adding regulators, by the solvent content, by varying the initiator concentration and by varying the temperature. After completion of the polymerization, the solvent and, if appropriate, excess monomer and regulator are distilled off.

The saponification of the vinyl ester polymers is carried out in a manner known per se, for example after the belt or kneading process, in the alkaline or acidic state with the addition of acid or base. The vinyl ester solid resin is preferably taken up in alcohol, for example methanol, while setting a solids content of 15 to 70% by weight. Preferably, the hydrolysis is carried out in the basic, for example by addition of NaOH, KOH or NaOCH ₃ . The base is generally used in an amount of from 1 to 5 mol% per mole of ester units. The hydrolysis is carried out at temperatures of 20 ⁰ C to 7O ⁰ 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 as an aqueous solution by a succesive addition of water while the solvent is distilled off. Fully hydrolyzed vinyl ester polymers are understood as meaning those polymers whose degree of hydrolysis is> 96 mol%. Partially hydrolysed polyvinyl esters are to be understood as those having a degree of hydrolysis of> 50 mol% and <96 mol%. The partially or fully saponified vinyl ester polymers preferably have a degree of hydrolysis of from 50 mole% to 99.9 mole%, more 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) is 1 to 30 mPas, preferably 1 to 10 mPas, and serves as a measure of the molecular weight and the degree of polymerization of partially or fully hydrolyzed vinyl ester polymers. The degree of polymerisation of the polyvinyl alcohol used is at least 130.

Preferred aldehydes are aliphatic and aromatic aldehydes having 1 to 15 carbon atoms and mixtures thereof. Particularly preferred aldehydes from the group of aliphatic aldehydes having 1 to 15 carbon atoms are formaldehyde, acetaldehyde, propionaldehyde and most preferably butyraldehyde, or a mixture of butyraldehyde and acetaldehyde. For example, benzaldehyde or its derivatives can be used as aromatic aldehydes. The aldehydes can also be used in the form of their half or full acetals or their aldehyde hydrates. The amount of aldehyde added depends on the desired degree of acetalization. Since the acetalization proceeds with almost complete conversion, the addition amount can be determined by a simple stoichiometric calculation.

For the acetalization, the partially or completely hydrolyzed polyvinyl esters are preferably taken up in an aqueous medium. Usually, a solids content of the aqueous solution is adjusted from 4 to 30% by weight. The acetalization takes place in the presence of acidic catalysts such as hydrochloric acid, sulfuric acid, salicylic acid or phosphoric acid.

After addition of the catalyst, the solution is preferably -10 ⁰ C to + 30 ° C cooled. The following applies: the lower the molecular weight of the modified polyvinyl alcohol used, the lower the precipitation temperature is selected. The acetalization reaction is started by adding the aldehyde or its hemiacetal or acetal.

Preferably, the aldehyde or hemiacetal or Vollace- tal component within a maximum of 10 minutes, more preferably be¬ preferably within a maximum of 5 minutes added. In this case, the addition of the aldehyde within this time can be carried out continuously, for example, or in the form of a gradient, that is to say in different metering rates, or in stacks. The addition of the aldehyde component can be carried out in this time in one step or in several steps, that is in the form of intervals. Preference is given to the addition of the aldehyde in one step.

The acetalization is completed after the addition of the aldehyde by heating the batch to 2O ⁰ C and 6O ⁰ C and stirring mehrstündi- ges, preferably 1 to 6 hours, and the powdery reaction product by filtration and washing step nach¬ switched isolated. For stabilization, alkalis may also be added. During the precipitation and the aftertreatment it is possible to work with emulsifiers in order to stabilize the aqueous suspension of the polyvinyl acetal.

This approach makes it possible to obtain high-shear-thinning polyvinyl acetals, which are characterized by a very pronounced structural viscosity in organic solvents. Under high scherverdünnend is to be understood that the

Solution viscosity of a 30% strength 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 the person skilled in the art with commercially available rheometers, for example with a cone-plate measuring system It is possible, for example, to use the measuring method for viscosity measurement described in the examples. The high shear thinning polyvinyl acetals are particularly suitable for use as binders in printing inks. Suitable ink formulations are known to the person skilled in the art and generally contain from 5 to 50% by weight of pigment, for example disazo or phthalocyanine pigments, from 4 to 25% by weight of polyvinyl acetal binder and solvent, for example alcohols, such as ethanol or esters such as ethyl acetate. If appropriate, further additives such as retarders, adhesion promoters, plasticizers and other additives, such as fillers or waxes, may be present.

The highly shear thinning polyvinyl acetals are also very well suited for laminated safety glass and glass composites, high-security glass or pane foils.

The highly shear thinning polyvinyl acetals may also find advantageous use as binders in aqueous based or organic solvent based finishes, for example, as binders 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 high-shear-thinning polyvinyl acetals are also suitable as binders in the ceramics industry, especially as binders for ceramic green bodies. Also to be mentioned is the use as a binder for Keramikpul¬ ver and metal powder in the injection molding (powder injection molding).

The high shear thinning polyvinyl acetals may also be used as binders for photographic films. Ge winnbringend they can be used in particular as a binder for photothermographic materials.

The following examples serve to further illustrate the invention without restricting it in any way:

Example 1: In a 6 liter glass reactor, 2715 ml of dist. Water, 500 ml of 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, method according to Hoppler, 4% aqueous solution) , The template was under

Stirred within one hour to -2 ⁰ C (precipitation temperature) cooled abge. 200.5 g of butyraldehyde, precooled to -4 ° C., were added over a period of 7 minutes. The internal temperature rose briefly to ⁰ ° C. About three to five minutes after addition of the butyraldehyde, the initially clear mixture turned milky cloudy, and the product precipitated just eight minutes later. For ^'40 minutes of reaction time at -2 ° C, the temperature was raised over a period of 3.5 hours at 25 ° C and kept at this temperature for a further 2.5 hours. The product was then filtered off with suction and washed with distilled water until the filtrate was neutral. The drying was then carried out to a solids content of at least 98%, first at 22 ⁰ C, then at 35 ⁰ C in vacuo. There was obtained a white, powdered polyvinyl butyral with 12.7 wt .-% of vinyl alcohol units. The vinyl acetate content was below 2.0 wt .-%. The viscosity (10% in EtOH) was 25.4 mPas.

Example 2:

In a 6 liter glass reactor, 1200 ml of dist. Water, 500 ml of 35% nitric acid and 2400 ml of a 10.0% aqueous solution of a mixture of two fully saponified, commercially available polyvinyl alcohols (mixture Clariant Mowiol 4-98 (20%) and Clariant Mowiol 6-98 (80%). Viscosity 5.4 mPas (DIN 53015; Höppler's method; 4% aqueous solution) .The original was cooled to 1 ° C. (precipitation temperature) with stirring within one hour, and then 216.5 g were added over a period of 3 minutes butyraldehyde, cooled presented on -4 ⁰ C, was added. the internal temperature increased briefly to 3 ⁰ C to. about two to four minutes after the addition of the butyraldehyde, the initially clear mixture became milky cloudy, and already seven minutes later, the product fell out. After 40 minutes reaction time at I ⁰ C, the temperature was increased over a period of 3.5 hours at 26 ⁰ C and held this temperature for a further 2.5 hours. The product was then filtered off with suction and washed with distilled water until the filtrate was neutral. Then er¬ followed drying to a solids content of at least 98%, first at 22 ° C, then at 35 ° C in vacuo.

A white, powdery polyvinyl butyral containing 11.2% by weight of vinyl alcohol units was obtained. The vinyl acetate content was below 2.0 wt .-%.

Example 3:

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

There was obtained a white, powdered polyvinyl butyral with 13.6 wt .-% vinyl alcohol units. The vinyl acetate content was below 2.0 wt .-%.

Comparative Example 4

A commercially available polyvinyl butyral with an analogous 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 the dynamic viscosity of a solution of polyvinyl acetals:

90.00 +0.01 g of ethanol and 10.00 + 0.01g polyvinyl acetal wur¬ solves the einge¬ weighed in a 250 ml Erlenmeyer flask with ground stopper and fully aufge¬ at 50 ⁰ C in the shaker. The mixture was then cooled to 20 ⁰ C and dynamic viscosity (DIN 53015; Höppler method) at 2O ⁰ C and ei¬ ner suitable ball, for example, the ball 2 or 3 is determined.

2. Determination of the vinyl alcohol content The content of vinyl alcohol groups in the polyvinyl acetals was determined by the acetylation of the hydroxyl groups with acetic anhydride in the presence of pyridine and 4-dimethylamino-pyridine. 1 g + 0.001 g of polyvinyl acetal in 24 ml of pyridine and 0.04 g of 4-dimethylaminopyridine were dissolved at 50 ^° C. in the course of 2 hours. The cooled to 25 ⁰ C solution was washed with 10 ml of a mixture of pyridine and acetic anhydride (87/13 Volumentei¬ le) and intensively mixed 1 hour. Thereafter, 30 ml of a mixture of pyridine / water (5/1 Volumentei¬ le) was added and shaken for a further hour. Subsequently, it was titrated to pH 7 with methanolic 0.5 N KOH.

3. Determination of the Viscosity of the Polyvinyl Alcohol Solutions: The viscosity of the partially or fully saponified solid resins used as starting materials was determined analogously to the determination of the dynamic viscosity of the polyvinyl acetals; only 4% aqueous solutions were used.

Application testing:

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

75 g of polyvinyl acetal were dissolved in 175 g of methyl ethyl ketone (MEK) in a closable glass vessel with a volume of 500 ml at 23 ° C and stirred with the aid of a dissolver (mechanical stirrer at 3000 rpm) intensively for at least 15 min. The vessel was then closed and stirred with a magnetic stirrer for a further 3 h 45 min. After 4 hours, the polyvinyl acetal was completely and homogeneously dissolved in MEK. The solution was then characterized rheologically (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 2O ⁰ C. In order to avoid evaporation, the measuring system was covered with a solvent trap. For measurement within approx. 1.5 min approx. 4 g of the solution is added to the measuring system. After these 1.5 minutes, the solution was continuously pre-stressed for 90 s at a constant shear rate of 10 s ^-1, then 60 s were maintained and then a preset measurement program was started, starting at 0.3 s ^-1 and a shear rate of 500 s s ^"1 ends and then goes back to a shear rate of 0.3 s ^{" 1} . Within this shear rate range of 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) on 30% solutions of polyvinyl acetal in MEK.

Table 1:

As the table shows, the production method according to the invention leads to polyvinyl showing in solution highly pseudoplastic rheological behavior, that is the Vis¬ viscosity by these solutions fall in the shear rate range 1 to 100 s ^"1 dramatically. This is evidenced by Examples 1 to 3, where the decrease in viscosity at 100 s ^-1 relative to the value at 1 s ^-1 amounts to more than 30%, the decrease even amounts to more than 50% in example 3. Commercially available polyvinyl acetals show this pronounced pseudoplastic viscosity Do not behave, here the decrease of the viscosity contributes the shear rate 100 s ^-1 relative to the value at the shear rate 1 s ^-1 only to 26.6% (Comparative Example 4). It is also evident from the examples that the structural viscosity of the polyvinyl acetals according to the invention in organic solvents is greater, the faster the aldehyde addition in the synthesis was carried out (Comparison Example 1 with 7-minute aldehyde addition with Examples 2 and 3 with 3 minutes Aldehyde addition). A rapid acetalization apparently leads to a polyvinyl acetal with inhomogeneously distributed acetal groups which exhibit this particular rheological behavior.

Claims

claims:

1. High-shear-thinning polyvinyl acetals, characterized gekenn¬ 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%.

2. A process for the preparation of high shear-thinning polyvinyl acetals according to claim 1, by acetalization of partially hydrolyzed or fully saponified vinyl ester polymers with>; 50 mol% of vinyl alcohol units with one or more aldehydes, optionally in the ^'form of their hydrates, half or full acetals, characterized in that the aldehyde is completely dosed within a maximum of 15 minutes.

3. A process for the preparation of high shear-thinning polyvinyl acetals according to claim 1 to 2, characterized gekennzeich¬ net that is acetalated with one or more aldehydes from the group comprising aliphatic and aromatic aldehydes having 1 to 15 carbon atoms.

4. A process for the preparation of high shear-thinning polyvinyl acetals according to claim 1 to 3, characterized in that the aldehyde content is completely metered in within a maximum of 10 minutes.

5. A process for the preparation of high shear-thinning polyvinyl acetals according to claim 4, characterized in that the aldehyde is completely added within a maximum of 5 minutes.

6. Use of high shear thinning polyvinyl acetals according to claim 1 as a binder in printing inks.

7. Use of high shear thinning polyvinyl acetals according to claim 1 as a binder in paints and Korrosions¬ protectants.

8. Use of high shear thinning polyvinyl acetals according to claim 1 as a binder for ceramic green bodies, ceramic powder and metal powder.

9. Use of high shear thinning polyvinyl acetals according to claim 1 as a binder for photographic films.

10. Use of high shear thinning polyvinyl acetals according to claim 1 as a binder for photothermographic materials.