WO2008011658A1

WO2008011658A1 - Redispersible polymer powders

Info

Publication number: WO2008011658A1
Application number: PCT/AU2007/000952
Authority: WO
Inventors: Valentino De Fazio
Original assignee: Acquos Pty Ltd
Priority date: 2006-07-26
Filing date: 2007-07-10
Publication date: 2008-01-31

Abstract

A redispersible polymer powder including : a polymer to be redispersed; and a sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof.

Description

REDISPERSIBLE POLYMER POWDERS

FIELD OF THE INVENTION

The present invention relates to redispersing aids for use in the manufacture of redispersible polymer powders and processes for making same. In particular, the invention relates to polymers useful as redispersing aids for redispersible polymer powders, the polymers including a sulfated hydroxyl alkyl (meth)acrylate monomer, polymer and/or salt thereof.

BACKGROUND TO THE INVENTION

The use of redispersible film forming polymers in powder form finds widespread use throughout a number of industries. For example, such redispersible film forming polymers are used as construction binders for tile adhesives, synthetic resin plasters, floor levelling mixes and in areas where a waterless system is generally desirable. These systems in general are produced by the dry blending of the raw materials, such as sand, cement, calcium carbonate, silica flour, modified cellulose based thickeners, and the dry polymer powder, to obtain a ready to use finished product for site mixing where water is added at the point of use. These systems are advantageous as they avoid the need for a two component system, one component containing an aqueous polymer dispersion and the other component containing the powder component which may contain a hydraulic setting component such as cement. Avoiding such systems may be advantageous for a number of reasons such as economy, utility and environmental considerations.

To obtain a film forming polymer in powder form, a liquid dispersion of the polymer is subjected to a drying operation where the water is removed by a suitable method such as spray drying or freeze drying. Spray drying is a widely used and understood method that gives a fine powder which, under well controlled predetermined conditions, usually does not have to be further processed. This method is therefore generally preferred. In order to manufacture a redispersible film forming polymer powder with glass transitions below 50°C, it is generally necessary to add to the liquid dispersion before spray drying a quantity of redispersing aid. Redispersing aids act to coat the individual polymer particles to prevent irreversible primary particle formation. Such aids also advantageously increase the yield during the spray drying process by minimizing sticking of the dried polymer to the walls of the spray dryer. The redispersing aid may also improve the storage stability of the polymer powder by minimizing "blocking" (the thermoplastic fusion of the polymer particles under weight pressure), and should generally have some hydrophilic properties to aid redispersability of the polymer powder on the reintroduction of water.

The redispersible polymer powders known to date generally comprise a redispersing aid that is water soluble and which is generally added to the polymer dispersion before spray drying. As stated above, this advantageously prevents or reduces the formation of primary particles during the spray drying operation.

Polyvinyl alcohols have historically been used as redispersing aids for ethylene vinyl acetate (EVA) dispersions for many years. For example, United States Patent No. 3,883,489 assigned to Hoechst Aktinengellschaft makes use of polyvinyl alcohol as a redispersing aid for ethylene vinyl acetate dispersions. Whilst not as effective, polyvinyl alcohols can also be used as redispersing aids in the manufacture of redispersible acrylic or styrene-acrylic polymer powders. For example, United States Patent No. 5,567,750 assigned to Wacker-Chemie GmbH makes use of a polyvinyl alcohol along with an amino functional polyvinyl alcohol for the manufacture of a redispersible styrene-acrylic polymer powder. United States Patent No. 5,519,084 assigned to Air Products and Chemicals makes use of a polyvinyl alcohol as a redispersing aid with an acrylic polymer consisting of up to 15% olefinically unsaturated carboxylic acid. However, polyvinyl alcohols are not entirely satisfactory as redispersing aids for acrylics or styrene acrylics or styrene butadiene dispersions as they are for ethylene vinyl acetate dispersions.

The use of salts of arylsulfonic acid - formaldehyde condensates as redispersing aids is also known, especially for acrylic dispersions. German Offenlegungsschrift 24 45 813 translated as "Redispersible synthetic powder and method of production" describes the use of phenol sulfonic acid formaldehyde condensates and naphthalene sulfonic acid formaldehyde condensates and their alkali salts or their alkali earth metal salts as redispersing aids for redispersible powders. United States Patent No. 5,225,478 assigned to BASF also describes the use of phenol sulfonic acid formaldehyde condensates and their alkali salts or alkali earth metal salts as a redispersing aid. United States Patent No. 6,028,167 assigned to BASF describes an improvement by controlling the molecular weight of the redispersing aids. Likewise, Australian Patent No. 718,907 describes an improvement in naphthalene sulfonic acid formaldehyde condensates by controlling or restricting the molecular weight of the redispersing aids.

Australian application number 2003904725 to Acquos Pty Ltd describes an ortho- cresol sulfonate condensate based oligomer where a low molecular weight product is obtained with high molecular weight condensates practically eliminated. This provides for considerable improvements in the properties of the manufactured redispersible powders. International Publication No. WO2006/034531 also to Acquos Pty Ltd provides for further improvements.

Whilst the abovementioned low molecular weight product aryl sulfonic acid formaldehyde condensates, such as the phenol sulfonic acid formaldehyde condensate as in United States Patent No. 6,028,167 and the naphthalene sulfonic acid formaldehyde condensate in Australian Patent No. 718,907, are effective redispersing aids, with Australian application number 2003904725 being an especially effective redispersing aid, they all suffer from some drawbacks in that the finished colour of the final dry polymer comprising this class of condensation redispersing aid is not entirely satisfactory. Mention of this deficiency is made in United States Patent Number

6,127,483 with improvement in colour achieved only by moving away from this class of condensation polymer. Whilst colour is not usually considered an issue when low polymer contents are used in the finished mortars, the problem is exacerbated in higher performance systems and in one pack membrane systems. That is, systems where high levels of redispersible polymer powders are used doing away with a liquid latex component as has been a trend of recent times. Polyvinyl alcohols are not entirely satisfactory as redispersing aids for acrylics or styrene acrylics or styrene butadiene dispersions as they are for ethylene vinyl acetate dispersions. However, they do have the advantage that the polyvinyl alcohol contributes to the final film of the redispersible polymer. Comparatively, the arylsulfonic acid condensation polymers act more like surfactant type systems.

The potential use of polymers of sulfonic acid as redispersing aids for redispersible polymer powders is well known. US Patent 5,462,978 and US Patent 5,604,272 teach the use of sulfonic acid polymers of general formula:

FIGURE 1

X = O or NH₂

R₁, R₂ or R₃ = C₁-C₃ alkyl

R₄ = C₁-C₅ alkyl

in the range of 20 to 85%.

Likewise Uminski and Saija in their contributed paper to Pigment and Resin Technology Volume 32 Number 6 2003 pp.364-370 teach the use of "AMPS monomer" (2-acrylamido-2-methylpropanesulfonic acid) in core shell redispersible polymer powders.

Although these unsaturated sulfonic acid polymers are effective redispersing aids for redispersible polymer powders or effective monomers for use in redispersible polymer powders, their commercial cost is one disadvantage. US patent 6,444,729 partially addresses this cost issue with the use of ethylenically unsaturated C₃ to C₆ carboxylic acids and their hydroxylalkyl esters as assistants. However, the lack of ionic charge makes them an inferior polymer for use in such redispersing aids and redispersible polymer powders in their own right. SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a redispersible polymer powder including :

a polymer to be redispersed; and

a sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof.

The redispersing aid, therefore, is the sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof. It should be appreciated that as used herein the term "polymer" includes within its scope copolymers or terpolymers of the hydroxyl alkyl (meth)acrylate.

The redispersing aid, when in the form of a salt, will generally include an alkali metal salt or alkaline earth metal salt. Ammonium salts or organic amine salts may also be used. Preferred salts are the ammonium salts, calcium salts or sodium salts or combinations of these.

In a particular embodiment the invention relates to redispersible polymer powders including a polymer to be redispersed and a sulfated hydroxyl alkyl (meth)acrylate monomer and/or polymer of the formula:

FIGURE 2

X = 1- 5 Y = 1- 3 R1 = H or C₁-C₃ alkyl The redispersing aids of the invention may be prepared by any suitable method. Generally, preparation is based on the sulfation of hydroxyl alkyl (meth)acrylate monomers and polymerising such monomers to obtain polymers of sulfated (as opposed to sulfonated) hydroxyl alkyl esters of carboxylic acid. The sulfation process may include, for example, sulfation using sulfamic acid or other means. The use of the sulfate group, as opposed to a sulfonate group, in the residpersing aids has been found to give redispersible polymer powders having improved redispersability and other commercial advantages. More particularly, products formed using the invention are advantageously devoid of significant colour and have good final film properties.

There is also provided a product including, as a binder, the redispersible polymer powder discussed in accordance with this invention. There is still further provided the use of such a redispersible polymer powder as a binder for a product, such as for example hydraulically setting compositions, adhesives, coating compositions, synthetic resin renders, and for modifying building materials.

The polymers that may be used in combination with the sulfated hydroxyl alkyl (meth)acrylate monomer, polymer or salt thereof are generally those with glass transitions below 50°C. Most preferred are flexible polymers which have a glass transition below 10°C. For example, polymers manufactured using emulsion polymerisation techniques may be appropriate. For example, the polymer may include pure acrylic polymers (for example methylmethacrylate and alkyl acrylates, such as butyl acrylate), styrene-acrylic (for example based on styrene and alkyl acrylates, such as 2-ethylhexyl-acrylate), vinyl acetate copolymers with alkyl acrylate or ethylene or maleates, and styrene-butadiene based polymers. More particularly, the polymer preferably contains two or more monomers selected from the group consisting of styrene, methylmethacrylate, vinyl acetate, butadiene, n-butyl acrylate, 2-ethylhexylacrylate, ethylacrylate, methylacrylate, isopropylacrylate, vinyl propionate, dibutyl maleate, ethylene, tert-butyl acrylate, methacrylic acid, acrylic acid, acrylamide, methacrylamide, hydroxyethyl methacrylate. The polymer may also contain within its polymerises units of sulfated hydroxyl alkyl (meth)acrylates and/or salt thereof and/or conventional AMPS monomer. The type of polymer to be used within this invention, however, is not restricted on the combination referred to above, but most polymers used in industry, used in the manufacture of construction products, and used as anionic or nonionic dispersion polymers in water, will generally be able to be used with the sulfated hydroxyl alkyl (meth)acrylate monomer, polymer or salt thereof so long as the two components are compatible when mixed in liquid form before drying, particularly before spray drying. Examples of these types of polymers are generally those referred to in the description in Australian Patent No. 717,206 which is incorporated herein in its entirety by reference thereto. It will be appreciated that the type of polymer is not critical for the use of the invention.

The sulfated hydroxyl alkyl (meth)acrylate monomer, polymer or salt thereof, generally as a dispersion, is advantageously mixed with the polymer dispersion before drying. However, this component may also be used during the polymerisation stage, for example during the preparation of the polymer as a protective colloid. The resultant mixture is then preferably spray dried using conventional spray drying techniques. For example, rotating disc atomization, single fluid nozzles or multi fluid nozzles may be used for the atomization step along with a drying operation in a chamber, preferably using air heated from 120 to 180⁰C. The resultant polymer powder is preferably collected in cyclones or filter bag houses. Anti-caking agents may also be metered in whilst the polymer powder is suspended in the air stream.

The redispersing aid, generally in the form of a colloid or dispersion may be manufactured by sulfating an hydroxyl alkyl (meth)acrylate such as HEMA (hydroxyl ethyl methacrylate) with sulfamic acid under anhydrous conditions using a catalyst such as described in US 6,149,549. Urea has proven to be a suitable catalyst. The sulfation generally proceeds to completion when an excess of sulfamic acid is used under favourable conditions, with the ammonium salt being the ready salt once completed. Alternatively, sulfation is only partially effected with the resultant polymer being a polymer of an hydroxyl alkyl (meth)acrylate with pendant sulfate groups. On completion, the sulfated hydroxyl alkyl (meth)acrylate may be diluted and brought to a pH>7 with ammonia. The sulfated hydroxyl alkyl (meth)acrylate may be used as the ammonium salt, or some of the ammonium salt can be readily displaced with concentrated sodium hydroxide to form a sodium salt, or with lime to form a calcium salt. The ammonium salt is preferably used for the next stage of the reaction as is.

The second stage of the process, if desired, involves the polymerisation of the sulfated hydroxyl alkyl (meth)acrylates to form a final colloid or dispersion. Preference is given to dosing the fully or partially sulfated monomer into a polymerisation vessel with or without other monomers whilst a second solution of an initiator is also dosed into the polymerisation vessel. A third reducing solution may also be dosed into the vessel for molecular weight control or a reducing solution can optionally be in the polymerisation vessel at the start of the polymerisation. The polymerisation temperature may be from room temperature up to 100 degrees Celcius depending on reactants, initiator, and molecular weight required. The initiator used may be any one known to workers in the field such as ammonium persulfate, sodium persulfate, potassium persulfate, TBHP (tertiary butyl hydroperoxide).

The polymerised redispersing aid may be used as is as the ammonium salt, or the ammonium salt may be partially or fully substituted as mentioned above (if not substituted prior).

It has been found that a molecular weight of less than 20,000 daltons is a very effective molecular weight for the redispersing aid. However, aids with molecular weights greater than 20,000 may also be used in accordance with the invention. Molecular weights less than 5,000 are preferred, with molecular weights less than 2,500 being especially preferred.

The dispersion including the redispering aid of the invention may, if desired, also be used with colloids of prior art developments such as aryl sulfonic acid condensates ( eg: naphthalene sulfonic acid formaldehyde condensates) and polyvinyl alcohols.

The monomer used as a starting material may be any one of a variety of hydroxyl alkyl (meth)acrylates, such as hydroxyl propyl methacrylate (HPMA), hydroxyl ethyl acrylate (HEA) and hydroxy ethyl methacrylate (HEMA). It will be appreciated that other monomers may be used. Following from the above, it will be appreciated that according to another aspect of the invention there is provided use of a sulfated hydroxyl ethyl (meth)acrylic based monomer, polymer and/or salt thereof as a redispersing aid for a redispersible polymer powder.

EXAMPLES

Embodiments of the invention will now be discussed in more detail with reference to the following examples which are provided for exemplification only and which should not be considered limiting on the scope of the invention in any way.

Preparative Example Dl

A glass 1 litre laboratory reactor equipped with 2 dosing lines, a variable speed mechanical stirrer, a reflux condenser, a glass thermometer, and a water bath was loaded with 77 grams of deionised water, 0.8 grams of sodium bicarbonate, 0.5 grams of a nonyl phenol ethoxylate with 30 moles of ethylene oxide, 0.35 grams of a solid sodium salt of a sulfated nonyl phenol ethoxylate with 30 moles of ethylene oxide. To the above was added 17 grams from a Feed Mix 1 comprising 78 grams of water, 2 grams of a nonyl phenol ethoxylate with 30 moles of ethylene oxide, 0.7 grams of a solid sodium salt of a sulfated nonyl phenol ethoxylate with 30 moles of ethylene oxide, 5 grams of acrylamide, 144 grams of butyl aery late, and 96 grams of styrene and was heated to 85 degrees celcius. Once the temperature had reached 85°C, 2 grams of a Feed Mix 2 was added which comprised 22 grams of water with 1.6 grams of sodium persulfate. The reactor loading was allowed to react for 10 minutes. The remainder of Feed Mix 1 was then fed over 2 hours whilst the remaining Feed Mix 2 was fed over 2 hours and 10 minutes. The content of the reactor flask was held at 85°C by controlling the temperature of the water bath. The agitator speed was around 400 rpm. At the end of the feeds, the reaction product was held for 30 minutes at 85°C. 0.5 grams of TBHP (70% solution) was then added in 2 grams of water and the reaction product was allowed to cool to room temperature. A mixture comprising 2 grams of ammonia in 2 grams of water was then added to bring the pH above 7. The product was filtered through a 200 micron screen and gave a polymer dispersion with a solids content of 57% with an onset glass transition (as measured with a Shimadzu DSC-60 differential scanning colorimeter) of -3⁰C.

Preparative Example Cl

A dry glass 5 L Laboratory reactor was charged with 56Og of hydroxyl ethyl methacrylate containing 200ppm of MEHQ inhibitor and heated with 25g of urea prill. At 85 degrees Celsius 535g of sulfamic acid was added and reacted for 2 hours whereupon completion, 3000g of water was added to cool to room temperature and 330g of 25% ammonia was immediately added without delay. Obtained was a partially sulfated hydroxyl ethyl methacrylate polymer.

Spray drying

A 68Og portion of preparative example Cl colloid solution was mixed with 50g of Lime and 200Og of preparative example Dl was then added with mixing along with 2g of Defoamer (Foamaster 8034e from Cognis). The solution was spray dried in a "Niro production minor" spray drier as manufactured by Niro Denmark refitted with a "Nubilosa" nozzle as manufactured by Nubilosa Germany. The inlet temperature was 130⁰C and the air outlet was set to 50% maximum. Fine clay was metered into the air stream at 10% based on solid polymer.

The fine polymer powder obtained was free flowing and readily redispersible.

The invention has been described by way of non-limiting example only and many modifications and variations may be made without departing from the spirit and scope of the invention described.

Claims

CLAIMS:

1. A redispersible polymer powder including : a polymer to be redispersed; and a sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof.

2. A redispersible polymer powder according to claim 1, wherein the sulfated hydroxyl alkyl (meth)acrylate is an alkali metal salt, alkaline earth metal salt, ammonium salt or organic amine salt.

3. A redispersible polymer powder according to claim 2, wherein the sulfated hydroxyl alkyl (meth)acrylate salt is an ammonium salt, calcium salt or sodium salt or a combination thereof.

4. A redispersible polymer powder including: a polymer to be redispersed; and a sulfated hydroxyl alkyl (meth)acrylate monomer and/or polymer of the formula:

X = 1- 5 Y = 1- 3 R1 = H or C₁-C₃ alkyl

5. A redispersible polymer powder according to claim 1 or 4, wherein the polymer to be redispersed has a glass transition below 50⁰C.

6. A redispersible polymer powder according to claim 5, wherein the polymer to be redispersed has a glass transition below 10°C.

7. A redispersible polymer powder according to claim 6, wherein the polymer to be redispersed includes a pure acrylic polymer, styrene-acrylic polymer, vinyl acetate copolymer with alkyl acrylate or ethylene or maleate, or styrene- butadiene based polymer.

8. A redispersible polymer powder according to claim 7, wherein the polymer to be redispersed includes two or more monomers selected from the group consisting of styrene, methylmethacrylate, vinyl acetate, butadiene, n-butyl acrylate, 2-ethylhexylacrylate, ethylacrylate, methylacrylate, isopropylacrylate, vinyl propionate, dibutyl maleate, ethylene, tert-butyl acrylate, methacrylic acid, acrylic acid, acrylamide, methacrylamide, hydroxyethyl methacrylate.

9. A redisperible polymer powder according to claim 8, wherein the polymer to be redispersed contains, within its polymerises, units of sulfated hydroxyl alkyl (meth)acrylate, a salt thereof or AMPS monomer, or a combination thereof.

10. A redisperible polymer powder according to claim 1 or 4, wherein the sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof has a molecular weight of less than 20,000 daltons.

11. A redispersible polymer powder according to claim 10, wherein the sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof has a molecular weight of less than 5,000 daltons.

12. A redispersible polymer powder according to claim 11, wherein the sulfated hydroxyl alkyl (meth)acrylate based monomer, polymer and/or a salt thereof has a molecular weight of less than 2,500 daltons.

13. A redispersible polymer powder according to claim 1 or 4, further including a colloid selected from an aryl sulfonic acid condensate and polyvinyl alcohol.

14. Use of a sulfated hydroxyl ethyl (meth)acrylic based monomer, polymer and/or salt thereof as a redispersing aid for a redispersible polymer powder.

15. A product including, as a binder, the redispersible polymer powder according to claim 1 or 4.

16. A product according to claim 15, the product being selected from hydraulically setting compositions, adhesives, coating compositions, synthetic resin renders, and building materials

17. Use of a redispersible polymer powder according to claim 1 or 4 as a binder for a product.

18. Use according to claim 17, wherein the product is selected from hydraulically setting compositions, adhesives, coating compositions, synthetic resin renders, and building materials.