WO2013188975A1

WO2013188975A1 - Aqueous wax dispersion

Info

Publication number: WO2013188975A1
Application number: PCT/CA2013/050471
Authority: WO
Inventors: Laurence Anthony Sinnige; Maria Racota; Jan COCQUYT; Patrick HAERENS
Original assignee: Walker Industries Holdings Limited; Govi Nv
Priority date: 2012-06-19
Filing date: 2013-06-19
Publication date: 2013-12-27

Abstract

An aqueous dispersion comprising water, a hydrocarbon wax and a copolymer of ethylene and vinyl acetate, a gypsum compositions including said aqueous dispersion and the use of the aqueous dispersion or gypsum composition to produce water resistant gypsum products.

Description

AQUEOUS WAX DISPERSION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority under the Paris Convention to US Application Number 61/661 ,716, filed June 19, 2012, the entire contents of which are incorporated herein by reference. FIELD OF INVENTION

[0001] This invention relates to aqueous wax dispersions and their use to impart water- repellent properties to gypsum products, such as gypsum blocks, gypsum wallboards or gypsum panels.

BACKGROUND OF THE INVENTION

[0002] In the production of gypsum products, calcium sulfate hemihydrate is hydrated with water. Before the calcium sulfate slurry sets to the calcium sulfate dihydrate, it can easily be shaped into a board or block. After the slurry has set to a solid gypsum product, the excess water is removed usually through conventional drying methods. [0003] In the production of a gypsum board the gypsum slurry is brought in between 2 liners that are usually made from paper. Set accelerators, such as ball-milled calcium sulfate dihydrate and potassium sulfate and/or set retarders such as

diethylenetriaminepentacetic acid are used to optimize the setting behavior of the slurry. Dispersing agents, such as lignin sulfonates, naphthalene sulfonates or sulfonated melamine polycondensates, can be added to increase the fluidity of the gypsum slurry. Fluidity means the ability of the gypsum slurry to flow and is important in order to have a smooth production process and to maintain the dimensions of the gypsum boards. Foaming agents are used to control the density of the board through the incorporation of air. Starch is mainly used to improve the bond between the paper liner and the gypsum core in a gypsum board. The gypsum slurry may contain many other chemicals in addition to the ones listed above.

[0004] Gypsum products absorb water. This not only leads to visual defects but also to a dramatic loss of the strength of the product. It is a well-known practice to add hydrophobic agents to the gypsum slurry. Asphalt emulsions, metallic soaps and resin-based products have been used. Polysiloxane based systems are known as relatively effective hydrophobing agents. However, they are prone to large fluctuations in price and availability. In addition, their handling and use is difficult and they give rise to defoaming problems, increased emissions and silica buildup in dryers and on equipment. [0005] Suitable hydrocarbon wax dispersions are known to provide water-repellent properties to gypsum products. These products are often also referred to as paraffin emulsions. The paraffin wax based dispersed phase is normally melted before dispersion in water. Strictly speaking, only above the melting temperature of the dispersed phase, when this phase is in the liquid state, can paraffin wax dispersions also be referred to as paraffin wax emulsion. However, the term paraffin emulsion is often used in the art even though the temperature may be below the melting point.

[0006] Paraffin wax dispersions used as hydrophobing agents for gypsum products, such as gypsum wallboards, often also contain a polar wax-like component in addition to paraffin. Examples of such polar compounds described in literature are oxidated paraffins as described in US Patent No. 4042409, polyolefin maleic anhydride graft polymers as described in US Patent No. 6890976 B1 , mixtures of longchain fatty acids and longchain fatty esters as described in CA2226246, resins like a colophonium resin as described in EP1907480 B1 , or a styrene - maleic anhydride resin as described in US Patent No.

5098943 A. Nevertheless, the use of a saponifiable wax is common in the art. Some patents describe the use of carnauba wax as shown in BG466188 A1 , but the use of montan wax is more widespread as described in US2007245931 A1 , US2006283356 A1 ,

WO9809925 A1 , and US5437722 A.

[0007] Most paraffin wax dispersions described in the literature contain a film-forming substance or polymer in addition to the paraffin and a polar wax-like component. Examples of film forming polymers described in the prior art include acrylates as in US4042409 or cellulose derivatives as in US2006283356 A1 and more commonly polyvinyl alcohol as in US6890976 B1 , US5437722 A, US6946504 B2, and WO9809925 A1 which may be combined with a crosslinking agent as in US4094694 A.

[0008] However, a number of problems are associated with the known wax emulsions for gypsum slurries.

1 . An essential ingredient in many conventional hydrocarbon wax dispersions is montan wax. However, in the last decade, the availability of montan wax has become relatively poor and consequently the price has risen dramatically. Further, unbleached montan wax grades are somewhat cheaper but often have an undesirable darkening effect on the final gypsum product. Furthermore, montan wax is a crude natural product that contains a variety of components. The composition of montan wax varies over time and also by the geographic region of the mine from which it originates. This leads to variable hydrophobing characteristics of the hydrocarbon wax dispersion containing the montan wax. 2. In order to obtain sufficient water-repellent characteristics, conventional hydrocarbon wax dispersions are usually based on relatively expensive synthetic or refined hydrocarbon wax. Synthetic hydrocarbon waxes are usually made with the well-known Fisher Tropsch process. Refined hydrocarbon waxes are obtained in base oil refineries by extensive de-oiling or through hydrocracking. The oil content of refined waxes is typically below 3%, measured with ASTM D721 :

Standard Test Method for Oil Content of Petroleum Waxes. By contrast, paraffin slack wax is obtained from base oil refineries using the solvent extraction principle, contains between 3 and 50% oil and is considerably cheaper than refined or synthetic hydrocarbon wax. However, the use of paraffin slack wax in conventional hydrocarbon wax dispersions has been known to lead to drastically reduced hydrophobing effect in the resulting gypsum products. 3. Polyvinyl alcohol (PVA) can also be used to enhance the performance of

conventional wax dispersions for gypsum. One drawback, as outlined in US Patent No. 6,946,504 "Formulation Containing Polyvinyl Alcohol and Sulphonated Melamine Polycondensate for Gypsum Slurries", is that with increasing PVA content comes decreasing fluidity of the gypsum slurry. This can be remedied with the addition of the aforementioned Sulphonated Melamine, but with this comes added cost. In addition, high levels of PVA can contribute to defects in gypsum panels, such as blisters and secondary foam. [0009] Accordingly, there is a need of a hydrophobing additive which is easy and economical to apply without negatively affecting fluidity, foamability or set time and characterized by a low variability in quality.

SUMMARY OF THE INVENTION

[0010] In one aspect, the present invention provides an aqueous dispersion, for addition to an aqueous gypsum slurry comprising:

i) about 5 to 95% water;

ii) a hydrocarbon wax having a melting point of 40-80°C and

iii) A copolymer of ethylene and vinyl acetate in an amount of 1 to 200 parts per 100 parts of said hydrocarbon wax ii) [0011] In another aspect, the invention provides a gypsum slurry composition for use in making a water-resistant gypsum product comprising:

a) 100 parts of an aqueous gypsum slurry and

b) 1 to 40 parts, by weight of said aqueous gypsum slurry a), of an aqueous

dispersion comprising:

i) about 5 to 95% water;

ii) a hydrocarbon wax having a melting point of 40-80°C and iii) a copolymer of ethylene and vinyl acetate in an amount of 1 to 200 parts per 100 parts of said hydrocarbon wax ii)

[0012] Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention provides a wax dispersion for imparting water repellency to gypsum products comprising various components. In a first aspect of the invention, there is provided an aqueous dispersion for use in making gypsum products, containing a hydrocarbon wax and a copolymer of ethylene and vinyl acetate (EVA). In a particular aspect the copolymer of ethylene and vinyl acetate contains between 1 and 50% polyvinylacetate.

[0014] In another aspect, the copolymer of ethylene and vinyl acetate is present in an amount of about 1 to 200 parts, by weight, per 100 parts of said hydrocarbon wax. In another embodiment, the amount is 1 to 50 parts, by weight, per 100 parts of said hydrocarbon wax.

[0015] In a further aspect the hydrocarbon wax has a melting point of 40-80°C. A number of hydrocarbon waxes are suitable including, for example, paraffin slack wax, refined paraffin wax, Fisher Tropsch wax, polyethylene wax or mixtures thereof.

[0016] Copolymers of ethylene and vinyl acetate have been found to have a relatively good compatibility with hydrocarbon wax. The melting point of most available ethylene vinyl acetate copolymers lies in the range of 40-90°C, which is similar to most available paraffin waxes. The copolymer melt index generally changes relative to the chain length. Lower melt indexes generally indicate longer polymer chains and more difficult dissolution into molten hydrocarbon wax dispersion. The melt index of common ethylene vinyl acetate copolymers lies between 1 and 1000 g per 10 minutes. Without wishing to be bound by theory, it is believed that the polarity of the copolymer of ethylene and vinyl acetate leads to a better affinity and a better adhesion to the gypsum air interface. Additionally, the EVA also has film forming properties.

[0017] Examples of suitable EVA polymers include products under the brand name Elvax™, all produced by DuPont, or Evatane™, produced by Arkema. One particular example is Evatane™ 28-420, which is a random copolymer of ethylene and vinyl acetate made by high-pressure radical polymerization process. This particular example has a vinyl acetate content of 27-29% wt, a melt index (190°C/2.16 kg) of 370-470 g/10 min and a melting point of 69°C.

[0018] One embodiment of the present invention consists of a formulation including water, paraffin, EVA and PVA wherein the PVA is dissolved in the water phase and provides strengthening properties to the gypsum product and the EVA is added to the paraffin wax phase and reduces the water uptake of the final gypsum product. In a particular embodiment the PVA is in a concentration between about 0.01 and about 5% wt.

[0019] Another embodiment of the present invention consists of a formulation comprising EVA and paraffin slack wax, which is optionally combined with one or more refined hydrocarbon waxes.

[0020] In a particular aspect of the present invention, the hydrocarbon wax fraction of the present EVA-containing hydrophobing dispersions for gypsum may consist partly or exclusively of paraffin slack wax, while still maintaining acceptable hydrophobing activity in the final gypsum product.

[0021] In a further aspect of the invention the aqueous dispersions described above may be added to an aqueous gypsum slurry. The aqueous gypsum slurry may then be used to make gypsum products.

[0022] In a particular embodiment there is provided a gypsum composition used to make a water-resistant gypsum product comprising:

a) 100 parts of an aqueous gypsum slurry and

b) 1 to 40 parts, by weight of said aqueous gypsum slurry a), of an aqueous

dispersion comprising:

i) about 5 to 95% water;

ii) a hydrocarbon wax having a melting point of 40-80°C and iii) a copolymer of ethylene and vinyl acetate in an amount of 1 to 200 parts per 100 parts of said hydrocarbon wax ii) [0023] In another embodiment the copolymer of ethylene and vinyl acetate is in an amount of 1 to 50 parts per 100 parts of said hydrocarbon wax ii). In a further embodiment the copolymer of ethylene and vinyl acetate has a vinyl acetate content between 1 and 50% wt.

[0024] The gypsum products made from the gypsum compositions include wallboards, panels, blocks, and the like.

[0025] In a further aspect of the invention, the aqueous gypsum slurry may include any combination of the following:

Ingredients

Stucco

Accelerator

Pulp

Potash

Starch

Dispersant, 42%

Wax Emulsion

Water

Foam

Water

Soap, 5% EXAMPLES OF THE INVENTION

[0026] The present invention will be further explained and illustrated by the following comparative examples and test results. These examples are intended to describe the properties of this invention and not to limit the invention in any way.

[0027] Various comparative samples were prepared using an emulsion composition as described in United States Patent 6890976, 'Wax emulsion formulation and gypsum composition containing same", incorporated herein by reference. A base emulsion composition comprising a paraffin wax, polyethylene wax, a maleic anhydride graft polymer (Ceramer® 67 manufactured by Baker Petrolite) as well as ancillary dispersants and stabilizers (see Table 1 ), was prepared in combination with various levels of EVA and PVA according to Table 3. Table 1 : The Composition of the Base Emulsion

Paraffin Wax 30.6%

Ethylene Vinyl Acetate (Evatane) 3.62%

Oxidized polyethylene wax 1 .0%

Maleated polyethylene wax 1 .0%

Polyvinyl Acohol (98% hydrolyzed) 1 .0%

Water solution comprising sodium

lignosulfonate, potassium hydroxide,

and a polyacrylic acid dispersant 62.78%

[0028] The above-mentioned emulsions were individually mixed into a slurry of calcium sulfate hemi-hydrate according Table 2: Table 2

Dry Ingredients Grams

Calcium Sulphate 870

Hemihydrates

Calcium Sulphate Dihydrate 5.5

Pulp

Potash 0.25

Corn or Wheat Based Starch 5

DISAL™ from Handy Chemicals 3

Poly naphthalene sulphonate

sodium salt, 42%

Wax Emulsion 60

Water 638

Foam

Water 151

Alpha Foamer™ FA-406 from 4.8

Stepan Chemicals, 5% [0029] The resulting mixture was set in the form of board panels ½" thickness and 12" X 12" diameter. The boards were heated to dryness in a convection oven, cooled overnight to ambient temperature, cut down to 6" X 6" and weighed (initial wt). The panels were then immersed in water for 2 hours and weighed again (final wt). The percentage of water absorbed by these samples was calculated using the following formulation:

Abs% =100^*((final wt) - (initial wt))/initial wt)

[0030] The absorption of each sample was compared against a commercially available product, Coreshield® 800 using the following calculation:

Relative % = (Abs% sample)/(Abs% control) ^* 100% [0031] Absorptions less than 100% indicate a better performance than the control. Results are summarized in the following table:

Table 3

Factor 1 Factor 2 Response 1

A:pva B:eva absorption

% by wt % by wt Relative %

1 .00 3.62 81 .5

2.62 2.00 82.7

2.00 2.00 89.6

1 .62 3.00 84.4

0.00 0.00 349

0.00 5.00 1 13 [0032] From the results in Table 3 it can be seen that significant reductions in the level of PVA can be obtained by the addition of EVA into the wax phase while still retaining good relative absorption rates.

[0033] Reducing the amount of PVA in the emulsion improves the fluidity of the composition

as is demonstrated by the results shown in Table 4:

Table 4

PVA EVA Change in Fluidity

2.62 0.00 - 17%

2.00 0.00 -12%

0.00 2.00 +5.5%

[0034] The change in fluidity was measured by mixing 4 parts emulsion, 54 parts water, 0.4 parts naphthalene sulfonate (dispersant) and 100 parts stucco. The resulting mixture was poured onto a glass plate and the diameter measured. The percent change relative to a control sample without emulsion was then calculated. As can be seen, a reduction in PVA results in a less negative impact on the fluidity. Complete removal of PVA results in a positive shift. This further allows for a reduction in the use of dispersant required in the emulsion.

[0035] While the invention has been described with reference to specific embodiments, various modifications thereof will be apparent to those of skill in the art. It is intended that the claims should not be limited to the embodiments or examples described in the description but rather should be given the broadest interpretation consistent with the description as a whole.

[0036] All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present application is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

Claims

We Claim

1 . An aqueous dispersion for addition to an aqueous gypsum slurry comprising:

i) about 5 to 95% water;

ii) a hydrocarbon wax having a melting point of 40-80°C and

iii) a copolymer of ethylene and vinyl acetate in an amount of 1 to 200 parts per 100 parts of said hydrocarbon wax ii)

2. An aqueous dispersion according to claim 1 , wherein said copolymer of ethylene and vinyl acetate is present in an amount of about 1 to 50 parts, by weight, per 100 parts of said hydrocarbon wax.

3. An aqueous dispersion according to claim 1 or 2, wherein said copolymer of ethylene and vinyl acetate has a vinyl acetate content between 1 and 50% wt.

4. An aqueous dispersion according to claim 1 or 2, further comprising polyvinyl alcohol in a concentration between 0.01 and 5% wt.

5. The emulsion of claim 1 or 2, wherein the hydrocarbon wax is paraffin slack wax, refined paraffin wax, Fisher Tropsch wax, polyethylene wax, such as oxidized polyethylene wax or maleated polyethylene wax, or mixtures thereof.

6. A gypsum composition used to make a water-resistant gypsum product, comprising: a) 100 parts of an aqueous gypsum slurry and

b) 1 to 40 parts, by weight of said aqueous gypsum slurry a), of an aqueous dispersion comprising:

i) about 5 to 95% water;

7. A composition according to claim 6, wherein said copolymer of ethylene and vinyl acetate is present in an amount of about 1 to 50 parts, by weight, per 100 parts of said hydrocarbon wax.

8. The composition of claim 6, wherein said copolymer of ethylene and vinyl acetate has a vinyl acetate content between 1 and 50% wt.

9. The composition of claim 6, further comprising polyvinyl alcohol in a concentration between 0.01 and 5% wt.

10. The composition of claim 6, wherein the hydrocarbon wax is paraffin slack wax, refined paraffin wax, Fisher Tropsch wax, polyethylene wax, such as oxidized polyethylene wax or maleated polyethylene wax, or mixtures thereof.

1 1 . The composition of any one of claims 6-10 wherein the gypsum product is a wallboard a panel or a block.

12. A water-resistant gypsum block, board or panel, prepared from a gypsum composition described in claim any one of claims 6-10.

13. The use of an aqueous dispersion according to any one of claims 1-5 or a gypsum composition according to any one of claims 6-10 to produce a water resistant gypsum block, board or panel.