DE69602591T2 - METHOD FOR PRODUCING HIGH-ALKALINE DETERGENT TABLETS - Google Patents

Description

History of the invention

The institutional detergent market includes a variety of products for cleaning silverware, pots and pans, bowls, floors, walls, stainless steel surfaces, tiles and other areas.

Unlike products used in the home, institutional detergents are often sold in bulk and dispensed from mechanical dispensers. There are a number of different physical forms they can take, including liquids, powders, solidified bricks, granules, and tablets. Several factors contribute to which a particular physical form is particularly suitable for the desired application.

Enema is a very important consideration. With a liquid in which the product is directly injected for use, the use concentration will be easy to control. Unfortunately, with liquids, the concentration of the active components in the product is usually relatively low and therefore the container size can be prohibitively large. DE 33 26 459 discloses a liquid dishwashing detergent containing bicarbonate, metasilicates, phosphate, chlorine, surfactants, acoustic precursor and water. EP 0297273 discloses a solid alkali- Cleaning material containing alkali phosphates, silicates, carbonates and phosphoric acid partial esters. With solid forms dissolved in water, the dissolution rate will affect the wash-in rate.

The supply of compatible starting material is very important. With a brick-shaped formulation, product consistency can be maintained to a certain extent, but the dissolution rate can be slow and there can also be problems with container placement with many molded parts.

Another very important factor in dispensing institutional detergents is packaging. For environmental reasons, it is preferable to reduce packaging. U.S. Patent 5,078,301 describes a pouch of detergent tablets wherein the pouch is a water-soluble material. This product is apparently designed to reduce packaging, but has several significant disadvantages. Water will primarily act with a water-soluble pouch to dissolve the plastic pouch. However, the undissolved residue from such pouches tends to clog the dispenser. Even with a water-soluble pouch, there is a need for an outer overwrap to keep moisture or external water from destroying the water-soluble pouch during loading and storage.

All of these problems are combined with highly hygroscopic (highly caustic) and/or hydratable materials. Of course, operators should never physically handle the detergent with caustic materials. Powdered cleaning compounds typically do not require water. Given that premature exposure to water tends to increase the tendency of powders to caking, clogging of the dispenser, and even dispensing of powder systems, especially those prone to extended periods of inactivity, can be a problem.

Many detergents, especially highly caustic detergents, dissolve in water and release a large amount of heat. It is therefore preferable to avoid tempera temperature peaks in the distribution device to control the dissolution rate of these detergents.

Another problem can be encountered with tableted high-caustic detergents. Anhydrous sodium hydroxide and potassium hydroxide are of course very hygroscopic. Typical detergent formulations generally contain some unbound water and undoubtedly water of hydration from sources such as sodium tripolyphosphate hexahydrate. During tableting, the caustic comes into very close physical proximity to the water. The water is necessary for tableting to occur at reasonable pressures. But once combined together, the caustic will react exothermically with the unbound water. For tableted high-caustic detergents, the mechanical strength of the tablet will be reduced if this reaction occurs after compression.

Summary of the invention

Accordingly, it is an object of the present invention to provide a process for forming a tableted detergent which includes phosphate sequestrant, unbound water and high levels of caustic. It is a further object of the present invention to provide such a product wherein the tablets formed do not deteriorate rapidly after formation.

These objects and advantages of the present invention can be achieved by combining the individual components of the detergent, including the phosphate together with unbound water and caustic, in such a manner and/or order of addition that the overall temperature of the product never exceeds 75°C and preferably never exceeds 50°C and most preferably never exceeds 40°C. Careful mixing, selection of raw materials and precise order of addition, which are factors in the hygroscopic nature of the materials and the lability of water, once absorbed, combine to achieve this result.

Accordingly, in one aspect, the present invention provides a process for forming a tableted detergent from a formulation containing a partially hydrated phosphate mixture including at least 10% hydrated phosphate based on the formulation, anhydrous caustic, 0.5% to 5% non-bound water and 0 to 40% filler, said formulation containing from 2 to 10% liquid components and from 2 to 10% by weight water of hydration, the process comprising:

- adding said unbound water to said phosphate mixture without adding said filler and allowing said water to be absorbed by said phosphate mixture; and

- subsequently adding 20 to 70% of caustic to said phosphate mixture to form a second mixture, whereby the temperature of said second mixture is maintained at less than 75°C, preferably less than 50°;

- Compacting the said second mixture to form tablets.

In this method according to the invention, it is preferred to add at least 5% filler to said phosphate mixture after said etchant has been added to said phosphate mixture.

In a second aspect, the present invention provides a process for forming a compacted detergent tablet, said tablet comprising:

From 20 to 70 weight percent anhydrous etchant;

from 20 to 60 percent by weight of a sequestering agent consisting of a combination of sodium tripolyphosphate and sodium tripolyphosphate hexahydrate, said agent contains at least 10% hydrated phosphate, based on the formulation;

from 0 to 4% by weight of polycarboxylic acid with a molecular weight of from 2000 to 20 000;

from 0 to 5% by weight of an antifoam agent, and from 0 to 4% by weight of propylene glycol and from 5 to 40% filler;

and unbound water, wherein said tablet contains from 2 to 10% liquid components and from 2 to 10 percent by weight water of hydration;

said process comprising combining said propylene glycol, said ethylene oxide, said propylene oxide copolymer, said polycarboxylic acid and said unbound water to form a liquid mixture, combining said liquid mixture with said sequestering agents, and allowing said liquid mixture to be adsorbed by said sequestering agents to form a first detergent mixture;

then combining said filler and said etching agent to said first detergent mixture to form a second detergent mixture and compacting said second detergent mixture to form tablets, wherein the order of addition of the detergent components prevents the second detergent mixture from reaching a temperature above 50°C.

In a third aspect, the invention provides a process for forming a compacted tablet product containing from 40 to 70% of non-hydrated caustic; from 20 to 60% of a sequestering agent consisting of a mixture A mixture of sodium tripolyphosphate and sodium tripolyphosphate hexahydrate, the mixture containing at least 10% hydrated phosphate based on the formulation; from 5 to 20% filler and from 1 to 5% non-bound water, wherein said tablet product contains from 2 to 10% liquid components and from 2 to 10% water of hydration by weight, said process comprising combining said water with said sequestering agent and allowing said water to be absorbed into said sequestering agent to form a detergent mixture, then combining said caustic agent and said filler with said sequestering agent, thereby preventing the temperature of said detergent mixture from reaching 50°C, compressing said detergent mixture to form tablets.

In a preferred embodiment of the present invention, wherein fillers are included in the detergent formulation, the phosphate sequestering agents, i.e. sodium tripolyphosphate, anhydrous and hexahydrate, are combined with each other with any liquid components, all of which contain non-bound water. After the liquid components are absorbed into the sequestering agents, caustics, fillers and any bleaching agents are added. The product can then be compressed to form tablets. In this way, the hydration reaction is sufficiently controlled, i.e. the non-bound water is absorbed by the species particularly capable of retaining it in the presence of caustic, thus reducing the potential for an exothermic reaction and subsequent deterioration of the tablet.

In an alternate embodiment of the present invention, cooling can be used to physically control the temperature of the mixture, thereby preventing an undesirable excessively exothermic reaction. However, this requires a significant cooling time.

The objects and advantages of the present invention will be further assessed in the light of the detailed description below.

Detailed description

The present invention is a process for preparing a highly caustic tableted detergent, particularly a fabric-washing detergent. This fabric-washing detergent will include a caustic source, a hardness sequestering system comprising a hydrated phosphate, water-soluble low molecular weight polymers, non-ionic defoaming surfactants, processing aids and optionally bleach sources.

The etchant source may be sodium or potassium hydroxide, with sodium hydroxide being preferred. Generally, for use in the present invention, it will contain from about 20% to 70% etchant, with about 45% to 57% etchant being preferred. The etchant is essentially anhydrous.

The hardness sequestering system can be a variety of different chemical components. The primary sequestering agents are alkali metal salts of polyphosphates. Optional sequestering agents include alkali metal salts of phosphonic acid and of gluconic acid, alkali metal salts of ethylenediaminetetraacetic acid (EDTA), alkali metal salts of nitrilotriacetic acid (NTA), and alkali metal salts of polycarboxylic acids such as polyacrylic acid, polymaleic acid, and mixtures thereof.

Phosphates are usually available in anhydrous or hexahydrate forms. For the purposes of the present invention, a mixture of anhydrous and hydrated phosphates is preferred. The composition should include at least 10% hydrated phosphate sequestrant based on the total formulation.

Generally, the hardness sequestering system of the present invention will comprise 20 to 80% of the total mass of the detergent composition, preferably 20 to 60%, and preferably ter 35 to 40%. A mixture of hydrated (hexahydrate) and anhydrous sodium tripolyphosphate in the mass ratio of 3:1 to 1:3, and preferably 1:1 to 2:1. In areas where the amount of phosphates is regulated, it may be necessary to supplement the water hardness control ability of the product by adding other sequestering agents such as the alkali metal salts of NTA or EDTA.

The present invention may optionally include a chlorine source. A preferred chlorine source is dichloroisocyanurate. This is added in amounts of up to 7% by weight. Other bleaching aids, including alkali metal perborates and percarbonates, may also be used.

In addition to the above, the detergent composition may contain defoaming surfactants. A typical class of anionic defoaming surfactants are the phosphate esters. The defoaming nonionic surfactant used herein is selected from the group consisting of alcohol alkoxylates, alkyl alkoxylates, block copolymers and mixtures thereof. Usually, these nonionic surfactants are prepared by the condensation reaction of a suitable amount of ethylene oxide and/or propylene oxide with a selected organic hydrophobic base under suitable oxyalkylation conditions. These reactions are well known and documented in the art. Generally, these will have a molecular weight of from 900 to about 4000. One such surfactant is an ethylene oxide-propylene oxide block copolymer. Commercially available surfactants include Triton CF32*, Triton DF12*, Plurafac LF131*, Plurafac LF132*, Plurafac LF231*, Industrol N3* and Genapol PN30* (* trademarks). These may be present in an amount of from about 0.5 to about 5%, with about 1.5% being preferred.

In addition, water-soluble polybasic acids of low molecular weight (2000 to 20,000), such as polyacrylic acid, polymaleic or polymethacrylic acid or copolymeric acids can be used as sequestration aids to to inhibit growth of calcium carbonate crystals and to improve rinsability. Preferably, the water-soluble polymer will be a polycarboxylic acid, such as polyacrylic acid, having a molecular weight of about 5,000. In general, the present invention should include from about 1% to about 4% polyacrylic acid on an active basis, with about 2% being preferred.

The detergent formulation may also contain 1% to 5% of a polyhydric water-soluble alcohol. Suitable water-soluble polyhydric alcohols include propylene glycol, ethylene glycol, polyethylene glycol, glycerin, pentaerythritol, trimethylolpropane, triethanolamine, triisopropanolamine, and the like. Propylene glycol is preferred, used in an amount of up to 4% by weight of the formulation. This acts as both a processing aid and a dissolution aid for the tablet, as discussed below.

To provide a strong tablet, the present invention will contain from 2 to 10% liquid components, preferably less than 8%. Generally, this may be suggested for the non-ionic surfactant, the polyalcohols and/or unbound water. The formulation should also contain from 2% to 10% by weight water of hydration. This is also suggested for a stronger tablet. Generally, there will be at least 0.5% up to 5% unbound water in the composition. This may be the solvent for the polymer or the surfactant. It is preferred to keep the unbound water to less than 5% and the total liquid to less than 10% to keep the product flowable and non-sticky during tableting. When in the process of the invention the temperature of the second mixture is maintained at less than 50°C, it is preferred to maintain the non-bound water content at 1 to 3%.

In addition to the above, the detergent formulation may optionally include ingredients, commonly referred to as fillers, such as soda ash, silicates such as sodium and potassium silicate and polysilicate, and sodium meta silicate and hydrates thereof, alkali metal chloride, alkali metal sulfates and alkali metal bicarbonate. These can be present in an amount of 1 to 30 percent by weight.

A preferred formulation for use in the present invention includes the following formulations:

Table 1 Fixed components:

10.0%........ Calcined soda

21.0%.........sodium tripolyphosphate.hexahydrate (18% water of hydration)

16.3%.........Sodium tripolyphosphate powder

0.2%........ Sodium dichloroisocyanurate (ACL-60)

45.0%........ Etched pearl

Liquid components:

4.5%........ Polyacrylic acid with molecular weight 5000 (48% active in water)

1.5%........ Ethylene oxide-propylene oxide block copolymer nonionic surfactant

1.5%........ Propylene glycol

In this formulation, the sodium tripolyphosphate hexahydrate provides 3.8% water of hydration and the polyacrylic acid provides about 2.3% non-bound water.

A very strong caustic formula includes:

Table 2 Fixed components:

21.0%........ Sodium tripolyphosphate.Hexahydrate (18% water of hydration)

16.3%.........Sodium tripolyphosphate powder

56.7%........ Etched pearl

Liquid components:

3.0%........ Polyacrylic acid with molecular weight 5000 (48% active in water)

1.5%........ Ethylene oxide-propylene oxide block copolymer nonionic surfactant

1.5%........ Propylene glycol

A third formulation containing trisodium NTA is given in Table 3.

Table 3

21.0%........ Sodium tripolyphosphate.Hexahydrate (18% water of hydration)

16.3%........ Sodium tripolyphosphate anhydrous

10.0%........ Trisodium NTA

1.7%........ Calcined soda

45.0%........ Etched pearl

3.0%........ Acrylic acid with molecular weight 5000 (48% active)

1.5%........ EOPO block copolymer

1.5 s........ Propylene glycol

To formulate the detergent of the present invention, the phosphates are combined and mixed in a countercurrent or paddle mixer. The fillers and other non-hygroscopic materials are not added at this time. Since a very low concentration of the liquid compo components is added to the formulation, the liquid components should be combined with the sequestrants before mixing. Normally, the ethylene oxide-propylene oxide block copolymer will react with the polyacrylic acid to form a solid or a gel. However, mixing the propylene glycol with these two liquid components prevents this reaction.

Therefore, any liquid components such as polyacrylic acid dissolved in water, the non-ionic surfactant and the propylene glycol are carefully mixed together and evenly sprayed onto the phosphate while mixing and allowing penetration into the phosphate. The etchant is added, then the fillers and finally the dichloroisocyanurate. If NTA or EDTA are added, they should usually be added with the fillers, i.e. after the etchant.

It is very important that during all mixing stages, and even after formulation, the temperature is maintained at less than 75°C, preferably less than about 50°C, and most preferably less than 40°C. It is theoretical that hydration of the caustic will generate heat which, if excessive, will cause the STPP hexahydrate to release water, most likely accompanied by decomposition of the tripolyphosphate anion which will generate more heat while weakening the tablet. However, by allowing the unbound water to be fully effectively absorbed by the phosphate, the hydration reaction is sufficiently slowed and excessive heat is not generated and the hexahydrate does not release water. The phosphate mixture binds tightly to the unbound water. When the etchant as such is combined with the mixture of phosphate and now bound water, hydration of the etchant is avoided. This prevention of hydrated etchant in turn keeps the temperature decreasing. Therefore, applicants' process provides a method of temperature control so as to control or prevent the autocatalytic reaction by maintaining the mixing temperature below 75ºC.

If instead unbound water is added to the filler fen, or even added to a mixture of fillers and sequestrants, then this water which hydrates the filler is relatively easily accessible by the caustic and the resulting hydration is so rapid, generating so much heat, that the hydrated phosphate gives up water, causing the tablets formed to crumble or weaken.

The detergent mixture is then pressed to form tablets using a standard tabletting machine. One such machine suitable for use in the present invention is the Stokes brand tabletting machine. Typically the powder is subjected to a pressure of 4 to 10 tons of pressure to form tablets. Typically the tablets will have a thickness of about 12 to 13 mm and a diameter of about 20 mm. The maximum diameter will be a function of the distributor/feed water interface area.

The tablets of the final product do not significantly weaken over time after they are manufactured. These can then be used in a typical laundry machine equipped with a water spray detergent dispenser.

There are various methods of achieving this same result. A first method of achieving this result is to omit the blend additives and form the detergent with anhydrous and hydrated sequestrants, together with the liquid components mentioned earlier, as shown in Table 2. The phosphates are combined with the liquid component so that any unbound water present is adsorbed onto the sequestrants. The caustic is then added and the mixture tabletted. Because the phosphates again hold the water relatively firmly, the temperature is maintained at all times at less than 75°C and usually less than 50°C and the hexahydrate will therefore not release water which can react with the caustic. The tablets formed do not deteriorate rapidly after formation.

In a second alternating procedure of practical In practicing the invention, the fillers may be combined with the phosphates and the water subsequently added. This may then be mixed together with the etchant, provided that sufficient cooling is provided so that the temperature is maintained below 50°C and preferably below 40°C. This temperature is maintained for a sufficient time to allow the etchant to react fully with any labile water prior to the tabletting process. Of course, this requires additional handling time.

By using the preferred process, the tablets formed have a greatly improved storage stability and shelf life. The final products are more stable, meaning they are less likely to break apart during shipping and will dissolve more slowly and evenly during use, providing an even distribution of the detergent dissolved in water without the formation of an extreme exotherm. Overall, this system provides many unique advantages and although several embodiments of the present invention have been disclosed, the invention itself should be defined only by the following claims, in which we claim:

Claims (10)

1. A process for forming a tabletted detergent from a formulation containing a partially hydrated phosphate mixture containing at least 10% hydrated phosphate based on the formulation, anhydrous caustic, 0.5% to 5% non-bound water and 0 to 40% filler, said formulation containing from 2 to 10% liquid components and from 2 to 10% by weight water of hydration, comprising: adding said unbound water to said phosphate mixture without adding said filler, and allowing said water to be absorbed by said phosphate mixture; and then adding 20% to 70% of caustic to said phosphate mixture to form a second mixture, the temperature of said second mixture being maintained at less than 75°C; Compressing the second mixture mentioned above to form tablets. 2. The method of claim 1, wherein at least 5% filler is added to said phosphate mixture after said etchant is added to said phosphate mixture. 3. The process of claim 1, wherein said temperature of said second mixture is maintained at less than 50°C. 4. The process according to claim 2, wherein said hydrated sequestrant comprises a mixture of sodium tripolyphosphate (STPP) and STPP hexahydrate. 5. The method of claim 3, comprising adding fillers to said phosphate mixture after said water has been absorbed by said phosphate. 6. The process according to claim 3, containing 1% to 3% unbound water. 7. The method according to claim 2, wherein said filling substance is selected from the group consisting of calcined soda, alkali metal silicates, alkali metal polysilicates, alkali metal metasilicates, alkali metal chloride, alkali metal sulfates and alkali metal bicarbonates. 8. The process of claim 3, wherein the temperature of said second mixture is maintained at less than 40°C. 9. A process for forming a compacted detergent tablet, the tablet containing: From 20% to 70% by weight anhydrous etchant; from 20% to 60% by weight of a sequestrant consisting of a combination of sodium tripolyphosphate and sodium tripolyphosphate hexahydrate, said agent containing at least 10% hydrated phosphate based on the formulation; from 0 to 4 percent by weight of polycarboxylic acid with a molecular weight of 2000 to 20000; from 0 to 5% by weight of an antifoam agent, and from 0 to 4% by weight of propylene glycol and from 5% to 40% filler; and unbound water, wherein said tablet contains from 2 to 10% liquid components and from 2 to 10% by weight water of hydration; said process comprising combining said propylene glycol, said ethylene oxide, said propylene oxide copolymer, said polycarboxylic acid and said unbound water to form a liquid mixture, combining said liquid mixture with said sequestering agents, and allowing said liquid mixture to be adsorbed by said sequestering agents to form a first detergent mixture; subsequently combining said filler and said etchant into said first detergent mixture to form a second detergent mixture and compressing said second detergent mixture to form tablets, wherein the order of addition of the detergent components causes the second detergent mixture to reach a temperature temperature of more than 50ºC. 10. A process for forming a compacted tablet product containing from 40% to 70% non-hydrated caustic; from 20% to 60% of a sequestrant consisting of a mixture of sodium tripolyphosphate and sodium tripolyphosphate hexahydrate, said mixture containing at least 10% hydrated phosphate based on the formulation; from 5% to 20% filler, and from 1% to 5% unbound water, wherein said tablet product contains from 2 to 10% liquid components and from 2 to 10% by weight water of hydration, said process comprising combining said water with said sequestering agent and allowing said water to be absorbed into said sequestering agent to form a detergent mixture, then combining said caustic and said filler with said sequestering agent, thereby preventing said detergent mixture from reaching a temperature of 50°C, compacting said detergent mixture to form tablets.