Calcium hypochlorite tablets

A calcium hypochlorite tablet useful as a toilet bowl cleaner, said tablet being prepared by compressing a dry mixture of granular calcium hypochlorite and a finely divided water-insoluble resin having a molecular weight of between about 10,000 to about 1,000,000, which resin is inert to calcium hypochlorite and which has good cold flow characterisitics, said resin comprising from about 10 to about 50% by weight, based on the total weight of the composition.

BACKGROUND OF INVENTION 
This invention relates to calcium hypochlorite tablets that are useful as 
toilet bowl cleaners. More particularly, it concerns tablets of this 
character that may be employed in single automatic dispensers in toilet 
bowl tanks. This type of dispenser is characterized as being an aquatic 
dispenser that is intended to confine the calcium hypochlorite tablet in a 
space and release small metered doses of chlorine solution at regular 
intervals. 
Calcium hypochlorite tablets conventionally supplied tend to dissolve 
rapidly on contact with water. This is accompanied by the evolution of 
large quantities of gas and an enlargement of the tablets. These 
characteristics are difficult to manage in the aquatic dispensers referred 
to above. 
SUMMARY OF INVENTION 
It has now been found that the rate of dissolution of calcium hypochlorite 
tablets and the enlargement of the volume of these tablets on contact with 
water (as for example in the aquatic dispensers noted above) can be 
controlled if said tablets are made by compressing a dry mixture of 
granular calcium hypochlorite and a sizeable amount of a finely divided 
water insoluble, high molecular weight resin which is inert to calcium 
hypochlorite and which has good cold flow characteristics. In a preferred 
form of this invention, the tablets are also provided with a shell of 
preformed inert polymer which is open, in a limited fashion, to the 
surrounding water when the tablet is disposed in the aquatic dispenser. 
PRIOR ART 
U.S. Pat. No. 4,087,360 to Faust et al discloses the preparation of calcium 
hypochlorite tablets intended for use in sanitizing the water supply such 
as in swimming pools. The patentees suggest that their tablets be prepared 
from mixtures of calcium hypochlorite with low molecular weight 
polyacrylic acid compounds. The latter are characterized by the patentees 
as being readily soluble in water. In contrast, the resins employed in the 
present invention are water insoluble. Although Faust et al broadly 
suggest that the amount of polyacrylic acid compound that they employ may 
range from about 0.0001 to 10 percent by weight of the calcium 
hypochlorite used in the examples they give, this amount never exceeds 
about 1% by weight. This is far below the quantity of resin utilized in 
the present tablets. 
U.S. Patent 4,035,484,to Faust et al discloses the use of a hydrazide of a 
monocarboxylic acid in calcium hypochlorite composition for the purpose of 
controlling the availability of chlorine to bodies of water such as 
swimming pools. In discussing the prior art, these patentees call 
attention to the fact that it is known in the prior art to use calcium 
hypochlorite in mixtures containing, as a binding agent, metal salts of 
carboxylic acids having at least 10 carbon atoms (German 
Offenlegungschrift 1,959,708). The use of the synthetic resin employed in 
the present invention is not disclosed. 
The U.S. Patent to Kooichi et al 4,218,433 discloses a constant rate 
eluting medicinal tablet having at least one hollow depression in the 
surface of the tablet, the tablet containing a water-soluble active 
medicament, and, optionally, an inert carrier, said tablet being coated 
with a water-soluble, water-permeable coating agent. Kooichi et al teaches 
that the hollow depression provides a site for the elution of the active 
provided the width thereof is between 0.1 and 1.0 mm and the depth is 
between 0.1 to 0.4 mm. The coating agent includes methacrylic 
acid-methacrylic acid ester copolymers and methyl acrylate-methacrylic 
acid-methyl methacrylate copolymers. The former, in pulverized form, may 
also be used as the inert carrier. 
The Kooichi et al patent is not concerned with the calcium hypochlorite 
cleaning tablets of the present invention. Furthermore, there is no 
teaching in Kooichi et al that their methacrylic inert carriers can 
control the swelling or volume of the tablets, as is characteristic of the 
present invention. Their teaching is rather that their coating in 
combination with their depression are the critical elements required to 
control the rate of elution. 
U.S. Pat. No. 3,856,932 to May teaches a tablet containing a solid chlorine 
releasing compound having a water impervious band circumscribing the 
tablet side walls. The use of the synthetic resin in the body of the 
tablet which characterizes the present invention is not shown. 
DESCRIPTION OF THE INVENTION 
As pointed out above, it is a feature of the present invention to employ as 
a binder for the calcium hypochlorite, certain organic synthetic resins 
defined in more detail below. As a group, organic materials would 
generally be considered unsuitable admixtures for binding together 
particles of calcium hypochlorite, because of chemical incompatibility. 
For example, exothermic reactions and fires have resulted from mixing 
materials such as glycols, polyglycols, and ether structure with calcium 
hypochloride. 
However, in accordance with the present invention, certain organic resins 
have been found to be effective binders of calcium hypochlorite, without 
indications of incompatibility. These resins, when finely divided and 
mixed with granular hypochlorite, assist the formation of strong tablets. 
Moreover, both the rate of dissolution of calcium hypochlorite and the 
enlargement of volume are reduced. 
To be suitable for use in the present invention, the organic resin selected 
should have a number of characteristics. An essential characteristic is 
that it be insoluble in water. It is also necessary that the resin be 
inert to calcium hypochlorite. It is further important that it show good 
cold flow properties. Ordinarily, the useful resins will be synthetic in 
character and will be of high molecular weight, e.g., from about 10,000 to 
about 1,000,000, preferably from about 50,000 to about 200,000. 
A number of resins are known in the prior art which meet these criteria. 
One class of resins are polymers prepared from chlorinated unsaturated 
hydrocarbons. These are exemplified by such materials as chlorinated 
polyethylene, chlorinated polybutadiene, chlorinated polyisoprene, 
copolymers of ethylene and vinyl chloride and copolymers of vinylidene 
chloride. The characterisitcs common to these materials are cold flow 
capability and inertness to calcium hypochlorite. 
Another class of resins that is useful for the present purpose are polymers 
of alkenyl acid esters where the esterifying alcoholic moiety is of 
sufficient length to promote cold flow and insolubility of hypochlorite 
within the tablet matrix. A number of resins of this type are available in 
the prior art. These include such materials as poly n-butyl methacrylate, 
poly 2-ethylhexyl methacrylate, polypropyl methacrylate, polyisobutyl 
methacrylate, polyethyl acrylate, polybutyl acrylate, polypropyl acrylate, 
polyhexyl acrylate, polyhexyl methacrylate, and other acrylic materials, 
including copolymers of the foregoing, that are not easily oxidized by 
calcium hypochlorite and that are capable of cold flow when compressed 
during tabletting. 
Especially good results have been obtained with poly n-butyl methacrylates. 
One such material that is available commercially is Elvacite 2044 from 
DuPont. This is a homopolymer of n-butyl methacrylate of high molecular 
weight and having an inherent viscosity of about 0.50 dl./g. (0.25 grams 
polymer in 50 ml. methylene chloride, measured at 20.degree. C. using a 
No. 50 Cannon-Fenske viscometer). 
The quantity of resin that will be contained in the tablets of the present 
invention may vary somewhat. What is critical is that a sizeable quantity 
be present which will give the desired solubility and stability 
characteristics as well as the cold flow characteristics. Generally the 
resin will constitute between about 10% and about 50% by weight based on 
the total weight of the tablet. Preferably, it will be present in the 
range of from about 15% to about 30% by weight based on the same weight 
basis. 
The bulk of the remaining portion of the tablets of this invention (i.e. 
over and beyond the resin) will comprise calcium hypochlorite. Other 
constituents may also be present in this portion of the tablets. Usually, 
the calcium hypochlorite will constitute from about 50% to about 90% (as 
is) by weight based on the total weight of the composition. In the 
preferred aspect of this invention, this will constitute between about 70% 
to about 85% (as is) by weight on the same weight basis. Typically, 
commercial calcium hypochlorite has an assay of between about 60 to about 
70%, the impurities including, for example, calcium chloride, sodium 
chloride, calcium chlorate, calcium hydroxide and water. 
In addition to the resin and calcium hypochlorite, the tablets of this 
invention may contain other adjuvants sometimes found in tablets of this 
character. These include such materials as inert fillers and lubricants 
utilized in tabletting. 
In preparing the tablets of this invention, a dry mix of finely divided 
resin and granular calcium hypochlorite will first be prepared. The 
particle size of the resin employed can vary somewhat. Usually, this will 
be in the range of from about 0.01 to about 1 mm, preferably from about 
0.1 to about 0.5 mm. Similarly, the size of the granules of calcium 
hypochlorite utilized may range over a variety of sizes. For the most 
part, this particle size will fall within the range of about 0.01 to 0.5 
mm, preferably from about 0.05 to about 0.2 mm. The more finely ground the 
particulate constituents, the more efficient will be the mixing with 
concommitent reduction in the cold flow requirements of the resin 
component. 
The mix of resin particles and granular calcium hypochlorite will then be 
pressed in a tabletting machine in accordance with the procedures well 
known to those skilled in the tabletting art. The specific manner of doing 
this may vary and does not constitute a part of this invention. 
In an alternative form of this invention, the resin bonded calcium 
hypochlorite tablet described above is emcompassed in a preformed shell of 
an inert polymer. This shell is fabricated so that it is open, to a 
limited extent, to permit the water to contact the tablet contained 
therein. This serves to prolong the integrity of the tablet and controls 
the admission of water and the release of the desired aqueous solution. It 
will be recognized that this arrangement provides a monolithic, 
slow-release device i.e. a controlled-release device that maintains a 
constant area for dissolution of the bound matrix of active ingredient. 
A variety of polymers may be employed in fabricating the preformed shell 
that will contain the tablet described above. By way of example mention 
may be made of the following: polyethylene, polypropylene, chlorinated 
polyethylene, and polymeric esters of methacrylic acid, e.g., Lucite.RTM.. 
One material that was found to be particularly good for calcium 
hypochlorite is polyvinyl chloride (PVC). 
The following Examples are given to further illustrate the present 
invention. It is understood, however, that this invention is not limited 
thereto.

EXAMPLE 1 
A mixture of ground poly n-butyl methacrylate (Elvacite 2044, DuPont), 20% 
by weight, and commercial calcium hypochlorite granules (assay 68.5%), 
said mixture having an average particle size of about 0.1 mm, was pressed 
into cylindrical tablets at a pressure of about 2,000 psi. One 40 gram 
tablet was immersed in 80 milliliters of water, producing a total volume 
of 102 ml. The total volume was observed periodically for a period of 14 
days and found not to exceed 107% of the initial volume. By contrast, a 
similar experiment with a tablet of unmodified commercial calcium 
hypochlorite in water experienced a progressive increase in total volume, 
reaching 154% of the initial volume in a 12-day period. 
Subjecting resin-modified tablets to elevated temperatures produced only 
slight discoloration and no evidence of significant exothermic reaction. 
Thus, when the resin-modified tablet was heated overnight in a forced 
draft oven at 165.degree. F., there was no visual change and no exothermic 
decomposition was observed. 
EXAMPLE 2 
Tablets were formed within cylindrical lengths of PVC pipe, using (1) 
unmodified commercial calcium hypochlorite granules and (2) the mixture of 
Example 1 (with 20% resin). Each pipe section was of 38 mm inside diameter 
and 20 mm axial length, and each resulting weight (of chemical charge) was 
approximately 34 grams. As compared to the unmodified hypochlorite 
tablets, the resin-modified tablets had exposed faces that seemed harder 
and stronger. 
One end of each pipe section was covered with a PVC sheet, cemented in 
place. The resulting specimens were then placed in beakers of water into 
which a continuous stream of water was directed. After 18 hours of such 
activity, the unmodified tablet had disintegrated and dispersed 
completely, while the resin-modified tablet exhibited only slight erosion 
of the exposed face. 
EXAMPLE 3 
Tablets were prepared as in Example 2 but with both ends covered with PVC 
sheet. Four holes of approximately 1 mm were then pierced into one end 
face of each specimen, roughly central to equal areas of the face. Plain 
and resin-modified specimens were placed within water-filled chambers (of 
toilet cleaning dispensers) that periodically were partially flushed with 
fresh water. In both specimens, the rate of chlorine release was found to 
be reduced as compared to that of corresponding hypochlorite tablets not 
having the monolithic shell, and the rate could be increased by increases 
of the number (and presumably, the size and position) of the holes in the 
shell. Only minor enlargement of the volume of solids was evident, as 
indicated by the slight convexities that appeared in the PVC sheets which 
formed the ends of the cylindrical shells. However, as between the resin 
bonded and non-bonded tablets contained in the cylindrical shells, the 
non-bonded tablet disintegrated within the shell quite rapidly.