Antifouling tile containing antifoulant reservoirs for in situ replenishment

A modular antifouling tile is formed with a plurality of reservoirs that contain antifoulant which diffuses therefrom through the matrix of the coating. The coating matrix is preferably formed of an elastomeric material selected from the group of butyl and natural rubbers, neoprene, polybutylene, polyisoprene, polybutadiene, polysulfides, polyurethanes, vinyls, polyacrylonitriles, and copolymer blends thereof. Selected antifoulants that diffuse through a coating matrix of the abovementioned materials include tributyltin oxide and 2, 4, 5, 6-tetrachloroisophthalonitrile.

BACKGROUND OF THE INVENTION 
This invention generally relates to an antifouling system and, more 
particularly, to a modular arrangement of rubber tiles provided with a 
repetitive pattern of cells filled with compatible antifoulant materials 
which diffuse through the matrix of the rubber tile material. 
Effective antifouling coatings include a means for transporting the 
antifouling materials to the boundary layer of the coating where fouling 
occurs. Mechanisms for transporting and releasing antifoulant include 
contact leaching and hydrolysis of the antifoulant; leaching of the 
antifoulant from a soluble matrix; and diffusion of antifoulant through 
the matrix. One problem encountered in utilizing the aforementioned 
release mechanisms is the difficulty of controlling the release rate of 
antifoulant from the coating. For example, too high of an antifoulant 
release rate has led to rapid exhaustion of antifoulant, and too low of a 
release rate often fails to adequately protect the coating surface from 
fouling. After a period of time, antifouling materials in coating matrixes 
become so diluted that the coatings lose antifouling effectiveness the 
coating must be replaced. The antifouling coating system of the present 
invention overcomes problems of the prior art by utilizing reservoirs that 
permit insitu replenishment of antifoulant. 
In a diffusion type of coating, the antifoulant diffuses throughout the 
coating matrix. As the antifoulant material passes into the seawater from 
the boundary layer of the coating, the remaining antifouling material 
redistributes itself in an attempt to maintain equilibrium within the 
coating. If the diffusion or migration rate is suitably controlled it is 
possible to maintain an antifouling environment in which the release rate 
of antifoulant from the boundary layer of the coating is slightly greater 
than the threshold tolerance levels of the fouling organisms. One type of 
diffusion system utilized to control the rate of release and thereby 
provide a long service life involves the use two coating layers where the 
outer coating serves as a diffusion layer and the inner layer served as a 
reservoir for the surplus antifoulant. However, multi-coat systems are 
difficult to manufacture and properly apply to the ship hull, and the 
release rate is greatly affected by the thickness of the outer diffusion 
layer. 
SUMMARY OF THE INVENTION 
The antifouling coating of the present invention overcomes drawbacks with 
the prior art by utilizing a modular antifouling system in which the 
individual tile modules are provided with a plurality of reservoirs that 
contain antifoulant. The antifoulant migrates/diffuses from the reservoirs 
to the boundary layer of the tiles whereupon it precludes the attachment 
of fouling organisms thereto. Insitu replenishment of antifoulant in the 
reservoirs is accomplished by inserting a syringe device into a depleted 
reservoir or cell and injecting the antifoulant therein. Various types of 
identifying indicia and self-sealing plugs may be incorporated into the 
tiles to indicate the location and depleted condition of the antifouling 
cavities. The particular reservoirs or cavities in the tiles may be 
cellular, in which they are isolated from each other, or interconnected, 
in which passages extend between adjacent cavities. 
The antifouling tiles are preferably constructed of elastomeric materials 
selected from the group of butyl rubber, neoprene (polychloroprene), 
natural rubber, polybutylene, polyisoprene, polybutadiene, polysulfide 
rubbers, polyurethanes, vinyls, polyacrylonitriles and copolymer blends 
thereof. One means for adjusting the diffusion rate of antifoulant through 
the abovementioned elastomer materials comprises blending selected resins 
into the elastomeric matrix. Preferred resins include polyvinyl chloride, 
polystyrene, chlorinated natural rubber, polypropylene and polyethylene. 
Selected antifoulant materials designed to diffuse through the 
elastomer-resin matrix include chlorinated cyano-benzene compounds and 
organotin compounds. Another means for controlling the diffusion rate of 
antifoulant through the elastomeric matrix comprises mixing selected 
antifoulants, such as organotin oxides or 2, 4, 5, 
6-tetrachloroisophthalonitrile, with selected plasticizers, such as 
chlorinated aliphatic hydrocarbons. 
Accordingly, an object of the present invention is to provide a diffusion 
type antifouling coating which has a controlled rate of release and a 
means of holding excess antifoulant. 
Another object of this invention is the provision of a modular system of 
antifouling tiles which facilitates rapid, efficient replacement and 
repair of selected sections of the coating system. 
A further object of the present invention is to provide a modular, long 
lasting antifouling coating having antifouling reservoirs formed therein 
to permit insitu replenishment of antifoulant and thereby avoid costly 
drydocking procedures required for other types of antifouling coatings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings and to FIG. 1 in particular there is shown a 
plurality of modular antifouling tiles 15 secured to the hull surface 11 
of a vessel. The antifouling tiles 15 are provided with a plurality of 
cellular cavities 22 or reservoirs which contain antifoulant 23 that 
diffuses therefrom into the matrix of the modular tile 15. Upon depletion 
of antifoulant material 23 in the reservoirs 22, insitu replacement 
thereof may be accomplished by inserting a syringe device into the 
reservoirs 22 and filling them with selected antifoulants 23. This not 
only eliminates the necessity of drydocking the ship to replace depleted 
antifouling coatings, as with conventional antifouling coating systems, 
but also reduces the potential contamination of the environment with 
debris associated with the removal and disposal of worn out antifouling 
coatings. The location of the reservoirs 22 by a diver can be determined 
by providing the surface 19 of the tiles with various indicia, such as 
protrusions 20 and/or grooves. 
The tiles 15 are preferably formed of composite sections that are bonded 
together to facilitate construction of the modular tiles and to improve 
the durability and structural integrity of the tiles 15. In FIGS. 3A, 3B, 
for example, the tiles 15 include a body section formed of two elastomeric 
sections 16, 17 that are bonded together along the interface 18. The outer 
section 16 is molded to provide protrusions 20 on the exposed surface 19 
of the tiles 15 and corresponding depressions in the opposite interface 
surface 18. The inner section 17 is preferably formed by positioning a 
support plate 25, which is provided with a plurality of support pegs 26, 
into a mold and then molding the elastomer therearound to provide locking 
protrusions therein. The body section is then prepared by bonding the 
inner and outer sections together along the interface surface 18 so that 
antifoulant reservoirs 22 are formed of the corresponding recesses in the 
sections. A circumferential strip 29 of material is then applied to the 
periphery of the body section to provide additional reinforcement and 
preclude separation of the body sections along the interface surface 18. 
The support pegs 26 may be provided with enlarged distal end portions or 
other locking features to prevent separation of the inner section 17 from 
the support plate 25. The backing plates for the tile structures may be 
constructed of hard rubbers, plastic materials, and composite materials 
such as fiberglass. The inner and outer body sections 16, 17, as well as 
the circumferential strip 29, are constructed of selected rubbers and 
elastomeric materials. 
The tile structure of FIGS. 4A, 4B are similar in construction to the tile 
structures of FIGS. 3A, 3B except that the outer section 16 is provided 
with valve means in the form of passages containing one-way valve elements 
31 so that a syrings device can be inserted and withdrawn therefrom 
without loss of antifoulant therethrough. Also, a lattice type of 
reinforcing means 27 is utilized instead of the support pegs to provide 
additional support for the inner and outer elastomeric sections. 
The tile structure 15 of FIGS. 5A, 5B is provided with interconnecting 
passages 33 so that insitu replenishment of the reservoirs can be 
accomplished by selectively filling one of the reservoirs 22 with excess 
antifoulant 23 overflowing into the other reservoirs 22. For example, 
antifoulant can be injected into the lower reservoirs and "old" 
antifoulant can be simultaneously withdrawn from the upper reservoirs in 
FIGS. 5A, 5B. The backing plate 25 for the tile structure 15 is planar to 
enable the tile 15 to conform to curved surfaces of the ship hull. 
The tile structure 15 of FIGS. 6A, 6B is similar in construction to the 
tile structure of FIGS. 5A, 5B except that the interconnected reservoirs 
22 are elongated and no backing plate support is utilized. 
The inner and outer body sections 16, 17 of the antifouling tiles 15 are 
preferably constructed of selected elastomers such as butyl rubber, 
neoprene (chloroprene), natural rubber, polybutylenes, polyisoprene, 
polybutadiene, polysulfide rubbers, polyurethanes, vinyls, 
polyacrylonitriles, polyisobutylene, and copolymer blends thereof. Since 
the outer section 16 serves as the primary diffusion layer, it can be 
constructed of a different elastomeric material than the inner elastomeric 
section 17. Thus, the outer layer 16 can be constructed of the 
abovementioned elastomeric materials and the inner layer 17 can be molded 
of a hard rubber to improve the strength characteristics of the tile 15. 
One means for adjusting the diffusion rate of selected antifoulants 23 
through the elastomeric matrix is to blend selected resins with the 
elastomeric materials during the molding process. Preferred resin 
materials include polyvinyl chloride, polystyrene, chlorinated natural 
rubber, polypropylene, and polyethylene. Selected antifoulant materials 
designed to diffuse through the elastomer-resin matrix include chlorinated 
cyano-benzene compounds such as 2, 4, 5, 6-tetrachloroisophtalonitrile, 
and organotin compounds, such a tributyltin oxide tributyltin fluoride, 
tripropyltin oxide, and tripropyltin fluoride. The molding process should 
be carried out by using elastomeric materials having a low glass 
transition temperature (below an ambient temperature range of 65.degree. 
F. to 75.degree. F.) and a resin material having a high glass transition 
temperature (above 75.degree. F.). 
Another means for adjusting the diffusion rate of selected antifoulant 23 
through the elastomeric matrix is to combine the selected antifoulant with 
a plasticizer that is compatible with both the elastomer and the 
antifoulant. Selected antifoulants found compatible with the 
abovementioned groups of elastomeric materials include tributyltin oxide 
and 2,4,5, 6-tetrachloroisophtalonitrile. Compatible plasticizers include 
chlorinated aliphatic hydrocarbons such as chlorinated liquid paraffins 
(i.e. Chlorowax 40 manufactured by Diamond Shamrock Co.). The plasticizer, 
which like the antifoulant also passes into the water from the surface 19 
of the antifouling tile 15, is mixed with the antifoulant in weight 
proportions which preferably range from about 1:1 to about 20:1 parts of 
plasticizer to parts of antifoulant. 
Obviously many modifications and variations of the present invention are 
possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.