Method of waterproofing the surface of a polymer work piece

Details Method of waterproofing the surface of a polymer work piece Method of waterproofing the surface of a polymer work piece

2003-03-10

2004-11-02

Cameron, Erma (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C264S343000

Reexamination Certificate

active

06811822

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a method for waterproofing the surface of a polymer workpiece.
BACKGROUND OF THE INVENTION
Waterproofing makes it possible to prevent liquid or gaseous hydroxyl group (OH group)-containing substances, such as water, water vapor, or glycein, from diffusing into a polymer surface.
It is know that the diffusion of liquids, such as water or glycerin, into the polymer surface is enhanced by a specific interaction between the functional groups of the polymer surface, e.g. carbonyl groups, and the hydroxyl groups of the liquid. Consequently, various known coating processes for modifying polymer surfaces aim to neutralize the functional ester or carbonyl groups. For this purpose, the polymer surface is treated, for instance, by using an oxygen plasma so that functional groups, such as OH groups, are formed on the polymer surface. Usually, the polymer surface is then chemically coated by a grafting reaction to prevent a specific interaction of the OH groups of the liquid with the carbonyl groups of the polymer surface.
In one method of this grafting technique, the chemical substance provided for the coating is added directly as a gas to the plasma and is thereby deposited on the polymer surface. This gas phase coating process makes it possible, for instance, to form Teflon-like coatings on the polymer surface by adding C
4
F
8
, or SiO-type coatings by adding hexamethyl disiloxane. In another method of the grafting technique, the chemical substance provided for the coating is mixed into a solution for wet application and is then applied to the polymer surface by means of this solution. This method is used, for instance, to produce a silane coating on the polymer surface by treating the polymer surface with an octadecyl trimethoxy silane/toluene solution. Both of these methods, however, can be used only at locations on the polymer surface where the functional OH groups were created, for instance by the oxygen plasma treatment.
These coating methods presume corresponding ion or plasma sources and vacuum technology and thus involve substantial equipment complexity and costs. These methods are moreover time-consuming since the polymer surface to be simultaneously treated is limited to the diameter of the ion beam. A further drawback of these methods is that they are direction-dependent, i.e. good results are obtained only if the surface of the workpiece to be treated can be oriented nearly perpendicularly to the ion or plasma beam. As a result, polymer surfaces with cavities and curvatures as well as wall areas that are oriented parallel to the ion beam cannot be adequately treated.
SUMMARY OF THE INVENTION
Thus, the object of the invention is to provide a method for waterproofing the surface of a polymer workpiece, which is suitable also to treat polymer surfaces with cavities and curvatures in a simple and cost-effective manner.
The method for waterproofing the surface of a polymer workpiece is characterized by the following process steps:
a) the workpiece is treated with at least one organic solvent that swells the surface of the polymer workpiece and
b) at least one waterproofing substance, which is an organosilicon compound dissolved in the solvent, diffuses into the surface of the polymer workpiece, and
c) after a contact time, the solvent is removed from the polymer workpiece, and at least a portion of the waterproofing substance remains embedded in the surface of the polymer workpiece.
This method is used to waterproof the surface of a polymer work piece by using an organic solvent to swell the polymer surface and to serve as a carrier for at least one waterproofing substance contained in the solvent. This causes the waterproofing substance, which is an organosilicon compound, to diffuse into the surface of the polymer workpiece together with the solvent. After a contact time, the organic solvent is removed from the polymer workpiece, while at least a portion of the waterproofing substance remains embedded in the surface of the polymer work piece. This embedding advantageously takes place due to the interaction of the waterproofing substance with the polymer chains in the surface of the polymer work piece. To foster this embedding of the waterproofing substance into the surface of the polymer material, the organosilicon compound preferably has bulky organic groups, which through steric interaction with the polymer chains prevent the embedded waterproofing substance from diffusing out of the surface of the polymer material. As a result, as well as due to the hydrolysis stability of the organosilicon compound relative to water, a long-term effect of the inventive waterproofing of the surface of a polymer material is achieved. Furthermore, the treated polymer workpiece can be used in areas with elevated temperatures and/or regions with high outside temperatures.
The inventive embedding of a waterproofing substance, which is an organosilicon compound, into the surface of the polymer workpiece reliably prevents the specific interaction between the hydroxyl groups and the functional groups of the polymer matrix, e.g. carbonyl groups, and thus blocks access to the polymer matrix for liquid or gaseous hydroxyl group-containing substances, such as glycerin, water or water vapor.
The preferred treatment method of a polymer workpiece is to immerse the polymer workpiece into a bath with an organic solvent that contains the inventive waterproofing substance. After a brief contact time, during which the polymer surface swells due to the solvent and the waterproofing substance diffuses into the polymer surface, the polymer workpiece is removed from the bath. The polymer workpiece is then dried, which causes the solvent to evaporate out of the polymer matrix and at least a portion of the waterproofing material to remain embedded between the polymer chains in the polymer workpiece. Consequently, the inventive method for waterproofing the surface of a polymer workpiece can be used to treat any polymer surfaces with cavities and curvatures. This method is furthermore particularly simple and cost-effective and can be used at almost any place since only a bath and small amounts of the inventive waterproofing substance are required.
The publication by Katz et al., “Ultraviolet Protection of Transparent PVC Sheets by Diffusion Coatings,” Proceedings of the A.C.S. Div. of Org. Coatings and Plastics, 36 (1), pp. 202-205 (1976) describes a diffusion or impregnation process of a UV absorbing material into a PVC workpiece to increase UV resistance. In this process, an organic solvent is used as the carrier for the UV stabilizer. The PVC workpiece is swelled by means of the organic solvent and the UV stabilizer is thereby introduced into the polymer workpiece. After drying, the UV stabilizer remains in the polymer surface.
Variations of this method for introducing a UV stabilizer into the polymer surface are known and are described in European Patent Application EP 0 306 006 A2. The described methods disclose no hints regarding either a method for waterproofing the surface of a polymer workpiece or the inventive waterproofing substance, which is an organosilicon compound.
Preferably the waterproofing substance is an organosiloxane, an alkyl silyl fluoride, an aryl silyl fluoride, an alkyl aryl silyl fluoride, or an alkoxy silyl fluoride.
According to a first embodiment, the organosilicon compound is an organosiloxane. Organosiloxanes comprise both linear molecules of the formula R
3
Si—[OSiR
2
]
n
—O—SiR
3
with n≧0, as well as cyclic molecules of the formula [OSiR
2
]
m
with m≧3, where R represents same or different organic groups. Preferably R is an alkyl group R′ or an aryl group R″, as specified in further detail below. An example of a linear organosiloxane according to the first formula given above is 1,1,3,3-tetraisopropyl disiloxane-1,3-diyl. An example of a cyclic organosiloxane according to the second formula given above is octamethyl cyclotetrasiloxane.
According to embodiments 2 to 5, the organosilicon compound i

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