Cleaning and liquid contact with solids – Processes – Paints – varnishes – lacquers – or enamels – removal
Reexamination Certificate
1998-09-12
2001-03-06
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Paints, varnishes, lacquers, or enamels, removal
C134S003000
Reexamination Certificate
active
06197124
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for removing a multiple coating film, or an adhering substance and a layer of a cured adhesive agent, and a process for forming a multiple coating film.
Presently, recycling of resources is an important problem. In order to recycle resources efficiently, and to reuse the substrate (or base material) of a coated material, removal of the coating from the substrate is necessary. Also, in order to reuse a substrate to which a layer such as cloth or paper is adhered with an adhesive, removal of the adhering layer and the cured adhesive itself is necessary.
Several well-known processes have previously been used for removing a coating layer from a substrate. These include mechanical removal by impact, combustion, dissolving with organic solvent and scraping away a coating film swelled with a solvent. None of these has been entirely satisfactory. Mechanical removal by impact and combustion are often difficult to use with plastic substrates. Processes involving dissolution by an organic solvent and scraping away a coating film swelled with a solvent are limited in their applicability because of dissolution of the substrate with the solvent. It is especially difficult to remove a coating film containing a resin which has a high molecular weight and has a low crosslinking degree as a binder, since the coating film is apt to cling to the substrate. In the case of a coating film having a high degree of crosslinking, it is not always easy to remove the coating from the substrate.
A dried layer of an adhesive agent obtained from an emulsion of non-crosslinkable adhesive agent typically has poor water resistance. As a result, such adhesive agents exhibit poor adhesion when wetted with water. In addition, a cured layer of an adhesive agent obtained from a crosslinkable adhesive agent has good performance in both water resistance and adhesion, but otherwise it is difficult to remove an adhering substance such as cloth and paper and the cured layer of adhesive agent itself.
SUMMARY OF THE INVENTION
The present invention provides a process for easily removing multiple layers from a substrate, including the cured adhesive used to adhere the layers to the substrate. The present invention permits the removal of the coating layers easily, regardless of the specific coating method originally used, and is applicable to coated substrates which include a cured adhesive which would normally be difficult to remove, including those adhesive agents having good water resistance and good adhesive properties. The process permits removing the layer of the cured adhesive agent and the coating layer or layers simultaneously.
The present invention also permits recycling of the substrates with retention of their original coating properties.
Still other features and advantages of the present invention will be apparent from the following description.
Specifically, the present invention provides a process for removing multiple layers from a substrate, wherein the multiple layers comprise at least one cured binder layer adjacent the substrate, the binder comprising at least about 25% by weight of a cured binder resin having a chemical structure shown by the following chemical formula (1)
the coating further comprising at least one upper layer bonded to the binder layer, the process comprising contacting the multiple layers with a mixture comprising at least one acidic compound and at least about 0.001% water.
The present invention further provides a process for forming a multiple coating layer comprising:
(1) forming a lower coating layer on a substrate and
(2) forming an upper coating layer on the lower coating layer, the lower coating layer containing a cured binder resin having a chemical structure shown by the above-mentioned chemical formula (1).
DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on the discovery that cured binder resin having a chemical structure as shown by formula (1) above is decomposed and changed to low molecular components and removed rapidly when contacted with a mixture comprising an acidic compound and water. Based on this discovery, an original upper coating layer formed on a lower coating layer containing the cured binder resin, and an adhering substance being allowed to adhere to a substrate by the layer of the cured adhesive agent can be removed, because the layer for attaching the original upper coating layer or the adhering substance is decomposed and disappears.
The process of the present invention for removing cured binder resin is applicable to substrates having at least one cured binder layer adjacent the substrate, the bind layer comprising at least about 25% by weight of a cured binder resin of chemical formula (1) as indicated above. Accordingly, the binder layer can consist essentially of binder resin or comprise a blend of binder resin with up to 75% by weight of other polymers, depending on the performance characteristics desired in the final multiple-layered construction. Thus, the binder layer can bind another coating to the substrate or an upper layer which is preformed, such as cloth, paper, leather and performed plastic films.
Regardless of the particular construction of the structure treated according to the present invention, the multiple layers are removed by contacting the structure with a mixture of at least one acidic compound and at least about 0.01% water (hereinafter “Mixture C”). This mixture dissolves the cured binder resin of Chemical formula (1), resulting in removal of the upper coatings or layers from the substrate as well as the cured binder.
The specific cured binder resin adjacent to the substrate can vary widely, so long as the cured binder resin has the chemical structure shown by the afore-mentioned chemical formula (1).
Specific examples of the cured binder resin having a chemical structure shown by the afore-mentioned chemical formula (1) include a cured binder resin obtained by a curing reaction of a carbonyl group-containing compound with a compound having two or more groups in all, selected from the hydrazido group shown by the following formula (2), the hydrazido group bonding to a carbon atom directly
and the semicarbazido group shown by the following formula (3), and so on.
A wide variety of compositions are reported in the literature which can form the cured binder resin having the chemical structure shown by the aforementioned chemical formula (1) including, for example, The Chemistry of Amides PART TWO (INTERSCIENCE PUBLISHERS),1970, Chapter 10, 515-600; Japanese Patent Application Kohkai No. 08/206585 (1996); and Japanese Patent Application Kohkai No. 09/057183 (1997).
In the process of the present invention, specific examples of the above-mentioned carbonyl group-containing compound which can be used include carbonyl group-containing resins such as carbonyl group-containing acrylic resins, carbonyl group-containing epoxy resins, carbonyl group-containing alkyd resins, carbonyl group-containing polyester resins, carbonyl group-containing urethane resins and the like; carbonyl group-containing compound having a low molecular weight such as glyoxal, diacetyl, butanedione, 2,4-pentanedione, 2,4-hexanedione, heptanedione, octanedione, diacetylbenzene and the like. Among these, carbonyl group-containing acrylic resins are preferred.
The carbonyl group-containing acrylic resins which can be used include copolymers of a vinyl monomer containing a carbonyl group and the other vinyl monomer.
Representative examples of the vinyl monomer containing a carbonyl group mentioned above include acrolein, diacetone acrylamide, diacetone methacrylamide, formyl styrol, vinyl alkyl ketones which have 4 to 7 carbon atoms (such as vinyl methyl ketone, vinyl ethyl ketone and vinyl butyl ketone), acetoacetoxyethyl acrylate, acetoacetoxyethyl methacrylate, an addition compound of a polymerizable unsaturated monomer having isocyanato group (such as m-isopropenyl-&agr;,&agr;(-dimethylbenzyl isocyanate, isocyanatoethyl methacrylate and methacryloylacyl isocyanate and the l
Gulakowski Randy
Huntley & Associates
Kansai Paint Co. Ltd.
Wilkins Yolanda E.
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