Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-03-12
2002-07-30
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S391000, C427S393400, C428S447000, C428S452000
Reexamination Certificate
active
06426120
ABSTRACT:
The present invention relates to a process for the treatment of cellulose substrates which makes it possible to reduce the penetration of adhesive-resistant agents into the substrates and/or to decrease their sensitivity to water, by bringing these cellulose substrates into contact with aqueous emulsions based on grafted functionalized polyorganosiloxane, and to the use of said aqueous emulsions as adhesive-resistant and/or water-repellent coating on cellulose substrates in the manufacture of pressure-sensitive adhesives.
Self-adhering products or pressure-sensitive adhesives generally comprise a frontal material composed of a paper or of a polymer film, such as of PVC, PBE, PP or PET, this part of the product generally being printed and acting as label, which will subsequently be adhesively bonded to the article to be identified. The adhesive bonding of the label is carried out on the article by simply pressing a layer of pressure-sensitive adhesive applied to the back of the label. Protection of the adhesive or sticky layer of the self-adhesive label, at the time when the latter is applied to the product concerned, is provided by a protective paper or polymer film to which has been applied a fine silicone layer, usually in the form of a deposit of 1 to 2 g/m
2
. The silicone layer which is brought into contact with the adhesive layer makes it possible to easily remove the protective paper or film at the time of use of the self-adhering label. The force which will have to be exerted to separate the two constituents is known as the release force. This force must be controlled for the majority of label applications, in which the labels are applied automatically, and must remain stable over time.
A large proportion of self-adhesive complexes are available in the form of rolls and use, as protective film or paper, a paper of the glassine type with a density of 60-65 g/m
2
. It is a paper manufactured from a highly beaten bisulfite pulp. The exhaustive beating makes possible significant entangling of the fibers and contributes to “closing up” the paper. To further reduce the penetration of the silicone which will subsequently be deposited on the surface of the glassine paper, a solution of carboxymethylcellulose/polyvinyl alcohol (CMC/PVA) is applied to both faces of the paper with the size press of the papermaking machine. The paper is subsequently calendered off the machine. This final operation puts the finishing touches to the “closing up” of the paper and confers a degree of transparency on the latter. This transparency is necessary when photoelectric cells are used to provide for automatic control of the positioning or of the progression of the paper web on various machines, such as printing machines or applicator machines.
Other protective papers are used in the field of self-adhesive products and in particular papers coated with kaolin. The inorganic coating makes possible good surface maintenance of the silicone deposited (which is not the case for a paper of the glassine type) but does not exhibit the advantage of the transparency of glassine. The protective paper of the type coated with kaolin will thus, in the majority of cases, be used in the form of sheets in applications of a more manual nature.
However, standard glassine paper coated with carboxymethylcellulose/polyvinyl alcohol exhibits certain disadvantages, including:
a large amount of silicone has to be deposited on its surface to provide the desired release force with respect to a given adhesive layer. This is because a preliminary study of the profile of penetration of a silicone through a paper carried out by analyzing the section of the paper using a scanning electron microscope coupled to an X-ray dispersive energy analyzer made it possible to establish that approximately 60% of the silicone applied to a glassine paper is found in the body of the paper (depth of penetration of up to 11 microns) and thus only the remaining 40% are of use in providing the desired release value.
the standard CMC/PVA coating leads, under certain conditions (hydrometric or abrasive conditions), to fluffing on the machine.
very poor dimensional stability. In fact, because of its highly beaten and strongly calendered nature, glassine paper varies dimensionally in a very significant fashion with hygrometric variations in the surroundings in which it is moved and thus develops very significant curl when it is complexed in the form of a self-adhesive product with a frontal product generally exhibiting better dimensional stability toward moisture. The protective frontal components in fact form a kind of “double strip” which reacts differentially toward variations in humidity. In fact, the curl often prevents the adhesive product from being satisfactorily used, for example when it is passed through photocopiers, laser printers or ink jet printers. Furthermore, if a standard glassine directly receives water on its surface, it instantaneously develops a curl such that the sheet of paper will roll up on itself.
In view of the abovementioned disadvantages, it is consequently difficult to conceive of using this type of cellulose substrate for silicone treatment in an aqueous base if the silicone coating machines are not entirely suitable for this type of silicone treatment, such as insufficient web tension, thermal ovens with a flat outline and with hot air being blown into the ovens, which are not of the flotation type.
It should also be noted that Abstract XP-002136528 (corresponding to Patent Application JP 06 248244A) is completely different from the subject matter of the present invention in that it relates to the preparation of a release paper of the Kraft type pretreated with silicone which does not exhibit specific optical properties and thus does not relate to the treatment of a cellulose substrate of the glassine type which has not been pretreated with silicone. Furthermore, the viscosity modifier added to the emulsion, which emulsion is used for this purpose, acts solely as thickener.
One of the aims of the present invention consequently consists in overcoming the abovementioned disadvantages and in providing a process for the treatment of a cellulose substrate and in particular of a paper of the glassine type which makes it possible to reduce the penetration of adhesive-resistant agent or agents into the substrate and/or to decrease its sensitivity to water by bringing the cellulose substrate into contact with an aqueous emulsion based on a grafted functionalized polyorganosiloxane.
To this end, according to the present invention, the aqueous emulsion based on a grafted functionalized polyorganosiloxane furthermore comprises a polymeric material of the acrylic type.
The polymeric material of the acrylic type advantageously originates from an acrylic monomer chosen from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, methyl acrylate and methacrylate, ethyl acrylate and methacrylate, propyl acrylate and methacrylate, butyl acrylate and methacrylate, hexyl acrylate and methacrylate, cyclohexyl acrylate and methacrylate, benzyl acrylate and methacrylate, isopropyl acrylate and methacrylate, octyl acrylate and methacrylate, methyl &agr;-chloroacrylate, ethyl &agr;-ethoxyacrylate, 2-ethylhexyl acrylate and methacrylate, phenyl acrylate and methacrylate, &agr;-chloroacrylonitrile, N,N-dimethylacrylamide, N,N-dibenzylacrylamide, hydroxyethyl acrylates and methacrylates, and mixtures of at least two of these acrylic monomers.
According to an advantageous embodiment of the invention, the polymeric material of the acrylic type comprises a styrene fraction and is an acrylic/styrene copolymer.
According to an advantageous embodiment of the invention, the acrylic/styrene copolymer is chosen from the group consisting of copolymers of acrylic or methacrylic acid and of styrene, copolymers of butyl acrylate or methacrylate and of styrene and copolymers of methyl acrylate or methacrylate, of acrylonitrile or methacrylonitrile, of styrene and of 2-ethylhexyl acrylate or methacrylate.
The invention also relates
Stocq Robert
Waegemans Laure
Cameron Erma
Morgan Adhesives Company
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