Adhesion Promoter

1. Field of the Invention

The present invention relates to an adhesion promoter for organopolysiloxane compositions which are cured by radiation, such as by an electron beam and ultraviolet radiation.

2. Prior Art

While heating is primarily used in the prior art to cure organopolysiloxane compositions, this approach does require high temperatures and long curing times. Accordingly, the last several years have been witness to research into compositions and methods by which curing can be conducted at lower temperatures and in shorter times. This research has resulted in the appearance of organopolysiloxane compositions which are cured by exposure to radiation such as an electron beam, ultraviolet radiation, etc. Such compositions are exemplified by compositions which are obtained by mixing a photosensitizer into the mixture of a mercapto group-containing organopolysiloxane and a vinyl group-containing organopolysiloxane as described in Canadian Patent No. 1,019,693 issued to Gant Oct. 25. 1977. and by compositions composed of photosensitizer plus organopolysiloxane having acryloxy or methacryloxy groups as described in Japanese Patent Publication Number 53-2911[2.911/78].

3. Problem to Be Solved by the Invention

However, these organopolysiloxane compositions do not adhere well to the surfaces of various substrates, such as plastics, rubbers, metals etc., after curing, and as a consequence are easily removed by rubbing with the finger, etc.

The present inventors carried out vigorous research with a view to the elimination of the above problem and this invention was developed as a consequence.

The object of the present invention is to provide an adhesion promoter which, when blended into radiation-curable organopolysiloxane or a composition thereof, will generate a substantial increase in adhesion for various substrates.

4. Means Solving the Problem and Functions Thereof

The present invention comprises an adhesion promoter for radiation-curable organopolysiloxane, or a composition thereof, wherein said adhesion promoter consists of silane or polysiloxane having in each molecule at least one organic group possessing aliphatic unsaturation and at least one organic group possessing the amino group, or of silane or polysiloxane having in each molecule at least one organic group possessing both aliphatic unsaturation and the amino group.

The adhesion promoter of the present invention is a silane or polysiloxane which have organic groups possessing aliphatic unsaturation exemplified by lower alkenyl groups such as vinyl, allyl, propenyl etc.. and gamma-acryloxypropyl, gamma-methacryloxypropyl, gamma-acrylamidopropyl and gammamethacrylamidopropyl and organic groups posessing the amino containing organic groups exemplified by aminoalkyl groups such as aminomethyl, aminoethyl, aminopropyl, etc. Organic groups possessing both aliphatic unsaturation and the amino group are exemplified by the N-beta-(aminoethyl)-gamma-aminopropyl group which has been acrylamidated or methacrylamidated at an amino group.

The adhesion promoters of the present invention are exemplified by organofunctional silanes such as vinylbenzylamino- propyltrimethoxysilane, vinylbenzylaminopropyltriethoxysilane, N-beta-(N-vinylbenzylaminoethyl)-gamma-aminopropyltrimethoxy-silane, N-beta-(N-vinylbenzyl-aminoethyl)-gamma-aminopropyltri-ethoxysilane, etc.; organopolysiloxanes which are cohydrolysis condensates involving vinyl-containing alkoxysilanes such as, vinylmethylsiloxane-aminopropylmethylsiloxane-dimethylsiloxane copolymers composed of vinylmethylsiloxane units, aminopropylmethylsiloxane units, and dimethylsiloxane units; acryloxypropylmethylsiloxane-aminopropylmethylsiloxanedimethylsiloxane copolymers; and organopolysiloxanes obtained by the acrylamidation of part of the amino groups of an aminoalkyl group-containing organopolysiloxane. Preferred among these are organopolysiloxanes obtained by the cohydrolysis condensation of vinyl-containing alkoxysilane and aminoalkyl-containing alkoxysilane, vinylmethylsiloxane-aminopropylmethylsiloxanedimethylsiloxane copolymers, and acryloxypropylmethylsiloxane-aminopropylmethylsiloxane-dimethylsiloxane co polymers. The cohydrolysis condensates of vinyl-containing alkoxysilane and aminoalkyl-containing alkoxysilane are particularly preferred.

As examples of the synthesis of such organopolysiloxanes, one can cite the reaction of vinylbenzyl chloride with gamma-(2-aminoethyl)aminopropyltrimethoxysilane; the reaction of benzyl chloride with aminopropyltrialkoxysilane; the cohydrolysis in the presence of traces of water of vinyl-containing alkoxysilane, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(beta-methoxyethoxy)silane, etc., with aminoalkyl-containing alkoxysilane such as aminomethyltrimethoxysilane, beta-aminoethyltrimethoxysilane gamma-aminopropyltrimethoxysilane N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane, etc.; the partial amidation of the amino groups of an aminoalkyl-containing polysiloxane using acrylic chloride or methacrylic chloride in a molar deficiency based on the amino groups in said polysiloxane and copolymerization of a vinyl group-containing siloxane with an aminoalkyl group-containing siloxane.

The adhesion promoter of the invention is used by adding and blending it into a silicone composition which can be cured by exposure to radiation such as an electron beam, ultraviolet radiation, etc. In such a case, the adhesion promoter can be used as the single species, or as the mixture of two or more species.

Radiation-curable organopolysiloxanes and their compositions into which the adhesion promoter of the present invention may be blended are exemplified by compositions having as their essential component at least one type of mercaptoalkyl group-containing organopolysiloxane, organopolysiloxane having alkenyl groups such as vinyl, allyl propenyl, etc.. acryloxy group-containing or methacryloxy group-containing organopolysiloxane, styryl group-containing organopolysiloxane, or acrylamide-containing or methacrylamide-containing organopolysiloxane, and containing as necessary various additives such as, for example reinforcing fillers extender fillers, dyes and pigments, heat stabilizers, flame retardants, etc.

The quantity of addition of this invention's adhesion promoter to the radiation-curable organopolysiloxane or composition thereof will depend on the type of organopolysiloxane, and on whether optional additives are present, and if so, on their type and compounding proportions. As a consequence, this value cannot be given unconditionally, but roughly will be 0.1 to 30 weight parts.

Radiation-curable organopolysiloxane compositions which contain the invention's adhesion promoter have an excellent radiation curability, and adhere well to diverse substrates in contact with such compositions during their curing.

The invention will be explained in the following with reference to illustrative examples. In the examples, parts=parts by weight and curability and adhesion testing was conducted as follows.

The radiation-curable organopolysiloxane composition containing adhesion promoter was coated on the surface of the substrate and then cured by exposure to radiation. The surface of the obtained cured coating was then rubbed with a finger ten times. Curing of the coating was taken to be unsatisfactory when a cloudiness was induced, a condition denoted as "smearing." Furthermore, in the event of exfoliation, adhesion by the coating to the substrate was also taken to be unsatisfactory, a condition denoted as "rub off."

An electron beam-curable organopolysiloxane composition was prepared in the form of the mixture of 50 parts of a trimethylsiloxy-terminated dimethylsiloxane-gamma-mercaptopropylmethylsiloxane copolymer having ten gamma-mercaptopropylmethylsiloxane units in each molecule and having a degree of polymerization of 200. and 50 parts of a dimethylvinylsiloxy-terminated dimethylsiloxane--methylvinylsiloxane copolymer having 3 methylvinylsiloxane units and a degree of polymerization of 300. One part N-beta-(N-vinylbenzylaminoethyl)-gamma-aminopropyltrimethoxysilane (SH6032 from Toray Silicone Co., Ltd.) was added and mixed to homogeneity into 100 parts of this electron beam-curable organopolysiloxane composition. The obtained mixture was applied uniformly in a thickness of 1.0 g per square meter on a polyethylene-laminated paper, and was then cured by exposure to a 5 Mrad electron beam. The results of the curability and adhesion testing of this cured coating are reported in Table 1.

For comparison, the same curability and adhesion testing was conducted on the composition prepared without the addition of the adhesion promoter, and these results are also reported in Table 1 as Comparison Example 1.

148 Parts vinyltrimethoxysilane (SZ6300 from Toray Silicone Co.. Ltd.) and 228 parts N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane (SH6020 from Toray Silicone Co., Ltd.) were placed in a three-neck flask equipped with stirrer and reflux condenser. This was stirred at 50.degree. C. for 10 minutes while 6 g ion-exchanged water was added dropwise in order to prepare an adhesion promoter in the form of the cohydrolyzate of vinyltrimethoxysilane and N-beta-(aminoethyl)-gamma-aminopropyl-trimethoxysilane. One part of this adhesion promoter was added and mixed to homogeneity into 100 parts of an electron beam-curable organopolysiloxane composition prepared as in Example 1. The obtained mixture was uniformly applied in a thickness of 1.0 g per square meter on polyethylene-laminated paper, and was then cured by exposure to a 5 Mrad electron beam. The cured coating was tested for curability and adhesion, and these results are reported in Table 2.

For comparison, compositions were prepared in which one contained only vinyltrimethoxysilane in place of the above adhesion promoter (Comparison Example 2). and in which one contained only N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane in place of the above adhesion promoter (Comparison Example 3). These compositions were tested for curability and adhesion, and these results are reported in Table 2 as Comparison Example 2 and Comparison Example 3, respectively.

2 Parts benzophenone was added and blended into 100 parts of the electron beam-curable organopolysiloxane composition whose preparation is described in Example 1 to afford an ultraviolet-curable organopolysiloxane composition. To 100 parts of this composition was added 10 parts of a trimethylsiloxy- terminated organopolysiloxane (degree of polymerization=70) composed of gamma-acryloxypropylmethylsiloxane units: gamma-aminopropylmethylsiloxane units: dimethylsiloxane units in a 3:3:64 molar ratio, followed by mixing to homogeneity. This was applied in a thickness of 1.0 g per square meter on glassine paper, and was then exposed to ultraviolet energy from a 160 kW/cm mercury lamp for 1 second at a distance of 10 cm. The curability and adhesion of the cured coating were then evaluated, and these results are reported in Table 3.

For comparison, the curability and adhesion of the above ultraviolet-curable organopolysiloxane composition, without the addition of the adhesion promoter, were evaluated as above, and these results are reported in Table 3 as Comparison Example 4.

To prepare the adhesion promoter, a mixture of aminoethylaminopropyldimethoxysilane hydrolyzate, polydimethylsiloxane cyclics, polymethylvinylsiloxane cyclics, and hexamethyldisiloxane was equilibrated to afford a trimethylsiloxy-terminated organopolysiloxane (degree of polymerization =202) composed of gamma-aminopropylmethylsiloxane units: vinylmethylsiloxane units: dimethylsiloxane units in a 5:5:190 molar ratio. An electron beam-curable organopolysiloxane composition was prepared by mixing 50 parts of this organopolysiloxane to homogeneity with 50 parts of a trimethylsiloxy-terminated organopolysiloxane composed of mercaptopropylmethylsiloxane units : dimethylsiloxane units in a 15:185 molar ratio. The resulting composition was uniformly applied at 1.0 g per square meter on polyethylene-laminated paper, and was then cured by exposing this coated surface to a 1 Mrad electron beam. Curability and adhesion tests were then conducted on this cured coating, and the these results are reported in Table 5.

For comparison, a composition was prepared which contained, in place of the above adhesion promoter, a trimethylsiloxy-terminated organopolysiloxane composed of vinylmethylsiloxane units : dimethylsiloxane units in a 5:190 molar ratio. It was subjected to curability and adhesion testing, and these results are also reported in Table 4 as Comparison Example 5.

To prepare an organopolysiloxane having both the acrylic group and amino group in the same molecule, acrylic chloride (at 0.8 moles per 1 mole amino hydrogen in the following polysiloxane) was added to and reacted with a trimethylsiloxy- terminated organopolysiloxane (degree of polymerization=77) composed of 5 moles N-beta-(aminoethyl)-gamma-aminopropylmethylsiloxane units and 70 moles dimethylsiloxane units.

An ultraviolet-curable organopolysiloxane composition was prepared by mixing 5 parts dimethyl benzil ketal into the electron beam-curable organopolysiloxane composition used in Example 1. Ten parts of the organopolysiloxane prepared as described above was added to 100 parts of this UV-curing organopolysiloxane composition. This mixture was uniformly applied at 0.3 g per square meter on polyethylene film, followed by exposure to ultraviolet radiation from a 160 W/cm high-pressure mercury lamp for 0.05 seconds. The curability and adhesion were then evaluated, and these results are reported in Table 5.

For comparison, organopolysiloxane in which all amino groups were amidated was synthesized as above with the exception that the acrylic chloride was added at twice the above quantity. Using this organopolysiloxane in place of the above adhesion promoter, the curability and adhesion of the cured coating were examined as above, and these results are reported in Table 5 as Comparison Example 6.

Because the adhesion promoter of the present invention is a silane or polysiloxane having in each molecule at least one organic group possessing aliphatic unsaturation and at least one organic group possessing the amino group, or a silane or polysiloxane having in each molecule at least one organic group containing both aliphatic unsaturation and the amino group, when it is blended into a radiation (electron beam, ultraviolet radiation, etc.)-curable organopolysiloxane or composition thereof, it characteristically provides a substantial improvement in the adhesion of such organopolysiloxanes or their compositions to various substrates.