JP3394164B2 - Peelable UV-curable silicone composition - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone composition having excellent ultraviolet curability and having a cured film after irradiation with ultraviolet light, which has excellent release properties from an adhesive substance. . 2. Description of the Related Art Conventionally, a silicone composition has been cured on the surface of a substrate in order to prevent adhesion and sticking of an adhesive substance to a solid substrate such as paper, processed paper, metal foil, and plastic film. 2. Description of the Related Art Forming a film to impart releasability has been performed. In this case, as a method for forming a cured film of the silicone composition on the surface of the solid base material, [1] an organopolysiloxane containing an aliphatic unsaturated group in the silicone composition and an organohydrosiloxane are used as a catalyst with a platinum compound as a catalyst. A method of forming a releasable cured film by an addition reaction with genpolysiloxane, [2] using an organometallic catalyst such as an organotin compound to cause a condensation reaction of the organopolysiloxane in the silicone composition to release the mold. A method of forming a hardened cured film is known. However, any of the silicone compositions used in these methods forms a cured film by heating, and therefore cannot be used for a heat-sensitive substrate, and requires a large amount of energy for curing. In order to improve these disadvantages, as a composition curable by ultraviolet irradiation, a composition comprising a vinyl group-containing organopolysiloxane and a mercapto group-containing organopolysiloxane to which a photoinitiator has been added is disclosed in JP-A-52-40334. No. 1993. However, in order to cure this composition, it is necessary to perform ultraviolet irradiation for a long time, and the ultraviolet curability is not always satisfactory. Therefore, in order to improve the ultraviolet curability, a method of increasing the vinyl group content in the vinyl group-containing organopolysiloxane or increasing the amount of the mercapto group-containing organopolysiloxane has been adopted. However, although these methods improve the ultraviolet curability, they have a disadvantage that the peeling force of an adhesive tape or the like increases. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an excellent peeling property, which is excellent in ultraviolet curability and has a small peeling force of an adhesive tape or the like and a large residual adhesion rate. An object of the present invention is to provide a peelable ultraviolet-curable silicone composition that gives a cured film having characteristics. The present inventors have conducted intensive studies to achieve the above object, and as a result, have at least one alkenyl group at each molecular terminal, and have a branched molecular structure. Group-containing organopolysiloxane having at least two mercaptoalkyl groups bonded to a silicon atom in one molecule, and a photoinitiator. The present invention was found to cure satisfactorily by short-time irradiation of ultraviolet rays, to improve the curability, and to find that the cured film had excellent peeling properties, thereby forming the present invention. According to the present invention, there is provided (1) a siloxane unit represented by the following formulas (I) to (III), wherein an average of 1 to 3 siloxane units represented by the formula (III) is contained in one molecule; Viscosity at 25 ° C is 100-1
100,000 parts by weight of an alkenyl group-containing organopolysiloxane of 00,000 cP [Where R ¹ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group, ¹ to 10 mol% of R ¹ is a phenyl group, and R ² is a group represented by the formula (IV) -C _n H _2n —CH = CH ₂ (IV) (where n is an integer of 0 to 8), and R ³ is R ¹ or R ² . (2) 1 to 30 parts by weight of an organopolysiloxane containing at least two mercaptoalkyl groups bonded to a silicon atom in one molecule, and (3) a photoinitiator compatible with the organopolysiloxane. To provide a peelable ultraviolet-curable silicone composition. Hereinafter, the present invention will be described in more detail. The organopolysiloxane of the component (1), which is the most important component constituting the peelable ultraviolet-curable silicone composition of the present invention, comprises siloxane units represented by the above formulas (I) to (III). R ¹ in the formula is a hydrogen atom, an alkyl group or a phenyl group having 1 to 4 carbon atoms, 1 in R ¹ to obtain the characteristics such as excellent UV-curable
1010 mol% is phenyl groups. 1 mol% of phenyl groups
If it is less than 10%, the ultraviolet curability will be reduced. In addition, 3 in R ¹
It is preferred that about 5 mol% is a phenyl group, and the others are methyl groups from the viewpoint of peeling properties. R ² is an alkenyl group represented by the above formula (IV), which reacts with a mercaptoalkyl group to effect crosslinking (curing). From the viewpoint of curability, n in the formula is an integer of 0 to 8, preferably 0 (vinyl group), and at least one R ² must be present at each molecular terminal. R ³ is R ¹ or R ² , and at least about 0.5 to 1 mol% of R ³ is preferably R ² from the viewpoint of curability. Further, the amount of R ² is preferably 10 mol% or less in R ³ . If it exceeds 10 mol%, the peeling properties tend to decrease due to heavy peeling. The siloxane unit represented by the formula (III), which defines the molecular structure of the organopolysiloxane of the component (1), must be present on average in one to three siloxane units per molecule.
If the average value is less than 1, excellent ultraviolet curability cannot be obtained, and if it is more than 3, the viscosity becomes high and the synthesis is difficult. Further, the organopolysiloxane of the component (1) is preferably in the form of an oil having a viscosity at 25 ° C. of 100 to 100,000 cP, preferably 200 to 10,000 cP, in view of the performance of the formed cured film. The organopolysiloxane of the component (2) is
A compound having at least two mercaptoalkyl groups bonded to a silicon atom in one molecule and having the following average composition formula (V) R ⁴ _e SiO _{(4-e) / 2} (V) Can be. Here, R ⁴ is an organic group having 1 to 8 carbon atoms, preferably 1 to 3 carbon atoms, and at least two of R ^{4 in} one molecule are mercaptoalkyl groups. Further, the amount of the mercaptoalkyl group is preferably from 10 to 50 mol% based on all the organic groups, from the viewpoint of crosslinking efficiency. Examples of the mercaptoalkyl group include a mercaptomethyl group, a mercaptoethyl group, a mercaptopropyl group, and a mercaptohexyl group. Of these, a mercaptopropyl group is preferred in view of availability of raw materials and ease of synthesis. . Examples of the organic group other than the mercaptoalkyl group include an alkyl group such as a methyl group, an ethyl group and a propyl group, an aryl group such as a phenyl group and a tolyl group, or a part of a hydrogen atom bonded to a carbon atom of these groups. Or a group in which all are substituted with a halogen atom, a cyano group, or the like. The organic group other than the mercaptoalkyl group bonded to the silicon atom is preferably a methyl group at 50 mol% or more based on all the organic groups from the viewpoint of releasability and compatibility with the component (1). In the formula (V), e is a positive number of 1 to 3, and the structure of the component (2) may be linear, branched or cyclic.
It may have an alkoxyl group such as an ethoxy group and a propoxy group. The viscosity of the organopolysiloxane (2) is not particularly limited.
The one of 0cP can be used. The amount of the component (2) is 1 to 30 parts by weight, preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of the component (1). When the amount is less than 1 part by weight, the ultraviolet curability is reduced, and when the amount is more than 30 parts by weight, the property of peeling the adhesive substance is sometimes reduced. Further, the molar ratio of the mercaptoalkyl group to the alkenyl group is 1 to the alkenyl group in the component (1).
It is preferable to make the above. The photoinitiator of the component (3) is not particularly limited as long as it is compatible with the organopolysiloxane and promotes the reaction between the alkenyl group and the mercaptoalkyl group. Methyl-1-phenylpropan-1-one, acetophenone, 3-methylacetophenone, 3-methoxyacetophenone, propiophenone, benzophenone, 3-methoxybenzophenone, 4,4'-dimethoxybenzophenone, anthraquinone, triphenylamine, carbazole, etc. Is exemplified. The compounding amount of the photoinitiator may be an amount necessary for ultraviolet curing, and is usually 0.1 to 20% by weight, preferably 1 to 10% by weight based on the total amount of the components (1) and (2). . [0013] Other optional components can be added to the composition comprising the above components (1) to (3), for example, a stabilizer, a heat resistance improver, a filler, a coloring dye, a pigment,
Leveling agents, solvents and the like can be added. When a release paper is produced using the silicone composition of the present invention, a composition obtained by mixing a predetermined amount of the above-described components is coated on a base material such as paper, a plastic film, or the like, using a roll coater, a gravure coater, a gravure offset, or a screen. Using a printing machine or the like, the substrate is partially applied to the entire surface of the substrate or to a portion requiring releasability so as to have a film thickness of 0.1 to 10 μm, and then cured by irradiating ultraviolet rays. In addition, as the ultraviolet light source, a xenon lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp and the like are exemplified. The silicone composition of the present invention has a good curability since the component (1) has a siloxane unit represented by the formula (III), so that the amount of ultraviolet irradiation may be small and 10 to 100 mJ / c.
It can be cured at m ^2. EXAMPLES The present invention will now be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples, all parts are parts by weight, and the viscosity is a value at 25 ° C. Further, the ultraviolet curability, the peeling force, and the residual adhesiveness of the silicone composition were measured by the following methods. (Ultraviolet curable) An 80 W high-pressure mercury lamp, H
Using I-20N (trade name, manufactured by Nippon Battery Co., Ltd.), irradiate from a distance of 8 cm, rub the film 10 times with a finger, and then apply the minimum UV irradiation energy (smearing, rub-off (dropping)) that does not occur. mJ / cm ² ) was determined, and the result was regarded as ultraviolet curable. (Release Force) After irradiating the silicone composition with ultraviolet rays on the surface of the solid substrate to form a cured film, an acrylic emulsion-type pressure-sensitive adhesive, Olivine BPW-3110H (manufactured by Toyo Ink Manufacturing Co., Ltd.) is applied to the cured film surface. , And a heat treatment at 100 ° C. for 3 minutes. Next, a high-quality paper having a basis weight of 64 g / m ² was stuck to the coated surface and aged at 25 ° C. for 20 hours. Then, the sample was cut into a width of 5 cm, and a peeling speed of 0.3 m was obtained at an angle of 180 ° by a tensile tester. The bonded paper was pulled at a rate of / min, and the force (g / 5cm) required for peeling was measured. (Residual adhesion ratio) A polyester adhesive tape 31B (trade name, manufactured by Nitto Denko Corporation) is adhered to the cured film surface in the same manner as in the peel force measurement, and a load of 20 g / cm ² is applied thereto, followed by heat aging at 70 ° C. for 20 hours. After that, the tape was peeled off and attached to a stainless steel plate. Next, remove this tape from the stainless steel plate
Peel off at an angle of 180 ° at a peeling speed of 0.3 m / min. Measure the force (g) required for peeling, and measure the force (g) required for peeling an unused standard tape from the stainless steel plate. And these ratios were expressed as percentages. Example 1 Average composition formula And 100 parts of an organopolysiloxane (A) having a viscosity of 800 cP, 10 parts of a siloxane containing a mercaptoalkyl group having a viscosity of 50 cP, and 2-hydroxy-2-photonic as a photoinitiator.
3 parts of methyl-1-phenylpropan-1-one were mixed to prepare a silicone composition [1]. The obtained composition was measured for ultraviolet curability, peeling force, and residual adhesiveness. The results are shown in Table 1. Example 2 Average composition formula And 100 parts of an organopolysiloxane (B) having a viscosity of 800 cP, 10 parts of a siloxane containing a mercaptoalkyl group having a viscosity of 50 cP, and 2-hydroxy-2- as a photoinitiator.
3 parts of methyl-1-phenylpropan-1-one were mixed to prepare a silicone composition [2]. The obtained composition was measured for ultraviolet curability, peeling force, and residual adhesiveness. The results are shown in Table 1. Comparative Example 1 Average composition formula A silicone composition [3] was prepared in the same manner as in Example 1 except that the organopolysiloxane (C) having a viscosity of 1,000 cP was used instead of the organopolysiloxane (A). The obtained composition was measured for ultraviolet curability, peeling force, and residual adhesiveness. The results are shown in Table 1. Comparative Example 2 Average composition formula And a silicone composition [4] was prepared in the same manner as in Example 1 except that the organopolysiloxane (D) having a viscosity of 800 cP was used instead of the organopolysiloxane (A). The obtained composition was measured for ultraviolet curability, peeling force, and residual adhesiveness. The results are shown in Table 1. Comparative Example 3 Average composition formula And a silicone composition [5] was prepared in the same manner as in Example 1 except that the organopolysiloxane (E) having a viscosity of 4,000 cP was used instead of the organopolysiloxane (A). The obtained composition was measured for ultraviolet curability, peeling force, and residual adhesion ratio, and the results are shown in Table 1. Comparative Example 4 Average Composition Formula And 30 parts of the organopolysiloxane (F) having a viscosity of 200 cP and 70 parts of the organopolysiloxane (E) used in Comparative Example 3 were used in place of the organopolysiloxane (A). In the same manner as in Example 1, a silicone composition [6] was prepared. The viscosity of the mixture of the organopolysiloxanes (E) and (F) was 850 cP. The obtained composition was measured for ultraviolet curability, peeling force, and residual adhesiveness. The results are shown in Table 1. [Table 1] In Comparative Examples 1 and 2, peelability was not measured because of poor curability. EFFECTS OF THE INVENTION The releasable ultraviolet-curable silicone composition of the present invention is excellent in ultraviolet curability, can improve the productivity in the production of release paper, reduce the energy cost, and improve the release characteristics. Provides excellent cured film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI // (C08L 83/07 C08L 83:08 83:08) (56) References JP-A-8-157725 (JP, A) JP-A-6-16944 (JP, A) JP-A-3-227365 (JP, A) JP-A-2-245060 (JP, A) JP-A-2-202551 (JP, A) JP-A-53-55362 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 83/00-83/16

Claims (1)

(57) [Claim 1] (1) Consisting of siloxane units represented by the following formulas (I) to (III), and the siloxane unit represented by the formula (III) is averaged in one molecule. 100 parts by weight of an alkenyl group-containing organopolysiloxane containing from 1 to 3 and having a viscosity at 25 ° C. of from 100 to 100,000 cP, [Where R ¹ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group, ¹ to 10 mol% of R ¹ is a phenyl group, and R ² is a group represented by the formula (IV) -C _n H _2n —CH = CH ₂ (IV) (where n is an integer of 0 to 8), and R ³ is R ¹ or R ² . (2) 1 to 30 parts by weight of an organopolysiloxane containing at least two mercaptoalkyl groups bonded to a silicon atom in one molecule, and (3) a photoinitiator compatible with the organopolysiloxane. UV curable silicone composition.