Solvent-free silicone adhesive composition

Abstract

To provide a solvent-free silicone adhesive composition that shows excellent adhesion to a plastic film substrate and an adherend, and does not impair optical properties.SOLUTION: A solvent-free silicone adhesive composition is a solvent-free one and comprises (A) an organopolysiloxane having at least two alkenyl group in one molecule, (B) an organohydrogen polysiloxane having at least three hydrogen atoms each binding to a silicon atom, in such an amount so that silicon-binding hydrogen atoms become 0.1-10 mol relative to 1 mol of the alkenyl groups of (A), (C) a platinum catalyst, (D) a silane coupling agent having an epoxy group, and (E) an alkoxide compound selected from titanium, aluminum, and zirconium. The viscosity at 25°C is 10-10,000 mPa s. When the solution is cured at a thickness of 40 μm on a 75 μm PET, the total light transmittance is 90% or more and the haze is less than 1%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a solventless silicone adhesive composition that exhibits good adhesion to a plastic film substrate and an adherend and does not impair optical properties.

Background Art

[0002] Adhesive tapes and adhesive labels using a silicone adhesive composition are used in severe environments where organic adhesives such as acrylic adhesives and rubber adhesives are deteriorated because the silicone adhesive layer is excellent in heat resistance, cold resistance, weather resistance, electrical insulation, and chemical resistance. For example, when heat treatment is performed during component manufacturing or processing, masking or temporary fixing for protecting the substrate entirely or partially may be required. An adhesive tape used for such applications is preferably one using a silicone adhesive composition having heat resistance.

[0003] Conventional silicone adhesive compositions are generally solvent-based. When coating and curing or molding into a thick film having a thickness of 0.1 mm or more, bubbles are generated during heat curing. Therefore, a solventless type is desirable for such applications. In addition, in applications such as sticking agents, bandages, surgical tapes, and sports taping tapes that are directly attached to the skin, if there is a residue of an aromatic hydrocarbon solvent, irritation to the skin becomes a problem.

[0004] In addition, in applications of adhesive tapes and adhesive labels in architecture, interior decoration, etc., if an aromatic hydrocarbon solvent remains and volatilizes and stays in the indoor air, even if it is an extremely small amount, it may cause chemical substance allergy, sick house syndrome, chemical substance hypersensitivity, etc.

[0005] In response to these demands, solvent-free silicone adhesive compositions have been developed. Patent documents 1 to 3 are publications relating to solvent-free silicone adhesive compositions, but these silicone-based pressure-sensitive adhesive compositions and silicone compositions for adhesives often do not have sufficient adhesion to sheet-like substrates such as plastic films, and it was often necessary to pre-prime the plastic film. Furthermore, despite the need for excellent transparency, such as in protective sheets for electronic components, none of these documents describe the optical properties of the compositions. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-160923 [Patent Document 2] Japanese Patent Publication No. 2008-274251 [Patent Document 3] Japanese Patent Publication No. 2012-041504 [Patent Document 4] Japanese Patent Publication No. 2021-021058 [Patent Document 5] International Publication No. 2019 / 142779 [Patent Document 6] Special table number 2020-523422 [Patent Document 7] Japanese Patent Publication No. 2011-102336

[0007] Patent Document 4 relates to a hot-melt curable silicone composition that exhibits excellent mechanical properties, particularly strength and elongation, even when molded into a film or sheet shape. However, its high viscosity posed a problem for use as an adhesive composition for adhesive tapes. Patent Document 5 relates to a silicone adhesive composition that exhibits excellent adhesion to a substrate and a small increase in adhesive strength over time, as well as to an adhesive film and adhesive tape having a cured layer of the adhesive composition. Patent Document 6 states that a solvent-free silicone pressure-sensitive adhesive composition can be cured by a hydrosilylation reaction. It states that a pressure-sensitive adhesive laminate article prepared by curing this composition on a substrate is useful for protection and / or masking during processing in electronics applications. In both publications, there was room for improvement in reducing viscosity. Patent Document 7 relates to an adhesive film and a silicone adhesive composition used to form the adhesive layer of the film, but there was room for improvement in terms of adhesion. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention provides a solvent-free silicone adhesive composition that exhibits good adhesion to plastic film substrates and adherends, and does not impair optical properties. [Means for solving the problem]

[0009] A solvent-free silicone adhesive composition comprising an organopolysiloxane (A) having at least two alkenyl groups in one molecule, an organohydrogen polysiloxane (B) containing at least three hydrogen atoms bonded to silicon atoms in an amount such that the amount of hydrogen atoms bonded to silicon atoms is 0.1 to 10 moles per mole of alkenyl groups in (A), a platinum catalyst (C), a silane coupling agent (D) containing epoxy groups, and an alkoxide compound (E) selected from titanium, aluminum, and zirconium, wherein the viscosity at 25°C is 10 to 10,000 mPa·s, and when this solution is cured on a 75 μm PET to a thickness of 40 μm, the total light transmittance is 90% or more and the haze is less than 1%. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a colorless, transparent, solvent-free silicone-based pressure-sensitive adhesive composition that exhibits excellent adhesion to plastic film substrates and adherends, and an adhesive tape using the same. [Modes for carrying out the invention]

[0011] The following describes in detail a solvent-free silicone adhesive composition according to the present invention, which exhibits good adhesion to a plastic film substrate and an adherend, and does not impair optical properties.

[0012] <Organopolysiloxane (A) having at least two alkenyl groups in one molecule> Organopolysiloxane (A), having at least two alkenyl groups in one molecule, is a so-called Vi (vinyl)-modified silicone oil. Its viscosity is 1 to 10,000 mPa·s, more preferably 10 to 5,000 mPa·s. If this upper limit is exceeded, the viscosity of the composition becomes too high, reducing its coatability, and if it falls below the lower limit, it may cause repulsion on the substrate during coating.

[0013] <Organohydrogen polysiloxane (B)> The organohydrogen polysiloxane (B) contains at least three hydrogen atoms bonded to silicon atoms, with 0.1 to 10 moles, more preferably 0.5 to 5 moles, of silicon-bonded hydrogen atoms per mole of alkenyl group (A). Exceeding this upper limit may cause foaming or yellowing, while falling below the lower limit may result in insufficient hardening.

[0014] Multiple organopolysiloxanes (A) and organohydrogen polysiloxanes (B), each having at least two alkenyl groups in a single molecule, can be used in combination.

[0015] <Platinum catalyst (C)> The platinum catalyst (C) is an addition reaction catalyst for an organopolysiloxane (A) having at least two alkenyl groups in one molecule and an organohydrogenpolysiloxane (B). Examples include chloroplatinic acid, an alcohol solution of chloroplatinic acid, a reaction product of chloroplatinic acid and alcohol, a reaction product of chloroplatinic acid and an olefin compound, a reaction product of chloroplatinic acid and a vinyl group-containing siloxane, a platinum-olefin complex, a platinum-vinyl group-containing siloxane complex, a rhodium complex, a ruthenium complex, etc. Also, those obtained by dissolving or dispersing these in a solvent such as isopropanol or toluene, or in a silicone oil, etc. may be used. As the addition amount, it is 0.1 to 1000 ppm, more preferably 1.0 to 50 ppm as platinum based on the total of the organopolysiloxane (A) having at least two alkenyl groups in one molecule and the organohydrogenpolysiloxane (B).

[0016] <Silane coupling agent (D) containing an epoxy group> The silane coupling agent (D) containing an epoxy group is a component that ensures adhesion to the plastic film substrate. Functionally, a low molecular weight silane coupling agent to a high molecular weight silane coupling agent, any molecular weight silane coupling agent may be used. From the viewpoint of controlling the increase in viscosity, a low molecular weight silane coupling agent is more suitable. Specifically, when listing compound names, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane are mentioned. As the addition amount, it is 0.1 to 3 parts by mass, more preferably 0.2 to 1 part by mass based on 100 parts by mass in total of the organopolysiloxane (A) having at least two alkenyl groups in one molecule and the organohydrogenpolysiloxane (B). If the addition amount is too small, the adhesion to the substrate may be insufficient, and if it is too large, the film may become cloudy.

[0017] <Alkoxide compound (E) selected from titanium, aluminum, zirconium> The alkoxide compound (E) selected from titanium, aluminum, and zirconium is a component that acts on the alkoxide group of the silane coupling agent (D) containing an epoxy group to improve the adhesion performance. In order to ensure adhesion and not impair the optical properties, it must have a structure and addition amount that show compatibility with the organopolysiloxane (A) having at least two alkenyl groups in one molecule, the organohydrogenpolysiloxane (B), and the platinum catalyst (C). In particular, when an alkoxide (-OCnH2n+1) with n < 3 is used, the activity is extremely high, so it may react with a small amount of moisture present in the air or the composition, resulting in cloudiness or precipitation. Therefore, those satisfying n > 4 are desirable. The organopolysiloxane (A) having at least two alkenyl groups in one molecule, containing at least three hydrogens bonded to silicon atoms, and the organohydrogenpolysiloxane (B) in an amount such that the silicon-bonded hydrogen atoms are 0.1 to 10 moles per mole of the alkenyl groups of (A) are 0.01 to 1 part, more preferably 0.1 to 0.8 parts, based on 100 parts by mass in total. If the addition amount is too small, the adhesion to the substrate may be insufficient. If it is too large, cloudiness may occur in the film by reacting with the silane coupling agent (D) containing an epoxy group.

[0018] The adhesive strength of the adhesive may be required to be slightly adhesive as used for temporary fixing or strongly adhesive so that it cannot be easily peeled off once applied. As the adhesive strength of the slight adhesion, it is sufficient if it is 1 mN / 25 mm or more in the "180° peel test" described below. When increasing the adhesive strength, it can be increased by adding an adhesive strength increasing component, such as a so-called MQ resin.

[0019] The solvent-free silicone adhesive composition of the present application can be added with a filler, an antioxidant, etc. within a range that satisfies the coating performance and adhesiveness. The range that satisfies the coating performance means that it can satisfy the coating performance if it is 10 to 10,000 mPa·s in the "viscosity measurement" described below.

[0020] Fillers include calcium carbonate, silica, kaolin, calcined kaolin, clay, and silicic acid. Calcium, calcium sulfate, aluminum oxide (alumina), aluminum hydroxide, silica Inorganic fillers such as aluminum, titanium oxide, zinc oxide, magnesium carbonate, magnesium silicate, talc, zeolite, glass beads, and shirasu balloons can be added. In addition, organic fillers such as polyethylene, polypropylene, polymethyl methacrylate, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-vinyl acetate copolymer, nylon, polyethylene terephthalate, polybutylene terephthalate, polystyrene, ABS resin, acrylonitrile-styrene copolymer, and polycarbonate can also be added.

[0021] Antioxidants such as naphthylamines, phosphorus-based compounds, hydroquinones, bistris-polyphenols, thiobisphenols, and hindered phenols can be added. [Examples]

[0022] Next, the solvent-free silicone adhesive composition of the present application will be described in detail with reference to examples and comparative examples.

[0023] <Viscosity measurement> The viscosity of silicone materials and silicone compositions at 23°C was measured using a Type B viscometer (Toki Sangyo TVB-25M). Furthermore, the low-viscosity addition-type silicone composition of this application exhibits behavior approximating that of a Newtonian fluid, and is basically unaffected by differences between different rheometer types, such as cone-plate and Brookfield types, as well as differences between model numbers of the same type. However, viscosity measurements as described in this paper are based on the above conditions. The judging criteria were that a viscosity within the range of 10 to 10,000 mPa·s was considered a pass, and anything outside that range was considered a fail. The results are shown in Tables 3 and 4.

[0024] <180° peel test> A silicone adhesive composition solution was applied to a 75 μm thick PET film (Toray Lumirror S10) using an applicator so that the cured thickness would be 40 μm. The film was then cured by heating at 130°C for 3 minutes to create an adhesive film. This film was then cut into 25 mm wide strips to form tapes. The adhesive tape was attached to the glass and pressed down by passing a roller covered with a 2kg rubber layer back and forth twice. After being left at room temperature for approximately 20 hours, the force (mN / 25mm) required to peel the tape from the glass at a speed of 300mm / min at a 180° angle was measured using a tensile testing machine. The criteria for evaluation were that a reading of 1 mN / 25 mm or higher was considered a pass, and a reading of less than 1 mN / 25 mm was considered a fail. The results are shown in Tables 3 and 4.

[0025] <Adhesion Test> A film coated with a 25 mm wide adhesive to a thickness of 40 μm was obtained using the same method as in the 180° peel test. The adhesive layer was scratched with a cutter, and this area was rubbed with a fingertip and evaluated as follows. The evaluation criteria were as follows: a pass (○) was given if the adhesive layer did not peel off the substrate, and a fail (×) was given if the adhesive layer peeled off the substrate. The results are shown in Tables 3 and 4.

[0026] <Optical properties> A film was obtained by coating a 25 mm wide adhesive to a thickness of 40 μm using the same method as in the 180° peel test and adhesion test. The total light transmittance and haze of the film were measured using a Haze Guard II haze meter manufactured by Toyo Seiki Co., Ltd. The criteria for evaluation were: a total light transmittance of 90% or higher and haze of 1% or less was considered a pass (:○), while a total light transmittance of less than 90% or haze of 1% or higher was considered a fail (:×). The results are shown in Tables 3 and 4.

[0027] <Organopolysiloxane (A) having at least two alkenyl groups in one molecule> As an organopolysiloxane (A) having at least two alkenyl groups in one molecule, a linear silicone oil with Vi groups at both ends and a viscosity of 1,000 mPa·s at 23°C was prepared.

[0028] <Organohydrogen polysiloxane (B)> A linear organohydrogen polysiloxane was prepared, containing 0.7% hydrogen atoms bonded to silicon atoms in part of the side chains, with a viscosity of 30 mPa·s at 23°C.

[0029] <Platinum catalyst (C)> As the platinum catalyst (C), a platinum-vinyl group-containing siloxane complex was prepared by dispersing it in a 1,000 mPa·s silicone oil containing 0.24% platinum.

[0030] <Silane coupling agent containing epoxy groups (D)> As silane coupling agents (D) containing epoxy groups, 3-glycidoxypropyltrimethoxysilane:(D)-1 and 3-glycidoxypropyltriethoxysilane:(D)-2 were prepared, and as a component that is not a silane coupling agent (D) containing epoxy groups, 3-methacryloxypropyltrimethoxysilane:(D')-3 was prepared.

[0031] <Alkoxide compounds selected from titanium, aluminum, and zirconium (E)> As alkoxide compounds (E) selected from titanium, aluminum, and zirconium, titanium tetrano-malbutoxide:(E)-1, titanium tetra-2-ethylhexoxide:(E)-2, and aluminum trisecondary butoxide:(E)-3 were prepared, and as a component that is not an alkoxide compound (E) selected from titanium, aluminum, and zirconium, aluminum tris(ethyl acetacetate):(E')-4 was prepared.

[0032] <Preparation of the composition of Example 1> 98.4 parts by mass of a linear silicone oil having Vi groups at both ends and a viscosity of 1,000 mPa·s at 23°C, 1.6 parts by mass of a linear organohydrogen polysiloxane with a viscosity of 30 mPa·s at 23°C and containing 0.7% hydrogen bonded to silicon atoms in part of the side chains, a platinum-vinyl group-containing siloxane complex in an amount equal to 5 ppm of platinum, 0.5 parts by mass of 3-glycidoxypropyltrimethoxysilane:(D)-1, and 0.5 parts by mass of titanium tetranormal butoxide:(E)-1 were weighed into a container and stirred until homogenized. Furthermore, if we let [Vi] be the number of moles of vinyl groups in the Vi (vinyl)-modified silicone oil and [H] be the number of moles of hydrogen groups in the organohydrogen polysiloxane, then [H] / [Vi] is 1, because the amount of vinyl groups in a linear silicone oil with Vi groups at both ends and a viscosity of 1,000 mPa·s at 23°C is 0.115 mmol / g, and the amount of hydrogen groups in a linear organohydrogen polysiloxane with a viscosity of 30 mPa·s at 23°C and containing 0.7% hydrogen bonded to silicon atoms in part of the side chain is 7.0 mmol / g.

[0033] <Preparation of compositions for Examples 2-4 and Comparative Examples 1-6> Compositions for Examples 2-4 and Comparative Examples 1-6 were prepared using the same procedure as for the composition of Example 1, in the proportions shown in Tables 1 and 2. Furthermore, if we let [Vi] be the number of moles of vinyl groups in the vi (vinyl)-modified silicone oil and [H] be the number of moles of hydrogen groups in the organohydrogen polysiloxane, then [H] / [Vi] is always 1, as mentioned above.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] Table 4

Claims

1. It is solvent-free. The molecule comprises an organopolysiloxane (A) having at least two alkenyl groups, an organohydrogen polysiloxane (B) containing at least three hydrogen atoms bonded to silicon atoms in an amount such that the amount of hydrogen atoms bonded to silicon atoms is 0.1 to 10 moles per mole of alkenyl groups in (A), a platinum catalyst (C), a silane coupling agent containing epoxy groups (D), and an alkoxide compound (E) selected from titanium, aluminum, and zirconium. (A) and (B) together comprise 100 parts by mass, with (D) being 0.1 to 3 parts by mass and (E) being 0.01 to 1 part by mass. The viscosity at 25°C is 10 to 10,000 mPa·s. A solvent-free silicone adhesive composition characterized in that, when this solution is cured on 75 μm PET to a thickness of 40 μm, the total light transmittance is 90% or more and the haze is less than 1%.

2. The solvent-free silicone adhesive composition according to claim 1, wherein the silane coupling agent (D) containing an epoxy group is a silane coupling agent selected from 3-glycidoxypropyltrimethoxysilane or 3-glycidoxypropyltriethoxysilane.

3. A solvent-free silicone adhesive composition according to claim 1 or claim 2, wherein the alkoxide of the alkoxide compound (E) selected from titanium, aluminum, and zirconium is represented by the chemical formula (-OCnH2n+1), and n > 4.

4. An adhesive tape made using the solvent-free silicone adhesive composition described in any one of claims 1 to 3.

Images