Sealant application method

Abstract: A sealant application method for applying a first sealant as a preliminary sealant to a second sealant as a subsequent sealant, comprising the steps of subjecting a surface of the first sealant to an electric discharge treatment; and applying the second sealant directly to or through a primer to the first sealant after the electric discharge treatment. The first sealant preliminarily applied is first subjected to the electric discharge treatment to thereby reform the surface of the first sealant into an optimum-condition, thereby ensuring strong adhesion of the second sealant to the first sealant.

Description: BACKGROUND The present invention relates to sealant application methods involving applying a second sealant onto a first sealant. Conventionally, application of a sealant is widely made to give water-tightness and air-tightness to a building or the like. Examples of such a sealant widely used at present include a silicone sealant, MS sealant (alkoxy silicone functionalized polyoxypropylene polymer base sealant), polysulfide sealant, polyurethane sealant, acrylic urethane sealant, and acrylic sealant. A proper kind of sealants for a proper place of application is selected according to the performances of the sealants, and several kinds of the sealants are always used. For example, in the case of a silicone sealant, it is widely used for the surrounding of a windowpane or the like owing to its excellence of weather resistance and durability. However, the outer periphery of a joint is largely contaminated with the sealant, so that actual use of the sealant is largely limited. In the case of a modified silicone sealant, it cannot be used for the surrounding of a windowpane which requires weather resistance. In the case of a polysulfide sealant, it is inferior to a modified silicone sealant and a silicone sealant in responsiveness to movement of a joint, so that it cannot be used for a joint of a metal curtain wall with large movement. Thus, a proper sealant is used for a proper place according to the structure, material, etc. of a building. Accordingly, different sealants are applied to carry out successive jointing, causing a problem in adhesion. Such application of different sealants in succession is called successive jointing of sealants, and the problem in adhesion due to the successive jointing frequently arises at an actual sealant application site. Further, in sealant modification work, a refilling process is generally carried out in such a manner that an old sealant before modification is first removed and a new sealant-is therefore filled. Also in this case, there is a problem in adhesion between the old sealant and the new sealant. In such successive jointing of sealants, the adhesion between the sealants may become insufficient depending on the kinds of sealants, and it is therefore important to check the adhering condition at the joint. That is, in the case of preliminarily applying a first sealant and thereafter applying a second sealant to the first sealant, a technique for improving the adhesion of the second sealant to the first sealant is required. In the case that the first sealant is a silicone sealant, there is a difficulty in adhesion in respect of the combination of the first and second sealants used in successive jointing or modification as described in Sealant Handbook (issued by Japan Sealant Industry Association) p31 and p151. That is, in the case that the first sealant preliminarily applied is a silicone sealant, only a silicone sealant that can adhere to the first sealant is usable as the second sealant to be next applied, and the other sealants including a modified silicone sealant, polysulfide sealant, polyurethane sealant, acrylic urethane sealant, and acrylic sealant cannot adhere to the first sealant. Further, in the case that the first sealant is a modified silicone sealant, adhesion of a polysulfide sealant, polyurethane sealant, and acrylic urethane sealant to the first sealant is difficult. Accordingly, it has been desired to find a way of enabling or improving the adhesion of a second sealant to a first sealant, preferably over a range of types of the first and/or second sealant, and these are aims of the present disclosure. From a detailed study for achievement of the above object, the present inventors have found out the fact that adhesion of the first sealant (preliminary sealant) to the second sealant (subsequent sealant) can be improved by subjecting an adhering portion of the first sealant to a given electric discharge treatment. More specifically, by subjecting the surface of the first sealant to an electric discharge treatment such as corona treatment, plasma treatment, blow treatment by corona discharge or arc discharge in a gas flow, and plasma torch treatment, the surface of the first sealant can be reformed into a condition providing wettability and reactivity (adhesiveness) of the surface of the first sealant to result in great improvement of adhesion of the first sealant to the second sealant. Even when the first sealant is a silicone sealant or a modified silicone sealant, causing an outstanding problem in the prior art, reliable adhesion of the second sealant was achieved to allow excellent successive jointing by adopting these methods in our researches. According to the present invention, the following sealant application method is provided. Claim 1: A sealant application method for applying a second, subsequent sealant onto a first, preliminary sealant, comprising the steps of subjecting a surface of said first sealant to an electric discharge treatment; and applying said second sealant directly to or through-a primer to said first sealant after said electric discharge treatment. Claim 2: A sealant application method according to claim 1, wherein each of said first and second sealants is selected from the group consisting of a silicone sealant, modified silicone sealant, polysulfide sealant, polyurethane sealant, and acrylic urethane sealant. Claim 3: Said electric discharge treatment is advantageously a corona treatment or plasma treatment. Claim 4: Or, said electric discharge treatment is a blow treatment by corona discharge or arc discharge blown in a gas flow. Claim 5: Or, said electric discharge treatment is a plasma torch treatment by plasma discharge blown in a gas flow. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an adhesion test sample. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail. According to the sealant application method of the present invention, the first sealant is first subjected to a given electric discharge treatment, and the second sealant is next applied directly to or preferably through a primer to the first sealant. The materials of the first and second sealants are not especially limited, but include a silicone sealant, modified silicone sealant, polysulfide sealant, polyurethane sealant, acrylic urethane sealant. Preferable examples of the electric discharge treatment in the present invention include a corona treatment, plasma treatment, blow treatment by corona discharge or arc discharge blown in a gas flow, and plasma torch treatment. We find that any one of these treatments can provide a useful effect. Subjecting the surface of the first sealant to the above electric discharge treatment, the surface of the first sealant can be reformed into an optimum condition, thereby remarkably improving wettability and reactivity (adhesiveness) of the surface of the first sealant, so that the bonding strength between the first sealant and the primer or the second sealant can be remarkably improved. Usually, sealant application is carried out at a building site, so from the viewpoints of simplicity of the treatment and portability of a treating device, the corona treatment or the blow treatment by corona discharge blown in a gas flow is more preferable. The corona treatment may be realized by an electric discharge treatment including the steps of generating an electric discharge between first and second electrodes opposed to each other at a high-frequency high voltage, and passing the sealant through the discharge space. If the first sealant is on a conductive substrate e.g. a metal panel and the sealant has a small thickness, the sealant itself may be used as the second electrode to generate an electric discharge between the first electrode and the sealant/substrate, thereby reforming the surface of the sealant. In this case, the electric discharge treatment is carried out usually with an output of 10 to 1000 W for about 0.1 to 30 seconds. The plasma treatment may be realized by an electric discharge treatment using ions, electrons, radicals, photons, atoms, molecules, etc. in a plasma to reform the surface of the sealant, which treatment includes the steps of generating an electric discharge by applying a dc or ac electric field to a gas at a given pressure (low pressure or atmospheric pressure), and placing the sealant in the electric discharge or downstream of the electric discharge in respect of a gas flow. In this case, the electric discharge treatment is carried out usually under a gas pressure of 1,33×10 -6 to 1,33 bar (0.001 to 1000 Torr) and a frequency of the electric field for plasma such as a dc, constant-frequency ac of 50 Hz, ac of about 1 to 100 kHz, radio wave of 13.56 MHz, or microwave of 2.45 GHz. Examples of the gas include argon (Ar), oxygen, air, nitrogen, helium (He), and CF 4 . The blow treatment by corona discharge or arc discharge blown in a gas flow may be realized by an electric discharge treatment including the steps of generating a corona discharge or arc discharge between electrodes, blowing the discharge with a gas flow such as air flow, and subjecting the sealant to the downstream blown discharge in respect of the gas flow. In this case, the electric discharge treatment is carried out usually with a distance of 1 to 100 mm between a discharge outlet port and a treatment surface of the sealant for about 1 to 30 seconds. The plasma torch treatment may be realized by an electric discharge treatment including the steps of generating a plasma discharge at an atmospheric pressure or the like, blowing the discharge with a gas, and subjecting the sealant to the downstream blown discharge. In this case, the electric discharge treatment is carried out usually by using helium, argon, or the like as the gas at a gas pressure of 0,67 to 2,67 bar (500 to 2000 Torr) at a frequency of 50 Hz to 100 MHz for about 1 to 30 seconds. In the sealant application method of the present invention, a primer is preferably applied to the first sealant after the above electric discharge treatment. However, the second sealant may be applied directly to the first sealant without using the primer. The primer used in the present invention is a substrate treating material to be preliminarily applied to the first sealant before applying the second sealant to the first sealant, so as to improve the adhesiveness between the first and second sealants. The material of the primer is not especially limited in the present invention, but various materials known in the art may be used. Examples of the primer include synthetic rubber, acrylic, urethane, epoxy, and silane primers in which a silane coupling agent, polyiscyanate, epoxy resin, synthetic rubber, acrylic resin, etc. are compounded. The adhesiveness between the first sealant and the primer can also be improved by the above electric discharge treatment, thereby ensuring strong adhesion of the first sealant and the second sealant. The primer is applied to the first sealant by using a brush or the like and thereafter air-dried. Thereafter, the second sealant is applied to the primer. Thus, the sealant application method of the present invention can exhibit an effect that the second sealant can be firmly bonded to the first sealant by the electric discharge treatment of the first sealant. In the following, the present invention is illustrated by means of examples in connection with comparisons. It is to be noted that the present invention is not limited to the examples. EXAMPLE Various preliminary sealants (Petam MS1000, one-part modified silicone sealant; Petam MS2000, two-part modified silicone sealant; Petam SR1100, one-part silicone sealant; and Petam SR2000, two-part silicone sealant, all manufactured by Bridgestone Corp.) were applied with a thickness of 3 mm to alumite sample panels each having a size of 50 mm x 50 mm x 3 mm as shown in FIG. 1. Thereafter, the sealants were allowed to stand for curing at room temperature for one month. Thereafter, the sealants were subjected to various electric discharge treatments under the following conditions (Examples A to D). Comparison E is a reference in which no electric discharge treatment was carried out: (A) Corona treatment Output: 300 W Treatment time: 5 seconds Treating device: HV05-2 manufactured by TANTEC Co., Ltd. (B) Plasma treatment Pressure: 1,33×10 -3 bar (1 Torr) Gas used: Ar gas Output: 100 W Treatment time: 30 seconds Treating device: Asher PC101A manufactured by Yamato Scientific Co.,Ltd. (C) Blow corona treatment Distance: 40 mm Treatment time: 4 seconds Treating device: Plasma treater manufactured by Arbrant Co., Ltd. (D) Plasma torch treatment Pressure: 1,013 bar (760 Torr) Gas used: He gas Frequency: 13.56 MHz Output: 100 W Treatment time: 5 seconds (E) Untreated Thereafter, a primer (Petam Primer No. 3 manufactured by Bridgestone Corp.) was applied to the preliminary sealants, and various subsequent sealants (Petam MS2000, two-part modified silicone sealant; Petam PS2000, two-part polysulfide sealant; and Petam PU2000, two-part polyurethane sealant, all manufactured by Bridgestone Corp.) were then applied through the primer to the preliminary sealants, thus preparing H-type samples in accordance with JIS A5758. These samples were allowed to stand for precuring at 20°C at 55% in RH for one week, and then stand for postcuring at 50°C for one week. The samples obtained were subjected to an adhesion test in accordance with JIS A5758. The results are shown in Table 1. In FIG. 1, reference numerals 1, 2, 3, and 4 denote the alumite sample panel, preliminary sealant, subsequent sealant, and alumite (aluminum alloy anodized in a sulfuric acid), respectively. Preliminary Sealant Subsequent Sealant Kind Treatment Petam MS2000 Petam PS2000 Petam PU2000 Bonding Strength (N/cm 2 ) Comparison 1 Petam MS1000 Untreated(E) 31.4 18.4 38.4 Example 1 A 37.4 27.9 44.5 Example 2 B 37.7 28.4 43.5 Example 3 C 38.5 27.7 44.6 Example 4 D 36.9 28.8 45.6 Comparison 2 MS2000 Untreated(E) 28.4 19.5 36.4 Example 5 A 35.4 26.8 43.3 Petam Example 6 B 34.7 26.7 42.5 Example 7 C 35.5 28.1 43.1 Example 8 D 33.0 27.7 43.9 Comparison 3 Petam SR1100 Untreated(E) 10.6 3.1 22.3 Example 9 A 37.6 37.3 41.1 Example 10 B 36.4 34.6 42.3 Example 11 C 35.4 35.8 44.6 Example 12 D 33.5 36.4 45.7 Comparison 4 Petam SR2000 Untreated(E) 11.5 3.0 25.9 Example 13 A 39.4 38.2 53.8 Example 14 B 37.4 33.5 51.9 Example 15 C 34.9 35.6 54.3 Example 16 D 33.7 36.4 53.0 As apparent from Table 1, the bonding strength between the preliminary sealant and the subsequent sealant is remarkably improved by the electric discharge treatment of the preliminary sealant, thereby improving successive jointing of the subsequent sealant. In use, typically the second sealant is applied to the first sealant when the first sealant is already in a sealing location in relation to a structural joint.

Claims: A sealant application method for applying a second sealant as a subsequent sealant onto a first sealant as a preliminary sealant, comprising the steps of: subjecting a surface of said first sealant to an electric discharge treatment; and applying said second sealant directly to or through a primer to said first sealant after said electric discharge treatment. A sealant application method according to claim 1, wherein each of said first and second sealants is selected from the group consisting of a silicone sealant, MS sealant (alkoxy silicone functionalized polyoxypropylene polymer base sealant), polysulfide sealant, polyurethane sealant, and acrylic urethane sealant. A sealant application method according to claim 1 or claim 2 wherein said electric discharge treatment is a corona treatment or plasma treatment. A sealant application method according to claim 1 or claim wherein said electric discharge treatment is a blow treatment by corona discharge or arc discharge blown in a gas flow. A sealant application method according to claim 1 or claim wherein said electric discharge treatment is a plasma torch treatment by plasma discharge blown in a gas flow.

Inventors: SAITO SHINJI, TAKIZAWA TOSHIKI, SAITO, SHINJI, TAKIZAWA, TOSHIKI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1998
Main classification: C09K3
IPC codes: E04C2, B05D3, E04B1, C09K3, E04G23