AU2009206189A1

AU2009206189A1 - Bonding method between secondary gas barrier and insulation panel using insulated heating pad

Info

Publication number: AU2009206189A1
Application number: AU2009206189A
Authority: AU
Inventors: Seong-Uk Lee
Original assignee: HAN KUK FIBER GLASS CO Ltd
Current assignee: HAN KUK FIBER GLASS CO Ltd
Priority date: 2009-08-06
Filing date: 2009-08-06
Publication date: 2011-02-24

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention title: Bonding method between secondary gas barrier and insulation panel using insulated hearing pad The invention is described in the following statement: BONDING METHOD BETWEEN SECONDARY GAS BARRIER AND INSULATION PANEL USING INSULATED HEARING PAD DESCRIPTION Technical Field The present invention relates to a method for bonding a secondary gas barrier to an insulation panel in a liquefied 5 natural gas (LNG) carrier or storage tank, and more particularly, to a method for bonding a secondary gas barrier to an insulation panel wherein curing of an adhesive is perfectly carried out, thereby expecting the reduction of a construction period and the improvement of productivity, and 10 thereby reducing the installation costs of the bonding equipment and the repairing costs for the uncuring and defective bonding of the adhesive. Background Art In this specification where a document, act or item of 15 knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date publicly available, known to the public, part of the common general knowledge or known to be relevant to an 20 attempt to solve any problem with which this specification is concerned. As shown in FIG. 6, an LNG container of an LNG carrier or an LNG storage tank includes a primary gas barrier 10, an insulation panel 20, and a secondary gas barrier 30, for the 25 purpose of stably preventing LNG at a liquefaction temperature of -163 0 C or less from leaking to the outside under any bad conditions, and of enduring the impact and pressure of the internal LNG or external impacts. At this time, the primary gas barrier 10 is configured to be 30 in direct contact with the LNG in the LNG carrier or storage tank, while enduring the contraction stresses and impacts due 2 to a very low temperature, which is generally formed of a stainless steel membrane (STS). The insulation panel 20 is made by attaching a plywood onto both surfaces of a heat insulating material formed of a 5 reinforced polyurethane foam (R-PUF), so as to endure the impact and pressure of LNG and maintain the temperature of LNG of -1630C at the liquefied state. Further, the secondary gas barrier 30 has a property of secondarily preventing the LNG from leaking to the outside, 10 if the primary gas barrier 10 is damaged, and it is made by laminating synthetic rubber and glass fiber fabric on both surfaces of an aluminum foil so as to mold them as a unitary body, or by laminating an epoxy/polyamide film and a reinforcing fiber fabric on both surfaces of an aluminum foil 15 so as to mold them as a unitary body. Conventionally, an adhesive is applied on the insulation panel 20, and a triplex strip is placed thereon. After that, the insulation panel 20 is pressurized by using an air bag and is cured at a room temperature. Then, the secondary gas 20 barrier 30 is bonded to the insulation panel 20. Such a conventional bonding method, however, entails problems in that the surface temperature of the insulation panel 20 is not constantly maintained well and the environmental conditions of a working place are not made constantly, 25 thereby failing to obtain constant strengths of the adhesive. This causes the adhesive to remain in an not-curing or incomplete curing state, which yields defective bonding results. Thus, it may reduce the lifespan of the LNG carrier or storage tank or even may cause an accident therefrom. 30 More especially, the bonding strength of the adhesive varies depending on a low temperature in the winter season and a high temperature difference in a change of season.

3 Since an uneven pressure is applied to the insulation panel 20 during a pressurizing step, also, loose spaces between the insulation panel 20 and the secondary gas barrier 30 are partially formed, which fails to obtain perfect bonding 5 results. There is other problem related to the adhesive. If the adhesive functions in full, the surface of adhesion has squeeze-out shape. But if the adhesive functions incompletely, a shape of wave happens on the surface of adhesive squeeze 10 out shape. One reason of such problem is that uniform pressure can not be applied on the surface of the heating pad owing to some flow of the adhesive. The flow may be caused by the low viscosity of the adhesive under high temperature during adhesion. The other reason of such problem is that the 15 variation layer for heating may be transformed into certain wave form in part to cause the variation of other layer. To overcome the above difficulty regarding the process of adhesion, Korean Patent No. 0886654 discloses a heating pad with insulating property having a wood sandwich panel layer. 20 The wood sandwich panel layer is laminated on a heating layer and has a structure of self-insulating. But it is difficult to produce the wood sandwich panel layer due to the complex structure. And the panel layer has not bending property under the variation of temperature, while other layers tend to be 25 transformed according to the variation of temperature. Hence, if the panel layer is to be used under sharp variation of temperature, it may be detached from the other layers. Furthermore, the panel layer may not be applied on a curved surface. 30 Considering the above-mentioned problem of the prior art, an insulating layer that has property of flexibility according to the variation of temperature and versatility to all the shape of layer together with improved insulation is required.

4 -The present invention is a purpose to suggest an invention to solve the problem of the prior art as well as to have the requisite property. Disclosure 5 Technical Problem Accordingly, it is an object of the present invention to provide a method for bonding a secondary gas barrier to an insulation panel wherein a temperature higher than a room temperature is provided under curing conditions of an 10 adhesive applied for bonding the secondary gas barrier to the insulation panel, thereby obtaining a best bonding strength, and thereby preventing the uncuring or semi-curing of the adhesive, even though a relatively long time period is elapsed during the curing of the adhesive. 15 It is another object of the present invention to provide a method for bonding a secondary gas barrier to an insulation panel wherein no partial loose space is formed between the insulation panel and the secondary gas barrier, thereby obtaining perfect bonding results. 20 Technical Solution To achieve the above objects, according to the present invention, there is provided a method for bonding a secondary gas barrier to an insulation panel in an LNG carrier or an LNG storage tank, the method including the steps of: applying 25 an adhesive onto the surface of the insulation panel; sequentially laminating the secondary gas barrier, a release film, a cushion pad, a heating pad, and a rigid plate on the adhesive applied on the surface of the insulation panel; insulating by laying an insulating sheet 97 on the rigid 30 plate for avoiding dispersion of heat, heating the adhesive up to a temperature approaching best bonding characteristics by using the heating pad; pressurizing through a pressurizing 5 device the adhesive between the secondary gas barrier and the insulation panel under an even pressure by using the elastic force of the cushion pad and the rigidity of the rigid plate; and hardening the adhesive completely by maintaining the 5 heating temperature under the pressurizing state at a given constant level to conduct full curing of the adhesive. The insulating sheet has single layer or multi layers and is made of organic fabric coated with aluminum, inorganic fabric coated with aluminum, nonwoven fabric coated with aluminum 10 foil, organic fabric coated with thermosetting resin or thermoplastic resin, or inorganic fabric with coated thermosetting resin or thermoplastic resin. At this time, the heating pad is formed of a heating means covered with a coating material. 15 Also, the heating means is formed of one selected from a carbon plane heating element, a metal heating wire, and a ceramic heating element, and the coating material is formed of one selected from a thermosetting resin, a thermal plastic resin, and a composite material made of a fabric or an 20 organic or inorganic textile. Further, the cushion pad is formed of a synthetic resin or rubber. Further, the rigid plate is formed of a plywood, a honeycomb panel, or a laminated board. 25 The above and other objects and features of the present invention will be better understood from the following description of the preferred embodiment with reference to the drawings. Advantageous Effects 30 According to the present invention, there is provided a method for bonding a secondary gas barrier to an insulation 6 panel, thereby obtaining an excellent bonding strength of an adhesive, thereby reducing the curing time period of the adhesive to improve the productivity, thereby reducing the installation costs necessary for bonding the secondary gas 5 barrier, and thereby decreasing the repairing costs for the defective bonding due to the not-curing or semi-curing of the adhesive. As the adhesive that is applied between the secondary gas barrier and the insulation panel is pressurized through a 10 pressurizing device under an even pressure by using the elastic force of the cushion pad and the rigidity of the rigid plate, no partial loose space is formed between the insulation panel and the secondary gas barrier, thereby obtaining perfect bonding results. 15 Description of Drawings FIG.1 is a view showing a method for bonding a secondary gas barrier to an insulation panel according to the present invention; FIG.2 is a sectional view showing an example of a heating pad 20 employed in the bonding method according to the present invention; FIG.3 is a sectional view showing another example of a heating pad employed in the bonding method according to the present invention; 25 FIG.4 is a sectional view showing yet another example of a heating pad employed in the bonding method according to the present invention; FIG.5 is a sectional view showing an example where a cushion pad, a heating pad, and a rigid plate that are formed as an 30 integral body in the bonding method according to the present invention; and 7 FIG.6 is a partly cut perspective view showing a sectional structure of an LNG carrier adopting the bonding method according to the present invention. Best Mode for Invention 5 Hereinafter, an explanation of a method for bonding a secondary gas barrier to an insulation panel according to the present invention will be given with reference to the attached drawings. FIG.1 is a view showing a method for bonding a secondary gas 10 barrier to an insulation panel according to the present invention, FIG.2 is a sectional view showing an example of a heating pad employed in the bonding method according to the present invention, FIG.3 is a sectional view showing another example of a heating pad employed in the bonding method 15 according to the present invention, FIG.4 is a sectional view showing yet another example of a heating pad employed in the bonding method according to the present invention, and FIG.5 is a sectional view showing an example where a cushion pad, a heating pad, and a rigid plate that are formed as an integral 20 body in the bonding method according to the present invention. As shown in FIG.1, there is provided a method for bonding a secondary gas barrier 30 to an insulation panel 20 according to the present invention, the method including the steps of: applying an adhesive 40 onto the surface of the insulation 25 panel 20; sequentially laminating the secondary gas barrier 30, a release film 50, a cushion pad 90, a heating pad 60, and a rigid plate 95 on the adhesive 40 applied on the surface of the insulation panel 20; insulating by laying an insulating sheet 97 on the rigid plate 95 for avoiding 30 dispersion of heat, heating the adhesive 40 up to a temperature approaching best bonding characteristics by using the heating pad 60; pressurizing through a pressurizing 8 device 70 the adhesive 40 provided between the secondary gas barrier 30 and the insulation panel 20 under an even pressure by using the elastic force of the cushion pad 90 and the rigidity of the rigid plate 95; and hardening the adhesive 40 5 completely by maintaining the heating temperature under the pressurizing state at a given constant level to conduct full curing of the adhesive 40, thereby finishing bonding of the secondary gas barrier 30 onto the insulation panel 20. At this time, the temperature and heating time period where 10 the adhesive 40 approaches the best bonding characteristics are depending upon the type of an adhesive. For example, an epoxy adhesive or a polyurethane adhesive is heated for 3 to 6 hours at a temperature between 25 0 C and 100*C. In the preferred embodiment of the present invention, the 15 insulation panel 20 is made by attaching a plywood 24 on both surfaces of a heat insulating material 22 formed of a reinforced polyurethane foam (R-PUF), and the secondary gas barrier 30 is made by laminating an epoxy/polyamide film and a reinforcing fiber fabric on both surfaces of an aluminum 20 foil, thereby molding them as a unitary body. In this case, the insulation panel 20 and the secondary gas barrier 30 of the present invention are freely made, while not being limited to those as mentioned above. Also, the adhesive 40 is formed of an LNG epoxy adhesive made 25 by Gaztransport & Technigaz in France, and the release film 50 is formed of a vinyl film. In this case, they are freely made, while not being limited to those as mentioned above. On the other hand, the heating pad 60 serving to heat the adhesive 40 for fully curing the adhesive 40 is formed of a 30 heating means 62 covered with a coating material 64 that has heating time period and temperature controlled by means of a control unit 80, such that under the controlled heating time 9 and temperature, the adhesive 40 can have a high curing strength, thereby achieving a full curing state. At this time, the heating pad 60, as shown in FIG.2, is formed of the heating means 62 containing a carbon plane 5 heating element 62a, which is covered with the coating material 64 formed of one selected from a thermosetting resin, a thermal plastic resin, and a composite material made of a fabric or an organic or inorganic textile. However, as shown in FIG.3, a metal heating wire 62b may be used as the heating 10 means 62, and the coating material 64 of the metal heating wire 62b is formed of one selected from a thermosetting resin, a thermal plastic resin, and a composite material made of a fabric or an organic or inorganic textile. On the other hand, a ceramic heating element 62c may be used as the heating 15 means 62, and the coating material 64 of the metal heating wire 62b is formed of one selected from a thermosetting resin, a thermal plastic resin, and a composite material made of a fabric or an organic or inorganic textile. While the secondary gas barrier 30 is being pressurized under 20 an even pressure through the pressurizing device 70, the cushion pad 90 that is disposed between the release film 50 and the heating pad 60 serves to evenly spread the adhesive 40 to conduct the full bonding between the secondary gas barrier 30 and the insulation pad 20, and it is formed of an 25 elastic material, preferably, a synthetic resin or rubber. Also, the rigid plate 95 is formed of a material having predetermined rigidity capable of evenly transmitting the pressurizing force of the pressurizing device 70, and preferably, it is formed of a plywood, a honeycomb panel, or 30 a laminated board. On the other hand, as shown in FIG.5, if the cushion pad 90, the heating pad 60, and the rigid plate 95 are formed 10 integrally to one another, the adhesive 40 can be more evenly pressurized when compared with those that are separately made. The insulating sheet 97 may cover the rigid plate 95 for preventing heat from be conducted to the outside of the rigid 5 plate 95. In course of hardening the adhesive 40, it is preferably required that the temperature be constant for avoiding the viscosity variation of the adhesive 40 and shape alteration of the heat pad 60 or the rigid plate 95. The insulating sheet 97 may be formed as single layer or multi 10 layers and be made of organic fabric, inorganic fabric or nonwoven fabric coated with aluminum foil. Alternatively, the insulating sheet 97 may be organic or inorganic fabric with coated thermosetting resin or thermoplastic resin. The insulating sheet 97 consisting of one ply or multi-ply 15 sheet has function that the temperature of the heating pad is maintained constant and prevent heat from precipitating out of the heating pad. As result, the adhesive 40 can be hardened in constant temperature without some flow. In addition, the close contact between the insulating sheet 97 20 and rigid plate 95 may be preserved regardless of the temperature variation, since the insulating 97 is made of fabric having flexibility. Therefore the insulating capability may be improved. This invention having been disclosed, a number of variations 25 will now become apparent to those skilled in the art. Whereas the invention is intended to encompass the foregoing preferred embodiments as well as a reasonable range of equivalents, reference should be made to the appended claims rather than the foregoing discussion of examples, in order to 30 assess the scope of the invention in which exclusive rights are claimed.

11 Industrial Applicability According to the present invention, there is provided a method for bonding a secondary gas barrier to an insulation panel wherein curing of an adhesive is perfectly carried out, 5 thereby causing the reduction of a construction period and the improvement of productivity, and thereby reducing the installation costs of the bonding equipment and the repairing costs for the uncuring and defective bonding of the adhesive. The word 'comprising' and forms of the word 'comprising' as 10 used in this description and in the claims does not limit the invention claimed to exclude any variants or additions.

Claims

1. A method for bonding a secondary gas barrier to an insulation panel in an LNG carrier or an LNG storage tank, the method comprising the steps of: applying an adhesive 40 onto the surface of the insulation panel 20; sequentially laminating the secondary gas barrier 30, a release film 50, a cushion pad 90, a heating pad 60, and a rigid plate 95 on the adhesive (40) applied on the surface of the insulation panel 20; insulating by laying an insulating sheet 97 on the rigid plate 95 for avoiding dispersion of heat, heating the adhesive 40 up to a temperature having best bonding characteristics by using the heating pad 60; pressurizing through a pressurizing device 70 the adhesive provided between the secondary gas barrier 30 and the insulation panel 20 under an even pressure by using the elastic force of the cushion pad 90 and the rigidity of the rigid plate 95; and hardening the adhesive completely by maintaining the heating temperature under the pressurizing state at a given constant level to conduct full curing of the adhesive 40.

2. The method according to claim 1, wherein the insulating sheet 97 has single layer or multi layers and is made of organic fabric coated with aluminum, inorganic fabric coated with aluminum, nonwoven fabric coated with aluminum foil, organic fabric coated with thermosetting 13 resin or thermoplastic resin, or inorganic fabric with coated thermosetting resin or thermoplastic resin.

3. The method according to claim 1, wherein the heating pad 60 is formed of a heating means 62 covered with coating material 64.

4. The method according to claim 3, wherein the heating means 62 is formed of any one selected from a carbon plane heating element 62a, a metal heating wire 62b, and a ceramic heating element 62c, and the coating material 64 is formed of any one selected from a thermosetting resin, a thermal plastic resin, and a composite material made of a fabric or an organic or inorganic textile.

5. The method according to any one of claims 1 to 3, wherein the cushion pad 90 is formed of a synthetic resin or rubber.

6. The method according to any one of claims 1 to 3, wherein the rigid plate 95 is formed of a plywood, a honeycomb panel, or a laminated board.