A fast-reacting epoxy adhesive film, its preparation method and its application

Abstract

The present invention provides a fast-reacting epoxy adhesive film, a preparation method thereof and an application thereof. The epoxy adhesive film of the present invention comprises a substrate layer, an epoxy adhesive layer and a release film layer which are sequentially stacked. By weight percentage, the adhesive of the epoxy adhesive layer comprises the following raw material components: 40% to 60% of epoxy resin, 20% to 40% of toughening agent, 5% to 20% of filler, 5% to 15% of curing agent, wherein the curing agent comprises a first curing agent and a second curing agent. The first curing agent is an isocyanate-capped imidazole curing agent with a deblocking temperature of 60°C to 90°C, and the second curing agent is an isocyanate-capped imidazole curing agent with a deblocking temperature of 90°C to 120°C, and the deblocking temperature of the first curing agent is less than that of the second curing agent. The epoxy adhesive film of the present invention has good and stable adhesiveness, can react rapidly (within dozens of seconds) at a relatively high temperature (160 to 180°C) in a short time, and has good storage stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of tapes, and particularly relates to a fast-reacting epoxy adhesive film, a preparation method thereof, and an application thereof. Background Art

[0002] So far, flexible printed circuit boards (FPCs) have become one of the faster-growing varieties in the printed circuit industry due to their light weight, thinness, small size, flexibility, and three-dimensional wiring capabilities. In the current rapid development of the electrical and electronics industries, it meets the needs of the development of electronic products towards being lightweight, small-sized, high-density, and highly reliable, and has become an essential and important part of electronic products. Its application scope has been continuously expanding, and the usage has also been increasing year by year. Twenty years ago, there were already 30 to 40 FPC manufacturers in China, with an output value reaching 3 billion yuan.

[0003] The basic properties of printed circuit boards depend on the performance of the base substrate. Therefore, to improve their performance, it is necessary to first improve the performance of the base substrate, and the same is true for flexible printed circuit boards (FPCs). The structure of the FPC base substrate usually consists of three layers, including an insulating film, an adhesive, and a copper foil (or stainless steel SUS). Among them, the designability of the adhesive performance is relatively the largest, and it has a great impact on the quality of the final FPC substrate performance. Therefore, numerous adhesives related to FPC substrate bonding have emerged in an endless stream. After nearly 50 years of development, the adhesives used for FPC substrates at home and abroad are mainly of two types: modified epoxy resin-based (EP) and polyacrylate-based (PEA). In order to obtain greater economic benefits, raw material cost and production efficiency are two crucial factors. In terms of cost, epoxy resin-based adhesives with lower costs while ensuring that the performance meets the requirements will be more favored. In terms of production efficiency, a faster reaction rate of the adhesive is particularly crucial for improving production efficiency. Conventional solvent-based adhesives (except for microcapsule types) are difficult to achieve rapid reactions at relatively high temperatures (160 - 180 °C) (the fastest requires at least several minutes). During the use of traditional pure adhesive films for FPC bonding, high temperature and high pressure are often required, and the time is as long as dozens of minutes. Even the later-emerged fast-pressing process shortens the time to dozens of seconds, but post-baking and curing are still required, which greatly wastes manpower and production capacity. When using epoxy adhesive films to achieve rapid reactions, it is also necessary to consider that they have a long storage period (at room temperature) to maintain their good performance, including good adhesiveness, etc. Therefore, many conventional solvent-based adhesives (with low requirements for the preparation environment, soluble in conventional industrial solvents such as methyl ethyl ketone and ethanol, suitable for production by many relatively low-end enterprises) can no longer meet the market's needs, requirements, and competition from peers. Therefore, it is extremely urgent to develop an epoxy adhesive film that can react rapidly at high temperatures and has good storage properties, which can also meet some special market needs, such as adhesives for mobile phone side key FPCs, etc. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-temperature fast-reacting epoxy adhesive film.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A quick-reaction epoxy film comprises a substrate layer, an epoxy adhesive layer and a release film layer which are stacked in sequence. The adhesive of the epoxy adhesive layer comprises the following raw material components by weight percentage:

[0007] Epoxy resin 40%~60%;

[0008] Toughening agent 20% to 40%;

[0009] Filler 5% to 20%;

[0010] Curing agent 5%~15%,

[0011] The epoxy resin is a mixture of one or more of bisphenol S epoxy resin, bisphenol A epoxy resin, novolac epoxy resin, phenol epoxy resin, and rubber modified products, polyurethane modified products, and acrylic modified products of the above resins.

[0012] The curing agent includes a first curing agent and a second curing agent, the first curing agent is an isocyanate-terminated imidazole curing agent with a deblocking temperature of 60°C to 90°C, the second curing agent is an isocyanate-terminated imidazole curing agent with a deblocking temperature of 90°C to 120°C, and the deblocking temperature of the first curing agent is lower than the deblocking temperature of the second curing agent.

[0013] Preferably, the weight ratio of the first curing agent to the second curing agent is (2-4):1.

[0014] Further preferably, the weight ratio of the first curing agent to the second curing agent is (2.4-3.6):1.

[0015] Preferably, the imidazole curing agent is some modified latent imidazoles, including but not limited to CUREZOL2MZ-A of Shikoku Chemical, GY8000K of Huakai, and some isocyanate-modified curing agents.

[0016] Further preferably, the isocyanate-modified imidazole curing agent is one or more isocyanate-terminated imidazole curing agents having deblocking temperatures of 60° C., 90° C., 110° C. and 120° C., respectively.

[0017] According to some preferred embodiments, the first curing agent is IPDI-2E4MI having a deblocking temperature of 60°C, and the second curing agent is IPDI-2E4MI having a deblocking temperature of 90°C.

[0018] Preferably, the epoxy resin is one or a mixture of two or more of bisphenol A epoxy, phenolic epoxy, and rubber-modified epoxy.

[0019] Preferably, the toughening agent is one or more of nitrile rubber, acrylic rubber, and polysulfone.

[0020] More preferably, the nitrile rubber is a nitrile rubber capped with carboxyl, hydroxyl, and amine groups, which has good affinity with the resin.

[0021] More preferably, the nitrile rubber includes, but is not limited to, CTBN 1300X13 and ATBN1300X21 such as CVC; the acrylic rubber includes, but is not limited to, HyTemp acrylic rubber 4051CG and AR12; the polysulfone includes, but is not limited to, P1700, P3500, P3700 of Solvay, S2010, S3010, S6010 of BASF, and VT5H of Switzerland.

[0022] Preferably, the filler is an inorganic filler and / or an organic filler.

[0023] Preferably, the organic filler includes, but is not limited to, the halogen-free phosphorus-based filler DISFLAMOLL DPO of Lanxess Germany, the phosphite filler OP935 of Clariant Chemicals, and the phosphite fillers Hy-803 and Hy-935 of Huaya.

[0024] Preferably, the inorganic filler includes, but is not limited to, talcum powder, silica powder, aluminum hydroxide, and titanium dioxide.

[0025] Preferably, the epoxy resin is a mixture of any two of epoxy resin YD134, epoxy resin NPPN-638S, epoxy resin SQAN201, and epoxy resin NPES901, and the mass ratio of the two epoxy resins is 1:0.5 to 1.5. By appropriately using specific epoxy resins, on the one hand, the adhesiveness and stability of the adhesive can be improved by using higher activity, and the storage property of the adhesive is also avoided from being affected by excessive activity. On the other hand, the heat resistance of the adhesive can be improved by adding heat-resistant epoxy resin.

[0026] According to some preferred embodiments, the epoxy resin is a mixture of epoxy resin NPES901 and epoxy resin NPPN-638S or epoxy resin YD134. Preferably, the weight ratio of epoxy resin NPES901 and epoxy resin NPPN-638S or epoxy resin YD134 is (1.2 to 1.5):1.

[0027] Preferably, by weight percentage, the adhesive of the epoxy adhesive layer comprises the following raw material components:

[0028]

[0029] Preferably, both the base material layer and the release film layer are made of polyester film, and a release agent is provided on the surfaces of the base material layer and the release film layer. The release agent is a long-chain alkyl compound or a silicone polymer. The release force of the base material layer is 50-100 g, and the release force of the release film layer is 5-20 g. The base material layer is a heavy release layer, and the release film layer is a light release layer.

[0030] Preferably, the thickness of the epoxy adhesive layer is 10-25 μm.

[0031] Preferably, the thickness of the base material layer is 50-80 μm.

[0032] Preferably, the thickness of the release film layer is 20-25 μm.

[0033] The present invention also provides a method for preparing the above-mentioned fast-reacting epoxy adhesive film. The preparation method includes the following steps:

[0034] (1) Add epoxy resin, toughening agent, filler, and curing agent to an organic solvent, and mix to obtain a glue solution;

[0035] (2) Coat the glue solution on the base material layer, dry the organic solvent at 60°C-100°C, and then compound it with a release film to obtain the fast-reacting epoxy adhesive film.

[0036] Preferably, the drying temperature is 60-80°C, and the drying time is 5-10 min.

[0037] According to the types of resin and curing agent, the bonding interface of the adhesive may also show phenomena such as orange peel texture or bubble points due to actual application conditions such as high temperature. For specific performance requirements such as temperature resistance, the selection and combination of resin and curing agent are very important. By optimizing the formula of the epoxy adhesive, the present invention obtains a thermosetting adhesive that can react quickly at a relatively high temperature and can maintain a relatively high bonding strength for a long time. While providing an effective solution for the efficient production of actual FPC, it also meets some special market demands.

[0038] The present invention also provides the application of the above-mentioned fast-reacting epoxy adhesive film in the bonding of FPC base materials. The fast-reacting epoxy adhesive film is used to bond an insulating film and a metal sheet together.

[0039] Preferably, the insulating film is a polyester film or a polyimide film

[0040] Preferably, the thickness of the insulating film is 25-100 μm.

[0041] Preferably, the metal plate is made of stainless steel SUS or copper foil.

[0042] Preferably, the thickness of the metal plate is 200-500 μm.

[0043] Preferably, the release film layer and the substrate layer in the quick-reacting epoxy film are torn off, and hot pressed between a polyester film or a polyimide film and a copper foil or stainless steel SUS, the hot pressing temperature is 160°C to 180°C, the hot pressing pressure is 0.5 to 2Mpa, and the hot pressing time is 15 to 25s.

[0044] The invention overcomes the problem that traditional adhesives, especially adhesives for FPC, cannot be cured quickly, and is simple to prepare and easy to implement.

[0045] The present invention overcomes the poor storage problem of the epoxy system by combining a specific curing agent with the overall adhesive formula, and further utilizes the curing agent itself to be able to self-unseal at medium and high temperatures to achieve a rapid reaction of the system, and the use of curing agents with different unsealing temperatures can achieve a rapid reaction while further ensuring the storage of the adhesive. The process preparation operation is simple, there is no special reaction, and it is beneficial to environmental protection.

[0046] Compared with the prior art, the present invention has the following advantages:

[0047] The invention optimizes the formula of the epoxy adhesive, so that the epoxy film obtained has good and stable adhesion, can react quickly (within tens of seconds) at a relatively high temperature (160° C. to 180° C.) in a short time, and has good storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a schematic structural diagram of a fast-reacting epoxy film according to an embodiment,

[0049] In the figure: 1, release film layer; 2, adhesive layer; 3, substrate layer. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0051] In the following examples and comparative examples, unless otherwise specified, the raw materials used can all be commercially available products.

[0052] In the following examples and comparative examples, some of the raw materials are from the following sources:

[0053] Epoxy resin YD134, Guodu Chemical;

[0054] Epoxy resins NPES901, NPPN - 638S, Nan Ya Plastics Corporation, Taiwan Province, China;

[0055] Nitrile rubber CTBN 1300X13, CVC, USA;

[0056] Phosphate filler Hy - 935, Shenzhen Huiya;

[0057] DDS, Asahi Kasei Corporation, Japan;

[0058] (Unsealing at 60°C) IPDI - 2E4MI, (Unsealing at 90°C) IPDI - 2E4MI, Suzhou Sunwave Technology;

[0059] 2MZA - PW, Shikoku Kasei Co., Ltd., Japan.

[0060] The technical solutions and effects of the present invention will be further elaborated below in combination with specific examples and comparative examples.

[0061] Example 1

[0062] This example provides a fast - reacting epoxy adhesive film, the structure of which is as Figure 1 shown, including a base material layer 3, an epoxy adhesive layer 2, and a release film layer 1 stacked in sequence from bottom to top. Among them, the base material layer is a polyester film (heavy release layer) with a release agent coated on its surface and a release force of 80 g, and the thickness of the base material layer is 60 μm. The release film layer is a polyester film (light release layer) with a release agent coated on its surface and a release force of 15 g, the thickness of the release film layer is 20 μm, and the thickness of the epoxy adhesive layer is 20 μm.

[0063] The adhesive in the epoxy adhesive layer is composed of the following components in parts by weight:

[0064] Epoxy resin YD134 / 40 parts, epoxy resin NPPN - 638S / 60 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy - 935 / 20 parts; curing agent: (Unsealing at 60°C) IPDI - 2E4MI / 18 parts.

[0065] Preparation method:

[0066] (1) Add the above raw materials to 100 parts of methyl ethyl ketone for dissolution or dispersion, and mix to obtain a glue solution.

[0067] (2) Coat the glue solution on the base material layer, dry the solvent at 80°C for 5 min, and then laminate with the release film to obtain a fast - reacting epoxy adhesive film.

[0068] Example 2

[0069] This embodiment provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Embodiment 1. The only difference from Embodiment 1 is that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this embodiment is composed of the following components in parts by weight: Epoxy resin YD134 / 60 parts, Epoxy resin NPPN-638S / 40 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: (unblocked at 60°C) IPDI-2E4MI / 14 parts, (unblocked at 90°C) IPDI-2E4MI / 4 parts.

[0070] Embodiment 3

[0071] This embodiment provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Embodiment 1. The only difference from Embodiment 1 is that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this embodiment is composed of the following components in parts by weight: Epoxy resin YD134 / 60 parts, Epoxy resin NPPN-638S / 40 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: (unblocked at 90°C) IPDI-2E4MI / 18 parts.

[0072] Embodiment 4

[0073] This embodiment provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Embodiment 1. The only difference from Embodiment 1 is that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this embodiment is composed of the following components in parts by weight: Epoxy resin NPES901 / 60 parts, Epoxy resin NPPN-638S / 40 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: (unblocked at 60°C) IPDI-2E4MI / 14 parts, (unblocked at 90°C) IPDI-2E4MI / 4 parts.

[0074] Embodiment 5

[0075] This embodiment provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Embodiment 1. The only difference from Embodiment 1 is that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this embodiment is composed of the following components in parts by weight: Epoxy resin NPES901 / 60 parts, Epoxy resin YD134 / 40 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: (unblocked at 60°C) IPDI-2E4MI / 14 parts, (unblocked at 90°C) IPDI-2E4MI / 4 parts.

[0076] Comparative Example 1

[0077] This comparative example provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Example 1. The difference from Example 1 is only that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this example is composed of the following components in parts by weight: epoxy resin YD134 / 100 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: (60°C deblocking) IPDI-2E4MI / 18 parts.

[0078] Comparative Example 2

[0079] This comparative example provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Example 1. The difference from Example 1 is only that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this example is composed of the following components in parts by weight: epoxy resin NPES901 / 60 parts, epoxy resin NPPN-638S / 40 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: DDS / 24 parts; epoxy curing accelerator: 2MZA-PW / 5 parts.

[0080] Comparative Example 3

[0081] This comparative example provides a fast-reacting epoxy adhesive film, whose structure is the same as that of Example 1. The difference from Example 1 is only that the components of the adhesive in the epoxy adhesive layer are slightly different. The adhesive in the epoxy adhesive layer of the fast-reacting epoxy adhesive film in this example is composed of the following components in parts by weight: epoxy resin NPES901 / 60 parts, epoxy resin NPPN-638S / 40 parts; toughening agent: CTBN 1300X13 / 60 parts; filler; Hy-935 / 20 parts; curing agent: dicyandiamide / 6.2 parts; epoxy curing accelerator: 2MZA-PW / 5 parts.

[0082] The fast-reacting epoxy adhesive films of each example and each comparative example were respectively used for FPC substrate pasting, and the PI film was adhered to the stainless steel plate (or copper foil) to obtain an FPC substrate assembly. The pasting method is as follows:

[0083] Tear off the release film layer of the fast-reacting epoxy adhesive films of each example and each comparative example, pre-paste this side onto the stainless steel plate (or copper foil), perform roll pasting at 80°C / 0.5 Mpa / 2 s, so that the epoxy adhesive film tightly adheres to the stainless steel plate (or copper foil), then tear off the substrate layer, pre-paste a 100-μm PI film on this side, and perform hot pressing treatment at 180°C / 25 s / 2 Mpa to obtain the corresponding FPC substrate assembly.

[0084] The quality of the fast-reacting epoxy films of the embodiments and comparative examples was evaluated. The results are shown in Table 1.

[0085] Table 1

[0086]

[0087] OK: It means that the bending sample has no delamination or debonding. Otherwise, it means "NG"

[0088] “○” represents qualified performance, “◎” represents excellent performance, “△” represents average performance, and “×” represents poor performance.

[0089] Evaluation method:

[0090] Bonding strength: After the FPC substrate component sample is hot-pressed, use a small utility knife to gently cut the PI film into 1cm×20cm strips (the stainless steel plate is difficult to be cut with a utility knife), push away the PI film at the end of the longer side (initially with a small section of PI for tearing off the stainless steel), peel it at 90°, and peel it at a speed of 100mm / min.

[0091] Gel time test method: Use a viscometer with a built-in heat preservation device to test the viscosity of the mixed system of curing agent and resin at 180°C at regular intervals. Stop the test when the viscosity reaches the critical value corresponding to the gel point. The time at this time is the gel time (test at 180°C and stir the mixed system of curing agent and resin with a glass cup at regular intervals until obvious wire drawing and climbing phenomena appear, indicating that the system has reached a gel state. The viscosity at this time is defined as the critical value of the viscosity corresponding to the gel point).

[0092] Calculation of storage time at room temperature: Test the peel strength of the film every day and observe the state of the film when it is transferred. If the peel strength of the film is lower than 8N / cm on the nth day or the film is too brittle when transferred and only part of the film can be transferred to the stainless steel sheet (or copper foil), it is considered to be invalid. The storage time of the film at room temperature is n-1 days.

[0093] Separation interface situation: "Glue / glue" represents the cohesive failure of the adhesive, which is considered an ideal state; "Glue / PI, glue / glue (partial)" represents the separation or partial separation of the adhesive and the adhesive film (PI film), both of which are considered irrational states.

[0094] Bending process 120℃ / 1h baking test: Since the FPC needs a 120℃ / 1h baking process in the subsequent assembly, the prepared FPC substrate component sample is bent 90° with the glue side facing outward, and then the sample is baked at 120℃. After the test, observe whether there is any delamination or debonding. If there is, it is recorded as NG, otherwise it is recorded as OK.

[0095] The above has described the present invention in detail, aiming to enable those skilled in this field of technology to understand the content of the present invention and implement it. However, it should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A fast-reacting epoxy adhesive film, which comprises a base material layer, an epoxy adhesive layer and a release film layer stacked in sequence, and is characterized in that, By weight percentage, the adhesive in the epoxy adhesive layer comprises the following raw material components: Epoxy resin: 40% - 60%; Toughening agent: 20% - 40%; Filler: 5% - 20%; Curing agent: 5% - 15%. The epoxy resin is a mixture of any two of epoxy resin YD134, epoxy resin NPPN-638S and epoxy resin NPES901, and the weight ratio of the two epoxy resins is 1:0.5 - 1.

5. The curing agent includes a first curing agent and a second curing agent. The first curing agent is an isocyanate-capped imidazole curing agent with a deblocking temperature of 60°C - 90°C, and the second curing agent is an isocyanate-capped imidazole curing agent with a deblocking temperature of 90°C - 120°C, and the deblocking temperature of the first curing agent is lower than that of the second curing agent.

2. The fast-responsive epoxy adhesive film according to claim 1, wherein The weight ratio of the first curing agent to the second curing agent is (2 - 4):

1.

3. The fast-responsive epoxy adhesive film according to claim 1, wherein The toughening agent is one or more of nitrile rubber, acrylic rubber and polysulfone; And / or, the filler is an inorganic filler and / or an organic filler.

4. The fast-reactive epoxy adhesive film according to claim 1, wherein By weight percentage, the adhesive in the epoxy adhesive layer comprises the following raw material components: Epoxy resin: 45% - 55%; Toughening agent: 25% - 35%; Filler: 5% - 20%; Curing agent: 8% - 12%.

5. The quick-response epoxy adhesive film according to claim 1, wherein Both the base material layer and the release film layer are made of polyester film. A release agent is provided on the surfaces of the base material layer and the release film layer. The release agent is a long-chain alkyl compound or an organosilicon polymer. The release force of the base material layer is 50 - 100 g, and the release force of the release film layer is 5 - 20 g; And / or, the thickness of the epoxy adhesive layer is 10 - 25 μm; And / or, the thickness of the base material layer is 40 - 50 μm; And / or, the thickness of the release film layer is 20 - 25 μm.

6. The preparation method of the fast-responsive epoxy adhesive film according to any one of claims 1 to 5, characterized in that, The preparation method comprises the following steps: (1) Add epoxy resin, toughening agent, filler and curing agent into an organic solvent, and mix to obtain a glue solution; (2) Coat the glue solution on the base material layer, dry the organic solvent at 60°C - 100°C, and then laminate it with a release film to obtain the fast-reacting epoxy film.

7. Application of the fast-responsive epoxy adhesive film according to any one of claims 1 to 5 in bonding of FPC substrates, characterized in that, The fast-reacting epoxy film is used to bond an insulating film and a metal sheet together.

8. The application according to claim 7, wherein Tear off the release film layer and the base material layer in the fast-reacting epoxy film, and hot-press it between the insulating film and the metal sheet. The hot-pressing temperature is 160°C - 180°C, the hot-pressing pressure is 0.5 - 2 Mpa, and the hot-pressing time is 15 - 25 s.

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