WO2004108401A2

WO2004108401A2 - Flange section seal material

Info

Publication number: WO2004108401A2
Application number: PCT/US2004/016329
Authority: WO
Inventors: Yasuhiro Mino
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2003-06-03
Filing date: 2004-05-25
Publication date: 2004-12-16
Anticipated expiration: 2005-12-03
Also published as: WO2004108401A3; JP2004360756A

Abstract

A flange section seal material that allows satisfactory and easy sealing of flange sections for vehicles. A flange section seal material for sealing of the flange section of metal panels in a vehicle, comprising at least two layers of an inner layer and an outer layer which are formed into the desired shape allowing it to sandwich and cover the flange section. The inner layer contains a hot-melt/fluidizable thermosetting resin with a curing temperature of 80-200° C, the outer layer exhibits no significant fluidizing shape change at 80-200° C, and the inner layer contains foaming beads.

Description

Flange Section Seal Material

Field of the Invention The present invention relates to a flange section seal material for sealing of a superimposed flange section of metal panels for vehicles.

Background of the Invention

Metal panel joints, i.e., flange sections, formed by superimposing metal panels (steel sheets) for vehicles, are sealed by sealing materials which provide a satisfactory outer appearance while preventing rust due to moisture and the like that can penetrate into the flange section. Sealing of flange sections has commonly been accomplished in the past by applying a paste-like sealer and then heating it for curing. Here, as shown in Fig. 1, a paste section 4 is formed by an extension of one of the metal panels 3 in order to prevent dripping of the sealer 2 from the flange section 1, and the sealer 2 is applied onto this paste section 4. i this method, however, the formation of the paste section requires extra metal panel and thus impedes weight reduction of the vehicle. In addition, a design is necessary such that the panel forming the paste section is positioned on the underside, while adequate sealing can only be accomplished by a design in which a wide paste section is formed to ensure a sufficient seal material adhesion area. Handling of conventionally used paste-like sealers has also required skill to achieve a consistent coating amount and coating width and a uniform outer appearance after coating, while considerable time has also been necessary for coating. Moreover, the paste section is rarely horizontal, as most areas are either sloping or vertical. For this reason it has been necessary to adjust the viscosity of the paste to be high enough to allow it to support its own weight. Most of such paste-like seal materials are composed mainly of vinyl chloride sols, which have posed an environmental problem in recent years.

Techniques have also been developed for improving the problems of such pastelike seal materials. For example, Japanese Unexamined Patent Publication HEI No. 3- 35076 discloses a seal material wherein a pressure-sensitive adhesive layer is provided on at least one side of a material containing a thermoplastic resin and a thermosetting agent. However, since these materials are attached by an adhesive layer, care must be taken to avoid inclusion of air bubbles during attachment, and reattachment after a first attachment is difficult. Furthermore, since a release liner is required to protect the adhesive layer, the release liner becomes a waste product during the operation.

Japanese Unexamined Patent Publication HEI No. 4-192280 discloses a sealing method wherein metal panels are spot welded together through a foaming sealer, and a paste-like sealer is applied at the edges of both panels. The steps of this method, however, have been time consuming because of the need to adhere the foaming spot sealer before attachment of the panels and then apply the sealer to the edges after spot welding.

Japanese Unexamined Patent Publication SHO No. 64-16479 discloses a seal material obtained by molding a material composed mainly of a synthetic resin material into the desired shape and fitting and welding the molded article onto the joint section. However, because the seal material disclosed in this publication is a thermoplastic material, it softens and becomes fluidized whenever heat is applied, such that melt flow occurs during the heating cycle in the application step and results in cracks or wrinkles in the coated film.

Summary of the Invention

One object of the present invention can be to provide a flange section seal material that allows satisfactory and easy sealing of flange sections in vehicles. In one aspect of the present invention a flange section seal material is provided for sealing of the flange section of metal panels in a vehicle. The flange section seal material comprises at least two layers of an inner layer and an outer layer which are formed into the desired shape allowing it to sandwich and cover the flange section. The inner layer contains a hot-melt/fluidizable thermosetting resin with a curing temperature of 80-200°C, the outer layer exhibits no significant fluidizing shape change at 80-200°C, and the inner layer contains foaming beads.

With this type of seal material, the thermosetting resin in the inner layer is hot- melted and fluidizes when heated after fitting onto the flange section, while the outer layer maintains the molten resin without changing its form, and therefore a satisfactory sealing can be accomplished without impairment of the seal performance or outer appearance due to fluid dripping. Furthermore, foaming beads contained in the inner layer are foamed by heating, thereby making it possible to fill the space surrounded by the outer layer with the resin in the inner layer without forming any unfilled portion, and therefore adequate sealing can be accomplished.

Brief Description of the Drawings Fig. 1 shows the cross-section of a flange section that has been sealed with a conventional paste-like sealer.

Fig. 2 shows the cross-section of an embodiment of a seal material according to the present invention.

Fig. 3 shows the cross-section of a seal material composed of a single layer for comparison.

Figs. 4(a) and 4(b) show the cross-section of a flange section formed by metal panels (cationic electrodeposition coated sheets).

Figs. 5(a) and 5(b) are a pair of schematic drawings showing the directions of the metal panels for the shape retention test. Fig. 6 is a schematic drawing showing the constitution in a panel gap seal test.

Fig. 7 is a schematic drawing showing the constitution in an antigravity seal test. Fig. 8 is a schematic drawing showing the constitution in a spot indentation masking test.

Fig. 9 is the cross-section showing the constitution of a flange section that has been sealed with a seal material of the present invention.

Fig. 10 is the cross-section showing the constitution of a flange section that has been sealed with a seal material containing no foaming beads.

Detailed Description of the Invention The present invention will now be described with reference to the accompanying drawings. Fig. 2 shows the cross-section of an embodiment of a seal material for a flange section of the present invention. The seal material 10 for the flange section is a molded article which has a U-shaped cross-sectional shape allowing it to sandwich and cover the , flange section, and comprises at least two layers of an inner layer 12 and an outer layer 11. The inner layer 12 contains a hot-melt/fluidizable thermosetting resin with a curing temperature of 80-200°C. The inner layer has a hot-melt/fluidizable thermosetting composition which contains such a thermosetting resin. The hot-melt/fluidizable thermosetting composition usually includes an epoxy-containing material and a curing agent for the epoxy-containing material, and can be fluidized by heating. The epoxy- containing material includes an epoxidized thermoplastic resin, and preferably a low- hygroscopic epoxidized thermoplastic resin. That is because when a low-hygroscopic resin is used, it prohibits the seal material from swelling due to moisture foaming during the thermosetting which interferes the seal of the flange section.

The epoxy-containing material in the thermosetting composition of the inner layer 12 preferably contains a low-hygroscopic epoxidized thermoplastic resin, as mentioned above. Here, "low-hygroscopic" means that the epoxidized thermoplastic resin has a saturation water absorption of no greater than 0.2 wt% at 35°C, 80% RH. Such an epoxidized thermoplastic resin will usually have a solubility parameter (SP) of about 9 or below. Throughout the present specification, the sqlubility parameter is defined according to the Small formula (P. A. Small, J. Appl. Chem., 3, 71 (1953)). An epoxidized thermoplastic resin is a thermoplastic resin with epoxy groups. A thermoplastic resin will generally provide the thermosetting composition with a consistent shape. The epoxidized thermoplastic resin also contributes to the thermosetting reaction due to the presence of the epoxy groups. The cured thermosetting composition will thus be provided with heat resistance or durability.

The epoxidized thermoplastic resin usually has a molecular weight of 1000-10,000 in consideration of the fluidity during the shaping step and during hot melting. The epoxidized thermoplastic resin also usually has 200-15,000 epoxy equivalents in consideration of the heat resistance, durability and water absorption.

A typical example of the aforementioned epoxidized thermoplastic resin is an epoxidized ethylene-based thermoplastic resin. This resin exhibits low hygroscopicity due to the presence of the ethylenic portion. Ethylene-glycidyl (meth)acrylate copolymer is preferred as an epoxidized ethylene-based thermoplastic resin. Ethylene-glycidyl (meth)acrylate copolymer is epoxidized polyethylene, which is disclosed as a component of adhesives and hot-melt compositions in Japanese Unexamined Patent Publication HEI No. 9-137028, Japanese Unexamined Patent Publication HEI No. 10-316955 and elsewhere, and it is usually obtained by copolymerization of ethylene and glycidyl methacrylate. Ethylene-glycidyl (meth)acrylate copolymer therefore comprises an ethylene portion and a glycidyl (meth)acrylate portion. The ethylene portion thereof contributes to low hygroscopicity of the thermosetting composition, while the glycidyl (meth)acrylate portion contributes to adhesion with cationic electrodeposition-coated automobile steel sheets (metal panels) and the outer layers of flange section seal materials. The ethylene-glycidyl (meth)acrylate copolymer preferably comprises ethylene and glycidyl (meth)acrylate in a monomer weight ratio in the range of 50:50-99: 1. With an ethylene-glycidyl (meth)acrylate copolymer containing ethylene above this range, it is difficult to yield a cured product exhibiting the desired mechanical strength and durability. Conversely, if the ethylene-glycidyl (meth)acrylate copolymer contains ethylene below this range, it may not be possible to obtain the desired low hygroscopicity. A typical ethylene-glycidyl (meth)acrylate copolymer melts easily at a relatively low temperature of about 80°C or below, and when a thermosetting composition containing it is heated to fluidity to accomplish sealing, high fluidity is obtained and the uniformity and smoothness are also high as a result. Also, since kneading can be carried out at relatively low temperature during the heating and mixing process during manufacture of the inner layer material, the risk of reaction between the thermosetting components and the curing agent during the kneading is reduced, and a curing agent of higher reactivity can therefore be selected.

So long as the effect of the present invention is not impaired, the epoxidized thermoplastic resin may even be an ethylene-glycidyl (meth)acrylate terpolymer obtained by copolymerization or graft polymerization of a third component with ethylene and glycidyl (meth)acrylate. Examples of such terpolymers include those obtained by copolymerization with alkyl (meth)acrylates, vinyl acetate and the like, while graft polymers include those obtained by grafting polystyrene, polyalkyl (meth)acrylate, acrylonitrile-styrene copolymer and the like. Another typical example of an epoxidized thermoplastic resin is an epoxidized styrene-based thermoplastic resin, which exhibits low hygroscopicity due to the presence of a conjugated diene. An epoxidized styrene-based thermoplastic resin is a block copolymer comprising, for example, a hard segment composed of polystyrene and a soft segment composed of epoxidized polybutadiene which confers rubber elasticity to the elastomer. Alternatively, an epoxidized polyisoprene may be used instead of an epoxidized polybutadiene, or together with an epoxidized polybutadiene. The glass transition temperature (Tg) of an epoxidized styrene-based thermoplastic resin is usually very low from -70 to -50°C, and this allows reinforcement of the durability (particularly the vibration tolerance) of the cured thermosetting composition at temperatures as low as about -30°C. Examples of such epoxidized styrene-based thermoplastic resins include styrene- epoxidized butadiene-styrene copolymer and styrene-epoxidized isoprene-styrene copolymer. h either case, the epoxidation is accomplished by epoxidation of the unsaturated bond of the conjugated diene.

Epoxidized thermoplastic resins as described above are preferably present at 10-90 wt% in the thermosetting composition. At less than about 10 wt% the heat resistance is reduced, and at greater than about 90 wt% the amount of filler that may be added, as described below, is relatively lower such that a low linear expansion coefficient cam ot be achieved.

The epoxy-containing material may contain a liquid or solid epoxy resin such as a bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, novolac-type epoxy resin or glycidylamine-type epoxy resin in addition to the aforementioned epoxidized thermoplastic resin, as these can give the thermosetting composition further reinforced heat resistance, durability and adhesion with electrodeposition coated steel sheets. Preferred epoxy resins are relatively low polar epoxy resins such as, for example, hydrogenated bisphenol A-type epoxy resins, alicyclic epoxy resins, linear aliphatic epoxy resins such as butadiene skeleton epoxy resins, and glycidyl ester-type epoxy resins such as diner acid-modified epoxy resins. This is because such epoxy resins have excellent compatibility with the low-hygroscopic components, for example, the ethylene portion and butadiene portion, in the aforementioned epoxidized thermoplastic resins. It also can prevent absorption of water into the cured composition and is advantageous during heating for the steps of automobile painting, etc. The amount of epoxy resin will usually be 0-500 parts by weight, and preferably 5-400 parts by weight, with respect to 100 parts by weight of component (1), i.e. the low-hygroscopic epoxidized thermoplastic resin.

If necessary, the epoxy-containing material may also contain a compatibilizer. More specifically, a compatibilizer may be included at usually 0-300 parts by weight and preferably 1-100 parts by weight with respect to 100 parts by weight of the epoxidized thermoplastic resin, in order to increase the miscibility between the epoxidized theπnoplastic resin and the epoxy resin. There are no particular limitations on a compatibilizer used for the present invention so long as it allows miscibility, but it preferably contains polyester resin or an ethylene-vinyl acetate (EVA) copolymer. That is because polyester resin, in particular, when mixed at a certain proportion with the epoxidized thermoplastic resin, not only prevents separation between the epoxidized thermoplastic resin and the epoxy resin, but can also vastly improve the fluidity at the curing temperature of the thermosetting composition (80-200°C).

The curing agent cures the epoxy groups in the epoxy-containing material to form a crosslinked structure in the thermosetting composition, to allow a cured product to be obtained. According to the present invention, there are no restrictions on the curing agent so long as it can give a cured product. The curing agent may therefore include, for example, amine compounds such as dicyandiamide, acryl compounds and rosins with carboxyl groups in the molecule (including acid anhydrides), imidazole derivatives, BF₃ complexes, organic acid hydrazides, diaminomaleonitriles and melamines, as well as mixtures thereof. The degree of polarity of the curing agent is not important. However, for curing of the glycidyl groups of an ethylene-glycidyl (meth)acrylate copolymer, it is necessary to use a curing agent containing an acryl compound or a rosin with a carboxyl group in the molecule, as disclosed in Japanese Unexamined Patent Publication HEI No. 9-137028 and Japanese Unexamined Patent Publication HEI No. 10-316955. Compared to highly polar curing agents which are incompatible with ethylene-glycidyl (meth)acrylate copolymers and substantially cannot react therewith, such a curing agent is more easily miscible with ethylene-glycidyl (meth)acrylate copolymers and more readily cures the glycidyl groups of ethylene-glycidyl (meth)acrylate copolymers.

The curing agent may be used in combination with a curing accelerator. In particular, a curing accelerator containing a phenol, imidazole derivative or tertiary amine can be advantageously used for reaction between a carboxyl-containing curing agent and the epoxy.

The thermosetting composition preferably further includes a filler containing, for example, calcium carbonate, silica or a mixture thereof. A filler can lower the linear expansion coefficient of the cured product. As a result, the cured product will have a lower linear expansion coefficient and reduced shrinkage at low temperature, and less stress will be exerted on coatings formed by application of automobile paints onto the seal material, especially with temperature changes at low temperature. Such formed coatings will therefore be resistant to cracking even at low temperature.

When such a filler is added, the thermosetting composition will often exhibit an undesirable flow property during hot melting. The thermosetting composition of the present invention may therefore also contain a plasticizer. Including a plasticizer will ensure that the thermosetting composition maintains the desired fluidity. This is because plasticizers generally have low viscosity and can help to improve the fluidity of the composition.

Plasticizers that may be added to the thermosetting composition include plasticizers containing, for example, phthalic acid esters such as di-2-ethylhexyl phthalate or diisononyl phthalate, adipic acid esters, epoxidized fatty acid esters, epoxidized soybean oil, epoxidized linseed oil, liquid terpene resins, liquid terpene-phenol copolymers, liquid terpene-styrene copolymers, azelaic acid esters, sebacic acid esters, epoxy hexaphthalic acid esters and mixtures thereof. Such plasticizers can provide flexibility to the cured thermosetting composition. They can also lower the glass transition temperature of the cured product and lower the elastic modulus even at low temperatures of -20 to -40°C. As a result, the cured product will be capable of considerable stretching at such low temperatures, and improvement may be achieved in the dynamic durability, such as the vibration tolerance. The outer layer 11 features that it exhibits no significant fluidizing shape change at

80-200°C. The material composing the outer layer 11 is not particularly restricted so long as it can support its shape in this temperature range. As such materials there may be mentioned theπnoplastic resins that exhibit no molten fluidity at the above specified temperature range, such as general use engineering plastics such as polyamide resin, polyacetal, polybutylene terephthalate and modified polyphenylene oxide, special use engineering plastic synthetic resins such as polyimides, polyetherimides and polyethersulfones, and thermoplastic elastomers, for example, polystyrene-based, polyurethane-based and polyolefin-based thermoplastic elastomers, materials that they retain their shape at the above specified temperature, such as metals and vulcanized synthetic rubbers, which are typically butadiene rubber, isoprene rubber, styrene-butadiene rubber or ethylene-propylene rubber, as well as thermosetting resin such as phenol resins, melamine resins, epoxy resins, urethane resins, unsaturated polyester resins which is inhibited from fluidization upon heating to the above specified temperature range, and the like.

A resin which melt-fluidizes at the above specified temperature range such as polyethylene, polypropylene, polystyrene, ethylene-vinyl acetate copolymer, ethylene- glycidyl methacrylate copolymer, ethylene-acrylate copolymer, ethylene-ethyl acrylate copolymer and ethylene-acrylic acid copolymer can retain its shape, if its surface is crosslinked by electron beam irradiation to the extent that it has a storage elastic modulus of 5.0 x 10^s Pa or more at the above specified temperature range, and such treated resin can be used as an outer layer. In this case, irradiation dosage of 10 Mrad or more with an accelerating voltage of 200 KeV or more is preferred.

As materials for the outer layer 11, there are preferred materials which have sufficient adhesion with adjacent layers such as the inner layer 12, while also exhibiting adhesion with automobile paints (for example, organic solvent-based acryl paints or organic solvent-based alkyd paints) that are ordinarily applied over the outer layer 11. Furthermore, since the edge of the flange section will sometimes have a curved shape, the material preferably has flexibility allowing it to follow such curved shapes. From this standpoint, the material for the outer layer 11 is preferably one Similar to the material for the inner layer 12 but with low fluidity during heating. Specifically, such materials include resins preferably with a storage elastic modulus of 5.0 x 10^s Pa or greater at 80- 200°C. If the storage elastic modulus is within this range, no significant fluidity will be exhibited during heating. In order to achieve adequate flexibility, the storage elastic modulus at room temperature is preferably 1.0 x 10⁶ - 1.0 x 10⁸ Pa.

When a thermosetting composition containing such a thermosetting resin is used as the outer layer 11, it may contain the same type of curing agent, curing accelerator and filler as the thermosetting composition of the inner layer 12. The outer layer 11 may also be crosslinked by EB irradiation treatment for increased shape retention.

In the flange section seal material of the present invention, the inner layer 12 is characterized by containing foaming beads (not shown). The foaming beads are granular substances which are foamed by heating, and are preferably thermal expanding microcapsules comprising a capsule-shaped outer shell made of a polymer, which is softened by heating, and a volatile liquid foaming agent contained in the outer shell. The volatile liquid includes, for example, isobutane, isopentane, normal butane, normal pentane, neopentane and hexane, which are liquid at normal temperature and are vaporized by heating during the melting of the inner layer, and hydrocarbons including isobutane and isopentane are preferably used. Examples of the usable other volatile liquid include, but are not limited to, specific fluorenes such as trichlorofluoromethane, dichlorofluoromethane, dichlorofluoroethane, dichlorotrifluoroethane, trichlorotrifluoroethane and dichloropentafluoropropane; substitute Freons; hydrocarbons such as petroleum ether; and chlorinated hydrocarbons such as methyl chloride, methylene chloride, dichloroethylene, trichloroethane and trichloroethylene. The volatile liquid foaming agent preferably accounts for 5-30 wt% of the thermal expanding microcapsules.

The outer shell of the polymer composing the foaming beads is composed of a thermoplastic material, which is softened when heated to 100-200°C, preferably 120- 140°C, and expanded as a result of the volatilization and expansion of the volatile liquid contained therein. It is necessary that the polymer composing the outer shell has adequately large viscosity even at the heating temperature so as to maintain the capsule state without being broken upon thermal expansion. As the polymer, which meets these conditions, there can be used copolymers of one or more kinds of vinylidene chloride, acrylonitrile, methacrylonitrile and methyl methacrylate, for example, vinylidene chloride- acrylonitrile copolymer, vinylidene chloride-acrylonitrile-methyl methacrylate copolymer, acrylonitrile-methacrylonitrile copolymer, and copolymers of one more kinds of these polymers and various monomers including vinyl halide, styrene monomer, vinyl acetate, butadiene, vinyl pyridine and chloroprene. The thermoplastic resin may be crosslinked or made to be crosslinkable by crosslinking agents such as divinylbenzene, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, triacrylformal and triallyl isocyanate. Among these theπnoplastic resins, a homopolymer of (meth)acrylonitrile or a copolymer having a high (meth)acrylonitrile content, which has high expansion initiation temperature or maximum expansion temperature, is preferably used.

The non-expanded expanding microcapsule thus composed includes, for example, EXPANCEL (trade name of Nihon Phylite Co., Ltd.) and MICROSPHERE F (trade name of Matsumoto Yushi-Seiyaku Co., Ltd.). The expanding microcapsule is obtained by using the above vinylidene chloride-acrylonitrile copolymer or acrylonitrile- methacrylonitrile copolymer as the polymer for capsule-shaped outer shell and using isobutane or isopentane as the volatile liquid contained therein. For example, EXPANCEL 642 (trade name, vinylidene chloride-acrylonitrile copolymer + isobutane) is expanded at about 90°C or higher, EXPANCEL 551 (trade name, vinylidene chloride- acrylonitrile copolymer + isobutane) is expanded at about 100°C or higher, EXPANCEL

461 (trade name, vinylidene chloride-acrylonitrile copolymer + isobutane) is expanded at about 110°C or higher, and EXPANCEL 091 and EXPANCEL 092 (trade name, acrylonitrile-methacrylonitrile copolymer + isopentane) are expanded at about 130°C or higher, by about four times at most, and therefore they are expanded by about 60 times in terms of volume. Since the non-expanded particles have a diameter within a range from about several μm to several tens of μm, the non-expanded particles having a diameter of about 15 μm are expanded to form particles having a diameter of about 50 μm. The time required for expansion is approximately from 30 seconds to one minute, though it varies depending on the temperature. The size upon expansion is fixed when rapidly cooled after expansion. For example, when 1% by weight of non-expanded microcapsules

EXPANCEL are added to the thermoplastic resin composing the base of a film packaging material, the volume of the film increases by about 10-50% after foaming if the foaming degree is adjusted to 10-50 times. The volume increases by about 30-50% when 3% by weight of the microcapsules are added. The amount of the foaming beads is preferably from 0.1 to 20 parts based on 100 parts of the material for the inner layer. If the amount exceeds 20 parts, the melt flowability is likely to be lowered. On the other hand, if the amount is less than 0.1 parts, adequate expansion effect can not be exerted. Furthermore, the foaming temperature of the foaming beads, i.e. softening temperature of the outer shell is preferably lower than the melting temperature and the curing temperature of the resin in the inner layer by the following reason. That is, when the resin is not expanded upon melting and curing, a desired effect can not be exerted.

In case of sealing the flange section with the flange section seal material, as described above, sealing is accomplished by filling the space between the outer layer and the panel with the molten resin in the inner layer and curing the resin. However, if the resin in the inner layer does not exist in an amount enough to fill the space between the outer layer and the panel, the molten resin is fluidized to the lower portion of the space between the outer layer and the panel to generate the unfilled portion at the upper portion of the space. According to the present invention, when the inner layer contains the foaming beads, the resin is melted by heating and the foaming beads are foamed, and therefore volume swell of the molten resin occurs, thereby making it possible to adequately fill the space between the outer layer and the panel without remaining the unfilled portion. Furthermore, sealing can be accomplished by using a small amount of the resin as compared with the case of using no foaming beads.

To completely seal the flange section, cells in the resin filling the space between the outer layer and the panel must be closed cells. According to the present invention, when expansion is conducted using the foaming beads, the outer shell of the beads is not broken upon expansion, and therefore all cells thus obtained are closed cells. The foaming conditions must be controlled so as not to form the closed cells, though a chemical foaming agent used commonly in the production of the foam can be used in the present invention so long as the closed cells are obtained. Another layer may also be included between the inner layer 12 and outer layer 11 of the flange section seal material of the present invention. Such an additional layer include, for example, one or more barrier layers composed of a nonwoven fabric, a resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) or a metal may also be provided. Even if air bubbles infiltrate during the sealing, such a barrier layer will prevent the air bubbles from appearing on the surface.

When the material for the outer layer can be afforded adequate fluidity by shear force by the screw of a screw extrusion molding machine such as single or twin screw extruder which is widely used for molding of plastic materials, the flange section seal material of the present invention may be produced using such an extrusion molding machine, by shearing and melting the thermosetting composition (containing foaming beads) for the inner layer and the material for the outer layer, and then coextruding them into the desired shape. In cases where the material of the outer layer does not exhibit adequate plasticity and flow properties even by shearing with such a screw extruder, the production may involve application of a melt of the material for the inner layer onto the outer layer which has been molded into the desired shape. Further, apart from a profile extrusion process, a seal material can be molded in a desired shape by extruding each layer as a sheet and pressing the layers in a press machine. By fitting the flange section seal material of the present invention onto a flange section and heating at a temperature of 80-200°C, the hot-melt/fluidizable thermosetting resin of the inner layer is fluidized and the^' foaming beads are foamed, and then the resin is cured to form a seal. Here, since the outer layer exhibits no significant shape change, fluid dripping can be prevented when the resin of the inner layer is fluidized. Furthermore, the foaming beads are foamed in the fluidized resin, thereby making it possible to fill the space surrounded by the outer layer with the resin without remaining any unfilled portion. This sealing step may be caπied out during the baking step (at a heating temperature of, for example, 80-200°C) for intercoating or overcoating, which is carried out subsequently in an automobile painting line.

Examples Example 1

The following composition: (i) 60 parts by weight of ethylene-glycidyl methacrylate copolymer containing 18 wt% glycidyl methacrylate (CG5001, trade name of Sumitomo Chemical Industries), (ii) 6 parts by weight of a carboxyl group-containing rosin with an acid value of 240 mgKOH/g (curing agent, KE604, trade name of Arakawa Chemical Co.), (iii) 1.5 parts by weight of an imidazole derivative (curing accelerator, 2MOAK, trade name of Shikoku Chemical Corp.), (iv) 3 parts by weight of calcium carbonate (filler, WHITEON SB, trade name of

Shiraishi Calcium Co., Ltd.), as the inner layer, 2 parts by weight of Microsphere F-82D (trade name of Matsumoto Yushi-Seiyaku Co., Ltd.) and the following composition:

(i) 48 parts by weight of ethylene-glycidyl methacrylate copolymer containing 12 wt% glycidyl methacrylate (BONDFAST E, trade name of Sumitomo Chemical Industries),

(ii) 12 parts by weight of ethylene-glycidyl methacrylate copolymer containing 18 wt% glycidyl methacrylate (CG5001, trade name of Sumitomo

Chemical Industries), (iii) 6 parts by weight of a carboxyl group-containing rosin with an acid value of 240 mgKOH/g (curing agent, KE604, trade name of Arakawa Chemical Co.), (iv) 1.5 parts by weight of an imidazole derivative (curing accelerator, 2MOAK, trade name of Shikoku Chemical Corp.),

(v) 3 parts by weight of calcium carbonate (filler, WHITEON SB, trade name of Shiraishi Calcium Co, Ltd.), as the outer layer were kneaded with a twin-screw extruder (TSE) and subjected to shaping coextrusion to obtain a laminated body with the cross-sectional shape shown in Fig. 2. The outer layer of the laminated body was exposed to electron beam (EB) treatment (250 KeV, 30 Mrad) for crosslinking, to obtain a flange section seal material according to the present invention.

Example 2 In the same manner as in Example 1, except that the amount of

MICROSPHERE F-82D was changed to 4 parts by weight, a flange section seal material was obtained.

Example 3 hi the same manner as in Example 1, except that the amount of

MICROSPHERE F-82D was changed to 6 parts by weight, a flange section seal material was obtained.

Example 4 In the same manner as in Example 1 , except that the amount of

MICROSPHERE F-82D was changed to 8 parts by weight, a flange section seal material was obtained.

Example 5 In the same manner as in Example 1, except that the amount of

MICROSPHERE F-82D was changed to 20 parts by weight, a flange section seal material was obtained. Comparative Example 1

In the same manner as in Example 1, except that the outer layer was not formed, a flange section seal material comprising only the inner layer was obtained. That is, the following composition:

(i) 60 parts by weight of ethylene-glycidyl methacrylate copolymer containing 18 wt% glycidyl methacrylate (CG5001, trade name of Sumitomo Chemical

Industries), (ii) 6 parts by weight of a carboxyl group-containing rosin with an acid value of 240 mgKOH/g (curing agent, KE604, trade name of Arakawa Chemical Co.),

(iii) 1.5 parts by weight of an imidazole derivative (curing accelerator, 2MOAK, trade name of Shikoku Chemical Corp.), (iv) 3 parts by weight of calcium carbonate (filler, WHITEON SB, trade name of

Shiraishi Calcium Co, Ltd.), was kneaded with a twin-screw extruder (TSE) and subjected to shaping extrusion to obtain a single-layer seal material as shown in

Fig. 3.

Comparative Example 2

A paste-like PVC (polyvinyl chloride) sealer (SUNDINE 1361-5, trade name of Asahi Corporation) was used as a sample. In the evaluation test described below, it was coated onto metal panels superimposed in the manner shown in Fig. 4(a) to a thickness of about 2 mm using a brush and spatula without including air, and smoothed for the test (see Fig. 1).

Comparative Example 3

After hot kneading of 100 parts by weight of calcium carbonate (WHITEON SB, trade name of Shiraishi Calcium Co, Ltd.), 20 parts by weight of an tackifier (PICCOLITE A135, trade name of Hercules Co.) and 15 parts by weight of a polyester-based plasticizer (POLYCIZER W230-S, trade name of DaiNippon Ink Co.) to 100 parts by weight of ethylene-vinyl acetate copolymer resin (H2031, trade name of Sumitomo Chemical Co.) using a twin-screw extruder (TSE), a U-shaped nozzle was fitted on the tip of the extruder along the shape of the panel joint, and extrusion was followed by cooling for molding into the shape shown in Fig. 3.

Comparative Example 4 In the same manner as in Example 1, except that the foaming beads were not used, a flange section seal material was obtained. That is, the following composition: (i) 60 parts by weight of ethylene-glycidyl methacrylate copolymer containing 18 wt% glycidyl methacrylate (CG5001, trade name of Sumitomo Chemical Industries), (ii) 6 parts by weight of a carboxyl group-containing rosin with an acid value of 240 mgKOH/g (curing agent, KE604, trade name of Arakawa Chemical Co.), (iii) 1.5 parts by weight of an imidazole derivative (curing accelerator, 2MOAK, trade name of Shikoku Chemical Corp.), (iv) 3 parts by weight of calcium carbonate (filler, WHITEON SB, trade name of Shiraishi Calcium Co., Ltd.), as the inner layer and the following composition:

(i) 48 parts by weight of ethylene-glycidyl methacrylate copolymer containing 12 wt% glycidyl methacrylate (BONDFAST E, trade name of Sumitomo Chemical Industries), (ii) 12 parts by weight of ethylene-glycidyl methacrylate copolymer containing 18 wt% glycidyl methacrylate (CG5001, trade name of Sumitomo

Chemical Industries), (iii) 6 parts by weight of a carboxyl group-containing rosin with an acid value of 240 mgKOH/g (curing agent, KE604, trade name of Arakawa Chemical Co.), (iv) 1.5 parts by weight of an imidazole derivative (curing accelerator,

2MOAK, trade name of Shikoku Chemical Corp.), (v) 3 parts by weight of calcium carbonate (filler, WHITEON SB, trade name of Shiraishi Calcium Co, Ltd.), as the outer layer were kneaded with a twin-screw extruder (TSE) and subjected to shaping coextrusion to obtain a laminated body with the cross-sectional shape shown in

Fig. 2. The outer layer of the laminated body was exposed to electron beam (EB) treatment (250 KeV, 30 Mrad) for crosslinking, to obtain a flange section seal material according to the present invention.

Comparative Example 5 h the same manner as in Example 1, except that the amount of the foaming beads was changed to 30 parts by weight, a flange section seal material was obtained.

The samples obtained in the above-mentioned examples and comparative examples were evaluated by the following method.

Evaluation method

1. Handleability for fitting onto panels

The ease of handleability was evaluated for fitting to cover the edges of cationic electrodeposition coated sheets superimposed as shown in Figs. 4(a) and (b) ((a): Comparative Example 3, (b): others). A: Fitting accomplished in short time without requiring jig

B: Jig required, some time necessary

C: Jig required, time and skill necessary

2. Absorption of gap (seal property) Two 25 mm x 150 x 0.8 mm cold-rolled steel sheets coated with a cationic electrodeposition coating (E-COATING U-600 BLACK by Nihon Paint Co.) were attached together with very thin double-sided tape. The sample was fitted or coated along the joint, maintained at 120°C for 10 minutes, and after which it was allowed to stand for 30 minutes in a thermostatic oven at 140°C, to simulate a situation in which the flange section to be sealed is subjected to an ordinary coating step. The sample was then taken out of the oven and the gap seal property of the steel sheets was visually observed. A: Complete sealing of gap B : Unfilled portion found in gap

3. Coating.outer appearance

The sample was fitted or coated with a brush and spatula onto cationic electrodeposition coated sheets superimposed as shown in Figs. 4(a) and (b) ((a): Comparative Example 3, (b): others). The sample was then allowed to stand for 10 minutes in an oven preheated to 120°C. It was then coated with a paint used for automobile body painting (i.e., an aminoalkyd paint obtained by crosslinking polyester with melamine) by bell-type spraying and allowed to dry at room temperature for about 5 minutes, after which it was allowed to stand for 30 minutes in an oven at 140°C. After removing it from the oven and allowing it to stand at room temperature for about 5 minutes, it was coated with a paint used for automobile body painting (i.e., an aminoalkyd-type solid paint obtained by crosslinking polyester with melamine) by bell- type spraying and allowed to dry at room temperature for about 5 minutes, after which it was allowed to stand for 30 minutes in an oven at 140°C. The dry thickness of each coating was approximately 40 μm for both the intercoating and overcoating. The surface appearance of each of the painted samples was evaluated visually.

A Satisfactory B Surface satisfactory, but seal line not even C Notable wrinkles and paint film cracking occuπed

4. Shape retention after heat treatment (horizontal and vertical directions') The sample was fitted or coated with a brush and spatula onto cationic electrodeposition coated sheets superimposed as shown in Figs. 4(a) and (b) ((a): Comparative Example 3, (b): others).

The fitted or coated sample was then placed (a) in the horizontal direction and (b) in the vertical direction (with the seal hanging downward) as shown in Figs. 5(a) and (b) (only Example 1 is shown for illustration), and allowed to stand for 15 minutes in an oven preheated to 120°C. The sample was then removed from the oven and it was visually determined whether or not it retained its original shape.

A: Satisfactory B Deformation or dripping under its own weight C Dropping 5. Seal test of panel gap

The sample was fitted or coated onto a panel having the unfilled portion of 1 mm, as shown in Fig. 6, and allowed to stand at 120°C for 10 minutes, then at 140°C for 30 minutes. It was determined whether or not it seals the unfilled portion.

A Satisfactory seal property B Some unfilled portion remained C Impossible to seal

6. Antigravity seal property

The sample was fitted or coated onto a panel whose surface to be sealed facing downward, as shown in Fig. 7, and allowed to stand at 120°C for 10 minutes, then at 140°C for 30 minutes. Then, the seal property was evaluated.

A: Satisfactory seal property B Some unfilled portion remained C Impossible to seal

7. Evaluation of indentation masking property

After providing the cationic electrodeposition coated sheet with an indentation of 6 mm in diameter and 0.3 mm in depth, the indentation was coated with the sample, the sample was coated onto the indentation 5, as shown in Fig. 8, and allowed to stand at 120°C for 10 minutes, then at 140°C for 30 minutes. Then, the indentation masking property was evaluated.

A Nearly complete masking of indentation B Some sink mark occurred C Notable sink mark occurred

The results of these evaluation tests are summarized in the following table. Table 1

Examples 1-5 had satisfactory handleability for fitting, while the side contacting the adherend (metal panel) had increased fluidity by heating, and therefore exhibited an excellent seal property. The outer layer exhibited no significant fluidity upon heating and therefore the shape retention was satisfactory, while the coating adhesion was also excellent and the resin composing the seal material, which was thermosetting, also had excellent heat resistance. As shown in Fig. 9, the seal layer 12 of the inner layer is fluidized and expanded by the foaming beads, and therefore adequate sealing can be accomplished without remaining any unfilled portion between the panel 3 and the outer layer 11 and, furthermore, sealing can be accomplished at the antigravity portion. Comparative Example 1, which was a single-layer seal material composed of a resin for the inner layer of a seal material according to the present invention, had good handleability for fitting, good absorption of gap and good appearance, but was fluidized by heating. Therefore, it had an insufficient storage elastic modulus at high temperature, deformed under its own weight, and exhibited inferior shape retention and inferior cap seal property. As a matter of course, sealing can not be accomplished at the antigravity portion.

Comparative Example 2 was a common PVC (polyvinyl chloride) sealer. Because it is liquid, coating of the prescribed amount was difficult and operator skill was required. It deformed under its own weight, and exhibited insufficient shape retention. Comparative Example 3 was a thermoplastic resin with high fluidity, and therefore the seal property was satisfactory, but the thermoplastic property resulted in wrinkles upon repeated heating carried out in the coating step, and the shape could not be retained.

Comparative Example 4, which was a multi-layer seal material comprising a layer capable of retaining the shape as an outer layer and an inner layer composed of a thermosetting resin with high fluidity, had good handleability for fitting, good seal property, good shape retention and good adhesion of coating. However, the inner layer does not contain the foaming beads, and therefore the volume of the resin does not change and sealing of gap of 1 mm is hardly accomplished. As shown in Fig. 10, the molten resin 12 is fluidized downward through gravity to generate the unfilled portion 13 between the outer layer 11 and the panel 3, and therefore sealing is hardly accomplished at the antigravity portion. Comparative Example 5 contained an excess amount of foaming beads and the fluidity of the molten resin is suppressed, resulting in inferior seal property. Also the coating outer appearance is inferior because of large unevenness of the outer appearance.

The seal material of the present invention has satisfactory handleability for fitting, an excellent seal property and satisfactory shape retention.

Claims

Claims:

1. A flange section seal material for sealing of the flange section of metal panels in a vehicle, comprising at least two layers of an inner layer and an outer layer which are molded into the desired shape allowing it to sandwich and cover the flange section, characterized in that the inner layer contains a hot-melt/fluidizable thermosetting resin with a curing temperature of 80-200°C, the outer layer exhibits no significant fluidizing shape change at 80-200°C, and the inner layer contains foaming beads.

2. A flange section seal material according to claim 1, wherein said outer layer contains a resin with a storage elastic modulus of 5.0 x 10⁵ Pa or greater at 80- 200°C.

3. A flange section seal material according to claim 1, wherein said hot- melt/fluidizable thermosetting resin contains an epoxidized thermoplastic resin.

4. A flange section seal material according to claim 1 , wherein said foaming beads are thermal expanding microcapsules containing a foaming agent.

5. A flange section seal material according to claim 1, wherein the content of said foaming beads is from 0.1 parts by weight to 20 parts by weight based on 100 parts by weight of the material for the inner layer.