WO2012098961A1 - Steering wheel having in-mold film - Google Patents

Abstract

[Problem] To provide a steering wheel having an in-mold film in which very small, bubble-shaped spaces do not form in the cross section of the in-mold film, and in which improved mechanical properties and durability can be obtained. [Solution] A protective film that forms the outermost layer of the steering wheel is an in-mold film having a monolayer structure formed by in-mold molding. The in-mold film contains particle clusters formed by laying out, accumulating, and cross-linking polymer particles. The film has very small, discontinuous, hairline spaces formed by a portion of the surface of the polymer particles not bonding together between these particle clusters.

Description

Steering wheel with in-mold coating

The present invention relates to a steering wheel provided with an in-mold coating capable of improving mechanical properties and durability so as not to generate a bubble-like minute space in the cross-section of the in-mold coating.

For example, in a method for manufacturing a steering wheel of an automobile, a resin layer is formed by setting a core metal of a steering wheel in a mold cavity and then injecting and curing a resin material into the mold cavity. As a resin material, urethane resin is used because of its excellent tactile sensation. However, since urethane resin has the disadvantage of being inferior in light resistance and yellowing, a film for imparting light resistance to the surface of the urethane resin layer is formed. There is a need.

The film forming method for forming the film is classified into a post-coating method and an in-mold coating method (see Patent Document 1). Further classified by construction methods, the post-coating method includes a spray method, and the in-mold coating method includes a spray method and a reduced pressure method.

In the in-mold coating method by the decompression method, a method of forming a film using a so-called solvent-type paint in which a resin is dissolved in an organic solvent or an ionic resin is dissolved in water can be considered. In the organic solvent type, (1) the resin does not exist as particles, (2) there is no cross-linking of the resins after the solvent scatters, and (3) the organic solvent has a small surface tension and hardly generates bubbles. Even in the aqueous solution type, as in the organic solvent type, (1) the resin does not exist as particles, (2) there is no crosslinking between the resins, and (3) no foaming agent (surfactant) is added. Foaming is not good.

Japanese Patent No. 3573013

Of course, in the in-mold coating method using the spray method, even in the in-mold coating method using the reduced pressure method using the solvent-type paint, a large number of microscopic space portions remain in the cross section of the coating. When there are many foam-like minute space portions, there is a problem that the coating properties such as mechanical properties and durability against wear, temperature and humidity are inferior, and the solution has been desired.

The present invention was devised in view of the above-described conventional problems, and it is possible to improve mechanical properties and durability by preventing the formation of minute bubble-like spaces in the cross-section of the in-mold coating. An object is to provide a steering wheel provided with a possible in-mold coating.

The steering wheel provided with the in-mold coating according to the present invention is a single-layer in-mold coating in which the protective coating that is the outermost layer of the steering wheel is formed by in-mold molding. There is a “particle swarm” composed of particles arranged, stacked, and cross-linked, and a part of the surface of the polymer particle is bonded between these “particle swarm” and “particle swarm”. It is characterized by having a minute and discontinuous fine-line-like space portion that occurs without any damage.

In the cross section of the in-mold coating, when a grid in which 100 small squares each having a side of 1 μm are arranged in a large square region having a side of 10 μm is set, the number of the grids in which the thin line-shaped space portions are 10 It is preferable that there are at least one large square which is not more than one.

The emulsion paint used for forming the in-mold coating is preferably a water-based paint.

In the steering wheel provided with the in-mold coating according to the present invention, it is possible to improve the mechanical properties and the durability by preventing the formation of minute foamy spaces in the cross-section of the in-mold coating. .

It is a figure for demonstrating the in-mold coating method by the pressure reduction construction method applied to suitable embodiment of the steering wheel which provided the in-mold film concerning this invention. As an Example, it is a CCD microscope image photograph of the film structure obtained by the in-mold coating method by the decompression method using a water-based emulsion paint. As a comparative example, it is a CCD microscope photograph of a film structure obtained by an in-mold coating method using a spray method using a water-based emulsion paint. FIG. 3 is a photograph in which a grid is superimposed on the CCD microscope photograph of FIG. 2 to confirm the existence of a space portion. FIG. 4 is a photograph in which the existence of a space portion is confirmed by overlaying a grid on the CCD microscope photograph of FIG. 3.

Hereinafter, a preferred embodiment of a steering wheel provided with an in-mold coating according to the present invention will be described in detail with reference to the accompanying drawings. In the steering wheel provided with the in-mold coating according to this embodiment, the protective coating that is the outermost layer of the steering wheel is basically an in-mold coating having a single layer structure formed by in-mold molding. The coating consists of a “cluster of particles” composed of polymer particles arranged, deposited and cross-linked, and a part of the surface of the polymer particles between these “particle clusters” and “particle clusters”. Has a fine and discontinuous fine-line-like space portion generated without joining.

The fine and discontinuous thin line-shaped space portion is a portion that is recognized as a black elongated shape in a monochrome image or photograph when the cross-section of the in-mold coating is enlarged by about 3000 times. . Black is a gray color depending on the image quality and contrast, and it appears darker than the surrounding area, or it appears white or a lighter gray color when the image is reversed positive / negative.

Also, the fact that a part of the surface of the group of particles in this discontinuous space part does not join means that a part of the polymer particles are not fused or not crosslinked.

Furthermore, the fine line shape means a narrow and closed part, and is composed of a complicated shape in which countless curves and straight lines are combined. However, when the whole image or the like is looked down on, the thin line shape is a state in which it looks like an elongated string-like line.

As the cross-sectional structure of the coating, it is known that if there are a lot of fine foam-like spaces, the mechanical structure is brittle, and therefore the mechanical properties and durability are not high. Here, although empirically, the film structure in which minute fine line-like space portions exist is more than the film structure in which many such fine bubble-like space portions are generated. Judging from the cross-sectional performance, it was found that the mechanical properties and durability were more excellent.

Specifically, in the cross section of the in-mold coating, when a grid in which 100 small squares each having a side of 1 μm are arranged in a large square region having a side of 10 μm is set, the number of grids in which thin line-shaped space portions exist is set. There are at least one large square of 10 or less.

Although it is very difficult to control the coating structure, it is a coating in which there are one or more large squares of 10 μm per side with 10 or less fine fine line-shaped space portions captured by a small square grid of 1 μm per side. It was found that it was obtained from the results of the demonstration experiment of the following example.

For example, as shown in FIG. 1, a steering wheel is manufactured by the in-mold coating method. A predetermined amount of emulsion paint M as a coating is accumulated in the cavity 5 of the lower mold 2 of the mold 1, and the core of the steering wheel is stored in the cavity 5. A mold (not shown) is set, and the mold 1 is closed with the upper mold 3. The mold 1 is configured to be accommodated in a box 13 including a frame body 11 and a lid body 12. Then, when the inside of the box 13 is decompressed by the vacuum pump 20, the inside of the cavity 5 is also passed through 21. Is reduced in pressure. When the inside of the cavity 5 is depressurized, the emulsion paint M bumps and increases in volume and foams, and the emulsion paint M is applied to the inner wall 6 of the cavity 5. Next, by injecting urethane resin into the cavity 5 by an injection nozzle (not shown) communicating with the cavity 5, the coating film of the emulsion paint M formed on the inner wall 6 of the cavity 5, the core metal of the steering wheel, A urethane resin is filled in the gap. Then, by curing the urethane resin and opening the mold 1, the urethane resin layer is covered with an in-mold film having a single layer structure made of the emulsion paint M, and the outermost layer is covered with this protective film. Is obtained.

The formation principle of the in-mold film by emulsion paint is that when the pressure is reduced, the bumped dispersion medium evaporates while bubbling, and polymer particles are deposited in close contact while being laid out like snow. In this deposition process, the polymer particles are joined together and fused or cross-linked to form a strong “particle cluster”. In some parts, the surface of the polymer particles does not crosslink. Therefore, a fine and discontinuous thin-line space portion is generated between the “particle swarm” and the “particle swarm”.

On the other hand, in the spray method, since a spray mist is deposited, a space portion is easily generated between polymer particles.

For example, in the case of a water-based paint, the emulsion paint used for forming the in-mold coating according to the present embodiment is mainly composed of water and a film-forming aid, and 10 g is placed in an acrylic pipe having a height of 1 m and an inner diameter of 34 mm. The foam height reached when the pressure is reduced by a vacuum pump is 400 mm or more. In addition, the coating material includes solids such as a polymer, a pigment, and a leveling agent. Details of each will be described below.

As the polymer, those conventionally used for paints such as acrylic resin, urethane resin, vinyl acetate resin, silicone resin and the like can be used. Among these, acrylic resins can be preferably used in consideration of various properties such as film strength and light resistance. As the acrylic resin, for example, polymerizable unsaturated carboxylic acid or anhydride thereof, (meth) acrylic acid esters and acrylic monomers other than (meth) acrylic acid, and styrene, vinyl acetate and the like as necessary, Examples thereof include acrylic resins obtained by copolymerization by a polymerization method such as emulsion polymerization, solution polymerization, and bulk polymerization. The above resins can be used alone or in combination of two or more.

Examples of pigments include colored pigments such as titanium oxide, carbon black, bengara, barita powder, precipitated barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, alumina white, gloss Various pigments conventionally used in paints such as extender pigments such as white can be selected according to the target color. The pigment content in the paint is preferably 0.1 to 5% by mass, and more preferably 0.5 to 3% by mass. If the pigment content is less than 0.1% by mass, sufficient coloration cannot be obtained, and if it exceeds 5% by mass, color unevenness tends to occur.

As the film forming aid, one having a boiling point higher than that of water and capable of semi-dissolving polymer particles is used. Since the boiling point of water is higher than that of water, it is possible to maintain the fluid state of the paint even after the water has evaporated, and since the polymer particles are semi-dissolved, bonding between polymers, that is, bonding such as fusion is promoted. The resulting coating is smooth. In the present embodiment, N-methylpyrrolidone, methyl cellosolve, carbitol, triethylene glycol, texanol or the like is used to obtain such an effect. Of these, N-methylpyrrolidone, methyl cellosolve and the like are preferable. The said film-forming aid can be used individually by 1 type, and can also use 2 or more types together. Further, the content of the film-forming auxiliary in the coating is preferably 0.3 to 3% by mass, more preferably 0.5 to 2% by mass. When the content of the film-forming auxiliary is less than 0.3% by mass, the coating film is not sufficiently smoothed, and when it exceeds 3% by mass, the film thickness becomes uneven.

In addition, the film-forming auxiliary occupies 65 to 98% by mass, preferably 70 to 97% by mass of the total amount of the paint as a total amount with water.

The leveling agent is a component that promotes foaming of the paint and sufficiently adheres the paint to the inner wall of the cavity. In the present invention, silicone oil, silicon varnish, dimethylsiloxane, methylpolysiloxane polyalkyloxide, perfluoroalkyl group-containing oligomer, polyoxyethylene alkyl ester, sorbitan alkyl ester, polyoxyethylene sorbitan alkyl ester, polyalkylene oxide modified siloxane Etc. are used. Among these, polyalkylene oxide-modified siloxane is preferable. The above various leveling agents can be used alone or in combination of two or more. The content of the leveling agent in the coating is preferably 0.3 to 3% by mass, more preferably 0.5 to 2% by mass. When the content of the leveling agent is less than 0.3% by mass, the film is not sufficiently foamed and a coating film is not partially formed. When the content exceeds 3% by mass, the film is excessively foamed and the film thickness is uneven.

In the water-based paint, a water-soluble emulsifier may be added in place of a part of the polymer, pigment, film-forming aid and leveling agent. Examples of the water-soluble emulsifier include alkyl sulfates such as sodium alkyl sulfate and potassium alkyl sulfate, alkylbenzene sulfonates such as sodium alkylbenzene sulfonate and potassium alkylbenzene sulfonate, sodium dialkylsulfosuccinate and potassium dialkylsulfosuccinate. Alkylsulfosuccinic acid ester salts and the like can be used. The said water-soluble emulsifier can be used individually by 1 type, and can also use 2 or more types together. Further, the content of the water-soluble emulsifier in the coating is preferably 0.01 to 1% by mass, more preferably 0.05 to 0.5% by mass. By adding a water-soluble emulsifier, the dispersibility of the polymer powder and the pigment is increased. However, even when added in excess of 1% by mass, no further improvement in dispersibility is seen, but rather the polymer, pigment, film-forming aid. In addition, the content of the leveling agent is relatively reduced and a good coating film cannot be obtained.

Also, if necessary, the water-based paint may further include an appropriate amount of various additives such as a plasticizer, a wetting agent, and a precipitation inhibitor that are generally used in water-based paints. However, these additives need to replace a polymer, a pigment, a film-forming aid and a leveling agent, and a part of the water-soluble emulsifier. Further, the antifoaming agent is not used because it eliminates the action of the leveling agent.

The embodiment according to the present invention is an in-mold method in which a water-based emulsion paint is applied to the decompression method. The comparative example is an in-mold method in which a water-based emulsion paint is applied to the spray method.

In the film forming method according to the present embodiment, since the paint is an emulsion type, (1) the resin exists as particles, (2) the particles are cross-linked when the surrounding water is scattered, and (3) a large amount instantaneously in a reduced-pressure atmosphere. It is possible to obtain the feature that the foaming property is excellent and the foaming property to fill the inside of the mold is excellent.

FIG. 2 shows a CCD microscope photograph of a film structure according to an example of the present embodiment. FIG. 3 shows, as a comparative example, a photograph taken with a CCD microscope having a film structure obtained by a spray method. FIG. 4 shows a photograph in which a grid is superimposed on the CCD microscope photograph of FIG. 2 and the existence of a space portion is confirmed. FIG. 5 shows a photograph in which a grid is superimposed on the CCD microscope photograph of FIG. 3 and the existence of a space portion is confirmed. Both of these photos are magnified 3000 times.

The shooting conditions for the photos are as follows.
・ Photographing equipment / CCD microscope (manufactured by KEYENCE)
Body: VHX-1000, Lens: VH-Z100UR
・ Procedure for creating a cross-section of an object to be photographed / photographed in a room temperature environment (i) Cutting the object to be measured.
(ii) Using a polishing machine (Marumoto Kogyo Co., Ltd. Marumoto Sample Polishing Machine 5629) set with No. 800 water-resistant paper, the cut surface is water-polished.
(iii) Water polishing using No. 2000 water-resistant paper in the same manner as (ii).
(iv) The polished surface is observed and photographed with the above photographing apparatus.

The coating structure prepared by reducing the pressure in FIGS. 2 and 4 is a water-based emulsion paint having a solid content of 12.5 and using a surfactant (foaming accelerator; emulsifier, leveling agent). is there.

3 and 5 is a water-based emulsion paint having a solid content of 35.0 and using an antifoaming agent.

When actually created, as can be understood from FIGS. 2 to 5, in the embodiment, the shape of the space portion is a fine line shape including a minute and discontinuous curve that looks like a curly and thin hair. . For example, in an emulsion-type paint, the polymer particles themselves are substantially spherical, and are dispersed in the solvent as the original polymer. At the stage of film formation, spherical polymer particles are deposited and cross-linked, whereby a very strong film can be obtained. At this time, a part that is not partially crosslinked is observed as a fine thin line-shaped space part. On the other hand, in the spray method, it is clearly foamy, and many space portions are observed.

In the example according to the present embodiment, 1 to several μm of polymer particles are deposited in the cross section of the film magnified 3000 times, and the thin line-shaped space between the polymer particles has a length of less than 5 μm. It was. When viewed in the area of each large square, there are six, nine, and fifteen grids each having a thin line-shaped space portion, and at least one large square having ten or fewer grids. It can be seen that this is a coating structure.

In the comparative example by the spray method, it can be seen that the coating structure has 40, 51, and 53 grids each having a bubble-like space in each large square region.

The steering wheel provided with the in-mold coating described above is a preferred example of the present invention, and other embodiments can be implemented or performed by various methods. In particular, the present invention is not limited to the detailed shape, size, configuration, and the like of the components shown in the accompanying drawings unless otherwise stated in the present specification. In addition, expressions and terms used in the present specification are for the purpose of explanation, and are not limited thereto unless otherwise specified.

Claims (3)

1. The protective coating that is the outermost layer of the steering wheel is an in-mold coating having a single layer structure formed by in-mold molding, and the in-mold coating is formed by arranging, depositing, and crosslinking polymer particles. There is a “cluster of particles”, and a minute, discontinuous thin line-shaped space portion formed without joining a part of the surface of the polymer particle between these “particle cluster” and “particle cluster”. A steering wheel provided with an in-mold coating.
2. In the cross section of the in-mold coating, when a grid in which 100 small squares each having a side of 1 μm are arranged in a large square region having a side of 10 μm is set, the number of the grids in which the thin line-shaped space portions are 10 The steering wheel provided with the in-mold coating according to claim 1, wherein there are at least one or more large squares.
3. The steering wheel provided with the in-mold coating according to claim 1 or 2, wherein the emulsion coating used for forming the in-mold coating is a water-based coating.

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