JPH09225394A - Decorative part for electric appliance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exterior trim part for an electric appliance made by forming a precoated steel plate, which is free from deterioration of brightness at a worked portion and has a superior stain-resistant property. SOLUTION: By using a precoated steel plate formed by forming on a steel plate a primer coating film of a heat curing resin having a modulus of elasticity of 5×10<3> to 9×10<3> N/mm<2> at a temperature of 20 deg.C and a finishing coating film of a heat curing resin overlaid thereon and having a modulus of elasticity of 1×10<3> to 3.5×10<3> N/mm<2> at a temperature of 20 deg.C, a part having a finishing coating film having a surface free energy of 25-38erg/cm<2> is formed by working.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exterior member for home electric appliances which is formed by processing a coated steel sheet.

[0002]

2. Description of the Related Art Electric warming pots, electric warming pots, hot plates, electric grill pans, electric mixers, coffee makers.
For the top cover or the top cover or outer plate of such home electric appliances, plastic molded products have been mainly used from the viewpoint of easiness of manufacturing and lightness of members. Since these plastic members are discarded while they are still attached when household appliances cannot be used, non-combustible waste increases with the increase in the number of discarded home appliances, and a reduction in the waste is screaming. Further, in recent years, the Product Liability Law has been implemented, and the demand for recyclability of discarded home electric appliances has become stricter than ever.

For this reason, home electric appliances manufacturers are also under pressure to study the recyclability of plastic members. When recycling plastic members, it is necessary to sort them by type of plastic, but the type of plastic used is usually different depending on the product and the mounting member even with the same home appliance manufacturer, so it is very important to sort plastic members. It involves a lot of labor and cost. Therefore, it is considered to use a pre-coated steel plate member manufactured by forming a pre-coated steel plate on the portion where the plastic member was used. That is, since the pre-coated steel plate member can be recycled as iron scrap without being sorted according to the type like the plastic member, the labor and cost can be extremely reduced as compared with the case of the plastic member.

By the way, in this pre-coated steel sheet member, a primer coating film of thermosetting resin such as polyester or epoxy is formed on a steel sheet such as a zinc-based plated steel sheet or an aluminum-based plated steel sheet, and a high coating film is formed thereon. It is manufactured by cutting a precoated steel sheet on which a top coating film of thermosetting resin such as molecular polyester is formed into a predetermined size and then subjecting it to drawing, tensioning or bending. In order to improve the workability of the pre-coated steel sheet, the pre-coated steel sheet is given a strain processing with a coating film elongation rate of 50% or more.
The primer coating has an elastic modulus at 20 ° C. of 1 × 10 ^{3 to} 2.0.
X10 ³ N / mm ² , a thermosetting resin having a breaking elongation of 50 to 150%, and a top coating film having a higher elastic modulus than the primer coating film and a breaking elongation of about 100%. The elongation at break was increased for both the primer coating film and the top coating film. However, there has been a problem that the exterior member of a home electric appliance formed by processing this pre-coated steel sheet has a reduced gloss at the stretched portion of the top coating film, and the appearance is not in harmony with other portions.

This decrease in the gloss of the coating film is caused by the fact that the roughened surface of the processed part of the coating base plate and the change in the refractive index due to the orientation of the molecular chains of the coating film promote the diffuse reflection of light. Since it was estimated, when manufacturing precoated steel sheets, the surface of the coated original plate was roughened by using a coated original plate with a mirror-finished surface or by devising the processing shape during processing. However, it was difficult to prevent the deterioration of gloss.

Further, when the breaking elongation of the top coating film is increased as described above, the coating film becomes soft and the surface free energy thereof becomes as large as 44 erg / cm ² or more.
In the case of household electric appliances handling food, there is a problem that the food easily adheres to the exterior member during use, and once the food adheres, it is difficult to remove and the coating film has poor stain resistance.

[0007]

SUMMARY OF THE INVENTION The present invention provides an exterior member for home electric appliances which solves the above problems.

[0008]

The present invention is applied to a steel sheet at 20 ° C.
Forming a primer coating film of a thermosetting resin having an elastic modulus of 5 × 10 ^{3 to} 9 × 10 ³ N / mm ² at 20 ° C.
A coated steel sheet on which a top coating film of a thermosetting resin having an elastic modulus of 1 × 10 ^{3 to} 3.5 × 10 ³ N / mm ² is formed, and the surface free energy of the surface of the top coating film is 25 to 38 erg. /
The material having a size of cm ² was molded and used as an exterior member for home electric appliances.

[0009]

As a result of studying the conventional precoated steel sheet member, the inventors of the present invention have found that the conventional precoated steel sheet has insufficient elastic modulus of the primer coating film of the thermosetting resin and the surface of the coated original plate accompanying the processing. The influence of the orientation of the molecular chains due to the roughening of the film and the processing strain of the coating film cannot be suppressed only by the primer-coating film, and the top coating film is also affected, resulting in the surface roughening and the orientation of the molecular chains, To reduce the gloss of the processed part of the pre-coated steel sheet member,
Further, it was found that the surface free energy of the surface of the top coating film of the thermosetting resin is large and thus the stain resistance is inferior.

Therefore, as a result of various studies on the method for suppressing the decrease in gloss of the coating film and the method for improving the stain resistance, the present inventors have found that both are a thermosetting resin primer coating film and a top coating film. And the elastic modulus of the two coating films are made larger than the conventional one by increasing the elastic modulus of the primer coating film by increasing the elastic modulus of the former and the latter. It has been found that, when the top coating film is made of a material having a large relaxation ability for the molecular chain orientation and easily elastically deformed by rubber, it is possible to suppress the deterioration of gloss and improve the stain resistance.

That is, in the present invention, the primer coating film of the precoated steel sheet has an elastic modulus at 20 ° C. of 5 × 10 ^{3 to} 9 ×.
In addition to 10 ³ N / mm ² , the top coating film has an elastic modulus at 20 ° C. of 1 × 10 ^{3 to} 3.5 × 10 ³ N / mm ² and the surface free energy of the top coating film surface. -Is 25 ~
It was set to 38 erg / cm ² . Here, when the elastic modulus of the primer-coating film is smaller than the above range,
When the elastic buffering effect is small and, conversely, when it is larger than the above range, cohesive failure of the primer coating film occurs. Further, in the case of the top coating film, when the elastic modulus is smaller than the above range, rubber elastic deformation is small, so that the orientation of the molecular chain is likely to occur, and conversely, when the elastic modulus is larger than the above range, coating distortion occurs due to processing strain, and Sex is impaired. Further, when the surface free energy of the surface of the top coating film is smaller than 25 erg / cm ² , the surface becomes tan, and when it is larger than 38 erg / cm ² , the stain resistance is not improved so much.

In order to adjust the elastic modulus of the primer coating film to the above range, a resin having a relatively large molecular weight, for example, a polyester resin or an epoxy resin having a number average molecular weight of about 10,000 is used as the coating resin and blended therein. The type and amount of the curing agent to be used may be adjusted. Further, in order to adjust the elastic modulus and surface free energy of the top coating film as described above, a resin coating having a relatively large molecular weight is used as the coating resin, for example, a polyester resin or a high molecular weight polyester having a number average molecular weight of 15,000 to 35,000. The type and the amount of the curing agent mixed in the resin may be adjusted.

For example, when the top coating film is a high molecular polyester resin, if a melamine resin as a curing agent is added in excess of the reaction equivalent or an amino-modified silicone resin is added, these curing agents become high molecular polyester. Since it has low compatibility with the base resin, it is difficult to uniformly disperse it throughout the coating film.
For this reason, when a topcoat paint is applied, the reaction equivalent of the melamine resin reacts and crosslinks in the wet coating film during heating and drying, but the reaction equivalent is larger than the reaction equivalent at the interface between the coating film and air with low surface energy. Collected and react in a concentrated state on the surface layer of the coating film. Also, in the case of amino-modified silicone resin, it reacts and crosslinks in a concentrated state near the surface of the coating film. As a result, a thickened layer of the curing agent is formed on the surface of the coating film, and the elastic modulus and the surface free energy are lowered. The amount of the curing agent may be appropriately adjusted depending on the structure of the main resin of the coating film, the molecular weight, the hydroxyl group, etc. When the butylated melamine is used for the melamine resin, it is 1 to 100 parts by weight of the solid content of the coating than the reaction equivalent. 5 parts by weight is added, and in the case of amino-modified silicone resin, 0.2 to 1 parts by weight is added.

The coating thickness of the primer coating and the top coating may be the same as conventional ones, and the primer coating may have a thickness of 3 to 15 .mu.m.
., 10 to 25 .mu.m for the top coating film. Coloring pigments, rust preventive pigments, extender pigments and the like may be added to the primer coating film, if necessary, and coloring pigments and extender pigments may also be added to the overcoat coating film.

The precoated steel sheet member of the present invention is manufactured by subjecting a plated steel sheet, a stainless steel sheet or the like to a pretreatment such as a chromate treatment or a phosphate treatment, followed by a roll coat method or a carten coat method. -Coating method, a primer coating of a thermosetting resin by a known coating method such as a spray method, and after baking and drying, a top coating composition of a thermosetting resin is coated thereon,
A pre-coated steel sheet may be manufactured by baking and drying, and the pre-coated steel sheet may be formed into a desired member for home electric appliances. Molds and processing conditions for forming may be the same as those for processing a conventional pre-coated steel sheet, and there is no particular limitation.

[0016]

EXAMPLE Hot-dip galvanized steel sheet (plate thickness: 0.5 mm, zinc adhesion: 60 g / m ^{2 on} one side) plated with a cold-rolled titanium killed steel sheet was subjected to coating-type chrome treatment to prepare various polyester series. A resin primer coating was applied to a dry coating film thickness of 10 μm, baked and dried at 215 ° C. for 50 seconds, and then a topcoat paint of various polyester resins to which a curing agent was added was dried to a dry coating film thickness. To 20 μm, and baked and dried at 230 ° C. for 60 seconds. The coated steel plate thus obtained was drawn into outer plates for electric insulation ovens, hot plates, and co-makers, and the workability of the coating film in the processed portion, change in gloss and The stain resistance was investigated as follows. Table 1 shows coating film physical properties and curing agents. In addition, Tables 2 to 4 show the performance of the obtained outer panels for home electric appliances.

(1) Appearance The appearance of the pre-coated steel sheet before being processed into a member is visually observed, and if the coating film has no irregularities and is smooth, the symbol ◯ indicates that the coating film has a dull surface. Those that became negative were evaluated by the symbol X.

(2) Workability of coating film The state of cracks in the coating film at the corner of each member is ruled at a magnification of 10 times.
When observed with a pe, the film with no abnormalities is marked with ◎, the film with slight cracks is marked with ○, the one with significant cracks is marked with △, and the film is visible to the naked eye. Those in which cracks were observed were evaluated by the symbol x.

(3) Gloss change 1 Measure the gloss of the unprocessed steel plate and the processed part of the processed member,
If the gloss retention after processing is 80% or more, the symbol is ○, 60
˜79% was evaluated by the symbol Δ, and 59% or less was evaluated by the symbol x.

(4) Gloss change 2 Visually comparing the unprocessed part and the processed part of the processed member with a mark, the one showing almost no difference, and the one having a slightly decreased gloss in the processed part Δ, the case where the gloss of the processed portion was clearly reduced was evaluated by the symbol x.

(5) Contamination resistance The ink is applied with a red felt pen and left in a constant temperature and humidity chamber at 20 ° C. and a relative humidity of 65% for 24 hours, and then the ink is wiped off with ethanol to leave the ink. By visually observing the state, there is an evaluation point of 5 with no color residue, an evaluation point of 4 with a slight color residue, an evaluation point of 3 with a color residue, an evaluation point of 2 with a significant color residue, and a color loss. There is no evaluation score 1
And

[0022]

[Table 1] (Note) A of the curing agent is a butylated melamine resin, B is an amino-modified silicone resin, and the addition amount is per 100 parts by weight of the coating solid content.

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

As described above, the electric home appliance component of the present invention does not deteriorate the gloss of the processed part and is excellent in stain resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yoshiko Sakamoto, 1 Nisshin Steel Co., Ltd. R & D Coupling Research Department, 7-1 Takatani Shinmachi, Ichikawa City, Chiba Prefecture

Claims (1)

[Claims] 1. A steel sheet having a modulus of elasticity of 5 × 10 ³ at 20 ° C.
~ 9 × 10 ³ N / mm ² thermosetting resin primer
A coating film is formed, on which the elastic modulus at 20 ° C is 1 × 10 ^3.
~ 3.5 × 10 ³ N / mm ² coated steel sheet with a top coating film of thermosetting resin formed, and having a surface free energy of the top coating film surface of 25 to 38 erg / cm ² An exterior member for home appliances characterized by the above.