JP6419553B2 - Water-based paint composition and electronic device - Google Patents

Description

  The present invention relates to an aqueous coating composition and an electronic device including a casing coated with the aqueous coating composition.

  In recent years, the amount of volatile organic compounds (VOC) discharged from organic solvent-type paints accounts for 30% of the VOC emissions of society as a whole. Therefore, the paint is required to be converted from the organic solvent-type paint to the water-type paint.

In addition, plant-derived raw materials have attracted attention from the viewpoints of reducing CO ₂ emissions and deoiling. Plant-derived raw materials have zero or more carbon dioxide emissions and absorption in the life cycle and do not increase carbon dioxide in the atmosphere, so the environmental burden can be reduced compared to petroleum-based materials.

  Therefore, it is expected to use the plant-derived raw material for the paint.

  On the other hand, it is natural that the coating material is required to have good appearance and adhesion, and the required coating film performance varies depending on the object and purpose to be used. In coating films used for electronic devices, particularly ICT devices, higher performance is required, and the appearance, adhesion, hardness, sweat resistance, and chemical resistance are particularly emphasized.

As a technique using plant-derived raw materials, techniques using starch, polylactic acid, and the like have been proposed (see, for example, Patent Documents 1 to 6).
However, in these proposed techniques, a water-based coating composition that uses a plant-derived raw material to obtain a coating film excellent in all of appearance, adhesion, hardness, sweat resistance, and chemical resistance has not been obtained. .

  Accordingly, an aqueous coating composition that uses a plant-derived raw material to obtain a coating film that is excellent in appearance, adhesion, hardness, sweat resistance, and chemical resistance, and a casing coated with the aqueous coating composition Currently, there is a demand for provision of electronic devices including the above.

Japanese Patent Laid-Open No. 2004-224887 Japanese Patent Laid-Open No. 10-101911 JP 2003-321600 A JP 2005-290156 A JP 2002-241629 A JP 2004-18744 A

  The present invention relates to an aqueous coating composition that uses a plant-derived raw material to obtain a coating film having excellent appearance, adhesion, hardness, sweat resistance, and chemical resistance, and a casing coated with the aqueous coating composition. An object is to provide an electronic device including a body.

Means for solving the above-described problems are as described in the following supplementary notes. That is,
The disclosed aqueous coating composition contains polylactic acid, an isocyanate curing agent, a glycol ether solvent, and water.

  The disclosed electronic device includes a casing coated with the disclosed aqueous coating composition.

According to the disclosed water-based coating composition, the above-mentioned problems can be solved and the above-mentioned object can be achieved, using plant-derived raw materials, appearance, adhesion, hardness, sweat resistance, and chemical resistance. An excellent coating film can be obtained.
According to the disclosed electronic device, the conventional problems can be solved and the object can be achieved, using plant-derived raw materials, all in appearance, adhesion, hardness, sweat resistance, and chemical resistance. An electronic device including a housing on which an excellent coating film is formed can be provided.

FIG. 1 is a perspective view of a notebook personal computer as an example of the disclosed electronic apparatus. FIG. 2 is a photograph showing the front cover of the notebook computer of FIG. FIG. 3 is a photograph showing the back cover of the notebook computer of FIG. FIG. 4 is a photograph showing the upper cover of the notebook computer of FIG. FIG. 5 is a photograph showing a lower cover of the notebook computer of FIG.

(Water-based paint composition)
The disclosed aqueous coating composition contains at least polylactic acid, a glycol ether solvent, an isocyanate curing agent, and water, and further contains other components as necessary.

<Polylactic acid>
There is no restriction | limiting in particular as said polylactic acid, According to the objective, it can select suitably, For example, poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA), L-lactic acid, and D-lactic acid And a random copolymer. These may be used alone or in combination of two or more.
There is no restriction | limiting in particular as said polylactic acid, According to the objective, it can select suitably, A commercial item may be sufficient and the synthetic | combination product synthesize | combined suitably may be sufficient.
Examples of the commercially available products include Terramac (registered trademark) TE-2000 (manufactured by Unitika Ltd.), Lacia (registered trademark) H-100J, 100H (all manufactured by Mitsui Chemicals, Inc.), Ecodia (registered trademark) ( Toray Industries, Inc.).
There is no restriction | limiting in particular as said synthetic product, According to the objective, it can select suitably. Examples of the method for synthesizing the synthetic product include a method of polymerizing a polylactic acid precursor. The polylactic acid precursor is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include L-lactide and D-lactide.

There is no restriction | limiting in particular as a weight average molecular weight of the said polylactic acid, Although it can select suitably according to the objective, 50,000 or less are preferable and 5,000-20,000 are more preferable.
The weight average molecular weight can be measured, for example, by gel permeation chromatography (GPC) in which a calibration curve is prepared using polystyrene.

In preparing the water-based coating composition, the polylactic acid is usually used in the state of a polylactic acid emulsion. The polylactic acid emulsion contains at least water and the polylactic acid, and further contains other components such as a plasticizer and a dispersant (emulsifier) as necessary.
Examples of the polylactic acid emulsion include KN-26 manufactured by Toho Chemical Industry Co., Ltd. and Randy PL-2000 manufactured by Miyoshi Oil & Fat Co., Ltd.

There is no restriction | limiting in particular as the method of emulsifying the said polylactic acid, According to the objective, it can select suitably, For example, Unexamined-Japanese-Patent No. 2001-354841, Unexamined-Japanese-Patent No. 2002-3607, Unexamined-Japanese-Patent No. 2002-121288. And the method disclosed in Japanese Patent Laid-Open No. 2004-276781.
Specifically, (1) a pressure dispersion method in which polylactic acid, a plasticizer, a dispersant and water are charged simultaneously in a closed tank having a stirring device, and the polylactic acid is dispersed by applying pressure while heating and stirring; (2 ) A direct dispersion method in which a melt containing polylactic acid, a plasticizer, and a dispersant is added and stirred in hot water maintained at normal pressure or under pressure, and (3) an organic solvent solution of polylactic acid is dispersed. , A method of adding and stirring and dispersing in an aqueous solution containing a plasticizer and a dispersant, and then removing the organic solvent, (4) heating and melting polylactic acid, and adding and stirring an aqueous solution containing the plasticizer and the dispersant And a phase inversion method in which polylactic acid is dispersed in water.

  There is no restriction | limiting in particular as content of the said polylactic acid in the said polylactic acid emulsion, Although it can select suitably according to the objective, 10 mass%-50 mass% are preferable, and 25 mass%-45 mass% are more. preferable.

<Isocyanate curing agent>
The isocyanate curing agent is not particularly limited as long as it is a water-dispersible isocyanate curing agent, and can be appropriately selected according to the purpose. Examples of the water-dispersible isocyanate curing agent include a self-emulsifying isocyanate curing agent and an external emulsification type isocyanate curing agent.

  Examples of the self-emulsifying type isocyanate curing agent include an isocyanate curing agent obtained by dispersing a hydrophobic polyisocyanate compound using a polyisocyanate compound (dispersant) modified with a polyoxyethylene group, and a hydrophobic type. Examples include an isocyanate curing agent obtained by dispersing a polyisocyanate compound using a dispersant having both a hydrophobic group and a hydrophilic group.

  Examples of the polyisocyanate compound used in the isocyanate curing agent include aliphatic diisocyanate compounds, alicyclic diisocyanate compounds, aromatic diisocyanate compounds, burette type adducts of these isocyanate compounds, and isocyanurates of these isocyanate compounds. Examples include cycloaddition products.

Examples of the aliphatic diisocyanate compound include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate.
Examples of the alicyclic diisocyanate compound include isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1,3- (or 1, 4-) Di (isocyanatomethyl) cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate and the like.
Examples of the aromatic diisocyanate compound include xylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4 , 4'-Toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-) phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene Examples thereof include diisocyanate, bis (4-isocyanatophenyl) sulfone, and isopropylidenebis (4-phenylisocyanate).

  A commercially available product may be used as the isocyanate curing agent. Examples of the commercially available products include DIC Burnock (for example, DNW-5500, DNW-6000), Asahi Kasei Duranate (for example, WB40-100, WB40-80D, WT20-100, WT30-100, WE50). -100).

  There is no restriction | limiting in particular as content of the said isocyanate hardening | curing agent in the said water-based coating composition, Although it can select suitably according to the objective, 45 mass% or less is preferable with respect to the said polylactic acid, and 10 mass% -40 mass% is more preferable.

<Glycol ether solvent>
The glycol ether solvent is a solvent having at least one ether bond (C—O—C) formed by glycol in the molecule.

Examples of the glycol ether solvent include the following solvents.
Dipropylene glycol dimethyl ether (boiling point: 171 ° C., solubility in water: 32.6 g / 100 g)
Diethylene glycol butyl methyl ether (boiling point: 212 ° C., solubility in water: 9.2 g / 100 g)
Tripropylene glycol dimethyl ether (boiling point: 215 ° C., solubility in water: 23.6 g / 100 g)
Ethylene glycol monophenyl ether (boiling point: 245 ° C., solubility in water: 2.6 g / 100 g)
Diethylene glycol dibutyl ether (boiling point: 256 ° C., solubility in water: 0.3 g / 100 g)
Propylene propylene diglycol (boiling point: 212 ° C., solubility in water: 4.8 g / 100 g)
Methyl propylene glycol acetate (boiling point: 146 ° C., solubility in water: 20.5 g / 100 g)
Butylpropylene glycol (boiling point: 170 ° C., solubility in water: 6.4 g / 100 g)
Butylpropylene diglycol (boiling point: 229 ° C., solubility in water: 3.0 g / 100 g)
Dimethylpropylene diglycol (boiling point: 171 ° C., solubility in water: 37.0 g / 100 g)
Texanol (boiling point: 255 ° C., solubility in water: 2.0 g / 100 g)
In addition, propyl propylene diglycol (Propyl Propylene Di Glycol) is also called dipropylene glycol monopropyl ether (Dipropylene Glycol Monopropyl Ether).
Butyl propylene glycol (Butyl Propylene Glycol) is also called propylene glycol monobutyl ether (Propylene Glycol Monobutyl Ether).

  The solubility of the glycol ether solvent in water is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably finite, more preferably 3.0 g / 100 g or more, It is particularly preferably from 3.0 g / 100 g to 25.0 g / 100 g. When the solubility of the glycol ether solvent in water is within the particularly preferable range, the glycol ether solvent can be sufficiently added to water, and the film forming property is excellent.

Here, the fact that the solubility in water is finite means that the solubility in water is not infinite. For example, diethylene glycol monomethyl ether has an infinite solubility in water. The solubility is measured at 25 ° C. The solubility in water is expressed by, for example, the number of grams of organic solvent (g / 100 g) dissolved in 100 g of water.
Here, the boiling point is a boiling point measured at 1 standard atmospheric pressure (atm).
The solubility is determined according to OECD Chemical Test Guideline No. It can be obtained by the method defined in 105.

  The glycol ether solvent is preferably used in combination of two or more different boiling points. By doing so, the coating film which is very excellent in film formability and curability can be obtained.

  There is no restriction | limiting in particular as content of the said glycol ether solvent in the said water-based coating composition, Although it can select suitably according to the objective, 35 mass% or less is preferable with respect to the said polylactic acid, and 5 mass% -30 mass% is more preferable. When the content of the glycol ether solvent exceeds 35% by mass, the hardness of the coating film may be lowered and the water resistance may be lowered.

<Water>
There is no restriction | limiting in particular as said water, According to the objective, it can select suitably, For example, a pure water, an ultrapure water, etc. are mentioned. Examples of the pure water include ion exchange water, ultrafiltrated water, reverse osmosis water, and distilled water.

<Other ingredients>
Examples of the other components include a plasticizer, a dispersant (emulsifier), a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, a pigment dispersant, an antiseptic, and an antifungal agent. It is done.

  The aqueous coating composition is preferably a two-component aqueous coating composition of a main agent and a curing agent from the viewpoint of liquid stability. At that time, the main agent preferably contains the polylactic acid, the glycol ether solvent, and the water, and the curing agent preferably contains the isocyanate curing agent. In the main agent, the polylactic acid is preferably in the state of the polylactic acid emulsion.

  The disclosed water-based coating composition is excellent in all of appearance, adhesion, hardness, sweat resistance, and chemical resistance, and can provide a coating film that can further reduce the environmental load. Although it can be used, it is particularly suitably used for coating of coating films and electronic devices described below.

<Coating film>
The coating film is not particularly limited except that it is obtained by coating the disclosed aqueous coating composition, and the shape, structure, size, and the like can be appropriately selected.

  The method for applying the water-based paint composition is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a bar coater method, a spray coat method, a curtain coat method, a spin coat method, a gravure coat method, a dip Law.

After coating, it is preferable to heat and dry to remove water and solvent and to cause a crosslinking reaction.
The heating temperature in the heat drying can be appropriately selected depending on the purpose as long as it is within a temperature range in which the object to be coated is not deformed, but is preferably 50 ° C to 100 ° C, more preferably 60 ° C to 80 ° C. .
There is no restriction | limiting in particular as said heat drying time, According to the objective, it can select suitably, For example, 10 minutes-60 minutes etc. are mentioned.

  The average thickness of the coating film is preferably 5 μm to 30 μm, and more preferably 15 to 25 μm.

  The coating film is excellent in all of appearance, adhesion, hardness, sweat resistance, and chemical resistance, and can further reduce the environmental load, and thus can be suitably used in various fields. It can be suitably used for a coating film of a casing of an electronic device such as a personal computer or a mobile phone.

(Electronics)
The disclosed electronic device is not particularly limited except that it includes a housing coated with the disclosed aqueous coating composition, and the shape, structure, size, and the like can be selected as appropriate.
There is no restriction | limiting in particular as said electronic device, According to the objective, it can select suitably, For example, a personal computer (notebook personal computer, desktop personal computer), a telephone, a mobile phone, a copy machine, a facsimile, various printers, a digital camera TV, video, CD device, DVD device, air conditioner, remote control device and the like. Among these, notebook computers and mobile phones (including smartphones) are particularly preferable in terms of carrying and using.
The casing of the electronic device can be coated using the disclosed water-based coating composition.

Here, FIG. 1 shows a notebook personal computer as an example of the disclosed electronic apparatus.
The notebook personal computer 20 of FIG. 1 includes a notebook personal computer main body 21 and a liquid crystal display panel 22 that is rotated and opened. The notebook personal computer main body 21 has a keyboard portion 23 and a pointing device 24 as input means on an upper surface of a flat housing 25. The housing 25 accommodates a hard disk device, a printed circuit board on which a CPU, a memory, and the like are mounted, a battery, and the like.
The notebook personal computer casing is divided into a front cover shown in FIG. 2, a back cover shown in FIG. 3, an upper cover shown in FIG. 4, and a lower cover shown in FIG. Any of these can be applied using the disclosed water-based paint composition.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the disclosed technology is not limited to these examples.

  In the following examples, a flat plate of an ABS material often used for a housing of an electronic device was used as a base material to be coated.

  The tests in the following examples and comparative examples were performed by the following methods.

<Appearance evaluation>
The appearance of the coating film was visually observed and evaluated according to the following criteria.
〔Evaluation criteria〕
◎: Transparent, glossy ○: Not glossy △: Slightly white ×: Cloudiness

<Adhesion test>
Based on JIS K5600-5-6, always use a new cutter knife blade, insert 11 notches reaching the flat plate of ABS resin at 1mm intervals, then change 90 ° direction and further cut 1mm intervals 11 was attached, and an adhesive tape (manufactured by Nichiban Co., Ltd., cello tape (registered trademark) 18 mm width) was attached so as to adhere about 50 mm to the cut coating surface. One minute to two minutes after the adhesive tape was attached, the edge of the adhesive tape was held and kept at a right angle to the coating surface, and peeled off instantaneously. The adhesion was evaluated by the number of grid cells remaining without peeling in 100 squares. Evaluation was made according to the following criteria.
In addition, the state which does not peel in all the grid squares was represented as 100/100, and the state which peeled in all the grid squares was represented as 0/100.
〔Evaluation criteria〕
A: 100/100
○: 71/100 to 99/100
Δ: 51/100 to 70/100
X: 0/100 to 50/100

<Pencil hardness>
The coating film was scratched with a load of about 1 kg using a predetermined pencil (Uni, manufactured by Mitsubishi Pencil Co., Ltd.). If the coating did not tear, the pencil hardness was increased by one step and the coating was further scratched. And the hardness of the hardest pencil which a coating film cannot tear was made into pencil hardness.

<Sweat resistance>
An acidic artificial sweat solution as defined in JIS L0848: 2004 was prepared. The coating film was immersed in artificial sweat and kept at 40 ° C. for 48 hours. Thereafter, the coating film was washed and dried, and the surface was visually observed. Evaluation was made according to the following criteria.
〔Evaluation criteria〕
◎: No change in coating film ○: Gloss decreased Δ: Whiteness ×: Changed to pure white Similar results were obtained with alkaline artificial sweat.

<Chemical resistance>
Hand cream (Atrix, manufactured by Kao Co., Ltd.) was applied to the coating film, kept at 40 ° C. for 2 days, and the changes after washing and drying were confirmed visually and by touch. Evaluation was made according to the following criteria.
〔Evaluation criteria〕
A: No change in both visual and finger touch.
○: There is a change in gloss and there is no change in touch.
Δ: Change in finger touch (with tackiness)
×: Further change in touch (hardness is greatly reduced).

(Comparative Example 1)
As a polylactic acid emulsion, KN-26 (35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000) manufactured by Toho Chemical Industry Co., Ltd. was used.
When the obtained coating film was smooth, the polylactic acid emulsion was spray-coated on the ABS flat plate so that the average thickness was 20 μm, and dried by heating at 70 ° C. for 30 minutes to obtain a coating film.
The obtained coating film was an opaque film with a lot of bubbles and bubbles and poor adhesion.
In the adhesion test, peeling of the coating film occurred just by making a cut.

(Comparative Example 2)
120 g of polylactic acid emulsion (KN-26, manufactured by Toho Chemical Co., Ltd., 35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000), and isocyanate curing agent (Bernock DNW-5500, manufactured by DIC Corporation, solid content) 80% by weight) and 20 g. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
The obtained coating film was an opaque film with a lot of stuffiness.
In the adhesion test, although it was not peeled when the cut was made, it was almost peeled off when the tape was attached and peeled off.

Example 1
100 g of polylactic acid emulsion (KN-26, manufactured by Toho Chemical Industry Co., Ltd., 35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000) and 8 g of methylpropylene glycol acetate were mixed. The obtained mixture was stirred at 600 rpm for 5 minutes using a propeller stirrer to obtain a main agent.
The obtained main agent and 17 g of an isocyanate curing agent (Bernock DNW-5500, manufactured by DIC Corporation, solid content: 80% by mass) were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
A smooth and transparent film was obtained.
In the adhesion test, all grids remained on the substrate without peeling off.

(Comparative Example 3)
100 g of polylactic acid emulsion (KN-26, manufactured by Toho Chemical Industry Co., Ltd., 35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000) and 15 g of butylpropylene glycol were mixed. When the obtained mixture was stirred for several minutes at 600 rpm using a propeller stirrer, the emulsion was broken and solid matter was generated.

(Comparative Example 4)
100 g of polylactic acid emulsion (KN-26, manufactured by Toho Chemical Industry Co., Ltd., 35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000) and 5 g of normal butanol (boiling point: 118 ° C.) were mixed. When the obtained mixture was stirred for several minutes at 600 rpm using a propeller stirrer, the emulsion was broken and solid matter was generated.

(Comparative Example 5)
100 g of polylactic acid emulsion (KN-26, manufactured by Toho Chemical Industry Co., Ltd., 35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000) and 5 g of butyl acetate (boiling point: 126 ° C.) were mixed. When the obtained mixture was stirred for several minutes at 600 rpm using a propeller stirrer, the emulsion was broken and solid matter was generated.

(Example 2)
100 g of polylactic acid emulsion (KN-26, manufactured by Toho Chemical Industry Co., Ltd., 35% by mass of polylactic acid, weight average molecular weight of polylactic acid 16,000), 4 g of methylpropylene glycol acetate, and 2 g of butylpropylene glycol were mixed. The obtained mixture was stirred at 600 rpm for 5 minutes using a propeller stirrer to obtain a main agent.
The obtained main agent and 17 g of an isocyanate curing agent (Bernock DNW-5500, manufactured by DIC Corporation, solid content: 80% by mass) were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.

(Comparative Example 6)
Randy PL-2000 (polylactic acid 40 mass%, polylactic acid weight average molecular weight 16,000) manufactured by Miyoshi Oil & Fat Co., Ltd. was used as the polylactic acid emulsion.
The polylactic acid emulsion was spray-coated on the ABS flat plate and dried by heating at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
The obtained coating film was opaque.
In the adhesion test, more than half of the mass was peeled off by tape peeling.

(Comparative Example 7)
100 g of a polylactic acid emulsion (Randy PL-2000, manufactured by Miyoshi Oil & Fats Co., Ltd., polylactic acid 40 mass%, weight average molecular weight of polylactic acid 16,000) and 5 g of diethylene glycol butyl methyl ether were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
In the adhesion test, although better than Comparative Example 6, about 30% of the mass was peeled off by tape peeling.

(Example 3)
100 g of a polylactic acid emulsion (Randy PL-2000, manufactured by Miyoshi Oil & Fats Co., Ltd., polylactic acid 40 mass%, weight average molecular weight of polylactic acid 16,000) and 5 g of diethylene glycol butyl methyl ether were mixed. The obtained mixture was stirred at 600 rpm for 5 minutes using a propeller stirrer to obtain a main agent.
The obtained main ingredient and 18 g of isocyanate curing agent (Duranate WB40-80D, manufactured by Asahi Kasei Corporation, solid content 80% by mass) were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
A transparent and glossy film was obtained.
In the adhesion test, all grids remained on the substrate without peeling off.

Example 4
100 g of polylactic acid emulsion (Randy PL-2000, manufactured by Miyoshi Oil & Fats Co., Ltd., polylactic acid 40 mass%, polylactic acid weight average molecular weight 16,000) and 8 g of diethylene glycol monomethyl ether were mixed. The obtained mixture was stirred at 600 rpm for 5 minutes using a propeller stirrer to obtain a main agent.
The obtained main ingredient and 18 g of isocyanate curing agent (Duranate WB40-80D, manufactured by Asahi Kasei Corporation, solid content 80% by mass) were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
A transparent and glossy film was obtained.
In the adhesion test, all grids remained on the substrate without peeling off.

(Example 5)
A polylactic acid emulsion was prepared by the following method.
A polylactic acid solution obtained by dissolving polylactic acid (weight average molecular weight 60,000) in an organic solvent was poured into stirred water, dispersed and emulsified. Then, the polylactic acid emulsion (PLAEm, polylactic acid 30 mass%) was obtained by removing the said organic solvent from the obtained emulsion.
100 g of the obtained polylactic acid emulsion (PLAEm) and 8 g of methylpropylene glycol acetate were mixed. The obtained mixture was stirred at 600 rpm for 5 minutes using a propeller stirrer to obtain a main agent.
The obtained main ingredient and 6 g of isocyanate curing agent (Duranate WB40-80D, manufactured by Asahi Kasei Co., Ltd., solid content: 80% by mass) were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
A transparent film was obtained.
In the adhesion test, about 30% of the grids were peeled off.

(Example 6)
100 g of the polylactic acid emulsion (PLAEm) obtained in Example 5 and 8 g of methylpropylene glycol acetate were mixed. The obtained mixture was stirred at 600 rpm for 5 minutes using a propeller stirrer to obtain a main agent.
The obtained main ingredient and 18 g of isocyanate curing agent (Duranate WB40-80D, manufactured by Asahi Kasei Corporation, solid content 80% by mass) were mixed. The obtained mixture was stirred at 600 rpm for 10 minutes using a propeller stirrer to obtain an aqueous coating composition.
The obtained aqueous coating composition was filtered through a # 200 mesh, sprayed onto the ABS flat plate, and heated and dried at 70 ° C. for 30 minutes to obtain a coating film having an average thickness of 20 μm.
A transparent film was obtained.
In the adhesion test, about 30% of the grids were peeled off.

In Table 1, the numerical value in parentheses in the column of solvent represents the amount (% by mass) relative to polylactic acid.
In Comparative Examples 1 and 6, the adhesion was too bad, and other coating films could not be evaluated.
In Comparative Examples 3 to 5, a coating film could not be formed and the coating film could not be evaluated.

Methyl propylene glycol acetate (boiling point: 146 ° C., solubility in water: 20.5 g / 100 g)
Butylpropylene glycol (boiling point: 170 ° C., solubility in water: 6.4 g / 100 g)
Diethylene glycol butyl methyl ether (boiling point: 212 ° C., solubility in water: 9.2 g / 100 g)
Diethylene glycol monomethyl ether (boiling point 194 ° C, easily soluble in water)

As shown in Example 2, by using two kinds of glycol ether solvents having different boiling points, a coating film having excellent appearance and curability (pencil hardness, sweat resistance, chemical resistance) was obtained. .
As Example 4 shows, when the glycol ether solvent used is easily soluble in water (the solubility in water is not finite), the solubility of the glycol ether solvent in water is finite (for example, Example Compared to 1), sweat resistance and chemical resistance were lowered.
As Example 5 shows, when the weight average molecular weight of polylactic acid exceeds 50,000, the number of crosslinking points is small, so compared to the case where the weight average molecular weight of polylactic acid is 50,000 or less (for example, Example 1). , Adhesion decreased.
In Example 6, since the content of the isocyanate curing agent was increased, the adhesion was improved as compared with Example 5, but on the other hand, the pencil hardness and sweat resistance were slightly lowered.

Regarding the embodiment including the above Examples 1 to 6, the following additional notes are disclosed.
(Additional remark 1) The water-based coating composition characterized by containing polylactic acid, an isocyanate hardening | curing agent, a glycol ether solvent, and water.
(Additional remark 2) The water-based coating composition of Additional remark 1 whose weight average molecular weights of the said polylactic acid are 50,000 or less.
(Additional remark 3) The water-based coating composition in any one of Additional remark 1 or 2 whose boiling point of the said glycol ether solvent is 110 to 250 degreeC.
(Additional remark 4) The water-based coating composition in any one of Additional remark 1 to 3 whose solubility with respect to the water of the said glycol ether solvent is finite.
(Additional remark 5) The water-based coating composition in any one of Additional remark 1 to 4 whose content of the said glycol ether solvent is 35 mass% or less with respect to the said polylactic acid.
(Additional remark 6) The water-based coating composition in any one of Additional remark 1 to 5 whose said glycol ether solvent is 2 or more types from which a boiling point differs.
(Appendix 7) An electronic apparatus comprising a casing coated with the water-based paint composition according to any one of appendices 1 to 6.

20 notebook computer 21 notebook computer body 22 liquid crystal display panel section 23 keyboard section 24 pointing device 25 housing

Claims (4)

An aqueous coating composition comprising polylactic acid, an isocyanate curing agent, a glycol ether solvent containing at least one of methyl propylene glycol acetate, diethylene glycol butyl methyl ether, and diethylene glycol monomethyl ether, and water.   The water-based coating composition according to claim 1, wherein the polylactic acid has a weight average molecular weight of 50,000 or less. 3. The aqueous coating composition according to claim 1, wherein a content of the glycol ether solvent is 35% by mass or less based on the polylactic acid. An electronic device comprising a casing coated with the water-based paint composition according to claim 1.