JPH0480837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of dyeing and painting the surface of a plastic molded product, in which a pattern, characters, etc. are printed on the surface of the molded product immediately after molding using ink containing a sublimable dye. In the next step, this is heated to transfer the dye into the plastic, resulting in a painting with excellent abrasion resistance.

Generally speaking, the methods of painting on the surface of plastic molded products include screen printing using pigment-based ink,
There are octopus printing, transfer using adhesives, and label pasting, but these have drawbacks such as abrasion resistance, solvent resistance, weather resistance, etc., and the sharpness of patterns, letters, etc. decreases over time. At present, practical use is extremely limited due to problems with functionality and design. A method to solve these problems, that is, to obtain patterns and letters with excellent abrasion resistance, solvent resistance, and weather resistance, is to use a multicolor injection molding machine, or to obtain a method using a multicolor injection molding machine, or to obtain a method using a multicolor injection molding machine, or to obtain a method using a multicolor injection molding machine.
There is a method using sublimation transfer as described in .

A supplementary explanation of the above two methods is as follows. In other words, the method using a multicolor injection molding machine involves preparing two sets: a mold for molding the pattern and a mold for molding other parts, molding the design in the first step, and then molding the other parts. The pattern is molded with a different colored resin. However, in this case, there are disadvantages such as high mold cost, inability to express complicated patterns, characters, etc., and considerable restrictions on the shape of the molded product.

In addition, the sublimation transfer method involves setting the molded product in a predetermined jig in a separate process after molding the molded product, and applying transfer paper printed with ink containing a sublimable dye prepared in advance to the surface of the molded product. The dye and the molded article are heated by pressing a heating plate onto the back side of the transfer paper, and the dye sublimates and permeates into the molded article.

However, in this case, the process of setting the molded product on the transfer jig is complicated, it is difficult to obtain an accurate positional relationship between the pattern and characters printed on the transfer paper, and the molded product is difficult to transfer. There are drawbacks such as the need to raise the temperature of the molded product to a predetermined temperature, which lengthens the transfer cycle, and the possibility that the molded product may be deformed during heating.

The present inventor aims to invent a method for painting patterns and letters on the surface of plastic injection molded products that has excellent wear resistance, solvent resistance, and weather resistance, and that improves the drawbacks of the conventional method described above. It has arrived. That is, after injection molding, the molded product is heated on the surface of a plastic molded product formed by an injection molding machine, and before the molded product is placed in a male mold and discharged, the male mold is heated, and a sublimable dye, a heat-melting migration dye, etc. By printing patterns, letters, and figures on molded products using ink containing a migratory dye, the dye in the ink sublimates with heating in the next process, allowing the dye to penetrate into the injection molded product. This is a method for painting injection molded products.

In addition, the cooling pipe in the male mold is used to heat the male mold before discharging the molded product after injection molding, and the cooling water is discharged by blowing high pressure steam into the pipe in the male mold. In addition, it is a method of heating to a high temperature.

The present invention will be explained in detail below.

The present invention is a method for painting plastic molded products, and the target products include, for example, computers, key tops used in telephones, electrical and building material-related parts that require durability, and harsh boiling,
Containers, etc. used under abrasive conditions. Thermoplastic materials used as plastic molding materials include polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyamide resins,
Cellulose modified resin, acrylic resin, ABS (acrylonitrile-butadiene-styrene copolymer) resin, AS (acrylonitrile-styrene) resin, polycarbonate resin, vinyl chloride resin, etc. or,
As the thermosetting resin, epoxy resin, urethane resin, urea resin, phenol resin, polyester resin, melamine resin, etc. can be used.

The equipment constituting the present invention is basically an injection molding machine, a mold, a concave offset printing (hereinafter referred to as octopus printing) machine, or a screen printing machine. or,
The ink used to decorate molded products contains sublimable dyes, but dyes such as oil-based dyes, disperse dyes, and basic dyes can be used, and should be selected depending on the plastic molded product to be painted. I can do it. For example, when dyeing polyester resin, disperse dyes are suitable, and CIPisperse
A dye with a heat transfer property of about Red 60 can be used.
For polyimide resins, disperse dyes or basic dyes can be used, such as CIPisperse Red 8 or CI
You can choose Basic Blue 5 etc. Direct dyes and reactive dyes can be used for cellulose-modified resins, and cationic dyes are preferred for acrylic resins, ABS resins, and AS resins. On the other hand, disperse dyes are generally suitable for thermosetting resins, and CIBasic
You can use dyes like Orange 7 or CIBasic Orange 8.

In an injection mold, the female and male molds are tightened and the plastic is injected, but when the mold is opened, the molded product remains in the male mold. The mold is opened at a temperature slightly lower than the softening point of the molded product, and heating is performed using a cooling water pipe or a temperature control pipe to prevent the molded product from cooling. Of course, an internal heater may be used for heating. It is desirable to keep the heating temperature slightly lower than the softening point of the molded product. In the above state, patterns, characters, etc. are printed using ink containing a migratory dye such as a sublimation dye or a heat-melting migratory dye using a concave plate offset printing method or a silk screen printing method. The printed ink dries by heating, and the dye in the ink migrates into the molded product. At this time, according to the method of the present invention, there is almost no gap between the male mold and the molded product, so heat conduction is sufficient, and since the temperature on the inner surface side is high, the amorphous inside of the resin constituting the molded product is The intermolecular distance of the mass part is sufficiently large in the interior, so that the dye can penetrate well into the interior. Here, the molded product is discharged from the male mold, and is further dried and impregnated with dye while being heated. The male mold is used in injection molding of thermoplastic resin.
The temperature at which the molded product can be taken out after filling with resin,
That is, it is necessary to cool the product to a temperature below its softening point. In this case, it is preferable to use a medium with a high specific heat, such as water, but such a medium is not suitable for heating the molded product in the next step. Therefore, it is best to attach a switching valve to the inlet of the male cooling pipe, discharge the cooling medium after cooling, and heat it with high-pressure steam or the like. This method also has the advantage that the mold is at a high temperature when filling with resin, making it easier to fill, and even complex shapes can be injection molded with almost no difficulty, making molding easier. Furthermore, since it is easy to change the mold temperature, the molding cycle is shortened and productivity is improved.

In addition to the above, according to the present invention, since printing is performed while the molded product remains in the mold, the positional accuracy is higher than printing after it is placed in the jig offline, and
Since it is in close contact with the male mold, it has the advantage of being able to print with sufficient pressure even on thin-walled molded products.

Next, specific examples of the present invention will be explained using the drawings.

This specific example is a method for molding and painting a key top, which is a molded product A that is made of polybutylene terephthalate resin and has letters on its top surface, as shown in FIG.
First of all, as shown in Figure 2, the vertical injection molding machine 1
A molded article 2 without decoration is molded. At this time, a mold consisting of a female mold 3 and a male mold 5 is set in the injection molding machine 1, and the female mold 3 is attached to the nozzle 4 side of the injection molding machine 1, and when injecting and cooling the resin, It moves downward and is combined with the male mold 5. The male mold 5 is attached to a rotary table 6, and the female mold 3 is used during resin injection and cooling.
, and the others move to the printing station 7. Molding conditions such as resin injection temperature, injection pressure, and molding cycle are general conditions for molding polybutylene terephthalate. During molding, when the molded product A falls sufficiently below the softening point, the female mold 3
opens upwards. At this time, the molded product A remains on the male mold 5 side. When the mold opening is completed, the male mold 5 on the movable table is moved to the printing station 7 with the molded product A attached.
Move to. Also, before and after this, the water in the cooling water pipe in the male mold is discharged with high pressure steam, and the temperature of the male mold and molded article is maintained at the heat transfer temperature of the dye. An intaglio offset printing machine is installed in the printing station. The intaglio offset printing machine is composed of an intaglio plate 8, a doctor 9, a pad 10 made of silicone, and a rod for moving the pad 11. Here, first, ink is placed on the intaglio plate 8, and the doctor 9
The ink 12 is filled into the recesses 13 of the intaglio plate having a predetermined character shape, and then the pads 10 are filled with the ink 12.
is brought into close contact with the concave portion 13 of the intaglio plate 8, and the ink 12 is transferred onto the surface of the pad 10. At the same time as the male mold 5 stops at a predetermined position on the printing station 7, the male mold 5
The pad 10 is moved to a predetermined position on the upper molded product and brought into close contact with the pad, and the ink 12 on the pad is transferred to the molded product 2. When the transfer is completed, the pad 10 separates from the molded article A and returns to its predetermined position (directly above the intaglio). At this time, the temperature of the male type is 130-200℃, preferably
Heat to 140-170℃. The male mold 5 may be further heated in a heating step, or may be heated in a separate step. Heat for about 10 seconds to 10 minutes, long enough to prevent the dye from bleeding, and then
The molded product A is promptly discharged from the male mold 5 and cooled. The male mold returns to the molding station and is clamped. When the resin is injected into the mold, the water vapor in the cooling water pipe 14 is discharged, cooling flows, and the resin in the mold is injected. It is quickly cooled and solidified, and the next cycle is started. A series of operations of the injection molding machine, printing machine, mold temperature control valve, etc. are all made to be interlocked.

The penetration of the dye into the molded product is several tens of micrometers, and as a result, a molded product with a pattern excellent in abrasion resistance, solvent resistance, and weather resistance can be obtained.

Furthermore, even after drying, dyes that do not penetrate into the molded product or various binders in the ink may remain on the surface of the molded product, but this can be removed if necessary using a solvent suitable for the ink composition. I think it's appropriate.

The above is the explanation of the present invention. By using the present invention, the cost is significantly lower than the method using a multicolor molding machine, which has been conventionally used as a method of painting plastic molded products that require durability. It is now possible to down-size the product, and it is now possible to decorate the molded product with no restrictions on the shape of the pattern. Also, compared to conventional methods and methods that use sublimation dyes, that is, methods in which molding and painting are done off-line, it is possible to utilize the heat of the molded product immediately after molding, and it is possible to repaint the molded product after molding. There is no need to reinsert it into the painting jig,
The positional accuracy of painting is greatly improved, the need for a painting jig is eliminated, and the preheating of the molded product can be used to sublimate the dye by heating the molded product after painting. Plastic has a number of advantages, such as being able to easily improve cycle times, being able to perform friction-resistant printing on thin-walled molded products and molded products with complex shapes, and heating the male mold to further heat the material from within, resulting in faster penetration. It is thought to be a method of painting molded products.

Examples of the invention will be shown below.

<Example> Using polybutylene terephthalate resin, a vertical injection molding machine with a rotary table [manufactured by Yamashiro Seiki Co., Ltd.]
It is molded using a 16-cavity mold measuring 18.2 mm x 18.2 mm x 10.5 mm. The mold was a cold runner type, and the gate was a tunnel gate type. Molding conditions are cylinder temperature
200-260℃, molding cycle is 15 seconds, molding and painting cycle including slide table movement is 18
Second, 3 male molds are used. During molding, cooling water at 12℃ is flowed through the male mold, and at other times, the temperature is 150℃.
The male mold was heated by flowing water vapor. The printing machine used was a modified pad printing machine manufactured by Taihei Kogyo Co., Ltd. The pads are made of silicone rubber. Alphabetical characters were printed for the designs and characters.

Ink composition Dye: Sumikalon FB Conc [Sumitomo Chemical
Co., Ltd.] 10 parts Binder: Ethyl cellulose 15 parts Solvent: Isopropyl alcohol 50 parts Methyl cellosolve 25 parts Printing was carried out using the above ink composition. The depth is 25
A micrometer was used. The ink was dry to the touch on the molded article in 1-2 seconds and immediately began to penetrate. The top surface was also heated at 160°C for 10 and 12 seconds, for a total of 22 seconds, to obtain a penetration of 60 micrometers.

After that, the binder was washed away from the above molded product with toluene, and a molded product with a good and clear pattern was obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a molded product A obtained by the painting method of the present invention, FIG. 2 is an explanatory diagram showing the injection molding process of the present invention, and FIG. 3 is an explanatory diagram showing the painting process of the present invention. , FIG. 4 is an explanatory diagram showing the discharge process of the present invention. A... Molded product, 1... Vertical injection molding machine, 2...
Unpainted molded product, 3...female mold, 4...
Nozzle, 5...male type, 6...rotary table, 7...
... Printing station, 8 ... Intaglio, 9 ... Doctor, 10 ... Pad, 11 ... Pad movement rod, 12 ... Ink, 13 ... Recess, 14 ... Cooling water pipe, 15 ... Ejector pin .

Claims (1)

[Claims] 1. On the surface of a plastic molded product molded by an injection molding machine, if the molded product is in a male mold after injection molding,
Before being discharged, injection molded products are produced by heating the male mold and printing patterns, letters, figures, etc. on the molded products using ink containing sublimation dyes or heat-transferable dyes. A method of painting plastic molded products that involves penetrating the inside with dye. 2. A patent claim characterized in that the heating means of the male mold utilizes a cooling water pipe in the male mold and blows high pressure steam into the cooling water pipe to discharge the cooling water and heat it to a high temperature. A method for painting plastic molded products according to item 1.