JPH083350A - Surface coating of polyolefin resin formed article - Google Patents

Abstract

PURPOSE:To achieve excellent adhesive strength of a coating-film layer even by a short-time modification treatment and reduce a cost for the coating treat ment in surface coating of a polyolefin resin formed article. CONSTITUTION:This surface modification of a resin formed article 2 is carried out by using a powered washing apparatus 4 and a surface modification apparatus 5. The surface modification apparatus 5 is provided with an ozone generator 8, a heater 9, a spray nozzle 10, a drain 11, etc. After subjected to a power- washing treatment, the resin formed article 2 is made to contact with a running aqueous ozone solution in the surface modification apparatus 5, and the surface of the resin formed article 2 is evenly oxidized by an oxidizing activity of ozone remaining in the water and accordingly polarized. Further, a coating film is formed with a paint compounded with Tchlorinated polypropylene. Even in a short time of composed of the ozone aqueous solution, sufficient adhesive strength of the coat-film layer is achieved by virtue of a synergic effect between the surface modification by the oxidation and the bonding strength by the chlorinated polypropylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface coating method for a polyolefin resin molded article such as polypropylene having a relatively small surface polarity.

[0002]

2. Description of the Related Art Conventionally, when a polyolefin resin molding having a relatively small surface polarity represented by polypropylene is subjected to secondary processing such as painting, the surface of the resin molding is first cleaned and surface-modified with a solvent such as trichloroethane. (Roughening) is performed. Next, the surface is subjected to primer coating or plasma treatment. By performing such a treatment, the surface is polarized and the resin molded product and the topcoat paint are firmly bonded. However, in recent years, there has been an increasing demand for regulation of cleaning using halogenated hydrocarbon-based organic solvents such as trichloroethane, and a new method for modifying the surface of a polyolefin resin molded article instead of the above solvent has been newly developed. The method of becoming is studied in various fields.

Therefore, as one of the techniques for responding to the above-mentioned demand, there is a technique disclosed in, for example, Japanese Patent Laid-Open No. 3-103448. In this technique, a polypropylene resin molded article is treated under an ozone stream to oxidize its surface and impart hydrophilicity to the surface. However, in the above technique, since the polypropylene resin molded product is treated under the ozone stream, it is difficult to uniformly modify the entire surface of the resin molded product. That is, in order to uniformly modify the surface, it is necessary to apply the ozone stream to all the surfaces substantially uniformly and to each surface for substantially the same time. Therefore, if the resin molded product has a complicated shape, the entire surface of the resin molded product cannot be uniformly modified unless the resin molded product or the air flow is appropriately moved. As a result, it was very difficult to apply a uniform coating.

In order to deal with the above problems, the applicant of the present application has
Japanese Patent Application No. 5-163619 discloses that a polyolefin resin molded product is brought into contact with an ozone aqueous solution to oxidize the surface of the polyolefin resin molded product.
According to this method, the surface of the resin molded product can be easily and uniformly modified by omitting the use of the organic solvent before the modifying step. Further, the subsequent coating makes it possible to firmly form a coating layer on the surface of the resin molded product.

[0005]

However, with the above technique, although a certain excellent reforming result was obtained, there were the following problems. That is, taking a typical polypropylene resin material as a current polyolefin resin molded product, the resin molded product contains polypropylene as a main component and EPM (ethylene-propylene random copolymer), talc, etc. ing. However, these components do not include substances that easily react with ozone. Therefore, in order to obtain a sufficient degree of modification to firmly adhere the coating layer to the surface of the resin molded product,
It took a considerable amount of processing time (for example, about 20 minutes). As a result, the cost required for the modification is increased.

The present invention has been made in order to solve the above-mentioned problems, and in the surface coating of a polyolefin resin molded product having a relatively small surface polarity, even if it is a short-time modification treatment, it is extremely difficult. An object of the present invention is to provide a surface coating method for a polyolefin resin molded article, which can obtain good coating film adhesive strength and can reduce the cost required for coating.

[0007]

In order to achieve the above object, in the invention described in claim 1, an aqueous solution of ozone is brought into contact with the polyolefin resin molded product to form a surface of the polyolefin resin molded product. A coating layer formed on the surface of the polyolefin-based resin molded article by applying a coating material containing chlorinated polypropylene to the surface of the modified polyolefin-based resin molded article, which is oxidized, and the surface of the modified polyolefin-based resin molded article. The gist is a surface coating method of a polyolefin-based resin molded article, which comprises a coating layer forming step of forming a.

[0008]

According to the invention described in claim 1, the aqueous ozone solution comes into contact with the polyolefin resin molded product. At this time, the surface of the polyolefin resin molded product is oxidized and polarized due to the oxidizing power of ozone remaining in water.
Here, no matter what shape the polyolefin resin molded product has, the ozone aqueous solution can surely contact the entire surface of the resin molded product. Therefore, reaction spots are unlikely to occur at various points on the surface of the resin molded product, and the oxidation reaction is uniformly performed on each surface.

Next, a coating material containing chlorinated polypropylene is applied to the surface of the modified polyolefin resin molded product. By this coating, a coating layer is formed on the surface of the polyolefin resin molded product. Here, the chlorinated polypropylene in the paint can be joined to the unoxidized portion of the surface of the resin molded product by the compatibility of the non-chlorinated portion of the chlorinated polypropylene. Further, the chlorinated portion also interacts with the oxidation functional (polar) group and joins. Therefore, even if the above modification is not sufficient, the coating film formed by the synergistic action of the bonding with the chlorinated polypropylene and the bonding of the polar group of the resin molded product surface and the polar group of the paint. The layer will adhere extremely strongly to the surface of the resin molding.

[0010]

As described above, according to the present invention, when coating the surface of a polyolefin resin molded product having a relatively small surface polarity, a very good coating film adhesion strength can be obtained even by a short-time modification treatment. An excellent effect is obtained in that the cost required for coating can be reduced.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 2, a resin product 1 such as an automobile bumper includes a resin molded product 2 and a coating layer 3 formed on the surface thereof. The resin molded product 2 is molded from polypropylene with a mold, and its surface is modified (oxidized). Then, in this embodiment, the surface of the resin molded product 2 is directly coated. The coating material forming the coating layer 3 is formed by blending chlorinated polypropylene with polyester coating material, for example.

Next, in manufacturing the resin product 1,
The surface reforming process from the molding of the resin molded product 2 to the pre-painting stage will be described with reference to the process diagram showing the reforming device of FIG.

As shown in the figure, when the surface of the resin molding 2 is modified, a power wash cleaning device 4 and a surface modification device 5 are used. Further, the conveyor 6 is used during the series of steps, and the resin molded product 2 is conveyed to the right in the figure by the movement of the conveyor 6, for example. The power wash cleaning device 4 is a device for simply cleaning and removing dirt on the surface of the resin molded product 2, and includes a pump, a nozzle 7 and the like (not shown). Then, jet water is sprayed onto the resin molded product 2 from the tip of the nozzle 7.

Further, the surface reforming device 5 has an ozone generator 8, a heater 9, a spray nozzle 10, a drain 11 and a hose for connecting the respective members. The ozone generator 8 can change oxygen into ozone and dissolve ozone in water. Further, the ozone generator 8 is provided with a pump (not shown) inside so that the ozone aqueous solution can be pressure-fed to the heater 9. Further, the heater 9 provided in the middle of the hose can heat the flowing ozone aqueous solution to a predetermined temperature.

In addition, the spray nozzle 10 provided at the tip of the hose is arranged so that the heated ozone aqueous solution sent from the heater 9 side hits the resin molding 2 in a spray form.

Further, the drain 11 is provided below the conveyor 6 and stores the ozone aqueous solution after coming into contact with the resin molding 2. This drain 1
The ozone aqueous solution accumulated in 1 is again introduced into the ozone generator 8 through the pipe 12 at a constant speed.

The relationship between the solubility coefficient of ozone and the temperature of water is as shown in FIG. That is, ozone becomes less likely to be dissolved as the temperature of water rises, and ozone becomes more likely to be decomposed as the temperature rises. Contrary to this, it is also generally known that the higher the temperature of water, the higher the reaction rate (surface modification rate). Therefore, the ozone concentration is as high as possible, and
It is desirable that the heater 9 be appropriately adjusted for heating so that the temperature of the ozone aqueous solution becomes as high as possible.

The resin molded product 2 whose surface has been modified by the surface modifying device 5 is dried by the drying device 13 and then subjected to the coating process. Next, a method of modifying the surface of the resin molded product 2 by using the above-mentioned surface modification device 5 and the like, and a function effect at the time of modification will be described.

First, a resin molded product 2 molded in a predetermined shape by a mold is placed on an operating conveyor 6 with its design surface facing upward, and moved to the right in FIG. go.
Then, by using the power wash cleaning device 4, jet water is sprayed from the tip of the nozzle 7 onto the surface of the resin molded product 2. Then, dirt such as dust and dust attached to the surface of the resin molded product 2 is washed and removed.

Next, the resin molded product 2 is further moved to the right in the figure by the conveyor 6 and provided to the surface reforming device 5. At this time, the sprayed ozone aqueous solution comes into contact with the resin molded product 2. The surface of the resin molded product 2 is oxidized by the oxidizing power of ozone remaining in water accompanying this contact,
Is polarized.

Resin molded product 2 surface-modified as described above
Is dried by the drying device 13 and provided for the next coating step. In the coating process, as described above,
For example, a paint in which chlorinated polypropylene is mixed with a polyester paint is applied. Then, by drying again, the coating layer 3 is formed on the surface of the resin molded product 2.

As described above, in this embodiment, the resin molded product 2 is used.
Aqueous ozone solution comes into contact with the surface of the resin, and the surface of the resin molded product is oxidized and polarized due to the oxidizing power of ozone. Here, no matter what shape the resin molded product 2 has (the shape of the bumper in this embodiment), the ozone aqueous solution can surely contact the entire design surface of the resin molded product 2. . Therefore, reaction spots are unlikely to occur at various points on the surface of the resin molded product 2, and the oxidation reaction is uniformly performed on each surface.

Further, in this embodiment, a coating material containing chlorinated polypropylene is applied to the surface of the modified resin molding 2 to form the coating layer 3. Here, the chlorinated polypropylene in the paint can be joined to the unoxidized portion of the surface of the resin molded product by the compatibility of the non-chlorinated portion of the chlorinated polypropylene. Further, the chlorinated portion also interacts with the oxidation functional (polar) group and joins. Therefore, the time for the modification process is short,
Even if the above modification is not sufficient,
Due to the synergistic effect of the bonding with chlorinated polypropylene and the bond between the polar group on the surface of the resin molded product 2 and the paint, the coating layer 3 formed is extremely strongly adhered to the surface of the resin molded product 2. As a result, an extremely good adhesive strength of the coating film layer 3 can be obtained even by a short-time modification treatment, and thus the cost required for the entire coating process can be reduced.

Further, as a peculiar effect of this embodiment,
Since the aqueous ozone solution is sprayed during the reforming process, the amount of ozone that hits the surface of the resin molded product 2 per unit time is relatively large. Therefore, the time for contacting the ozone aqueous solution as a whole is extremely short as compared with the case where the resin molded product is simply immersed in the ozone aqueous solution.

Further, since the ozone aqueous solution is sprayed on the surface of the resin molded product 2, the film diffusion layer of the ozone aqueous solution formed on the surface of the resin molded product 2 is formed relatively thin. In this state, the ozone aqueous solution is further hit by hitting the boundary film diffusion layer, so that the diffusion layer is compressed. In addition, the compression disturbs the diffusion layer discontinuously, further promoting the oxidation reaction. Therefore, the contact time of the ozone aqueous solution can be further shortened.

Further, unlike the case where the resin molded product is immersed in the ozone aqueous solution, it is only necessary to apply the spray-shaped ozone aqueous solution to the resin molded product 2, so that the ozone aqueous solution can be contacted in a series of steps. That is,
After the power wash cleaning, the resin molding can be temporarily removed from the conveyor and immersed in the container, which is different from the conventional technique. As a result, the reforming equipment and the installation space can be simplified and the cost can be reduced.

In addition, in the present embodiment, unlike the prior art in which it was necessary to heat the ozone aqueous solution in the container, the ozone aqueous solution was heated by the heater 9 immediately before being applied to the resin molding 2. . Therefore, the decomposition of ozone during the period when the high temperature state is maintained can be suppressed to the minimum. Therefore, the ozone concentration in the sprayed Othon aqueous solution can be increased, and the reforming efficiency can be improved.

In addition, in the present embodiment, since only the aqueous solution applied to the resin molded product 2 needs to be heated, the energy for heating can be relatively small. As a result, the energy cost can be reduced.

[Experiment] Next, in order to confirm the above-mentioned effects, an experiment was conducted to measure the coating film adhesive strength when coating was performed with or without surface modification and when the coating material was changed. To do.

(Production of polyolefin resin molded product and simple cleaning) First, in this example, a homopolymer of polypropylene was used as the polyolefin resin. And the said polymer was shape | molded in the size of "100x150x3mm", and it was set as the test piece P.

Further, the test piece P was subjected to power wash cleaning. That is, at a water temperature of “60 ° C.”, water having a water pressure of “100 kPa” is applied to the surface of the test piece P,
Dust and the like adhering to the surface was removed.

(Apparatus) Next, an experimental apparatus used for surface modification will be described. However, the device used here is merely an experimental device. Now, as the means (flowing means) for applying the ozone aqueous solution to the test piece P, the same one as the surface reforming apparatus 5 described in the above-mentioned embodiment was used. That is, as shown in FIG. 4, a type in which an ozone aqueous solution was sprayed onto the test piece P from the spray nozzle 10 was used. Further, the followings were used for each means other than the above-mentioned running water means. That is, as shown in the figure, an ozone generator 32 is connected to the oxygen gas cylinder 31, and ozone generated here is supplied to a mixer 35 via a valve 33 and a backflow prevention trap 34. The mixer 35 is supplied with the ozone aqueous solution (water) pumped from the pump 36, and the ozone gas is dissolved in the ozone aqueous solution (water) in the mixer 35. Further, the ozone aqueous solution and a part of the ozone gas are introduced into the next mixer 37, and the above dissolution is continued here. The heater 38 provided around the mixer 37 heats the ozone aqueous solution to a predetermined temperature.

The ozone aqueous solution that has passed through the mixer 35 is introduced into the excess gas separation trap 39. Then, excess ozone gas is introduced from the separation trap 39 to the activated carbon filter 42 via the valve 40 and the aggregation trap 41. In the activated carbon filter 42, the ozone gas is decomposed into oxygen gas, and the oxygen gas is aspirated by the aspirator 4.
3 is discharged to the outside. On the other hand, the ozone aqueous solution that has passed through the excess gas separation trap 39 hits the test piece P on the mounting table 44 through the above-described flowing means. Then, the subsequent ozone aqueous solution is placed on the mounting table 44.
Is stored in a glass tank 45 for storing the gas, and then introduced into the pump 36 again. Then, in the present experiment, the above-mentioned series of flow is repeated.

In the above apparatus, the ozone concentration of the ozone aqueous solution immediately before each flowing means is "7 ppm", the hydrogen ion concentration (pH) is "about 3.7",
The temperature is "50 ° C" and the running water volume is "1.7 liters /
It was a minute '. The processing time was 100 seconds. On the other hand, as the ozone generator 32, a silent discharge type (OZSD-5A manufactured by EBARA CORPORATION) was used, and the amount of ozone gas generated at this time was “3 g / hr”. Further, the concentration of the aqueous ozone solution was measured using a commercially available ozone water concentration measuring instrument (trade name: Kentaro, manufactured by EBARAJIYOKU). .

(Experimental content) [0035] Using the above-mentioned apparatus, a modified material was prepared and dried (80 ° C x 10 minutes), and a sample not modified was also prepared. Then, painting was performed. As the paint for this coating, there were used three kinds of paints such as polyester paints, acrylic paints, and paints in which chlorinated polypropylene (7% by weight) was mixed with polyester paints. Then, after coating, apply each paint to “80
After being dried at "° C" to form a coating layer, a peel strength test of the coating layer was performed. The peeling strength was measured by using a tensile tester (Tensilon) to measure the peeling strength of the coating layer (however, the pulling angle is "180 °" and the pulling speed is "50 mm / sec").

(Experimental Results) Table 1 below shows the results of measuring the peeling strength of the coating layer at the central portion of each test piece P described above.

[0037]

[Table 1]

As is clear from the above results, it can be seen that the peeling strength is increased when the treatment is carried out with the ozone aqueous solution as in this embodiment. It is also found that the peeling strength is increased when a coating material containing chlorinated polypropylene (chlorinated PP) is used. Further, it is understood that the synergistic effect of these results in the highest peeling strength when the coating material treated with the ozone aqueous solution and containing the chlorinated PP is used.

[Additional Experiment] Next, the peeling strength (coating adhesion strength) was measured when the treatment and coating were performed under the same conditions as in the above experiment except the time of ozone treatment, and the time was variously changed. . The result is shown in the graph of FIG.

As is clear from the figure, compared with the case of the conventional paint (polyester paint), when the paint of this embodiment (containing chlorinated PP) is used, the time required is shorter. It can be seen that sufficient peeling strength can be obtained even with the modification treatment. In other words, it can be said from the results of this experiment that the treatment time of the ozone aqueous solution can be significantly shortened.

The present invention is not limited to the above embodiment, but may be configured as follows, for example. (1) In the above-described embodiment, the ozone aqueous solution is sprayed from the design surface (upper surface) of the resin molded product 2 (test piece P), but the resin molded product 2 (test piece P) is used.
When all of the surfaces are designed surfaces, an ozone aqueous solution may be sprayed from each surface. Further, the spraying is not limited to the above spraying, and the resin molded product may be immersed in an ozone aqueous solution so as to be in contact with it, or the ozone aqueous solution may be applied to the surface of the resin molded product in running water (waterfall) form. You may

(2) In the above-described embodiment, the case where the power wash cleaning device 4 is used to perform the simple cleaning in the pre-modification stage is embodied, but such cleaning may be omitted. (3) In the above examples, polypropylene was used as the material for the polyolefin resin molded product, but if the material is mainly composed of polyolefin, the resin molded product made of polyethylene and other secondary components are blended. It goes without saying that the present invention can be applied to the surface modification of any material such as a mold. Also, the shape is not limited to the shape of the bumper, for example, grill, garnish,
It may have any shape, including various vehicle exterior parts such as moldings, spoilers, lamps, marks, emblems, and wheel covers.

(4) In the above embodiment, the heaters 9 and 38 are provided immediately before the ozone aqueous solution is applied to the resin molded product 2 (test piece P), but the heaters 9 and 38 may be provided at an earlier stage. Therefore, depending on the case, it may be provided in the glass tank 45 shown in the experimental example.

(5) In the above-mentioned embodiment, the paint in which chlorinated polypropylene is blended with the polyester paint is used.
A paint obtained by graft-polymerizing or block-polymerizing chlorinated polypropylene on polyester may be used.

A technical idea which is not described in each claim of the claims and which can be understood from the above-mentioned embodiment will be described below together with its effect. (A) In the method for coating a surface of a polyolefin resin molded article according to claim 1, the surface is modified by applying the aqueous ozone solution in a running water form or a spray form. With such a configuration, a sufficient modifying effect can be obtained even with a short treatment, and the time and cost required for the entire coating can be reduced.

[Brief description of drawings]

FIG. 1 is a system diagram showing a surface reforming device and the like in an embodiment embodying the present invention.

FIG. 2 is a cross-sectional view showing a resin product in one example.

FIG. 3 is a graph showing the relationship between the solubility coefficient of ozone and the temperature of water in one example.

FIG. 4 is a schematic diagram showing an experimental apparatus when a surface modification test is performed in one example.

FIG. 5 is a graph showing the relationship between the peeling strength of the coating film layer and the treatment time of the ozone aqueous solution in one example in comparison with the prior art.

[Explanation of symbols]

 2 ... Resin molded product.

Claims (1)

[Claims] 1. A surface reforming step of bringing an aqueous solution of ozone into contact with a polyolefin-based resin molded article to oxidize the surface of the polyolefin-based resin molded article, and the surface of the modified polyolefin-based resin molded article. On the other hand, a polyolefin-based resin molding comprising a coating layer forming step of forming a coating layer on the surface of the polyolefin-based resin molded article by applying a coating material containing chlorinated polypropylene. How to paint the surface of an object.