JP3183045B2 - Surface coating method for molded polyolefin resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, when a polyolefin resin molded product having a relatively small surface polarity represented by polypropylene is subjected to secondary processing such as painting, first, the surface of the resin molded product is washed 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 article and the topcoat paint are firmly joined. However, in recent years, there has been an increasing demand to regulate the use of a halogenated hydrocarbon-based organic solvent such as trichloroethane for cleaning, and a new method for modifying the surface of a polyolefin resin molded article instead of the above-mentioned solvent has been required. Various methods are being studied in various fields.

Accordingly, as one of the techniques to meet the above demand, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. 3-103448. In this technique, the surface of a polypropylene resin molded product is oxidized by being treated under an ozone stream, and hydrophilicity is imparted to the surface. However, in the above technique, since the polypropylene resin molded article is treated under an ozone stream, it has been difficult to uniformly modify all surfaces of the resin molded article. That is, in order to uniformly modify the surfaces, the ozone gas stream must be applied to all the surfaces almost uniformly and to each surface for almost the same time. Therefore, in the case where the resin molded product has a complicated shape, all surfaces of the resin molded product cannot be uniformly modified unless the resin molded product or the airflow is moved appropriately. It was very difficult to apply a uniform coating.

[0004] In order to address the above problems, the present applicant has
Japanese Patent Application No. 5-163319 discloses that a polyolefin resin molded article is brought into contact with an aqueous ozone solution to oxidize the surface of the polyolefin resin molded article.
According to this method, the surface of the resin molded product can be easily and uniformly modified without using an organic solvent before the modification step. In addition, a coating layer can be firmly formed on the surface of the resin molded product by the subsequent coating.

[0005]

However, in the above-mentioned technology, although a certain excellent reforming result can be obtained, there are the following problems. That is, as an example of a typical polyolefin resin molded article as a current polyolefin resin molded article, the resin molded article is mainly composed of polypropylene, and is mixed with EPM (ethylene-propylene random copolymer), talc, and the like. ing. However, these components do not contain a substance that easily reacts 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,
A considerable processing time (for example, about 20 minutes) was required. As a result, the cost required for the reforming increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is very effective in coating a polyolefin-based resin molded product having a relatively small surface polarity even in a short-time modification treatment. It is an object of the present invention to provide a surface coating method for a polyolefin-based resin molded product which can obtain good coating film adhesive strength and can thereby reduce the cost required for coating.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, an ozone aqueous solution is brought into contact with a polyolefin-based resin molded product, so that the surface of the polyolefin-based resin molded product is modified. A surface modification step of oxidizing, and applying a coating obtained by blending chlorinated polypropylene to a polyester coating to the surface of the modified polyolefin-based resin molded product, thereby obtaining a surface of the polyolefin-based resin molded product. SUMMARY OF THE INVENTION The gist of the present invention is to provide a method for coating a surface of a polyolefin-based resin molded product, which comprises a coating film layer forming step of forming a coating film layer on a surface of a molded article.

[0008]

According to the first aspect of the present invention, the aqueous ozone solution comes into contact with the polyolefin resin molded article. At this time, the surface of the polyolefin resin molded article is oxidized and polarized by the oxidizing power of the ozone remaining in the water.
Here, regardless of the shape of the polyolefin-based resin molded product, the ozone aqueous solution can reliably contact the entire surface of the resin molded product. Therefore, reaction spots are less likely to occur at each location on the surface of the resin molded product, and the oxidation reaction is uniformly performed on each surface.

Next, a coating obtained by blending chlorinated polypropylene with a polyester coating is applied to the surface of the modified polyolefin resin molded product. By this application, a coating layer is formed on the surface of the polyolefin-based resin molded product. Here, the chlorinated polypropylene in the coating material can be joined to the unoxidized portion of the surface of the resin molded product by the unchlorinated portion of the chlorinated polypropylene being compatible. Further, the chlorinated portion also has an interaction with the oxidized functional (polar) group and forms a bond. For this reason, 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 very firmly to the surface of the resin molding.

[0010]

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

[0011]

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

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

As shown in FIG. 1, a power wash cleaning device 4 and a surface reforming device 5 are used for modifying the surface of the resin molded product 2. In addition, a conveyor 6 is used when going through a series of these steps, and the resin molded product 2 is conveyed by moving the conveyor 6, for example, to the right in the figure. The power wash cleaning device 4 is a device for easily 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-like water is blown from the tip of the nozzle 7 to the resin molded product 2.

The surface reforming apparatus 5 has an ozone generator 8, a heater 9, a spray nozzle 10, a drain 11, and a hose for connecting each member. The ozone generator 8 converts oxygen into ozone and can dissolve ozone in water. The ozone generator 8 is provided with a pump (not shown) inside so that the ozone aqueous solution can be pumped toward 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 end of the hose is arranged so that the heated ozone aqueous solution sent from the heater 9 side hits the resin molded product 2 in a spray form.

Further, a drain 11 is provided below the conveyer 6 and stores an ozone aqueous solution after contacting the resin molded product 2. This drain 1
The ozone aqueous solution accumulated in 1 is introduced again into the ozone generator 8 at a constant speed via the pipe 12.

The relationship between the solubility coefficient of ozone and the temperature of water is as shown in FIG. That is, ozone is less likely to be dissolved as the temperature of water rises, and the ozone is more likely to be decomposed as the temperature rises. On the contrary, it is generally known that the higher the temperature of water, the higher the reaction rate (surface modification rate). Therefore, the concentration of ozone is as high as possible, and
It is desirable that the heating adjustment by the heater 9 be appropriately performed 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 a drying device 13 and then supplied to a coating step. Next, a method of modifying the surface of the resin molded product 2 using the above-described surface modifying device 5 and the like, and the operation and effect at the time of the modification will be described.

First, a resin molded product 2 molded into 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, jet water is sprayed onto the surface of the resin molded product 2 from the tip of the nozzle 7 using the power wash cleaning device 4. Then, dirt such as dust and dirt attached to the surface of the resin molded product 2 is washed and removed.

Next, the resin molding 2 is further moved rightward in the figure by the conveyor 6 and supplied to the surface reforming apparatus 5. At this time, the sprayed ozone aqueous solution comes into contact with the resin molded product 2. The surface of the resin molded article 2 is oxidized by the oxidizing power of the ozone remaining in the water due to this contact,
Polarized.

The resin molded product 2 whose surface has been modified as described above
Is dried by the drying device 13 and supplied to the next coating step. In the painting process, as described above,
For example, a paint in which chlorinated polypropylene is blended with a polyester paint is applied. Thereafter, 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
An aqueous solution of ozone comes into contact with the surface of the resin molding, and the surface of the resin molded product is oxidized and polarized by the oxidizing power of ozone. Here, no matter what shape the resin molded product 2 has (in this embodiment, the shape of a bumper), the ozone aqueous solution can reliably contact the entire design surface of the resin molded product 2. . Therefore, reaction spots are less likely to occur at each location on the surface of the resin molded product 2, and the oxidation reaction is uniformly performed on each surface.

In the present embodiment, a paint containing chlorinated polypropylene is applied to the surface of the modified resin molded product 2 to form the coating layer 3. Here, the chlorinated polypropylene in the coating material can be joined to the unoxidized portion of the surface of the resin molded product by the unchlorinated portion of the chlorinated polypropylene being compatible. Further, the chlorinated portion also has an interaction with the oxidized functional (polar) group and forms a bond. For this reason, the time of the reforming process is short,
Even if the above modification was not enough,
By the synergistic action of the bonding with the chlorinated polypropylene and the bonding between the polar group and the paint on the surface of the resin molded product 2, the formed coating layer 3 adheres very firmly to the surface of the resin molded product 2. As a result, an extremely good adhesion strength of the coating film layer 3 can be obtained even in a short-time modification treatment, so that the cost required for all steps of the coating can be reduced.

Further, the specific effects of this embodiment are as follows.
Since the aqueous ozone solution is sprayed during the reforming process, the amount of ozone per unit time hitting the surface of the resin molded product 2 is relatively large. For this reason, as a whole, the contact time with the ozone aqueous solution is extremely short as compared with the case where the resin molded product is simply immersed in the ozone aqueous solution.

Further, since the aqueous ozone solution is applied to the surface of the resin molded product 2 in a spray form, the boundary film diffusion layer of the aqueous ozone solution formed on the surface of the resin molded product 2 is formed relatively thin. In this state, an aqueous ozone solution hits the film diffusion layer so as to hit it, so that the diffusion layer is compressed. In addition, due to the compression, the diffusion layer is discontinuously disturbed, and the oxidation reaction is further promoted. Therefore, the contact time of the ozone aqueous solution can be further reduced.

Further, unlike the case where the resin molded product is immersed in the ozone aqueous solution, the spray-shaped ozone aqueous solution may be applied to the resin molded product 2, so that the ozone aqueous solution can be brought into contact in a series of steps. That is,
After the power wash cleaning, the resin molded product can be once removed from the conveyor and subjected to a modification treatment on the conveyor 6, unlike the conventional technology in which it is necessary to immerse the resin molded product in a container. As a result, the reforming equipment and 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 aqueous ozone solution in the container, the heater 9 was heated immediately before applying the aqueous ozone solution to the resin molded article 2. . For this reason, the decomposition of ozone during the period in which the high temperature state is maintained can be suppressed to a minimum. Therefore, the ozone concentration in the spray-type oson aqueous solution can be increased, and the reforming efficiency can be improved.

In addition, in this embodiment, since only the aqueous solution to be applied to the resin molded product 2 needs to be heated, relatively little energy is required for heating. As a result, energy costs can be reduced.

[Experiment] Next, in order to confirm the above-mentioned functions and effects, an experiment was conducted to measure the presence or absence of surface modification and the adhesion strength of the coating film when the coating was changed and the coating was changed. I do.

(Preparation of Polyolefin Resin Molded Product and Simple Cleaning) First, in this example, a homopolymer of polypropylene was used as the polyolefin resin. Then, the above polymer was molded into a size of “100 × 150 × 3 mm” to obtain a test piece P.

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

(Apparatus) Next, an experimental apparatus used for surface modification will be described. However, the apparatus used here is only experimental. As a means (flowing water means) for applying an ozone aqueous solution to the test piece P, the same one as the surface reforming apparatus 5 described in the above embodiment was used. That is, as shown in FIG. 4, a type in which an ozone aqueous solution was applied to the test piece P in a spray form from a spray nozzle 10 was used. In addition, as for each means other than the above-mentioned water flowing means, the following were used. That is, as shown in the figure, an ozone generator 32 is connected to the oxygen gas cylinder 31, and the ozone generated here is supplied to a mixer 35 via a valve 33 and a backflow prevention trap 34. Further, an ozone aqueous solution (water) fed from a pump 36 is supplied to the mixer 35, 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 pulverizer 37, and the dissolution is continued here. Further, the ozone aqueous solution is heated to a predetermined temperature by a heater 38 provided around the admixer 37.

The aqueous ozone solution passed through the mixer 35 is introduced into an excess gas separation trap 39. The excess ozone gas is guided 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 supplied to the aspirator 4.
3 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-mentioned water flowing means. Then, the subsequent aqueous ozone solution is supplied to the mounting table 44.
Is stored in a glass tank 45 containing the water, and then introduced into the pump 36 again. And in this experiment, the above-mentioned series of flows are repeatedly performed.

In the above apparatus, the ozone concentration of the aqueous ozone solution immediately before each water flowing means is "7 ppm", the hydrogen ion concentration (pH) is "about 3.7",
The temperature was “50 ° C.” and the amount of flowing water was “1.7 liter /
Minutes. The processing time was 100 seconds. On the other hand, as the ozone generator 32, a silent discharge type (trade name: 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 ozone aqueous solution was measured using a commercially available ozone water concentration measuring device (trade name: Kentaro manufactured by Ebara Jitsugyo). .

(Experiment Details) A sample which had been subjected to a reforming treatment and dried (80 ° C. × 10 minutes) using the above-described apparatus was prepared, and a sample not subjected to the reforming treatment was also prepared. Thereafter, painting was performed. As the paint at the time of this coating, three kinds of paint were used: polyester paint, acrylic paint, and polyester paint mixed with chlorinated polypropylene (7% by weight). Then, after application, each paint is set to “80
C. "to form a coating layer, and then a peel strength test of the coating layer was performed. For the measurement of the peel strength, the peel strength of the coating layer was measured using a tensile tester (Tensilon) (however, the tensile angle was “180 °” and the tensile speed was “50 mm / sec”).

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

[0037]

[Table 1]

As is evident from the above results, it is found that the peeling strength increases when the treatment is performed with the ozone aqueous solution as in this embodiment. Further, it can be seen that the peeling strength is also increased when a paint containing chlorinated polypropylene (chlorinated PP) is used. Further, it can be seen that the peeling strength becomes highest when a treatment with an ozone aqueous solution and a coating material containing chlorinated PP are used due to a synergistic effect thereof.

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

As can be seen from the drawing, compared to the case of the conventional paint (polyester paint), the use of the paint (compounded with chlorinated PP) of the present embodiment has a shorter time. It can be seen that sufficient peeling strength can be obtained even in the modification treatment. In other words, from the results of this experiment, it can be said that the processing time of the aqueous ozone solution can be significantly reduced.

The present invention is not limited to the above-described embodiment, and 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).
In the case where the entire surface is a design surface, an ozone aqueous solution may be sprayed from each surface. Further, the present invention is not limited to the above spray-type spraying, and the resin molded product may be immersed in an aqueous ozone solution and brought into contact with the resin molded product, or the aqueous ozone solution may be applied to the surface of the resin molded product in a flowing (waterfall) shape. It may be.

(2) In the above embodiment, the simple cleaning is performed by using the power wash cleaning device 4 before the reforming, but such cleaning may be omitted. (3) In the above embodiment, polypropylene was used as the material of the polyolefin resin molded product. However, if the material is mainly composed of polyolefin, a polyethylene resin molded product and other secondary components are blended. It is needless to say that the present invention can be applied to the surface modification of any material such as a material. In addition, 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 a mall, a spoiler, a lamp, a mark, an emblem, and a wheel cover.

(4) In the above embodiment, the heaters 9 and 38 are provided immediately before the aqueous ozone solution is applied to the resin molded product 2 (test piece P). However, 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-described embodiment, a paint obtained by blending chlorinated polypropylene with a polyester paint was used.
A coating material obtained by graft polymerization or block polymerization of chlorinated polypropylene to polyester may be used.

The technical idea which is not described in each claim of the claims and can be grasped from the above embodiment is described below together with its effects. (A) The method for coating a surface of a polyolefin resin molded article according to claim 1, wherein the surface is modified by applying the ozone aqueous solution in a flowing or spray state. With this configuration, a sufficient reforming effect can be obtained with a short processing time, and the time and cost required for the entire coating can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view illustrating a resin product according to one embodiment.

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

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

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

[Explanation of symbols]

 2 ... Resin molding.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08J 7/12 C08J 7/04 C09D 123/28 C09D 167/00-167/08

Claims (1)

(57) [Claims] A surface modification step of oxidizing a surface of the polyolefin resin molded article by bringing an aqueous ozone solution into contact with the polyolefin resin molded article; On the other hand, a coating film layer forming step of forming a coating film layer on the surface of the polyolefin resin molded product by applying a coating material containing chlorinated polypropylene to a polyester coating material is provided. Surface coating method for molded polyolefin resin.