JP2019151905A - Method for subjecting polypropylene resin to hydrophilic treatment - Google Patents

Abstract

To provide a method for subjecting a polypropylene resin free from chromium and manganese to hydrophilic treatment, capable of forming plating sufficiently stuck to the surface of the polypropylene resin.SOLUTION: An apparatus 1 for subjecting a polypropylene resin to hydrophilic treatment includes a treatment tank 2 having a thermostatic heater 3 provided in the outer periphery and a supply tank 6 connected through a pipe line 4 and a pump 5. Persulfate solutions S and S1 having a predetermined sulfuric acid concentration and persulfuric acid concentration are charged into the treatment tank 2 and the supply tank 6, respectively; a polypropylene resin plate 7 as a polypropylene resin to be treated is suspended and treated in the vertical direction in the treatment tank 2; and the persulfate solutions S and S1 have a sulfuric acid concentration of 75-98wt%, a persulfate acid concentration of 2 g/L or more and a temperature of 80-130°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for hydrophilizing a polypropylene resin, which is performed as a pretreatment for plating a polypropylene resin (resin molded product).

  In parts where metal is used as a structural material or component material, plastics are substituted by taking advantage of advantages such as light weight, low cost, freedom of shape, and ease of mass production. At present, it is widely used not only for decoration but also for automobile exteriors, interior parts, and home appliances. At that time, in order to improve rigidity, wear resistance, weather resistance, heat resistance and the like, the plastic surface is often plated.

  Since plastic is non-conductive, it is necessary to first form a metal film as a conductor on the plastic in order to perform plating. The methods are roughly classified into dry methods such as CVD (chemical vapor deposition) and PVD (physical vapor deposition), and wet methods of electroless nickel plating. Since the dry method is mostly a film formation in a vacuum state and is not suitable for mass production or application to a large part, the wet method has been adopted so far.

Polypropylene resin, which is a general-purpose plastic, has a specific gravity of 0.93 to 0.96 g / cm ³ and is lightweight. It is thermoplastic and has good moldability. Among general-purpose resins, it has excellent mechanical strength and can be recycled. Since it is possible, it is used for home appliance parts such as food trays, carpets, and TV cases, and automobile parts such as bumpers.

  There is chromic acid treatment as a treatment method before plating of such a plastic molded article made of polypropylene resin. However, chromic acid has a weak oxidizing power, so it is difficult to make the surface of the polypropylene resin hydrophilic. Further, as an environmentally conscious technique that replaces chromic acid, Patent Document 1 describes that etching is performed with a mixed solution of a permanganate and an inorganic salt. Furthermore, Patent Document 2 and Patent Document 3 disclose a pretreatment method for electroless plating in which the surface of a plastic molded product is roughened using ozone-dissolved water.

JP 2008-31513 A JP 2002-121678 A JP 2012-52214 A

  However, in the method of etching with a mixed solution of permanganate and inorganic salt described in Patent Document 1, there is a problem that it is difficult to make the polypropylene resin hydrophilic and the adhesion to the metal plating film is not good. In addition, it is difficult not only to make the polypropylene resin hydrophilic by the pre-plating method of the plastic surface described in Patent Document 2 and Patent Document 3, but also because ozone has a high decomposition rate, high-concentration ozone water is produced, In addition, since a high concentration must be maintained, not only a large facility is required, but also there is a problem in that unevenness is likely to occur in the processing due to a difference in local ozone concentration. Thus, it has been very difficult to apply metal plating such as chromium or nickel to polypropylene resin.

  This invention is made | formed in view of the said subject, and it aims at providing the hydrophilization processing method of the chromium and manganese free polypropylene resin which can form the plating fully adhere | attached on the polypropylene resin surface.

  In order to achieve the above object, the present invention firstly relates to a method for hydrophilizing a polypropylene resin as a pretreatment for plating, wherein the polypropylene resin contains a persulfate dissolved in a sulfuric acid concentration of 75 to 98 wt%. Provided is a method for hydrophilizing a polypropylene resin, wherein the solution is treated with a chromium-free solution having a sulfuric acid concentration of 2 g / L or more and the temperature of the solution in which the persulfate is dissolved is 80 to 130 ° C. (Invention 1).

  According to this invention (Invention 1), the surface of the polypropylene resin is slightly dissolved and roughened by the strong oxidizing action of persulfuric acid, and hydrophilic functional groups such as hydroxyl groups and carboxyl groups are exposed. By performing a plating treatment after the treatment, a sufficiently adhered plating can be obtained. At this time, by adjusting the sulfuric acid concentration to 75 to 98 wt%, the degree of treatment of the polypropylene resin surface can be adjusted by adjusting the sulfuric acid concentration. Moreover, the surface of a polypropylene resin can be suitably hydrophilized, suppressing decomposition | disassembly of persulfuric acid by making the temperature of a hydrophilization process into 80-130 degreeC. Furthermore, by setting the concentration of persulfuric acid in the solution to 2 g / L or more, the strong oxidizing action of persulfuric acid is sufficiently exerted, so that the surface of the polypropylene resin can be suitably roughened to expose hydrophilic functional groups. It is possible to obtain a plating having particularly excellent adhesion by performing a plating treatment after this treatment.

  In the present specification, the polypropylene resin is not only a propylene homopolymer, but also other resin components such as polyethylene and polybutadiene are blended with the polypropylene resin in an amount of about 20 wt% or less with respect to a total of 100 wt% of both. It also includes a polypropylene resin composition or a copolymer mainly composed of propylene obtained by blocking or randomly copolymerizing propylene with other olefins such as ethylene and butadiene in a total amount of 100 wt% of about 20 wt% or less.

  In the said invention (invention 1), the mixed solution which melt | dissolved inorganic salts other than this persulfate in the solution which melt | dissolved the said persulfate can be used (invention 2).

  According to this invention (invention 2), the degree of treatment of the polypropylene resin surface can be adjusted.

  In the said invention (invention 1 and 2), the persulfate which supplies the solution which stored the solution which melt | dissolved the said persulfate, and processes a polypropylene resin, and the solution which dissolved the persulfate in this process tank It is preferable to treat the surface of the polypropylene resin by immersing a polypropylene resin in the treatment tank of a treatment apparatus provided with a salt solution storage tank and a constant temperature heater for heating the treatment tank (Invention 3).

  According to this invention (invention 3), it is possible to perform the treatment only by immersing the polypropylene resin in the treatment tank storing the persulfate solution. Further, when the concentration of persulfuric acid is lowered, the processing capacity can be maintained by replenishing the persulfate solution from the persulfate solution storage tank to the treatment tank.

  The present invention is secondly a hydrophilic treatment method for polypropylene resin as a pretreatment for plating, wherein the polypropylene resin is mixed with sulfuric acid and hydrogen peroxide, and the sulfuric acid concentration is 75 to 98 wt% and the persulfuric acid concentration. Is treated with a chromium-free solution of 2 g / L or more, and a temperature of the mixed solution of sulfuric acid and hydrogen peroxide is 80 to 130 ° C. (invention 4).

  According to this invention (Invention 4), the surface of the polypropylene resin is slightly dissolved and roughened by the strong oxidizing action of persulfuric acid produced by mixing sulfuric acid and hydrogen peroxide solution, and hydroxyl groups and carboxyl groups are formed. Since a hydrophilic functional group such as the above is exposed, sufficiently adhered plating can be obtained by performing a plating treatment after this treatment. At this time, by adjusting the sulfuric acid concentration to 75 to 98 wt%, the degree of treatment of the polypropylene resin surface can be adjusted by adjusting the sulfuric acid concentration. Moreover, the surface of a polypropylene resin can be suitably hydrophilized, suppressing decomposition | disassembly of persulfuric acid by making the temperature of a hydrophilization process into 80-130 degreeC. Furthermore, by setting the concentration of persulfuric acid in the solution to 2 g / L or more, the strong oxidizing action of persulfuric acid is sufficiently exerted, so that the surface of the polypropylene resin can be suitably roughened to expose hydrophilic functional groups. It is possible to obtain a plating having particularly excellent adhesion by performing a plating treatment after this treatment.

  In the said invention (invention 4), the said process of the processing apparatus provided with the processing tank for storing the sulfuric acid and processing the polypropylene resin provided with the hydrogen peroxide solution addition mechanism, and the constant temperature heater which heats the said processing tank It is preferable to immerse the polypropylene resin in the tank and treat the surface of the polypropylene resin (Invention 5).

  According to this invention (invention 5), the treatment can be performed simply by immersing the polypropylene resin in a treatment tank in which sulfuric acid and hydrogen peroxide water are mixed to produce persulfuric acid. Further, when the concentration of persulfuric acid is lowered, the treatment capacity can be maintained by replenishing the treatment tank with sulfuric acid and hydrogen peroxide solution.

  According to the method for hydrophilizing a polypropylene resin of the present invention, the surface of the polypropylene resin is dissolved and roughened by the strong oxidizing action of persulfuric acid, and hydrophilic functional groups such as hydroxyl groups and carboxyl groups are exposed. Therefore, it is sufficiently submerged, and a sufficiently close plating can be obtained by performing a plating treatment after this treatment.

It is the schematic which shows the processing apparatus which can apply the hydrophilization treatment method of the polypropylene resin by 1st embodiment of this invention.

  FIG. 1 shows a treatment apparatus suitable for carrying out a hydrophilic treatment method for polypropylene resin according to a first embodiment of the present invention. In FIG. 1, a polypropylene resin hydrophilization treatment apparatus 1 includes a treatment tank 2 provided with a constant temperature heater 3 on the outer periphery, and a supply tank 6 connected via a pipe 4 and a pump 5. In addition, in the processing tank 2, you may install stirring means, such as an air diffuser and a liquid circulation function, for stirring the inside of a tank as needed. In addition, a persulfate and sulfuric acid supply means (not shown) is connected to the supply tank 6, and a persulfate solution S 1 can be prepared and supplied to the treatment tank 2 as necessary.

  In such a processing apparatus 1, the supply tank 6 is filled with a persulfate solution S1 having a predetermined sulfuric acid concentration and persulfate concentration, and the persulfate solution S1 is supplied from the supply tank 6 to the treatment tank 2. By being supplied, a solution S of persulfate having a predetermined concentration is filled. And in the processing tank 2, the polypropylene resin board 7 which is a to-be-processed object is suspended in the up-down direction in the state fixed to the jig | tool which is not shown in figure.

  In the present embodiment, the persulfate used in the persulfate solutions S and S1 may be any persulfate that produces peroxomonosulfate and / or peroxodisulfate in the solution, such as sodium persulfate, potassium persulfate, Monosulfates or disulfates such as ammonium persulfate can be used. Of these, sodium persulfate is preferred. Other inorganic salts such as phosphates, sulfates, and sodium chloride can be appropriately added to the persulfate solutions S and S1.

  The sulfuric acid concentration of the persulfate solutions S and S1 is 75 to 98 wt%, preferably 85 to 98 wt%, and particularly 90 to 95 wt%. When the sulfuric acid concentration is less than 75 wt%, the sulfuric acid concentration of the persulfate solution S is too thin to sufficiently expose hydrophilic functional groups such as hydroxyl groups and carboxyl groups on the surface of the polypropylene resin plate 7. Therefore, the effect of improving the adhesion of plating cannot be sufficiently obtained. Although it is preferable that the sulfuric acid concentration is high, sulfuric acid having a concentration exceeding 98 wt% is not commercially available and is difficult to obtain.

  Moreover, the persulfate concentration of the solutions S and S1 after dissolving the persulfate is 2 g / L or more. When the concentration of persulfuric acid is less than 2 g / L, hydrophilic functional groups such as hydroxyl groups and carboxyl groups cannot be sufficiently exposed on the surface of the polypropylene resin plate 7, and a sufficient plating adhesion improving effect is obtained. I can't. A preferable persulfuric acid concentration is 3 g / L or more, particularly 5 g / L or more. In addition, although there is no restriction | limiting in particular about the upper limit of the density | concentration of persulfuric acid, even if it exceeds 20 g / L, the improvement of the said effect is not acquired but it is not economical.

  Next, a method for hydrophilizing a polypropylene resin using the processing apparatus 1 as described above will be described. First, the polypropylene resin plate 7 is degreased, and then the surface of the polypropylene resin plate 7 is treated by immersing the polypropylene resin plate 7 in the treatment tank 2 containing the persulfate solution S.

  At this time, the persulfate solution S is heated by the constant temperature heater 3 as necessary so that the temperature of the persulfate solution S is 80 to 130 ° C., preferably 100 to 130 ° C., particularly 110 to 120 ° C. If the temperature of the persulfate solution S is less than 80 ° C., the hydrophilic group cannot be sufficiently exposed on the surface of the polypropylene resin plate 7, and the effect of improving the adhesion of plating cannot be sufficiently obtained. When it exceeds ℃, decomposition of persulfuric acid is promoted and the processing efficiency is lowered. Then, when the persulfate solution S in the treatment tank 2 reaches the above-described temperature and persulfate concentration, the surface of the polypropylene resin sheet 7 is treated by immersing the degreased polypropylene resin sheet 7 in the treatment tank 2. At this time, in order to suppress bubbles adhering when immersed in the persulfate solution S, the polypropylene resin plate 7 is preferably subjected to a wet treatment in advance.

  By immersing the polypropylene resin plate 7 in the persulfate solution S in the treatment tank 2 for 30 to 120 minutes, the surface of the polypropylene resin plate 7 is dissolved and the surface is roughened, and hydroxyl groups, carboxyl groups, etc. The hydrophilic functional group is exposed. By these, the adhesiveness of plating can be improved in the subsequent plating treatment.

  After activating the functional group expressed on the surface of the polypropylene resin plate 7 in the above process, neutralization / reduction treatment, conditioning treatment, or the like may be performed as necessary. And after water washing, it is plated. As the plating method, first, an electroless nickel plating having autocatalytic properties is deposited, and then plating such as electrolytic nickel and electrolytic chromium is performed. The metal to be electrolessly plated may be any of nickel, copper, etc. The metal to be electroplated may be any of nickel, chromium, copper, cobalt, and alloys thereof. As a result, a polypropylene resin plated product in which the surface of the polypropylene resin plate 7 is plated with nickel or the like having good adhesion can be obtained.

  Such treatment may be carried out continuously by replacing the polypropylene resin plate 7, but since the sulfuric acid concentration of the persulfate solution S in the treatment tank 2 is decomposed along with the treatment, the pump 5 is activated to supply the tank. A new persulfate solution S <b> 1 from 6 may be replenished to the treatment tank 2 from the pipe 4.

  Next, the method for hydrophilizing a polypropylene resin according to the second embodiment of the present invention will be described. In this embodiment, sulfuric acid and hydrogen peroxide are used in place of the chromium-free solution in which the sulfuric acid concentration in which the persulfate is dissolved is 75 to 98 wt% and the persulfuric acid concentration is 2 g / L or more. This is a method for hydrophilizing a polypropylene resin under the same conditions except that a chromium-free solution having a sulfuric acid concentration of 75 to 98 wt% mixed with water and a persulfuric acid concentration of 2 g / L or more is used. Thus, the polypropylene resin can be hydrophilized also by preparing a persulfuric acid solution by mixing sulfuric acid and hydrogen peroxide. Here, the amount of hydrogen peroxide mixed with sulfuric acid may be appropriately set within a range in which the sulfuric acid concentration is 75 to 98 wt% and the persulfuric acid concentration is 2 g / L or more.

  Moreover, what is necessary is just to employ | adopt the thing provided with the hydrogen peroxide solution addition mechanism as the processing tank 2 in the processing apparatus 1 shown in FIG.

  As mentioned above, although the hydrophilic treatment method of the polypropylene resin of this invention has been demonstrated based on said each embodiment, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible. For example, various inorganic salts can be added to the persulfate solutions S and S1. Further, for example, the present invention can be applied not only to batch processing as in the present embodiment but also to continuous processing. Furthermore, it goes without saying that the polypropylene resin is applicable not only to the plate as in the present embodiment but also to molded bodies having various shapes. Furthermore, a persulfate aqueous solution may be prepared in the supply tank 6 and sulfuric acid may be separately supplied to the treatment tank 2.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited by these descriptions. In the following Examples and Comparative Examples, the persulfuric acid concentration measurement and the adhesion test were performed as follows.

<Persulfuric acid concentration measurement method>
First, the total oxidant concentration contained in the treatment liquid (persulfate solution S) is measured by iodine titration. In this iodine titration, potassium iodide (KI) is added to the persulfate solution S to release iodine (I ₂ ), and this I ₂ is titrated with a sodium thiosulfate standard solution to determine the amount of I _2. The oxidant concentration is obtained from the amount of I ₂ . Next, only the hydrogen peroxide concentration of the persulfate solution S was determined by potassium permanganate titration, and the persulfate concentration was calculated by subtracting the potassium permanganate titration value from the iodine titration value.

<Plating adhesion test>
The polypropylene resin plate 7 hydrophilized with the persulfate solution S was plated according to the flow shown in Table 1 below to obtain an adhesion test sample.

  In accordance with the adhesion test method stipulated in JIS H8630 “Decoration electroplating on plastic”, the peel strength test is performed on the obtained adhesion test sample to measure the adhesion strength of the plating film. did.

[Example 1]
The surface treatment of the polypropylene resin plate 7 was performed using the apparatus shown in FIG. The specifications and conditions of the treatment tank 2 are as follows.

<Treatment tank>
Volume of treatment tank 2: 40L
Size of the polypropylene resin plate 7: 500 mm × 500 mm × thickness 5 mm
<Properties and Surface Treatment Conditions of Persulfate Solution S>
Sulfuric acid concentration: 92 wt%
Persulfuric acid concentration: 10 g / L
Processing temperature: 120 ° C
Processing time: 60 minutes

  When the polypropylene resin plate 7 is dipped in a wet treatment tank containing a surfactant for 10 minutes and then hydrophilized by dipping in the treatment tank 2 filled with the persulfate solution S for 60 minutes, it is taken out from the treatment tank 2. After washing with tap water, electroless nickel plating was performed in the steps shown in Table 1. Thereafter, copper sulfate plating was finally applied. And the adhesion strength of the plating film of the polypropylene resin plate 7 plated with copper sulfate was measured. The results are shown in Table 2 together with the hydrophilic treatment conditions.

[Examples 2 to 7]
Chromium plating was performed in the same manner as in Example 1 except that various settings were changed as shown in Table 2, and the adhesion of the plating was evaluated. The results are shown in Table 2 together with the hydrophilic treatment conditions.

[Comparative Example 1]
Chromium plating was performed in the same manner as in Example 1 except that a sulfuric acid solution having a sulfuric acid concentration of 92 wt% was used instead of the persulfate solution, and the adhesion of the plating was evaluated. The results are shown in Table 2 together with the processing conditions.

  As is apparent from Table 2, according to the method for hydrophilizing polypropylene resins of Examples 1 to 7, adhesion strength of 0.4 kN / m or more was obtained by plating the polypropylene resin plate 7 after the treatment. . In particular, in Examples 1 to 3, which were treated at a treatment temperature of 100 ° C. or more and a persulfuric acid concentration of 3 g / L or more for a sufficient time, for example, 60 minutes or more, an adhesion strength of 0.8 kN / m or more was obtained. On the other hand, in Comparative Example 1 treated with 92 wt% sulfuric acid containing no persulfuric acid, the adhesion strength was as low as 0.3 kN / m even when the treated polypropylene resin plate 7 was plated.

DESCRIPTION OF SYMBOLS 1 Processing apparatus 2 Processing tank 3 Constant temperature heater 4 Piping 5 Pump 6 Supply tank 7 Polypropylene resin board S, S1 Persulfate solution

Claims (5)

  A method for hydrophilizing a polypropylene resin as a pretreatment for plating, wherein the polypropylene resin is treated with a chromium-free solution having a sulfuric acid concentration of 75 to 98 wt% and a persulfuric acid concentration of 2 g / L or more dissolved in persulfate. And a method for hydrophilizing the polypropylene resin, wherein the temperature of the solution in which the persulfate is dissolved is 80 to 130 ° C.   The method for hydrophilizing a polypropylene resin according to claim 1, wherein a mixed solution in which an inorganic salt other than the persulfate is dissolved in the solution in which the persulfate is dissolved is used.   A treatment tank for storing the solution in which the persulfate is dissolved and treating the polypropylene resin, a persulfate solution storage tank for supplying a solution in which the persulfate is dissolved in the treatment tank, and the treatment tank are heated. The method for hydrophilizing a polypropylene resin according to claim 1 or 2, wherein a polypropylene resin is immersed in the treatment tank of a treatment apparatus equipped with a constant temperature heater to treat the surface of the polypropylene resin.   A method for hydrophilizing a polypropylene resin as a pretreatment for plating, wherein the polypropylene resin is a chromium-free material having a sulfuric acid concentration of 75 to 98 wt% and a persulfuric acid concentration of 2 g / L or more mixed with sulfuric acid and hydrogen peroxide. A method for hydrophilizing a polypropylene resin, wherein the temperature of a solution obtained by treating with a solution and mixing the sulfuric acid and hydrogen peroxide is 80 to 130 ° C.   Immersing the polypropylene resin in the treatment tank of a treatment apparatus comprising a treatment tank for storing a sulfuric acid and treating a polypropylene resin having a hydrogen peroxide solution addition mechanism, and a constant temperature heater for heating the treatment tank; The method for hydrophilizing a polypropylene resin according to claim 4, wherein the surface of the polypropylene resin is treated.

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