JPH0374694B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for surface treatment of polypropylene resin, and more specifically, it is a method for surface treatment of polypropylene resin, which greatly improves the physical properties of polypropylene resin, particularly adhesiveness, paintability, printability, etc., and which is relatively easy to operate. This is a surface treatment method for polypropylene resin that can be carried out at low cost. [Prior Art and Problems to be Solved by the Invention] Conventionally, polypropylene resins have excellent heat resistance, strength, moisture permeability, etc., and have been used as various materials. However, since polypropylene resin is non-polar and crystalline, its surface properties, particularly adhesiveness, paintability, and printability, are poor, and its use has been limited. Therefore, various surface treatments have been carried out to improve these surface properties. In addition, various methods have been proposed for laminating with other functional materials by improving adhesion through surface treatment and by using adhesives. For example, (1) a method in which the surface of a molded product made of an ethylene-containing ethylene-propylene block copolymer or a mixture of polyethylene and polypropylene is subjected to low-temperature plasma treatment under conditions of 100 mmHg or less (Japanese Unexamined Patent Publication No. 1983
(2) A method in which ozone-containing gas is sprayed in a molten state on the polyethylene layer side of a multilayer material consisting of a layer made of a mixture of polyethylene and polypropylene and a polyethylene layer, and an anchor-coated material is laminated on this side. (Japanese Unexamined Patent Publication No. 112740/1983), (3) Corona discharge treatment is applied to the film immediately after extrusion,
Method of adhering to base material (Special Publication No. 1112/1983),
(4) When adhering polypropylene and ethylene-vinyl alcohol copolymer via a specific adhesive resin, there is a method in which a corona discharge treatment is performed in advance (Japanese Patent Laid-Open No. 60-15129). However, (1)
Method (2) requires a high vacuum state, has high equipment costs, and is difficult to perform continuous processing due to the high vacuum.Method (2) requires anchor coating, and the equipment and process for anchor coating are difficult. In addition to being expensive, there are safety issues due to the anchor coat treatment. Furthermore, method (3) had a low adhesive strength, and method (4) required an adhesive resin and had a low adhesive strength level. As described above, a fully satisfactory method for improving the surface properties of polypropylene resins has not yet been found. [Means for Solving the Problems] Therefore, the present inventors investigated methods for improving the surface properties of polypropylene resins, and found that the objective could be achieved by performing a specific treatment on a specific resin. The present invention was completed based on this finding. That is, in treating the surface of polypropylene resin, the present invention uses propylene-ethylene random copolymer,
Alternatively, using a mixture of 80 to 95% by weight of homopolypropylene and 20 to 5% by weight of ethylene polymer, at a temperature of 1 to 60°C higher than the melting point of the polypropylene resin,
The present invention provides a method for surface treatment of polypropylene resin, which is characterized by carrying out corona discharge treatment in an atmosphere with an oxygen content of 5% by volume or less. The polypropylene resin used as a raw material in the present invention is a propylene-ethylene random copolymer or a mixture of homopolypropylene and an ethylene polymer. In the present invention, sufficient effects can be obtained by specifying these raw materials. Here, the propylene-ethylene random copolymer is a usual one, and contains an ethylene component of about 20% by weight at most. The melt index (MI) of this propylene-ethylene random copolymer is not particularly limited, and is usually 0.1 to 20.
g/10 minutes is used. In addition, mixtures of homopolypropylene and ethylene polymers include homopolypropylene, polyethylene, ethylene-α-olefin copolymer, ethylene-propylene rubber (EPR), and ethylene and propylene copolymerized with a small amount of diene. It is a blend of ethylene polymers such as terpolymer (EPDM) and ethylene-unsaturated acid copolymer. The mixing ratio of homopolypropylene and ethylene polymer is 80 to 95% by weight of the former and 20 to 5% by weight of the latter. In any case, in the present invention, if homopolypropylene is used alone as the polypropylene resin, the object of the present invention cannot be achieved at all. Therefore, it is necessary to contain an ethylene component in the polypropylene resin molded product, and the ethylene component can be replaced by a propylene-ethylene random copolymer (random polypropylene) or a mixture of homopolypropylene and an ethylene polymer. obtained by using The polypropylene resin of the present invention consists of the above-mentioned copolymer or mixture, and various additives can be added thereto as desired. Additives include inorganic powders such as titanium oxide, talc, calcium carbonate, barium sulfate, and clay, stabilizers against oxidation, heat, and light, reinforcing materials such as glass fiber and carbon fiber, rubbers, lubricants, antistatic agents, Plasticizers, colorants, etc. can be added as appropriate. In the present invention, the above-mentioned raw materials are first thoroughly kneaded and then molded into various shapes using a conventional molding method. Molding is generally carried out by extrusion molding, and is formed into a membrane-like film, sheet, etc., or into a desired irregular shape. If it is made into a film or sheet, it may be formed by multilayer coextrusion molding with other resins, or may be lined with aluminum foil or other heat-resistant resin sheets, if necessary. Next, the resin thus formed into a shape such as a film-like object or an irregularly shaped object is subjected to a corona discharge treatment. Here, the corona discharge treatment is performed at a temperature 1 to 60°C higher than the melting point of the polypropylene resin (in the present invention, polypropylene resin refers to random polypropylene and homopolypropylene), preferably about 2 to 40°C higher than the melting point of the polypropylene resin. It is carried out at high temperature in an atmosphere with an oxygen content of 5% by volume or less. That is, when the molded product is molded by extrusion molding and the surface of the molded product is maintained at a temperature 1 to 60° C. higher than the melting point, corona discharge can be continuously performed as it is. Moreover, if the temperature is lower than the melting point, it may be reheated to a temperature 1 to 60° C. higher than the melting point, and a corona discharge treatment may be performed. In the case of a sheet or film, reheating may be performed using a heating roll, radiation heating, hot air heating, or the like. Furthermore, in the case of a lined film, it is sufficient to heat only the side to be treated. In any case, the treatment temperature of the present invention is such that the temperature of the treated surface is 1 to 60 degrees higher than the melting point of the polypropylene resin.
The temperature may be as high as 0.degree. C., and the most suitable method may be selected depending on the processing equipment and process. In this way, corona discharge treatment is performed on the surface of the molded product at a temperature 1 to 60° C. higher than the melting point. This treatment must be carried out in an atmosphere with an oxygen content of 5% by volume or less. Methods of performing corona discharge treatment under such an atmosphere include a method of performing corona discharge treatment in a gas atmosphere treatment tank containing carbon dioxide gas, nitrogen monoxide gas, water vapor, argon, helium, etc., or a method of performing corona discharge treatment on the surface treated with corona discharge as described above. Examples include a method of performing corona discharge treatment while spraying gas. Particularly preferred as the processing gas here are carbon dioxide gas and dinitrogen monoxide gas. In the present invention, oxygen is present in the atmosphere at 5% by volume.
Preferably, it may be contained in a proportion of 3% by volume or less. Here, if the oxygen content increases, the effects of the present invention cannot be fully achieved. In corona discharge treatment, a high voltage is applied between a grounded dielectric-coated roll or a dielectric-coated metal plate and a knife-shaped electrode placed a few millimeters apart, and a corona is discharged between the electrode and the roll. This is done by running the sheets. Processing conditions may be arbitrarily determined depending on the processing effect, purpose, etc. Specifically, in the case of a resin sheet, the treatment method of the present invention described above can be carried out using the apparatus shown in FIG. That is, the sheet 4 extruded from the die exit of an extrusion molding machine and having a temperature above the melting point is directly extruded into a predetermined gas atmosphere chamber 1, and then a predetermined amount of corona discharge treatment is performed between the corona discharge treatment electrodes 2, and then,
A surface-treated resin sheet can be obtained by methods such as cooling and winding. Here, as the processing electrode 2, for example, a pair of ceramic electrodes is used. The surface of the film-like object or the irregularly shaped object subjected to the corona discharge treatment has excellent adhesion, paintability, printability, etc. Therefore, a laminate or a laminate can be easily produced with a material different from the polypropylene type resin and with high adhesive strength. As such materials, single-layer or multi-layer sheets or films made of functional materials such as ethylene-vinyl alcohol copolymer, polyamide, polyvinylidene chloride, and polyester are preferable. Examples include a laminate. By laminating such a material with the corona discharge treated surface of a sheet or film made of polypropylene resin treated with corona discharge as described above, a laminate consisting of two or more layers can be produced. The material to be laminated with the corona discharge treated polypropylene resin does not need to be corona discharge treated, but may be corona discharge treated. Further, it is preferable to heat the above-mentioned materials before laminating them. Lamination is usually carried out at a temperature range not lower than the melting point of the polypropylene resin, preferably 2 to 10° C. higher than the melting point. For example, when manufacturing a laminate, if the apparatus is used as shown in FIG. 2, it is possible to continuously and efficiently manufacture a laminate with high adhesive strength. That is, the resin sheet 4 and the sheet 5 made of another material are each introduced into the predetermined gas atmosphere chamber 1 by guide rolls, and the polypropylene resin is subjected to corona discharge treatment by the corona discharge electrode 2A, and if necessary, the sheet 5 is also subjected to corona discharge treatment. process,
A laminate 6 is obtained by stacking the treated surfaces. Here, the surface of the sheet 4 is heated by a heating roll 3 to maintain the corona treatment temperature, which is 1 to 60° C. higher than the melting point of the polypropylene resin. In addition, when laminating both sheets, it is necessary that the polypropylene resin has a melting point or higher, and although it is preferable that the sheet 5 is heated, the temperature does not need to be higher than the melting point of the resin. As shown in FIG. 1 as the sheet 4 in FIG. 2, corona treatment can also be performed by directly extruding the sheet from a T-die into the processing chamber. [Effects of the Invention] As described above, according to the surface treatment method for polypropylene resin of the present invention, the surface properties of the polypropylene resin as described above, particularly adhesiveness, paintability, printability, etc., are greatly improved. Furthermore, since the high vacuum equipment required in conventional low-temperature plasma processing is not required, this greatly contributes to reducing equipment costs and simplifying processing operations, especially continuous processing.
Further, the treatment method of the present invention has a very high effect of improving adhesiveness, and a laminate with excellent adhesiveness can be produced at low cost and with high safety. That is, since adhesive resin is not required, extrusion equipment and raw materials are not required, and it is also advantageous in terms of molding workability. Furthermore, since surface treatment and anchor treatment of other materials to be laminated are not required,
It becomes possible to manufacture a laminate at a lower cost and with high safety. Therefore, the present invention is extremely useful for improving the surface properties of various molded products, particularly for producing laminates. [Example] Next, the present invention will be explained in detail with reference to Examples. Examples 1 to 9 and Comparative Examples 1 to 4 A polypropylene resin (PP) sheet with a thickness of 300 μm formed by molding a resin made by blending predetermined amounts of each component shown in Table 1, and an ethylene-vinyl alcohol copolymer. (EVOH) (ethylene content 32 mol%, MI 1.3 g/10 min, density 1.19 g/cm ³ , melting point 181
℃, 200μ thick sheet made of Kuraray Co., Ltd. "Eval EP-F101") is treated with the corona discharge treatment equipment shown in Figure 2 (heating roll diameter 35mmφ, corona output
It was treated for a predetermined time using a cooling roll of 7,000 V and a cooling roll of 50° C., then taken off, subjected to corona treatment, and heated and pressed with two rolls to obtain a laminate. The peel strength of the obtained laminate was measured. The results are shown in Table 1.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 shows a schematic diagram of an apparatus for carrying out the treatment method of the present invention, and FIG. 2 shows a schematic diagram of an apparatus for producing a laminate using the treatment method of the present invention. 1...Corona treatment gas atmosphere chamber, 2A, 2B...
... Corona discharge electrode, 3 ... Heating roll, 4 ... Polypropylene resin sheet, 5 ... Resin sheet of other material, 6 ... Laminate, 7 ... Power supply for corona discharge.

Claims (1)

[Claims] 1 When treating the surface of polypropylene resin, propylene-ethylene random copolymer or homopolypropylene 80 to 95% by weight and ethylene polymer 20 to 5% by weight are used as polypropylene resin.
1. A method for surface treatment of polypropylene resin, which is characterized by carrying out corona discharge treatment using a mixture of polypropylene resin in an atmosphere containing 5% by volume or less of oxygen at a temperature 1 to 60° C. higher than the melting point of the polypropylene resin.