JPH0322895B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for coating a polypropylene composition with good coating properties, low mold shrinkage, and excellent appearance and mechanical strength of molded products. Recently, automobiles and home appliances are becoming lighter in weight for the purpose of conserving resources and energy, as well as in response to requests for aesthetic appeal, and efforts are being made to use plastics. In particular, automobile parts such as bumpers and instrument panels are required to be painted to match the color tone of the vehicle body. The most preferred plasticizing materials are polypropylene and polyurethane. Although polyurethane is easy to paint, it has problems due to its low productivity.On the other hand, polypropylene has excellent productivity and physical properties, but has a disadvantage that it cannot be painted because it has low polarity, is poorly soluble in solvents, and does not swell easily. has. The purpose of the present invention is to eliminate this drawback and provide a molded product that satisfies the strict performance requirements (especially high impact resistance, high rigidity, and molded product appearance) in the field of industrial parts such as automobile parts and home appliance parts. It was discovered that this purpose could only be achieved by subjecting a particular composition to a special cleaning treatment. That is, the present invention uses 54 to 84 parts by weight of a crystalline propylene polymer with an MFR of 14 to 80 g/10 minutes, and 32 to 15 parts by weight of an ethylene-propylene copolymer rubber having a Mooney viscosity (ML ₁₊₄ at 100°C) of 15 to 90. and MFR0.6~
1 molded product made by blending 14 to 1 part by weight of high-density polyethylene with a density exceeding 0.94 g/cm ³ at 25 g/10 minutes.
This is a method for coating a polypropylene molded article, which is characterized by coating after steam washing with 1,1-trichloroethane. Since the product according to the present invention is excellent in the above points, it is particularly suitable for automobile exterior parts such as bumpers, fenders, and side panels that require paintability and low-temperature impact resistance, and is particularly suitable for bumpers. The propylene polymer used in the present invention is MFR14
~80 g/10 min, preferably 15-30 g/10 min, crystalline, homopolymer of propylene or block of majority, preferably 70 mol% or more of propylene and ethylene or α-olefin other than propylene. Or a random copolymer or a mixture thereof is preferable, but propylene polymers graft-modified with unsaturated organic acids such as acrylic acid and maleic anhydride, or styrene, chlorine, etc. or oxidized propylene polymers are preferably used. It may be a mixture of less than % by weight. When this MFR is less than 14 g/10 minutes, not only is moldability poor and productivity low, but also flow marks are likely to occur and the appearance of the molded product is likely to deteriorate. on the other hand,
When MFR exceeds 80g/10 minutes, low-temperature impact resistance decreases significantly. In addition, the ethylene-propylene copolymer rubber used in the present invention has a Mooney viscosity (ML ₁₊₄ 100℃)
is preferably 15 to 90, preferably 20 to 75, and the ethylene content is 20 to 85 mol%, preferably 50 to 80 mol%. This rubber is composed of ethylene and propylene (EPM), ethylene, propylene and non-conjugated diene (EPDM), and each of these rubbers contains α-olefin other than propylene as a copolymerized component. Good too. If the Mooney viscosity is less than 15, the coating adhesion of the molded product will be low, while if it exceeds 90, flow marks will easily occur on the molded product. Furthermore, the high density polyethylene used in the present invention is
Manufactured by a medium-low pressure method with a density exceeding 0.94 g/cm ³ , preferably 0.95 g/cm ³ or more, and an MFR of 0.6 to 25
g/10 minutes, preferably 3 to 10 g/10 minutes. If the density is lower than the above range, it is not preferable in terms of low-temperature impact resistance and molding shrinkage of the molded product. Also,
If the MFR is less than 0.6 g/10 min, flow marks will easily occur on the molded product, while if the MFR is less than 0.6 g/10 min,
If the amount is exceeded, the low-temperature impact resistance of the molded article will decrease. The blending ratio of these three components is 54 to 84 parts by weight, preferably 63 to 78 parts by weight of the crystalline propylene polymer, and 32 to 84 parts by weight of the ethylene-propylene copolymer rubber.
15 parts by weight, preferably 27-20 parts by weight and high density polyethylene 14-1 parts by weight, preferably 10-2 parts by weight. If the crystalline propylene polymer is less than 54 parts by weight,
The molded product becomes too soft, causing problems such as deformation and scratching. On the other hand, if it exceeds 84 parts by weight, the coating film adhesion strength decreases and low-temperature impact resistance also deteriorates. If the amount of ethylene-propylene copolymer rubber is less than 15 parts by weight, the coating adhesion and low-temperature impact strength of the molded product will not be sufficient, and the anisotropy will also increase, making warping and deformation more likely. On the other hand, if it exceeds 32 parts by weight, the elastic modulus is low, and the coating film tends to sag and deform when baked, and the product surface is easily scratched, and even if touched with work gloves, the surface will be scratched and whitened. If the amount of high-density polyethylene is less than 1 part by weight, the weld strength of the molded product will be low, while if it exceeds 14 parts by weight, the gloss will decrease significantly during subsequent washing treatment, and flow marks will occur, resulting in poor appearance. outside,
Sink marks in thick parts become noticeable. In the present invention, in addition to the above-mentioned components, various additives such as pigments, stabilizers, nucleating agents, and fillers may be used as necessary. In order to obtain a molded product using these components, the composition is first made into pellets using a conventional kneading machine such as a Banbury mixer, roll, Brabender Plastograph, or extruder, and then molded by injection molding, extrusion molding, etc. Although this is practical, so-called direct molding, in which each component is immediately placed in a molding machine, is also possible. Although the order of blending the components in preparing the composition is arbitrary, the best kneading machine is a co-rotating twin screw extruder, and the best molding is injection molding. Note that a master batch method can also be adopted. Next, in the method of evaporative cleaning of the molded body with 1,1,1-trichloroethane, the molded body is exposed to a container containing boiling 1,1,1-trichloroethane filled with steam. The heat of the 1,1,1-trichloroethane vapor is removed by the molded body, dew condenses on the surface of the molded body, the phase changes to liquid 1,1,1-trichloroethane, and the vapor drips. This cleans the surface of the molded body. At this time, the vapor height of 1,1,1-trichloroethane temporarily decreases, but it is desirable that the vapor height be above the top of the exposed compact. The washing time is preferably 30 seconds to 120 seconds, but periods before or after that are not excluded. After 1,1,1-trichloroethane steam cleaning,
Store the item as dust-free, sweat-free as possible, and then paint it. A two-coat type paint is suitable.
For the undercoat, we use a paint that has a formulation that improves the adhesion of the molded object and allows for reactive adhesion with the topcoat, while for the topcoat, we use a urethane-based, acrylic-based paint that forms a coating film through reaction curing. is used. It is best to apply both the undercoat and topcoat by spray painting. The baking temperature depends on the paint composition.
It is carried out at 80°C to 120°C for 10 to 30 minutes until the coating film is cured. Of course, in the case of two coats, it is desirable to perform baking twice. Examples As shown in Table 1, a para-tertiary nucleating agent containing a total of 100 parts by weight of crystalline propylene polymer (PP), ethylene-propylene copolymer rubber (EPM), and high-density polyethylene (PE) 0.2 parts by weight of aluminum salt of butylbenzoic acid, bis(2,2,6,6-tetramethyl-4
0.3 parts by weight of (piperidine) sebacate and 3.3 parts by weight of polypropylene blended with 30% by weight of carbon black were added, mixed in a tumbler, and kneaded and extruded in a co-directional twin-screw extruder to obtain resin composition pellets. Desired test pieces were molded using a small injection molding machine and tested. Test method: MFR is JIS
−K6758 method (230℃), Izot impact test is JIS
-K7110 method (-40℃, processing notch), bending elastic modulus is JIS-K7203 method, molding shrinkage rate is ASTM-D
-955-73 (3mm thickness), and the gloss reduction rate due to cleaning was compared with the untreated state after 30 seconds of 1,1,1-trichloroethane (TCE) steam cleaning.
The peel strength of the paint film was measured at 110℃ after TCE washing with R291 undercoat and R263 topcoat from Nippon B Chemical Co., Ltd.
After baking for 30 minutes, the coating film was divided into 1 cm wide pieces and peeled at a speed of 25 mm/min using a Tensilon tester. In addition, in Comparative Examples 8 to 13 in Table 1,
Test pieces that were not steam-washed with 1,1,1-trichloroethane were evaluated. The results are shown in Table 1.

【table】

Claims (1)

[Claims] 1 MFR14-80g/10min crystalline propylene polymer 54-84 parts by weight, Mooney viscosity (ML ₁₊₄ 100℃)
15-90 ethylene-propylene copolymer rubber 32
~15 parts by weight and density exceeding 0.94 g/cm ³ and
MFR0.6~25g/10min high density polyethylene 14~
1. A method for coating a polypropylene molded body, which comprises steam-washing a molded body containing 1 part by weight of 1,1,1-trichloroethane and painting the molded body.