JPS63182078A - Painting pretreatment of urethane resin - Google Patents

Abstract

PURPOSE:To prevent the generation of gas at the time of painting and drying, by applying sufficient moisture to an urethane resin molded product to perform pretreatment deactivating the unreacted isocyanate group in a resin. CONSTITUTION:As a method for applying moisture to an urethane resin molded product, the molded product is held for about 1-10min in water, for example, having temp. of ambient temp. - 60 deg.C or held for about 5-10min in a high humidity atmosphere having relative humidity of 80-98% at 40-65 deg.C. By this treatment, the unreacted isocyanate group in the urethane resin molded product is deactivated to make it possible to prevent such a phenomenon that gas is generated through the reaction of the isocyanate group at the time of painting and drying and the pinhole flaw of a film being generated in coating, is eliminated.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for pre-painting urethane resin, and more specifically to a pre-treatment method for preventing the occurrence of pinhole defects in the coating film of a urethane resin coated molded product. Regarding the method.

(Prior Art) Urethane resin has excellent impact resistance and flexibility, and is widely used in automobile bumpers and the like. When these urethane resins are coated, unreacted incyanate groups in the resin are heated (approximately 80 to 130°C) during coating drying.
It reacts with other substances and generates certain gases. When this gas passes through the uncured coating film, it can cause defects such as pinholes, so conventionally, before painting the molded product, a process called "bost cure" is performed in which the molded product is heated in a heating furnace, or An aging operation is performed in which the product is left at room temperature for 8 to 24 hours.

(Problem to be solved by the invention) However, the post-cure process requires a heating furnace that can withstand temperatures of 100 to 120°C, separate from the paint drying furnace, which increases the size of the equipment and requires the above-mentioned temperature. Therefore, a jig such as a mold is required to prevent thermal deformation of the urethane resin molded product, resulting in problems such as complicated operations.

In addition, the aging operation requires a long time and a large space.

The present invention was made to solve these problems, and its purpose is to inactivate the unreacted incyanate groups of urethane resin by treatment at a lower temperature and in a shorter time. The aim is to provide a method that allows

(Means for Solving the Problems) The urethane resin pre-painting treatment method of the present invention is characterized by holding the urethane resin molded article in water or in a high humidity atmosphere before painting the urethane resin molded article. .

In the method of the present invention, the urethane resin molded product is kept in water or in a high humidity atmosphere as described above in order to sufficiently moisten the molded product and inactivate unreacted incyanate groups in the resin. When holding in water, it is preferable that the temperature of the water is between room temperature and 60°C, and the holding time is particularly as follows:
Although not limited, 1 to 10 minutes is sufficient.

In addition, when holding in a high humidity atmosphere, a high humidity atmosphere with a temperature of 40 to 65°C and a relative humidity of 80 to 98% is preferable, and the holding time is not particularly limited as in the case of water, but it is 5 to 10 minutes. It is enough.

(for production) The method for pre-painting urethane resin of the present invention is as follows.

Before painting a urethane resin molded product, the molded product is kept in water or in a high humidity atmosphere to give the molded product an appropriate amount of moisture and to remove unreacted incyanate groups in the urethane resin molded product. Activate. Therefore, the method of the present invention prevents the generation of gas due to the reaction of incyanate groups during the subsequent drying of the coating.

(Example) Next, the present invention will be described in more detail based on Examples, but the present invention is not limited thereto.

Example 1 A bumper molded product made of urethane resin was preheated at 80°C for 5 minutes, kept in a humidified reaction chamber adjusted to a temperature of 50°C and relative humidity of 88% for 5 minutes, and painted after the surface was dry. Do the following. The reason why the molded product is preheated first is to prevent dew condensation on the molded product in the humidification reaction chamber.

Example 2 The same operation as in Example 1 is performed except that the molded article in Example 1 is held in warm water at 50° C. for 5 minutes instead of being held in the humidification reaction chamber.

Comparative Example 1 A bumper molded product made of urethane resin was painted as is.

Comparative Example 2 A preheated urethane resin bumper molded product in the same manner as in Example 1 was placed in a mold to prevent thermal deformation and heated to a temperature of 12
The sample is kept in a humidified reaction chamber adjusted to 0° C. and 30% relative humidity for 30 minutes, and the surface is dried before coating.

The occurrence of pinholes in the paint film of the painted urethane bumper thus obtained was investigated. Also, from each of the above urethane resin bumpers before painting, 100X 100X 3t
Take a test piece of m■, crush it, and then heat it to 120°C.
Gas chromatography analysis of the gas generated by heating was performed. These results are shown in the table below.

Table Test results 1 Number of pinholes per 100 crn' of coating film cross section Ratio of peak areas at the same elution time According to this, the pretreatment according to the present invention was performed (Examples 1 and 2)
), similar to the conventional pretreatment (Comparative Example 2), no pinholes were observed in the coating film, and the gas chromatography results were similar to those of Examples 1 and 2 and Comparative Example 2. This indicates that almost no gas was generated from the molded product during coating drying.

From these facts, it is considered that the pre-painting treatments of Example 1.2 and Comparative Example 2 inactivate the incyanate groups that cause gas generation during paint drying. However, while the conventional method shown in Comparative Example 2 requires holding at 120°C for 30 minutes, the methods of the present invention in Examples 1 and 2 achieve the same effect by only holding at 50°C for 5 minutes. can get. This shows that the method of the present invention can perform pre-painting treatment of urethane resin molded products more quickly with simpler equipment.

(Effects of the Invention) The urethane resin pre-painting treatment method of the present invention changes water to the urethane resin molded product to inactivate unreacted incyanate groups before painting the molded product. The inocyanate groups do not react to generate gas upon heating, and therefore the method of the present invention prevents pinhole defects from occurring in the coating.

In addition, the method of the present invention enables processing at a much lower temperature than conventional methods, so it does not require special jigs such as molds, and the processing time is significantly shortened, resulting in faster processing. It will be done.

Patent applicant: Toyota Motor Corporation (2 others)

Claims (1)

[Claims] 1. A method for pre-painting urethane resin, which comprises holding a urethane resin molded article in water or in a high humidity atmosphere before painting the urethane resin molded article.