JPH0622875B2 - Method for producing hollow molded article made of amorphous resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a hollow molded article made of an amorphous resin, which is excellent in heat resistance, surface appearance and dimensional accuracy.

[Prior Art] A molten parison is placed in a mold, and then a gas is blown into the parison to bring the parison into close contact with the mold cavity to form a hollow molded product. So-called blow molding is polyethylene, polypropylene, or polychlorination. It is mainly used for general-purpose resins such as vinyl and polystyrene.

Recently, it has been attempted to manufacture large products such as bumpers and spoilers for automobiles by blow molding an amorphous resin having excellent heat resistance such as modified polyphenylene oxide and polycarbonate. −
In Japanese Patent No. 25154, a blow-moldable polycarbonate resin composition is described. Further, it is known that blow molding is also possible for modified polyphenylene oxide, but it has a higher melting point than crystalline general-purpose resins such as polyethylene and polypropylene and amorphous general-purpose resins such as polyvinyl chloride and polystyrene, and the temperature It is said that the blow moldability is inferior because the melting year changes abruptly with a slight change in B, and the surface appearance of the blow molded product after blow molding is also impaired.

Therefore, for example, when an amorphous resin is blow-formed and then the surface is painted to manufacture an automobile spoiler, it is necessary to polish and blow the surface of the blow-molded hollow molded product for a long time as a coating process. Therefore, a great deal of labor is spent to improve the surface appearance. On the other hand, as a method of improving the surface appearance of the blown hollow formed article, a method of producing the mold temperature at the time of blow molding at a high temperature close to the melting point is also known, and Japanese Patent Laid-Open No. 58-102734 discloses a mold temperature. There is described a hollow molding die which can be molded at a high temperature.

Thus, it is said that the surface appearance is improved by making the mold cavity temperature, which is normally cooled to 5 ° C to 20 ° C, almost equal to the Parisn temperature, but it takes time to cool the molded product, and the manufacturing efficiency decreases. There was a problem of doing.

[Conventional issues to be solved]

As described above, in the conventional amorphous resin hollow molded article excellent in heat resistance, since the melting point is high, a gas is blown into the parison so that the parison is closely adhered to the mold cavity. On the surface of the manufactured hollow body, surface defects due to parison such as die lines and air marks, and surface defects due to close contact with the mold cavity appear as spots or linear marks and impair the surface appearance. It was a thing. It was also known that the mold cavity temperature was raised to a temperature near the melting point of the parison to improve the surface appearance, but after raising the mold cavity temperature to a high temperature before removing the molded product from the mold. Since it is necessary to cool the mold cavity temperature, the molding cycle becomes longer and the manufacturing efficiency is lowered.

The present inventors have examined the surface appearance of the amorphous resin hollow molded product at the mold cavity temperature, and as a result, have focused on the specific relationship between the temperature at which the tensile elastic modulus is 2000 kg / cm ² and the mold cavity temperature. However, even if the temperature is much lower than the melting point of the amorphous resin, it is possible to obtain an amorphous resin hollow molded product having excellent surface appearance and excellent dimensional accuracy within a certain specific range. I found it.

That is, the present invention improves the surface appearance of an amorphous resin hollow molded product excellent in heat resistance without lengthening the molding cycle as in the past, and suppresses the deformation associated with molding shrinkage of the resin and the dimensional accuracy. It aims at providing the manufacturing method which improves.

[Means for Solving the Problems]

In the present invention, the temperature at which the tensile elastic modulus is 2000 kg / cm ² is 7
When a parison made of an amorphous resin is placed in the mold at 5 ° C. or higher, and then gas is blown into the parison to bring the parison into close contact with the mold cavity, the mold cavity temperature y
(℃) is set to be within the range of y = (0.96x−37) to (0.96x + 3) with respect to the temperature x (℃) at which the tensile modulus of the amorphous resin is 2000 kg / cm ^2. The present invention relates to a method for producing a hollow molded article made of an amorphous resin, which is characterized in that they are closely attached.

The tensile elastic modulus in the present invention means JIS-K-7113.
In accordance with the above, the value measured by using a No. 2 type test piece at a test speed of 2 mm / min is not necessarily correlated with the melting point and the Vicat softening point, and it is an amorphous resin of the same type. However, each shows different values depending on the characteristics of the resin.

Amorphous resins having a tensile elastic modulus of 2000 kg / cm ² at a temperature of 75 ° C. or higher, more preferably 85 ° C. or higher, have excellent heat resistance. For example, modified polyphenylene oxide, polycarbonate, amorphous polyamide, ABS resin, polysulfone, polyethersulfone, polyarylate, and polyetherimide. The amorphous resin blend is a blend of ABS resin and polycarbonate, a blend of polysulfone and ABS resin, and the like.

Further, the amorphous resin in the present invention is a blend of an amorphous resin and a crystalline resin in which the amorphous resin component is 30% by weight or more, and the temperature at which the tensile elastic modulus is 2000 kg / cm ^2. May be a resin having a temperature of 75 ° C. or higher. For example, a blend of an amorphous resin and a crystalline resin is a blend of modified polyphenylene oxide and polyamide, a blend of polycarbonate and polybutylene terephthalate, and the like. Figure 5 shows the tensile modulus of the amorphous resin is 2000kg.
It shows the relationship between the temperature x (° C) which becomes / cm ² and the mold cavity temperature y (° C) when the parison made of the above resin is brought into close contact, y <0.96X-37 ... (Fig. 5). When the parison is in close contact with the mold cavity, the die line, melt fracture and air marks and other spots or linear marks generated between the parison and the mold cavity do not adhere well when the parison adheres to the mold cavity. A defective appearance occurs in the molded product. When y> 0.96x + 3 (part b in FIG. 5), deformation such as sink marks and warpage occurs after molding, resulting in poor dimensional accuracy. Therefore, in the manufacturing method of the present invention, it is necessary to set within the range of y = (0.96x-37) to (0.96x + 3) ... (Part c in FIG. 5). Further, it is preferable to set y = (0.96x−27) to (0.96x−2) in terms of surface appearance and dimensional accuracy, and it is preferable that x is within 180 ° C. of the molding cycle. It is preferable in terms of shortening and simplification of the molding process.

The hollow molded article obtained in the present invention is an air spoiler,
Automotive parts such as bumpers, fenders, side moldings, armrests, furniture parts such as tables, cabinets, racks, housing panels for copying machines, computers, etc., other tanks, bottles, trays, cases, etc., glossy surface, engraved surface , A hollow molded product having a fine uneven surface. In particular, the hollow-molded product having a hollow double-wall structure having a high flatness of the hollow portion is likely to be deformed after molding, so that the production method of the present invention is useful.

Further, since the hollow molded article obtained by the production method of the present invention has an excellent surface appearance, it is suitable for applications where appearance is important, but in particular, it is hollow after blow molding by the production method of the present invention. A hollow molded article in which a coating film is laminated on the surface of the molded article by air spray gun coating, electrostatic coating, or dip coating is particularly useful. That is, according to the production method of the present invention, the surface appearance of the hollow molded article can be improved much more than the conventional method, but in order to further improve the surface appearance and improve the glossiness, the hollow molding is required. It is also possible to paint the molded surface of the product. That is, after the blow molding by the manufacturing method of the present invention, after a simple pretreatment or without pretreatment, the total film thickness of the primer layer and the coating layer is 5 μm to 150 μm, preferably 20 μm to 100 μm.
By coating within the range of m, even if slight spots or linear scratches are generated on the surface after blow molding, the present invention can almost completely eliminate the appearance defect by coating. Since the surface can be molded to the extent possible, it is possible to greatly simplify the polishing, pre-treatment such as water removal, and the coating process as compared with the conventional method. If the total film thickness is less than 5 μm, the glossiness of the surface will be lost and fine skin roughening will occur. The problem occurs, while 15
If the thickness exceeds 0 μm, the problem that the discolored skin appears remarkably when the pretreatment such as water stripping is not completely performed occurs. Therefore, the total film thickness when coating is 5 μm to 150 μm.
μm is preferred.

Also, the material of the mold used in the manufacturing method of the present invention,
The mold cavity can be made of iron, aluminum, chromium or the like, and a skin layer of fluorine or the like can be formed in the mold cavity. Further, as the temperature control means of the mold cavity, known temperature control methods such as a method of circulating oil or steam in the mold, a method of heating the mold cavity with an electric heater, a method of heating with high frequency induction heating, etc. Means can be used.

[Action]

The temperature x at which the tensile elastic modulus of the amorphous resin reaches 2000 kg / cm ² is a temperature much lower than the melting point of the amorphous resin.

Generally, it is said that if the temperature difference between the mold cavity temperature for molding and the melting point of the resin to be molded is increased, the surface appearance is impaired to that extent. Then, it was found that the deterioration of the surface appearance can be suppressed.

Also, after placing the amorphous resin in the mold, blowing gas into the mold to bring the mold into close contact with the mold cavity, and immediately after cooling the molded product in the mold, the normal molded product is completely It is not in a solidified state. Therefore, even after the molded product is cooled in the mold and the molded product is taken out of the mold, the amorphous resin hollow body may be deformed such as sink marks and warps. Particularly, in the conventional means for increasing the temperature of the mold cavity to improve the surface appearance, the mold cavity is in contact with the molded amorphous resin mold cavity although the cooling time in the mold is long. Temperatures are generated on the outer surface side, the inner surface side into which gas is blown, and the inside of the wall, and there is a high possibility that deformation such as sink marks and warpage will occur after molding. However, in the present invention, the temperature difference is relatively small, deformation such as sink marks and warpage does not occur, and the molding cycle does not become long.

[Experimental example]

Each amorphous resin shown in Table 1 was blow-molded by the method shown below to obtain hollow molded article samples of Experimental Examples 1-10.
In each experimental example, blow molding was performed while changing the mold cavity temperature to obtain hollow molded product samples of each sample No.
Then, the surface appearance of the molding surface after blow molding was measured in the state of spots and linear marks, and the dimensional accuracy was measured by the degree of deformation.

Then, after coating the molded surface of the hollow molded product by the method described below, the surface appearance of the coated surface was measured by the same method as the molded surface of the hollow molded product. The evaluation results are as shown in Table 3. The evaluations shown in Table 3 were obtained by measuring 5 samples of each sample No. and calculating the average value, and the detailed evaluation method is as shown below.

Blow molding Amorphous resin is melted by an extruder with a screw diameter of 90 mm, and then the molten resin is accumulated in an accumulator, and then extruded as a cylindrical parison 2 from an extrusion head 1 as shown in FIG. It was placed between the molds 3 and 4. In addition,
Table 2 shows set melting temperatures in the extruder in Examples 1 to 10.

Further, the materials of the molds 3 and 4 were iron, and the mold cavities 5 and 6 used were mirror-finished with a surface roughness of 0.8 μ or less.

Then, the molds 3 and 4 are clamped, and as shown in FIG. 2, air is blown into the parison 2 with a blow pressure of 7 kg / cm ² , and the parison 2 is closely attached to the mold cavity to form a three-dimensional shape. Molded into. Then, after cooling the molded product 2'in the molds 3 and 4, the molds 3 and 4 are opened as shown in FIG.
Then, the excess burr 2a in the vicinity of the die mating surface PL was removed to obtain a hollow molded product 2'having an automobile spoiler-shaped hollow double wall structure as shown in FIG. The length L of the hollow molded product 2'is 120 cm and the width D is 1
The average resin wall thickness t having a height of 8 cm and a height of 9 cm was 3 mm.

Coating Two-component urethane paint manufactured by Origin Electric Co., Ltd. was coated on the molding surface of the hollow molded product after blow molding with an air spray gun to a total film thickness of 55 μm (primer film thickness 1
5 μm, top coating thickness 40 μm).

Method of measuring molding conditions 1. Mold cavity temperature: y (° C.) A resin thermometer (Rika Kogyo Digital Thermometer) was pressed against the surface of the mold cavity immediately before the parison was extruded and measured.

2. Molding cycle (Sec) The time from the start of extrusion of the parison to the completion of taking out the molded product from the mold was measured. The reason why the molding cycle becomes longer as the mold temperature is set higher is that the molded product is deformed when the molded product is taken out unless the mold holding time is extended.

Evaluation method 1. Spots (number / 100 cm ² ) For each sample No. of the experimental example, the number of spots appearing in an area of 1000 cm ² was visually measured and then converted to the number of spots per 100 cm ² , and then 5 molded products Was calculated.

2. Linear Scratch For each sample No. of the experimental example, the unevenness state and the number of linear scratches generated due to die line, melt fracture, and other factors were evaluated visually and by hand for each of five poor moldings.

⊚: No linear mark is observed ○: Slightly visible but no hand feel △: Inconspicuous but hand feel ×: Conspicuous line mark Deformation Degree For each sample No. of the experimental example, 5 molded products were placed on a flat surface (see Fig. 4), the center height h of each was measured, and the maximum mold temperature of each experimental example was measured. The difference (cm) was measured based on the average height of the low sample No.

As is clear from Table 3, the mold cavity temperature y is within the range of y = (0.96x−37) to (0.96x + 3) with respect to the temperature x at which the tensile modulus of the amorphous resin is 2000 kg / cm ² . Sample No. 2, 3 of Experimental Example 1, Sample No. 3, 4, 5 of Experimental Example 2, Sample No. 3, 4 of Experimental Example 3, Sample No. 3, 4 of Experimental Example 4 5 sample No. 3, 4 Experimental example 6 sample No. 3, 4 Experimental example 7 sample No. 2, 3, 4 Experimental example 8 sample No. 2, 3, 4 Experimental example 9 sample No. 2 Sample Nos. 3 and 4 of Experimental Example 10 have less generation of spots and linear scratches on the molding surface than other sample Nos., Have an excellent surface appearance, and have a low degree of deformation. The dimensional accuracy was excellent. In particular, it was found that those molded within the range of y = (0.96x-27) to (0.96x + 2) showed the most remarkable improvement in surface appearance and dimensional accuracy.

Further, in the evaluation of the coated surface after coating, the state of the spots was remarkably improved by the coating film obtained by the method of the present invention. Further, the state of linear scratches has not been much improved by the coating film, and it has been found that it is important to perform the method according to the present invention at the time of molding in this respect. It is considered that the reason why the spots on the molding surface of the hollow molded product were remarkably improved by the coating was that the minute spots were smoothed to the extent that they were inconspicuous with respect to the entire coating film thickness.

〔effect〕

INDUSTRIAL APPLICABILITY The present invention improves the surface appearance of an amorphous resin molded product having excellent heat resistance as described above without lengthening the molding cycle as in the conventional case, and suppresses the deformation due to the molding shrinkage of the resin to improve the dimensional accuracy. Can be improved.

[Brief description of drawings]

FIGS. 1 to 3 show the process of manufacturing a molded product of an experimental example. FIG. 1 is a front view of a die in a state where a parison is extruded, and FIG. 2 is a mold clamping and gas in the parison. FIG. 3 is a front view of the mold in which the molded product is opened after cooling the molded product in the mold, and FIG.
A perspective view of a molded product molded by the method shown in FIGS.
FIG. 5 is a diagram showing the relationship between the temperature x at which the tensile elastic modulus of the amorphous resin reaches 2000 kg / cm ² and the mold cavity temperature y. 1: Extrusion head, 2: Paris 3, 4: Mold, 5, 6: Mold cavity

Claims (1)

[Claims] 1. A parison made of an amorphous resin having a tensile elastic modulus of 2000 kg / cm ² and a temperature of 75 ° C. or higher is placed in a mold, and then gas is blown into the parison to form the mold cavity in the mold cavity. When making close contact, the mold cavity temperature y (° C.) was adjusted so that the tensile modulus of the amorphous resin was 2000 kg / cm ²
To a temperature x (° C) at which y = (0.96x-37) to (0.96x + 3), and closely adhere to each other. Method.