JPH01301320A - Manufacture of hollow molded produce made of noncrystalline resin - Google Patents

Abstract

PURPOSE:To improve an external appearance of the surface and dimensional accuracy, by a method wherein at the time when parison comprising specific noncrystalline resin is arranged within a mold and the parison is stuck close to a mold cavity, a mold cavity temperature is set up so that the same falls within a specific sphere. CONSTITUTION:Parison comprised of noncrystalline resin whose temperature where the tensile modules of elasticity becomes 2,000kg/cm<2> is at least 75 deg.C is arranged within a mold, gas is blown into the parison and the parison is stuck close to a mold cavity. In this instance, the parison is stuck close to the mold cavity by setting up a mold cavity temperature y deg.C so that the same falls within a sphere of y=(0.96x-37) to (0.96x+3) to a temperature x deg.C where the tensile modulus of elasticity of amorphous resin becomes 2,000kg/cm<2>. When y<0.96x-37 is attained, at the time of sticking of the parison close to the mold cavity, the parison does not favorably stick close to the mold cavity and defective external appearances such as a die line and melt fracture on the surface of the parison and an air mark and the other spot or a linear streak to be generated between the parison and mold cavity are generated on a molded product. When y>0.96x+3 is attained, it follows that deformations such as a sink/warp are generated after molding and the molded product becomes inferior in dimensional accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an amorphous resin blow molded article having excellent heat resistance, surface appearance, and dimensional accuracy.

[Conventional technology]

The so-called blow molding process involves placing a molten parison in a mold, then blowing gas into the parison to bring the parison into close contact with the mold cavity to form a hollow molded product. It is widely used mainly in general-purpose resins.

Recently, attempts have been made to manufacture large products such as automobile bumpers and spoilers by blow molding amorphous resins with excellent heat resistance such as modified polyphenylene oxide and polycarbonate. 62-
No. 25154 describes a polycarbonate resin composition that can be blow molded. It is also known that modified polyphenylene oxide can be blow molded, 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 It is said that the blow moldability is poor because the melt viscosity changes rapidly due to a slight change in the melt viscosity, and the surface appearance of the blow molded product is also impaired.

Therefore, for example, when manufacturing a spoiler for an automobile by painting the surface after blow molding an amorphous resin, the surface of the blow molded hollow molded product is polished and blotted for a long time as a painting process. This requires a great deal of effort to improve the surface appearance. On the other hand, as a method for improving the surface appearance of blown hollow molded products, a method is known in which the mold temperature during blow molding is set to a high temperature close to the melting point. A hollow molding die that can be molded at a high temperature is described.

In this way, it is said that the surface appearance will improve if the mold cavity temperature, which is normally cooled to 5°C to 20°C, is made almost equal to the parison temperature, but it will take time to cool the molded product, reducing manufacturing efficiency. There was a problem.

[Conventional issues to be solved]

As explained above, conventional hollow molded products made of amorphous resin with excellent heat resistance have a high melting point, so a manufacturing method that involves blowing gas into the parison and bringing the parison into close contact with the mold cavity is used. The surface of the manufactured hollow body has surface appearance defects caused by parisons such as guiline and air marks.
In addition, surface appearance defects caused by close contact with the mold cavity appeared as spots or linear marks, impairing the surface appearance. It was also known that the surface appearance could be improved by increasing the mold cavity temperature to a temperature close to the melting point of the parison. Since it is necessary to cool down the mold cavity temperature, the molding cycle becomes longer and manufacturing efficiency decreases.

As a result of examining the mold cavity temperature and the surface appearance of an amorphous resin hollow molded product, the present inventors focused on a specific relationship between the temperature at which the tensile modulus becomes 2000 kg/a+t 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 amorphous resin hollow molded products with excellent surface appearance and dimensional accuracy within a certain range. I found it.

In other words, the present invention improves the surface appearance of amorphous resin hollow molded products with excellent heat resistance, as compared to conventional methods (without prolonging the molding cycle), and suppresses deformation caused by molding shrinkage of the resin, etc. The purpose is to provide a manufacturing method that improves accuracy.

[Means to solve the problem]

In the present invention, a parison made of an amorphous resin whose temperature at which the tensile modulus is 2000 kg/cal is 75°C or higher is placed in a mold, and then gas is blown into the parison to bring the parison into close contact with the mold cavity. When setting the mold cavity temperature y (℃) to the tensile modulus of the amorphous resin of 2000k
g/cnl for the temperature x (℃) y = (0,96x -37) ~ (0,96x +
3) It relates to a method for manufacturing a hollow molded product made of amorphous resin, characterized in that the method is set so as to fall within the range of (3) and brought into close contact with each other.

The tensile modulus in the present invention refers to JIS-71
13, using a No. 2 test piece, at a test speed of 2fl/
It shows the value tested at 11in, and there is not necessarily a correlation with the melting point and Vikatto softening point, and even the same type of amorphous resin shows different values depending on the characteristics of the resin. .

The temperature at which the tensile modulus becomes 2000 kg/c++1 is 7.
Amorphous resins with a temperature of 5° C. or higher, and even 85° C. or higher, have excellent heat resistance. Examples include modified polyphenylene oxide, polycarbonate, amorphous polyamide, ABS resin, polysulfone, polyethersulfone, polyarylate, and polyetherimide. Blends of amorphous resins include blends of ABS resin and polycarbonate, blends of polysulfone and ABS resin, and the like.

In addition, the amorphous resin in the present invention refers to a blend of an amorphous resin and a crystalline resin in which the amorphous resin component accounts for 30% or more, and the temperature at which the tensile modulus becomes 2000 kg/aJ. may be a resin whose temperature is 75°C or higher. For example, blends of amorphous resins and crystalline resins include blends of modified polyphenylene oxide and polyamide, blends of polycarbonate and polybutylene phthalate, and the like. Figure 5 shows that the tensile modulus of the amorphous resin is 2000k.
g/cnl temperature x (°C) and the mold cavity temperature y (°C) when the parison made of the above resin is brought into close contact.
C). When y < 0.96X -37. , melt fractures, and appearance defects such as air marks and other spots or linear marks occurring between the parison and the mold cavity occur on the molded product. Also, y〉0.96x+3...(5th
If this occurs (the part shown in the figure), deformations such as sink marks and warpage may occur after molding, resulting in poor dimensional accuracy. Therefore, in the manufacturing method of the present invention, y= (0,96x-37) to (0,96x +3)
...(Part C in Figure 5) It is necessary to set it within the range of 't = (0,96x -27) ~ (0,96x
-2) is preferable in terms of surface appearance and dimensional accuracy, and setting X within 180°C is preferable in terms of shortening the molding cycle and simplifying the molding process.

The hollow molded products obtained by the present invention include air spoilers,
Automotive parts such as bumpers, fenders, side moldings, and armrests; furniture parts such as tables, cabinets, and racks; housing panels for copiers and computers; and other tanks, bottles, trays, cases, etc.
This is a hollow molded product with a glossy surface, a carved surface, and a finely uneven surface.

Among these, the manufacturing method of the present invention is particularly useful for hollow double-walled hollow molded products having a high oblateness of the hollow portion, since these products tend to be easily deformed after molding.

In addition, since the hollow molded product obtained by the manufacturing method of the present invention has an excellent surface appearance, it is suitable for applications where appearance is important. Particularly useful are hollow molded products in which a coating film is laminated on the surface of the molded product by air spray gun painting, electrostatic painting, or dip coating. In other words, according to the manufacturing method of the present invention, the surface appearance of a blow molded product can be much improved compared to conventional methods, but in order to further improve the surface appearance and gloss, blow molding is It is also possible to paint the molded surface of the product. That is, after blow molding according to the production method of the present invention, the total film thickness of the primer layer and the coating layer is 5μI11 to 150μm, preferably 20μ11 to 150μm, after a simple pretreatment or without pretreatment.
By painting within the range of 00 μm, even if there are slight spots or linear marks on the surface after blow molding, in the present invention, the appearance defects can be almost completely eliminated by painting. Since the surface can be molded to the desired level, pre-treatments such as polishing and water scrubbing and painting processes can be significantly simplified compared to conventional methods. If the total film thickness is less than 5 .mu.I, the surface loses its glossy appearance and the surface of the substrate becomes finely rough. On the other hand, if the thickness exceeds 150 μm, there will be a problem that citron skin will appear prominently if pre-treatment such as water removal is not completely performed, so the total film thickness when painting is 5 μm or more.
150 μm is preferred.

Furthermore, the mold cavity used in the manufacturing method of the present invention may be made of iron, aluminum, chromium, etc., and the mold cavity may have a skin layer made of fluorine or the like. You can also do it. In addition, as a means for controlling the temperature of the mold cavity, there are 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 the mold cavity with high-frequency induction heating, etc. Means can be used.

[Effect]

The temperature X at which the tensile modulus of the amorphous resin is 2000 kg/cm2 is much lower than the melting point of the amorphous resin.

Generally, it is said that the wider the temperature difference between the mold cavity temperature for molding and the melting point of the resin to be molded, the more the surface appearance will be impaired, but according to the research of the present inventors, within a certain range. It has been found that deterioration in surface appearance can be suppressed.

In addition, the molded product is usually completely finished immediately after placing the amorphous resin in a parison in the mold, blowing gas into the parison to bring the parison into close contact with the mold cavity, and then cooling the molded product in the mold. It is not in a solidified state. Therefore, even after the molded product is cooled in the mold and taken out from the mold, the amorphous resin hollow body may be deformed by sink marks, warpage, etc. In particular, in the conventional method of raising the temperature of the mold cavity to improve the surface appearance, although the cooling time within the mold is long, the molded amorphous resin comes into contact with the mold cavity. Temperatures occur on the outer surface side, the inner surface side where gas is blown, and inside 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 also compared. There are no deformations such as sink marks or warpage, and the molding cycle does not become long.

[Experiment example]

Each amorphous resin shown in Table 1 was blow molded by the method shown below to obtain blow molded product samples of Experimental Examples 1 to 10.

In addition, in each experimental example, blow molding was performed while changing the mold cavity temperature, and hollow molded product samples were obtained in each sample space. Then, the surface appearance of the molded surface after blow molding was measured in terms of spots and linear marks, and the dimensional accuracy was measured in terms of the degree of deformation.

Next, the molded surface of the hollow molded product was coated by the method shown below, and the surface appearance of the painted surface was measured in the same manner as the molded surface of the hollow molded product.

The evaluation results are shown in Table 3. Note that the evaluation shown in Table 3 was obtained by measuring five samples for each sample and calculating the average value, and the detailed evaluation method is as shown below.

After melting the expanded amorphous resin in an extruder with a screw diameter of 90 mm, 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. 1 and divided. It was placed between 3 and 4 types of molds. In addition,
The melting temperatures set in the extruder in Experimental Examples 1 to 10 are shown in Table 2.

In addition, the material of the mold 3.4 is iron, and the mold cavity 5
．． In No. 6, a mirror-finished product with a surface roughness of 0.8 μm or less was used.

Next, the mold 3.4 is clamped, and as shown in Fig. 2, air is blown into the parison 2 at a blowing pressure of 7 kg/c+a, and the parison 2 is brought into close contact with the mold cavity to form a three-dimensional shape. Molded. Next, after cooling the molded product 2' in the mold 3.4, the mold 3.4 is opened as shown in FIG.
The mold was taken out, and excess burrs 2a near the mold mating surface PL were removed to obtain a hollow molded product 2' having a hollow double wall structure in the shape of an automobile spoiler as shown in FIG. The set dimensions of the hollow molded product 2' were a length of 120 cm, a width of 18 C11, a height of 9 am, and an average resin wall thickness t of 3 mm.

A two-component urethane paint manufactured by Origin Electric Co., Ltd. was applied to the molded surface of the hollow molded product after the infant blow molding with an air spray gun to a total film thickness of 55 μm (primer film thickness 1
5μ-1 top coat thickness 40μm).

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

2. Molding cycle (Sea) 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 if the molded product is not held in the mold for a longer time, the molded product will be deformed when taken out from the mold.

For each sample fish in the experiment, the number of spots that appeared in an area of 1000 cni was visually measured, converted to the number of spots per 1004 cd, and then 5 spots were calculated. The average value of the molded products was calculated.

2. For each sample in the linear scar experiment example, the unevenness and number of linear scars caused by guinea, melt fracture, and other factors were evaluated for each of the five molded products by visual inspection and hand feel.

◎: No 'fs-like marks are seen.○: Slightly seen but not felt by hand. △: Not noticeable but can be felt by hand. ×: VA-like marks are noticeable. For each sample area, place five molded products on a flat surface (see Figure 4), measure the center height h of each, and measure the average height of the sample area with the lowest mold temperature among each experimental example. The difference (cm2) was measured using this as a reference.

Table 1 Table 2 Table 3-1 Table 3-2 Table 3-3 Table 3-4 Table 3-5 As is clear from Table 3, the mold cavity temperature y is y = (0,96x-37) to (0,96x +3
) Sample IIkL2.3.4 of Experimental Example 1 Sample depth 3.4.5 of Experimental Example 2 Sample 11h3.4 of Experimental Example 3 Sample depth 3.4 of Experimental Example 5 Sample size 3.4 Sample 11h of Experimental example 6 3.4 Sample size 2.3.4 of Experimental example 7 Sample size 2.3.4 of Experimental example 8 Sample size 2.3.4 of Experimental example 10 Sample No. 3.4 had less spots and linear marks on the molded surface than the other sample fish, had an excellent surface appearance, had a suppressed degree of deformation, and had excellent dimensional accuracy. In particular, V = (0,96x-27) ~ (0,96x -2)
It was found that the surface appearance and dimensional accuracy of molded products within the range of

Furthermore, in the evaluation of the painted surface after painting, the condition of spots was significantly improved by the coating film obtained by the method of the present invention. Furthermore, the condition of the linear marks has not been significantly improved by the coating film, and in this respect, it has been found that it is important to perform the method according to the present invention during molding. The reason why the spots on the molded surface of the hollow molded product were significantly improved by painting is thought to be because the overall thickness of the coating smoothed out minute spots to the point where they were not noticeable.

〔effect〕

The present invention improves the surface appearance of amorphous resin molded products with excellent heat resistance as described above without prolonging the molding cycle as in conventional methods, and improves dimensional accuracy by suppressing deformation caused by molding shrinkage of the resin. can be improved.

[Brief explanation of the drawing]

Figures 1 to 3 show the process of manufacturing the molded product of the experimental example. Figure 1 is a front view of the mold with the parison extruded, and Figure 2 is a mold clamping process to create gas inside the parison. Figure 3 is a cross-sectional view of the mold with the molded product injected with
A perspective view of a molded product formed by the method shown in FIGS.
Figure 5 shows that the tensile modulus of the amorphous resin is 2000 kg/cJ.
It is a figure showing the relationship between temperature X and mold cavity temperature y. 1: Extrusion head 2: Parison

Claims (1)

[Claims] The temperature at which the tensile modulus is 2000 kg/cm^2 is 7.
A parison made of an amorphous resin with a temperature of 5°C or higher is placed in a mold, and then gas is blown into the parison to bring the parison into close contact with the mold cavity.
°C), the tensile modulus of the amorphous resin is 2000 kg/cm^
y=(0.96x-37
) to (0.96x+3) and bringing them into close contact with each other.