JPS5840504B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection molding method for obtaining a thermoplastic resin injection molded article with a good appearance.

The thermoplastic resin injection molded product obtained by the method of the present invention has a good appearance because there are no flow marks, etc. Especially in the case of the filler Jinnetsucho resin, there is no silver streak because the filler is not exposed on the surface. The appearance is extremely good.

In other words, the effects of the present invention are particularly significant for injection molded products of filled thermoplastic resins, where the surface of the injection molded product is rough and it is not possible to obtain the soft, glossy appearance inherent to thermoplastic resins using normal injection molding methods. This is the most prominent injection molding method.

Conventionally, in injection molding of thermoplastic resin molded products, the plasticity of the thermoplastic resin is utilized, in other words, the thermoplastic resin is heated and fluidized using a screw, and then cooled in a mold. The basic principle is to obtain molded products through solidification.

That is, in order to solidify, release the molded product from the mold, and take it out (1) Cool it below the heating deformation temperature of the thermoplastic resin and take it out of the mold.

Therefore, the mold is generally maintained at a temperature lower than the heating deformation temperature.

Furthermore, in order to increase productivity, a refrigerant is used to cool the mold to a temperature on the verge of condensation.

Even when cooling the mold and heating and storing heat at the temperature of the molten resin, in principle the mold temperature is controlled so as not to exceed the heating deformation temperature of the thermoplastic resin.

In other words, when the mold surface and thermoplastic resin come into contact, the thermoplastic resin is rapidly cooled at the contact surface and the fluidity of the thermoplastic resin becomes extremely poor, resulting in poor adhesion of the thermoplastic resin to the mold surface and Even if the mold surface is mirror-like, the transferability from the mold is poor and the surface of the molded product is extremely uneven.

In addition, in the case of a filler, the filler and the thermoplastic resin generally have poor compatibility, so it is thought that minute voids are created at the interface between the filler and the thermoplastic resin, resulting in silver streaks when injection molded.

That is, the filler material appears on the surface of the molded product, the surface of the molded product is severely uneven, and the molded product has a so-called poor appearance.

The present inventors have discovered that by setting the mold surface temperature to a temperature higher than the heating deformation temperature of the thermoplastic resin, it is possible to mold the resin while maintaining its plasticity, without causing flow marks, silver streaks, etc. as described above. This made it possible to obtain injection molded products with extremely excellent transferability from the mold.

In other words, according to the method of the present invention, jetting and
A molded product can be obtained without defects such as flow marks and weld lines, and without gloss differences (glossy spots) between the gate area of the injection molding machine and the resin flow end (dead end) area.

Particularly when a filler is present, the appearance of the filler also disappears.

Further, by selectively heating the mold surface to a temperature higher than the heating deformation temperature of the thermoplastic resin, the molded article surface also selectively does not suffer from the above-mentioned defects.

Furthermore, even when trying to obtain a molded product having a surface that is not smooth, such as a rough uneven pattern, grain, satin (frosted glass), etc., the method of the present invention has excellent transferability from the mold, making it very suitable. You can get a nice look.

Furthermore, by adopting a high-frequency induction heating method as a means of heating the mold surface, we succeeded in improving productivity.

The explanation will be given below.

It is impossible to release the mold from the mold while keeping the surface of the thermoplastic resin at a temperature higher than the heat deformation temperature of the thermoplastic resin.In order to obtain the desired molded product without deformation, the mold must be cooled and the temperature of the molded product must be lowered. It is necessary to cool and solidify the resin to a temperature lower than the heating deformation temperature of the thermoplastic resin before releasing it from the mold.

However, injection molding molds are usually made of steel and are many times larger in weight and capacity than the shape of the molded product, and require a large amount of heat and time for heating and cooling.

That is, there are problems in industrial production in obtaining the above-mentioned molded product.

That is, when molding is performed by such a method, a molding cycle of 40 to 60 minutes is required.

Therefore, if the principle of high-frequency induction heating is used for heating, it is possible to selectively heat the surface layer of the mold, and it is also possible to rapidly heat and cool the mold surface.

According to this method, the influence of thermal expansion, contraction, etc. of the entire mold is eliminated, the dimensional accuracy of the injection molded product is improved, and there is no appearance of unevenness.

The heating deformation temperature in the present invention is measured by the method specified in JIS K6871, but when specifying the mold surface temperature, the test piece should be heated so that the bending stress is 4.6 kg/-. This refers to the heating deformation temperature when a load is applied.

Next, the injection molded product obtained by the method of the present invention will be explained.

In particular, injection molded plastic resin products with fillers will be explained.

Thermoplastic resin molded products containing various fillers such as glass fiber, inorganic substances, metal powder, etc. have higher tensile strength, bending strength, bending modulus, and heat resistance than molded products that do not contain such fillers. It has improved dimensional stability, etc., and has been used as a useful material for automobile parts and electrical appliance parts.

On the other hand, Natsumachi Plastic Resin used its plasticity to make molded products through a procedure of heating fluidization, shaping, and cooling solidification, but since the filler mentioned above does not have fluidity, thermoplastic resin molded products with fillers are The surface of the molded product was severely roughened, making it difficult to use it for products that required a beautiful appearance, and it was only used for internal structural parts, taking advantage of its good physical properties.

When used as a molded product that requires a beautiful appearance, paint it.

If other methods such as pasting a film are used to attach a thin film material to the surface of the filled thermoplastic resin molded product, it is not possible to obtain a molded product with the soft luster inherent to the thermoplastic resin. It also has drawbacks such as being time consuming and expensive to manufacture.

Furthermore, in the case of painting, mechanical strength such as impact strength is reduced because the thermoplastic resin is melted to form a coating film.

Also, when applying a film, if the shape of the molded product is complex, it is nearly impossible to cover the entire surface of the molded product in terms of industrial production.

However, according to the method of the present invention, in a thermoplastic resin molded product, the filler is not exposed on the surface of the molded product.In other words, it is possible to form a thin skin layer of thermoplastic resin on the surface of the molded product. Has gloss, flow marks,
It is possible to obtain a filled thermoplastic resin molded product having a good appearance and free of appearance defects such as silver streaks.

The molded article may have a complex shape.

Observation of the surface of this molded product reveals that a thermoplastic resin skin layer of 1 to 100 μm is formed, and the surface gloss of the molded product is A.
Glossiness Gs(60)% specified in STMD523 is 6
It has a gloss of 0 or more, more preferably 80 or more.

In addition, the molded product of the present invention not only has a good gloss on the surface of the molded product, but also has problems such as appearance of filler on the surface, silver streaks, flow marks, etc., which are serious drawbacks of filled thermoplastic resin molded products. This is a filled thermoplastic resin injection molded product that has a good appearance and is free from defects in appearance caused by the flow and uneven flow of the filled thermoplastic resin during injection molding.

In other words, it is a filled thermoplastic resin injection molded product that has a smooth molded surface, has a soft luster characteristic of thermoplastic resins, and is free from appearance defects such as silver streaks and flow marks.

In other words, by selectively heating the vicinity of the mold surface using high-frequency induction heating, the vicinity of the mold surface can be rapidly heated and rapidly cooled, making injection molding possible without significantly extending the molding cycle. is maintained above the heating deformation temperature of the thermoplastic resin, making it difficult for the thermoplastic resin to cool down during the entire flow in the mold.

Therefore, the transferability of the mold surface shape (smoothness and unevenness of the mold surface) to the surface of the molded product can be significantly improved.

In other words, if the surface of the mold has a smooth finish, as is the case with many mold surfaces, a molded product with excellent surface gloss can be obtained, and the gloss on the surface of the molded product cannot be improved by conventional injection molding methods. It is possible to obtain molded products with an unimaginable uniformity and high gloss.

In addition, in the case of a molded product with unevenness on the mold surface, such as a grained part, the reproducibility of the grained part is good and the grained part becomes uniformly glossy, so this injection molding method is used to obtain a molded part with a so-called smooth grain. I found out what happened.

Next, the molding method according to the present invention and the injection molded product obtained will be explained with reference to the drawings.

In injection molding of filled thermoplastic resin, a high-frequency induction heating inductor is installed between a stationary mold and a movable mold as shown in FIG.

When an inductor was inserted between the movable mold and the stationary mold and a high frequency was oscillated in the sandwiched state, only the mold surface (points A and B) suddenly changed as shown in Figure 2. It can be confirmed that the temperature increases, and the temperature inside the mold (points C and D) hardly increases due to high-frequency induction heating.

In the case of the example shown in FIG. 2, the mold is not cooled with cooling water, but simply shows an example of the change over time in the temperature distribution of the mold due to high-frequency induction heating.

After that, the mold was opened once and the inductor was pulled out from between the stationary and movable molds, and the mold was closed again and the filled thermoplastic resin was injection molded in the same manner as normal injection molding. A filled thermoplastic resin molded product with a beautiful appearance was obtained.

As the filled thermoplastic resin, a glass fiber reinforced acrylonitrile-styrene copolymer resin (acrylonyl-IJ loose styrene copolymer resin is hereinafter abbreviated as AS resin).

) was obtained.

The third optical microscope photograph of the cut surface of this molded product in the thickness direction is
The magnification shown in FIG. 4 is 440 times.

For reference, the same material was injection molded using the same mold at a mold temperature of 60° C., and the same cross section was photographed in the same manner as shown in FIGS. 5 and 6.

The magnification is 440 times.

In both photos, the island pattern is made of glass fiber, and the horizontal line is the surface of the molded product.

As is clear from comparing Figures 3 and 4 with Figures 5 and 6, in the case of the molded product obtained by the method of the present invention, filler glass fiber appears on the surface of the molded product. It can be seen that the thermoplastic resin layer with a thickness of at least 1 to 30 μm is formed on the surface layer of the molded product.

Also, as shown in Figures 3 and 4, when the glass fibers are placed relatively close to the surface of the molded product, the thermoplastic resin layer forms the surface layer, and at the same time, the glass fibers form slight irregularities on the surface layer. However, compared to the case shown in FIG. 6, a molded product with a glossy appearance can be obtained since it shows gentle unevenness.

On the other hand, in the case of normal molded products, as shown in Figures 5 and 6, if the glass fibers protrude from the surface of the molded product, or if the glass fibers are near the surface layer, the flow of resin on the mold surface is obstructed. Because of this, silver streak-like irregularities are formed on the surface, and only molded products with so-called dull and rough surfaces can be obtained.

AST
The glossiness Gs (60° C.) of the molded article was measured using MD523 and was 98 degrees.

On the other hand, the molded product produced at a mold temperature of 60° C. had a gloss level of 45, indicating that the molded product of the present invention had a smooth appearance and good gloss.

In addition, the molded product of the present invention has a low flow resistance during injection molding and is difficult to generate orientation strain, so when the heating deformation temperature specified in JIS K6871 was measured (bending stress 18
．． 6kg/-) Compared to normal molded products, the heating deformation temperature is improved by 3 to 5°C, so-called practical heat resistance temperature is improved, and as a result of comparing the drop strength of molded products, practical toughness is also improved. I confirmed that I would.

In the present invention, fillers include glass fibers, glass spheres, inorganic substances such as calcium carbonate, mica, asbestos, metal powders such as iron, copper, zinc, aluminum, and their oxides and hydroxides, and hollow particles. This term refers to particles with a small particle diameter of 5 mesh or less.

Thermoplastic resins in the present invention include polystyrene, rubber-reinforced polystyrene (hereinafter collectively abbreviated as PS), AS resin, acrylonitrile-butadiene-styrene copolymer,
Acrylonitrile-butadiene-styrene-α-methylstyrene, acrylonitrile-methyl methacrylate-
Butadiene-styrene (hereinafter collectively referred to as ABS resin)
, polyethylene, polypropylene, polycarbonate,
It includes all so-called thermoplastic resins such as polyphenylene ether, polyoxymethylene, and nylon.

As mentioned above, the injection molding method of the present invention is particularly effective when applied to thermoplastic resins containing fillers, but it is also effective when applied to injection molding of ordinary thermoplastic resins that do not contain fillers. It has the effect of making the appearance of injection molded products beautiful, and not only improves the gloss of the entire molded product, but also eliminates gloss unevenness and flow marks, especially in injection molded products with changes in wall thickness, and has a practical heat-resistant temperature range. It also has the same effects as the thermoplastic resin containing fillers, such as improving stiffness.

Example 1 A glass fiber having a diameter of 13μ and an AS resin having a weight of 20% by weight were molded using a normal in-line injection molding material.

The mold is made of regular S-45C steel and has a diameter of 10Cr.
The mold is capable of molding a dish-shaped product with a depth of 2 CrrL and an average wall thickness of 3.5 mm, and the gate is a center direct gate.

The inductor is made by molding a steel pipe with a diameter of 37rL7IL into a dish shape in a spiral shape with 5-space intervals, then casting it with epoxy resin to a thickness of 3cIrL, and fixing and hardening it into a flat plate.

The injection molding conditions are such that the temperature of the glass fiber-added As resin is 24
The cylinder temperature was set to 0°C.

Before injecting the glass fiber reinforced As resin into the mold, the above-mentioned inductor was inserted between the molds, and the inductor was heated to 400 KHz.
A 16 KW high frequency oscillator oscillated for 15 seconds, then the mold was opened, the inductor was pulled out from between the molds, and the mold was closed again.

During this time, make sure that the mold cooling water does not flow inside the mold.

Then, as in normal injection molding, the filled resin was injected into the mold at an injection pressure of 60 kg/cwt for 10 seconds, then cooling water was passed through the mold, and after cooling for 20 seconds, the molded product was taken out. .

Total cycle time was 60 seconds.

The surface of this molded product had an appearance similar to that of the As resin molded product, with no silver streaks or protrusion of glass fibers on the surface of the molded product, and a molded product with a very good appearance.

Example 2 An ABS resin with 20 weight modulus of glass fiber of 15 μm was molded using a conventional injection molding material at a resin temperature of 240°C.

The mold is a mold that can produce dumbbells and strips of shape specified in JIS K6871, and the material is S to 55C.
It is created with.

The inductor used was one in which copper tubes of three diameters were arranged in a spiral shape at five intervals, which was cast into a 2 cm thick flat plate with epoxy resin and solidified.

The molding method was the same as in Example 1, but at 400 KHz and 6
KW, high frequency oscillation time 10 seconds, injection 10 seconds, cooling 15
seconds, total molding cycle 50 seconds.

Injection pressure: 50 i<9/=0 The surface of this glass fiber-reinforced ABS resin molded product was covered with ABS resin, and a glossy molded product with a beautiful surface appearance was obtained.

The physical properties of the molded product were evaluated according to JIS K6871, and the results are shown in Table 1.

As is clear from the results in Table 1, a molded article with excellent appearance, gloss, and physical properties could be obtained.

Example 3 200 meshes of PS containing 50 parts by weight of iron powder were molded using a normal in-line injection molding material at a resin temperature of 220'C.

The mold is 5 CrrLX 8 crfLX 0.5 cm
It is a deep box-shaped molded product that can be molded in pairs at the same time, and by combining and molding them together, a case with a hinge can be created.

The gate is also a restricted side gate. The inductor consists of 5mm diameter steel pipes arranged in a spiral shape at 5-space intervals.
This was cast with epoxy resin to form a flat plate with a thickness of 2 cm, and a steel pipe was fixed and solidified.

This inductor was inserted between the molds, and the 400KH2
, 6 KW was oscillated for 15 seconds, and then the inductor was extracted from between the molds, and injection molding was performed in the same manner as in Example 1.

The surface of this molded product has no iron powder, silver streaks, flow marks, jetting, etc., and the surface gloss of the molded product is Gs (60% is 100% and there is no gloss gradient, in other words, uniform high gloss) A molded product was obtained.

Furthermore, the specific gravity of the molded product was 1.8, making it possible to mold a heavy, high-gloss product with a sense of weight that conventional PS molded products lack.

Comparative Example 1 Using the same molding machine and mold as in Example 2, using the same molding material, resin temperature 240°C, mold temperature 60°C, injection 1
0 seconds, cooling 15 seconds, total molding cycle 40 seconds, injection pressure 50
The results of measuring the physical properties of the molded product are shown in Comparative Example 1 in Table 1.

Example 4 In this actual case, a series of experiments were conducted using various resins and varying the mold surface temperature, and the resulting gloss was compared and studied.

The surface shape is as shown in Figure 7, and the wall thickness is 1.5 CrrL.
In the mold for producing an injection molded product with a holed chip, the gate is a 4×21n7IL restriction gate as shown by the arrow in FIG.

The mold material used was carbide mold material (NAK material), and the mold surface was given a mirror finish.

The inductor (coy/L/) consists of 10 copper pipes with a diameter of 5.
Arranged in a plane spiral shape at intervals of 300 mm and then coated with epoxy resin.
A material hardened to a CrIl thickness was used.

The high frequency oscillator was 7KHz, 10KW, and the output was steplessly variable.

The molding machine used was Toshiba l580 (50z, injection molding machine).

Using these devices, various resins were molded under normal injection molding conditions and the injection molding method using the inductor insertion method of the present invention, and the results of comparison are shown in Table 2.

As shown in Table 2, in all of the resins obtained by the method of the present invention, the surface gloss of the molded product is high, and there is a gloss gradient called uneven gloss (gloss unevenness). It can be seen that almost no molded product is obtained.

In other words, when comparing the gloss of the E part and the gloss of the F part, there is a difference in the case of ordinary injection molded products, but in the molded product of the present application, the molded product gloss of each part is almost the same, and has a high gloss. It can be seen that it is.

Furthermore, the molded product of the present invention has no flow marks, jetting, or silver streaks, and weld lines are not noticeable, and so-called weld lines are not visible, regardless of the resin used.

On the other hand, in the case of ordinary injection molding, as shown in Table 2, even if various resins are changed, it is not possible to obtain a high gloss product like the molded product by the method of the present invention, flow marks and jetting are observed, and filler In the case of filled resin, there are silver streaks and weld lines are also noticeable.

Furthermore, even if the molding conditions, particularly the mold temperature, are changed, the effect of improving the appearance and gloss is limited and does not reach the level of the present molded product.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an embodiment of the present invention. FIG. 2 shows an example of the temperature distribution of the mold in the apparatus shown in FIG. FIGS. 3 and 4 are cross-sectional photographs in the thickness direction of a glass fiber-reinforced As resin molded product, which is an example of a molded product obtained by the method of the present invention. FIG. 5 and FIG. 6 are comparative photographs, which are cross-sectional photographs in the thickness direction of a glass fiber-reinforced As resin molded product made by a conventional molding method. FIG. 7 is a diagram for explaining the appearance of the molded product obtained by the method of the present invention. Reference numeral 1 indicates a stationary die in the mold, and 2 indicates a movable die □. , 3 are inductors in the high frequency oscillation device. Points A and B indicate the surface of the mold, and points C and D indicate the inside of the mold.

Claims (1)

[Scope of Claims] 1. When injection molding a thermoplastic resin, the surface of the mold on which the surface of the injection molded product is to be formed is heated in advance to a temperature above the heating deformation temperature of the thermoplastic resin with no high frequency induction force, and then injection molding is performed. An injection molding method characterized by: 2. The injection molding method according to claim 1, wherein the thermoplastic resin is a filled thermoplastic resin.