JPS6258288B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an ABS resin injection molded product with a good appearance. ABS resin is an amorphous resin and has excellent moldability, and the molded products have many characteristics such as excellent rigidity, strength, toughness, dimensional accuracy, and dimensional stability, and can be easily colored. have For this reason,
It is widely used as materials related to our daily lives, such as housings for electrical equipment such as televisions, vacuum cleaners, and VCRs, daily necessities, and automobile parts. However
ABS resin uses rubber, which is mainly composed of the B component in so-called ABS resin, as a toughness reinforcing material, which is the purpose of ABS resin. For this reason, when ABS resin is molded, especially injection molded, when the ABS resin flows inside the mold, the rubber in the resin deforms due to the flow, and the deformation of the rubber causes contact with the mold. When cooled, the deformed rubber is exposed on the resin mold contact surface, that is, the surface of the injection molded product, or the deformed rubber causes appearance defects such as rough skin, flow marks, silver streaks, etc. on the surface of the injection molded product. . In addition, in molded products with L/t (the flow distance of the resin in injection molded products, the ratio of L to the average wall thickness t of the molded product) = 20 to 30 or more, the flow start part (gate part) of the resin and the There is a difference in gloss between the surface of the molded product and the flowing end (dead end), resulting in a so-called gloss gradient. These drawbacks have been commercialized even though they are unsatisfactory, based on the recognition that they cannot be avoided in principle considering the principles of injection molding described below. Furthermore, due to these drawbacks, the use of plastic molded products that require extremely high gloss has been abandoned. Furthermore, in order to reconsider the principles of injection molding of thermoplastic resins, mainly ABS resins, we will explain them in detail below. In general, injection molding of thermoplastic resin molded products utilizes the plasticity of the thermoplastic resin, in other words, the thermoplastic resin is heated and fluidized using a screw etc., then shaped and then cooled and solidified in the mold. The basic principle is to obtain molded products by doing this. That is, in order to solidify and release the molded product from the mold, it is cooled below the heating deformation temperature of the thermoplastic resin and taken 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, it is common practice to use a refrigerant to cool the mold to a temperature on the verge of condensation. In other words, in current injection molding, the mold is cooled, and even when heating and storing heat at the temperature of the molten resin, in principle the mold temperature is controlled so that it does not exceed the heating deformation temperature of the thermoplastic resin. and mold. 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 the molded product surface. The unevenness of the surface is severe. Although the cause is not necessarily clear, the inventors believe that ABS
As for the resin, as mentioned above, when the ABS resin flows inside the mold, the rubber in the resin deforms, and the deformation of the rubber comes into contact with the mold and is cooled, causing the resin to contact the mold, i.e. The above-mentioned appearance defects may occur because the deformed rubber is exposed on the surface of the resin injection molded product, or because the surface of the injection molded product becomes uneven due to the influence of the deformed rubber. When using these resins for molded products that require a beautiful appearance, methods such as painting, pasting a film, or attaching a thin film material to the surface of the thermoplastic resin molded product are used. This method has the disadvantage that it is not possible to obtain a molded product with an appearance that has the original soft luster, and that it is time-consuming and expensive to manufacture. Furthermore, in the case of painting, the paint component (thinner) used to form a paint film dissolves the thermoplastic resin, reducing mechanical strength such as impact strength. Furthermore, when applying a film, if the shape of the molded product is complex, it is almost impossible in terms of industrial production to cover the entire surface of the molded product. Buffing is also sometimes used as a method of partially modifying the appearance of a molded product and imparting gloss to it. However, buffing can only be used to correct minor appearance defects, and obtaining a uniform appearance through this work requires the skill of an expert. Also, even if you are an expert, the scratches caused by buffing (bubble scratches) remain on the molded product. Furthermore, if a molded product has unevenness or grooves, even if it is buffed, it will not be possible to obtain a molded product that shines uniformly. If buffing is applied forcefully, inconveniences will occur, such as the radius of the corners of the molded product being removed. A lot of research has been done to improve the appearance of ABS resin injection molded products, especially the gloss of the molded products mentioned above. According to this principle, the gloss decreases. In other words, it is still difficult to obtain a resin composition with excellent gloss and impact resistance.
It is not completed with resin. In order to solve such drawbacks, the inventors
In ABS resin molded products, a layer with little deformation of the rubber is formed near the surface of the molded product, and the surface of the molded product has the luster inherent to thermoplastic resins, and has no appearance defects such as flow marks or silver streaks. We succeeded in obtaining an ABS resin injection molded product with a similar appearance. has this good appearance
ABS resin injection molded products are not only molded products with simple shapes, but also injection molded products with complex lattice shapes. It is preferable that it is formed. That is, the present invention provides an injection molded product made of ABS resin, in which at least one to
A 100μ rubber layer with little deformation and a skin layer with little orientation are integrally formed during injection molding with virtually no bonding interface, and the surface of the molded product has a gloss level of Gs.
(60°)% (ASTMD523) is at least 90%, and a gloss gradient is within 0 to 0.2%/cm. In addition, the injection molded product of the present invention not only has a good gloss on the surface of the molded product, but also eliminates the appearance of rubber on the surface, which is a drawback of ABS resin molded products, and the injection molding of silver streaks, flow marks, weld lines, etc. This is an ABS resin injection molded product with a good appearance and no appearance defects caused by flow or uneven flow of ABS resin during molding. In other words, the surface of the injection molded product is smooth and has the soft luster characteristic of thermoplastic resins, and there are no appearance defects such as silver streaks or flow marks, and weld lines are virtually inconspicuous.
It is an ABS resin injection molded product. Furthermore, for conventional ABS resin injection molded products, L/t=
For molded products of 20 to 30 or more, there is a difference between the gloss of the gate part and the gloss of the dead end part (flowing end part), and the so-called gloss gradient is often 1 to 5%/cm. However, in the case of the injection molded product of the present invention,
Gloss gradient 0-0.2%/cm, preferably 0-0.1
It is an injection molded product that has a uniform and high gloss level with no gloss gradient, which is extremely small at less than %/cm, and is unimaginable for conventional injection molded products. In normal injection molding, a weld line is a confluence line that occurs at the confluence of resins, and when a vertical section of this line is observed under a microscope, it forms a recess with a width of 10 microns or more and a depth of 3 to 5 microns or more. In the present invention, "the weld line is substantially inconspicuous" refers to a concave portion with a width of 5 μm or less and a depth of 1 μm or less, where the line-like appearance is not visible. An explanation of the weld line is shown in FIG. There are various possible causes of flow marks. For example, when there is a variation in the wall thickness of a molded product, the flow of resin is disturbed or pressure is transmitted unevenly in that area, and the uneven resin is cooled and solidified on the mold surface, resulting in uneven appearance. Although this flow mark is thought to occur, the molded product of the present invention does not have this flow mark. Silver streaks occur when volatile substances in the resin volatilize during molding, and when the resin cools and solidifies during the volatilization, silver streaks occur on the surface of the molded product. There is no. Jetting is a phenomenon that is often seen in the gate area of molded products.During injection molding, the resin flow rate increases at areas where the resin flow path is narrowed, such as at the gate area, so the resin partially protrudes inside the mold. However, the product of the present invention does not have such jetting. In the product of the present invention, the appearance defects caused by the non-uniformity of the resin flow state in the mold are not cooled and solidified while the resin flow state is non-uniform. This makes it possible to produce molded products with uniform gloss. The method for obtaining the injection molded article of the present invention is as follows. In order to improve the adhesion between the resin and the mold, the surface of the mold is maintained at a temperature higher than the heating deformation temperature of the ABS resin to maintain its plasticity. On the other hand, it is impossible to release the mold while keeping the surface of the mold above the heating deformation temperature of ABS resin.In order to obtain the desired molded product without deformation, the mold must be cooled. The thermoplastic resin is cooled to a temperature lower than the heat deformation temperature of the thermoplastic resin and released from the mold in a solidified state. For this heating and cooling, the principle of high-frequency induction heating is utilized to selectively heat the surface layer of the mold, thereby rapidly heating and cooling the mold surface to obtain the injection molded product of the present invention. Next, the molded product according to the present invention and its molding method will be explained with reference to the drawings. In injection molding of ABS resin, a high-frequency induction heating inductor is installed between the stationary mold and the movable mold as shown in Figure 1. When an inductor was sandwiched between the movable mold and the stationary mold and a high frequency was oscillated while the inductor was sandwiched, the temperature of only the mold surface (points A and B) suddenly increased as shown in Figure 2. increases, and it can be confirmed that the temperature inside the mold (point C and point 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, the inductor was extracted from between the stationary side and movable side molds, the mold was closed again, and ABS resin was injected in the same manner as normal injection molding, resulting in ABS resin injection with the desired beautiful appearance. A molded product was obtained. An ABS injection molded article was obtained according to the present invention, and an electron micrograph of a cross section of the molded article in the thickness direction is shown in FIG. The magnification is 7000x. For reference, the same material was injection molded using the same mold at a mold temperature of 60°C, and a photograph of the same cross section was taken in the same manner as shown in Figure 4. The magnification is also 7000x. In both photos, the island pattern part is
It is the rubber in ABS resin, and the sea pattern part is AS resin (acrylonitrile-styrene copolymer). The horizontal line is the surface of the molded product. As is clear from comparing Figures 3 and 4, in the case of the molded product of the present invention, the rubber hardly deforms near the surface of the molded product, and the rubber does not appear on the surface of the molded product. . On the other hand, in the case of FIG. 4 obtained by a normal injection molding method, it can be seen that the rubber is deformed due to distortion due to insufficient flow during injection molding, and that the rubber is exposed on the surface of the molded product. For this reason, only molded products with poor appearance can be obtained. In order to quantify the appearance and gloss of the above-mentioned ABS resin molded product of the present invention, the glossiness Gs (60°) of the molded product was measured according to ASTM D523.
It was 100%. On the other hand, the molded product produced at a mold temperature of 70° C. had a gloss level of 70%, indicating that the molded product of the present invention had a smooth appearance and good gloss. Also, perhaps because the molded product of the present invention has low flow resistance during injection molding and is less likely to cause orientational distortion, when the heat deformation temperature specified in JIS K6871 was measured, the heat deformation temperature was 2 to 2. It was confirmed that the so-called practical heat resistance temperature was improved by 3°C, and as a result of comparing the drop strength of molded products, the practical toughness was also improved. The ABS resins used in the present invention include AAS (butyl acrylate rubber-acrylonitrile-styrene copolymer resin), AES (styrene-propylene rubber-acrylonitrile-styrene copolymer resin), and general ABS resins, [acrylonitrile-butadiene-styrene]. Polymer, acrylonitrile-butadiene-styrene-α-methylstyrene, acrylonitrile-methyl methacrylate-butadiene-
This refers to the so-called ABS resin, which collectively refers to styrene, etc. Furthermore, the rubber content in ABS resin, which is commonly referred to as ABS resin, is often 4% or more and is common, and the ABS resin referred to in this application also refers to those within this range. The frequency of the high frequency used for high frequency induction heating in the present invention is 50Hz to 10MHz, preferably 1KHz to 1000KHz.
is appropriate. In this application, when evaluating the gloss of molded products,
Gs (60°)% in ASTM D 523 is used, which has traditionally been used to evaluate the appearance and gloss of plastic molded products.
It follows the custom of using Gs (60°)%, and if you follow the specifications of ASTM D523 exactly, Gs (60°)% is used.
゜) If % is 70% or more, gloss Gs at an incident angle of 20 degrees
(20°)% is to be applied. Therefore, Gs (60°)% and Gs (20°)% were measured for molded products of the present invention and molded products including comparative examples, and the correlation between the two was determined, as shown in Figure 5. Therefore, if you follow ASTM D523 exactly, Gs (60
For molded products with a gloss level of 70% or more, the corresponding Gs(20°)% value should be displayed as shown in Figure 5, but the relationship between conventional industry practice and comparative examples Please note that I purposely used Gs (60°)% in the sense that the difference becomes clearer. Example 1 A conventional commercially available ABS resin was molded using a conventional in-line injection molding machine. The mold is made of regular S-45C steel and has a diameter of 10
The mold is capable of forming dish-shaped products with a diameter of 2 cm, a depth of 2 cm, and an average wall thickness of 3.5 mm, and the gate is a center direct gate. The inductor is made by spirally forming a 6mm diameter copper tube into a dish shape at 5mm intervals, then casting it with epoxy resin to a thickness of 3cm and solidifying it into a flat plate. As for the injection molding conditions, the cylinder temperature was set so that the temperature of the ABS resin was 230°C. Before injecting the ABS resin into the mold, the above-mentioned inductor was inserted between the molds and oscillated for 15 seconds using a 400KC, 6KW high-frequency oscillator.Then, the mold was opened, the inductor was extracted from between the molds, and the mold was inserted again. Closed. During this time, the mold cooling water is not allowed to flow inside the mold.Then, the ABS resin is injected into the mold for 10 seconds at an injection pressure of 60 kg/cm ² as in normal injection molding, and then the mold is molded. After cooling for 20 seconds through cooling water, the molded product was taken out. The total cycle time was 60 seconds. The surface of the molded product has a gloss that is unimaginable for conventional ABS resin molded products, and has a Gs (60°)%
was 100%. In addition, there was no flow mark at the gate part, and the gloss of the gate part and the edge of the plate (the flow end part of the molded product) was the same, so that a molded product without a so-called gloss gradient was obtained. We have created a molded product that is so tight that it overturns the concept of conventional ABS resin molded products. Example 2 A regular ABS resin was molded using a regular injection molding machine at a resin temperature of 230°C. The mold is a mold that can produce dumbbells and strips of shape specified in JIS K6871, and is made of S-55C. The inductor used was one in which 3 mm diameter copper tubes were spirally arranged at 5 mm intervals, which were cast into a 2 cm thick flat plate with epoxy resin and solidified. The molding method was the same as in Example 1, but 4KHz, 6KW, high frequency oscillation time 10 seconds, injection 10 seconds, cooling 15 seconds, total molding cycle 50.
seconds, injection pressure 50Kg/ ^cm2 . The ABS resin molded product had a beautiful surface appearance and a glossy appearance. The physical properties of the molded products 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. Comparative Example 1 The same molding machine and mold as in Example 2 were used, the same molding material was used, and the resin temperature was 230°C and the mold temperature was 60°C.
℃, injection 10 seconds, cooling 15 seconds, total molding cycle 40 seconds,
The molded product was molded at an injection pressure of 50 kg/cm ² and its physical properties were measured. The results are shown in Table 1, Comparative Example 1.

[Table] Example 3 Using a mold capable of molding a pair of audio cassette housings (referred to as cassette halves in the industry), ABS resin was molded using an ordinary injection molding machine. The inductor was made by arranging copper tubes with a diameter of 5 mm in a flat spiral shape at 5 mm intervals, casting them into a 3 cm thick flat plate with epoxy resin, fixing and solidifying the copper tubes. The inductor was inserted between molds, and a high frequency of 7 KHz and 20 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 molded product has a complex shape such as ribs, bosses, perforations, and textured parts, and in normal molding, flow marks and weld lines are noticeable, but the molded product in this example The appearance of the molded product was beautiful, there were no flow marks, no visible weld lines, and the grained areas had improved gloss, resulting in a so-called tight grained texture, which significantly increased the product value. The dimensional accuracy is also the same as the conventional product, and there is no warping. When the glossiness of the flat part of the molded product was measured, the Gs (60°) of the molded product of this example was 99 to 98.
%, the molded product is uniform and has a high gloss, but the Gs (60°) of the molded product made using the conventional injection molding method is 80 to 68%.
Therefore, only molded products with noticeable flow marks and weld lines and a large gloss gradient could be obtained. Incidentally, the mold temperature for obtaining molded products using this conventional method is 70°C, which is the upper limit temperature for industrial production. Example 4 In this example, a series of experiments were conducted using various ABS resins and varying the mold surface temperature, and the resulting gloss was compared and examined. The planar shape is shown in Figure 6, and the wall thickness is 3 mm and 1.5 mm.
In a mold for producing an injection molded product with a holed chip of cmφ, the gate is a 4×2 mm 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 (coil) is made by arranging 5mm diameter copper pipes in a plane spiral shape at 10mm intervals, and using epoxy resin to create a 3cm
I used one that had been hardened to a certain thickness. The high frequency oscillator used was a 7KHz, 10KW, steplessly variable output. The molding machine used was Toshiba IS80 (50 oz 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 the resins obtained by the method of the present invention, the surface of the molded product has high gloss and almost no gloss gradient called gloss unevenness. It can be seen that a molded product can be obtained. In other words, when comparing the gloss of part A and the gloss of part B, 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 high gloss. I understand.

[Table] Example 5 A pocket radio housing having external dimensions of 12 cm in length, 8 cm in width, and 2 cm in depth was molded from ABS resin. The inductor was created and molded in substantially the same manner as in Example 3. ABS resin temperature
Molding was performed at 240°C. This molded product is commercialized by covering the appearance defects by applying acrylic paint to prevent weld lines and flow marks from appearing on the speaker grille of pocket radios and parts with holes for various knobs. However, the molded product of this example had no flow marks or weld lines, and the gloss of each part was so uniform that there was no need to paint it, and it had a high gloss with a Gs (60) of 97 to 99%. A molded product was obtained. As mentioned above, the rubber-reinforced styrene resin molded product of the present invention has a molded product appearance that is so good that it overturns the concept of conventional ABS resin injection molded products.In other words, the gloss level of the molded product is very good, and there is no gloss or unevenness. There are no flow marks and no weld lines visible. Moreover, the advantages of conventional ABS resin, such as ease of molding, rigidity, toughness, and dimensional stability, remain unchanged, and productivity is slightly higher than that of conventional injection molding, but the total molding cycle is 20 to 50% faster. It just gets longer. The appearance of molded products has improved, eliminating the cheap image traditionally associated with plastics, and not only significantly increasing product value, but also eliminating the need for painting on parts that previously had to be painted to prevent appearance defects. The usefulness of inventions is immeasurable.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram for manufacturing a molded article according to the present invention. FIG. 2 shows an example of the temperature distribution of the mold in the apparatus shown in FIG. FIG. 3 is a cross-sectional micrograph (×7000 times) in the thickness direction of an ABS resin molded product according to one embodiment of the present invention. Figure 4 is a comparison micrograph (x7000x), which shows the result of the normal molding method.
This is a cross-sectional micrograph of an ABS resin molded product in the thickness direction. FIG. 5 is a curve showing the correlation between glossiness Gs (20°)% and glossiness (60°)%. 6th
The figure shows the dimensions and shape of the sample piece used in Example 4. FIG. 7 is an explanatory diagram of the weld line. 1: Fixed side mold in the mold; 2: Moving side mold; 3: Inductor in the high frequency oscillator;
Point A, point B: surface of the mold; point C, point D: inside of the mold; a: weld width; b: weld depth.

Claims (1)

[Scope of Claims] 1. In an injection molded product made of ABS resin, a layer with little rubber deformation of at least 1 to 100 μm and a skin layer with little orientation are formed in the vicinity of the surface of the molded product, and the injection molded product has substantially no bonding interface. Sometimes it is formed integrally, and the glossiness of the surface of the molded product is Gs (60°)%.
(ASTMD523) is at least 90%, and a gloss gradient is within 0 to 0.2%/cm. 2 Claim 1 in which the gloss level is 95% or more
Injection molded products as described in section. 3. The injection molded article according to claim 1 or 2, wherein the gloss gradient is within 0 to 0.1%/cm. 4. The injection molded product according to any one of claims 1 to 3, wherein the surface of the injection molded product is free from defects such as flow marks, jetting, and silver streaks, and has substantially inconspicuous weld lines.