JP2016083831A - Manufacturing method of injection molded article and injection molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a molded article excellent in appearance of a design surface side of the molded article obtained by injection molding a thermoplastic resin composition containing a flat filler by using general purpose injection molding and mold heating facility.SOLUTION: There is provided a manufacturing method of an injection molded article having a process for injecting from a gate 3 into a cavity 1 at a design face mold surface temperature of the injection molded article of 120°C or more, a process for further injecting from another gate 4 in a cross direction to a weld line 5 after the weld line 5 is formed by a flat filler orientation and a process for mold opening at the design face mold surface temperature of load strain temperature T(°C) of a thermoplastic resin composition or less and satisfying following formulae<1><2>, where a molding temperature of the thermoplastic resin composition is T(°C), a temperature with melting viscosity becoming 6,000 Pa s and 9,000 Pa s are T(°C) and T(°C) and the design face mold surface temperature is T(°C). Formula<1>T≤T≤(T+170). Formula<2>T≤100-(T-T).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing an injection molded product and an injection molded product.

  The thermoplastic resin composition containing a thermoplastic resin and a flat filler exhibits a metallic or pearl-like appearance due to the visual effect brought about by the flat filler, so that it is an injection molded product that requires the design of the product. It is preferably used. In particular, as a flat filler, a thermoplastic resin composition containing a metallic colorant made of aluminum flakes or the like as a raw material has a high designability, and is used for interior and exterior parts of vehicles, vacuum cleaners, telephones, refrigerators and other household appliances, personal computers, It is suitably used for electronic devices such as digital cameras, printers and audio devices, OA devices, toilets, vanity tables, sanitary products such as bathroom fixtures, toys, cosmetic containers and the like.

  When a thermoplastic resin composition containing a flat filler is injection-molded, there is a problem that a weld line is formed at a site where molten resins filled in a mold cavity are associated with each other, and the appearance is impaired.

  While the flat filler in the thermoplastic resin composition is oriented in parallel to the surface of the injection-molded product along with the flow of the resin composition at the time of injection molding, the desired design is expressed on the other hand. Thus, the flow pattern of the resin composition that cannot be discriminated is visible, and in particular in the vicinity of the weld, the orientation of the flat filler also makes the flow unevenness of the resin composition visible. This is because the flat filler in the thermoplastic resin composition is oriented at an angle close to parallel to the surface of the injection molded product at the association site between the resin compositions filled in the mold cavity. This is because the light reflection is different in the portions oriented at various angles. In the lower part of the weld line (inside the injection-molded product), there is a flat filler that is oriented upright with respect to the surface of the injection-molded product, and light is less likely to be reflected compared to the portion that is oriented parallel to the surface of the injection-molded product. In this case, the color unevenness is conspicuous because the color developability is affected. Although the thermoplastic resin composition containing a flat filler is a useful surface decorating means for increasing commercial value, there are problems as described above, and thus the shapes of applicable injection molded products have been limited.

As a means for producing a molded article having excellent appearance characteristics, for example, a mold surface on which a molded article surface is to be formed is selectively heated in advance to a heating deformation temperature or higher of the molding material, and the molten molding material is placed in the mold cavity. A molding method (for example, refer to Patent Document 1), a styrenic resin, and a filler that are supplied and made to flow by applying a shearing force to at least a part of the supplied melt molding material and then cooling and solidifying the molding material. The metallic resin composition obtained by blending is molded by an injection compression molding method or an injection press molding method, and the mold temperature T (° C.) is set to T with respect to the deflection temperature T ₁ (° C.) of the metallic tone resin composition. _A metallic resin molded product (for example, see Patent Document 2) formed by setting within a range of ₁ ≦ T ≦ (T ₁ +20) and molding at a melting temperature of 200 to 280 ° C. has been proposed. In the technique disclosed in Patent Document 1, a shearing force is applied in the vicinity of the weld line at the time of molding in order to make the weld line inconspicuous, but in the cavity in order to form an opening such as a hole in the synthetic resin molded product. In the case where the weld line and the alignment line are formed behind the opening forming body facing the gate, the flow of the molten synthetic resin by the shearing force is indirect and not so large. Therefore, it is difficult to make the alignment line caused by the filler being oriented perpendicular to the flow direction of the melted synthetic resin from the outside, and it is required to eliminate the weld line more effectively. It was. In addition, in order to apply a shearing force in the vicinity of the weld line generated on the back side of the opening forming body facing the gate, a larger shearing force is required. Therefore, only a cylinder head of a general injection molding machine can cope. In other words, the equipment needs to be enlarged and complicated peripheral equipment, and there has been a demand for a method for more easily producing an injection molded product having an excellent appearance using general-purpose equipment. Moreover, the technique by the injection compression molding method or the injection press molding method disclosed in Patent Document 2 is to erase the weld line generated on the surface of the molded product by applying pressure to the surface of the molded product after filling the mold. However, the effect is not sufficient, and it has been required to eliminate the weld line more effectively.

  On the other hand, as a means for making the appearance of the synthetic resin molded article excellent by making the alignment line formed behind the opening forming body facing the gate as invisible as possible from the outside, the synthetic resin is injected by the first gate, for example. After the alignment line is formed, the second gate starts injection of the synthetic resin toward the alignment line formed on the back side of the opening forming body facing the first gate, and by the first gate. An injection molding device has been proposed in which a lift pin whose upper end surface is flush with the cavity forming surface of the movable mold at the start of injection of the synthetic resin is lifted into the cavity and then lowered back to the original position. (For example, refer to Patent Document 3). However, in the technique disclosed in Patent Document 3, a defective appearance due to a flow mark is likely to occur in the vicinity of the weld line reflowed by a shearing force, and the resin filling pressure injected toward the filler orientation line corresponding to the flow end of the resin. Is concentrated in the vicinity of the gate, the shear force required to change the filler alignment line does not reach, and the filler orientation required to obtain an excellent weld appearance cannot be changed, so the appearance is still insufficient There was a problem. In addition, since it requires complicated equipment such as special temperature control equipment that can raise the mold temperature to 200 ° C. or higher, use a wide-spread type heating temperature control equipment using a steam medium or the like. Therefore, there has been a demand for a method for more easily producing an injection molded product having an excellent appearance.

Japanese Patent Laid-Open No. 9-1611 JP 2003-200767 A JP 2013-82230 A

  In view of the problems of the prior art, the present invention uses a general-purpose injection molding facility and a popular mold heating facility to injection-mold a thermoplastic resin composition containing a thermoplastic resin and a flat filler. An object of the present invention is to provide a method for producing an injection-molded article having an excellent appearance by suppressing generation of a thermal burn, spider and avatar due to a weld line, a flow mark and a molding gas on the design surface side of the obtained injection-molded article. .

The inventors of the present invention have arrived at the present invention as a result of intensive studies aimed at solving the above problems. That is, the present invention mainly has the following configuration.
A thermoplastic resin composition containing a thermoplastic resin and a flat filler is injection-molded using a mold that can repeatedly heat and cool the surface and has at least two gates for filling the cavity with the resin. A method for producing an injection-molded product, wherein at least (1) a mold is formed on a surface of a mold on which a design surface of the injection-molded product is to be formed at 120 ° C. Injecting into,
(2) Under the condition that the mold surface temperature for forming the design surface of the injection molded product is 120 ° C. or higher, the thermoplastic resin composition injected by the step (1) has a weld line due to the flat filler orientation. A step of further injecting a thermoplastic resin composition from another gate in a crossing direction with respect to the weld line after being formed and before holding pressure is started;
(3) A step of opening the mold under the condition that the mold surface temperature on which the design surface is to be formed is equal to or lower than the load deflection temperature T ₀ (° C.) of the thermoplastic resin composition after the step (2) is completed.
Have
The molding temperature T ₂ (° C.) of the thermoplastic resin composition in the steps (1) and (2), the deflection temperature T ₀ (° C.) of the thermoplastic resin composition, and the shear rate of the thermoplastic resin composition of 6.08 sec. ^The temperature T ₁ (° C.) at which the melt viscosity in ^-1 reaches 6,000 Pa · s satisfies the following formula <1>, and gold on the back side of the surface on which the design surface in the steps (1) and (2) is to be formed Mold surface temperature T ₃ (° C.), molding temperature T ₂ (° C.) of the thermoplastic resin composition, temperature T ₄ at which the melt viscosity of the thermoplastic resin composition at a shear rate of 6.08 sec ⁻¹ is 9,000 Pa · s. (° C.) satisfies the following formula <2>
Formula <1> T ₁ ≦ T ₂ ≦ (T ₀ +170)
Formula <2> T ₃ ≦ 100− (T ₂ −T ₄ )
A thermoplastic resin composition having a melt viscosity under a shear rate of 6.08 sec ⁻¹ measured using a capillograph of the thermoplastic resin composition and a deflection temperature under load T ₀ (° C.) T ₀ of less than 88 ° C. is 210 ° C. Is a thermoplastic resin composition having a T ₀ of 88 ° C. or higher at 240 ° C., and a thermoplastic resin composition having a T ₀ of 6,000 Pa · s or lower at 240 ° C.

  According to the manufacturing method of the present invention, the design surface side of an injection molded product is obtained by using a thermoplastic resin composition containing a thermoplastic resin and a flat filler by a general-purpose injection molding facility and a popular mold heating facility. Can suppress the generation of thermal burns, spiders, and avatars due to weld lines, flow marks and molding gas, and can produce an injection molded product with excellent appearance.

It is schematic structure explanatory drawing which looked at the mold cavity surface of an example of the injection molding apparatus used for the embodiment of this invention from the top (mold core surface). It is a schematic explanatory drawing of the position where the weld line by flat filler orientation is formed in the thermoplastic resin composition inject | emitted by the process (1) within the mold cavity shown in FIG. It is a schematic sectional drawing in the mold cavity in process (1) of the embodiment of the present invention. FIG. 4 is an enlarged view of FIG. 3. It is a general | schematic cross-sectional enlarged view in the metal mold | die cavity in process (2) of the embodiment of this invention. It is schematic structure explanatory drawing which looked at the metal mold | die cavity surface used for the comparative example 3 from the upper (metal mold | die surface). 6 is a schematic cross-sectional view inside a mold cavity in step (1) of Comparative Example 4. FIG.

  Hereinafter, the manufacturing method of the injection molded product of the present invention will be specifically described.

  The present invention relates to a gold resin having a thermoplastic resin composition containing a thermoplastic resin and a flat filler, the surface of which can be repeatedly heated and cooled, and at least two gates for filling the resin in the cavity. This is a method for manufacturing an injection-molded product that is injection-molded using a mold. In the method for producing an injection-molded article of the present invention, in step (1) described later, the mold surface temperature (design surface mold surface temperature) on which the design surface is to be formed is 120 ° C. or higher, and step (3) described later. In the above, the surface temperature of the design surface mold is set to be equal to or lower than the deflection temperature under load of the thermoplastic resin composition. The method for changing the mold surface temperature is not particularly limited, but so-called heat and cool molding techniques are preferably used in terms of shortening the molding cycle. Examples of the method for heating the mold in heat and cool molding include an oil method, a hot water method, a steam method, an electromagnetic induction method, and an electric heater method. In the present invention, any method can be used, and a method that can satisfy the required molding cycle can be appropriately selected. The number of gates may be three or more according to the number of weld lines generated in the injection molded product. The thermoplastic resin composition will be described later.

The method for producing an injection molded product of the present invention includes at least
(1) A step of injecting a thermoplastic resin composition into a cavity from a single gate under the condition that a mold surface temperature on which a design surface of an injection molded product is to be formed is 120 ° C. or higher.
(2) Under the condition that the mold surface temperature for forming the design surface of the injection molded product is 120 ° C. or higher, the thermoplastic resin composition injected by the step (1) has a weld line due to the flat filler orientation. A step of further injecting a thermoplastic resin composition from another gate in a crossing direction with respect to the weld line after being formed and before holding pressure is started;
(3) A step of opening the mold under the condition that the mold surface temperature on which the design surface is to be formed is equal to or lower than the load deflection temperature T ₀ (° C.) of the thermoplastic resin composition after the step (2) is completed.
Have

  First, step (1) will be described. The mold on which the design surface of the injection molded product is to be formed is heated to 120 ° C. or higher, and after the surface temperature of the design surface mold reaches 120 ° C. or higher, a thermoplastic resin is injected into the cavity from one gate. Although the timing which heats the metal mold | die which should form a design surface may be either before mold clamping, after mold clamping, and mold clamping simultaneously, in order to shorten a molding cycle, it is preferable before mold clamping. If the surface temperature of the design surface mold at the time of injection is less than 120 ° C., the flow resistance of the thermoplastic resin composition injected and filled in the mold increases, and a weld line is likely to occur. The surface temperature of the design surface mold is more preferably 130 ° C. or higher, and further preferably 140 ° C. or higher. On the other hand, the upper limit of the design surface mold surface temperature is not particularly limited.

In the present invention, the molding temperature T ₂ (° C.) of the thermoplastic resin composition in the step (1) satisfies the following formula <1>.
Formula <1> T ₁ ≦ T ₂ ≦ (T ₀ +170)
Where T ₀ is the deflection temperature under load of the thermoplastic resin composition (° C.), T ₁ is the temperature at which the melt viscosity of the thermoplastic resin composition at a shear rate of 6.08 sec ⁻¹ is 6,000 Pa · s (° C.), T ₂ represents a molding temperature (° C.). Incidentally, the molding temperature T ₂ refers to the set temperature of the heating cylinder of the injection molding machine. From the viewpoint of increasing the degree of freedom in setting the molding temperature _{T 2, T 1} is preferably 200 ° C. or less.

Also, the _{T 1,} the melt viscosity at a shear rate of 6.08sec ^-1, is an indicator of fluidity in the mold of the thermoplastic resin composition of the shear conditions by injection, at a shear rate 6.08Sec ^-1 The temperature at which the melt viscosity is 6000 Pa · s is an index of the temperature at which the melt viscosity is suitable for injection molding. In the present invention, attention was paid to the melt viscosity at a shear rate of 6.08 sec ⁻¹ from the viewpoint of melt viscosity measurement accuracy.

When the molding temperature T ₂ of the thermoplastic resin composition is less than T ₁ , the flow resistance of the thermoplastic resin composition injected and filled in the mold becomes large, and the thermoplastic resin composition is not filled in the mold. Part is likely to occur. In addition, there are weld lines, flow marks and hot burns caused by molding gas, spiders, and avatars (the gas component remaining in the mold becomes a space in which the resin cannot be filled and appears as a dent phenomenon on the surface of the molded product). Cheap. On the other hand, in the case of (T ₀ +170) <T ₂ , the thermoplastic resin is likely to be thermally decomposed, and burns, spiders and avatars due to the molding gas are likely to occur.

In the present invention, the load deflection temperature T ₀ of the thermoplastic resin composition can be measured by the following method. First, the pellets of the thermoplastic resin composition were dried in a hot air dryer at 105 ° C. for 3 hours, then filled in a molding machine set at a cylinder temperature of 250 ° C., and injection molded at a mold temperature of 80 ° C. A specimen of ISO 3167 (Type A) is obtained. Using the obtained test piece, the deflection temperature under load is measured in accordance with ISO75 under a 1.82 MPa load condition.

Moreover, in the step (1), the mold surface temperature on the back side of the surface on which the design surface is to be formed (design surface back side mold surface temperature) is preferably equal to or lower than the design surface mold temperature, and heat release after mold release From the viewpoint of suppressing deformation in the process, the glass transition temperature is preferably equal to or lower than the glass transition temperature of the thermoplastic resin composition. Accordingly, in the present invention, step design surface back mold surface temperature T _{3 (°} C.) in (1) satisfies the following equation <2>.
Formula <2> T ₃ ≦ 100− (T ₂ −T ₄ )
T ₄ represents a temperature (° C.) at which the melt viscosity of the thermoplastic resin composition at a shear rate of 6.08 sec ⁻¹ becomes 9,000 Pa · s. In addition, the design surface back side mold surface temperature T ₃ (° C.) in the present invention indicates a set temperature of the mold.

Further, the _{T 4,} the melt viscosity at a shear rate of 6.08sec ^-1, is an indicator of fluidity in the mold of the thermoplastic resin composition of the shear conditions by injection, at a shear rate 6.08Sec ^-1 The temperature at which the melt viscosity reaches 9000 Pa · s is an index of the temperature at which the thermoplastic resin composition in the mold starts to form a solidified layer by the shearing force due to injection. In the present invention, attention was paid to the melt viscosity at a shear rate of 6.08 sec ⁻¹ from the viewpoint of melt viscosity measurement accuracy.

By setting the design surface back side mold surface temperature to a low temperature with respect to the design surface mold temperature, the thermoplastic resin composition can be made to flow on the design side while the thermoplastic resin composition on the back side of the design surface. A solidified layer of the object can be formed. In the present invention, _{T 3} (℃) is, 95- _(T 2 -T ₄₎ is more preferably less, 90- _(T 2 -T ₄₎ or less is more preferable.

In step (1), the design surface mold surface temperature is set to 120 ° C. or higher, and the molding temperature T ₂ (° C.) and the design surface back side mold surface temperature T ₃ (° C.) are set to the above formulas <1> and <2 > So that the mold temperature on the design surface side and the design surface back side has a temperature distribution, thereby depending on the resin pressure injected to the weld line performed in step (2) described later. It is possible to generate a shearing force more efficiently and suppress the weld line of the injection molded product to improve the appearance.

In the present invention, the temperature at which the thermoplastic resin composition has a melt viscosity of 6000 Pa · s or 9000 Pa · s can be determined by the following method. First, the pellets of the thermoplastic resin composition were dried in a hot air dryer at 105 ° C. for 3 hours, and then sheared using a Capillograph 1C (capillary: L / D = 10 mm / 1 mm) manufactured by Toyo Seiki Seisakusho. The melt viscosity (Pa · s) is measured in increments of 10 ° C. from T ₀ + 170 ° C. under the condition of 6.08 sec ⁻¹ . From the obtained measurement results, the relationship between the measurement temperature and the melt viscosity is plotted to create an approximate curve, and the melt temperatures at two points of melt viscosity of 6,000 Pa · s and 9,000 Pa · s are read.

  Next, process (2) is demonstrated. In the step (2), after the weld line is formed by the flat filler orientation in the thermoplastic resin composition injected in the step (1), before the holding pressure is started, the weld line is transferred from the other gate to the weld line. In contrast, it is a step of further injecting the thermoplastic resin composition in the crossing direction.

  With respect to the weld line formed in the step (1), the timing for injecting from the other gate is after the weld line is formed and before the holding pressure is started. After the weld line is formed, the thermoplastic resin composition before the start of pressure holding is not completely filled in the cavity, and the thermoplastic resin composition is crossed with respect to the weld line from another gate. Furthermore, by injecting, the injected thermoplastic resin composition flows in the cavity, generating a shearing force against the weld line, thereby eliminating the weld line. The occurrence position of the weld line formed in step (1) can be predicted by CAE analysis or the like. The other gate arrangement in the step (2) is a design based on these CAE analyses, and a weld line that is confirmed in an injection molded product that is molded in advance only by injection of the thermoplastic resin composition from the gate in the step (1). It can arrange | position in the position which can inject in a cross direction. Here, the intersecting direction with respect to the weld line refers to a direction intersecting the center on the weld line with reference to the formed weld line. The range of 30 to 150 ° with respect to the center on the weld line is preferable, the range of 45 to 135 ° is more preferable, and the range of 55 to 125 ° is more preferable.

  In the vicinity of the weld on the design surface side that is formed after the thermoplastic resin composition containing the flat filler is filled in the mold cavity by the step (2), the flat filler is changed from a state parallel to the design surface to an upright state. By injecting the thermoplastic resin composition in the crossing direction from the other gate to the weld line, the state of being oriented at various angles is nearly parallel to the design surface of the injection molded product. It becomes possible to re-orient to an angle. Since the flat filler is oriented at an angle that is nearly parallel to the design surface of the injection molded product, the direction in which light from the flat filler is reflected is the same as that around the weld. Color unevenness caused by reflection of light from the flat filler as described above can be eliminated.

  In the present invention, as in step (1) and step (2), after the thermoplastic resin composition that forms the weld line is first filled, the molding is performed in which the thermoplastic resin composition is filled from another gate. The method is called delayed injection molding.

Next, process (3) is demonstrated. Step (3) is a step of opening the mold under the condition that the design surface mold surface temperature is equal to or lower than the deflection temperature under load (T ₀ ) of the thermoplastic resin composition after completion of the step (2). From the viewpoint of suppressing deformation of the injection molded product at the time of mold release, the design surface side mold surface temperature in the step (3) is more preferably (T ₀ -20) ° C. or less, and more preferably (T ₀ -40) ° C. or less. preferable. Furthermore, it is preferable to set the mold surface temperature on the back side of the design surface to be equal to or lower than the load deflection temperature (T ₀ ) of the thermoplastic resin composition of the material, and the deformation of the injection molded product at the time of mold release can be further suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic structural explanatory view of a mold cavity surface of an example of an injection molding apparatus used in an embodiment of the present invention as viewed from above (mold core surface), and FIG. 2 is a mold cavity shown in FIG. The schematic explanatory drawing of the position where the weld line by flat filler orientation is formed in the thermoplastic resin composition inject | emitted by the process (1) is shown. The mold shown in FIG. 1 has a cavity 1 having an opening forming body 2, a gate 3 and a gate 4. The gate 3 is disposed at a position facing the opening forming body 2, and the gate 4 is disposed at a position where the gate 3 can be ejected in a direction intersecting the position 5 where the weld line shown in FIG. 2 is formed. Furthermore, a medium passage (not shown) that can repeatedly heat and cool the mold surface is provided.

  Next, process (1) is demonstrated using FIG. 3 and FIG. FIG. 3 is a schematic cross-sectional view inside the mold cavity in step (1) of the embodiment of the present invention, and FIG. 4 is an enlarged view of FIG. In step (1), the design surface mold 7 is heated by the heat medium flowing through the medium passage 6, and after the surface temperature of the design surface mold 7 reaches 120 ° C. or higher, the thermoplastic resin composition 10 is fed from the gate 3. , 11 are injected into the cavity. A weld line 14 is once formed at the meeting portion of the thermoplastic resin compositions 10 and 11. The flat filler in the thermoplastic resin composition is oriented in the flow direction of the thermoplastic resin composition as indicated by reference numeral 12 except for the weld part, but in multiple directions as indicated by reference numeral 13 in the vicinity of the weld part. Orient.

  Next, process (2) is demonstrated using FIG. 1 and FIG. FIG. 5 is an enlarged schematic cross-sectional view of the inside of the mold cavity in the step (2). In the step (2), after the weld line 14 is formed in the step (1), the thermoplastic resin composition is further injected from the gate 4 before the holding pressure is started. By injecting the thermoplastic resin composition in the injection direction 17 with respect to the weld line 14 shown in FIG. 5, the weld line 14 moves by receiving the shearing force of the injected thermoplastic resin composition, and the weld line 16. And the orientation direction of the flat filler near the weld portion also changes as indicated by reference numeral 15.

Next, in step (3), after completion of the step (2), the design surface mold 7 is cooled by a cooling medium flowing through the medium passage 6, and the surface temperature of the design surface mold 7 is set to a thermoplastic resin composition. After the temperature is lowered below the deflection temperature (T ₀ ), the mold is opened.

  Next, the thermoplastic resin composition used in the present invention will be described. The thermoplastic resin composition used in the present invention contains a thermoplastic resin and a flat filler. By including a thermoplastic resin, it is excellent in handling at the time of molding. By including a flat filler, the appearance of a metallic tone or a pearl tone can be expressed by the visual effect of the flat filler, and the design can be improved.

When the deflection temperature T ₀ under load is less than 88 ° C., the thermoplastic resin composition used in the present invention has a melt viscosity of 60.8 sec ⁻¹ at 210 ° C. measured at a shear rate of 6.08 sec ⁻¹ measured using a capillograph. 000 Pa · s or less is preferable. When the melt viscosity at 210 ° C. is 6,000 Pa · s or less, the generation of flow marks can be further suppressed. The melt viscosity at 210 ° C. is more preferably 5,000 Pa · s or less, and more preferably 4,000 Pa · s or less. For the same reason, when the deflection temperature T ₀ is 88 ° C. or higher, the melt viscosity under the condition of a shear rate of 6.08 sec ⁻¹ measured using a caprograph is 6,000 Pa · s or less at 240 ° C. Preferably, 5,000 Pa · s or less is more preferable, and 4,000 Pa · s or less is more preferable. The general molding temperature of a thermoplastic resin composition having a deflection temperature under 88 ° C. is about 210 ° C., and the general molding temperature of a thermoplastic resin composition having a deflection temperature under 88 ° C. is 240 ° C. Therefore, in the present invention, attention was paid to melt viscosity at 210 ° C. and 240 ° C., respectively.

In the present invention, the melt viscosity of the thermoplastic resin composition can be determined by the following method. First, the pellets of the thermoplastic resin composition were dried in a hot air dryer at 105 ° C. for 3 hours, and then sheared using a Capillograph 1C (capillary: L / D = 10 mm / 1 mm) manufactured by Toyo Seiki Seisakusho. The melt viscosity (Pa · s) at 210 ° C. or 240 ° C. is measured under the condition of 6.08 sec ⁻¹ .

If the melt viscosity of the thermoplastic resin composition is within the above range, the thermoplastic resin contained in the thermoplastic resin composition is not particularly limited. For example, polystyrene resin (PS resin), acrylonitrile / styrene copolymer (AS resin) ), Polymethyl methacrylate resin (PMMA resin), high impact polystyrene resin (HIPS resin), acrylonitrile / butadiene / styrene copolymer (ABS resin), methyl methacrylate / acrylonitrile / butadiene / styrene copolymer (MABS resin) , Acrylonitrile / styrene / acrylate copolymer (ASA resin), acrylonitrile / silicone composite rubber / styrene copolymer (ASS resin), acrylonitrile / chlorinated polyethylene / styrene copolymer (ACS resin) acrylonitrile / ethylene propylene / Styrene copolymer (AES resin) and the like. Two or more of these may be included. Among these, ABS resin and MABS resin are preferable, and ABS resin is more preferable. By including an ABS resin, an injection molded product having excellent surface gloss can be obtained. In order to make the melt viscosity of the thermoplastic resin composition within the above range, the deflection temperature under load is less than 88 ° C., and the melt viscosity under the conditions of temperature 210 ° C. and shear rate 6.08 sec ⁻¹ is 6,000 Pa · or a thermoplastic resin having a deflection temperature under load of 88 ° C. or more, a melt viscosity of 6,000 Pa · s or less under the conditions of a temperature of 240 ° C. and a shear rate of 6.08 sec ^−1. It is preferable to select.

  As the flat filler, for example, aluminum, nickel, tin, copper, iron, gold, silver, platinum and other metal particles having a flat shape, brass using these metals as a substrate, alloy particles such as stainless steel, brass particles, Examples include metal-coated mica particles, wollastonite particles, carbon particles, glass flakes, and glass particles. Two or more of these may be included. Among these, aluminum, mica pearl pigments in which mica and glass particles are coated with titanium oxide are preferable.

  The content of the flat filler is preferably 10% by weight or less, more preferably 5% by weight or less in the thermoplastic resin composition from the viewpoint of further suppressing poor appearance such as a flow mark.

  The thermoplastic resin composition used in the present invention may contain other components as long as the effects of the present invention are not impaired. Examples of other components include antioxidants such as hindered phenols, sulfur-containing organic compounds, and phosphorus-containing organic compounds, thermal stabilizers such as phenols and acrylates, benzotriazoles, benzophenones, and salicylates. UV absorbers such as organic nickel, light stabilizers such as hindered amines, etc., metal salts of higher fatty acids, lubricants such as higher fatty acid amides, plasticizers such as phthalates and phosphates Flame retardants / flame retardants such as polybromodiphenyl ether, tetrabromobisphenol-A, brominated epoxy oligomers, brominated polycarbonate oligomers, phosphorous compounds, antimony trioxide, antistatic agents, carbon black , Titanium oxide, pigments and dyes, water and silicone oil, fluid paraffin Liquid, such as down, can be exemplified a reinforcing material or filler, such as carbon fiber.

  The thermoplastic resin composition used in the present invention can be obtained, for example, by melt-mixing a thermoplastic resin, a flat filler, and other components as necessary. Examples of the melt mixing method include a melt mixing method using a single-screw or twin-screw extruder having a heating device and a vent. The temperature at the time of melt mixing is generally in the range of 200 to 300 ° C., and the temperature gradient at the time of melt mixing can be freely set within a range that does not impair the object of the present invention.

  Next, the injection molded product of the present invention will be described. The injection-molded product of the present invention is obtained by the above-described manufacturing method, and is perpendicular to the filling direction of the thermoplastic resin composition in the weld portion on the design surface facing the weld portion on the back side of the design surface of the injection-molded product. In cross-sectional observation from the direction, 90% or more of the flat filler existing in the cross-sectional area having a width of 800 μm and a depth of 400 μm is preferably oriented at 20 degrees or less with respect to the design surface. As a thermoplastic resin composition, what was illustrated previously in the manufacturing method of an injection molded product can be used.

Here, the ratio of the flat filler oriented at 20 degrees or less with respect to the design surface can be calculated by the following method. First, a cross section of the weld portion is cut out from an injection molded product using a Zege microtome, and the cross section is observed at a magnification of 200 times using a Keyence digital microscope VHX-1000. With respect to the total number of flat fillers A ₀ (pieces) existing in the cross-sectional area of 800 μm width and 400 μm depth centering on the weld line, the angle between the straight line connecting both ends in the longitudinal direction of the flat filler and the design surface is measured. The ratio B (number%) of the number A ₁ (number) of flat fillers oriented at 20 degrees or less with respect to the design surface is calculated by the following formula.

Formula: B = (A ₁ / A ₀ ) × 100
When the flat filler is oriented at 20 degrees or less with respect to the design surface, since the influence on the weld line generation is small, in the present invention, the flat shape is oriented at 20 degrees or less with respect to the design surface. Attention was paid to the proportion of filler. The injection molded product can be obtained, for example, by the above-described method for manufacturing an injection molded product of the present invention.

  Hereinafter, the injection molded product of the present invention will be described in detail with reference to examples. First, an evaluation method in each example and comparative example will be described.

(1) Deflection temperature under load of thermoplastic resin composition The pellets of the thermoplastic resin composition obtained in Reference Examples 1 to 6 were dried in a hot air dryer at 105 ° C for 3 hours, and then set to a cylinder temperature of 250 ° C. The test piece of ISO3167 (Type A) was obtained by filling in a SE50DU molding machine manufactured by Sumitomo Heavy Industries and injection molding at a mold temperature of 80 ° C. Using the obtained test piece, the deflection temperature under load was measured under a load condition of 1.82 MPa in accordance with ISO75.

(2) Melt viscosity and melt temperature of thermoplastic resin composition The pellets of the thermoplastic resin composition obtained in Reference Examples 1 to 6 were dried in a hot air dryer at 105 ° C for 3 hours, and then Toyo Seiki Co., Ltd. Using a Capillograph 1C (capillary: L / D = 10 mm / 1 mm) manufactured by Seisakusho, melt viscosity (Pa · s) in a temperature range of 180 ° C. to 270 ° C. in increments of 10 ° C. under a shear rate of 6.08 sec ⁻¹ Measured with Moreover, from the obtained measurement results, the relationship between the measurement temperature and the melt viscosity was plotted to create an approximate curve, and the melt temperatures at two points of melt viscosity of 6,000 Pa · s and 9,000 Pa · s were read.

(3) Appearance 1 (weld line)
About the design surface of the injection-molded article obtained in each example and comparative example, the weld line is observed visually, and if no light reflection difference, hairline, color unevenness is confirmed compared to the non-weld part, `` ○ '' When one or more of these defects were confirmed, it was evaluated as “×”.

(4) Appearance 2 (flow mark)
About the design surface of the injection-molded product obtained in each example and comparative example, the whole is visually observed, and when the flow mark is not confirmed, it is evaluated as “◯”, and when the flow mark is confirmed, it is evaluated as “×”. did.

(5) Appearance 3 (discoloration, spider, avatar)
The design surface of the injection-molded product obtained in each example and comparative example is visually observed as a whole. If no discoloration, spider or avatar is confirmed, “○”, if one or more of these defects are confirmed Was evaluated as “×”.

(6) Ratio of flat filler oriented at 20 degrees or less with respect to the design surface From the injection-molded product obtained by each example and comparative example, a cross section of the weld portion is cut out using a Zege microtome. The cross section was observed at a magnification of 200 times using a digital microscope VHX-1000. With respect to the total number of flat fillers A ₀ (pieces) existing in the cross-sectional area of 800 μm width and 400 μm depth centering on the weld line, the angle between the straight line connecting both ends in the longitudinal direction of the flat filler and the design surface is measured. The ratio B (number%) of the number A ₁ (number) of flat fillers oriented at 20 degrees or less with respect to the design surface was calculated by the following formula.
Formula: B = (A ₁ / A ₀ ) × 100

  Next, the thermoplastic resin compositions used in Examples and Comparative Examples will be described.

[Reference Example 1]
An ABS resin composition containing 2% by weight of a flat filler composed of 98% by weight of ABS resin and aluminum particles having a particle diameter of 20 μm (aluminum paste Type E manufactured by Toyo Aluminum Co., Ltd.) was used. The ABS resin composition has a deflection temperature under load of 83 ° C., a melt temperature at which the melt viscosity becomes 6000 Pa · s at a shear rate of 6.08 sec ⁻¹ is 205 ° C., and a melt temperature at which the melt viscosity becomes 9000 Pa · s is 195 ° C. The melt viscosity at 210 ° C. was 5000 Pa · s.

[Reference Example 2]
A heat-resistant ABS resin composition containing 2% by weight of a flat filler made of aluminum particles (aluminum paste Type E manufactured by Toyo Aluminum Co., Ltd.) having a heat-resistant ABS of 98% by weight and a particle diameter of 20 μm was used. This heat-resistant ABS resin composition has a deflection temperature under load of 90 ° C., a melt temperature at which the melt viscosity is 6000 Pa · s at a shear rate of 6.08 sec ⁻¹ 237 ° C., and a melt temperature at which the melt viscosity is 9000 Pa · s is 224 ° C. Yes, the melt viscosity at 240 ° C. was 5500 Pa · s.

[Reference Example 3]
A PC / ABS resin composition containing 98% by weight of a polycarbonate / ABS alloy resin and 2% by weight of a flat filler made of aluminum particles (aluminum paste Type E manufactured by Toyo Aluminum Co., Ltd.) having a particle diameter of 20 μm was used. The deflection temperature under load of this PC / ABS resin composition was 102 ° C., the melting temperature at which the melt viscosity was 6000 Pa · s at a shear rate of 6.08 sec ⁻¹ was 235 ° C., and the melt temperature at which the melt viscosity was 9000 Pa · s was 232 ° C. The melt viscosity at 240 ° C. was 4200 Pa · s.

[Reference Example 4]
An ABS resin composition containing 2% by weight of a flat filler composed of 98% by weight of ABS resin and aluminum particles having a particle diameter of 20 μm (aluminum paste Type E manufactured by Toyo Aluminum Co., Ltd.) was used. This ABS resin composition has a deflection temperature under load of 83 ° C., a melt temperature at which the melt viscosity becomes 6000 Pa · s at a shear rate of 6.08 sec ⁻¹ 195 ° C., and a melt temperature at which the melt viscosity becomes 9000 Pa · s is 185 ° C. The melt viscosity at 210 ° C. was 3300 Pa · s.

[Reference Example 5]
An ABS resin composition containing 2% by weight of a flat filler composed of 98% by weight of ABS resin and aluminum particles having a particle diameter of 20 μm (aluminum paste Type E manufactured by Toyo Aluminum Co., Ltd.) was used. This ABS resin composition has a deflection temperature under load of 82 ° C., a melt temperature at which the melt viscosity becomes 6000 Pa · s at a shear rate of 6.08 sec ⁻¹ is 215 ° C., and a melt temperature at which the melt viscosity becomes 9000 Pa · s is 200 ° C. The melt viscosity at 210 ° C. was 6800 Pa · s.

[Reference Example 6] Heat-resistant ABS resin Heat-resistant ABS resin composition containing 98% by weight of heat-resistant ABS resin and 2% by weight of flat filler made of aluminum particles (aluminum paste Type E manufactured by Toyo Aluminum Co., Ltd.) having a particle diameter of 20 μm μm is used. did. This heat-resistant ABS resin composition has a deflection temperature under load of 103 ° C., a melting temperature of 256 ° C. at a melt viscosity of 6000 Pa · s at a shear rate of 6.08 sec ⁻¹ , and a melting temperature of 247 ° C. at a melt viscosity of 9000 Pa · s. Yes, the melt viscosity at 240 ° C. was 20000 Pa · s.

The mold temperature control equipment used in the examples and comparative examples is as follows.
Equipment 1: A heat and cool molding temperature control equipment that can repeat heating and cooling was used.
Equipment 2: General molding temperature control equipment that uses water as a heat medium and controls the temperature at a constant temperature was used.

[Examples 1-22, Comparative Examples 1, 5, 7-15]
Using the mold having the cavity 1 having the opening forming body 2 shown in FIG. 1, the gate 3 and the gate 4, and having the medium passages 6 and 8 shown in FIG. From the thermoplastic resin composition described in -4, an injection-molded product was produced under the conditions described in Tables 1 to 4 in accordance with steps (1) to (3) in the method for producing an injection-molded product of the present invention.

[Comparative Example 2]
An injection molded product was produced in the same manner as in Example 3 except that the step (2) was not performed.

[Comparative Example 3]
An injection-molded article was produced in the same manner as in Comparative Example 2 except that a mold having a cavity 1 having an opening forming body 2 shown in FIG. 6 and a gate 3 and having medium passages 6 and 8 shown in FIG. 3 was used. did.

[Comparative Example 4]
An injection molded product was produced in the same manner as in Example 3 except that the mold temperature control equipment 2 was used and the molding conditions were changed as shown in Table 3.

[Comparative Example 6]
An injection molded product was produced in the same manner as in Example 14 except that the molding conditions were changed as shown in Table 3.

  The evaluation result of each Example and a comparative example is shown to Tables 1-4.

  As is clear from the results of Examples 1 to 22, according to the present invention, an injection-molded article having an excellent appearance can be obtained.

By comparison between Comparative Example 1 and Examples 1-2, Comparison between Comparative Example 5 and Example 4, Comparative Example 7 and Examples 18-19, and Comparison between Comparative Example 10 and Example 9, the design surface back side mold surface temperature If the T ₃ does not satisfy the formula <2>, he can be seen that the appearance defect by flow marks occur.

  From the comparison between Comparative Examples 2 and 3 and Example 3, it can be seen that when there is no step (2), appearance defects due to the weld line occur.

  From the comparison between Comparative Example 4 and Example 3 and the comparison between Comparative Example 6 and Example 14, it can be seen that when the design surface mold surface temperature is less than 120 ° C., appearance defects due to weld lines occur.

Comparison with Comparative Example 8 to Example 19, comparison between Comparative Example 9 and Example 7, by contrast with Comparative Example 11 and Example 11, when the molding temperature T ₂ exceeds the range of the formula <1>, molding It turns out that the appearance defect by the heat | fever burning, spider, avatar by gas generate | occur | produces.

Comparison Example 12, the molding temperature T ₂ is less than the range of the formula <1>, when the melt viscosity of the thermoplastic resin composition is high, it can be seen that the poor appearance due weld lines and flow marks are generated.

Comparison Example 15 and Comparative Example 13, the molding temperature T ₂ exceeds the range of the formula <1>, when the melt viscosity of the thermoplastic resin composition is high, thermal burnt by flow marks and forming gas, fogging, defective appearance due avatar It can be seen that occurs.

  It can be seen from Comparative Example 14 that when the melt viscosity of the thermoplastic resin composition is high, appearance defects due to weld lines and flow marks occur.

DESCRIPTION OF SYMBOLS 1 Cavity 2 Opening formation body 3 Gate 4 Gate 5 Position where a weld line is formed 6 Medium passage 7 Design surface mold 8 Medium passage 9 Design surface back side mold 10, 11 Thermoplastic resin composition 12 Flatness oriented in flow direction Filler 13 Flat filler oriented in multiple directions 14 Weld line 15 Flat filler whose orientation direction has changed due to shear force 16 Weld line moved by shear force 17 Injection direction

Claims (4)

A thermoplastic resin composition containing a thermoplastic resin and a flat filler is injection-molded using a mold that can repeatedly heat and cool the surface and has at least two gates for filling the cavity with the resin. A method for producing an injection-molded product, wherein at least (1) a mold is formed on a surface of a mold on which a design surface of the injection-molded product is to be formed at 120 ° C. Injecting into,
(2) Under the condition that the mold surface temperature for forming the design surface of the injection molded product is 120 ° C. or higher, the thermoplastic resin composition injected by the step (1) has a weld line due to the flat filler orientation. A step of further injecting a thermoplastic resin composition from another gate in a crossing direction with respect to the weld line after being formed and before holding pressure is started;
(3) A step of opening the mold under the condition that the mold surface temperature on which the design surface is to be formed is equal to or lower than the load deflection temperature T0 (° C.) of the thermoplastic resin composition after the completion of the step (2).
Have
The molding temperature T ₂ (° C.) of the thermoplastic resin composition in the steps (1) and (2), the deflection temperature T ₀ (° C.) of the thermoplastic resin composition, and the shear rate of the thermoplastic resin composition of 6.08 sec. ^The temperature T ₁ (° C.) at which the melt viscosity in ^-1 reaches 6,000 Pa · s satisfies the following formula <1>, and gold on the back side of the surface on which the design surface in the steps (1) and (2) is to be formed Mold surface temperature T ₃ (° C.), molding temperature T ₂ (° C.) of the thermoplastic resin composition, temperature T ₄ at which the melt viscosity of the thermoplastic resin composition at a shear rate of 6.08 sec ⁻¹ is 9,000 Pa · s. (° C.) satisfies the following formula <2>
Formula <1> T ₁ ≦ T ₂ ≦ (T ₀ +170)
Formula <2> T ₃ ≦ 100− (T ₂ −T ₄ )
A thermoplastic resin composition having a melt viscosity under a shear rate of 6.08 sec ⁻¹ measured using a capillograph of the thermoplastic resin composition and a deflection temperature under load T ₀ (° C.) T ₀ of less than 88 ° C. is 210 ° C. Is a thermoplastic resin composition having a T ₀ of 88 ° C. or higher at 240 ° C., and a thermoplastic resin composition having a T ₀ of 6,000 Pa · s or lower at 240 ° C.   The method for producing an injection-molded article according to claim 1, wherein the thermoplastic resin contains acrylonitrile-butadiene-styrene.   An injection-molded product obtained by the method for producing an injection-molded product according to claim 1 or 2.   Present in the cross-sectional area of 800 μm wide and 400 μm deep in cross-sectional observation of the design surface facing the weld portion on the back side of the design surface of the injection molded product from the direction perpendicular to the filling direction of the thermoplastic resin composition of the weld portion The injection molded product according to claim 3, wherein 90% or more of the flat filler to be oriented is oriented at 20 degrees or less with respect to the design surface.