JP2018027640A - Injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding method capable of producing a molded body of a thermoplastic resin or a thermoplastic resin composite material with high appearance at a high cycle.SOLUTION: Provided is an injection molding method comprising: a first step where, using a die 100 including first temperature adjustment means 13, 23 capable of at least cooling cavity faces 31, 32 and second temperature adjustment means 14, 24 capable of at least heating the cavity faces at the sides opposite to the cavity faces of the first temperature adjustment means, the cavity faces are heated up to a heating temperature more than the melting point or glass transition temperature of a thermoplastic resin, and the thermoplastic resin is filled into the die; and a second step where, after the first step, it is temperature-reduced to a cooling temperature below the melting point or glass transition temperature of the thermoplastic resin to cool and solidify the thermoplastic resin, and subsequently, the die is released to take out a molded body, in which the temperature increasing rate in the first step is controlled to 80°C/min or more, the temperature decreasing rate in the second step is controlled to 100°C/min or more, and also, a difference between the heating temperature and the cooling temperature is controlled to 50°C or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an injection molding method capable of providing a molded product at a high cycle.

  The injection molding of a thermoplastic resin is generally based on a technique for molding a resin mixture in a mold using the plasticity of a thermoplastic resin. The thermoplastic resin was melted and injected into the mold, and then cooled and solidified in the mold under a holding pressure (sometimes referred to as holding pressure) by the injection cylinder to obtain a desired molded product. As described above, in order to solidify the resin mixture and release the molded product from the mold so as to satisfy the molded product, when the resin used is an amorphous resin, the heat deformation temperature or lower, In this case, it is necessary to cool the molding material below the melting point. When using the conventional molding method as described above, problems sometimes occur in the appearance and mechanical properties of the molded product.

  2. Description of the Related Art In recent years, techniques for obtaining molded products with excellent appearance have become important in various electrical and electronic parts and exterior parts such as interior and exterior of vehicles. When using a thermoplastic resin composite material added with glass fiber or carbon fiber, or a material with aluminum flake added to obtain a metallic appearance, especially for the purpose of obtaining high strength or high rigidity properties Performance was a problem.

  In order to prevent such an appearance defect, for example, Patent Document 1 to Patent Document 3 disclose a mold used when injection molding a thermoplastic resin material, and a cooling path and a heating path are provided in the mold. Thus, techniques for heating and cooling the mold have been proposed.

  First, regarding the appearance problem, it may occur in a non-reinforced thermoplastic resin and a thermoplastic resin composite material containing fillers and / or additives such as glass fiber, mica and metal. The cause is usually that the mold temperature is kept below the heat deformation temperature of the resin used. At present, in order to increase productivity, the mold is cooled by using a refrigerant whose temperature has been lowered to the level of condensation. However, the molten thermoplastic resin material in contact with the surface of the cold mold is rapidly cooled, the fluidity is rapidly lost in the vicinity of the mold surface, and as a result, the transferability of the mold surface is significantly impaired, There is a problem that the surface of the molded product becomes quite irregular.

  When a mold having a multi-point gate having a plurality of gates for injecting resin is used, there is a problem that a weld line is generated at a portion (weld portion) where the molten resin joins in the mold. The “weld line” includes not only a line-like dent generated on the surface of the molded product in the weld part but also black streaks generated in the vicinity of the weld. In addition, when a mold having an opening is used for a molded product, the molten resin filled in the mold may once flow after the molten resin is separated, and the resin may join again to form a weld line. . These weld lines are problematic because of poor appearance even when a non-reinforced thermoplastic resin or a thermoplastic resin composite material is used.

  Furthermore, in the thermoplastic resin composite material to which a filler such as glass fiber is added, there is a problem of poor appearance such that the gloss of the surface of the molded product is impaired. Conventionally, increasing the mold temperature has been proposed as a method for preventing the resin mixture from solidifying in an insufficient state.

  However, when the mold temperature is raised, the cooling time generally takes a long time, or the mold is taken out from the mold before it is completely solidified, so that there is a problem that only a molded product with very poor dimensional accuracy can be obtained. That is, in actual molding, an appropriate temperature is selected in consideration of the adverse effects of these two contradictory conditions.

  Therefore, as one effective injection molding technique for solving these problems, there is a method in which the mold surface is preheated using high frequency induction heating and the molten resin filled in the mold is reflowed after filling. Patent Document 4 describes. If this technique is used, the weld strength (strength of the weld portion) of the molded product to which glass fiber or aluminum flake is added can be increased, or the appearance can be improved.

JP 2014-226851 A Japanese Patent No. 4334469 JP 2014-226851 A Japanese Patent Laid-Open No. 9-1611

  However, the use of the technique described in Patent Document 4 requires a high-frequency induction heating device as a heating device and a piston installed outside the mold as a molten resin reflow device, so that there is still a problem that it is inferior in economic efficiency. Remaining.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an injection molding method capable of producing a molded product having an excellent appearance in a high cycle using a thermoplastic resin or a thermoplastic resin composite material. It is.

As a result of intensive studies by the present inventors, a molded product having an excellent appearance is manufactured at a high cycle by using a specific mold and performing injection molding by adjusting a temperature increase rate, a temperature decrease rate, and a temperature difference. Has been found to be possible to achieve the present invention.
That is, the present invention is as follows.

The injection molding method of the present invention is an injection molding method for obtaining a molded product by filling a mold having a cavity formed of a plurality of mold parts with a thermoplastic resin or a thermoplastic resin composite material,
The mold has a first temperature adjustment means capable of cooling at least the cavity surface, and a second temperature adjustment capable of at least heating the cavity surface on the opposite side of the cavity surface of the first temperature adjustment means. Means and
A first step of heating the cavity surface to a melting temperature of the thermoplastic resin or a heating temperature equal to or higher than the glass transition temperature and filling the mold with the thermoplastic resin;
After the first step, the second step of lowering the temperature to a cooling temperature lower than the melting point or glass transition temperature of the thermoplastic resin to solidify the thermoplastic resin, then opening the mold and taking out the molded product, With
The temperature increase rate in the first step is 80 ° C./min or more, the temperature decrease rate in the second step is 100 ° C./min or more, and the difference between the heating temperature and the cooling temperature is 50 ° C. or more.

Here, the heating temperature and the cooling temperature are based on the melting point or glass transition temperature. However, when the thermoplastic resin is a crystalline thermoplastic resin, the melting point is used as a reference, and the thermoplastic resin is an amorphous resin. Is based on the glass transition temperature. The temperature lowering rate is the temperature lowering rate when the cavity surface is cooled from the target high temperature to the target low temperature. The temperature increase rate is the rate of temperature increase when the cavity is heated from the target low temperature to the target high temperature.
Further, the temperature of the cavity surface is obtained in advance by calculating the correlation between the cavity surface and the temperature in the vicinity of the cavity surface, and the actual temperature control during molding is a value obtained by measuring the temperature in the vicinity of the cavity surface.

It is preferable that the distance L0 from the cavity surface to the first temperature adjusting unit and the distance L1 from the cavity surface to the surface opposite to the cavity surface satisfy the following relationship.
(L1 / L0)> 3

  The first temperature adjusting means preferably includes one or more cooling medium passages through which the cooling medium flows, and the second temperature adjusting means is preferably a heater for heating.

  The mold part preferably includes a first part having a first temperature adjusting means and a second part having a second temperature adjusting means.

In the mold part, the volume V (I) of the first part and the volume V0 of the mold part preferably satisfy the following relationship.
(V (0) / V (I))> 3

More preferably, the volume V (I) of the first part and the volume V0 of the second part satisfy the following relationship.
(V (0) / V (I))> 5

Volume V (I) of the first part and the thermal conductivity C (I) (J / s · m · K) of the material of the first part, and Volume V (II) of the second part and the heat conduction of the material of the second part It is preferable that the rate C (II) (J / s · m · K) satisfies the following relationship.
[{V (II) × (1 / C (II))} / {V (I) × (1 / C (I))}]> 3

  The thermal conductivity C (I) (J / s · m · K) of the material of the first part is 3.5 times the thermal conductivity C (II) (J / s · m · K) of the material of the second part. The above is preferable.

  When the cavity surface is cooled, it is preferable that the first portion and the second portion can be separated from each other.

  The second temperature adjusting means sets the average temperature of the second part to the glass transition temperature of the thermoplastic resin or the thermoplastic resin constituting the thermoplastic resin composite material + 50 ° C. or higher or the melting point + 50 ° C. or higher. It is preferable.

  It is preferable that the first temperature adjusting means includes a plurality of cooling medium passages, and has at least one manifold that allows the cooling medium of the same temperature to simultaneously flow through the plurality of cooling medium passages.

  According to the present invention, it is possible to provide a molded article of a thermoplastic resin or a thermoplastic resin composite material with a good appearance and high cycle and good productivity.

FIG. 1 is a schematic sectional view (vertical sectional view) of an embodiment of a mold used in the injection molding method of the present invention. FIG. 2 is a schematic cross-sectional view (vertical cross-sectional view) for explaining details of an embodiment of a mold used in the injection molding method of the present invention. FIG. 3 is a plan view of an embodiment of a mold used in the injection molding method of the present invention. FIG. 4 is a schematic top view of the molded product molded in Examples 1-4. FIG. 5 is a schematic top view of the molded product molded in Examples 5 and 6.

  Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist.

An embodiment of the injection molding method of the present invention will be described.
[Injection molding method]
The injection molding method of the present invention is an injection molding method for obtaining a molded product by filling a mold having a cavity formed of a plurality of mold parts with a thermoplastic resin or a thermoplastic resin composite material,
The mold has a first temperature adjustment means capable of cooling at least the cavity surface, and a second temperature adjustment capable of at least heating the cavity surface on the opposite side of the cavity surface of the first temperature adjustment means. Means and
A first step of heating the cavity surface to a melting temperature of the thermoplastic resin or a heating temperature equal to or higher than the glass transition temperature and filling the mold with the thermoplastic resin;
After the first step, the second step of lowering the temperature to a cooling temperature lower than the melting point or glass transition temperature of the thermoplastic resin to solidify the thermoplastic resin, then opening the mold and taking out the molded product, With
The temperature increase rate in the first step is 80 ° C./min or more, the temperature decrease rate in the second step is 100 ° C./min or more, and the difference between the heating temperature and the cooling temperature is 50 ° C. or more.

The rate of temperature increase is 80 ° C./min or more from the viewpoint of productivity, and the rate of temperature decrease is 100 ° C./min from the viewpoint of productivity. The temperature rising rate is preferably 100 ° C./min or more, more preferably 150 ° C./min or more, and the temperature lowering rate is preferably 150 ° C./min or more, more preferably 200 ° C./min or more.
In the case of a crystalline resin, the heating temperature is a melting point of −50 ° C. or higher, preferably a melting point or higher, and more preferably a melting point + 10 ° C. or higher. In the case of an amorphous resin, the glass transition temperature or higher, preferably the glass transition temperature + 10 ° C. or higher.
In the case of a crystalline thermoplastic resin, the cooling temperature is preferably a melting point of −100 ° C. or lower, and in the case of an amorphous resin, the cooling temperature is −20 ° C. or lower.
The difference between the heating temperature and the cooling temperature is to reflow the molten resin filled in the mold in order to improve the appearance defect due to the weld line when using materials containing aluminum flakes, etc. It is 50 degreeC or more, More preferably, it is 150 degreeC or more.

<Thermoplastic resin and thermoplastic resin composite material>
The “thermoplastic resin” used for the thermoplastic resin and the thermoplastic resin composite material in the present invention refers to all those generally referred to as thermoplastic resins. For example, polystyrene, high impact polystyrene, rubber reinforced styrene resin such as medium impact polystyrene, styrene-acrylonitrile copolymer (SAN resin), acrylonitrile-butyl acrylate rubber-styrene copolymer (AAS resin), acrylonitrile-ethylene Propyl rubber-styrene copolymer (AES), acrylonitrile-polyethylene chloride-styrene copolymer (ACS), ABS resin (for example, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene-alphamethylstyrene copolymer) Styrene resin such as acrylonitrile-methyl methacrylate-butadiene-styrene copolymer; acrylic resin such as polymethyl methacrylate (PMMA); Olefin resins such as ethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP); vinyl chloride resins such as polyvinyl chloride and polyvinylidene chloride; ethylene vinyl chloride vinyl acetate copolymer, ethylene vinyl chloride copolymer Polyvinyl chloride resins such as coalescence; Polyester resins such as polyethylene terephthalate (PETP or PET) and polybutylene terephthalate (PBTP or PBT); Polycarbonate resins such as polycarbonate (PC) and modified polycarbonate; Polyamide 66, Polyamide 6, Polyamide Polyamide resins such as 46; polyacetal (POM) resins such as polyoxymethylene copolymers and polyoxymethylene homopolymers; other engineering resins and super engineering resins; , Polyether sulfone (PES), polyetherimide (PEI), thermoplastic polyimide (TPI), polyetherketone (PEK), polyether ether ketone (PEEK), polyphenylene sulfide (PSU), and the like.
Cellulose derivatives such as cellulose acetate (CA), cellulose acetate butyrate (CAB), ethyl cellulose (EC); liquid crystal polymers (LCP) such as liquid crystal polymers and liquid crystal aromatic polyesters, thermoplastic polyurethane elastomers (TPU), thermoplastic styrene Examples thereof include thermoplastic elastomers such as butadiene elastomer (SBC), thermoplastic polyolefin elastomer (TPO), thermoplastic polyester elastomer (TPEE), thermoplastic vinyl chloride elastomer (TPVC), and thermoplastic polyamide elastomer (TPAE).
As the thermoplastic resin in the present invention, the thermoplastic resin as described above may be produced in the molding step of the present invention. You may shape | mold by the method of this invention using the blend body of a 1 type or more thermoplastic resin.
The thermoplastic resin composite material used in the present invention contains a filler and / or an additive.

An inorganic substance is mentioned as a filler added to a thermoplastic resin composite material. For example, glass fibers, glass beads, calcium carbonate, mica, asbestos, etc., metal powders such as iron, copper, zinc, and aluminum, hollow bodies, flakes, or metal oxides of these metals, metal hydroxides It can be a thing.
Examples of the additive added to the thermoplastic resin composite material include an antioxidant, an ultraviolet absorber, a release agent, a heat stabilizer, an antistatic agent, and a colorant.

  Furthermore, it is also effective for improving the appearance of a foam molded product in which a chemical foaming agent or a physical foaming agent such as nitrogen or carbon dioxide is added to a thermoplastic resin or a thermoplastic resin composite material.

  As the injection molding machine that can be used in the present invention, a known machine can be used.

  According to the present invention, before filling the mold with the thermoplastic resin, the cavity surface is rapidly heated above the melting point or glass transition temperature of the thermoplastic resin, and the mold is injected and filled with the thermoplastic resin. Can be obtained in a high cycle.

<Mold>
Next, an embodiment of a mold that can be used in the injection molding method of the present invention will be described with reference to the drawings. The metal mold | die which can be used for the injection molding method of this invention is not limited to what is demonstrated below. In the present embodiment, description will be made using a mold having a vertical mold clamping mechanism shown in FIGS. 1 and 2, but a mold having a horizontal mold clamping mechanism can also be used in the same manner. FIG. 1 shows a schematic cross-sectional view of an embodiment of a mold.
As shown in FIG. 1, the mold 100 includes a mold part 10, a mold part 20, and heat insulating plates 15 and 25, and the cavity 30 is defined by the mold part 10 and the mold part 20. Form. The cavity 30 is filled with a thermoplastic resin (in the following description, a thermoplastic resin or a thermoplastic resin composite material will be described as a thermoplastic resin for simplicity), and a molded product is molded. The molten resin is filled into the cavity 30 through the runner portion 33 from the nozzle (not shown) of the cylinder of the injection molding machine.

The mold part 10 includes a first temperature adjusting unit 13 including a plurality of cooling medium passages capable of cooling at least the cavity surface 31 in the vicinity of the cavity surface 31, and a cavity surface 31 of the first temperature adjusting unit 13. On the opposite side, a second temperature adjusting means 14 comprising a plurality of rod-shaped cartridge heaters capable of at least heating the cavity surface 31 is provided.
Similarly, the mold portion 20 also includes a first temperature adjusting means 23 including a plurality of cooling medium passages capable of cooling at least the cavity surface 32 in the vicinity of the cavity surface 32, and a cavity of the first temperature adjusting means 23. On the opposite side of the surface 32, a second temperature adjusting means 24 comprising a plurality of bar-shaped cartridge heaters capable of at least heating the cavity surface 32 is provided.

The mold part 10 has a structure divided into a first part 11 having a first temperature control means 13 and a second part 12 having a second temperature control means 14, and the first part 11 and the second part 12. However, the spring 40 can be separated.
Similarly, the mold part 20 has a structure divided into a first part 21 having a first temperature adjusting means 23 and a second part 22 having a second temperature adjusting means 24. The second portion 22 is configured to be separated by a spring 40.

Next, the details of the mold part will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view for explaining details of the mold, and some components are omitted.
As shown in FIG. 2, the mold portion (reference numerals 10 and 20 in FIG. 1) has a distance L0 from the cavity surface 31 to the first temperature adjusting means 13, and a surface opposite to the cavity surface 31 from the cavity surface 31. The distance L1 up to 16 satisfies the following relationship.
(L1 / L0)> 3

  When the molding die is composed of a plurality of mold parts, it is sufficient that at least one mold part satisfies the above numerical range, but it is more preferable that all the mold parts satisfy the above numerical range.

Here, the distance L0 from the cavity surface to the first temperature adjusting means means the distance from the cavity surface to the center of the first temperature adjusting means in a cross section perpendicular to the cavity surface of the mold.
Further, the distance L2 from the first temperature adjusting means to the second temperature adjusting means is the second temperature adjusting means from the center of the first temperature adjusting means in the cross section perpendicular to the cavity surface of the mold. Means the distance to the center of
Further, the distance L1 from the cavity surface to the surface opposite to the cavity surface means a distance in a cross section perpendicular to the cavity surface of the mold.

When the cavity surface has an uneven shape and the distance from the cavity surface to the first temperature adjusting means varies depending on the location, the distance L0 from the cavity surface to the center of the first temperature adjusting means is the shortest distance among them. Means.
Further, when the cavity surface has an uneven shape and the first temperature adjusting means is provided at the same distance from the cavity surface along the uneven shape, the first temperature adjusting means to the second temperature adjusting means. The distance L2 is different depending on the location. In this case, the distance L2 from the first temperature adjusting means to the second temperature adjusting means means the shortest distance among different L2.
In addition, when the cavity surface is uneven, the distance L1 from the cavity surface to the surface opposite to the cavity surface means an average distance of different L1.

  In the case where the first temperature adjusting means and the second temperature adjusting means include a plurality of cooling medium passages or a plurality of heaters, the distance from the cavity surface of one passage or the heater differs depending on the location. The average value of the shortest distances for all passages or heaters.

  Further, when the first part and the second part are integrally formed of the same material, the boundary between the first part and the second part is the second from the center of the first temperature control means in the cross section perpendicular to the cavity surface. The position is L0 away from the temperature adjusting means side.

  The mold according to the present embodiment has a structure in which at least a first temperature adjusting means for cooling is provided in the vicinity of the cavity surface, and the second temperature at least farther from the cavity surface than the first temperature adjusting means. A temperature adjusting means is provided. The second temperature adjusting means heats the cavity surface by heating the entire mold part.

  The first temperature adjusting means is preferably closer to the cavity surface, but it is necessary to provide the first temperature adjusting means at a certain distance due to the strength of the mold and design restrictions. The distance L0 from the cavity surface to the first temperature adjusting means is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 10 mm or less, although it depends on the size of the first temperature means. Although there is no particular limitation on the lower limit value of L0, although it depends on the size of the first temperature means, the distance from the end of the first temperature means to the cavity surface is 3 mm due to restrictions on the strength of the mold. The above is preferable, and 6 mm or more is more preferable.

In the mold of the present embodiment, the relationship between the distance L0 from the cavity surface to the first temperature adjusting means and the distance L1 from the cavity surface to the surface opposite to the cavity surface is (L1 / L0)> 3. Yes, more preferably (L1 / L0)> 5, and most preferably (L1 / L0)> 10.
By setting (L1 / L0)> 3, the capacity of the heat storage part, which is higher than that of the cooling part, is increased, so that rapid heating at the time of mold heating can be performed efficiently. Furthermore, the closer the first temperature control means for cooling is to the cavity surface, the quicker the molded product can be cooled during cooling. Further, the smaller the cooling portion, the quicker the mold can be heated when the mold is heated.
Here, a cooling part is a part cooled by the 1st temperature control means, Comprising: At least 1st part is shown. Further, the heat storage portion is a portion heated by the second temperature adjusting means and indicates at least the second portion.

Furthermore, the distance L2 from the first temperature adjusting means to the second temperature adjusting means is L2> L0, and preferably 2 <L2 / L0 <10.
By setting L2> L0, it is possible to satisfactorily prevent cooling to the second temperature adjusting means at the time of cooling, while preventing disturbance of the control power of the second temperature adjusting means at the time of heating. Can do.
In temperature control of the cavity surface, when the temperature above and below the cavity temperature is slight, L0 and L2 should be as close as possible. However, when molding a composite material, the difference between the upper limit value and the lower limit value of the cavity temperature is large, for example, 50 ° C. or higher, preferably 100 ° C. or higher, and more preferably 150 ° C. or higher. preferable.

  The mold part may include a first part having a first temperature adjusting means and a second part having a second temperature adjusting means. In this case, the first part and the second part may be made of the same material, but more preferably, the first part is made of a material having a higher thermal conductivity than the second part. By using a material having a good thermal conductivity for the first portion, the first portion can be rapidly cooled during cooling. Furthermore, it is possible to quickly conduct the heat stored in the second part having the second temperature adjusting means when the first temperature adjusting means of the first part is stopped and heated.

  Moreover, in the case of the structure provided with the 1st part which has a cooling-medium channel | path which is a 1st temperature control means, and the 2nd part which has a 2nd temperature control means, as shown in FIG. The relationship between I) and the volume V0 of the substantially heated mold part is preferably (V0 / V (I))> 3, more preferably (V0 / V (I))> 5 and most preferably (V0 / V (I))> 10.

  That is, the heating of the cavity surface can heat and melt the thermoplastic resin of the material installed in the cavity by rapidly heating the cavity surface by supplying heat from the second part having the role of a heat storage part that stores a certain amount of heat. . Here, the larger the capacity of the heat storage portion, the more effectively the cavity surface can be heated. However, the capacity of the heat storage portion can be appropriately determined according to the size of the mold and the molding equipment from the viewpoint of the amount of energy consumed for heating due to the equipment.

  On the other hand, for cooling the cavity surface, for example, when the first temperature adjusting means is a plurality of cooling medium passages, the cavity surface is rapidly cooled by circulating the cooling medium through the cooling medium passages near the cavity surface. The molten thermoplastic resin can be cooled and solidified. At this time, in order to cool only the vicinity of the cavity surface, it is preferable that the mold capacity of the portion having the refrigerant passage is smaller, and the cooling medium passage is preferably closer to the cavity surface.

The same material may be used for the first part and the second part, but materials having different thermal conductivities may be used.
Volume V (I) of the first part and the thermal conductivity C (I) (J / s · m · K) of the material of the first part, and Volume V (II) of the second part and the heat conduction of the material of the second part The rate C (II) (J / s · m · K) satisfies the following relationship.
[{V (II) × (1 / C (II))} / {V (I) × (1 / C (I))}]> 3
More preferably,
[{V (II) × (1 / C (II))} / {V (I) × (1 / C (I))}]> 5
Most preferably,
[{V (II) × (1 / C (II))} / {V (I) × (1 / C (I))}]> 10
It is.
By setting [{V (II) × (1 / C (II))} / {V (I) × (1 / C (I))}]> 3, the cavity surface can be quickly cooled during cooling. During heating, the temperature can be quickly raised by the heat storage in the second part.

  Further, the thermal conductivity C (I) (J / s · m · K) of the material of the first part is equal to the thermal conductivity C (II) (J / s of the material of the second part having the second temperature adjusting means. -It is preferable that it is 3.5 times or more of m * K). That is, the higher the thermal conductivity during cooling, the faster the cooling, and the higher the thermal conductivity during heating, the quicker the heat can be removed from the heat storage section. In particular, when the first part is cooled, a higher effect can be obtained by separating the first part and the second part. When not separating at the time of cooling, if the thermal conductivity of the first part is good, the second part having the function of the heat storage part may be cooled at the time of cooling, and it is necessary to optimize the material appropriately.

More preferably, the first part and the second part have a separable structure. After heating the cavity to the desired temperature, the mold is slightly opened with the cavity closed, and the first part and the second part are separated, and an insulating layer of air is provided to increase the molding cycle. It is effective for.
As a specific method, the first part and the second part can be separated while the cavity is closed by inserting a spring between the first part and the second part to slightly open the mold. it can. Separation may be performed with at least one of the plurality of mold parts.

  With the mold separated, cooling water is pressed into the cooling medium passage or the like to rapidly cool the first part including the cavity. At this time, the cavity surface is kept closed by using a spring or a hydraulic cylinder so that the cavity is not opened. The cooling water is stopped after the cavity surface has become below the heat deformation temperature of the thermoplastic resin for a certain time, compressed air is introduced into the cooling medium passage as necessary, and the water in the cooling medium passage is discharged.

The cooling of the first part can be achieved by circulating the cooling medium when the first temperature control means is constituted by a plurality of cooling medium passages. It depends on whether or not rapid cooling is possible.
Therefore, it is preferable to have a structure that allows the cooling medium to flow through each cooling medium passage independently. As a specific example, a manifold capable of simultaneously circulating a cooling medium having the same temperature can be given. The manifold may be installed on the inflow side of the cooling medium passage outside the mold, and the cooling medium may be simultaneously circulated from the manifold to each cooling medium passage. Further, if the manifold is installed on the cooling medium discharge side and discharged, More efficient.
The flow rate greatly affects the cooling efficiency, and the refrigerant may be circulated using a pressure pump or the like as necessary. It is also possible to use a commercially available pressurized temperature controller.

  Water, chiller liquid, carbon dioxide gas, compressed gas, etc. can be raised as a medium to be circulated through the cooling medium passage. Further, one type of medium may be used, but media having different temperatures may be distributed in multiple stages. For example, when the cavity temperature is heated to 220 ° C., 150 ° C. pressurized hot water flows for several seconds, then 60 ° C. temperature-controlled water and 10 ° C. cooling water flow in multiple stages, and the mold reaches a constant temperature. Then, it is possible to adjust the cavity surface to a uniform temperature by flowing pressurized hot water at 70 ° C. again.

Depending on the type of thermoplastic resin, the second temperature adjusting means is the average temperature of the second part, in the case of non-crystalline resin, preferably above the glass transition temperature of the thermoplastic resin material installed in the cavity, preferably When molding a glass transition temperature + 10 ° C. or higher and a material containing aluminum flakes, the glass transition temperature is set to + 50 ° C. or higher. In the case of a crystalline resin, the melting point is set to be equal to or higher than the melting point of the thermoplastic resin material placed in the cavity, preferably the melting point is + 10 ° C. or higher.
The average temperature of the second part is the average temperature of the second part of the mold. As an example of the measuring method, a thermometer is inserted in the mold in the vicinity of the second temperature adjusting means and 10 mm to 30 mm away. The method of measuring the temperature is used. When a cartridge heater is used as the second temperature control means, the temperature control detects the aforementioned temperature and controls the power on / off or adjusts the capacity of the power by PID control (Proportional-Integral-Differential Controller) There are ways to do it.

  There are no particular restrictions on the second temperature control means. In addition to the rod-shaped cartridge heater, there are heaters that use electric resistance even with heating media such as heating oil and water vapor, but the mold is the melting point of the thermoplastic resin. In order to maintain the above high temperature, a heater is preferable from the viewpoint of versatility and performance. Examples of the heater include a ceramic heater and a sheathed heater. A rod-shaped cartridge heater is preferably used in terms of simplicity and performance.

  In the present embodiment, the mold part 10 and the mold part 20 have been described so that the first parts 11 and 21 and the second parts 12 and 22 can be separated from each other, but the spring 40 is not provided. It may be integrally formed by bolting or the like.

  Since the heat insulating plates 15 and 25 have a role of suppressing heat flow due to heat conduction to the molding machine, it is preferable to provide them at the connecting portion between the mold 100 and the molding machine.

FIG. 3 shows a plan view of the mold. As shown in FIG. 3, the core convex portion 34 is provided so as to form openings (portions 244 and 344 in FIGS. 4 and 5) in the molded product. The molten resin enters from the runner portion 33, flows in the mold, wraps around the core convex portion 34, and joins in the vicinity of the weld line generation position 37.
When molding a material containing a filler such as aluminum flakes, just by raising the mold temperature and removing the weld line on the surface of the molded product, the weld line inside the molded product can be seen and the molded product is very poor in appearance. Can do. Therefore, a very good appearance can be obtained by reflowing the resin merged in the vicinity of the weld line. As a method for reflowing the molten resin filled in the cavity, as shown in FIG. 3, it is possible to provide a shut-off valve 36 in a mold having a discarded cavity portion 35. The resin is filled in the cavity with the shut-off valve 36 closed, and the molten resin joins at the weld line generation position 37, and at the same time, the shut-off valve 36 is opened with the resin holding pressure applied, so that the weld line A part of the molten resin joined at the generation position 37 moves to change the orientation of the filled material.

[Example 1]
The metal mold | die shown in FIGS. 1-3 was used for the metal mold | die. 1 and 2 are vertical sectional views of the mold, FIG. 3 is a plan view of the mold, and FIG. 4 is a schematic top view of the molded product obtained.
In the first embodiment, the shut-off valve 36 (see FIG. 3) was molded in a closed state, and the discarded cavity portion 35 was not molded.
The first part (11 and 21) having the cooling medium passages 13 and 23 in FIG. 1 uses a Corson alloy (Matelion Brush, Mold Max-V) having a thermal conductivity of 165 J / s · m · K. Carbon steel (S55C) having a thermal conductivity of 40 J / s · m · K was used for the second part (12 and 22) having 14 and 24.
The cooling medium passages 13 and 23 are installed at an interval of 20 mm (L) at a position where the inner diameter is 8 mm and the distance L0 from the center to the cavity surface is 10 mm.
The distance L2 from the center of the cooling medium passage to the center of the rod-shaped cartridge heater is 40 mm.
A rod-shaped cartridge heater 1000 W (10 mmΦ × 400 mm, watt density 8.3 W / cm ² ) (GLE4103 manufactured by Yako Electric Co., Ltd.) was used.
The core convex part 34 in FIG. 1 and FIG. 2 forms the opening part 244 of the molded article 200 shown in FIG. Here, as shown in FIG. 3, the weld line generation position 37 is a portion where the thermoplastic molten resin injected and filled in the mold wraps around the core portion 34 and collides with it.
For the resin, a parting injection method in which a runner portion was provided on the parting surface of the mold was used.
As a material to be used, a high gloss black material obtained by adding a colorant to an ABS (acrylonitrile butadiene styrene) resin having a glass transition temperature of 105 ° C. was used.

A molded article was produced according to the injection molding process shown below.
As the molding machine, Toshiba Machine (S100V-8A) having a maximum clamping force of 300 tons was used.

[Step 1] The mold was heated and kept at a constant 120 ° C., and the mold was clamped.
[Step 2] (Resin Filling) The thermoplastic resin was filled with the mold clamped.
[Step 3] (Mold separation, cooling) With the mold clamping force lowered and the cavity closed, the first part and the second part are separated by 5 mm each, and 25 ° C cooling water is passed through the cooling medium passage. The cavity surface was cooled rapidly.
Water flow was stopped after the cavity temperature reached 70 ° C., the mold was opened 10 seconds after the water flow stopped, and water in the cooling medium passage was simultaneously discharged with compressed air.
[Step 4] (Release) Immediately after mold release, the molded body was taken out and the mold was clamped.
[Step 5] (Die Heating) The cavity surface was rapidly heated to 120 ° C. by heat transfer in the die heating part, and the process was returned to Step 1.

  The mold heating rate in Example 1 was 200 ° C./min, the temperature lowering rate was 500 ° C./min, and the molding cycle was 30 seconds.

The obtained molded body 200 had dimensions of 200 mm × 150 mm and a wall thickness of 2 mm, and had a 20 × 100 mm opening 244 and a runner portion 233 in the molded product as shown in FIG.
The appearance of the molded product was good, and no weld line was observed on the appearance, and the appearance was extremely excellent.

[Example 2]
Molding was performed using the same mold as in Example 1 except that the material of the first parts 11 and 21 on the cavity surface side of the mold was changed to the carbon steel used in the second part of Example 1. In Example 2, the mold heating rate was 150 ° C./min, the temperature falling rate was 300 ° C./min, and the molding cycle was 45 seconds.
The molded product of Example 2 was able to obtain a good appearance as in Example 1.

Example 3
A molded body was produced in the same manner as in Example 1 except that the first portions 11 and 21 and the second portions 12 and 22 were not separated when the cavity surface was cooled. The temperature increase rate of the mold in Example 3 was 70 ° C./min, the temperature decrease rate was 400 ° C./min, and the molding cycle was 70 seconds.
The molded product of Example 3 was able to obtain a good appearance as in Example 1.

Example 4
The material of the first parts 11 and 21 on the cavity surface side is changed to the carbon steel used in the second part of Example 1, and the first parts 11 and 21 and the second parts 12 and 22 are not separated when the cavity surface is cooled. Produced a molded body by the same method as in Example 1. The temperature increase rate of the mold in Example 4 was 100 ° C./min, the temperature decrease rate was 300 ° C./min, and the molding cycle was 80 seconds.
The molded product of Example 4 was able to obtain a good appearance as in Example 1.

Example 5
The same operation as in Example 1 was performed using 20% by mass of a glass fiber reinforced SAN (styrene acrylonitrile) resin as the thermoplastic resin. The initial mold temperature was set to 220 ° C. and cooling was performed to 70 ° C.
The heating rate was 200 ° C./min, the cooling rate was 500 ° C./min, and the molding cycle was 90 seconds.
FIG. 5 shows a schematic top view of the molded product 300 obtained in this example. In this example, the cavity was filled with the thermoplastic resin, and at the same time, the shut-off valve 36 shown in FIG. At this time, the resin filling from the injection molding machine was continued, so that a part of the resin at the weld line generation position moved to the discarded cavity portion 35.
As shown in FIG. 5, the obtained molded product 300 has a 20 × 100 mm opening 344, a runner portion 333 in the molded product, and a discarded mold portion 335 in the molded product, and has an excellent appearance. There was no weld line.
Further, after molding, a molded piece (A) including the weld line generation position 37 was cut out and the weld strength was measured.
The weld strength was a tensile strength of 90 MPa, and the strength was excellent.

Example 6
As a material used as a thermoplastic resin, a molded product was obtained in the same manner as in Example 5 except that an ABS resin containing 1.5% by mass aluminum flakes prepared by compounding aluminum flakes having an average particle size of 30 μm and transparent ABS was used. Was made.
The obtained molded article was excellent in appearance, and a metallic-like molded article having excellent appearance and no weld line was obtained.

[Comparative Example 1]
A molded product was produced in the same manner as in Example 1 except that the molding was performed at a constant mold temperature of 70 ° C. The molded product was inferior in appearance with a weld line in the center of the opening. The cycle time was 30 seconds.

[Comparative Example 2]
A molded product was produced in the same manner as in Example 5 except that the molding was performed at a constant mold temperature of 70 ° C. The molded product was inferior in appearance with a weld line in the center of the opening. Moreover, as a result of measuring the weld strength in the same manner as in Example 5, the tensile strength was 40 MPa and the strength was inferior. The cycle time was 30 seconds.

[Comparative Example 3]
A molded product was produced in the same manner as in Example 6 except that the molding was performed at a constant mold temperature of 70 ° C. The molded article was inferior in appearance with a black, very conspicuous weld line in the center of the opening. The cycle time was 30 seconds.

[Comparative Example 4]
Molding was performed in the same procedure as in Example 1, except that the mold had the same structure and material as in Example 4 except that the position of the heater and the position of the cooling water pipe were different. That is, the installation position of the heater was 200 mm from the cavity surface, and the cooling water pipe was installed at a position of L0 = 400 mm behind the heater (opposite side of the cavity surface). In the same manner as in Example 1, the mold cavity surface was raised and lowered at temperatures of 70 ° C. and 120 ° C. The heating rate was 20 ° C./min, the cooling rate was 10 ° C./min, and the molding cycle was 8 minutes. An appearance having no weld line was obtained on the surface of the molded product.

[Evaluation conditions]
(Tensile strength)
The tensile strength was measured according to ISO 527-1 under the following conditions.
・ Test environment: 23 ° C, 50RH%
・ Molded product: JIS K7113 No. 3 test piece ・ Tensile speed: 5 mm / min
・ Chuck interval: 50mm
-Equipment used: Instron 50kN (Instron)

As described above, the examples using the injection molding method of the present invention were capable of being molded at a high cycle, and did not generate weld lines and were excellent in appearance.
On the other hand, in the comparative example in which the mold temperature is constant, the molding cycle time is long, or a weld line is generated and the appearance is inferior.

  ADVANTAGE OF THE INVENTION According to this invention, the injection molding method which can shape | mold the thermoplastic resin molded object by which the external appearance characteristic in a high level is requested | required with a high cycle, such as external components, such as various electrical appliances and a motor vehicle, can be provided.

100 Mold 10, 20 Mold part 11, 21 First part 12, 22 Second part 13, 23 First temperature adjusting means (cooling medium passage)
14, 24 Second temperature adjusting means (bar-shaped cartridge heater)
15, 25 Heat insulation plate 16, 26 Surface opposite to the cavity surface 30 Cavity 31, 32 Cavity surface 33 Runner part 34 Mold core convex part 35 Waste mold part 36 Shut-off valve 37 Weld line generation position 40 Spring 200, 300 Molded product 233, 333 Runner portion 244, 344 opening 335 in molded product Discarded mold portion in molded product

Claims (8)

An injection molding method for obtaining a molded product by filling a mold having a cavity formed of a plurality of mold parts with a thermoplastic resin or a thermoplastic resin composite material,
The mold can at least heat the cavity surface on a side opposite to the cavity surface of the first temperature adjusting means, and first temperature adjusting means capable of cooling at least the cavity surface. A second temperature control means,
A first step of heating the cavity surface to a heating temperature equal to or higher than a melting point of the thermoplastic resin or a glass transition temperature and filling the thermoplastic resin in a mold;
After the first step, the thermoplastic resin is cooled and solidified by cooling to a cooling temperature below the melting point of the thermoplastic resin or below the glass transition temperature, and then the mold is opened to take out the molded body. Including two processes,
The temperature increase rate in the first step is 80 ° C./min or more, the temperature decrease rate in the second step is 100 ° C./min or more, and the difference between the heating temperature and the cooling temperature is 50 ° C. or more. An injection molding method. The injection molding method according to claim 1, wherein a distance L0 from the cavity surface to the first temperature adjusting means and a distance L1 from the cavity surface to a surface opposite to the cavity surface satisfy the following relationship.
(L1 / L0)> 3   The injection molding method according to claim 1 or 2, wherein the first temperature adjusting means includes one or more cooling medium passages through which a cooling medium flows, and the second temperature adjusting means is a heater.   The injection molding method according to any one of claims 1 to 3, wherein the mold part includes a first part having the first temperature adjusting means and a second part having the second temperature adjusting means. The volume V (I) (cm ³ ) of the first part (I) and the thermal conductivity C (I) (J / s · m · K) of the material of the first part (I), and the second part (II ⁵ ) and the thermal conductivity C (II) (J / s · m · K) of the material of the second part (II) satisfy the following relationship. Injection molding method.
[{V (II) × (1 / C (II))} / {V (I) × (1 / C (I))}]> 3)   The thermal conductivity C (I) (J / s · m · K) of the material of the first part (I) is the thermal conductivity C (II) (J / s · m of the material of the second part (II). 6. The injection molding method according to claim 5, which is at least 3.5 times K).   The injection molding method according to any one of claims 4 to 6, wherein when the cavity surface is cooled, the first portion and the second portion can be separated from each other.   8. The system according to claim 3, wherein the first temperature adjusting means includes a plurality of the cooling medium passages, and has at least one manifold for simultaneously circulating the cooling medium of the same temperature through the plurality of cooling medium passages. Injection molding method.