JPH07256704A - Injection mold and injection molding method using the same - Google Patents

Abstract

PURPOSE:To markedly reduce residual strain of a molded article and obtain a good molded article even in the case where molding is performed at ordinary mold temperatures by a method wherein apparent thermal conductivity is specified at least at a part of a cavity surface with which molten resin is brought into contact. CONSTITUTION:An injection mold has a movable mold 1 and a fixed mold 2, and a cavity part of the movable mold 1 is designed so as to freely move back and forth with respect to the fixed mold 2. At least a part of a cavity surface with which molten resin is brought into contact is made to have apparent thermal conductivity of 0.05 to 15kal/m.H. deg.C. By setting the apparent thermal conductivity in this range, residual strain of a molded article to be obtained is markedly reduced. This mold is used, and molten resin is injected into the cavity under a state that the cavity is a little opened. While the movable mold 1 is being pressed against the fixed mold 2, the molten resin is spread. Then, the feed of the molten resin is stopped and, while the movable mold 1 is further being pressed against the fixed mold 2, the molten resin in the cavity is cooled for hardening.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection compression molding die and a molding die for producing a molding with a small residual strain when a molding is manufactured from a thermoplastic resin by an injection compression molding method. It relates to the injection compression molding method used.

[0002]

2. Description of the Related Art As a method of reducing residual strain when a molded product is manufactured from a thermoplastic resin by injection molding, conventionally, a molding material is injected into an open mold and then the mold is closed at high pressure. Compression molding methods have been used.

[0003]

According to the injection compression molding method, after the molten resin is injected and filled, a part of the mold (movable mold) is moved or the mold clamping force is used to apply a uniform pressure to the entire molten resin. Is a method of molding while adding, and is characterized in that the residual strain of the molded product is reduced. However, the molten resin in the cavity immediately after filling usually has an uneven temperature distribution,
Pressure distribution etc. has occurred. Therefore, the residual stress in the molded product becomes uneven, and the transparent molded product causes image distortion, which is a cause that a good product cannot be obtained.

In order to solve such a problem, a method is generally used in which the mold temperature is set to be equal to or higher than the glass transition temperature of the resin so that the resin is relaxed so that the temperature and the pressure are made uniform and the residual stress unevenness is reduced. . However, if the mold temperature is raised, the cooling time becomes longer, and the molding efficiency is lowered. Therefore, there is a demand for a method of reducing residual strain without increasing the mold temperature.

On the other hand, it has been reported that reproducibility and the like of the mold surface are improved when injection molding is performed with a mold in which the mold wall surface forming the cavity is coated with a low heat conductive material. That is, in Japanese Patent Laid-Open No. 63-306017, the apparent thermal conductivity of the cavity surface of the mold into which the molten resin flows is 0.05 to 15.0 kc.
Disclosed is an injection molding die, which is characterized in that the pressure is set to al / m · Hr · ° C.

Molded products molded from a thermoplastic resin that can be generally used for injection molding using such a mold have a smaller residual strain than molded products conventionally obtained by using a mold. However, in the case of a molded product that is transparent and requires an optical image quality, excessive stress remains near the gate, causing image distortion, and a good molded product cannot be obtained.

[0007]

Means for Solving the Problems As a result of intensive investigations by the present inventors, an injection-molded article having less residual distortion as well as excellent reproducibility of the mold surface, etc., which satisfies the optical image quality, was obtained. , Using a mold for injection compression molding in which the apparent thermal conductivity of the cavity surface with which the molten resin comes into contact is 0.05 to 15 kcal / m · Hr · ° C, with the mold open The inventors have found that by adopting a new injection compression molding method in which a molten resin is injected into a cavity to perform injection compression molding, it is possible to obtain a good molded product with a remarkably small residual strain, and arrived at the present invention.

That is, the gist of the present invention is that the apparent thermal conductivity of at least a part of the surface of the cavity in contact with the molten resin is 0.05 to 15 kcal / m · Hr · ° C. A mold for molding, and using the mold, while injecting the molten resin into the cavity with the cavity opened, while spreading the molten resin in the cavity while pressing the movable mold against the fixed mold, Then, the injection compression molding method is characterized in that the supply of the molten resin is stopped and the molten resin in the cavity is cooled and solidified while further pressing the movable mold.

The present invention will be described in detail below. The mold of the present invention is a mold for injection compression molding. The mold for injection compression molding generally means that a part (movable mold) of the mold is moved after the molten resin is injected and filled. This is a method of molding while applying uniform pressure to the entire molten resin by utilizing the clamping force. In the present invention, there is no particular limitation as long as it is a conventionally used injection compression molding mold, but preferably,
A movable mold is used that can move back and forth with respect to a fixed mold. By moving the movable mold, molding is performed while applying pressure to the injected molten resin.

In the injection compression molding die of the present invention, the apparent thermal conductivity of at least a part of the die surface in the cavity filled with the molten resin is 0.05 to 15 kcal / m · Hr · ° C. Is characterized by. By controlling the apparent thermal conductivity within this range in the injection compression molding die, the residual strain of the obtained molded product is significantly reduced. On the other hand, this is 0.0
If it is less than 5 kcal / m · Hr · ° C, the solidification of the molten resin will be delayed,
The molding cycle becomes long and the practical value is drastically reduced. On the other hand, when it exceeds 15 kcal / m · Hr · ° C, the level is the same as that of a normal mold, and the excellent effect of reducing residual strain cannot be obtained.

In order to obtain a mold having such a specific thermal conductivity, it is considered that the cavity surface of the mold should be coated or coated with a resin as a thin film. On the other hand, it is weak and has a problem in wear resistance. Therefore, in order to obtain a mold according to the present invention, an apparent heat is applied along a part of the mold cavity surface or a stroke, particularly a mold cavity surface corresponding to a part of the molded article where abrasion resistance is required. A thermal conductive cushioning material having conductivity satisfying the above requirements is interposed.

Here, the apparent thermal conductivity in the present invention is the thermal conductivity at 0 ° C. of the cushioning material used,
When more than one type of cushioning material is used, calculate with the following formula.

[0013]

[Equation 1] l ₀ : Total thickness of the buffer materials that are stacked 1 _n : Thickness of each buffer material that is stacked λ ₀ : Thermal conductivity of the entire buffer material that is stacked at 0 ° C. λ _n : Of each buffer material that is stacked Thermal conductivity at 0 ℃

In order to interpose one or more heat-conducting buffer materials along the surface of the mold cavity, a mold in which two or more layers of materials, which cover the buffer material with a metal, are stacked, or Or, along the mold cavity surface, glassy or Al ₂ O ₃ , Si, SiO ₂ , MgO, TiN
A thermally conductive buffer material made of a metal or a metal compound-based ceramics may be coated.

The thickness of the thermally conductive cushioning material interposed along the surface of the mold cavity can be determined in consideration of the thermal conductivity of the material, but is preferably in the range of 0.05 to 5 mm. Specific examples of the buffer material used for the two or more heat conductive buffer layers having a metal layer on the surface include cellophane, cellulose acetate, polycarbonate, polyvinyl chloride, vinylidene fluoride, polyester, polysulfone, and epoxy resin. , Glass, ceramics, etc., but not limited to these examples.

As a method of interposing these heat-conductive cushioning materials on the surface of the mold cavity, if the surface of the mold cavity is curved or flat, it is melted and sprayed uniformly on the surface of the mold. Alternatively, a method of coating and solidifying after coating can be adopted, and when the cavity surface is flat, a method of previously processing a heat conductive cushioning material into a thin plate and attaching it to the mold cavity surface and fixing it Can also be adopted.

As a method for providing a metal layer on such a cushioning material, a low melting point alloy represented by a tin-based alloy is sprayed, or an iron plate of about 1 to 20 mm is uniformly formed along the shape of the cavity surface. It can be carried out by a conventionally known method, such as adhering to the cushioning material layer via an adhesive. Almost all adhesives such as acrylic, urethane, epoxy, polyester, etc. can be used as the adhesive, but thermosetting urethane-based and epoxy-based adhesives are particularly suitable to prevent thermal deterioration due to molten resin. Is.

Further, glass, metal, metal compound, etc.
How to provide which ceramic layer on the mold cavity surface
As for the paste-like ceramics,
Generally, the method of coating on the tee surface and then sintering
However, the entire cavity is made of ceramics.
It is also possible to use types. Also, chemical vapor deposition or
A on the surface of the mold cavity using a technique such as physical vapor deposition.
l₂O₃, Si, SiO ₂, MgO, TiN, etc.
Forming a metal or metal compound layer with low conductivity
Is also possible.

The material of the mold of the present invention is not particularly limited as long as it is a metal generally used for molds such as steel, alloys containing steel as a main component, aluminum alloy, zinc alloy and the like. The injection compression molding method of the present invention uses the above-mentioned mold of the present invention to inject molten resin into the cavity while the cavity is opened, and melt the interior of the cavity while pressing the movable die against the fixed die. While spreading the resin, then stopping the supply of the molten resin and further pressing the movable mold,
This is performed by cooling and solidifying the molten resin in the cavity.

Specifically, first, the mold is in a "closed" state, and the cavity has a product wall thickness of about 1 to 5 mm and a compression allowance of about 1 to 5.
The distance is set to 10 mm, and the molten resin is injected into the mold cavity. Well-known conditions are adopted as the molding conditions at this time, for example, the material temperature (resin temperature) is about 200 to
It is preferable that the temperature is 350 ° C., the mold temperature is about 50 to 150 ° C., and the resin injection speed is about 100 to 200 mm / sec.

While the molten resin is being injected, the movable die cavity is pressed against the stationary die by the injection compression piston, the molten resin in the cavity is spread and filled in the die cavity, and then the on-off valve of the injection molding machine is opened. Close. The injection pressure is preferably about 20 to 100 tonf, and the pressure control is preferably performed in multiple stages. After closing the on-off valve of the injection molding machine, the mold shrinks due to cooling in the cavity, and while pressing the movable mold cavity, the molten resin in the mold cavity is cooled and solidified, and then the mold is opened. Demold the molded product.

The type of molding material that can be used in the mold according to the present invention is not particularly limited, and any resin that can be injection-molded may be used, and examples thereof include polycarbonate, polyamide and polyester. .

[0023]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples without departing from the gist thereof. An outline of an injection molding die and a molding machine used in this example is shown in FIG. Figure 1
In the figure, 1 is a movable type, 2 is a fixed type, 3 is a heat conductive cushioning material, 4 is a back plate, 7 is an ejector plate, and 8 is a pressing rod, respectively. Is connected to a pressing rod and can move back and forth.

Further, two cavities were provided, and one of them was a comparative example, so that there was no heat conduction buffering material and only the back plate was used. Figure 1
Inside, 5 is an injection compression piston, 6 is an injection compression block, and 9
Is a nozzle part, 10 is an on-off valve, 11 is a resin material, 12 is a barrel, 13 is a screw, and 14 is an injection device. The mold clamping direction is the direction indicated by S.

The molding machine used in this experiment was SG75SYCAP-MIIIA manufactured by Sumitomo Heavy Industries, Ltd. (Example 1) The above-mentioned mold provided with two cavities each having a size of 100 mm x 100 mm x 3 mm was used, one of the cavities was a back plate made of carbon steel having a thickness of 9 mm, and heat was transferred to the back surface of the back plate. A 3 mm glass plate was provided as a buffer layer on the movable side and the fixed side, respectively, as a coating layer. The apparent thermal conductivity of the cavity surface was 0.80 kcal / m · Hr · ° C. The other cavity has 12m on both the movable and fixed sides.
m-thick carbon steel was provided for each of the comparative examples.

Flat plate molded articles were obtained by injection compression molding using this mold and molding machine. The resin used for molding and molding conditions are as follows. Resin: Polycarbonate (Novalex 7022L1 manufactured by Mitsubishi Kasei Co., Ltd.) Molding conditions: Material temperature 300 ° C, mold temperature 80 ° C, injection speed 150mm / sec Injection compression force 40tonf, pressure control 3 stages, injection compression stroke 5mm Molding In the operation, the mold is closed and the cavity has a product thickness of 3 mm and a compression allowance of 5 mm, the molten resin is injected into the mold cavity, and the movable mold cavity is pressed against the fixed mold by the injection compression piston. While expanding the molten resin in the cavity and filling the mold cavity, the on-off valve of the injection molding machine is closed, and the volume of the cavity shrinks as the cavity cools, while further pressing the movable mold cavity. After the molten resin in the mold cavity was cooled and solidified, the mold was opened and the molded product was demolded.

With respect to the obtained flat plate molded product, the strain (stress) in the transparent object is measured by a polarimeter (Toshiba Glass Co., Ltd., strain inspector S).
VP-100). The results are shown in Table 1.

(Embodiment 2) In the mold used in Embodiment 1, instead of the 3 mm glass plate, a thermal conductivity buffering material consisting of 3 layers of 1 mm urethane foam, 1 mm vinyl chloride, and 1 mm iron plate was used. Provided. Using this mold, a dwarf plate molded product was molded in the same procedure as in Example 1. Table 1 shows the apparent thermal conductivity of the thermal conductivity buffer material coating layer of this mold, and the strain (stress) measurement result in the transparent object by a polarimeter for the obtained molded product.

(Example 3) In the mold used in Example 1, the back plate was made of carbon steel having a thickness of 11 mm, and ZrO ₂ -Y ₂ O ₃ ceramics having a thickness of 1 mm was used on the front side of the back plate, that is, on the cavity surface. A thermal conductivity cushioning material coating layer was provided by plasma spraying. Using this mold, a flat plate molded product was molded in the same procedure as in Example 1. Table 1 shows the apparent thermal conductivity of the thermal conductivity buffer coating layer of this mold, and the strain (stress) measurement result in the transparent object by the polarimeter of the obtained molded product.

(Example 4) In the mold used in Example 1, 3 mm of stainless steel (SUS30) was attached to the back side of the back plate.
A flat plate molded product was molded under the same conditions as in Example 1 except that 4) was used, and the obtained molded product was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0031]

[Table 1]

[0032]

As described above, in the conventional injection compression molding, a method is generally used in which the mold temperature is set to the glass transition temperature of the resin (about 145 ° C. in the case of polycarbonate) or higher to reduce the residual strain in the molded product. Although it has been performed, it can be seen that the residual strain of the molded product obtained by using the mold and the molding method according to the present invention is significantly reduced even at a normal mold temperature.

[Brief description of drawings]

FIG. 1 is a schematic view of an injection molding die and a molding machine used in this embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Movable type 2 Fixed type 3 Thermally conductive buffer material 4 Back plate 5 Injection compression piston 6 Injection compression block 7 Ejector plate 8 Push rod 9 Nozzle part 10 Open / close valve 11 Resin material 12 Barrel 13 Screw 14 Injection device

Claims (3)

[Claims] 1. The apparent thermal conductivity of at least a part of the surface of the cavity in contact with the molten resin is 0.05 to 15 kcal.
Mold for injection compression molding, characterized in that / m ・ Hr ・ ° C. 2. A mold for injection compression molding according to claim 1, wherein the mold has a movable mold and a fixed mold, and the cavity of the movable mold is movable back and forth with respect to the fixed mold. 3. The apparent thermal conductivity of at least a part of the surface of the cavity in contact with the molten resin is 0.05 to 15 kcal.
/ m · Hr · ° C, using a mold for injection compression molding, the molten resin is injected into the cavity while the cavity is opened, and the cavity is pressed while the movable die is pressed against the fixed die. Characterized in that the molten resin in the cavity is spread, then the supply of the molten resin is stopped, and the molten resin in the cavity is cooled and solidified while pressing the movable mold.
Injection compression molding method.