JPH0691736A - Extrusion blow-molding method - Google Patents

Abstract

PURPOSE:To provide a non-circular extrusion blow-molded article which is superior in die surface reproductivity and luster by a method wherein a main die with a specified thermal conductivity, and a die with a die wall surface covering heat-insulating layer, which forms a cavity, are used, and the dies are closed while an extruded parison is not brought into contact with the die wall surface, and then, blow-molding is performed. CONSTITUTION:The surfaces of dies to form a cooled die cavity of main dies 1 made of a metal of which the thermal conductivity at a room temperature is 0.05cal/cm.sec. deg.C or higher are covered by a heat-insulating layer 2 in a mirror finished surface form, of which the thermal conductivity is 0.02cal/cm.sec. deg.C or lower with a thickness of 0.05-2mm. Using such dies, a parison 4 of a thermoplastic resin which is extruded into a circular shape is pinched by the dies, and the dies are closed. The parison 4 is deformed by the dies, and A part and B part of the parison 4 come into contact with the wall surfaces of the dies. A compressed gas body is blown into the parison, and a blow- molding is performed. By this method, a non-circular blow-molded article which is superior in die surface reproductivity can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin extrusion blow molding method.

[0002]

2. Description of the Related Art In blow molding of a thermoplastic resin, it is generally necessary to improve the reproducibility in imparting the shape condition of the mold surface to the molded product and to improve the gloss of the molded product, usually the mold temperature or the resin temperature. Can be achieved to some extent by selecting molding conditions such as increasing the pressure or increasing the blow pressure.

The mold temperature has the greatest effect among these factors, and the higher the mold temperature, the better.
However, if the mold temperature is increased, the cooling time required for the cooling and solidification of the plasticized resin becomes longer, and the molding efficiency is lowered.

Therefore, there is a demand for a method of improving the reproducibility of the mold surface without increasing the mold temperature, and not increasing the required cooling time even if the mold temperature is increased. There is also a method in which heating and cooling holes are attached to the mold and heating and cooling of the mold are repeated by alternately flowing a heat medium and a refrigerant, but this method also consumes a lot of heat, Cooling time becomes longer.

A method for improving mold surface reproducibility by coating a mold wall forming a mold cavity with a substance having a low thermal conductivity is disclosed in US Pat. No. 3,544,518 for injection molding. Polyethylene terephthalate, polyphenylene sulfide and the like are shown as substances having low conductivity. Also in extrusion blow molding, a method of coating the mold wall surface with a substance having a small thermal conductivity is disclosed in US Pat. No. 5,041,247. Compared to injection molding, extrusion blow molding takes a longer time from the time the resin contacts the mold to the time when high pressure is applied, the resin temperature of the extruded parison is low, or the parison has a high viscosity. For this reason, it is said that the effect of coating the mold wall surface with a substance having a small thermal conductivity is unlikely to appear.

[0006]

When a circular blow molded product such as a circular bottle or a circular drum is blow molded from a circular parison, the parison is blown and comes into contact with a mold, and at the same time, the parison is subjected to a high blow pressure, resulting in a resin. Is pressed against the mold wall with high pressure. In such a case, the effect of coating the mold wall surface with a substance having a small thermal conductivity is remarkable.

In recent years, blow-molded products have come to be molded from non-circular blow-molded products such as circular molded products to plate-shaped molded products or molded products having a more complicated shape. In such a case, the extruded parison comes into contact with the mold wall surface when the mold is closed. Then, the contacted parison immediately begins cooling. Even if the mold wall surface is coated with a substance having a low thermal conductivity, the effect is small in such a case. The present inventors have arrived at the present invention as a result of repeated research on a blow molding method for solving this problem.

[0008]

[Means and Actions for Solving the Problems]
Ming is extrusion blow molding of non-circular blow molding of thermoplastic resin
Shape, the thermal conductivity at room temperature is 0.05 cal /
cm ・ sec ・ Main mold made of metal above ℃
The thermal conductivity of the mold wall surface forming the bite is 0.002 ca.
l / cm ・ sec ・ 0.05 ~ 2mm with heat insulation layer below ℃
Using a thickly coated mold, push the extruded parison into the mold wall
Close the mold without substantially touching the surface, then blow
The extrusion blow molding method is characterized by molding.

The present invention will be described in detail below.

The synthetic resin that can be used in the extrusion blow molding of the present invention is a thermoplastic resin that can be used in general blow molding. For example, a general thermoplastic resin such as a styrene polymer or a copolymer thereof, an olefin polymer such as polyethylene or polypropylene or a copolymer thereof, a vinyl chloride polymer or a copolymer thereof, a polyamide or a polyester can be used.

When these resins are mixed with various reinforcing materials and various fillers, or when they are polymer alloys, a particularly great effect is obtained. For example, in the above resin,
One or more kinds of rubber, glass fiber, asbestos, calcium carbonate, talc, calcium sulfate, wood powder and the like can be blended.

The thermal conductivity described in the present invention is 0.05 cal.
/ Cm ・ sec ・ Main mold material above ℃ means iron or iron
Mainly steel, aluminum or aluminum which is the main component
For synthetic resin molds such as alloys and zinc alloys
Including the metals used. Especially steel is the best
Can be used.

Various synthetic resins can be used for the heat insulating layer of the present invention. Preferred conditions for the heat insulating material constituting the heat insulating layer are (1) low thermal conductivity, (2) excellent heat resistance,
(3) Tensile strength and elongation are large, and it is resistant to cooling and heating cycles.
(4) Large surface hardness, (5) Excellent wear resistance,
(6) Good application to the mold body, (7) Good adhesion to the mold body, (8) Surface polishing, etc.

Thermal conductivity is 0.002 cal / cm at room temperature
・ Sec ・ It is necessary to keep the temperature below ℃.
It meets this.

Since the heat-plasticized molten resin is extruded and molded in the mold cavity, it is exposed to a vigorous cooling / heating cycle between a high temperature of 200 ° C. or higher and room temperature of the mold body. It is preferable that the heat insulating material is a material that has a high strength and elongation, is heat resistant, and can withstand a heat cycle. Further, it is preferable that the adhesiveness to the main mold is good and peeling does not occur in the cooling / heating cycle. Further, it is preferable that the surface hardness is large, the abrasion resistance is excellent, and the surface is not easily scratched during use.

Further, in order to uniformly coat the surface of the mold having a complicated shape with a heat insulating layer, it is preferable that the heat insulating material has applicability. Further, since it is extremely difficult to apply the heat insulating material to the surface of a complicated mold cavity in a mirror surface, it is preferable to polish the surface of the applied heat insulating material to finish it in a mirror surface. Therefore, it is preferable that the heat insulating material can be polished and can be mirror-finished.

Polyimide is suitable as a substance satisfying these conditions.

There are various types of polyimide, and they are classified as shown in Table 1 below.

[0019]

[Table 1] In the present invention, it is preferably covered with a heat insulating layer of polyimide. For this coating, a linear polyimide ring-closed solution, a polyimide precursor solution, or a thermosetting polyimide oligomer or monomer solution can be used. The solvent of this solution is a solvent that evaporates prior to curing or concurrently with curing when applied to a mold and heated, and is a commonly used organic solvent.

The polyimide formed by applying the solution to the mold and then heating it adheres to the mold surface. The surface of the polyimide thus obtained has a large surface hardness, is excellent in abrasion resistance, and is hardly scratched during use.

In blow molding, a heated and plasticized synthetic resin is extruded into a cooled mold and then cooled and molded in the mold. For each molding, 100 is taken on the surface of the mold. The heating and cooling up to ℃ are repeated. Since the thermal expansion coefficients of polyimide and metal such as iron are different by one digit, a severe stress is generated at the interface between the metal and the polyimide every time heating and cooling up to 100 ° C. are repeated. As a polyimide capable of withstanding this stress thousands of times or tens of thousands of times, a tough linear high-molecular-weight polyimide having large breaking strength and breaking elongation is preferable.

When the temperature difference between heating and cooling is small, or when the number of moldings is small, a thermosetting polyimide can be used as the polyimide. Bismaleimide-based resins, acetylene-terminated polyimides, thermosetting polyimides such as nadic modified polyimide are highly crosslinked,
It is inferior to linear polyimides in terms of resistance to severe thermal cycling.

In particular, the polyimide which can be favorably used in the present invention is obtained by coating a linear high molecular weight soluble type polyimide precursor on the surface of a mold and then heating it to form an imide ring. Is a linear high molecular weight polyimide.

Table 2 shows examples of linear type high molecular weight polyimides which can be favorably used in the present invention. In addition, Tg represents a glass transition temperature.

[0025]

[Table 2] The Tg of the linear polyimide varies depending on the constituents, and examples are shown in Tables 3 and 4. According to the knowledge of the present inventors, Tg is preferably 200 ° C. or higher, more preferably 230
It was above ℃.

[0026]

[Table 3]

[0027]

[Table 4] In order to coat this complex mold surface with polyimide and firmly adhere it, it is most preferable to apply a polyimide precursor solution and then heat to form the polyimide.

In the present invention, a solution of a polyimide is used as described above, and a repeating unit of a typical example of polyamic acid which is the most preferable linear polyimide precursor is
Shown in.

[0029]

[Chemical 1] The polymer of the polyimide precursor has good adhesion to the mold because it is a carboxyl group or the like, and a polyimide thin layer adhered to the mold surface can be obtained by reacting and forming a polyimide on the mold surface.

To the polyimide precursor solution, an additive for adjusting the viscosity at the time of coating, adjusting the surface tension of the solution, adjusting the thixotropy, or / and adhering to the mold can be added. Additives for raising can be added. Among these polyimides, PMDA-based polyimides are most preferable because they are excellent in heat resistance and mechanical properties. In particular, a varnish modified for coating can be favorably used.
However, additives that greatly increase the thermal conductivity of polyimide are not preferred. Further, an additive that greatly reduces the adhesion between the polyimide and the mold is not preferable either.

Since the polymer of the polyimide precursor contains a carboxyl group and the like, it has good adhesion to the mold, and by reacting and forming polyimide on the mold surface, a polyimide thin layer adhered to the mold surface can be obtained.

Although the heat insulating material used in the present invention has been described using polyimide, the present invention has a thermal conductivity of 0.002 cal /
Basically, substances of cm / sec / ° C or less can be used.
However, it is necessary that the heat insulating layer is in close contact with the main mold.

The preferable adhesion with the main mold is 50 at room temperature.
0 g / 10 mm width or more, more preferably 1 kg /
The width is 10 mm or more. This is 10m with a tight insulation layer
It is the peeling force when cut into m width and pulled at a speed of 20 mm / min in the direction perpendicular to the adhesive surface. The peeling force varies considerably depending on the measurement location and the number of measurements, but the minimum value of the variation is important, and it is preferable that the peeling force is stable and large.

The thickness of the heat insulating layer is appropriately selected within the range of 0.005 to 2 mm. If the thickness is less than 0.005 mm, the effect of improving the surface of the molded product is small, and if it exceeds 2 mm, the cooling effect of the mold is reduced and the molding efficiency is reduced. The higher the mold temperature is, the thinner the heat insulating layer is, and the lower the mold temperature is, the thicker the heat insulating layer is.
It is properly selected within the range.

In order to further improve the surface smoothness of a thin layer of a heat insulating material such as polyimide or to further improve the scratch resistance of the surface, 1/10 of the thickness of the polyimide layer or the like
It is also possible to apply another material thinner than the vicinity to the surface of the polyimide, etc., and it is included in the present invention. It is also possible to apply a paint generally called a hard coat, which has been used for improving scratch resistance, to the surface of a synthetic resin sheet or mold. For example, a thermosetting type silicone hard coat agent can be favorably used and is preferable for the present invention.

Furthermore, by introducing a fluid such as a heated gas body into the mold cavity, a better molded product surface can be obtained. By introducing a heated fluid such as a gas body into the mold cavity, the mold wall surface forming the mold cavity can be selectively heated.

The temperature of the heating gas introduced into the mold cavity may be higher than the mold temperature, but it is more effective to introduce the high temperature gas for a short time, and the gas temperature is 100% higher than the mold temperature.
℃ or more, preferably 200 ℃ or more, more preferably 30
A gas having a temperature of 0 ° C. or higher is preferable.

Various methods can be considered as a method of introducing the heating gas into the mold cavity. As an example, a hole having a size that allows the gas to pass but the molten resin cannot pass is opened in the mold cavity. Heated gas is introduced through the holes. Therefore, pores must be provided at positions suitable for the inlet and outlet of the heating gas. The size of the pores through which gas can pass but molten resin cannot pass varies depending on the type of resin, molding conditions, etc.
Elongated pores with 0.2 mm voids are suitable. However, in a normal die, the airtightness is not airtight, and the parting surface satisfies the condition of this void. In particular, the die having the airtight parting surface is provided with the pores as described above to introduce the gas.

The non-circular blow molded product described in the present invention is
The outer dimension of the molded product after blow molding is measured in each direction perpendicular to the direction of extrusion of the parison, and the ratio of the longest direction to the shortest direction is 2 times or more, preferably 2.5 times or more, more preferably Means a molded product of 3 times or more and 10 times or less.

The term "closing the mold without substantially contacting the extruded parison with the mold wall surface" in the present invention means that the parison is not substantially in contact with the mold wall surface when the mold is closed. Say the state. When extrusion blow molding a circular blow molded product such as a drum container from a circular parison, the parison is molded without substantially contacting the wall surface of the mold when the mold is closed, but it is a non-circular blow molded product. In blow molding, a part of the parison often comes into contact with the wall surface of the mold when the mold is closed.

The contact described in the present invention excludes the contact between the die and the parison at the cut-out portion sandwiching the extruded parison with the die, and only the contact at the circumferential portion of the parison is a problem. In the invention, it is expressed as substantial.

The present invention is a method of deforming an extruded parison when the mold is closed so that the parison is substantially not in contact with the wall surface of the mold. According to the shape of the non-circular blow-molded product, an elliptical or square parison can be extruded to be substantially non-contact, which is also included in the present invention.

A method of deforming the extruded parison so that it is not in contact with the mold wall surface when the mold is closed is preferably used. As this method, a method of projecting pins or ribs from the mold wall surface can be favorably used. In this case, the pins and ribs come into contact with the parison, but this also falls within the range of substantially non-contact in the present invention.

At least one of the tips or side surfaces of the pins or ribs that come into contact with the parison is preferably covered with a heat insulating layer thicker than the heat insulating layer of the mold wall surface, which is 1.5 times the thickness of the heat insulating layer of the mold wall surface. The thickness is preferably the above, and more preferably twice the thickness of the heat insulating layer. Alternatively, the main body of the pin or rib can be made of a tough heat-resistant synthetic resin. The pin or rib preferably applies gas pressure to the inside of the parison to return the pin or the like to the mold wall surface during blow molding.
The timing for returning the pins and the like to the mold wall surface is selected from immediately before the pressurized gas body is blown to immediately after the parison is blown.

Pins, ribs, etc. are circular pins, square pins, and rib-shaped protrusions, and are 1/10 of the area of the mold wall surface.
Various protrusions having the following areas. In the present invention, it is preferable that the pins or the like protruding from the wall surface of the mold be returned to the wall surface of the mold during blow molding, and the shape of the molded product obtained depends on the timing of returning. For example, if the rib-shaped projection is returned to the wall surface of the mold immediately after the parison is blown, the rib-shaped material is formed in the hollow portion inside the blow-molded product.

The method of the present invention will be described with reference to the drawings.

FIG. 1 shows the stage immediately before the blowing step in the conventional extrusion blow molding. FIG. 2 shows the blow molded product molded in FIG. 3 to 5 show the steps of extrusion blow molding of the present invention.

In FIG. 1, the cooled mold surface of the main mold 1 is covered with a mirror-like heat insulating layer 2, and a parison 4 made of a thermoplastic resin extruded in a circular shape is sandwiched between the molds to close the mold. .
The parison 4 is deformed by the mold, and the parts A and B of the parison 4
The part contacts the wall surface of the mold. A pressurized gas body is blown into the parison and blow molding is carried out to obtain a non-circular blow molded product shown in FIG. In the non-circular blow molded product, the surfaces of the parts A'and B'that are blow molded after coming into contact with the wall surface of the mold have poor mold surface reproducibility, whereas the other parts have a mirror-like heat insulation. The surface of the layer has a well reproduced mirror surface.

When the heat-plasticized resin comes into contact with the surface of the heat-insulating layer coated on the surface of the mold, the surface of the heat-insulating layer is heated by the resin and cooling starts immediately. Therefore, when the resin is pressed against the mold wall surface with a high gas pressure at the time of contact, the mold surface reproducibility is improved. When the mold surface temperature when the resin is pressed against the mold wall surface with a high gas pressure is equal to or higher than the softening temperature of the resin, the mold surface reproducibility is remarkably improved.

The parts A'and B'shown in FIG. 2 have a long time from the contact with the mold surface to the blow molding, and therefore the mold surface reproducibility is poor and the effect of coating the mold surface with a heat insulating layer is shown. Almost never.

3 to 5 show the molding process of the present invention. A pin 6 driven by an actuator 5 such as an air cylinder is projected from the mold wall surface of the mold in which the cooled mold surface of the main mold 1 is covered with a mirror-like heat insulating layer 2. The tip of the pin 6 is covered with a heat insulating layer 7 that is thicker than the heat insulating layer on the mold wall. A circular parison 4 is extruded between the open molds (Fig. 3).

Next, the mold is closed to form the mold cavity 3. The parison 4 has a pin 6 in the mold cavity 3.
Therefore, there is no substantial contact with the direct mold wall (Fig. 4).

Next, the pressurized gas body is pressed into the parison and, at the same time, the protruding pins are returned to the mold wall surface, and blow molding is carried out to obtain a non-circular blow molding product 8 (FIG. 5).

The surface of the blow-molded product 8 has good mold surface reproducibility due to the effect of the heat insulating layer 2 on the mold surface, and a mirror-like surface is obtained. Although the pin 6 contacts the parison 4, its area is small, and the thickness of the heat insulating layer 7 at the tip of the pin 6 is preferably 1.5 times or more the thickness of the mold surface heat insulating layer, more preferably 2
The difference in appearance can be made inconspicuous by setting the time to be 10 times or more.

[0055]

EXAMPLE Extrusion blow molding was carried out by the method shown in FIG. 3 using the following molds and materials.

Main mold: made of steel (S55C), 3
00 × 95 × 20mm (Parison extrusion direction is 300m
m) has a rectangular parallelepiped mold cavity 3, and the mold surface is a mirror surface plated with hard chrome. The thermal conductivity of steel is 0.2 cal / cm · sec · ° C.

Pin: The main mold is provided with a steel pin 6 that can be projected from the mold wall surface by an air cylinder and returned to the mold wall surface.

Heat insulation layer: The surface of the main mold and the tip of the pin 6 are coated with polyimide.

As the polyimide, a linear PMDA polyimide precursor solution "Trenice # 3000" (trade name of Toray Co., Ltd.) is applied and then cured by heating to form a polyimide, and then the surface is polished to give a mirror-like polyimide. Form the layers. The polyimide on the surface of the main mold is 0.1 mm thick, and the tip of the pin is 0.4 mm thick.

The polyimide has a Tg of 300 ° C. and a thermal conductivity of 0.0007 cal / cm · sec · ° C.

Thermoplastic resin: ABS resin, Stylak ABS A4593 (trade name of Asahi Chemical Industry Co., Ltd.) A non-circular blow molded product was molded by the molding method described with reference to FIG. The surface of the ABS resin blow molded product is excellent in uniform gloss.

Glossiness: 80% Glossiness measurement method: JIS K7105, reflection angle 60 degrees Molding condition: Main mold temperature: 80 ° C. ABS resin extrusion temperature: 220 ° C. Blow molding gas pressure: 6 kg / cm ² G

[0063]

Comparative Example Using the pinless mold of the example, the same material and the same molding conditions as the example were used to obtain the molded product shown in FIG. 2 by the method shown in FIG.

A'part and B'of ABS resin blow molded product
The gloss of the part is poor, and the gloss of the other part is excellent.

Glossiness of A'part and B'part: 6% Glossiness of other part: 80%

[0066]

Industrial Applicability According to the method of the present invention, a non-circular blow molded product having extremely excellent mold surface reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a stage immediately before a blowing step in conventional extrusion blow molding.

FIG. 2 is a cross-sectional view of a blow molded product molded through the steps of FIG.

FIG. 3 is a cross-sectional view showing a stage before the mold is closed in the molding process of the present invention.

FIG. 4 is a cross-sectional view showing the stage immediately before the blowing process in the molding process of the present invention.

FIG. 5 is a cross-sectional view showing a stage at the time of completion of blowing in the molding process of the present invention.

[Explanation of symbols]

 1 main mold 2 heat insulation layer 3 mold cavity 4 parison 5 actuator 6 pin 7 heat insulation layer 8 non-circular blow molded product

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Claims (4)

[Claims] 1. Pressing a non-circular blow molded product of a thermoplastic resin.
In blow molding, the thermal conductivity at room temperature is 0.0
5 cal / cm ・ sec ・ Main mold made of metal above ℃
Of the mold cavity forming the mold cavity of
02cal / cm ・ sec ・ 0.05 for insulation layer below ℃
Extruded parison using mold coated to ~ 2mm thickness
Close the mold without substantially contacting the mold wall with
The extrusion blow molding method is characterized in that the blow molding is performed by. 2. The mold is closed by a pin, rib or the like protruding from the wall surface of the mold without substantially contacting the parison with the wall surface of the mold, and the pin, rib or the like is returned to the wall surface of the mold during blow molding. The method of claim 1 wherein: 3. The method according to claim 2, wherein at least one of the tips or side surfaces of the pins, ribs or the like is covered with a heat insulating layer having a thickness larger than that of the heat insulating layer on the mold wall. 4. The method of claim 1, wherein the heat insulating layer comprises linear polyimide.