JPH0813496B2 - Method for producing foam having fine cells - Google Patents

Description

[Detailed Description of the Invention] (Industrial field of application) Since foamed plastic products have improved properties such as heat insulation, lightness, appearance (pearly surface), and economic efficiency, they are added as products. It is manufactured by various methods as a method of increasing the value.

The extrusion foaming method using a chemical foaming agent to be improved in the present invention has been utilized as a method for producing a foamed product having a relatively low expansion ratio, but in recent years, the demand for its appearance has increased and the product has a wide variety of views. There has been a demand for miniaturization of influencing bubbles.

TECHNICAL FIELD The present invention relates to a method for making fine cells of a foam produced by an extrusion foaming method using a chemical foaming agent.

(Prior Art) In order to make fine bubbles in a foam produced by a method of extruding and foaming a thermoplastic resin using a chemical foaming agent,
The blowing agent does not completely decompose in the extruder and remains undecomposed in the extruder as the molten resin is extruded into the high pressure to low pressure region, such as when the extrudate is extruded from the mold. It is known that it is necessary to adjust the extrusion operating conditions so that the appropriate amount of blowing agent decomposes in the extrudate for a short time before the expansion of the cells has ended. Such a state is realized by adjusting the extrusion operation conditions so that the decomposition of the foaming agent reaches a peak when the molten resin is extruded from the mold. This prior art will be described in detail with reference to FIG.

FIG. 1 is a schematic view from above of an example of an apparatus conventionally used for extrusion foaming.

In extrusion foaming using this apparatus, the chemical foaming agent and the resin raw material are supplied from the hopper 1 to the extruder 2, melt-kneaded in the extruder and flow into the mold 3 from the extruder. In this case, the chemical foaming agent receives heat from the extruder, the mold and the resin to start decomposition, and the decomposition peak is adjusted so as to occur near the mold outlet 4 by adjusting the extrusion operation conditions.

The resin that has flowed into the mold 3 is shaped into a predetermined shape by the mold and extruded into the low pressure region. In this extrusion step, the gas generated by the decomposition of the foaming agent expands to form bubbles, and the molten resin becomes a foam, which is then sized and cooled and solidified to form a foam product.

The problem with the conventional method shown here is that the decomposition of the foaming agent is adjusted to reach a peak near the mold outlet by adjusting the extrusion operating conditions, but the decomposition of the chemical foaming agent is controlled at a certain time. , And the temperature range, the rise of the decomposition peak becomes gradual, and it is difficult to complete the decomposition within a short time before the expansion of the bubbles at the mold exit, and the foaming supplied. If the decomposition of all foaming agents is completed before the resin extruded from the mold is cooled and solidified in order to produce a foam with a foaming ratio that matches the amount of the agent, the decomposition peak rises slowly. Therefore, a considerable amount of foaming agent decomposes inside the mold and the gas melts in the resin, and the gas melted in the resin diffuses to the surface of the extrudate rather than as bubbles, and the number of bubbles Is small Ku, and the dimensions of a problem such increases, as a result, is believed to become larger bubbles resulting foam.

In order to solve the above-mentioned problems, the screw shape of the extruder and the length of the cylinder shape, etc. are examined from the device side, and it is possible to obtain a foam having fine cells of a substantially satisfactory level, but for a long period of time. A large investment is required. Furthermore, the decomposition behavior of the foaming agent also varies depending on its thermal history and pressure, so even if such an extruder facility could be achieved in an ideal state, the facility would be very limited for the foaming agent and resin. Therefore, it is extremely versatile.

(Means for Solving Problems) The present invention has been made to solve the above problems in the prior art, that is, before the decomposition of the chemical foaming agent is rapidly and near the die outlet, and before being discharged. Found a method for producing a foam having fine cells by creating a state in which most of the blowing agent is substantially undecomposed.

That is, according to the present invention, in a method of producing a foam by melting and kneading a chemical foaming agent that decomposes by heat to generate a gas and a thermoplastic resin with an extruder and extruding from a mold, chemical foaming in the molten resin is performed. A foam having fine cells characterized in that the agent is allowed to flow into the mold from the extruder without being substantially decomposed, the molten resin is rapidly heated in the mold part, and then extruded from the mold. A method of manufacturing the same is provided.

 Next, the present invention will be described with reference to the drawings.

FIG. 2 is a schematic view of an example of the apparatus used in the present invention as seen from above (the mold part is a sectional view).

The chemical foaming agent and the resin raw material are supplied from the hopper 1 to the extruder 2, melt-kneaded in the extruder, and flow from the extruder 2 into the mold 3. In order to rapidly heat the molten resin in the mold 3, a column 5 which is rotatable from the outside is inserted into the molten resin flow path inside the mold. Then, due to the rotation of the cylinder, a forced shearing force is applied to the resin between the resin flow path wall and the outer wall of the cylinder, and due to the shearing heat generated at that time, the molten resin in which the chemical foaming agent is dispersed is rapidly heated. The molten resin thus rapidly heated is extruded from the T-die 3'through the die outlet 4 to a low pressure and foamed.

When extrusion foaming is performed in this manner, it is necessary to operate the extruder under the conditions that do not substantially decompose the chemical foaming agent. Such operating conditions can be generally achieved by low-temperature operation, and the judgment that the foaming agent is not substantially decomposed is how much foaming occurs when the resin is extruded in the mold without heating. You can judge by. At this stage, the effect of the present invention becomes unclear when foaming occurs at about 80% or more of the final expansion ratio.

In this way, it is possible to easily find the optimum foaming state by adjusting the degree of heating the molten resin in which the foaming agent that has flowed from the extruder into the mold without being substantially decomposed, here, by adjusting the rotation speed of the cylinder. Yes, the bubbles become fine.

As described above, it is possible to produce a foam having fine cells by the method of the present invention. As described above, the decomposition of the chemical foaming agent is rapid near the die outlet, and the foaming agent is still large before being discharged. It is considered that this is because it is possible to create a state in which the part is substantially undecomposed.

The chemical foaming agent that can be used in the present invention is not particularly limited,
As a necessary condition for the combination with the polypropylene resin, it is necessary that the chemical foaming agent does not substantially decompose in the low temperature side condition range where the resin can be extruded.

The extruder that can be used in the present invention is not particularly limited, but if it has a large cooling capacity so that the decomposition of the foaming agent does not occur in the extruder and if the shear applied to the resin by the screw is large, the heat generated by shearing of the resin causes foaming. Since the decomposition of the agent may proceed from the extruder to the inside of the mold, it is preferable that the resin is not excessively sheared in the extruder.

As a method for heating the molten resin in the mold in the present invention, any method that utilizes the shearing heat generation described above may be used, and the resin may be heated by electric heater heating, ultrasonic heating, high frequency microwave heating, or the like. You may use together the method which can. Note that shearing heat is used because the state of dispersion of the foaming agent in the resin can be made uniform at the same time as heating.

〔Example〕

 Examples will be described below.

 The equipment used is that shown in FIG.

Melt index (MI) 1.0 g / 10 min 0.4 parts of polypropylene with 100 parts by weight of sodium bicarbonate and monosodium citrate were added to 100 parts by weight of polypropylene, cylinder diameter 65 mm, length / diameter ratio (L / D) = 25, and the hopper 1 supplies the extruder equipped with a full flight screw with a screw compression ratio of 2.5.

At the tip of the extruder 2, a column 5 having a length of 30 mm and a length of 60 mm, which can be rotated from the outside, is inserted inside a channel diameter of 40 mm, and the column 5 can be rotated by an external motor in the range of 0 to 250 rpm. did. Further, a T-die 3'having a diameter of 680 mm was attached to this tip, and the gap at the outlet was set to 1 mm, and the product was extruded at 70 rpm of the screw rotating part of the extruder. The temperature of the cylinder is C ₁ : 160 ℃, C ₂ : 160 ℃, C ₃ : 170 ℃, C ₄ : 170 ℃, C ₅ : 1 in order from the hopper 1 side in the area C, ~ C5 divided into 5 parts.
It was extruded at 70 ° C., mold temperature of 160 ° C., T-die temperature of 170 ° C., and was extruded without rotating the cylinder 5 in the mold. The sheet obtained here did not foam.

Next, the rotation speed of the cylinder 5 in the mold was sequentially increased to shear heat the resin. As the rotation speed of the cylinder 5 was increased and the resin was heated, the extruded sheet began to foam, and when the rotation speed of the cylinder 5 was 150 rpm, the bubbles became the finest, and the measured bubble diameter was 0.025 mm. It was

The result of this series of operations is shown in FIG. In FIG. 3, the curve-1 is the relationship between the column rotation speed and the expansion ratio, and the curve-
2 shows the relationship between the cylinder rotation speed and the bubble diameter.

According to FIG. 3, when the rotation speed of the cylinder is 50 rpm, the bubble diameter is 0.08 mm and the expansion ratio is about 1.02, and when the rotation speed of the cylinder is 150 rpm, the bubble diameter is 0.025 mm and the expansion ratio is
It is about 1.14 times. This indicates that the bubble diameter can be reduced and the expansion ratio can be increased as the rotation speed of the cylinder is increased. If the cylinder is not rotated at all, foaming does not occur at all and the expansion ratio is 1.0. Then, foaming was not confirmed until the rotation speed of the cylinder reached 50 rpm.

Comparative Example The equipment used is that shown in FIG. 1. The same extruder and raw material blend as in the example were used, and the tip of the cylinder (C5) with the T-die 3'attached directly to the tip of the extruder.
The temperature of the T-die 3'and the temperature of the T-die 3'were successively changed at the same temperature and the foaming state of the sheet was examined.

At the C5 temperature of 210 ° C. and the T-die temperature of 210 ° C., the bubbles were the finest, but the bubble diameter was 0.063 mm, and the bubbles were not uniform. The result of this series is shown in FIG.

According to FIG. 4, foaming was confirmed only when the temperature of the C ₅ and T dies was set to 190 ° C., and as the temperature increased, the bubble diameter increased and the expansion ratio increased.

According to the result of FIG. 4, at a temperature of about 210 ° C., the bubble diameter becomes the smallest and the expansion ratio also becomes the largest. However, when the bubble diameter is 0.063 mm,
It does not reach the result when the cylinder rotation speed is increased.

〔effect〕

As described above, according to the present invention, a foam having fine and uniform cells can be efficiently obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of an apparatus used in a conventional extrusion method as seen from above. 1 ... Hopper, 2 ... Extruder, 3 ... Mold, 3 '...
Mold (T-die), 4 ... Mold exit FIG. 2 shows a schematic view of an example of the apparatus used in the present invention as seen from above. 5. Cylinder that can be rotated from the outside FIG. 3 shows the relationship between the bubble diameter and the expansion ratio corresponding to the cylinder rotation speed of the sheet manufactured in this example. FIG. 4 illustrates the relationship between the bubble diameter and the expansion ratio with respect to the cylinder tip temperature (C5) and the T-die temperature of the sheet manufactured in the comparative example. 1 ... Hopper, 2 ... Extruder, 3 ... Mold, 3 '...
Mold (T-die), 4 ... Mold outlet, 5 ... Cylinder that can be rotated from the outside.

Claims (1)

[Claims] 1. A method for producing a foam by melting and kneading a chemical foaming agent that decomposes by heat to generate a gas and a polypropylene resin with an extruder and extruding from a mold to obtain a chemical foaming agent in the molten resin. It is made to flow from the extruder into the mold without being substantially decomposed, and the molten resin is made to flow in the mold at 50 rp at the mold part.
A method for producing a foam having fine bubbles, which comprises rapidly heating by utilizing shearing heat generation by rotating at m or more, and then extruding from a mold.