JPH06238763A - Production of low density thermoplastic resin foam - Google Patents

Abstract

PURPOSE:To easily produce especially large-sized foam uniformly foamed with high magnification using a thermoplastic resin as a material by providing a cooling device and an ageing device between an extruder and a cap and sending the molten resin to the cap while the flow of the molten resin is made uniform by the distribution mechanism of the ageing device. CONSTITUTION:In the production of low density thermoplastic resin foam, a cooling device 2 for a foamable molten resin and an ageing device 3 are provided between an extruder 1 and a cap 4 in this order and the foamable resin is cooled to proper foaming temp. under stirring in the cooling device 2 to be sent to the ageing device 3. The molten resin is allowed to collide with a torpedo 36 within the ageing device 3 to be changed to annular flow and allowed to collide with a grating 34 on the way to be introduced into a central part 32 through the small holes 35 of the grating and further passed through the small holes 35 of other grating when it flows from the central part 32 to an outlet 33 to uniformize the flow of the molten resin. By this constitution, the flow of the foamable molten resin becomes uniform and the molten resin with proper foaming temp. is aged to be sent to the cap 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin low density foam.

[0002]

Several methods are known for making foams of thermoplastics. The most widely used method is the extrusion foaming method. The method is a method in which a thermoplastic resin is melted in an extruder, a volatile foaming agent is pressed into the melted resin to form a foamable melt, and this is extruded from a die to form a foam. In this method, it is necessary to melt the resin by heating it to a high temperature when the foaming agent is pressed in, and when extruding from the die, it is necessary to cool the resin to a viscosity suitable for foaming. It needs to be heated and cooled.

[0003] Among thermoplastic resin foams, temperature control of the foamable melt has been considered to be very important for making low density foams, especially large foams. The reason is,
In order to make a large foam, the expandable melt must be made to flow uniformly as a lump with a large cross section, and when it becomes a lump with a large cross section, partial temperature variations easily occur,
This is because if there is a temperature variation, the foamable melt will greatly change the foaming ratio with a slight temperature difference, so that a uniform foam cannot be obtained. Particularly in extrusion foaming, heating up to resin melting and cooling to a foaming suitable temperature must be performed successively during a series of steps from press-fitting of a foaming agent to extrusion with a die, resulting in further temperature variations. Because it is easy. For this reason, various devices have been devised for cooling the foamable melt to a temperature suitable for foaming.

Japanese Patent Publication No. 59-6217 proposes a device for uniformly cooling a foamable melt heated in an extruder to a foaming suitable temperature. This device is provided with a torpedo in a cylinder for flowing the foamable melt, first flows the foamable melt into a columnar cross section, collides with the torpedo in the middle to make the cross-section into an annular shape once, and where the torpedo does not exist. It is made to flow again with a cylindrical shape in cross section, while passing through a perforated plate that supports the torpedo, and by cooling the perforated plate, the melt is cooled to an appropriate temperature for foaming, and then immediately sent to the die for extrusion and foaming. .

Japanese Patent Laid-Open No. 63-191842 proposes a method for producing a low density foam of polystyrene resin by extrusion foaming. In this publication, a polystyrene resin having a specific melt index is selected, and a foaming agent having a specific solubility parameter is used for this resin, and the foaming agent is injected into the resin at a constant ratio in an extruder. It is necessary to knead the obtained foamable melt and immediately send it to a die for extrusion foaming.

Japanese Unexamined Patent Publication (Kokai) No. 2-175222 proposes a method in which a non-crosslinked polyolefin resin is extruded and foamed to form a foam having fine cells. The method involves contacting a polyolefin resin and a foaming agent, and then placing this mixture in a closed system under high temperature and high pressure for 20 minutes or more, and setting an extrusion shear rate of 500 / sec or more and a foaming angle of 45 degrees or less. Needs to be pushed out.

As described above, various proposals have been made to uniformly expand the thermoplastic resin at a high magnification. For example,
Various proposals have been made such as selecting a specific thermoplastic resin, limiting the foaming agent to a specific one, adding special measures to the cooling device, devising the extrusion operation such as extrusion speed and foaming angle. Made However, all of these proposals have merits and demerits and are not satisfactory as a method for producing a foam having a low density.

[0008]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a method for easily producing a foamed product, particularly a large-sized foamed product, which is made of a thermoplastic resin and uniformly foamed at a high magnification.

[0009]

Means for Solving the Problems The present inventor has made various studies in order to obtain a foam which is uniformly foamed at a high magnification by extrusion foaming. As a result, in order to uniformly foam at a high magnification, it is possible to cool the foamable melt to the foaming suitable temperature and not immediately put it in the die, while keeping the foamable melt at the foaming suitable temperature. I realized that I needed to age it and then send it to the mouthpiece and push it out.

Japanese Unexamined Patent Publication No. 2-175222 teaches that a resin and a foaming agent are placed in a sealed system under high temperature and high pressure for 20 minutes or more after being brought into contact with each other. Not taught to age. This is because, when looking at the examples of the above publications, the time of 20 minutes or more is consumed to continue cooling the foamable melt. In other words, this publication merely teaches cooling to the foaming proper temperature in 20 minutes or more.

[0011] In extrusion foaming, it is not allowed to provide a storage tank and stand still when the foamable melt is aged. In other words, it has to be aged in a fluid state without stagnation. Further, since the foamable melt is at a temperature higher than that of the external environment, care must be taken so that it does not cool down during aging and fall below the temperature suitable for foaming. For this reason, it is necessary to keep heat during aging, and in some cases heating is required. In addition, the foamable melt must be allowed to flow evenly during aging so that the foamable melt does not become partially stagnant.

Based on this idea, the inventor of the present invention attaches a cooling device to the end of the extruder to cool the expandable melt to a suitable foaming temperature in the conventional manner, and then cools it to a new aging device. And to aged the foamable melt.
In that case, the following treatment was performed in the aging device.

That is, rather than cooling the foamable melt in the aging device, it was decided to heat the foamable melt rather to maintain the foaming suitable temperature. Further, mechanical agitation in the aging device causes partial heat generation, resulting in temperature imbalance. Therefore, in the aging device, the propulsive force so far is used to allow natural flow. In addition, a large amount of molten material had to be stored in the aging device, which greatly expanded the flow path in the diametrical direction, but there is a risk of flow imbalance there. did. As a rectifying mechanism, for example, a torpedo or a perforated plate is attached to the flow path, and it is possible to make the flow of the melt uniform by avoiding that the melt collides with it and the center part of the cross section becomes particularly easy to flow. It was. Thus, the expandable melt was stored in the aging device for, for example, 5 minutes or more. As a result, a low-density foam uniformly foamed at a high ratio was obtained. The present invention has been completed based on such knowledge.

The present invention relates to a method for producing a foamed product by making a foamable melt by incorporating a volatile foaming agent into a thermoplastic resin in an extruder, and extruding and foaming this melt from a die to produce a foam. In the meantime, a cooling device and an aging device for the foamable melt are provided in this order, while mechanically stirring the foamable melt in the cooling device, cooling to a foaming suitable temperature and sending to the aging device, In the aging device, the foaming melt is allowed to flow naturally with the propulsion force so far, heated as necessary to maintain the foaming melt at the foaming proper temperature, and by the rectification mechanism attached inside the aging device. The present invention is directed to a method for producing a thermoplastic resin low-density foam, which is characterized in that the foaming melt is sent to a die after being made to flow in an aging device while making the melt flow uniform.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An example of the method of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the method of the present invention together with an example of an apparatus used therein. 2 and 3 are cross-sectional views of another ripening apparatus that can be used in the method of the present invention.

In FIG. 1, 1 is an extruder, 2 is a cooling device, 3 is an aging device, and 4 is a die. The thermoplastic resin is put into the hopper 11 of the extruder 1 and is advanced in the barrel 13 by the screw 12.
In the meantime, the resin is heated and melted by the heating mechanism 14 attached to the outer circumference of the barrel 13, impregnated with the volatile foaming agent injected from the pressure inlet 15, and well kneaded with the foaming agent in the kneading section 16 to form the foaming melt. It becomes a thing. The foamable melt produced in this way is highly fluid and does not have a viscosity suitable for foaming.

The expandable melt extruded from the extruder 1 is sent to the cooling device 2 via the connecting mechanism 17. The connecting mechanism 17 is provided for adjusting the flow of the foamable melt in a uniform manner.
8 is provided, but the rectification mechanism 18 is not necessarily required.

The cooling device 2 has a mechanism for cooling the foamable melt and a mechanism for stirring the foamable melt. The cooling device 2 illustrated in FIG. 1 uses a cylinder 21 as a cooling mechanism and a refrigerant passage 22 attached therein, and uses a screw 23 rotating in the cylinder 21 as a stirring mechanism. Therefore, FIG.
The cooling device 2 is a kind of extruder, but differs from the extruder 1 in that the cooling device 2 does not heat at all. The refrigerant passage 22 is swirled around the cylinder 21, and the refrigerant enters from the inlet 24 and the outlet 2
It is supposed to go out from 5. 26 is a screw 2
An inlet of a refrigerant for cooling 3 and an outlet 27 thereof.

The aging device 3 has a heating mechanism 37 on its outer surface and a melt passage 30 penetrating therethrough.
Although the wall surface of the passage 30 is always circular in the circumferential direction, its inner diameter changes in the traveling direction, the inlet 31 has a small diameter, the central portion 32 has a large diameter, and the outlet 33 has a circular shape again. It has a small diameter. The inner diameter is gradually changed so that the melt does not stagnant. Central part 32
A cylindrical perforated plate 34 is attached to the inside of the perforated plate, and a large number of small holes 35 are bored through the entire face of the perforated plate 34 in the radial direction. Further, a torpedo 36 is attached to the center of the eye plate 34, and the torpedo 36 completely blocks the inner cavity of the eye plate 34.

The outlet of the ripening device 3 of the mouthpiece 4 is connected to the passage of the ring 33, and the opening at the open end has a desired shape. The base 4 is the same as the conventional one.

In the apparatus shown in FIG. 1, the method of the present invention is performed as follows. In the extruder 1, a volatile foaming agent is added to the thermoplastic resin to form a foamable melt, which is first placed in the cooling device 2 and the foaming melt is mechanically stirred by the screw 23 while the refrigerant is cooled. It is cooled to a suitable temperature for foaming and sent to the aging device 3. In the aging device 3, the foamable melt, which has been brought to the foaming proper temperature, is allowed to flow naturally by the driving force so far. In addition, heating is performed by the heating mechanism 37 when necessary so that the foamable melt is not cooled from the surroundings and falls below the foaming suitable temperature.

Further, inside the ripening device 3, the flowing foamable melt is collided with the torpedo 36 to convert the columnar flow into an annular flow and store it as an annular flow. In the middle of this process, the molten metal is allowed to collide with the perforated plate 34 so that the small holes 3
Introducing into the central portion 32 through 5 equalizes the flow of the melt. Also, when the melt flows from the central portion 32 to the outlet 33, the small holes 35 of the perforated plate 34 are similarly formed.
To even out the melt flow. Therefore, even if the inner diameter of the central portion 32 becomes large and a large amount of the molten material is stored in the central portion 32, the flow of the molten material becomes uniform and is sent to the die 4. In this way, the foamable melt at the foaming suitable temperature can be stored for 5 minutes or more, aged, and then sent to the die 4.

The following is an example of an example actually performed according to the method shown in FIG. In the following, simply "parts" means "parts by weight". Polystyrene as resin (Vicat softening point 103 ° C, melt index value 4.5) 1
Fine powder talc (particle size 2 to 4 μ) 1.1 parts to 00 parts by weight,
0.1 parts of stearic acid monoglyceride and 1.8 parts of hexabromocyclododecane were uniformly mixed, and this mixture was supplied to the extruder 1 having a diameter of 90 mm at a rate of 200 kg per hour. This mixture was heated and melted at 220 ° C., and 6 parts each of monochlorodifluoroethane and methyl chloride as a foaming agent were press-in from the pressure inlet 15. The resin and the foaming agent were kneaded while passing through the kneading section 16 and the connecting mechanism 17 to form a uniform foamable melt.

The cooling extruder 2 having a diameter of 150 mm is used, and hot water of about 60 ° C. is passed through the refrigerant passage 22 to cool it, and the temperature of the foamable melt at the outlet of the cooling device 2 is 125 ° C.
And sent to the aging device 3.

The aging device 3 was heated to 128 ° C. from the outside, and the resin passage 30 therein had an outer diameter of 410 mm and a total length from the inlet to the outlet of 630 mm. The passage 30 has an inlet girder passage 31 having a diameter of 80 mm, a conical shaft connecting to the passage has an outer diameter of 200 mm, and the total length from the inlet to the outlet is 260 mm.
Was taken.

The eyelet 34 is divided into an inlet and an outlet, each having a thickness of 5 mm and a diameter of 200 mm.
It is a cylinder with a length of 200 mm, and each eyelet has a total of 72 small holes with a diameter of 12 mm on the entire surface of the inlet and the outlet in two rows of 36 in the outer peripheral direction of the cylinder.
In addition, the center of each eyelet has a diameter of 10 mm on the entire surface of the saw.
There are also 36 small holes in the outer circumferential direction, totaling 43 in 12 rows.
Two holes were drilled. Since the inner diameter of the aging device 3 was 2.7 times the inner diameter of the cooling device and the volume was about 75 liters, the foamable melt slowly flowed over about 22 minutes and was supplied to the die.

As the die 4, an outlet having a slit having a thickness of 2 mm and a width of 300 mm was used. The expandable melt was extruded from the slits into the air, and a plate-like foam having a thickness of 55 mm and a width of 650 mm was obtained with two molding tools having a fluororesin attached to the inner surface.

The obtained foam plate was peeled 2.5 mm on each side to obtain a good quality foam plate having a thickness of 50 mm. The foam plate had a density of 0.035 g / cc and was uniformly foamed throughout, and the average diameter of the bubbles was 0.2-0.3.
It was mm. The compression strength measured according to JIS A9511 is 3.8 Kg / cm ² , and the thermal conductivity is 0.023.
It was Kcal / m hr ° C.

For comparison, without using the aging device 3,
When the die 4 was directly attached to the cooling device 2 and extruded under the same conditions, the obtained foam had a density of 0.037 g / c.
c The shape of the bubbles becomes non-uniform in the thickness direction, the diameter of the bubbles at the center is 0.5 to 1 mm, and the compressive strength is 4.0 Kg.
/ Cm ² , and the thermal conductivity is 0.029 Kcal / mh
It was r ° C. Therefore, the amount of resin supplied per hour is 1
When the pressure was lowered to 50 Kg, a foam similar to that in the case of using the aging device 3 was obtained.

[0030]

According to the method shown in FIG. 1, in the cooling device, the foamable melt is mechanically stirred and cooled to the foaming proper temperature and sent to the aging device, and the foaming property is set in the aging device. Since it was decided to let the melt flow naturally with the propulsive force so far, the foamable melt was placed in a state suitable for aging without heat generation by forced agitation, and required to maintain the foaming suitable temperature. Since it was only heated accordingly, the foamable melt was kept in a state suitable for aging. Further, since the flow of the molten material is rectified by collision with the torpedo and the perforated plate in the aging device, the molten material enters the mouthpiece as a uniform flow. In this way, in the aging device, the expandable melt is allowed to flow to the suitable foaming temperature for, for example, about 5 minutes or more, and during this time, sufficient aging is performed, so that the resin discharged from the die is uniformly and finely foamed to form a good low-density foam. Obtainable. Further, in the aging device 3 of FIG. 1, by expanding the inner diameter of the central portion to be twice or more the inner diameter of the cooling device, a larger amount of the foamable melt can be stored, and therefore the length of the device in the extrusion direction can be increased. It is possible to prolong the staying time of the melt and to perform aging sufficiently without extending the melt, whereby a low-density foam can be easily produced. The present invention provides such benefits.

[0031]

[Other aging apparatus] The aging apparatus is not limited to that shown in FIG. The ones shown in FIGS. 2 and 3 can also be used as the aging device in the method of the present invention. The ripening device 5 shown in FIG. 2 is similar to the ripening device 3 shown in FIG. 1, except that a perforated plate 51 is additionally attached to the central portion 32. A large number of small holes 52 are formed in the eyelet 51 to further straighten the melt flowing in the central portion 32 in the extrusion direction.

The ripening device 6 shown in FIG. 3 is similar to that shown in FIG. 2, but differs in that the eye plate 34 is eliminated. That is, the ripening device 6 is provided with the torpedo 36 in the central portion 32, but the torpedo 36 is supported by the perforated plate 51 that blocks the flow in the extrusion direction. A large number of small holes 52 are formed in the perforated plate 51.
In No. 1, the diameter of the inlet is made larger as the distance from the torpedo 36 increases, so that the melted material can easily pass therethrough, whereby the flow is balanced.

[Brief description of drawings]

1 schematically shows the method of the present invention together with the apparatus used therein.

FIG. 2 is a sectional view of another ripening device that can be used in the method of the present invention.

FIG. 3 is a cross-sectional view of still another aging apparatus that can be used in the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder 2 Cooling device 3 Aging device 5 Aging device 6 Aging device 4 Spindle 11 Hopper 12, 23 Screw 13 Barrel 14 Heating mechanism 15 Pressure inlet 16 Kneading part 17 Connecting mechanism 18 Rectifying mechanism 21 Cylinder 22 Refrigerant passage 24 Refrigerant inlet 26 Refrigerant Inlet 25 Refrigerant outlet 27 Refrigerant outlet 30 Foamed melt passage 31 Inlet gutter passage 32 Central part 33 Outlet gutter passage 34 Eye plate 51 Eye plate 35 Small hole 52 Small hole 36 Torpedo

Claims (1)

[Claims] 1. A method for producing a foam by melting a volatile foaming agent in a thermoplastic resin in an extruder to form a foamable melt, and extruding the melt from a die to produce a foam, which comprises a step from the extruder to the die. The cooling device and the aging device for the foamable melt are provided in this order, and the foaming melt is mechanically stirred in the cooling device, cooled to the foaming proper temperature and sent to the aging device, and the aging device. Among them, the foaming melt is allowed to flow naturally by the propulsion force so far, heated as necessary to maintain the foaming melt at the proper foaming temperature, and the melt is generated by the rectifying mechanism attached inside the aging device. A method for producing a low density thermoplastic resin foam, characterized in that the foamable melt is sent to a die after being made to flow in an aging device while making the flow of the resin uniform.