JPS5962121A - Manufacture of styrene resin foam - Google Patents

Abstract

PURPOSE:To allow even a resin foam having a large thickness to foam uniformly and to a high degree thereby to manufacture a high-quality foam best suitable for use as an heat insulating material, by a method wherein a resin is extrusion-foamed as a primary foaming, and the surface of the resin foam is subsequently heated under vacuum to effect a secondary foaming. CONSTITUTION:A molten styrene resin including a forming agent is extruded from an extruder into a low-pressure region so as to become a foam (a primary foaming). Under the state where the inside of the foam has a high temperature and the surface portion thereof has a temperature below the heat distortion point of the resin, the foam surfade is heated to a temperature above the heat distortion point under a vacuum below 500mm.Hg, which is lower than the low pressure in the case of the primary foaming, to allow the primarily foamed resin to foam to a high degree (a secondary foaming), thereby to manufacture a final foam.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a styrenic resin foam.

According to the extrusion molding method, a molded body can be manufactured continuously and efficiently, so the extrusion molding method is preferable in order to produce a foamed body having a constant cross-sectional shape. When making a thick foam called a slab using styrene resin, it is possible to produce a good foam using the extrusion molding method.

However, when the magnification of the slab becomes high, for example, 40 times or more, it becomes difficult to manufacture it by extrusion molding. This is because, as the magnification increases, the cell membrane strength of the foam becomes weaker and breaks during molding, making it difficult to uniformly foam the surface and interior. Therefore, it was necessary to devise a method suitable for uniformly foaming products with a high expansion ratio by extrusion molding.

Therefore, the inventor conducted various experiments in order to devise a method for uniformly foaming a thick styrene resin foam. At that time, when this inventor extruded the foam under low pressure from an extruder to form a thick foam, the inventor cooled it from the surface to solidify only the surface part to form a skin, while the inside was still hot. When it is in a state where soft foaming power remains, the surface skin is heated and the atmosphere is evacuated. As a result, with this twist, as the skin on the surface of the foam foams, the interior of the foam foams again due to the residual foaming force, and in the cross section, both the surface and the interior foam in the same way, resulting in a product with a high foaming ratio. I found it. This invention was made based on such knowledge.

This invention involves extruding a molten styrene resin containing a blowing agent from an extruder into a low-pressure region and foaming it to form a foam. This invention relates to a method for producing a styrenic resin foam, which is characterized by heating the surface of the foam to a temperature higher than the heat distortion temperature in a reduced pressure of 500 m 11 g or less to foam it to a high degree. .

It is already known that when a styrene resin foam is aged and heated, the foam undergoes secondary foaming and the expansion ratio increases. In this case, it was determined that a certain amount of time must be allowed between the initial foaming, or primary foaming, and the subsequent foaming, or secondary foaming. For example, it was necessary to leave it alone for at least one day and night. This means that when foaming beads made of styrene resin are placed in a perforated mold and water vapor is blown into the mold to form a foamed product, from the time the beads are firstly foamed to the time when they are secondarily foamed.
This is clear from the fact that it was usually necessary to leave it for several days. That is, conventionally, it has been thought that if secondary foaming is performed following secondary foaming, the effect of secondary foaming is not sufficient.

In this method of the invention, secondary foaming and secondary foaming are performed successively during the extrusion foaming process, so conventional wisdom suggests that the secondary foaming is not sufficiently effective and is therefore wasteful. It was done. However, contrary to common sense, if, following extrusion foaming, the surface of the once cooled foam is further heated and the atmosphere is reduced in pressure to perform secondary foaming, the effect of secondary foaming will appear and the foaming will become more advanced. It will be done.

In the conventional method, when extrusion foaming is performed in step 9, after foaming, the foam is shaped and continued to be cooled to form a molded product.
In the method of the present invention, the foam is foamed in the air, shaped, and cooled as in the conventional method, but the cooling is not continued until the molded product is obtained, but the cooling is temporarily stopped midway.

The point of termination is when only the surface portion of the foam is below the heat distortion temperature. That is, when the inside of the foam is at a high temperature, the foaming power is maintained, and only the surface is cooled, cooling is stopped and the foam is heated from the surface instead to reduce the pressure of the atmosphere.

Infrared rays and water vapor are used for heating. This point differs from the conventional method.

In the conventional method of cooling the foam, the surface of the foam expands to a low magnification, and the inside expands to a high magnification. Therefore, the obtained molded article had a hard skin on its surface. However, as mentioned above, if cooling is stopped midway and the atmosphere is reduced to a reduced pressure by reheating, the surface portion will foam again, and the residual foaming force inside will also be released and the whole will foam uniformly. .

As mentioned above, if cooling, which is performed in the post-extrusion process, is stopped midway through, and the surface is heated instead to allow secondary foaming under reduced pressure, the resulting molded product is only highly foamed. Not only that, but it will be even better in many ways. For example, the foam is generally uniform, has good dimensional stability, and has no directionality. this house,
In terms of high expansion ratio, an increase in expansion ratio of up to twice the maximum original expansion ratio (due to secondary foaming) was observed, and as a result, residual strain inside the foam was released, resulting in improved dimensional stability. Even when exposed to slightly higher temperatures, it does not expand or contract much. In other words, in the method of this invention, when the inside still has foaming power after some foaming, the surface is further heated and placed under reduced pressure, so both the inside and the surface foam freely and the directionality is maintained. will be reduced or eliminated. Therefore,
The product according to this invention has excellent quality.

The surface of the foam can be cooled by natural cooling, but a preferred method is to bring a cooling fluid into contact with the mold or the foam. Air or water can be used as the cooling fluid.

The point at which the surface portion of the foam has cooled below the heat distortion temperature while the interior is still at high temperature can be approximately estimated as the foam is continuously extruded from the extruder. That is, the extruded foam is gradually cooled from the surface, and the cooling progresses very slowly into the interior because the foam itself is covered with an insulating material.

Therefore, the interior of the foam remains at a higher temperature than the surface area for a considerable period of time. Therefore, when it comes out of the mold, a skin forms on the surface, and the outer dimensions are approximately determined, cooling is stopped, heating is switched on, and the atmosphere is reduced in pressure. If you do not know the relationship between the cooling of the skin and the internal temperature, cut the expanding foam in places and observe its cross section, select the point at which the interior expands with the remaining foaming power, and then switch to heating. The atmosphere can be depressurized.

In the method of this invention, switching from cooling to reduced pressure heating is performed by
If cooling is performed while the foam is too cool, a low-foaming intermediate layer will be formed in the center of the resulting foam.

On the other hand, if the foam is cooled insufficiently, the surface will crack and a good foam will not be obtained. Therefore, the switching point must be at a time when the cooled surface portion and the interior portion, which maintains residual foaming power at high temperature, coexist in an appropriate ratio. More preferably, the thickness of the surface portion cooled to below the heat distortion temperature in a suitable manner is within the range of approximately 1/50 to 1/2 of the thickness from the center to the surface of the foam. This is when t'i is within the range of 1/20 to 1/5.

Infrared rays (including far infrared rays) and water vapor can be used to heat the foam. In the case of steam heating, the ambient temperature #i
Preferably, the temperature is 80°C to 120°C. In the case of infrared heating, it is also possible to raise the ambient temperature even higher. The contact time is determined appropriately, taking into consideration the temperature of the atmosphere, the size of the foam, etc., and based on the criterion that the surface of the foam reaches a temperature higher than the heat deformation temperature and foams appropriately. The time is usually about 20 seconds to 10 minutes.

In the present invention, it is necessary to place the foam under a reduced pressure of 500 mHg or less. At low vacuum levels above 500 wx Hg, sufficient secondary foaming is not achieved and the uniformity and dimensional stability of the foam are not improved.

During and immediately after heating, the atmosphere is reduced to atmospheric pressure and the foam foams and increases in volume, so the foam must be maintained in a state where it can expand. At the same time, it is necessary to avoid undesirable deformations of the foam.

For this purpose, the foam is loosely sandwiched between Teflon-coated plate surfaces, or a large number of rolls are arranged in parallel to support the foam from at least the top and bottom. This secondary foaming by heating under reduced pressure can be carried out either continuously or discontinuously as long as the inside of the primary foam board is at a high temperature and foaming power remains. However, in order to foam to a higher degree, it is preferable to carry out the process discontinuously. Continuously, in row 9, the spacing between the plates or rolls is gradually widened from the inlet to the outlet, allowing the foam to expand as it spreads. This causes the foam to be heated from the surface while passing between the plates or rolls and at the same time pass through the vacuum chamber. In addition, when conducting discontinuously, the heating and depressurizing area is divided into one tank, and the cut foam is intermittently fed into the tank and held in the tank to perform secondary foaming by heating and depressurizing. You can. Of course, when performing this discontinuously, the heating zone and the depressurizing zone can each be made into one tank.

With this method, secondary foaming can be carried out in a vacuum chamber that is closed discontinuously or continuously, but can be left in the vacuum chamber for a long time, increasing the foaming ratio from 30% to a maximum of 100% of the primary foam. It is also desirable to use it during consecutive rotations because it can raise the amount.

The desirable magnification increase rate at this time is 50% to 80%. If the magnification is increased too much, it will cause shrinkage and dimensional changes, which is undesirable.0 The foam, which is heated from the surface and held in a vacuum tank to cause secondary foaming on the surface, is then cooled and then used as it is or cut into products. becomes. The product 11 thus obtained is characterized in that the surface portion is highly foamed like the inside, and there is no difference in expansion ratio, that is, no difference in density, between the surface portion and the inside. In addition, as mentioned above, it has other characteristics such as uniform foaming, no directionality, and little dimensional change due to temperature fluctuations. Therefore,
The products produced by the method of this invention are good as foams, and the plates produced by this method are particularly suitable for use as insulation in the ceilings of houses, the roofs of general buildings, or the external walls. Also, since it is highly foamed, it has great flexibility and is easy to use as a heat insulating material for curved surfaces such as tanks and large diameter pipes.

The styrenic resin used in the method of this invention is not limited to a styrene-based monopolymer, but also includes a copolymer. Styrenic monomers include styrene #1, methylstyrene, and ethylstyrene. Further, the copolymer includes a copolymer containing 50 moles or more of a styrene monomer. Examples of the monomer to be copolymerized include methyl methacrylate, acrylonitrile, maleic anhydride, and the like. The preferred resins are polystyrene, styrene-acrylonitrile copolymer, and styrene-maleic anhydride copolymer.

The blowing agent used in the method of this invention is an aliphatic hydrocarbon or a halogenated aliphatic hydrocarbon having a boiling point lower than the heat distortion temperature of the styrenic resin. Examples of aliphatic hydrocarbons are saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, and unsaturated aliphatic hydrocarbons such as acetic acid, propylene, butene. Further, examples of halogenated aliphatic hydrocarbons are methyl chloride, methylene chloride, dichloromethane, and fathom.

These materials can be used alone or in combination of two or more. Furthermore, the above various blowing agents and C02
It can also be used in combination with an inert gas such as N2.

The foaming agent may be added to the resin before the resin is supplied to the extruder, or during the extruder. The extruder may be a -screw or a twin-screw extruder.

The method of this invention is particularly effective when producing foams with large wall thicknesses, but it can also be applied to the production of foams with small wall thicknesses. Here, we refer to foams with a large wall thickness, and refer to foams with a thickness of 10+W or more.

Next, specific examples of the method of this invention will be described with reference to Examples.

In the following, parts simply mean parts by weight.

Example 1 Using polystyrene as the resin, 100 parts of polystyrene was mixed with 0.5 part of finely powdered talc (bubble control agent), and this mixture was fed to an extruder at a rate of 60 minutes per hour. The blowing agent was injected into the resin. As a blowing agent, 3 parts of dichlorodifluoromethane and 7 parts of methyl chloride
This mixture was injected at a rate of 1 iop per kg of resin.

The ferrule has an opening made of 2.5mm thick silk at the tip and a diameter of 10m below the opening, and while cooling the surface through 60°C water, heat the resin through this opening.
l 11 (Extruded at 1"C. The tip Ka of the die was held close to the molding tool to prevent deformation of the resin.

As a forming tool, the inlet dimensions are substantially equal to the opening of the cap, and the outlet dimensions are 82 mm thick, 130 mm wide, and 310 mm long.
m, and was equipped with a resin passageway that gradually expanded from the inlet to the outlet.

On the resin passage wall of the molding tool, water at 60°C was circulated inside the molding tool made of fluororesin.

The foam that came out of the molding tool was highly foamed. This foam was cooled by blowing air at 20°C. Cooling was performed up to 100 m from the end of the molding tool. At this time,
The foam surface temperature was 35°C, and the center temperature was 75°C. An infrared heating tank with a length of 2 m and a cooling tank with a length of 8 m were provided ahead of this, and the pressure inside the tank was reduced to -1 zsom + 1 lI (absolute pressure) to perform secondary foaming of the foam.

When the physical properties of the molded product thus obtained were measured, as shown in the Examples column of the following table, the density became uniform throughout, the expansion ratio increased, and the density became smaller.
Furthermore, it was observed that the directionality of compressive strength was reduced. In addition, the molded product obtained in this way was slightly flexible.0 For comparison, the molded product obtained by cooling directly without using a vacuum heating tank in the operation of the above example. The physical properties are listed in the column of comparative examples. In the case of the comparative example, 4Ct has a low expansion ratio and a large density difference in the thickness direction of the molded product.
The difference in the directionality of compressive strength is also large.

Below is a margin table Physical properties of the molded product /+y/) was measured.

*2 A test piece of 50 angles was cut out from the molded product and measured in the extrusion direction (MD), width direction (TI)) and thickness direction (VD).
The compressive strength was measured from each of the three directions, MD
The respective ratios were determined so that TD x Vl, )=1.

Example 2 The entire process was carried out in the same manner as in Example 1, except that a heating and depressurizing tank was provided separately from the extruder, and the cut foam was held in the heating and depressurizing tank for a long time.

That is, the primary foam having a surface layer temperature of 35° C. and a center temperature of 75° C. after exiting the molding tool was cut and placed in a heated and reduced pressure tank provided separately from the extruder.

The atmosphere inside the tank was brought to about 100° C. using an electric heater, and the heat source was immediately turned off after the foam was put in. At the same time, the pressure inside the tank was reduced to about +WLK (absolute pressure). When the secondary foam was taken out into the outside air after cooling the inside of the tank and maintaining it under reduced pressure for 15 hours, secondary foaming was observed mainly in the longitudinal direction, but also in the thickness direction and in the middle direction. Density 1
7) It was foamed at lx/P', but slight shrinkage was observed in the center of the cut surface.

However, when I left this at room temperature for 24 hours,
This shrinkage was recovered and a highly expanded foam with a density of 15 Kg/w/ was obtained.

1

Claims (1)

[Claims] 1. Molten styrene resin containing a blowing agent is extruded from an extruder to a low-pressure region and foamed to form a foam, and the interior of the foam is at a high temperature while the surface is below the heat distortion temperature. In this state, the surface is heated above the heat deformation temperature and the pressure is further lowered.
A method for producing a styrenic resin foam, the method comprising foaming under reduced pressure of 0.00 m lla or less. 2. Patent 4-7, characterized in that the extruded foam is cut and guided to a vacuum area provided separately from the extruder.
A method for producing a styrenic resin foam according to item 1.