JPH0586746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing microfoams made of thermoplastic resin.

Prior Art A method for foaming thermally expandable microspheres in which a volatile liquid foaming agent is encapsulated in a thermoplastic resin shell is described in, for example, U.S. Pat. Disclosed.

The technology described in U.S. Patent No. 3,611,584 spreads an aqueous solution (slurry liquid) in which thermally expandable microspheres are dispersed onto a moving horizontal belt, deposits the microspheres, and heats them with air or steam. In this method, water is removed and the microspheres are heated and foamed.

In this method, the microspheres are heated and foamed in a state where they are in contact with each other or deposited in a layered state on a belt, so that the particles not only coagulate due to fusion and form huge agglomerated particles, but also
Since the deposition state of the particles is not uniform, there are drawbacks such as the microspheres are not heated uniformly on the belt and the degree of foaming is uneven.

Furthermore, it is very difficult to disperse the generated agglomerated particles, and conventionally they were crushed and dispersed using a high-speed shearing machine such as a Henschel mixer or a dry crusher such as a hammer mill; It is not easy to disperse aggregated particles using this method, and there are problems such as large variations in particle size and the destruction of the foam fine particles themselves.The latter method has problems in terms of heat resistance and strength of the foam. There is. Furthermore, this method requires a pneumatic transport collection device, resulting in an increase in equipment.

The technique described in Japanese Patent Publication No. 59-53290 is a method of spraying a slurry of thermally expandable microspheres into heated air, drying and foaming the microspheres, and then separating and collecting the foamed microspheres from the air. It is.

However, in this method, the heat required for foaming is obtained from heated air, and a collection device must be used to separate the foam from the air, resulting in an increase in equipment.

The technique described in Japanese Patent Publication No. 47-25148 is a method in which thermally expandable microspheres themselves are dropped into an empty tower, and heated air or steam is injected onto the microspheres to foam the particles.

However, in this method, thermally expandable microspheres are heated by falling naturally, so individual microspheres are heated uniformly due to differences in falling speed depending on the size of the microspheres and non-uniformity of air flow within the sky column. However, there are drawbacks such as not only the degree of foaming becoming non-uniform but also the need for huge equipment such as empty columns.

Problems to be Solved by the Invention As mentioned above, when foamed microspheres are produced by the conventional method, the heat during foaming tends to cause the microspheres to fuse together and coagulate, forming huge aggregated particles. . Furthermore, there is no suitable method for uniformly dispersing the aggregated particles, and the particle sizes of the produced aggregated foams vary widely. Furthermore, it is difficult to obtain a product with uniform density because the degree of foaming of individual thermally expandable microspheres is not uniform. Further, there are problems such as the need for huge equipment in implementing the conventional method for manufacturing microfoams.

The present invention solves the above-mentioned problems, uniformly foams thermally expandable microspheres, minimizes their agglomeration, and easily disperses the generated giant agglomerated particles to a uniform particle size. It is an object of the present invention to provide a method and a method by which the above method can be achieved with a simple device.

Means for Solving the Problem That is, the present invention maintains a slurry liquid and steam of thermally expandable microspheres having a thermoplastic resin outer shell containing a volatile liquid blowing agent at a predetermined pressure and temperature in a foaming tube. The first step is to heat and foam the microspheres by continuously mixing them, and then rapidly cool the microspheres. The present invention relates to a method for producing microfoams, which comprises a second step of dispersing the agglomerated foams.

Thermally expandable microspheres that can be used in the present invention can be easily produced by the method described in US Pat. No. 3,611,583 and the like.

Thermally expandable microspheres have an outer shell of a thermoplastic resin such as acrylonitrile, methacrylate, styrene, vinyl chloride, vinylidene chloride, acrylate, etc., and a volatile liquid foam such as butane, propane, i-butane, n-pentane, i -Pentane, a hydrocarbon such as neo-pentane, a freon such as trichlorofluoromethane, etc. may be included. As a commercially available product, for example, Microsphere F-30 or F-50 (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) is easily available. Further, the size thereof is not particularly limited, and a diameter of 1 to 500 μm may be appropriately selected and used.

The thermally expandable microspheres are used as a slurry by dispersing them in water in a range of 2wt% to 30wt%. If it is less than 2wt%, the production efficiency will deteriorate, and if it is more than 30wt%, the fluidity of the slurry liquid will deteriorate and the production rate will not be equivalent to the increased amount.

The feature of the present invention is that heated steam (for example, 120 to 220°C) is blown into the slurry of thermally expandable microspheres while passing through a foaming tube to rapidly raise the slurry temperature to above the foaming temperature. After holding it for a predetermined time (for example, 0.1 to 1 second), it is brought into contact with cold water or the like to be rapidly cooled. By employing such means, continuous operation becomes possible and the temperature, pressure, residence time, etc. within the foaming tube can be controlled.
As a result, individual thermally expandable microspheres can be uniformly and easily foamed to any degree. The foaming tube may have any structure as long as it can be supplied with the slurry liquid and steam, mixed and discharged, and a cylindrical tube is preferable.

The size of the foaming tube can be appropriately selected depending on the production capacity. Generally diameter 10~50
mm, and a length of 150 to 1000 mm is practically preferable. Specifically, for example, if you use a cylindrical foam tube with a diameter of 16 mm and a volume of 60 ml, 2 tons of F-50E thermally expandable microspheres can be
It can be produced in 33 days.

According to the present invention, microfoams are produced by continuously mixing slurry liquid and steam using a compact foaming tube, so that no increase in equipment is required.

The mixed steam serves to stir and heat the slurry, and evenly heats the thermally expandable microspheres dispersed in the water, vaporizing the volatile liquid foaming agent within the microspheres and foaming them. .

The temperature inside the foaming tube is adjusted by the amount of slurry liquid flowing into the foaming tube, and the temperature and flow rate of water vapor mixed simultaneously with the slurry liquid.

The temperature in the foaming tube according to the present invention is preferably determined by the temperature measured by a thermocouple installed in the center of the foaming tube, and is determined by the residence time in the foaming tube and the desired degree of foaming of the thermally expandable microspheres. should be set accordingly. For example, if you want to increase the degree of foaming and obtain a foam with a low apparent density, you can increase the temperature and lengthen the residence time. Furthermore, when it is desired to reduce the degree of foaming and obtain a foam with a low apparent density, the temperature may be lowered and the residence time may be shortened.

The temperature inside the foaming tube is between 50℃ and 200℃, preferably
It should be set in the range of 80°C to 150°C. If the temperature is set higher than 200°C, foams tend to fuse or aggregate, and it becomes difficult to control the degree of foaming. If the temperature is set lower than 50°C, the microspheres cannot be foamed.

The pressure inside the foaming tube depends on the amount of slurry liquid flowing into the foaming tube and the pressure of the steam mixed in at the same time, and controls the degree of foaming of the microspheres.
There are two factors.

The residence time in the foaming tube should be set in accordance with the temperature and pressure in the foaming tube mentioned above and the desired degree of foaming of the thermally expandable microspheres. The flow rate of the steam, the flow rate of the slurry liquid flowing out from inside the foaming tube, and the pressure inside the foaming tube are adjusted.

Next, the heated and foamed microsphere foam-containing slurry liquid flows out of the foaming tube, is mixed with cooling water, and is rapidly cooled. Rapid cooling makes it difficult for foamed microspheres to aggregate. The larger the amount of cooling water, the greater the effect, but the amount of water may be sufficient as long as it can appropriately suppress agglomeration of particles.

Another feature of the present invention is that the foamed microsphere-containing slurry liquid foamed and rapidly cooled as described above is continuously passed between two rotating grindstones arranged with a certain gap between them. This makes it possible to efficiently disperse microsphere agglomerated particles produced during foaming to a uniform particle size without destroying the particles.

The grindstone used in the present invention may be of a type in which two disk-shaped pieces are placed facing each other and one or both of the grindstones are rotated.

The gap between the grinding wheels may be appropriately selected and set in consideration of the size of the thermally expandable microspheres used as raw materials and the degree of foaming of the microspheres, but it is preferably set to 125 μm or more. If it is smaller than 125 μm, the foamed microspheres themselves are likely to be destroyed. The particle size of the grinding wheel used can be selected depending on the type of thermoplastic resin that is the outer shell of the thermally expandable microspheres used as the raw material, and is 16 to 325 mesh, preferably 60 to 120 mesh.
Use the one. If it is smaller than 325mesh or larger than 16mesh, it will not be possible to disperse the aggregated particles well.

The rotation speed of the grindstone is set so that the relative rotation speed of one grindstone and the other grindstone is 500 rpm to 10000 rpm, preferably 2000 rpm to 5000 rpm.
If the speed is lower than 500 rpm, the agglomerated particles cannot be dispersed well, and if the speed is higher than 10,000 rpm, the foamed microspheres themselves will be destroyed.

After passing between the grinding wheels, the foam microspheres are separated from the slurry liquid and dried.

The microfoam produced as described above can be used in known applications such as, but not limited to, heat insulating agents, soundproofing agents, cushioning agents, and electrical insulating agents.

Yet another feature of the invention is that the apparatus for carrying out the invention can be compactly assembled.

The present invention will be explained in more detail below using examples.

Example 1 FIG. 1 is a flow sheet showing a schematic diagram of a foaming apparatus constructed according to the present invention.

Thermal expandable microspheres Microsphere F-30 (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.: outer shell resin; vinylidene chloride-acrylonitrile copolymer) (particle size 10~
20μm) 50wt% containing aqueous dispersion into the water inlet pipe 18.
The mixture was introduced into the slurry tank 1 and mixed with the stirrer 5 to prepare a 5 wt % slurry of F-30. The slurry liquid is passed through the slurry inlet pipe 2 by the pump 2 so that the flow meter 3 indicates a flow rate of 2.5 liters/min.
0 to a foaming tube (diameter 16 mm, volume 120 ml; made of stainless steel (SUS304TP)) 4, and then steam (temperature is 147°C and pressure is 3.0 as determined by pressure gauge 9).
Kg/cm ² ) was supplied from the steam introduction pipe 11 and mixed with the slurry liquid of the first stage. After mixing, the temperature of the slurry liquid is detected by a thermocouple 6 installed in the center of the foaming tube 4 and transmitted to a temperature indicating controller 7, and the amount of steam mixed in is adjusted by a flow rate control valve 8 so that the slurry liquid reaches a set temperature. Prepared. In this example, the temperature was set at 120°C. At that time, the pressure gauge 10 showed 1.8 Kg/cm ² .

The slurry liquid flowing out from the foaming tube discharge part 12 is
Cooling water supplied from the cooling water introduction pipe 22 (water temperature 15
℃) and cooled the slurry liquid to 50-60℃,
It was made to flow into the upper part of the colloider 14. At that time, the flow meter 13 indicated 12 liters/min. At this point, there are 60 non-agglomerated foam particles with a diameter of 30 to 70 μm.
~70%, and 30-40% of particles aggregated to a size of 100 μm or more.

Inside the colloider 14 are two disc-shaped grindstones 22 and 23 having a cross section as shown in FIG.
have. Arrows 24 in the figure indicate the flow of slurry liquid passing between the grindstones. Grinding wheels 22 and 23 are made with a grain size of 100mesh, and the clearance between them is 250 μm. Grinding wheel 22 is fixed and grinding wheel 2 is
3 was rotated at 3600 rpm. The slurry liquid accumulated at the top of the colloider 14 was flowed between the grindstones at a rate of 18 liters/min to disperse the aggregated particles.

After passing through the colloider 14, the slurry liquid is sent to an intermediate tank 15, mixed with a large amount of water supplied from a water introduction pipe 21, diluted, and further sent to a centrifugal dehydrator 17 by a pump 16. Centrifugal dehydrator 17
The microfoam was separated from the slurry liquid by the following steps. The separated microfoam was dried to form a product.

In the obtained microfoam, 97-99% of non-agglomerated foam particles were 30-70μm, and non-agglomerated foam particles
Only a few percent of the particles were larger than 100 μm. Moreover, the apparent density was 0.02 g/ml.

Example 2 The same procedure as in Example 1 was carried out except that the temperature setting of the foaming tube was varied.

The microfoams obtained at each temperature had 97-99% non-agglomerated foam particles of 30-70 μm.

FIG. 3 shows the relationship between the foaming tube temperature and the apparent density of the foam obtained.

As is clear from FIG. 3, if the present invention is used, approximately
Foams can be obtained with any apparent density in the range from 0.17 g/cm ³ to about 0.02 g/cm ³ .

Effects of the Invention According to the present invention, a microfoam having a predetermined apparent density within a wide range of apparent density and having a uniform particle size containing almost no aggregated particles can be obtained using a compact device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a flow sheet of the foaming device, FIG. 2 is a schematic cross-sectional view of a grindstone, and FIG. 3 is a diagram showing the relationship between apparent density and foaming tube temperature. The symbols in the figure are as follows. 1... Slurry tank, 2, 16... Tank, 3, 13... Flow meter, 4... Foaming tube, 5... Stirrer, 6... Thermocouple, 7... Temperature indicator controller, 8... flow control valve,
9, 10...Pressure gauge, 11...Steam introduction pipe, 12
...Discharge section, 14...Colloider, 15...Intermediate tank, 17...Centrifugal dehydrator, 18, 21...Water introduction tube, 19...Sample introduction tube, 20...Slurry introduction tube, 22...Cooling Water introduction section.

Claims (1)

[Claims] 1. A slurry of thermally expandable microspheres having a thermoplastic resin outer shell containing a volatile liquid blowing agent and steam are continuously mixed in a foaming tube to maintain a predetermined pressure and temperature to form the microspheres. The first step is to heat and foam the foam and then rapidly cool it, and the second step is to continuously pass the obtained foam slurry through the gap between two rotating grindstones to disperse the aggregated foam. A method for producing a microfoam, comprising the steps of: