JP4999096B2 - Thermoplastic resin foam - Google Patents

Description

  The present invention relates to a foam having fine bubbles obtained by extrusion foaming a thermoplastic resin composition.

  When the bubbles of the resin foam are made fine, various advantages such as improvement in specific strength, heat insulation, and light reflectivity can be obtained. Therefore, various studies have been made to make the bubbles fine. There is a batch method as a typical method for refining bubbles. As shown in Patent Document 1, the batch method is a method in which a resin is impregnated with a gas in an autoclave and then foamed by heating to a predetermined temperature. Since foaming is performed at a temperature not lower than the glass transition point and not higher than the melting point of the resin, crystals remain in the resin, and it is considered that the bubbles become fine because the crystals inhibit the growth of the bubbles. However, there are problems that it takes time to impregnate the resin with gas in an autoclave and that the production efficiency is low because it is a discontinuous process.

  On the other hand, the extrusion foaming method is an efficient method capable of continuously producing a foam. However, since the resin is foamed in a molten state, that is, without crystals, it is difficult to make the bubbles fine. Therefore, various studies have been made to make the bubbles fine by the extrusion foaming method (see, for example, Patent Documents 2 to 6).

JP-A-4-356540 (Section 0005) JP 10-000675 A (Claim 1) JP-A-12-264993 (Claim 1) Japanese Patent Laid-Open No. 13-150520 (No. 0007) Japanese Patent Laid-Open No. 14-501443 (Claim 1, Example 15) Japanese Patent Laying-Open No. 2006-102959 (Section 0014)

  Patent Document 2 discloses a method of suppressing the growth of bubbles by providing a pressurizing chamber immediately after the exit of the die and making the bubbles fine. In the examples, a foam having a cell diameter of 60 to 90 μm is obtained by foaming low density polyethylene with carbon dioxide. However, the technique of Patent Document 2 has a problem that the cost increases because it is necessary to design and manufacture a pressurizing chamber having a special structure.

  Patent Document 3 discloses that bubbles are made fine by adding citrate and a lithium compound to a chemical foaming agent. However, the technique of Patent Document 2 has a problem that the cost of the foaming agent increases because the components of the foaming agent are complex.

  Patent Document 4 discloses that fine bubbles can be obtained if the speed of the resin passing through the cylinder during extrusion foaming is 2 m / s or less. In the examples, polystyrene is foamed with carbon dioxide to obtain a foam having a bubble diameter of 0.3 to 17.8 μm. However, according to item 0035, an external stimulus such as an ultrasonic wave is essential for completion of extrusion molding, so that equipment costs are required. Moreover, although only the polystyrene which is easy to refine | miniaturize a bubble is used as resin, it was unclear whether this technique is applicable to resin which is hard to refine | miniaturize like polyolefin.

  In Patent Document 5, a flow of a molding material is divided by providing a nucleator, that is, a flow path having a large number of holes inside an extruder (see claim 1), and a high pressure drop rate is obtained when the flow is divided. Bubbles are refined by causing bubble nucleation. For example, in Example 15, a foam having an average cell diameter of 20 μm is obtained from polypropylene. However, in order to realize a high pressure drop rate of 15 GPa / s, extrusion is performed at a discharge amount of 3.45 lbs / hr (about 20 kg / hr) from a hole having a diameter of 0.04 inch (about 1 mm). Under such conditions, it is assumed that the die pressure is too high and extrusion becomes difficult, and there is a problem that it causes backflow and extrusion instability.

  In Patent Document 6, a foam having fine bubbles is obtained by passing a molding material through a die having a plurality of holes (Claim 1) at a high pressure drop rate (Clause 0003). However, in order to realize a high pressure drop speed, a small die outlet cross-sectional area and a large discharge amount are required, and there is a problem that stable operation is difficult because the die pressure is too high. .

  The present invention has been made in view of the above-described circumstances, and does not require a special device or external stimulus, and even if the pressure drop speed is not very high, a foam having fine bubbles by an extrusion foaming method. The technology that can be obtained is provided.

In order to achieve the above object, the present invention provides a thermoplastic resin foam shown in the following (1) to (8).
(1) A foam obtained by extrusion foaming a foamable resin composition containing a thermoplastic resin, particles having an average primary particle diameter of 30 nm or less, and an inorganic gas, wherein the foamable resin composition comprises: A thermoplastic resin foam, wherein a product of the concentration (mass%) of the particles and the concentration (mass%) of the inorganic gas is 60 or more.
(2) The thermoplastic resin foam according to (1), wherein the thermoplastic resin is a polyolefin resin.
(3) The thermoplastic resin foam according to (1) or (2), wherein the thermoplastic resin is a polypropylene resin.
(4) The thermoplastic resin foam according to (1) to (3), wherein the particles having an average primary particle diameter of 30 nm or less are calcium carbonate.
(5) The thermoplastic resin foam according to (4), wherein the surface of the calcium carbonate is coated with a surfactant.
(6) The thermoplastic resin foam according to (1) to (3), wherein the particles having an average primary particle diameter of 30 nm or less are silica.
(7) The thermoplastic resin foam according to any one of (1) to (6), wherein the inorganic gas is carbon dioxide.
(8) The thermoplastic resin foam according to (1) to (7), wherein an average cell diameter is 30 μm or less.

  According to the present invention, a foamable resin composition containing a thermoplastic resin, particles having an average primary particle diameter of 30 nm or less, and an inorganic gas is subjected to specific conditions, that is, the concentration (mass of particles in the foamable resin composition). %) And the concentration of inorganic gas (mass%) by extrusion foaming under conditions where the product is 60 or more, no special equipment or external stimulation is required, and a very high pressure drop rate is required. The foam having fine bubbles can be obtained by the extrusion foaming method.

  Hereinafter, the present invention will be described in more detail. In the present invention, when a foamable resin composition containing a thermoplastic resin, particles having an average primary particle diameter of 30 nm or less, and an inorganic gas is extruded and foamed under specific conditions, fine bubbles having an average cell diameter of 30 μm or less are formed. It has been found that a foam having the same properties can be obtained. The specific condition here is the product of the concentration (mass%) of particles having an average primary particle diameter of 30 nm or less in the foamable resin composition and the concentration (mass%) of inorganic gas in the foamable resin composition. Is a condition of 60 or more. Although the detailed mechanism is unknown, it is probable that both the concentration of particles and the concentration of inorganic gas influence the number of bubble nucleation, and fine bubbles can be obtained only when both meet certain conditions. . A more preferable value of the product is 80 to 300, particularly 100 to 300. The upper limit is set to 300. If this value exceeds 300, the amount of gas is too much with respect to the amount of particles, resulting in more gas escape immediately after being pushed out of the die, resulting in fine bubbles. Because it disappears.

  In the present invention, when a polyolefin resin is used as the thermoplastic resin, it is possible to obtain an advantage that the resin price is relatively low and the processability is good. Examples of polyolefin resins include low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, ethylene propylene rubber, ethylene propylene diene terpolymer, styrene butadiene rubber, ethylene vinyl acetate copolymer, ethylene vinyl. Alcohol resin, ethylene ethyl acrylate resin, ethylene acrylic acid resin and the like can be mentioned, but are not limited thereto. Furthermore, modified products such as silane-modified products and carboxylic acid-modified products of the above resins can be used, and these resins can be used alone or as a mixture of two or more.

  In the present invention, when a polypropylene resin is used as the thermoplastic resin, high rigidity and heat resistance can be obtained in addition to the advantages of the polyolefin resin. Examples of polypropylene resins include, but are not limited to, polypropylene homopolymers, propylene-ethylene block copolymers, propylene-ethylene random copolymers, and mixtures thereof.

  The thermoplastic resin, polyolefin resin, and polypropylene resin may include a heat stabilizer, a processing aid, a lubricant, an impact modifier, a filler, an antioxidant, an ultraviolet absorber, a light stabilizer, and a pigment as necessary. Etc. may be added as appropriate.

  The melt flow rate (MFR) (230 ° C., 2.16 kgf) of the thermoplastic resin used in the present invention is desirably in the range of 0.1 to 10 g / 10 min. This is because if the MFR is too high, the die pressure decreases, so that it is difficult to dissolve the gas in the resin. If the MFR is too low, the extrusion moldability is significantly impaired. Considering the balance between the die pressure and moldability, the MFR range is more preferably 0.5 to 7 g / 10 min, and further preferably 1.0 to 3 g / 10 min.

  The average primary particle diameter of the particles used in the present invention is 30 nm or less. When the average primary particle diameter exceeds 30 nm, the effect as a bubble nucleating agent is weakened, the number of generated bubble nuclei is reduced, and as a result, the bubbles become coarse. In order to enhance the bubble nucleation effect, the average primary particle size of the particles is more preferably 20 nm or less.

  Examples of the particles used in the present invention include, but are not limited to, calcium carbonate and silica. When calcium carbonate is used, there is an advantage that the amount of resin discharged during molding is increased. In addition, when calcium carbonate whose surface is coated with a surfactant is used, the primary particles are less likely to agglomerate, so that the bubble nucleation effect is increased and the bubbles become finer. Examples of the surfactant include, but are not limited to, a silane coupling agent. When silica is used as the particles, there is an advantage that fine bubbles can be realized relatively inexpensively. As particles, two or more kinds may be mixed and used.

  Examples of the inorganic gas include, but are not limited to, carbon dioxide, nitrogen, helium, and argon. When carbon dioxide is used as the inorganic gas, there is an advantage that a high gas concentration can be obtained at a relatively low gas supply pressure.

  Here, although an example of the manufacturing apparatus of the thermoplastic resin foam concerning this invention is shown, the manufacturing apparatus of this invention foam is not restricted to the following apparatus. FIG. 1 is a schematic view of the manufacturing apparatus. In the figure, 1 indicates an extruder. In the extruder 1, a hopper 2, a gas supply port 3, and a die 4 are installed. In the figure, reference numeral 5 denotes a gas supply pipe connected to the gas supply port 3, 6 denotes a carbon dioxide cylinder connected to the gas supply pipe 5, and 7 denotes a gas flow rate control device interposed in the gas supply pipe 5. The extruder 1 has a role of completely melting the resin and uniformly dispersing the gas in the resin. The extruder 1 may be a single-screw extruder alone, but in order to sufficiently cool the resin at the die outlet, it is desirable to use a tandem extruder in which two extruders are connected in series. The L / D (length / diameter of the extrusion screw) of the extruder (first-stage extruder in the case of a tandem extruder) is desirably 30 or more.

  Next, an example of a method for producing a thermoplastic resin foam according to the present invention will be described with reference to FIG. 1, but the method for producing the foam of the present invention is not limited to the following method. First, a dry blended resin and additive mixture (hereinafter simply referred to as resin) is supplied to the hopper 2 of the extruder 1. The resin advances while melting in the barrel of the extruder 1 as the screw in the extruder 1 rotates. On the other hand, a predetermined amount of carbon dioxide controlled by the gas flow rate control device 7 is supplied from the gas supply pipe 5 to the extruder 1 at the gas supply port 3 installed in the middle of the barrel of the extruder 1. The molten resin and gas come into contact with each other at the gas supply port, and the gas is dissolved in the resin by the high pressure in the extruder 1. The mixture of resin and gas that is homogeneously mixed in the extruder 1 is extruded from the die 4 and foamed at the same time. In this way, the foam 8 can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example and a comparative example, this invention is not limited to the following Example. First, measurement items in Examples and Comparative Examples will be described.

(Foaming ratio)
The expansion ratio is a value obtained by dividing the specific gravity of the resin before foaming by the specific gravity of the foam measured by an underwater substitution method (JIS K 7112). For measurement of the specific gravity of the foam, an electronic balance AG204 manufactured by Metradred was used.

(Resin temperature)
The resin temperature is a temperature measured with a thermocouple provided at a point 50 mm upstream from the exit of the die of the extruder. An auto probe 2 manufactured by Dynasco was used as the thermocouple.

(Gas concentration)
The gas concentration was calculated as a value obtained by dividing the gas flow rate [g / min] measured by a mass flow meter (D006H-SS-200 manufactured by Oval) by the discharge amount [g / min] and multiplying by 100. The discharge amount was calculated as an average value by performing the work of measuring the mass of the resin discharged from the die for 1 minute twice.

  Next, examples and comparative examples are shown. As resin PP1 in an Example and a comparative example, the block polypropylene whose MFR (230 degreeC, 2.16kgf) is 1.8g / 10min was used.

Example 1
A master batch in which PP1 and calcium carbonate (Activity 700 manufactured by Shiraishi Calcium Co., Ltd .: trade name, average primary particle size 20 nm) were mixed at a ratio of 70:30 was mixed with a 40 mm single screw extruder (FSM-40 manufactured by Ikegai Co., L / D = 34), and carbon dioxide was supplied from a gas supply port provided in the middle of the barrel of the extruder. The supply pressure of carbon dioxide was constant at 8 MPa, and the gas concentration at that time was measured by the method described above. The temperature of the extruder was set to 170 to 190 ° C. from the hopper to the center of the extruder, and thereafter the temperature was lowered stepwise so that the resin temperature at the die outlet was 158 to 170 ° C. As the die, a strand die having a diameter of 1.5 mm and a land length of 2 mm was used. Extrusion foaming was performed at a screw speed of 20 rpm and a discharge rate of about 40 g / min. At this time, the pressure drop rate at the die outlet was about 0.3 GPa / s.

  The foaming ratio of the obtained foam was measured and recorded by the method described above. Regarding the average cell diameter of the foam, first, the foam was cooled with liquid nitrogen, then folded with two pliers, and the exposed cross section was observed with a scanning electron microscope (JSM-6390-W, manufactured by JEOL Ltd.). The average value of the diameters of 30 randomly selected bubbles was calculated as the average bubble size.

(Example 2)
Except that the composition (calcium carbonate concentration is 10% by mass) obtained by mixing the calcium carbonate master batch and PPl used in Example 1 in a ratio of 33:67 was supplied to the single screw extruder, the same as in Example 1. Extruded foam and foam were investigated under various conditions.

(Example 3)
Extruded foam and foam were investigated under the same conditions as in Example 1 except that the supply pressure of carbon dioxide was changed to 4 MPa.

Example 4
Extruded foam and foam were investigated under the same conditions as in Example 1 except that the production conditions were changed as shown in Table 1.

(Comparative Example 1)
Extruded foam and foam were investigated under the same conditions as in Example 1 except that PPl was supplied to a single screw extruder alone.

(Comparative Example 2)
Except that the composition (calcium carbonate concentration is 1% by mass) obtained by mixing the calcium carbonate master batch and PPl used in Example 1 in a ratio of 3.3: 96.7 was supplied to a single screw extruder. Extruded foam and foam were investigated under the same conditions as in Example 1.

(Comparative Example 3)
Except that the composition (calcium carbonate concentration is 5% by mass) obtained by mixing the calcium carbonate masterbatch and PPl used in Example 1 in a ratio of 16.6: 83.4 was supplied to the single screw extruder. Extruded foam and foam were investigated under the same conditions as in Example 1.

(Comparative Example 4)
Extruded foam and foam were investigated under the same conditions as in Example 1 except that PPl was used alone and the carbon dioxide supply pressure was changed to 4 MPa.

(Rage example 5)
A comparison was made except that the calcium carbonate master batch used in Example 1 and PPl were mixed at a ratio of 3.3: 96.7 (the calcium carbonate concentration was 1% by mass) was supplied to the single screw extruder. Extruded foam and foam were investigated under the same conditions as in Example 4.

(Comparative Example 6)
A comparison was made except that a composition (calcium carbonate concentration of 5% by mass) obtained by mixing the calcium carbonate masterbatch used in Example 1 and PPl in a ratio of 16.6: 83.4 was supplied to the single screw extruder. Extruded foam and foam were investigated under the same conditions as in Example 4.

(Comparative Example 7)
The same as Comparative Example 4 except that the composition (calcium carbonate concentration is 10% by mass) obtained by mixing the calcium carbonate masterbatch and PPl used in Example 1 in a ratio of 33:67 was supplied to the single screw extruder. Extruded foam and foam were investigated under various conditions.

(Comparative Example 8)
Extruded foam and foam were investigated under the same conditions as in Example 1 except that the production conditions were changed as shown in Table 2.

(Comparative Example 9)
Extruded foam and foam were investigated under the same conditions as in Example 1 except that the production conditions were changed as shown in Table 2.

  Tables 1 and 2 show the measurement results of physical properties, expansion ratio, and average cell diameter of the resin. From Tables 1 and 2, a thermoplastic resin composition having an average primary particle size of 30 nm or less and a product of calcium carbonate concentration (mass%) and carbon dioxide concentration (mass%) in the foamable resin composition of 60 or more. According to this, it is understood that a foam having fine bubbles with an average cell diameter of 30 μm or less can be obtained. On the other hand, the thermoplastic resin composition having the above product of less than 60 cannot obtain a foam having fine bubbles having an average cell diameter of 30 μm or less.

It is the schematic which shows an example of the manufacturing apparatus of the thermoplastic resin foam which concerns on this invention.

Explanation of symbols

1 Extruder 2 Hopper 3 Gas Supply Port 4 Die 5 Gas Supply Pipe 6 Carbon Dioxide Cylinder 7 Gas Flow Control Device 8 Foam

Claims (8)

  A foam obtained by extruding and foaming a foamable resin composition containing a thermoplastic resin, particles having an average primary particle diameter of 30 nm or less, and an inorganic gas, wherein the particles in the foamable resin composition A thermoplastic resin foam, wherein a product of a concentration (mass%) and a concentration (mass%) of the inorganic gas is 60 or more.   The thermoplastic resin foam according to claim 1, wherein the thermoplastic resin is a polyolefin resin.   The thermoplastic resin foam according to claim 2, wherein the thermoplastic resin is a polypropylene resin.   The thermoplastic resin foam according to any one of claims 1 to 3, wherein the particles having an average primary particle diameter of 30 nm or less are calcium carbonate.   The thermoplastic resin foam according to claim 4, wherein a surface of the calcium carbonate is coated with a surfactant.   The thermoplastic resin foam according to any one of claims 1 to 3, wherein the particles having an average primary particle diameter of 30 nm or less are silica.   The thermoplastic resin foam according to any one of claims 1 to 6, wherein the inorganic gas is carbon dioxide.   The thermoplastic cell foam according to any one of claims 1 to 7, wherein an average cell diameter is 30 µm or less.

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