THERMALLY EXPANDABLE MICROCAPSULES AND FOAM MOLDING COMPOSITION

Abstract

The present invention provides a thermally expandable microcapsule having excellent heat resistance and high expansion ratio and enabling production of a light, high-hardness molded article having excellent physical properties (abrasion resistance), and a composition for foam molding containing the thermally expandable microcapsule. Provided is a thermally expandable microcapsule including: a shell containing a polymer; and a volatile expansion agent as a core agent encapsulated by the shell, the shell containing silicon dioxide and a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer, the thermally expandable microcapsule having a ratio of a peak intensity based on a C═O bond in the shell to a peak intensity based on the silicon dioxide in the shell (peak intensity based on C═O bond/peak intensity based on silicon dioxide) of 0.25 to 1.0 as determined by IR spectral analysis, the thermally expandable microcapsule having a maximum foaming temperature (Tmax) of 180° C. to 225° C.

Claims

1. A thermally expandable microcapsule comprising: a shell containing a polymer; and a volatile expansion agent as a core agent encapsulated by the shell, the shell containing silicon dioxide and a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer, the thermally expandable microcapsule having a ratio of a peak intensity based on a C═O bond in the shell to a peak intensity based on the silicon dioxide in the shell (peak intensity based on C═O bond/peak intensity based on silicon dioxide) of 0.25 to 1.0 as determined by IR spectral analysis, the thermally expandable microcapsule having a maximum foaming temperature (Tmax) of 180° C. to 225° C.

2. The thermally expandable microcapsule according to claim 1, which has an average particle size of 10 to 30 μm.

3. A composition for foam molding comprising: the thermally expandable microcapsule according to claim 1; a chemical foaming agent; and a matrix resin.

4. The composition for foam molding according to claim 3, which contains, relative to 100 parts by weight of the matrix resin, 0.1 to 3.0 parts by weight of the thermally expandable microcapsule and 0.5 to 4.0 parts by weight of the chemical foaming agent.

5. The composition for foam molding according to claim 3, wherein a ratio of an average particle size of the thermally expandable microcapsule to an average particle size of the chemical foaming agent (average particle size of thermally expandable microcapsule/average particle size of chemical foaming agent) is 1.0 to 7.5.

6. A composition for foam molding comprising: the thermally expandable microcapsule according to claim 2; a chemical foaming agent; and a matrix resin.

7. The composition for foam molding according to claim 6, which contains, relative to 100 parts by weight of the matrix resin, 0.1 to 3.0 parts by weight of the thermally expandable microcapsule and 0.5 to 4.0 parts by weight of the chemical foaming agent.

8. The composition for foam molding according to claim 4, wherein a ratio of an average particle size of the thermally expandable microcapsule to an average particle size of the chemical foaming agent (average particle size of thermally expandable microcapsule/average particle size of chemical foaming agent) is 1.0 to 7.5.

9. The composition for foam molding according to claim 6, wherein a ratio of an average particle size of the thermally expandable microcapsule to an average particle size of the chemical foaming agent (average particle size of thermally expandable microcapsule/average particle size of chemical foaming agent) is 1.0 to 7.5.

10. The composition for foam molding according to claim 7, wherein a ratio of an average particle size of the thermally expandable microcapsule to an average particle size of the chemical foaming agent (average particle size of thermally expandable microcapsule/average particle size of chemical foaming agent) is 1.0 to 7.5.

Description

DESCRIPTION OF EMBODIMENTS

[0113] Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

Example 1

(Production of Thermally Expandable Microcapsules)

[0114] An amount of 333.7 parts by weight (average particle size 20 nm) of colloidal silica having a solid content of 20% by weight, 6 parts by weight of polyvinylpyrrolidone, 1,094 parts by weight of sodium chloride, and 1.0 parts by weight of sodium nitrite were mixed with 3,100 parts by weight of ion-exchanged water, whereby an aqueous dispersion medium was prepared. The colloidal silica (aqueous dispersion) used was alkaline colloidal silica.

[0115] An amount of 722.2 parts by weight (43.33% by weight) of acrylonitrile, 157.6 parts by weight (9.46% by weight) of methacrylonitrile, 415 parts by weight (24.90% by weight) of methacrylic acid, 365.2 parts by weight (21.912% by weight) of methyl methacrylate, and 6.64 parts by weight (0.398% by weight) of trimethylolpropane trimethacrylate were mixed to prepare a monomer composition (the values in the parentheses indicate percentages by weight relative to the entire monomer composition) as a homogenous solution. To this composition were added 10 parts by weight of 2,2′-azobis(isobutyronitrile), 2.5 parts by weight of 2,2′-azobis(2,4-dimethylvaleronitrile), and 400 parts by weight of n-pentane. They were then charged into a tank 1 and mixed.

[0116] Subsequently, the aqueous dispersion medium was charged into a tank 2, to which the oily mixture in the tank 1 was added, followed by mixing. Thus, a primary dispersion was obtained. The primary dispersion had a pH of 3.5 to 4.0. The obtained primary dispersion was passed through a static mixer (produced by Fujikin Incorporated, Bunsankun) at a flow rate of 200 L/min and a pressure of 1.5 MPa. The liquid after passing was charged into an autoclave.

[0117] The element-type static disperser used had a shape tapered in the middle and included sheet elements each having a thickness of 5 mm, an effective diameter of 15 mm, and a hole size of 2 mm. The number of holes at least partially facing each other in adjacent sheet elements of different types was 78. The number of units each composed of a first element and a second element was 10. The units were set such that the primary dispersion as a fluid passed through the holes of each sheet element.

[0118] After nitrogen purging, reaction was performed at a reaction temperature of 60° C. for 15 hours. The reaction pressure was 0.5 MPa, and the stirring was performed at 200 rpm.

[0119] Thereafter, 8,000 L of the obtained polymerized slurry was fed in portions to a compression dehydrator (produced by Ishigaki Company, Ltd., Filter Press). After dehydration, a predetermined cleaning water was fed to the dehydrator to perform a cleaning step, followed by drying. Thus, thermally expandable microcapsules were obtained.

Examples 2 to 6 and Comparative Examples 1 to 7

[0120] Acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, trimethylolpropane trimethacrylate, isopentane, n-pentane, isooctane, and colloidal silica were mixed according to the formulation shown in Table 1 to prepare a monomer composition. Thermally expandable microcapsules were then obtained as in Example 1 except that emulsification was performed under the conditions shown in Table 1. Here, hydrochloric acid was added to the aqueous dispersion medium to adjust the pH to 3.5 to 4.0 in Comparative Example 1, in which the amount of methacrylic acid added was 0.1% by weight, and in Examples 4 and 6 and Comparative Example 2, in which the amount of methacrylic acid added was small.

[0121] The conventional stirring device used was a batch type high-speed rotary high-shear disperser (produced by M Technique Co., Ltd., CLEARMIX CLM-150S, rotor R2).

Examples 7 to 12 and Comparative Examples 8 to 16

(Production of Foam Molded Article)

[0122] Materials were mixed at the formulation shown in Table 2 in a Henschel mixer (dry up at 120° C.). The obtained compound was molded by core back molding (resin temperature 200° C., die temperature 40° C., core back amount 3.0 mm) in an injection molding machine (produced by The Japan Steel Works, Ltd., 350 t), whereby a foam molded article was obtained.

[0123] Bis(2-ethylhexyl)phthalate (DOP, produced by Mitsubishi Chemical Corporation) was used as a plasticizer. Heavy calcium carbonate (WHITON 305, produced by Shiraishi Kogyo Kaisha, Ltd.) was used as filler. A tin stabilizer (ONZ142AF, produced by Sankyo Organic Chem Co., Ltd.) was used as a thermal stabilizer. Polyethylene wax (AC316A, produced by Honeywell International Inc.) was used as a processing aid.

(1) Evaluation of Thermally Expandable Microcapsules

(1-1) Volume Average Particle Size and CV Value

[0124] The volume average particle size and CV value were measured with a particle size distribution analyzer (LA-950, produced by HORIBA, Ltd.).

(1-2) Foaming Starting Temperature, Maximum Foaming Temperature, and Maximum Displacement

[0125] The foaming starting temperature (Ts), maximum displacement (Dmax), and maximum foaming temperature (Tmax) were measured with a thermomechanical analyzer (TMA) (TMA2940, produced by TA Instruments). Specifically, 25 μg of a sample was placed in an aluminum container having a diameter of 7 mm and a depth of 1 mm, and heated at a temperature increase rate of 5° C./min from 80° C. to 220° C. with a force of 0.1 N applied from the top. The displacement was measured in the perpendicular direction of a measuring terminal. The temperature at which the displacement began to increase was defined as the foaming starting temperature. The maximum value of the displacement was defined as the maximum displacement. The temperature at which the maximum displacement was obtained was defined as the maximum foaming temperature.

(1-3) IR Spectral Analysis

[0126] For the thermally expandable microcapsules obtained in each of the examples and the comparative examples, multiple (two or more) thermally expandable microcapsules were collected with the core agent encapsulated therein. IR spectral analysis was performed using a FTIR spectrophotometer (produced by Thermo Scientific, Nicolet iS50). From the result of the (transmission) IR spectral analysis, the peak intensity based on a C═O bond (around 1,700 to 1,730 cm.sup.−1) in the shell and the peak intensity based on silicon dioxide (around 1,100 to 1,120 cm.sup.−1) in the shell were determined, and the ratio (peak intensity based on C═O bond/peak intensity based on silicon dioxide) was calculated. The measurement values were average values.

(1-4) Hopper Fluidity

[0127] A container for measuring bulk specific gravity specified in JIS K7370 was used. The obtained thermally expandable microcapsules were fed to the upper part of a hopper, and then allowed to fall by their own weight. The number of seconds at which the hopper was emptied (all the thermally expandable microcapsules fell down) was measured.

(2) Evaluation of Foam Molded Article

(2-1) Density

[0128] The density of the obtained foam molded article was measured by a method in accordance with JIS K 7112, Method A (water displacement method).

(2-2) A Hardness

[0129] The A hardness of the obtained foam molded article was measured by a method in accordance with JIS K 6253.

(2-3) Abrasion Amount

[0130] The volume loss per 1,000 revolutions was measured by a method in accordance with the Akron abrasion tester method (JIS K 6264) at a load of 26.5 N.

TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Comparative 1 2 3 4 5 6 Example 1 Composition Acrylonitrile 43.33 43.33 43.33 19.93 43.33 19.93 69.722 (parts by Methacrylonitrile 9.46 9.46 9.46 29.871 9.46 29.871 29.78 weight) Methacrylic acid 24.90 24.90 24.90 19.93 24.90 19.93 0.1 Methyl methacrylate 21.912 21.912 21.912 29.871 21.912 29.871 0 Trimethylolpropane 0.398 0.398 0.398 0.398 0.398 0.398 0.398 trimethacrylate Isopentane — — 24 19.2 — 19.2 — n-Pentane 24 24 — — 24 — 24 Isooctane — — — 4.8 — 4.8 — Colloidal silica (amount 3.23 3.23 4 3.23 3.23 3.23 3.23 relative to 100 parts by weight of oil phase) Stirring Static mixer ∘ ∘ ∘ ∘ ∘ ∘ — method Conventional — — — — — — ∘ stirring device Pressure in emulsification (MPa) 1.5 3.0 3 1.5 1.0 1.0 0 Flow rate in emulsification (L/min) 200 200 200 200 200 200 — Evaluation Volume average 30 25 23 28 33.3 25.2 30.1 particle size (μm) CV value (%) 23 20 19 25 35 27 32 [A] Peak intensity 0.188 0.188 0.196 0.132 0.187 0.132 0.025 based on C═O bond [B] Peak intensity 0.23 0.21 0.2 0.22 0.252 0.38 0.117 based on silicon dioxide [A]/[B] 0.817 0.895 0.980 0.600 0.742 0.347 0.214 Foaming starting 165 166 160 160 148 166 139 temperature (Ts) (° C.) Maximum foaming 215 220 208 221 188 219 173 temperature (Tmax )(° C.) Maximum 650 550 660 720 513 560 820 displacement (Dmax) (μm) Hopper fluidity 20 18 17.5 23 28 24 26 (seconds) Comparative Comparative Comparative Comparative Comparative Comparative Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Composition Acrylonitrile 59.762 43.33 43.33 43.33 33.33 43.33 (parts by Methacrylonitrile 9.96 9.46 9.46 9.46 9.46 9.46 weight) Methacrylic acid 19.92 24.90 27.90 24.90 29.90 24.90 Methyl methacrylate 9.96 21.912 18.912 21.912 26.912 21.912 Trimethylolpropane 0.398 0.398 0.398 0.398 0.398 0.398 trimethacrylate Isopentane — 24 — — — — n-Pentane 24 — — 24 24 24 Isooctane — — 24 — — — Colloidal silica (amount 2.2 2.4 3.23 10.5 3.23 3.23 relative to 100 parts by weight of oil phase) Stirring Static mixer — — ∘ ∘ ∘ — method Conventional ∘ ∘ — — — o stirring device Pressure in emulsification (MPa) 0 0 1.0 4 1.5 0 Flow rate in emulsification (L/min) — — 200 400 200 — Evaluation Volume average 41.6 38.6 30 8.6 30 30 particle size (μm) CV value (%) 44 40 24 16 23 23 [A] Peak intensity 0.132 0.188 0.188 0.188 0.25 0.176 based on C═O bond [B] Peak intensity 0.11 0.134 0.23 0.23 0.23 0.131 based on silicon dioxide [A]/[B] 1.200 1.403 0.817 0.817 1.087 1.344 Foaming starting 160 148 185 166 180 165 temperature (Ts) (° C.) Maximum foaming 221 188 232 177 225 215 temperature (Tmax )(° C.) Maximum 720 513 280 175 250 650 displacement (Dmax) (μm) Hopper fluidity 46 41 20 49 21 20 (seconds)

TABLE-US-00002 TABLE 2 Example Example Example Example Example Example Comparative Comparative 7 8 9 10 11 12 Example 8 Example 9 Formulation Resin Type PVC PVC PVC PVC PVC PVC PVC PVC Amount 49.0 49.0 49.0 49.0 49.0 49.0 49.0 49.0 [% by weight] Thermally Type Example Example Example Example Example Example Comparative Comparative expandable 1 2 3 4 5 6 Example 1 Example 2 microcapsule Amount 0.5 0.5 0.5 0.5 1.0 1.0 0.5 0.5 [% by weight] Chemical Type ADCA ADCA ADCA ADCA ADCA ADCA ADCA ADCA agent foaming Amount 1.0 1.0 1.0 1.0 0.5 0.5 1.0 1.0 [% by weight] Average 6 8 4 4 8 8 8 8 particle size (μm) Particle size ratio 5.00 3.125 5.75 7.00 4.16 4.16 3.76 5.20 (microcapsule/chemical foaming agent) Amount of plasticizer 37.00 37.00 37.00 37.00 37.00 37.00 37.00 37.00 [% by weight] Amount of filler 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 [% by weight] Amount of thermal 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 stabilizer [% by weight] Amount of processing 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 aid [% by weight] Evaluation Molded Density (g/cm.sup.3) 0.44 0.42 0.405 0.403 0.49 0.48 0.473 0.478 article A hardness 35.50 36.80 38.10 39.50 34.50 35.00 29.5 33.40 Abrasion 120 115 80 80 120 118 230 200 amount (ml) Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 Example 16 Formulation Resin Type PVC PVC PVC PVC PVC PVC PVC Amount 49.0 49.0 49.0 49.0 49.0 49.0 49.0 [% by weight] Thermally Type Comparative Comparative Comparative Comparative Comparative Comparative Comparative expandable Example 3 Example 3 Example 4 Example 5 Example 6 Example 7 Example 2 microcapsule Amount 0.5 0.5 0.5 0.5 0.5 0.5 0.5 [% by weight] Chemical Type ADCA ADCA ADCA ADCA ADCA ADCA ADCA agent foaming Amount 1.0 1.0 1.0 1.0 1.0 1.0 1.0 [% by weight] Average 8 20 6 6 6 6 4 particle size (μm) Particle size ratio 4.83 1.93 5.00 5.00 5.00 5.00 10.40 (microcapsule/chemical foaming agent) Amount of plasticizer 37.00 37.00 37.00 37.00 37.00 37.00 37.00 [% by weight] Amount of filler 10.00 10.00 10.00 10.00 10.00 10.00 10.00 [% by weight] Amount of thermal 2.00 2.00 2.00 2.00 2.00 2.00 2.00 stabilizer [% by weight] Amount of processing 0.50 0.50 0.50 0.50 0.50 0.50 0.50 aid [% by weight] Evaluation Molded Density (g/cm.sup.3) 0.469 0.485 0.491 0.490 0.492 0.485 0.415 article A hardness 34.40 29.00 28.50 27.50 28.80 30.00 28.50 Abrasion 190 250 260 280 280 245 255 amount (ml)

INDUSTRIAL APPLICABILITY

[0131] The present invention can provide a thermally expandable microcapsule having excellent heat resistance and high expansion ratio and enabling production of a light, high-hardness molded article having excellent physical properties (abrasion resistance), and a composition for foam molding containing the thermally expandable microcapsule.