THERMALLY EXPANDABLE MICROCAPSULES, EXPANDABLE MASTER BATCH AND FOAM MOLDED BODY

Abstract

The present invention provides a thermally expandable microcapsule from which a foam molded article that has a uniform surface, is less prone to surface unevenness, and has an excellently light weight can be produced. The present invention also provides a foamable masterbatch and a foam molded article each produced using the thermally expandable microcapsule. Provided is a thermally expandable microcapsule including: a shell; and a volatile expansion agent as a core agent encapsulated by the shell, the thermally expandable microcapsule satisfying D10/D50 of 0.6 or more and 1.0 or less and D99/D50 of 1.0 or more and 2.0 or less where D10 represents a particle size at a cumulative frequency of 10% by volume, D50 represents a particle size at a cumulative frequency of 50% by volume, and D99 represents a particle size at a cumulative frequency of 99% by volume in a cumulative undersize distribution of a volume-equivalent particle size determined using a laser diffraction/scattering particle size distribution analyzer.

Claims

1. A thermally expandable microcapsule comprising: a shell; and a volatile expansion agent as a core agent encapsulated by the shell, the thermally expandable microcapsule satisfying D10/D50 of 0.6 or more and 1.0 or less and D99/D50 of 1.0 or more and 2.0 or less where D10 represents a particle size at a cumulative frequency of 10% by volume, D50 represents a particle size at a cumulative frequency of 50% by volume, and D99 represents a particle size at a cumulative frequency of 99% by volume in a cumulative undersize distribution of a volume-equivalent particle size determined using a laser diffraction/scattering particle size distribution analyzer.

2. The thermally expandable microcapsule according to claim 1, wherein a volumetric ratio of D99 to D50 [(D99).sup.3/(D50).sup.3] is 1.0 or more and 8.0 or less.

3. The thermally expandable microcapsule according to claim 1, wherein a value obtained by dividing a difference between D99 and D10 by D50 [(D99D10)/D50] is 0 or more and 1.4 or less.

4. The thermally expandable microcapsule according to claim 1, wherein D99 is 15 m or larger and 80 m or smaller.

5. The thermally expandable microcapsule according to claim 1, wherein the shell contains a polymer of a monomer composition containing a nitrile monomer.

6. The thermally expandable microcapsule according to claim 1, wherein a shell thickness ratio (minimum shell thickness/maximum shell thickness) is 0.4 or more.

7. A foamable masterbatch comprising: the thermally expandable microcapsule according to claim 1; and a thermoplastic resin.

8. A foam molded article produced using the thermally expandable microcapsule according to claim 1, or a foamable masterbatch comprising the thermally expandable microcapsule according to claim 1 and a thermoplastic resin.

Description

DESCRIPTION OF EMBODIMENTS

[0149] Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

(Preparation of Composition 1 [Aqueous Dispersion Medium, Oily Mixture])

[0150] To 2,000 g of ion-exchanged water were added 300 g of colloidal silica having a solid content of 20% by weight, 7 g of polyvinylpyrrolidone, and 600 g of sodium chloride, followed by mixing and adjustment of the pH of the mixture to 3.5. Thus, an aqueous dispersion medium was prepared. An amount of 160 g of acrylonitrile, 180 g of methacrylonitrile, 250 g of methacrylic acid, 160 g of methyl methacrylate, and 6 g of trimethylolpropane trimethacrylate were mixed to obtain a monomer composition in the form of a uniform solution. To the monomer composition were added 10 g of 2,2-azobisisobutyronitrile, 200 g of n-pentane, and 50 g of isooctane. The mixture was put in an autoclave and mixed. Thus, an oily mixture was prepared.

(Preparation of Composition 2 [Aqueous Dispersion Medium, Oily Mixture])

[0151] Composition 2 [aqueous dispersion medium, oily mixture] was obtained as in the case of Composition 1 except that the oily mixture and the aqueous dispersion medium were prepared according to the formulations shown in Table 1. (unit in Table 1: gram (g))

TABLE-US-00001 TABLE 1 Composition 1 2 Oily Monomer Acrylonitrile 160 525 mixture Methacrylonitrile 180 210 Methyl methacrylate 160 9 Methacrylic acid 250 0 Trimethylolpropane 6 6 trimethacrylate Solvent n-Pentane 200 250 Isooctane 50 0 Initiator Azobisisobutylonitrile 10 10 Aqueous Dispersant Deionized water 2000 2000 dispersion Colloidal silica (solid 300 300 medium content 20 wt %) Polyvinylpyrrolidone 7 7 Sodium chloride 600 600 Hydrochloric acid 2.5

Example 1

(Production of Thermally Expandable Microcapsule)

[0152] The oily mixture obtained in Composition 1 was put into a tank 1, and the aqueous dispersion medium obtained in Composition 1 was put into a tank 2. To the tank 2 was added the oily mixture in the tank 1, followed by mixing. Thus, a primary dispersion was obtained.

[0153] The obtained primary dispersion was passed through a block-type static dispersion machine at a flow rate of 120 L/min. The liquid after passing was charged into an autoclave. The block-type static dispersion machine used included sheet blocks with 70 holes having a hole size of 2 mm. The number of blocks was 20.

[0154] After nitrogen purging, reaction was performed at a reaction temperature of 60 C. for 15 hours. The reaction pressure was set to 0.5 MPa, and the stirring was performed at 200 rpm.

[0155] Thereafter, 8,000 L of the resulting polymerized slurry was fed in portions to a compression dehydrator. After dehydration, a washing step was performed by feeding a predetermined amount of washing water to the dehydrator, followed by drying. Thus, thermally expandable microcapsules were obtained.

(Production of Foamable Masterbatch and Foam Molded Article)

[0156] An amount of 100 parts by weight of a base resin (low-density polyethylene), 100 parts by weight of the obtained thermally expandable microcapsules, and 10 parts by weight of a lubricant (stearic acid) were fed to a Banbury mixer and kneaded therein at 100 C. for 30 seconds. The kneaded mixture was extruded from the mixer into pellets. Thus, masterbatch pellets were obtained.

[0157] The obtained masterbatch pellets in an amount of 3 parts by weight were mixed with 100 parts by weight of an olefin-based thermoplastic vulcanizate (TPV, available from Mitsui Chemicals, Milastomer 7030BS, density 0.88 g/cm.sup.3). The obtained pellet mixture was fed to a hopper of an extrusion molding machine, melt-kneaded therein, and extrusion-molded into sheet foam molded articles having different thicknesses of 0.5 mm and 3 mm. The molding temperature was set to 210 C.

Examples 2 to 5, Comparative Example 1

[0158] Thermally expandable microcapsules, a foamable masterbatch, and foam molded articles were produced as in Example 1, except that the flow rate, the block hole size, and the number of blocks in dispersion using a block-type static dispersion machine were changed as shown in Table 2.

Example 6

[0159] The oily mixture and the aqueous dispersion medium obtained in Composition 1 were fed to a tank and mixed using a homogenizer (Homomixer available from Primix corporation) at a rotation speed of 10,000 rpm for a stirring time of 10 minutes.

[0160] After nitrogen purging, reaction was performed at a reaction temperature of 60 C. for 15 hours. The reaction pressure was set to 0.5 MPa, and the stirring was performed at 200 rpm.

[0161] Thereafter, 8,000 L of the resulting polymerized slurry was fed in portions to a compression dehydrator. After dehydration, a washing step was performed by feeding a predetermined amount of washing water to the dehydrator. The washed product was then dried.

[0162] Thermally expandable microcapsules, a foamable masterbatch, and foam molded articles were produced as in Example 1, except that the classification step was subsequently performed using a wind classifier (Donaselec, available from Aisin Nano Technologies Co., Ltd.).

Example 7, Comparative Examples 2 to 6

[0163] Thermally expandable microcapsules, a foamable masterbatch, and foam molded articles were produced as in Example 6, except that the rotation speed and stirring time in dispersion using a homogenizer and the presence or absence of the classification step were changed as shown in Table 2.

Comparative Example 7

[0164] Thermally expandable microcapsules, a foamable masterbatch, and foam molded articles were produced as in Example 6, except that the classification step was performed by using a vibrating sieve classifier (vibrating sieve available from Dalton Corporation).

Comparative Examples 10 to 12

[0165] Thermally expandable microcapsules, a foamable masterbatch, and foam molded articles were produced as in Example 1, except that the flow rate, the block hole size, the number of block holes, and the number of blocks in dispersion using a block-type static dispersion machine were changed as shown in Table 2.

Example 8

[0166] Thermally expandable microcapsules were obtained as in Example 1, except that the oily mixture and the aqueous dispersion medium obtained in Composition 2, instead of Composition 1, were used.

[0167] A foamable masterbatch and foam molded articles were produced as in Example 1, except that the olefin-based thermoplastic vulcanizate was replaced with a styrene-butadiene-styrene block copolymer (SBS, TR1600 available from JSR Corporation, density 0.96 g/cm.sup.3) and the molding temperature was set to 170 C.

Example 9

[0168] Thermally expandable microcapsules were obtained as in Example 6, except that the oily mixture and aqueous dispersion medium obtained in Composition 2, instead of Composition 1, were used.

[0169] A foamable masterbatch and foam molded articles were produced as in Example 1, except that the olefin-based thermoplastic vulcanizate was replaced with a styrene-butadiene-styrene block copolymer (SBS, TR1600 available from JSR Corporation, density 0.96 g/cm.sup.3) and the molding temperature was set to 170 C.

Comparative Example 8

[0170] Thermally expandable microcapsules were obtained as in Comparative Example 1, except that the oily mixture and aqueous dispersion medium obtained in Composition 2, instead of Composition 1, were used.

[0171] A foamable masterbatch and foam molded articles were produced as in Comparative Example 1, except that the olefin-based thermoplastic vulcanizate was replaced with a styrene-butadiene-styrene block copolymer (SBS, TR1600 available from JSR Corporation, density 0.96 g/cm.sup.3) and the molding temperature was set to 170 C.

Comparative Example 9

[0172] Thermally expandable microcapsules were obtained as in Comparative Example 7, except that the oily mixture and aqueous dispersion medium obtained in Composition 2, instead of Composition 1, were used.

[0173] A foamable masterbatch and foam molded articles were produced as in Comparative Example 7, except that the olefin-based thermoplastic vulcanizate was replaced with a styrene-butadiene-styrene block copolymer (SBS, TR1600 available from JSR Corporation, density 0.96 g/cm.sup.3) and the molding temperature was set to 170 C.

(Evaluation Method)

[0174] The properties of the obtained thermally expandable microcapsules and foam molded articles were evaluated by the following methods. Table 2 shows the results.

(1) Evaluation of Thermally Expandable Microcapsules

(1-1) Particle Size (D10, D50, D99) Measurement

[0175] The particle sizes (D10, D50, D99) of the obtained thermally expandable microcapsules were measured based on a cumulative undersize distribution of a volume-equivalent particle size determined using a laser diffraction/scattering particle size distribution analyzer (LA-950, available from Horiba, Ltd.). Also, D10/D50, D99/D50, (D99).sup.3/(D50).sup.3, and (D99D10)/D50 were calculated from the measured D10, D50 and D99 values.

[0176] The average particle size and standard deviation of particle size distribution were measured in the same manner as the above operation, and the CV value was calculated by dividing the average particle size by the standard deviation of particle size distribution.

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

[0177] The foaming starting temperature (Ts) and the maximum foaming temperature (Tmax) were measured with a thermomechanical analyzer (TMA) (TMA2940, available from TA Instruments). Specifically, 25 g 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 250 C. with a force of 0.1 N applied from above. 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. Also, the expansion ratio was measured, and the temperature at which the expansion ratio reached the maximum was defined as the maximum foaming temperature.

(1-3) Shell Thickness Ratio

[0178] The resulting thermally expandable microcapsules were embedded in a sample embedding resin for electron microscope (Epok812 available from Okenshoji Co., Ltd.) and heated in an oven at 60 C. for 15 hours.

[0179] The resulting cured product was cut using an ultramicrotome (available from Leica Microsystems), and the obtained cross section of the particles was observed with an SEM. The shell thickness of one thermally expandable microcapsule was measured at 10 points where the shell thickness was maximum and at 10 points where the shell thickness was minimum. The ratio of their average values (minimum shell thickness/maximum shell thickness) was calculated. The same operation was performed on 10 thermally expandable microcapsules in total, and the average value of the resultant ratios was defined as the shell thickness ratio.

[0180] The intermediate shell thickness [(maximum shell thickness+minimum shell thickness)/2] was calculated from the resulting minimum shell thickness and maximum shell thickness.

(2) Evaluation of Foam Molded Article

(2-1) Surface Roughness [Surface Property]

[0181] The surface roughness (Ra) of the foamed molded article was measured using a 3D measuring macroscope (VR-3000 available from Keyence Corporation).

[0182] Also, the rate of change in the surface property Ra of the molded article having a thickness of 0.5 mm with respect to the surface property Ra of the molded article having a thickness of 3 mm was taken as the surface property deterioration rate.

(2-2) Measurement of Density, Weight Reduction Rate

[0183] The density of the obtained foam molded article (post-foaming density) was measured by a method in conformity with JIS K-7112 A method (water displacement method).

[0184] Also, the percentage of the post-foaming density to the pre-foaming density was calculated as the weight reduction rate.

(2-3) Surface Unevenness of Molded Article

[0185] The entire foam molded article obtained was visually observed to determine the presence or absence of surface unevenness. A case where surface unevenness was not observed was evaluated as (good) and a case where surface unevenness was observed was evaluated as x (poor).

[0186] The surface roughness Ra is an actual value obtained by locally measuring the shape of the molded article, whereas the surface unevenness is evaluated by visually observing the entire surface of the molded article.

TABLE-US-00002 TABLE 2 Compar- ative Examl- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 1 Composition No. 1 1 1 1 1 1 1 1 Dispersion Type of dispersion machine Block Block Block Block Block Homo- Homo- Block step genizer genizer Number of block holes (pcs) 70 70 70 70 70 70 Block hole size (mm) 2 2 2 2 1 2 Flow rate (L/min) 120 100 120 150 120 30 Number of blocks (pcs) 20 20 10 20 20 20 Rotation speed (rpm) 10000 7000 Stirring time (min) 10 60 Classification step Wind Wind Measurement D10 18.8 24.2 17.3 12.4 8.2 10.8 8.9 17.2 of particle D50 25.1 33.6 26.2 16.1 11.2 16.1 14.3 33.6 size D99 38.8 58.9 45.6 24.4 15.8 29.8 26.8 72.4 D10/D50 0.749 0.720 0.660 0.770 0.732 0.671 0.622 0.512 D99/D50 1.546 1.753 1.740 1.516 1.411 1.851 1.874 2.155 (D99).sup.3/(D50).sup.33 3.69 5.39 5.27 3.48 2.8 6.34 6.58 10.00 (D99-D10)/D50 0.80 1.03 1.08 0.75 0.68 1.18 1.25 1.64 CV value 19.2 36.5 24.2 15.3 12.5 19.2 19.6 38.1 Intermediate shell thickness (m) 4.2 5.6 4.4 2.7 1.9 2.7 2.3 5.6 Shell thickness ratio 0.92 0.82 0.87 0.76 0.63 0.82 0.38 0.38 Foaming starting temperature (Ts) 166 165 163 168 167 166 169 164 Maximum foaming temperature (Tmax) 211 215 211 207 208 206 200 213 Evaluation of Surface property Ra (m) 14.69 20. 16.24 9.04 8.05 11.7 10.8 43.5 molded article Density (g/cm.sup.3) 0.51 0.48 0.52 0.55 0.58 0.55 0.60 0.64 (0.5 mm Weight reduction rate 41.9% 45.3% 41.3% 37.3% 33.6% 38.0% 31.8% 27.7% thickness) Evaluation of Surface property Ra (m) 13.0 18.0 14.0 8.0 7.0 10.1 9.6 32.0 molded article Density (g/cm3) 0.55 0.52 0.55 0.59 0.63 0.59 0.62 0.68 (3 mm Weight reduction rate 37.5% 41.2% 37.5% 33.3% 28.6% 33.3% 29.5% 23.1% thickness) Surface property deterioration rate 1.13 1.15 1.16 1.13 1.15 1.16 1.13 1.36 (Ra of 0.5 mm thickness/Ra of 3.0 mm thickness) Surface unevenness of molded article x Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 10 Composition No. 1 1 1 1 1 1 1 Dispersion Type of dispersion machine Homo- Homo- Homo- Homo- Homo- Homo- Block step genizer genizer genizer genizer genizer genizer Number of block holes (pcs) 50 Block hole size (mm) 2 Flow rate (L/min) 100 Number of blocks (pcs) 20 Rotation speed (rpm) 5000 5000 10000 10000 15000 10000 Stirring time (min) 10 10 10 30 10 10 Classification step Wind Vibrating sieve Measurement D10 20.7 18.2 10.0 7.4 7.9 7.6 18.3 of particle D50 39.0 33.4 16.5 14.1 12.2 15.3 35.6 size D99 108.3 72.1 36.5 34.8 26.2 30 81.2 D10/D50 0.531 0.545 0.606 0.525 0.648 0.497 0.514 D99/D50 2.777 2.159 2.212 2.468 2.148 1.961 2.281 (D99).sup.3/(D50).sup.33 21.41 10.06 10.82 15.03 9.90 7.54 11.87 (D99-D10)/D50 2.25 1.61 1.61 1.94 1.50 1.46 1.77 CV value 39.9 30.5 24.1 22. 19.8 18.2 40.1 Intermediate shell thickness (m) 6.5 5.6 2.8 2.4 2.0 2.6 6.0 Shell thickness ratio 0.66 0.35 0.35 0.28 0.33 0.39 0.37 Foaming starting temperature (Ts) 163 166 166 167 170 168 167 Maximum foaming temperature (Tmax) 209 210 210 207 205 208 215 Evaluation of Surface property Ra (m) 66.3 66 34 25.38 20.48 13.2 53.3 molded article Density (g/cm.sup.3) 0.55 0.58 0.63 0.68 0.64 0.67 0.66 (0.5 mm Weight reduction rate 38.0% 33.6% 28.5% 22.5% 27.7% 23.3% 25.0% thickness) Evaluation of Surface property Ra (m) 47.0 44.0 25.0 18.0 16.0 11.0 39.3 molded article Density (g/cm3) 0.59 0.63 0.68 0.73 0.68 0.73 0.68 (3 mm Weight reduction rate 33.3% 28.6% 23.1% 16.7% 23.1% 16.7% 23.1% thickness) Surface property deterioration rate 1.41 1.5 1.36 1.4 1.28 1.2 1.36 (Ra of 0.5 mm thickness/Ra of 3.0 mm thickness) Surface unevenness of molded article x x x x x x x Compar- Compar- Compar- Compara- ative ative ative tive Exam- Exam- Exam- Exam- Exam- Exam- ple 11 ple 12 ple 8 ple 9 ple8 ple 9 Composition No. 1 1 2 2 2 2 Dispersion Type of dispersion machine Block Block Block Homo- Block Homo- step genizer genizer Number of block holes (pcs) 70 70 70 70 Block hole size (mm) 4 2 2 2 Flow rate (L/min) 120 120 120 30 Number of blocks (pcs) 20 6 20 20 Rotation speed (rpm) 10000 10000 Stirring time (min) 10 10 Classification step Wind Vibrating sieve Measurement D10 21.1 33 19.1 11.0 17.4 7.5 of particle D50 33 39 26.7 15.5 35.3 16.1 size D99 76.2 81.2 43.8 28.8 76.5 32.1 D10/D50 0.639 0.846 0.715 0.710 0.493 0.466 D99/D50 2.309 2.082 1.640 1.858 2.167 1.994 (D99).sup.3/(D50).sup.33 12.31 9.03 4.41 6.4 10.18 7.93 (D99-D10)/D50 1.67 1.24 0.93 1.15 1.67 1.53 CV value 36.9 44.5 22.1 23.1 36.8 18.9 Intermediate shell thickness (m) 5.5 6.5 4.5 2.6 5.9 2.7 Shell thickness ratio 0.47 0.37 0.52 0.63 0.48 0.37 Foaming starting temperature (Ts) 165 167 126 129 122 128 Maximum foaming temperature (Tmax) 212 208 168 164 170 166 Evaluation of Surface property Ra (m) 52.0 48.0 15.82 8.96 25 12.7 molded article Density (g/cm.sup.3) 0.59 0.58 0.46 0.51 0.54 0.58 (0.5 mm Weight reduction rate 33.0% 34.1% 51.8% 47.0% 43.7% 39.9% thickness) Evaluation of Surface property Ra (m) 35.6 32.1 14.0 8.0 20.0 10.0 molded article Density (g/cm3) 0.59 0.62 0.49 0.55 0.59 0.63 (3 mm Weight reduction rate 33.0% 29.5% 48.8% 42.4% 38.8% 34.7% thickness) Surface property deterioration rate 1.46 1.50 1.13 1.12 1.25 1.27 (Ra of 0.5 mm thickness/Ra of 3.0 mm thickness) Surface unevenness of molded article x x x x

INDUSTRIAL APPLICABILITY

[0187] The present invention can provide a thermally expandable microcapsule from which a foam molded article that has a uniform surface, is less prone to surface unevenness, and has an excellently light weight can be produced.

[0188] The present invention can also provide a foamable masterbatch and a foam molded article each produced using the thermally expandable microcapsule.