FOAM AND METHOD FOR MANUFACTURING FOAM

Abstract

The present invention aims to provide a foam that is less likely to deflate even after prolonged or repeated load application, has low density, and has good appearance quality, and a method for producing the foam. Provided is a foam including cells dispersed in an elastomer resin, the cells having an average diameter of 40 to 60 μm and an average circularity of 0.990 or greater.

Claims

1. A foam comprising cells dispersed in an elastomer resin, the cells having an average diameter of 40 to 60 μm and an average circularity of 0.990 or greater.

2. The foam according to claim 1, wherein the foam has a thickness of 300 μm or greater, the foam has a surface layer that is a portion from a surface to a depth of 100 μm and a center portion that is a portion other than the surface layer, the cells in the surface layer have an average circularity of 0.980 or greater, and the cells in the center portion have an average circularity of 0.990 or greater.

3. The foam according to claim 1, wherein the cells of the foam are formed by thermal expansion of thermally expandable microcapsules, the thermally expandable microcapsules each containing: a shell containing a polymer; and a volatile liquid as a core agent encapsulated by the shell.

4. The foam according to claim 1, wherein the foam has an average surface roughness (Ra) of 5 μm or smaller.

5. The foam according to claim 1, wherein the foam has a compression set at 70° C. of 45% or smaller.

6. The foam according to claim 1, wherein the elastomer resin is a thermoplastic olefinic elastomer.

7. A method for producing the foam according to claim 1, comprising steps of: preparing a composition for foam molding containing thermally expandable microcapsules having an average particle size of 10 to 20 μm and an elastomer resin; and extrusion-molding the composition for foam molding, the step of extrusion molding being performed at a depressurizing speed in a die of an extrusion molding machine of 10 MPa/cm or greater.

Description

DESCRIPTION OF EMBODIMENTS

[0152] Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

(Production of Thermally Expandable Microcapsule)

[0153] A polymerization reaction container was charged with 300 parts by weight of water, 89 parts by weight of sodium chloride as an adjustor, 0.07 parts by weight of sodium nitrite as a water-soluble polymerization inhibitor, 8 parts by weight of colloidal silica (produced by Asahi Denka) as a dispersion stabilizer, and 0.3 parts by weight of polyvinylpyrrolidone (produced by BASF), whereby an aqueous dispersion medium was prepared. Subsequently, the aqueous dispersion medium was mixed with an oily mixture containing a metal salt, monomers, a volatile expansion agent, and a polymerization initiator in the amounts shown in Table 1, whereby a dispersion was prepared. The total dispersion was 15 kg. The obtained dispersion was stirred and mixed with a homogenizer, fed to a pressure polymerization vessel (20 L) purged with nitrogen, pressurized (0.2 MPa), and reacted at 60° C. for 20 hours to give a reaction product. The obtained reaction product was repeatedly dehydrated and water-washed with a centrifuge, and dried to give thermally expandable microcapsules (Nos. 1 to 3). The amount of colloidal silica added to the thermally expandable microcapsules was as shown in Table 1.

[0154] In Table 1, the polymerizable monomer (I) is denoted as Monomer (I), the radically polymerizable unsaturated carboxylic acid monomer (II) as Monomer (II), and the polymerizable monomer (III) as Monomer (III).

EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 6

[0155] An amount of 95 parts by weight of a resin and 5 parts by weight of thermally expandable microcapsules of the types shown in Table 2 were mixed in an extrusion molding machine (GT-40, produced by Research Laboratory of Plastics Technology Co., Ltd.) and extrusion-molded at a resin temperature of 200° C., a residence time of 1 minute, a screw rotation rate of 60 rpm, and a maximum pressure shown in Table 2, whereby a foam having a thickness shown in Table 2 was obtained. In Table 2, “Milastomer” denotes Milastomer 7030BS (elastomer resin, produced by Mitsui Chemicals, Inc.), “Non-crosslinked TPO” denotes EXCELINK 3700B (produced by JSR), and “Styrenic (thermoplastic elastomer)” denotes AR-1060 (produced by Aronkasei Co., Ltd.). The Milastomer 7030BS is an olefinic thermoplastic vulcanizate (TPV) having a sea-island structure composed of a sea phase of PP and an island phase of crosslinked EPDM. The EXCELINK 3700B is an elastomer matrix crystalline pseudo-crosslink type TPO (non-crosslinked TPO) in which a polyolefin resin forms a network structure in an EP rubber matrix. The AR-1060 is a styrene-ethylene/butene-styrene block copolymer (SEBS). Table 2 includes the details of the screw configuration (sub flight type, full flight type), the pressure before the die [MPa], the die outlet thickness [mm], and the depressurizing speed [MPa/cm].

[0156] The depressurizing speed is the value obtained by calculating the pressure at the die inlet from the melt viscosity data of the resin measured with Capilograph (Toyo Seiki Seisaku-Sho, Ltd. Capilograph 1B) under the following conditions and from extrusion molding conditions, and dividing the pressure by the die length.

[0157] [Capilograph Measurement Conditions]

[0158] test temperature: 180° C., 190° C., 200° C.

[0159] capillary length: 1 mm, capillary diameter: 1 mm

[0160] piston speed (mm/min): 0.5 to 300

(Evaluation)

[0161] The thermally expandable microcapsules (Nos. 1 to 3) and the foams obtained in Example 1 to 6 and Comparative Examples 1 to 6 were evaluated for the following performances. Table 1 and Table 2 show the results. [0162] (1) Evaluation of Thermally Expandable Microcapsules [0163] (1-1) Volume Average Particle Size

[0164] The volume average particle size was measured with a particle size distribution analyzer (LA-910, produced by HORIBA, Ltd.). [0165] (1-2) Foaming Starting Temperature, Maximum Foaming Temperature, and Maximum Displacement

[0166] 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 heating rate of 5° C./min from 80° C. to 220° C. with a force of 0.1 N applied from the top. The displacement of a measuring terminal in the perpendicular direction was measured. 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.

TABLE-US-00001 TABLE 1 Thermally expandable microcapsule No. No. 1 No. 2 No. 3 Thermally Amount Monomer (I) Acrylonitrile 20 20 20 expandable of oily Methacrylonitrile 30 30 30 microcapsule dispersion Monomer (II) Methacrylic acid 30 30 30 medium Monomer (III) Trimethylolpropane trimethacrylate 0 0 0 (parts by Trimethylolpropane triacrylate 0 0 0 weight) Metal salt (IV) Zinc hydroxide 1.5 1.5 1.5 Other monomers Methyl methacrylate 20 20 20 Volatile Isopentane 15 15 15 expansion agent Isooctane 10 10 10 Polymerization 2,2′-Azobisisobutyronitrile 0.8 0.8 0.8 initiator 2,2′-Azobis(4-methoxy-2,4- 0.6 0.6 0.6 dimethylvaleronitrile) Amount Water 300 300 300 of aqueous Sodium chloride 89 89 89 dispersion Sodium nitrite 0.07 0.07 0.07 medium Colloidal silica 12.5 7.5 11 (parts by Polyvinylpyrrolidone 0.3 0.3 0.3 weight) Evaluation Average particle size (μm) 18 26 20 Foaming starting temperature (Ts) (° C.) 179 175 177 Maximum foaming temperature (Tmax) (° C.) 220 216 220 Maximum displacement (Dmax) (μm) 650 950 730 [0167] (2) Evaluation of Cells [0168] (2-1) Average Diameter

[0169] The obtained foam was cut with a razor. The obtained cross section was sputtered with platinum and then observed with an electron microscope. For randomly selected 100 cells (air bubbles), the major axis and the minor axis of each projected air bubble were measured, and the average diameter was calculated by the method below. Here, the average diameter was measured for the cells in the entire cross section. The CV value (%) of the average diameter was shown in Table 2.

[0170] Average diameter: the diameter of each air bubble was determined from the average of the major axis and minor axis, and then the average of the diameters was calculated to determine the average diameter. [0171] (2-2) Average Circularity

[0172] A cross section was observed with an electron microscope in the same manner as in “(2-1) Average diameter”. For randomly selected 100 cells (air bubbles) in the surface layer (portion from the surface to a depth of 100 μm) and randomly selected 100 cells in the center portion (portion other than the surface layer), the area (projected area) and the perimeter of each projected air bubble were measured, and the average circularity was calculated by the method below. Here, the average circularity was calculated for the surface layer and the center portion separately, and then the average circularity for the entire foam was calculated according to the cross-sectional area ratio between the surface layer and the center portion.

[0173] Average circularity: the circularity of each air bubble was determined from the area (A) and the perimeter (B) according to the following equation, and the average was calculated to determine the average circularity. Circularity=4πA/B.sup.2

[0174] Moreover, the projected areas and the perimeters measured above were averaged over the entire foam. The results were shown in Table 2 as the average projected area and the average perimeter. [0175] (2-3) Average Minor-to-Major Axis Ratio

[0176] A cross section was observed with an electron microscope in the same manner as in “(2-1) Average diameter”. For randomly selected 100 cells (air bubbles) in the surface layer (portion from the surface to a depth of 100 μm) and randomly selected 100 cells in the center portion (portion other than the surface layer), the major axis and the minor axis of each projected air bubble were measured, and the average minor-to-major axis ratio was calculated by the method below. Here, the average minor-to-major axis ratio was calculated for the surface layer and the center portion separately, and then the average minor-to-major axis ratio for the entire foam was calculated according to the cross-sectional area ratio between the surface layer and the center portion.

[0177] Average minor-to-major axis ratio: the minor-to-major axis ratio of each air bubble was determined from minor axis/major axis, and the average was calculated to determine the average minor-to-major axis ratio. [0178] (3) Evaluation of Foam [0179] (3-1) Thickness Measurement

[0180] The thickness of the obtained foam was measured using a caliper (produced by Mitutoyo Corporation, CD-S10C). Here, the thickness was measured by measuring the length from one surface of the foam at any position to the other surface in the tangential direction. [0181] (3-2) Density Measurement

[0182] The density of the foam was measured by a method in conformity with JIS K 7112 Method A (water displacement method) with a densimeter MD-200S (produced by Alfa Mirage, Co., Ltd.). [0183] (3-3) Surface Roughness

[0184] The surface roughness (Ra) of the foam surface was measured using a 3D shape measuring device (produced by Keyence Corporation, VR-3000). [0185] (3-4) Compression Set Measurement

[0186] The compression set of the obtained foam was measured by a method in conformity with JIS K6262 under the conditions of 70° C., 22 hours, and 25% compression.

TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Formulation Resin Type Milastomer Milastomer Milastomer Non- Styrenic crosslinked thermoplastic TPO elastomer Amount [% by weight] 95.0 95.0 95.0 95.0 95.0 Thermally Type No. 1 No. 1 No. 1 No. 1 No. 1 expandable Amount [% by weight] 5.0 5.0 5.0 5.0 5.0 microcapsule Molding Resin temperature [° C.] 200 200 200 200 200 conditions Rotation rate [rpm] 60 60 90 60 60 Screw configuration Sub Full Sub Sub Sub flight flight flight flight flight Maximum pressure [MPa] 18.4 28.4 25.4 17.3 17.8 Pressure before die (Screw tip pressure) 9.5 8 9 9.3 8.6 Die structure Die outlet thickness 0.8 0.8 0.8 0.8 0.8 [mm] Pressure gradient Depressurizing 15.04 14.1 14.6 15.12 14.02 speed [MPa/cm] Cell Average diameter Measured value [μm] 47.54 47.51 46.50 47.44 44.64 evaluation CV [%] 20.23 22.36 27.30 21.89 22.23 Average circularity Entire foam 0.993 0.993 0.993 0.996 0.995 Surface layer 0.985 0.985 0.984 0.988 0.987 Center portion 0.995 0.995 0.995 0.997 0.997 Average Entire foam 0.905 0.902 0.905 0.904 0.893 minor-to-major Surface layer 0.849 0.813 0.823 0.833 0.828 axis ratio Center portion 0.918 0.923 0.925 0.921 0.908 Average projected Entire foam [μm.sup.2] 1775 1773 1698 1768 1565 area Average perimeter Entire foam [μm] 149.9 149.8 146.6 149.6 140.8 Foam Thickness [μm] 1050 1040 1040 1060 1060 evaluation Density [g/cm.sup.3] 0.598 0.631 0.626 0.615 0.608 Surface roughness (Ra) [μm] 4.04 3.66 3.86 3.75 3.91 Compression set [%] 38.1 43.1 42.1 40.0 41.4 Comparative Comparative Comparative Example 6 Example 1 Example 2 Example 3 Formulation Resin Type Milastomer Milastomer Milastomer Milastomer Amount [% by weight] 95.0 95.0 95.0 95.0 Thermally Type No. 3 No. 2 No. 2 No. 2 expandable Amount [% by weight] 5.0 5.0 5.0 5.0 microcapsule Molding Resin temperature [° C.] 200 200 200 190 conditions Rotation rate [rpm] 60 60 90 60 Screw configuration Sub Sub Sub Sub flight flight flight flight Maximum pressure [MPa] 16.3 16.5 11.8 17.2 Pressure before die (Screw tip pressure) 8.7 7.3 8.1 7.7 Die structure Die outlet thickness 0.8 1.4 1.4 1.4 [mm] Pressure gradient Depressurizing 13.89 6.46 6.87 7 speed [MPa/cm] Cell Average diameter Measured value [μm] 58.42 85.18 82.12 83.31 evaluation CV [%] 26.23 27.28 28.28 25.16 Average circularity Entire foam 0.996 0.993 0.994 0.994 Surface layer 0.989 0.972 0.986 0.982 Center portion 0.997 0.995 0.995 0.995 Average Entire foam 0.902 0.878 0.910 0.910 minor-to-major Surface layer 0.839 0.760 0.878 0.839 axis ratio Center portion 0.916 0.892 0.914 0.919 Average projected Entire foam [μm.sup.2] 2680 5699 5296 5451 area Average perimeter Entire foam [μm] 184.2 268.6 258.8 262.6 Foam Thickness [μm] 1070 1870 1860 1860 evaluation Density [g/cm.sup.3] 0.552 0.477 0.48 0.462 Surface roughness (Ra) [μm] 4.92 39.66 27.86 23.97 Compression set [%] 41.5 55.7 47.0 47.4 Comparative Comparative Comparative Example 4 Example 5 Example 6 Formulation Resin Type Milastomer Milastomer Milastomer Amount [% by weight] 95.0 95.0 95.0 Thermally Type No. 1 No. 2 No. 2 expandable Amount [% by weight] 5.0 5.0 5.0 microcapsule Molding Resin temperature [° C.] 200 200 200 conditions Rotation rate [rpm] 60 60 60 Screw configuration Sub Sub Full flight flight flight Maximum pressure [MPa] 16.2 16.6 24.8 Pressure before die (Screw tip pressure) 7.5 8.9 8.1 Die structure Die outlet thickness 1.4 0.8 0.8 [mm] Pressure gradient Depressurizing 6.39 14.98 13.97 speed [MPa/cm] Cell Average diameter Measured value [μm] 47.67 80.8 85.4 evaluation CV [%] 20.04 28.36 26.08 Average circularity Entire foam 0.988 0.994 0.991 Surface layer 0.973 0.996 0.981 Center portion 0.990 0.994 0.992 Average Entire foam 0.906 0.895 0.885 minor-to-major Surface layer 0.822 0.886 0.865 axis ratio Center portion 0.916 0.897 0.890 Average projected Entire foam [μm.sup.2] 1785 5125 5733 area Average perimeter Entire foam [μm] 150.7 254.5 269.7 Foam Thickness [μm] 1875 1080 1060 evaluation Density [g/cm.sup.3] 0.56 0.499 0.469 Surface roughness (Ra) [μm] 5.9 11.61 13.69 Compression set [%] 40.1 48.5 56.6

INDUSTRIAL APPLICABILITY

[0187] The present invention can provide a foam that is less likely to deflate even after prolonged or repeated load application, has low density, and has good appearance quality. The foam of the present invention, having low water absorption, can be suitably used as a foam layer of a pipe or the like in an application such as piping in which water passes through pipes. The present invention can also provide a method for producing the foam.