Foam molding masterbatch, and molded foam article

Abstract

The present invention aims to provide a masterbatch for foam molding which can be suitably used in molding involving high shear force or molding requiring low molding temperature and which can provide a foam molded article having a high expansion ratio and good appearance quality. The present invention also aims to provide a foam molded article formed from the masterbatch for foam molding. Provided is a masterbatch for foam molding, containing: a base resin; and a thermally expandable microcapsule, the masterbatch having a true specific gravity of 0.80 g/cm.sup.3 or more and a Mooney viscosity ML 1+4 (100° C.) of 20 to 90, the base resin containing an EPDM resin, the masterbatch containing the thermally expandable microcapsule in an amount of 40 to 300 parts by weight relative to 100 parts by weight of the base resin.

Claims

1. A masterbatch for foam molding, comprising: a base resin; and a thermally expandable microcapsule, the masterbatch having a true specific gravity of 0.80 g/cm.sup.3 or more and a Mooney viscosity ML 1+4 (100° C.) of 20 to 90, the base resin containing an EPDM resin, the masterbatch containing the thermally expandable microcapsule in an amount of 40 to 300 parts by weight relative to 100 parts by weight of the base resin, wherein the EPDM resin has a diene content of 2.3 to 9.5% by weight.

2. The masterbatch for foam molding according to claim 1, wherein the EPDM resin has an ethylene content of 50 to 72% by weight.

3. The masterbatch for foam molding according to claim 1, wherein the thermally expandable microcapsule includes: a shell containing a polymer; and a volatile expansion agent as a core agent encapsulated by the shell, and the shell contains a polymer obtained by polymerizing a monomer mixture that contains a polymerizable monomer containing at least one selected from acrylonitrile, methacrylonitrile, and vinylidene chloride.

4. The masterbatch for foam molding according to claim 1, wherein the thermally expandable microcapsule has a maximum foaming temperature of 180° C. or lower.

5. A foam molded article formed from the masterbatch for foam molding according to claim 1.

6. The masterbatch for foam molding according to claim 1, wherein the EPDM resin has an propylene content of 20 to 50% by weight.

7. The masterbatch for foam molding according to claim 1, wherein the thermally expandable microcapsule has a bulk specific gravity of 0.42 g/cm.sup.3 or more.

Description

DESCRIPTION OF EMBODIMENTS

(1) Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

(2) (Production of Thermally Expandable Microcapsule)

(3) 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 (available from Asahi Denka) as a dispersion stabilizer, and 0.3 parts by weight of polyvinylpyrrolidone (available from BASF), whereby an aqueous dispersion medium was prepared. Subsequently, the aqueous dispersion medium was mixed with an oily mixture containing the polymerizable monomer, volatile expansion agent, and polymerization initiator shown in Table 1 to prepare a dispersion. 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).

Examples 1 to 9 and Comparative Examples 1 to 3

(4) (Production of Masterbatch Pellet)

(5) The base resin, thermally expandable microcapsules, and process oil (available from Idemitsu Kosan Co., Ltd., Diana Process Oil PW-90, paraffinic process oil) shown in Table 2 were kneaded with 5 parts by weight of stearic acid as a lubricant with a pressurizing kneader at 70° C. for five minutes. The kneaded product was mixed with a roll machine at a roll temperature of 60° C., a roll speed of 20 rpm, and a distance between rolls of 1 cm for five minutes, whereby a sheet form masterbatch having a thickness of 1 cm was obtained.

(6) The following EPDMs were used.

(7) EPDM (1): Mooney viscosity [ML 1+4 (100° C.)]: 8, ethylene content: 54% by weight, diene component: ENB, diene content: 7.6% by weight, propylene content: 38.4% by weight

(8) EPDM (2): Mooney viscosity [ML 1+4 (100° C.)]: 24, ethylene content: 51% by weight, diene component: ENB, diene content: 8.1% by weight, propylene content: 40.9% by weight

(9) EPDM (3): Mooney viscosity [ML 1+4 (100° C.)]: 40, ethylene content: 56% by weight, diene component: ENB, diene content: 4.7% by weight, propylene content: 39.3% by weight

(10) EPDM (4): Mooney viscosity [ML 1+4 (100° C.)]: 44, ethylene content: 50% by weight, diene component: DCPD, diene content: 5.0% by weight, propylene content: 45.0% by weight

Comparative Example 4

(11) (Production of Masterbatch Pellet)

(12) An amount of 100 parts by weight of the base resin shown in Table 2 was kneaded with 10 parts by weight of a fatty acid ester as a lubricant with a Banbury mixer. When about 100° C. was reached, the obtained thermally expandable microcapsules were added in the amount shown in Table 2, followed by kneading for additional 30 seconds. The kneaded product was extruded and pelletized at the same time, whereby masterbatch pellets were obtained. The LDPE in Table 2 denotes low density polyethylene.

Comparative Example 5

(13) The base resin, thermally expandable microcapsules, and process oil (available from Idemitsu Kosan Co., Ltd., Diana Process Oil PW-90, paraffinic process oil) shown in Table 2 were kneaded with 5 parts by weight of stearic acid as a lubricant with a pressurizing kneader at 120° C. for five minutes. The kneaded product was mixed with a roll machine at a roll temperature of 80° C., a roll speed of 20 rpm, and a distance between rolls of 1 cm for five minutes, whereby a sheet form masterbatch having a thickness of 1 cm was obtained.

(14) The following EPDM was used.

(15) EPDM (1): Mooney viscosity [ML 1+4 (100° C.)]: 8, ethylene content: 54% by weight, diene component: ENB, diene content: 7.6% by weight, propylene content: 38.4% by weight

(16) (Production of Foam Molded Article)

(17) An EPDM composition was prepared by mixing 100 parts by weight of an EPDM resin (ethylene content: 63% by weight, diene content: 4.4% by weight), 335 parts by weight of other additives (zinc oxide, stearic acid, carbon black, heavy calcium carbonate, and paraffin oil), 1 part by weight of sulfur, and 4 parts by weight of a vulcanization accelerator. The obtained masterbatch pellets and 100 parts by weight of the EPDM composition prepared were mixed. The mixed pellets were fed to a hopper of an extruder, melted and kneaded, and extrusion molded into a sheet form molded article. The extrusion was performed at a mold temperature of 80° C. The sheet form molded article obtained by extrusion molding was heated in a hot air oven (available from Espec Corp.) at 200° C. for five minutes, whereby a foam molded article was obtained.

(18) Evaluation

(19) The thermally expandable microcapsules (Nos. 1 to 3) and the molded articles obtained in Examples 1 to 9 and Comparative Examples 1 to 5 were evaluated for the following properties. Table 1 and Table 2 show the results. In Comparative Example 2, the masterbatch could not be produced, so that the following evaluations were not performed.

(20) (1) Evaluation of Thermally Expandable Microcapsules

(21) (1-1) Volume Average Particle Size

(22) The volume average particle size was measured with a particle size distribution analyzer (LA-910, available from HORIBA, Ltd.).

(23) (1-2) Foaming Starting Temperature, Maximum Foaming Temperature, and Maximum Displacement

(24) The foaming starting temperature (Ts), maximum displacement (Dmax), and maximum foaming temperature (Tmax) were measured with a thermomechanical analyzer (TMA) (TMA2940, available from 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.

(25) TABLE-US-00001 TABLE 1 {circle around (1)} {circle around (2)} {circle around (3)} Thermally Amount Polymerizable Acrylonitrile 60 67 67 expandable (parts by monomer Methacrylonitrile 35 30 30 microcapsule weight) Dipentaerythritol 0.2 0.5 0.5 hexaacrylate Vinyl acetate 5 3 3 Volatile expansion Isopentane 20 15 25 agent Hexane 0 10 0 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) Volume average particle size (μm) 16 23 28 Foaming starting temperature (Ts) (° C.) 128 137 126 Maximum foaming temperature (Tmax) (° C.) 157 163 162 Maximum displacement (Dmax) (μm) 600 600 900
(2) Evaluation of Masterbatch
(2-1) Measurement of True Specific Gravity

(26) The true specific gravity of the masterbatch pellets was measured by a method in conformity with Method A (water displacement method) of JIS K 7112 with a densimeter MD-200S (available from Alfa Mirage, Co., Ltd.).

(27) (2-2) Measurement of Mooney Viscosity

(28) The Mooney viscosity of the obtained masterbatch pellets was measured at 100° C. by a method in conformity with JIS K 6300.

(29) (3) Evaluation of Molded Article

(30) (3-1) Density and Expansion Ratio

(31) The density before foaming and the density of the obtained molded article (after foaming) were measured by a method in conformity with Method A (water displacement method) of JIS K 7112.

(32) The expansion ratio was calculated from the density of the molded article before and after foaming.

(33) (3-2) Surface Properties

(34) The surface roughness (Rz) of the molded article surface was measured with a 3D shape form measurement system (available from Keyence Corporation). The surface properties were evaluated according to the following criteria.

(35) ∘ (Good): The measured Rz value was less than 50 μm.

(36) Δ (Fair): 50 μm≤Rz value≤100 μm

(37) × (Poor): The measured Rz value was more than 100 μm.

(38) (3-3) Dispersibility

(39) A cross section of the obtained molded article was visually observed with an electron microscope. The dispersibility of the thermally expandable microcapsules was evaluated according to the following criteria.

(40) ∘ (Good): Cell distribution was uniform.

(41) × (Poor): Cell distribution was not uniform.

(42) TABLE-US-00002 TABLE 2 Example Comparative Example (1) (2) (3) (4) (5) (6) (7) (8) (9) (1) (2) (3) (4) (5) Thermally expandable {circle around (1)} {circle around (1)} {circle around (1)} {circle around (1)} {circle around (2)} {circle around (2)} {circle around (3)} {circle around (1)} {circle around (1)} {circle around (1)} {circle around (1)} {circle around (1)} {circle around (1)} {circle around (3)} microcapsule No. Base resin EPDM (1) 100 0 0 0 100 0 100 100 100 100 100 100 0 100 used in EPDM (2) 0 100 0 0 0 100 0 0 0 0 0 0 0 0 masterbatch EPDM (3) 0 0 100 0 0 0 0 0 0 0 0 0 0 0 (parts by EPDM (4) 0 0 0 100 0 0 0 0 0 0 0 0 0 0 weight) LDPE 0 0 0 0 0 0 0 0 0 0 0 0 100 0 Process oil 100 100 100 100 100 100 100 100 100 100 100 30 0 100 Amount of thermally expandable 100 100 100 100 100 100 100 50 200 30 500 100 100 100 microcapsules in masterbatch relative to 100 parts by weight of base resin (parts by weight) Amount of masterbatch 5 5 5 5 5 5 5 5 5 5 5 5 5 5 in molded article relative to 100 parts by weight of EPDM resin (parts by weight) Masterbatch True specific 0.95 0.91 0.88 0.92 0.89 0.93 0.93 0.88 0.94 1.06 Masterbatch 0.88 0.96 0.76 evaluation gravity (g/cm.sup.3) production Mooney viscosity 42 66 73 76 44 69 45 33 55 28 failed 98 — 46 (ML (1 + 4) 100° C.) Molded Density (g/cm.sup.3) 0.83 0.84 0.82 0.82 0.88 0.86 0.81 0.93 0.72 1.01 0.83 0.88 1.05 article Expansion ratio 1.33 1.31 1.34 1.34 1.25 1.28 1.36 1.18 1.53 1.09 1.33 1.25 1.05 evaluation Surface properties ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Δ x Δ Dispersibility ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ x x x

INDUSTRIAL APPLICABILITY

(43) The present invention can provide a masterbatch for foam molding which can be suitably used in molding involving high shear force or molding requiring low molding temperature and which can provide a foam molded article having a high expansion ratio and good appearance quality. The present invention also aims to provide a foam molded article formed from the masterbatch for foam molding.