Thermally expandable microcapsule, method for producing thermally expandable microcapsule, foamable masterbatch, and foam molded article

Abstract

The present invention provides a thermally expandable microcapsule that is excellent in heat resistance and durability and exhibits an excellent foaming property in a wide temperature range from low temperatures to high temperatures. The present invention is a thermally expandable microcapsule, which comprises a shell containing a copolymer, and a volatile liquid as a core agent included in the shell, the copolymer being obtainable by polymerization of a monomer mixture containing a monomer A and a monomer B, the monomer A being at least one selected from the group consisting of a nitrile group-containing acrylic monomer and an amide group-containing acrylic monomer, the monomer B being at least one selected from the group consisting of a carboxyl group-containing acrylic monomer and an ester group-containing acrylic monomer, a total amount of the monomer A and the monomer B accounting for 70% by weight or more of the monomer mixture, and a weight ratio of the monomer A and the monomer B being 5:5 to 9:1.

Claims

1. A thermally expandable microcapsule, which comprises a shell containing a copolymer, and a volatile liquid as a core agent included in the shell, the copolymer being obtainable by polymerization of a monomer mixture containing a monomer A and a monomer B, the monomer A being at least one selected from the group consisting of a nitrile group-containing acrylic monomer and an amide group-containing acrylic monomer, the monomer B being t-butyl acrylate and acrylic acid, a total amount of the monomer A and the monomer B accounting for 70% by weight or more of the monomer mixture, and a weight ratio of the monomer A and the monomer B being 5:5 to 9:1, the monomer B being 10% to 30% by weight of t-butyl acrylate and 10% to 30% by weight of acrylic acid, wherein the weigh percentages of t-butyl acrylate and acrylic acid are relative to the total weight of the monomer A and the monomer B.

2. The thermally expandable microcapsule according to claim 1, wherein the nitrile group-containing acrylic monomer is acrylonitrile and the amide group-containing acrylic monomer is at least one selected from the group consisting of acrylamide, an N-substituted acrylamide, and an N,N-substituted acrylamide.

3. The thermally expandable microcapsule according to claim 2, wherein the N-substituted acrylamide is at least one selected from the group consisting of N-isopropylacrylamide, N-methylolacrylamide, N-methoxymethyl acrylamide, N-ethoxymethyl acrylamide, N-propoxymethyl acrylamide, N-isopropoxymethyl acrylamide, N-butoxymethyl acrylamide, N-isobutoxymethyl acrylamide, diacetone acrylamide, and N,N-dimethylaminopropyl acrylamide, and the N,N-substituted acrylamide is at least one selected from the group consisting of N,N-dimethylacrylamide, N,N-diethylacrylamide, and acryloyl morpholine.

4. The thermally expandable microcapsule according to claim 1, wherein the monomer A is acrylonitrile or acrylamide.

5. A method for producing the thermally expandable microcapsule according to claim 1, the method comprising the step of polymerizing a monomer mixture containing a monomer A and a monomer B, the monomer A being at least one selected from the group consisting of a nitrile group-containing acrylic monomer and an amide group-containing acrylic monomer, and the monomer B being t-butyl acrylate and acrylic acid.

6. A foamable masterbatch, which comprises the thermally expandable microcapsule according to claim 1, and a thermoplastic resin.

7. A foam molded article, which is obtainable by foam molding of a resin composition containing a thermoplastic resin and one of the thermally expandable microcapsule according to claim 1.

8. A foam molded article, which is obtainable by foam molding of a resin composition containing a thermoplastic resin and a foamable masterbatch according to claim 6.

Description

DESCRIPTION OF EMBODIMENTS

(1) The present invention is described in more detail with reference to examples in the following. The present invention is not limited only to these examples.

Examples 1 to 16, Comparative Examples 1 to 9

(2) (1. Production of Thermally Expandable Microcapsule)

(3) A polymerization reaction vessel was charged with water (250 parts by weight), and 20% by weight colloidal silica (20 parts by weight, Asahi Denka) and polyvinyl pyrrolidone (0.2 parts by weight, BASF) as dispersion stabilizers so that an aqueous dispersion medium was prepared. To the aqueous dispersion medium, an oily mixture containing monomers (100 parts by weight) at a blending ratio shown in Table 1, 2, or 3, azobisisobutyronitrile (AIBN, 0.8 parts by weight) and 2,2′-azobis(2,4-dimethylvaleronitrile) (ADVN, 0.6 parts by weight) as polymerization initiators, and isopentane (20 parts by weight) and isooctane (10 parts by weight) as volatile liquids were added so that a dispersion liquid was prepared. The dispersion liquid was stirred with a homogenizer and placed in a nitrogen-substituted pressure polymerization vessel. The dispersion liquid was allowed to react for 24 hours at 70° C. while being pressurized (0.5 MPa), so that a reaction product was obtained. The reaction product was filtered and the residue was washed with water. These processes were conducted repeatedly. The resulting matter was dried to give a thermally expandable microcapsule.

(4) (2. Production of Foamable Masterbatch)

(5) Low-density polyethylene (100 parts by weight, “SUNFINE PAK00720”, ASAHI KASEI) and a stearic acid (10 parts by weight) as lubricants were mixed with a Banbury mixer (twin screw conical extruder “OSC-30”, NAGATASEISAKUSYO CO., LTD.). When the temperature of the mixture reached about 100° C., the above thermally expandable microcapsule (100 parts by weight) was added thereto. The mixture was further kneaded for 30 seconds and then extruded and pelletized at the same time. In this manner, a foamable masterbatch was produced.

(6) (3. Production of Foam Molded Article)

(7) A thermoplastic elastomer (100 parts by weight, Hytrel #8752, DuPont) as a molding base, the above foamable masterbatch (2.5 parts by weight), and a color masterbatch (3 parts by weight, TOKYO PRINTING INK MFG. CO., LTD.) as a colorant were extrusion-molded by an extruder (“USV30-20”, Union Plastic Public Co., Ltd.) to give a foam molded article.

(8) (Evaluation 1)

(9) The thermally expandable microcapsules of examples and comparative examples were each evaluated as follows. Tables 1, 2, and 3 show the results. In addition, Tables 1, 2, and 3 show the nitrile group-containing monomer content (nitrile ratio) (% by weight) in the used monomers in the examples and the comparative examples.

(10) (1) Heat Resistance, Expansion Ratio, Durability, and Shear Strength of Thermally Expandable Microcapsule

(11) The resulting thermally expandable microcapsules were each heated from ambient temperature to 280° C. at a rate of 5° C./min with use of a heat foaming stage microscope (JAPAN HIGH TECH CO., LTD.). From any five images of the thermally expandable microcapsule, change of the average particle size was measured each time the temperature rises by 5° C. The maximum foaming temperature (Tmax) (° C.) was measured and the heat resistance was evaluated based on the following criteria.

(12) X: The maximum foaming temperature (Tmax) was lower than 185° C.

(13) Δ: The maximum foaming temperature (Tmax) was not lower than 185° C. and lower than 190° C.

(14) ◯: The maximum foaming temperature (Tmax) was not lower than 190° C. and lower than 200° C.

(15) ◯◯: The maximum foaming temperature (Tmax) was not lower than 200° C.

(16) The ratio of the average particle size of the thermally expandable microcapsule at the maximum foaming temperature (Tmax) to that at 30° C. herein was the expansion ratio at the maximum foaming temperature (Tmax).

(17) X: The expansion ratio at the maximum foaming temperature (Tmax) was less than 3.0 times.

(18) Δ: The expansion ratio at the maximum foaming temperature (Tmax) was not less than 3.0 times and less than 4.0 times.

(19) ◯: The expansion ratio at the maximum foaming temperature (Tmax) was not less than 4.0 times and less than 5.0 times.

(20) ◯◯: The expansion ratio at the maximum foaming temperature (Tmax) was not less than 5.0 times.

(21) The durability was evaluated by measuring ΔT½ that is herein a temperature width (half width) in which the expansion ratio is not lower than the half of the ratio at the maximum foaming temperature (Tmax) based on the following criteria.

(22) X: ΔT½ was narrower than 30° C.

(23) Δ: ΔT½ was not narrower than 30° C. and narrower than 40° C.,

(24) ◯: ΔT½ was not narrower than 40° C. and narrower than 50° C.

(25) ◯◯ T½ was not narrower than 50° C.

(26) The temperature at which foaming started herein was a foaming starting temperature (Ts) in static conditions. The temperature at which foaming started in the case where a stage of the above-mentioned heat foaming stage microscope was rotated during the heating was a foaming starting temperature (Tsd) in shear conditions. A difference (ΔTs=Ts−Tsd) between the foaming starting temperature (Ts) in static conditions and the foaming starting temperature (Tsd) in shear conditions was obtained and the shear strength was evaluated based on the following criteria.

(27) X: ΔTs was not less than 20° C.

(28) ◯: ΔTs was less than 20° C.

(29) TABLE-US-00001 TABLE 1 Total Expansion amount ratio Monomer of A Heat Expan- Shear Parts and B resistance sion Durability strength Ni- by (% by Tmax Evalu- ratio Evalu- ΔT½ Evalu- ΔTs Evalu- trile Kind weight weight) A:B (° C.) ation (times) ation (° C.) ation (° C.) ation ratio Exam- Monomer Acrylonitrile 70 100 7.00:3.00 207 ◯◯ 4.6 ◯ 91 ◯◯ 0 ◯ 70 ple 1 A (AN) Monomer Acrylic acid 30 B (AA) Exam- Monomer Acrylonitrile 50 100 5.00:5.00 224 ◯◯ 4.4 ◯ 120 ◯◯ 0 ◯ 50 ple 2 A (AN) Monomer Acrylic acid 50 B (AA) Exam- Monomer Acrylonitrile 90 100 9.00:1.00 190 ◯ 4.6 ◯ 48 ◯ 0 ◯ 90 ple 3 A (AN) Monomer Acrylic acid 10 B (AA) Exam- Monomer Acrylamide 70 100 7.00:3.00 204 ◯◯ 4.7 ◯ 46 ◯ 0 ◯ 0 ple 4 A (Am) Monomer Acrylic acid 30 B (AA) Exam- Monomer Acrylamide 70 100 7.00:3.00 191 ◯ 5.1 ◯◯ 42 ◯ 0 ◯ 0 ple 5 A (Am) Monomer t-Butyl acrylate 30 B (tBA) Exam- Monomer Acrylonitrile 70 100 7.00:3.00 195 ◯ 5.1 ◯◯ 49 ◯ 0 ◯ 70 ple 6 A (AN) Monomer t-Butyl acrylate 30 B (tBA) Exam- Monomer Acrylonitrile 60 100 6.00:4.00 212 ◯◯ 4.6 ◯ 89 ◯◯ 0 ◯ 60 ple 7 A (AN) Monomer Acrylic acid 30 B (AA) t-Butyl acrylate 10 (tBA) Exam- Monomer Acrylonrtrile 50 100 5.00:5.00 199 ◯ 4.5 ◯ 42 ◯ 0 ◯ 50 ple 8 A (AN) Monomer Acrylic acid 20 B (AA) Methyl acrylate 30 (MA) Exam- Monomer Acrylonitrile 60 100 6.00:4.00 198 ◯ 4.6 ◯ 42 ◯ 0 ◯ 60 ple 9 A (AN) Monomer Acrylic acid 30 B (AA) Methyl acrylate 10 (MA) Exam- Monomer Acrylonrtrile 50 100 7.00:3.00 212 ◯◯ 4.4 ◯ 110 ◯◯ 0 ◯ 50 ple 10 A (AN) Acrylamide 20 (Am) Monomer Acrylic acid 20 B (AA) t-Butyl acrylate 10 (tBA)

(30) TABLE-US-00002 TABLE 2 Total Expansion amount ratio Monomer of A Heat Expan- Shear Parts and B resistance sion Durability strength Ni- by (% by Tmax Evalu- ratio Evalu- ΔT½ Evalu- ΔTs Evalu- trile Kind weight weight) A:B (° C.) ation (times) ation (° C.) ation (° C.) ation ratio Exam- Monomer Acrylonitrile 80 100 8.00:2.00 202 ◯◯ 4.6 ◯ 65 ◯◯ 0 ◯ 80 ple 11 A (AN) Monomer Acrylic acid 20 B (AA) Exam- Monomer Acrylonitrile 70 90 7.78:2.22 218 ◯◯ 4.9 ◯ 94 ◯◯ 0 ◯ 80 ple 12 A (AN) Monomer Acrylic acid 20 B (AA) Other Methacrylonitrile 10 Monomer (MAN) Exam- Monomer Acrylonitrile 50 70 7.15:2.85 220 ◯◯ 4.9 ◯ 115 ◯◯ 0 ◯ 80 ple 13 A (AN) Monomer Acrylic acid 20 B (AA) Other Methacrylonitrile 30 Monomer (MAN) Exam- Monomer Acrylonitrile 50 80 6.25:3.75 223 ◯◯ 4.7 ◯ 116 ◯◯ 0 ◯ 70 ple 14 A (AN) Monomer Acrylic acid 30 B (AA) Other Methacrylonitrile 20 Monomer (MAN) Exam- Monomer Acrylonitrile 50 90 5.56:4.44 225 ◯◯ 4.4 ◯ 118 ◯◯ 0 ◯ 60 ple 15 A (AN) Monomer Acrylic acid 40 B (AA) Other Methacrylonitrile 10 Monomer (MAN) Exam- Monomer Acrylonitrile 80 90 8.89:1.11 215 ◯◯ 4.5 ◯ 55 ◯◯ 0 ◯ 90 ple 16 A (AN) Monomer Acrylic acid 10 B (AA) Other Methacrylonitrile 10 Monomer (MAN)

(31) TABLE-US-00003 TABLE 3 Total Expansion amount ratio Monomer of A Heat Expan- Shear Parts and B resistance sion Durability strength Ni- by (% by Tmax Evalu- ratio Evalu- ΔT½ Evalu- ΔTs Evalu- trile Kind weight weight) A:B (° C.) ation (times) ation (° C.) ation (° C.) ation ratio Compar- Monomer Acrylonitrile 22.4 22.4 10.00:0.00  222 ◯◯ 2 X 16 X 0 ◯ 44.8 ative A (AN) Exam- Other Methacrylic 53.8 ple 1 monomer acid (MAA) Other Ethylene 1.3 monomer glycol dimeth- acrylate (EGDMA) Other Methacryloni- 22.4 monomer trile (MAN) Compar- Monomer Acrylonitrile 95 100 9.50:0.50 182 X 3.3 Δ 38 Δ 0 ◯ 95 ative A (AN) Exam- Monomer Acrylic acid 5 ple 2 B (AA) Compar- Other Methacryloni- 44 0 — 225 ◯◯ 2.4 X 32 Δ 30 X 44 ative monomer trile (MAN) Exam- Other Methacrylic 56 ple 3 monomer acid (MAA) Compar- Monomer Acrylonitrile 60 60 10.00:0.00  178 X 42 ◯ 24 X 0 ◯ 100 ative A (AN) Exam- Other Methacryloni- 40 ple 4 monomer trile (MAN) Compar- Other Methacrylic 50 50  0.00:10.00 Not granulated 0 ative monomer acid (MAA) Exam- Monomer Acrylic acid 50 ple 5 B (AA) Compar- Monomer Acrylonrtrile 90 90 10.00:0.00  156 X 1.8 X 16 X 0 ◯ 90 ative A (AN) Exam- Other Styrene 10 ple 6 monomer Compar- Monomer Acrylonitrile 61.5 100 9.02:0.98 205 ◯◯ 3 Δ 25 X 0 ◯ 61.5 ative A (AN) Exam- Monomer N,N-Dimethyl- 21.9 ple 7 A acrylamide Monomer N-Methylol- 6.8 A acrylamide Monomer Acrylic acid 9.8 B (AA) Compar- Monomer Acrylonitrile 45 100 4.50:5.50 Not granulated 45 ative A (AN) Exam- Monomer Acrylic acid 55 ple 8 B (AA) Compar- Monomer Acrylonitrile 30 50 6.00:4.00 175 X 4.3 ◯ 25 X 0 ◯ 80 ative A (AN) Exam- Monomer Acrylic acid 20 ple 9 B (AA) Other Methacryloni- 50 monomer trile (MAN)
(Evaluation 2)

(32) The foam molded articles obtained in the examples and comparative examples were each evaluated as follows. Table 4 shows the results. Here, no evaluations were carried out for Comparative Examples 5, 6, 8, and 9.

(33) (1) Expansion Ratio of Foam Molded Article

(34) The specific gravity (D0) of a thermoplastic elastomer (Hytrel #8752, DuPont) as a molding base and the specific gravity (D1) of each foam molded article were measured using an electronic gravimeter (“ED-120T”, Mirage Trading Co., Ltd.). The expansion ratio of each foam molded article was calculated using the following equation (1):
Expansion ratio (times)=(D0/D1)  (1).
Evaluation was conducted based on the following criteria.

(35) X: The expansion ratio was less than 1.5 times.

(36) ◯: The expansion ratio was not less than 1.5 times and less than 2.0 times.

(37) ◯◯: The expansion ratio was not less than 2.0 times.

(38) (2) Tactile Impression of Foam Molded Article

(39) The durometer hardness was measured using a type A durometer in accordance with JIS-K-6253 and the tactile impression of each foam molded article was evaluated based on the following criteria.

(40) X: The durometer hardness was more than 70%.

(41) ◯: The durometer hardness was not more than 70% and more than 60%.

(42) ◯◯: The durometer hardness was not more than 60%.

(43) (3) Damping Property of Foam Molded Article

(44) The static rigidity and the static/dynamic ratio of each foam molded article were measured as follows and the damping property was evaluated. Smaller values of the static rigidity and the static/dynamic ratio indicate better damping properties of the foam molded article.

(45) (3-1) Measurement of Static Rigidity

(46) An indenter (stainless-steel, φ15 mm×10 mm cylinder shape) was placed on the surface of each obtained foam molded article, and the height thereof was marked as 0. A load of 91.5 N was applied to the indenter for 60 seconds and the displacement (S1) was measured using a static testing machine (“EZ Graph”, Shimadzu Corporation). Then, a load of 320 N was applied to the indenter for 60 seconds and the displacement (S2) was measured. The static rigidity was calculated based on the following equation (2):
Static rigidity (N/mm)=(320−91.5)/(S2−S1)  (2).
The evaluation criteria were as follows.

(47) X: The static rigidity was more than 300 N/mm.

(48) ◯: The static rigidity was not more than 300 N/mm and more than 250 N/mm.

(49) ◯◯: The static rigidity was not more than 250 N/mm.

(50) (3-2) Measurement of Static/Dynamic Ratio

(51) An indenter (stainless-steel, φ15 mm×10 mm cylinder shape) was placed on the surface of each obtained foam molded article, and the height thereof was marked as 0. Using a tensilon universal testing machine (“UTA-500”, A&D Company Limited), a cyclic load of 91.5 N at the minimum and 320 N at the maximum was applied to the indenter (1000 cycles). The average values of the following items between the 900th cycle and the 1000th cycle were obtained:

(52) Force (FU) applied and displacement (SU) of the indenter at the maximum pressure, and

(53) Force (FD) applied and displacement (SD) of the indenter at the minimum pressure.

(54) Based on the obtained values, the dynamic rigidity was calculated using the following equation (3).
Dynamic rigidity (N/mm)=(FU−FD)/(SU−SD)  (3)
Moreover, based on the obtained dynamic rigidity and the static rigidity, the dynamic/static ratio was obtained using the following equation (4).
Dynamic/static ratio (times)=dynamic rigidity/static rigidity  (4)
The evaluation criteria were as follows.

(55) X: The dynamic/static ratio was more than 1.5 times.

(56) ◯: The dynamic/static ratio was not more than 1.5 times and more than 1.0 time.

(57) ◯◯: The dynamic/static ratio was not more than 1.0 time.

(58) TABLE-US-00004 TABLE 4 Foam molded article Damping property Expansion ratio Tactile impression Static rigidity Dynamic/static ratio Expansion ratio Durometer Static rigidity Dynamic/static (times) Evaluation hardness (%) Evaluation (N/mm) Evaluation ratio (times) Evaluation Example 1 1.82 ◯ 58 ◯◯ 248 ◯◯ 1.28 ◯ Example 2 1.85 ◯ 61 ◯ 249 ◯◯ 1.25 ◯ Example 3 1.68 ◯ 67 ◯ 265 ◯ 1.24 ◯ Example 4 1.72 ◯ 68 ◯ 264 ◯ 1.24 ◯ Example 5 1.72 ◯ 69 ◯ 268 ◯ 1.2 ◯ Example 6 1.74 ◯ 67 ◯ 252 ◯ 1.28 ◯ Example 7 2.02 ◯◯ 57 ◯◯ 248 ◯◯ 1.36 ◯ Example 8 1.74 ◯ 69 ◯ 259 ◯ 1.28 ◯ Example 9 1.75 ◯ 69 ◯ 257 ◯ 1.28 ◯ Example 10 1.97 ◯ 57 ◯◯ 246 ◯◯ 1.34 ◯ Example 11 1.78 ◯ 61 ◯ 249 ◯◯ 1.32 ◯ Example 12 2.01 ◯◯ 58 ◯◯ 244 ◯◯ 1.36 ◯ Example 13 2 ◯◯ 59 ◯◯ 248 ◯◯ 1.36 ◯ Example 14 2 ◯◯ 58 ◯◯ 248 ◯◯ 1.34 ◯ Example 15 1.84 ◯ 62 ◯ 252 ◯ 1.32 ◯ Example 16 1.78 ◯ 65 ◯ 262 ◯ 1.29 ◯ Comparative 1.47 X 76 X 356 X 1.04 ◯ Example 1 Comparative 1.52 ◯ 72 X 305 X 1.18 ◯ Example 2 Comparative 1.76 ◯ 71 X 302 X 1.16 ◯ Example 3 Comparative 1.72 ◯ 68 ◯ 312 X 1.18 ◯ Example 4 Comparative 1.47 X 74 X 326 X 1.05 ◯ Example 7

INDUSTRIAL APPLICABILITY

(59) The present invention provides a thermally expandable microcapsule that is excellent in the heat resistance and the durability and exhibits an excellent foaming property in a wide temperature range from low temperatures to high temperatures. The present invention also provides a method for producing the thermally expandable microcapsule, and a foamable masterbatch and a foam molded article which are produced from the thermally expandable microcapsule.