JP2894990B2 - Thermally expandable microcapsules with excellent heat resistance and solvent resistance - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-expandable microcapsule, and more particularly to a heat-expandable microcapsule excellent in heat resistance and solvent resistance. 2. Description of the Related Art A method for producing thermally expandable microcapsules by using a thermoplastic polymer to microencapsulate a volatile expander which becomes gaseous at a temperature lower than the softening point of the polymer is known. (For example, see Japanese Patent Publication No. 42-26524). US Pat. No. 3,615,972 discloses that about 7 to 60% by weight of vinylidene chloride is copolymerized with an acrylonitrile-based polymer to produce microcapsules having a target (uniform) polymer shell thickness; It has been disclosed to use a crosslinking agent such as divinylbenzene to increase the melt or flow viscosity of the polymer shell. However, it has not been possible to obtain heat-expandable microcapsules having excellent heat resistance and solvent resistance by conventional methods. The present inventors have previously investigated that the use of at least 15% by weight of acrylonitrile as a monomer having a polymerizable unsaturated bond improves the solvent resistance of microcapsules (see Japanese Patent Publication No. 60-21770; In this case, the preferred amount of acrylonitrile used is at most about 70% by weight, as described in the official gazette, page 2, column 4, line 19 to line 22, and the amount used above is unreacted acrylonitrile. Was not intended at all in conjunction with the issue of
Moreover, heat resistance is inferior (expands and expands at about 80 to 130 ° C,
Foaming ratio decreases at high temperature and long time. ) There was room for improvement. SUMMARY OF THE INVENTION The present invention relates to a heat-expandable microcapsule which is superior in heat resistance to conventional products, does not foam at 140 ° C. or lower, and has excellent solvent resistance. It will not be provided. SUMMARY OF THE INVENTION The present invention provides a polymer obtained from a component containing at least 80% by weight of a nitrile monomer, at most 20% by weight of a non-nitrile monomer, and 0.1 to 1% by weight of a crosslinking agent. A heat-expandable microcapsule obtained by microencapsulating a volatile expander which becomes gaseous at a temperature equal to or lower than the softening point of the polymer, wherein the softening temperature of the shell wall is 135 ° C. or higher and 160 ° C. The present invention relates to a heat-expandable microcapsule, which has an expansion ratio of 7 or more upon heating for 1 minute and an expansion ratio of 3 or more upon heating for 4 minutes at 160 ° C. The nitrile monomers used in the present invention include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile,
Fumaronitrile or an arbitrary mixture thereof is exemplified, but acrylonitrile and / or methacrylonitrile are particularly preferred. The amount of the nitrile monomer used is 80% by weight or more, particularly 85 to 97% by weight, and if it is less than 80% by weight, the intended object of the present invention cannot be achieved. [0007] The non-nitrile monomer is selected from the group consisting of methacrylates and acrylates. Of these, methyl methacrylate, ethyl methacrylate and methyl acrylate are particularly preferred. The amount of the non-nitrile monomer used is 20% by weight or less, preferably 1% by weight.
5 to 3% by weight. Examples of the crosslinking agent include divinylbenzene, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, triacrylformal, trimethylolpropane trimethacrylate, allyl methacrylate,
Examples thereof include 1,3-butyl glycol dimethacrylate and triallyl isocyanate, and a trifunctional crosslinking agent such as triacrylformal or trimethylolpropane trimethacrylate is particularly preferable. The amount of crosslinking agent used is 0.1
１1% by weight, preferably 0.2-0.5% by weight. [0009] The wall material of the microcapsule according to the present invention is prepared by appropriately blending a polymerization initiator with the above components, if desired. Suitable polymerization initiators include azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, t-butyl peroxide,
2'-azobis (2,4-dimethylvaleronitrile) and the like are exemplified. The volatile swelling agent contained in the microcapsules is the softening point of the polymer prepared from the above ingredients.
(Generally about 120 to 150 ° C.) a substance which becomes gaseous at a temperature of not more than, for example, propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, hexane, heptane, petroleum ether, methane Low boiling point liquids such as halides (methyl chloride, methylene chloride, CCl ₃ F, CCl ₂ F ₂ etc.), tetraalkylsilanes (tetramethylsilane, trimethylethylsilane etc.) Examples include compounds such as AIBN, and low-boiling liquids such as isobutane, normal butane, normal pentane, isopentane, and petroleum ether are particularly preferred. The method for microencapsulating the volatile swelling agent using the above-mentioned wall material is not particularly limited, and may be in accordance with a conventional method. A particularly preferred method is described, for example, in JP-B-42-26.
No. 524, a method in which a polymerizable monomer and a crosslinking agent are mixed with a volatile swelling agent and a polymerization initiator, and the mixture is subjected to suspension polymerization in an aqueous medium containing an appropriate emulsifying and dispersing aid. It is. The formulation of the aqueous medium in which the suspension polymerization is carried out is not particularly limited, but usually, in addition to inorganic additives such as silica, calcium phosphate, calcium carbonate, sodium chloride and sodium sulfate, organic additives such as diethanolamine-adipin Acid condensates,
Gelatin, methylcellulose, polyvinyl alcohol,
Polyethylene oxide, dioctyl sulfosuccinate, sorbitan ester, etc. are appropriately mixed in deionized water,
The pH of the system is adjusted to about 3-4 with acid. The particle size of the heat-expandable microcapsules of the present invention is usually about 5 to 50 microns, especially about 12 to 25 microns, and the content of the volatile expander is about 10 to 20% by weight, especially about 13%. １７17% by weight. Hereinafter, the present invention will be described with reference to examples. Example 1 An oily mixture and an aqueous mixture prepared according to the following formulation were mixed under pressure (2 kg / m ^{2 of} nitrogen) at 10,000 rpm using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.).
After stirring and mixing for 0 second, the mixture was charged into a nitrogen-substituted pressure polymerization reactor (15 L), pressurized (2 kg / m ² ),
The reaction was performed at 0 ° C. for 20 hours. Oily mixture component parts by weight Acrylonitrile 2450 Methyl methacrylate 400 Triacrylformal 9 n-pentane 550 Azobisisobutyronitrile 15 Aqueous mixture (pH 3.2) Component part by weight Deionized water 6300 Silica dispersion (solid content 20%) ^{1 )} 1080 Potassium dichromate (2.5% aqueous solution) 30 Diethanolamine-adipic acid condensate ²⁾ (50% aqueous solution) 40 Sodium chloride 2200 Hydrochloric acid 1.5 1) Colloidal silica manufactured by Nissan Chemical Co., Ltd. 2) Acid value 100 mg KOH / g The obtained reaction product is repeatedly subjected to filtration using a centrifuge and washing with water to obtain a cake (water content: 32%), which is air-dried all day and night to obtain the heat-expandable microcapsules according to the present invention. An average particle size of about 21.4 microns) was obtained. After immersing the obtained microcapsules in various solvents at 40 ° C. for 10 days, the quality of the thermal expansion was judged, and the solvent resistance of the microcapsules was determined. Table 1 shows the results. The expansion ratio (coating thickness ratio) of the microcapsules under various heating conditions was examined. The results are shown in Table 2. Example 2 A heat-expandable microcapsule (average particle size: about 18.7 microns) was produced in the same manner as in Example 1 except that an oily mixture was prepared according to the following formulation. Ingredients by weight Acrylonitrile 1900 Methacrylonitrile 900 Methyl methacrylate 150 Trimethylolpropane trimethacrylate 9 n-Pentane 350 Petroleum ether 200 The solvent resistance and heat resistance of the obtained microcapsules are shown in Tables 1 and 2 below. It is shown in FIG. Example 3 A heat-expandable microcapsule (average particle size: about 23.2 microns) was produced in the same manner as in Example 1 except that an oily mixture was prepared according to the following formulation. Component parts by weight Acrylonitrile 1750 Methacrylonitrile 800 Methyl acrylate 300 Divinylbenzene 10 n-Hexane 350 Petroleum ether 200 The solvent resistance and heat resistance of the obtained microcapsules are shown in Tables 1 and 2, respectively. Comparative Example 1 Microcapsules (average particle size of about 20.000) were prepared in the same manner as in Example 1 except that an oily mixture was prepared according to the following formulation.
5 microns). Component weight parts Acrylonitrile 900 Vinylidene chloride 2100 Divinylbenzene 15 Isobutane 500 The solvent resistance and heat resistance of the obtained microcapsules are shown in Tables 1 and 2 below, respectively. Comparative Example 2 Microcapsules (average particle size of about 24.000) were prepared in the same manner as in Example 1 except that an oily mixture was prepared according to the following formulation.
7 microns). Component parts by weight Acrylonitrile 1700 Methyl methacrylate 1300 Divinylbenzene 15 Isopentane 350 Petroleum ether 200 The solvent resistance and heat resistance of the obtained microcapsules are shown in Tables 1 and 2, respectively. Comparative Example 3 Microcapsules (average particle size 22.5) were prepared in the same manner as in Example 1 except that the oily mixture was prepared according to the following formulation.
Micron) was prepared. Component parts by weight Acrylonitrile 2400 Vinylidene chloride 600 Divinylbenzene 15 Isobutane 500 The solvent resistance and heat resistance of the obtained microcapsules are shown in Tables 1 and 2, respectively. [Table 1] [Table 2] The heat-expandable microcapsules obtained according to the present invention have better heat resistance than conventional products of this type, do not foam at 140 ° C. or lower, and have excellent solvent resistance. Therefore, it is difficult to use conventional products (for example, polyvinyl chloride, PVC, sol, unsaturated polyester, epoxy resin, urethane resin, rubber, thermoplastic resin, solvent type binder, etc. Accordingly, it can be used in fields such as weight reduction, provision of cushioning property, improvement of rigidity, and foaming ink.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kikuo Niinuma               Matsu, 2-3 1-3 Shibukawacho, Yao City, Osaka Prefecture               Hon Yushi Pharmaceutical Co., Ltd.                (56) References JP-A-56-113338 (JP, A)                 Japanese Patent Publication No. 58-42209 (JP, B2)                 Tokiko Sho 53-45440 (JP, B2)

Claims (1)

(57) [Claims] 80% by weight or more of nitrile type monomer, 20% by weight or less of non-nitrile type monomer and 0.1 to 1% by weight of crosslinking agent
In a heat-expandable microcapsule obtained by microencapsulating a volatile expander that becomes gaseous at a temperature equal to or lower than the softening point of the polymer using a polymer obtained from the contained component, the non-nitrile monomer includes methacrylates and 1 selected from the group consisting of acrylic esters
A kind or two or more kinds of monomers, the softening point of the polymer is 135 ° C. or more, and the expansion ratio at heating at 160 ° C. for 1 minute is 7 or more, and the expansion ratio at heating at 160 ° C. for 4 minutes is 3 or more. A heat-expandable microcapsule, characterized in that: