Acrylic polymer particles, production process therefor, ink composition, and coating composition

Abstract

Particles of an acrylic polymer comprising a constituent unit (A) derived from methyl methacrylate and a constituent unit (B) derived from a (meth)acrylic acid alkyl ester in which the alkyl group has 2 to 8 carbon atoms, wherein the particles having electrostatic buildup inhibition rate of 90 to 99.9° as obtained by a specific method.

Claims

1. Particles of an acrylic polymer, comprising a constituent unit (A) derived from methyl methacrylate and a constituent unit (B) derived from a (meth)acrylic acid alkyl ester in which the alkyl group has 2 to 8 carbon atoms, wherein the particles are formed of one type of acrylic copolymer obtained by a single polymerization step, and wherein the particles having electrostatic buildup inhibition rate of 90 to 99.9% as obtained by the following method: (Method for obtaining electrostatic buildup inhibition rate): According to JIS K 7365:1999 “Plastics Method for determination of apparent density of material that can be poured from a specified funnel”, volume density (A) of the particles of an acrylic polymer is measured, In addition, an anti-static agent is added in an amount of 0.1 g per 100 mL of the particles of an acrylic polymer, volume density (B) of a mixture obtained by sufficiently mixing them is measured, and the electrostatic buildup inhibition rate is calculated based on the following mathematical equation (1).
Electrostatic buildup inhibition rate (%)=Volume density(A)/Volume density (B)×100  (1)

2. The particles of an acrylic polymer according to claim 1, wherein a sodium element amount in the particles of an acrylic polymer is 3.5 to 50 ppm.

3. The particles of an acrylic polymer according to claim 2, wherein the sodium element amount in the particles of an acrylic polymer is 3.5 to 30 ppm.

4. The particles of an acrylic polymer according to claim 1, wherein the particles have a mass average particle diameter of 100 to 1000 μm.

5. The particles of an acrylic polymer according to claim 1, further comprising a constituent unit (C) derived from α,β-unsaturated carboxylic acid.

6. Particles of an acrylic polymer, comprising a constituent unit (A) derived from methyl methacrylate and a constituent unit (B) derived from (meth)acrylic acid alkyl ester in which the alkyl group has 2 to 8 carbon atoms, the particles having a sodium element amount of 3.5 to 50 ppm, wherein the particles are formed of one type of acrylic copolymer obtained by a single polymerization step.

7. The particles of an acrylic polymer according to claim 6, wherein the sodium element amount in the particles of an acrylic polymer is 3.5 to 30 ppm.

8. The particles of an acrylic polymer according to claim 6, wherein the particles have a mass average particle diameter of 100 to 1000 μm.

9. The particles of an acrylic polymer according to claim 6, further comprising a constituent unit (C) derived from α,β-unsaturated carboxylic acid.

10. A process for producing particles of an acrylic polymer according to claim 1, the process comprising a step of washing the acrylic polymer obtained by suspension polymerization so as to have a sodium element amount of 3.5 to 50 ppm.

11. The process for producing particles of an acrylic polymer according to claim 10, wherein a dispersion agent containing sodium element is used for the suspension polymerization.

12. The process for producing particles of an acrylic polymer according to claim 11, wherein a use amount of the dispersion agent is an amount allowing that the sodium element amount contained in the dispersion agent is 0.0009 to 0.004 part by mass relative to 100 parts by mass of a raw material monomer of the particles of an acrylic polymer.

13. The process for producing particles of an acrylic polymer according to claim 10, wherein a dispersion aid containing sodium element is used for the suspension polymerization.

14. The process for producing particles of an acrylic polymer according to claim 13, wherein a use amount of the dispersion aid is an amount allowing that the sodium element amount contained in the dispersion aid is 0.06 to 0.35 part by mass relative to 100 parts by mass of a raw material monomer of the particles of an acrylic polymer.

15. The process for producing particles of an acrylic polymer according to claim 10, wherein the washing is carried out by using an aqueous solution of a sodium element-containing compound.

16. The process for producing particles of an acrylic polymer according to claim 15, wherein a use amount of the aqueous solution of a sodium element-containing compound is an amount allowing that the sodium element amount contained in the aqueous solution of a sodium element-containing compound is 0.03 to 0.1 part by mass relative to 100 parts by mass of the acrylic polymer.

17. The process for producing particles of an acrylic polymer according to claim 15, wherein mass of the aqueous solution of a sodium element-containing compound to be used for the washing is 1 to 3 times the acrylic polymer.

18. An ink composition, comprising the particles of an acrylic polymer according to claim 1.

19. A coating composition, comprising the particles of an acrylic polymer according to claim 1.

20. An article, comprising the coating composition of claim 19, wherein the article is a container, marine article, or a road marking.

Description

EXAMPLES

(1) Hereinbelow, the present invention is more specifically explained in view of Examples. However, the present invention is not limited thereto.

(2) Measurement and evaluation of each physical property in Examples and Comparative Examples were carried out according to the following methods.

(3) Furthermore, the dispersion agents that are used in Examples and Comparative Examples were prepared according to the following method.

(4) [Measurement⋅Evaluation]

(5) <Measurement of Sodium Element Amount>

(6) The particles of an acrylic polymer (0.15 g) were collected in a platinum crucible and heated on a hot plate over 1 hour from 150° C. to 540° C. and also for 30 minutes at 540° C. Subsequently, the particles of an acrylic polymer were turned into ash in a muffle furnace at 575° C. for 1 hour. To the resultant, 250 μL of 1% by mass aqueous solution of nitric acid were added for dissolution, and dilution to 25 mL was made with ultra pure water. The diluted product was applied to an ICP light emission spectrophotometer to measure the sodium element amount (Na element amount). Furthermore, the measurement conditions are as described in the followings.

(7) (ICP Measurement Conditions) Apparatus: iCAP 6500 manufactured by Thermo Fischer Scientific Inc. RF power: 750 w Pump flow rate: 50 rpm Assisting gas flow rate: 1 L/min Nebulizer gas flow rate: 0.5 L/min Coolant gas flow rate: 12 L/min Purge gas flow rate: Normal Wavelength for measurement: 589.592 (nm)

(8) <Measurement of Average Particle Diameter>

(9) The particles of an acrylic polymer were dispersed in water, and by using “LA-910”, which is a laser diffraction/scattering type particle size distribution analyzer manufactured by HORIBA, Ltd., mass-based particle size distribution was measured and mass average particle diameter was obtained from the obtained particle size distribution.

(10) <Evaluation of Electrostatic Buildup Inhibition Rate>

(11) According to JIS K 7365:1999 “Plastics—Method for determination of apparent density of material that can be poured from a specified funnel”, volume density (A) of the particles of an acrylic polymer was measured. In addition, an anti-static agent (“SILPHONITE M-1” manufactured by Mizusawa Industrial Chemicals Ltd.) was added in an amount of 0.1 g per 100 mL of the particles of an acrylic polymer, volume density (B) of a mixture obtained by sufficiently mixing them was measured, and the electrostatic buildup inhibition rate was calculated based on the equation (1) shown below. Furthermore, when the measurement is made without using an anti-static agent, there is generally a tendency of having smaller volume density as caused by electrostatic repulsion, and, when the measurement is made with use of an anti-static agent, there is a tendency of having higher volume density as caused by reduced electrostatic repulsion. Namely, as the electrostaticity decreases even without using an anti-static agent (that is, as electrostatic buildup is suppressed more), a smaller change in the volume density between a case before the addition of an anti-static agent and a case after the addition of an anti-static agent is yielded, and the electrostatic buildup inhibition rate obtained by the following mathematical formula (1) gets closer to 100%.
Inhibition rate (%)=Volume density(A)/Volume density(B)×100  (1)

(12) <Evaluation of Fluidity>

(13) The fluidity of the particles of an acrylic polymer was measured as follows; a powder funnel made of polyvinyl chloride, which has a mouth diameter of 15 cm and a foot diameter of 1 cm, was used, and while the funnel is fixed, 30 g of the particles of an acrylic polymer were added to the funnel, and the evaluation was made in view of the falling state of the particles.

(14) (Evaluation Criteria) A: The entire amount of the particles had fallen continuously. B: Particle clogging had occurred during the process so that not all of the entire amount had fallen.

(15) <Evaluation of Solubility of Particles of Acrylic Polymer in Toluene>

(16) Toluene (40 g) was added to a flask. While stirring it at room temperature using a stirrer, the particles of an acrylic polymer (60 g) were added thereto in small portions. After stirring them for 2 hours at 60° C., the solubility was determined by naked eye observation based on transparency of the solution.

(17) (Evaluation Criteria) A: The solution was transparent and excellent solubility was obtained. B: There was just slight white cloudiness of the solution, and the solubility was good. C: There was white cloudiness of the solution, and the solubility was poor.

(18) [Preparation of Dispersion Agent (1)]

(19) In a polymerization device equipped with a stirrer, a condenser, and a thermometer, 1230 part by mass of deionized water, 60 part by mass of sodium 2-sulfoethyl methacrylate, 10 parts by mass of potassium methacrylate, and 12 parts by mass of methyl methacrylate were added followed by stirring. Under nitrogen purging inside the polymerization device, the polymerization temperature was increased to 50° C., 0.08 part by mass of 2,2′-azobis (2-methylpropionamidin) dihydrochloride was added as a polymerization initiator, and the polymerization temperature was further increased to 60° C. Simultaneously with the addition of a polymerization initiator, methyl methacrylate was added continuously for 75 minutes at rate of 0.24 part by mass/min by using a dropping pump. After maintaining it for 6 hours at polymerization temperature of 60° C., cooling to room temperature was carried out to obtain dispersion agent (1). Solid content in the dispersion agent (1) was found to be 7.5% by mass.

Example 1

(20) To a polymerization device equipped with a stirrer, a condenser, and a thermometer, a monomer mixture in which 39.8 part by mass of methyl methacrylate, 60 part by mass of n-butyl methacrylate, and 0.2 part by mass of methacrylic acid are homogeneously dissolved, and 200 part by mass of pure water in which 0.25 part by mass of 2,2′-azobis (2-methylbutyronitrile) as a polymerization initiator, 0.3 part by mass of n-dodecylmercaptan as a chain transfer agent, 0.8 part by mass of the dispersion agent (1), and 1.0 part by mass of sodium sulfate as a dispersion aid are homogeneously dissolved were added, and nitrogen purging was carried out under stirring. After that, suspension polymerization was initiated at 75° C. After detecting an exothermic peak of the polymerization, the polymerization was further carried out for 30 minutes at 80° C. (polymerization step).

(21) Subsequently, the inside of the furnace was cooled to room temperature. One third of the amount of the generated slurry was collected, and then dehydrated by using a centrifuge type dehydrator (dehydration step).

(22) The obtained particles of an acrylic polymer and an aqueous solution of sodium sulfate as a washing solution in which the sodium sulfate concentration is 1000 ppm were added to a washing bath such that they are present at 1:2 in terms of the mass ratio (particles of an acrylic polymer:washing solution). After carrying out washing by stirring and mixing for 20 minutes (washing step), the resultant was dehydrated by using a centrifuge dehydrator (dehydration step).

(23) Subsequently, the dehydrated particles of an acrylic polymer were added to a fluid bath type dehydrator of which internal temperature is set at 50° C., and the particles were dried to have moisture content of 2% or less (drying step). Furthermore, the moisture content was calculated from the mass of an acrylic polymer after the drying step, when the particles of an acrylic polymer after the dehydration step are dried for 2 hours at 105° C. and the moisture content of the resulting acrylic polymer is set at 0%.

(24) Na element amount and average particle diameter were then measured for the particles of a powder-like acrylic polymer which have been obtained as described above, and the evaluation was made for electrostatic buildup inhibition rate, fluidity, and solubility in toluene. The results are shown in Table 1.

Example 2

(25) Particles of a powder-like acrylic polymer were produced in the same manner as Example 1 except that number of the washing step is modified to 3. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1. Furthermore, for each washing step, the washing solution was changed to a non-used solution.

Example 3

(26) Particles of a powder-like acrylic polymer were produced in the same manner as Example 1 except that ion exchange water is used as the washing solution. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Example 4

(27) Particles of a powder-like acrylic polymer were produced in the same manner as Example 1 except that ion exchange water is used as the washing solution and number of the washing step is modified to 3. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1. Furthermore, for each washing step, the washing solution was changed to a non-used solution.

Example 5

(28) Particles of a powder-like acrylic polymer were produced in the same manner as Example 2 except that the use amount of sodium sulfate in the polymerization step is modified to 0.2 part by mass. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Example 6

(29) Particles of a powder-like acrylic polymer were produced in the same manner as Example 5 except that the use amount of the dispersion agent (1) in the polymerization step is modified to 0.2 part by mass. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Example 7

(30) Particles of a powder-like acrylic polymer were produced in the same manner as Example 4 except that the use amount of methyl methacrylate in the polymerization step is modified to 40 part by mass and methacrylic acid is not used. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Comparative Example 1

(31) Particles of a powder-like acrylic polymer were produced in the same manner as Example 4 except that, in the polymerization step, the use amount of the dispersion agent (1) is modified to 0.2 part by mass and the use amount of sodium sulfate is modified to 0.2 part by mass. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Comparative Example 2

(32) Particles of a powder-like acrylic polymer were produced in the same manner as Example 4 except that the use amount of sodium sulfate in the polymerization step is modified to 0.2 part by mass. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Comparative Example 3

(33) Particles of a powder-like acrylic polymer were produced in the same manner as Comparative Example 1 except that the use amount of sodium sulfate in the polymerization step is modified to 1.0 part by mass and washing is not carried out. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

Comparative Example 4

(34) Particles of a powder-like acrylic polymer were produced in the same manner as Example 1 except that, in the polymerization step, the use amount of the dispersion agent (1) is modified to 0.1 part by mass and the use amount of sodium sulfate is modified to 0.6 part by mass, and, in the washing step, concentration of an aqueous solution of sodium sulfate is modified to 400 ppm. Various kinds of measurements and evaluations were then carried out. The results are shown in Table 1.

(35) TABLE-US-00001 TABLE 1 Na element Electrostatic Dispersion amount of buildup Average Acrylic agent (1) Dispersion Method for washing acrylic inhibition particle polymer Monomer [part aid [part Number polymer rate Solubility diameter composition by mass] by mass] Washing solution (times) [ppm] [%] Fluidity in toluene [mm] Example 1 Methyl methacrylic 0.8 1.0 Na.sub.2SO.sub.4 aqueous 1 41 97 A B 139 acid/n-butyl solution methacrylate/ [1000 ppm] Example 2 methacrylic 0.8 1.0 Na.sub.2SO.sub.4 aqueous 3 35 96 A B 138 acid = 39.8/60/0.2 solution [1000 ppm] Example 3 0.8 1.0 Ion exchange 1 19 94 A A 130 water Example 4 0.8 1.0 Ion exchange 3 7.3 92 A A 135 water Example 5 0.8 0.2 Na.sub.2SO.sub.4 aqueous 3 20 94 A A 220 solution [1000 ppm] Example 6 0.2 0.2 Na.sub.2SO.sub.4 aqueous 3 17 93 A A 269 solution [1000 ppm] Example 7 Methyl methacrylic 0.8 1.0 Ion exchange 3 7.3 92 A A 140 acid/n-butyl water methacrylate = 40/60 Comparative Methyl methacrylic 0.2 0.2 Ion exchange 3 0.3 82 B A 262 Example 1 acid/n-butyl water Comparative methacrylate/ 0.8 0.2 Ion exchange 3 2.2 86 B A 216 Example 2 methacrylic water Comparative acid = 39.8/60/0.2 0.2 1.0 No washing 0 73 100 A C 457 Example 3 Comparative 0.1 0.6 Na2SO4 aqueous 1 3 88 B A 550 Example 4 solution [400 ppm]

(36) As it is clearly shown from the results of Table 1, the particles of an acrylic polymer, which have been obtained from Examples 1 to 7 and satisfy the constitution of the present invention, have electrostatic buildup inhibition rate of 92% or more, thus showing sufficiently suppressed electrostatic buildup. Furthermore, the particles of an acrylic polymer, which have been obtained from Examples 1 to 7 and have Na element amount in a range of 3.5 to 50 ppm, have sufficiently suppressed electrostatic buildup. Furthermore, the particles of an acrylic polymer obtained from Examples 1 to 7 have excellent fluidity. Furthermore, the particles of an acrylic polymer which have been obtained from Examples 1 to 7 have excellent solubility in toluene.

(37) On the other hand, the particles of an acrylic polymer obtained from Comparative Examples 1, 2, and 4 have electrostatic buildup inhibition rate of 88% or less. Furthermore, the particles of an acrylic polymer, which have been obtained from Comparative Examples 1, 2, and 4 and have Na element amount of 3 ppm or less, exhibit poor fluidity. Furthermore, particles of an acrylic polymer obtained from Comparative Example 3 have electrostatic buildup inhibition rate of 100%, but they have insufficient solubility in toluene.

INDUSTRIAL APPLICABILITY

(38) According to the present invention, particles of an acrylic polymer having excellent fluidity due to suppressed electrostatic buildup, a process for producing the particles of an acrylic polymer, an ink composition, and a coating composition can be provided. As such, the present invention can be suitably utilized in the field of particles of an acrylic polymer, and thus it is industrially very important.