ISOPRENE-BASED POLYMER LATEX COMPOSITION

Abstract

An isoprene-based polymer latex composition includes a chloroprene polymer latex (A) and an isoprene polymer latex (B), in which the chloroprene polymer has a z-average particle size of 180 nm or greater and smaller than 300 nm, and a tetrahydrofuran-insoluble fraction of 80 to 99% by mass; the chloroprene polymer latex (A) is (1) a copolymer latex of chloroprene (A-1) and 2,3-dichloro-1,3-butadiene (A-2-1), or (2) a copolymer latex of the above (A-1) and (A-2-1), and another monomer (A-2-2); and the copolymer is obtained by copolymerization in which the ratio of 2,3-dichloro-1,3-butadiene (A-2-1) is 5.0 to 30.0% by mass relative to the total amount of the monomer components chloroprene (A-1) and 2,3-dichloro-1,3-butadiene (A-2-1) of 100% by mass. The isoprene-based polymer latex composition's quality is maintained, and the properties after cross-linking of a molded product obtained by dipping a dipping former into the composition multiple times do not deteriorate.

Claims

1. An isoprene-based polymer latex composition comprising a chloroprene polymer latex (A), an isoprene polymer latex (B), and an emulsifier (C), wherein the chloroprene polymer latex has a z-average particle size of chloroprene polymer particles contained therein of 180 nm or greater and smaller than 300 nm and a tetrahydrofuran insoluble fraction of 80 to 99% by mass, the chloroprene polymer latex (A) is (1) a copolymer latex of chloroprene (A-1) and 2,3-dichloro-1,3-butadiene (A-2-1), or (2) a copolymer latex of chloroprene (A-1), 2,3-dichloro-1,3-butadiene (A-2-1), and another monomer (A-2-2), and the copolymer is obtained by copolymerization in which the ratio of 2,3-dichloro-1,3-butadiene (A-2-1) is 5.0 to 30.0% by mass relative to the total amount of the monomer components chloroprene (A-1) and 2,3-dichloro-1,3-butadiene (A-2-1) of 100% by mass.

2. The isoprene-based polymer latex composition according to claim 1, comprising at least one of a metal oxide (D), a cross-linking accelerator (E), and an antioxidant (F).

3. The isoprene-based polymer latex composition according to claim 1, wherein the emulsifier (C) is an anionic surfactant.

4. The isoprene-based polymer latex composition according to claim 1, wherein the emulsifier (C) contains a rosin acid soap obtained by saponifying a rosin acid with sodium hydroxide and/or potassium hydroxide in an excess amount relative to the rosin acid.

5. The isoprene-based polymer latex composition according to claim 2, comprising, relative to 100 parts by mass of solid content contained in the isoprene-based polymer latex composition, the emulsifier (C) in a ratio of 1.0 to 30.0 parts by mass, the metal oxide (D) in a ratio of 0.1 to 20.0 parts by mass, the cross-linking accelerator (E) in a ratio of 0.1 to 10.0 parts by mass, and the antioxidant (F) in a ratio of 0.1 to 10.0 parts by mass.

6. The isoprene-based polymer latex composition according to claim 1, wherein the mass ratio of the solid content contained in the chloroprene polymer latex (A) to the solid content contained in the isoprene polymer latex (B) is 50:50 to 1:99.

7. The isoprene-based polymer latex composition according to claim 1, wherein the film forming rate of the chloroprene polymer latex is 0.15 mm/min or higher and 0.50 mm/min or lower.

8. The isoprene-based polymer latex composition according to claim 1, wherein the film forming rate of the chloroprene polymer latex is 41% or higher relative to the film forming rate of the isoprene polymer latex to be mixed.

9. The isoprene-based polymer latex composition according to claim 1, wherein the chloroprene polymer latex has a pH value of 10.5 or higher and 14.0 or lower.

10. The isoprene-based polymer latex composition according to claim 1, wherein the isoprene polymer particles in the isoprene polymer latex have a z-average particle size of 300 nm or greater and 1,000 nm or smaller.

11. A dip-molded product obtained by curing the isoprene-based polymer latex composition according to claim 1 by a dip-molding method.

12. The dip-molded product according to claim 11, which is a disposable rubber glove.

13. The isoprene-based polymer latex composition according to claim 2, wherein the mass ratio of the solid content contained in the chloroprene polymer latex (A) to the solid content contained in the isoprene polymer latex (B) is 50:50 to 1:99.

14. The isoprene-based polymer latex composition according to claim 2, wherein the film forming rate of the chloroprene polymer latex is 0.15 mm/min or higher and 0.50 mm/min or lower.

15. The isoprene-based polymer latex composition according to claim 2, wherein the film forming rate of the chloroprene polymer latex is 41% or higher relative to the film forming rate of the isoprene polymer latex to be mixed.

16. The isoprene-based polymer latex composition according to claim 2, wherein the chloroprene polymer latex has a pH value of 10.5 or higher and 14.0 or lower.

17. The isoprene-based polymer latex composition according to claim 2, wherein the isoprene polymer particles in the isoprene polymer latex have a z-average particle size of 300 nm or greater and 1,000 nm or smaller.

18. A dip-molded product obtained by curing the isoprene-based polymer latex composition according to claim 2 by a dip-molding method.

Description

EXAMPLES

[0095] The present invention is described by referring to examples and comparative examples below, but is not limited thereto.

Example 1

[0096] Preparation of Chloroprene Polymer Latex and Composition Thereof:

[0097] A reactor having an internal volume of 5 L was used, and 1.83 kg of 2-chloro-1,3-butadiene (chloroprene) (produced by Tokyo Chemical Industry, Co., Ltd.), 0.17 kg of 2,3-dichloro-1,3-butadiene (produced by Tokyo Chemical Industry, Co., Ltd.), 1.12 kg of pure water, 34 g of a rosin acid (R-300, produced by Arakawa Chemical Industries, Ltd.), 106.6 g of a 20% by mass aqueous potassium hydroxide solution (guaranteed reagent, produced by FUJIFILM Wako Pure Chemical Corporation), 24 g of a sodium salt of a β-naphthalene sulfonate formaldehyde condensate (produced by Kao Corporation), and 6.0 g of sodium dodecyl benzene sulfonate (NEOPELEX® G-15, produced by Kao Corporation) were fed into the reactor and emulsified. After the rosin acid was converted into a rosin acid soap, polymerization was performed for 5 hours in a nitrogen gas atmosphere at an initial temperature of 40° C., using potassium persulfate (1.sup.st grade, produced by FUJIFILM Wako Pure Chemical Corporation) as an initiator. When the polymerization conversion was confirmed to be 88 or higher, the polymerization was terminated. Subsequently, unreacted monomers were eliminated via steam distillation to obtain a chloroprene polymer latex (A). The pH value was 13.7, the Mw in terms of polystyrene measured by GPC was 1,390,000, a chloroprene polymer contained in the chloroprene polymer latex (A) had a z-average particle size measured with a dynamic light scattering photometer of 190 nm, the tetrahydrofuran insoluble fraction was 94.1%, the solid content was 52.9%, and the Brookfield viscosity was 18 mPa.Math.s.

[0098] To the chloroprene polymer latex (A) obtained above, a zinc oxide dispersion, cross-linking accelerators, and a phenolic antioxidant dispersion were added in the mixing ratios (parts by mass relative to 100 parts by mass of dry solids of the latex) shown in Table 1, and were mixed to prepare a chloroprene polymer latex composition. The chloroprene polymer latex composition exhibited a film forming rate of 0.21 mm/min.

[0099] The above polymerization conversion was obtained by the method below.

[0100] A latex after polymerization was collected and dried at a temperature of 141° C. for 30 minutes to obtain solid content, from which a polymerization conversion was calculated. The solid content and polymerization conversion were obtained by the following formulae.

Solid content after polymerization (% by mass)=[(mass after drying at 141° C. for 30 min.)/(mass of latex before drying)]×100

Polymerization conversion (%)=[(amount of formed polymer/feed amount of chloroprene monomer)]×100

[0101] Here, the amount of formed polymer was obtained by subtracting the solid content other than the polymer from the solid content after polymerization. As the solid content other than the polymer, the amount of components not volatilizing under the conditions at 141° C. was calculated from the feed amount of polymerization raw materials.

[0102] A z-average particle size of polymer particles contained in a latex was obtained by measuring a solution obtained by diluting the latex with pure water to have a concentration of 0.01 to 0.1% by mass, with a dynamic light scattering photometer (ZETASIZER® Nano-S, produced by Malvern Panalytical Ltd.)

[0103] Preparation of Isoprene Polymer Latex Composition:

[0104] As the isoprene polymer latex (B), Cariflex® IR0401SU produced by Kraton Polymers Japan Limited was used. An isoprene polymer contained in the latex had a z-average particle size of 680 nm. To the isoprene polymer latex (B), a zinc oxide dispersion, cross-linking accelerators, a cross-linking agent (aqueous sulfur dispersion), and a phenolic antioxidant dispersion were added in the mixing ratios (parts by mass relative to 100 parts by mass of dry solids of the latex) shown in Table 2, and were mixed to prepare an isoprene polymer latex composition. The pH value was 11.3, and the Mw in terms of polystyrene measured by GPC was 3,180,000. The isoprene polymer latex (B) exhibited a film forming rate of 0.44 mm/min.

[0105] Preparation of Isoprene-Based Polymer Latex Composition (Mixture of Chloroprene Polymer Latex (A) and Isoprene Polymer Latex (B)):

[0106] Both the above polymer latexes were fed into a stirring vessel equipped with a Three-One Motor® in a ratio of the chloroprene polymer latex:the isoprene polymer latex=10:90 (in terms of parts by mass of dry solids) and were stirred at a temperature of 23° C. at 300 rpm for 5 minutes to be homogeneously mixed. The composition after the stirring was left to age at a temperature of 20° C. for 24 hours. Before dipping a former, the thus-obtained isoprene-based polymer latex composition was fed into a stirring vessel equipped with a Three-One Motor® and was stirred at a temperature of 23° C. at 300 rpm for 5 minutes for use.

Comparative Example 1

[0107] Preparation of Chloroprene Polymer Latex and Composition Thereof for Comparison:

[0108] A reactor having an internal volume of 5 L was used, and 1.65 kg of 2-chloro-1,3-butadiene (chloroprene), 0.15 kg of 2,3-dichloro-1,3-butadiene, 1.45 kg of pure water, 77 g of a rosin acid (R-300, produced by Arakawa Chemical Industries, Ltd.), 102.6 g of a 20% by mass aqueous potassium hydroxide solution, 18.7 g of a 25% by mass aqueous sodium hydroxide solution, 9.5 g of a sodium salt of a β-naphthalene sulfonate formaldehyde condensate, and 1.08 g of n-dodecylmercaptan were fed into the reactor and emulsified, and after the rosin acid was converted into a rosin acid soap, polymerization was performed in a nitrogen gas atmosphere at an initial temperature of 40° C., using potassium persulfate as an initiator. When the polymerization conversion was confirmed to be 88% or higher, the polymerization was terminated. Subsequently, unreacted monomers were eliminated via steam distillation to obtain a chloroprene copolymer latex. A chloroprene polymer in the chloroprene polymer latex had a z-average particle size of 130 nm, the tetrahydrofuran insoluble fraction was 37.2%, the solid content was 50.5%, and the Brookfield viscosity was 16 mPa.Math.s.

[0109] To the chloroprene polymer latex obtained above, a zinc oxide dispersion, cross-linking accelerators, and a phenolic antioxidant dispersion were added in the mixing ratios (parts by mass relative to 100 parts by mass of dry solids of the latex) shown in Table 2, and were mixed to prepare a chloroprene polymer latex composition.

[0110] Using the same isoprene polymer latex as the one described in Example 1, a mixed composition and a mixed molded product were prepared in the same manner as described in Example 1. The chloroprene polymer latex composition exhibited a film forming rate of 0.18 mm/min.

[0111] Preparation and Cross-Linking of Dip-Molded Film:

[0112] Dip-molded films were prepared from the isoprene-based polymer latex compositions prepared in Example 1 and Comparative Example 1 by the method below.

[0113] A ceramic plate having a length of 200 mm, a width of 100 mm, and a thickness of 5 mm was used as a former of a dip-molded film. The entire surface of the former was dipped in a 30% by mass aqueous calcium nitrate solution as a coagulation liquid. After being pulled up, the former was dried in an oven at a temperature of 40° C. for 5 minutes. The above operation was performed on 10 formers.

[0114] The 10 formers were dipped in 400 g of each of the isoprene-based polymer latex compositions and were pulled up in order, and 10 sheets of films in total were formed. (Each of the films are referred to as the 1.sup.st-prepared sample to the 10.sup.th-prepared sample.) The obtained films were dried in an oven at a temperature of 70° C. for 30 minutes. Subsequently, the films were cross-linked by heating in an oven at a temperature of 110° C. for 30 minutes. After left to cool at a temperature of 20° C., the films were cut out from the formers. Thereby cross-linked films were obtained.

[0115] Evaluation of Physical Properties after Cross-Linking:

[0116] The cross-linked sheets were each cut with a No. 6 dumbbell-shaped cutting blade specified in JIS-K6251-2017 to obtain test pieces. The thickness of each test piece was adjusted to 0.15 to 0.25 mm.

[0117] Tensile Test

[0118] A tensile test after cross-linking and heat aging (at 110° C. for 16 hours) was performed by a method in accordance with JIS-K6251-2017. During the test, a modulus at 100% elongation (M100), a modulus at 300% elongation (M300), a modulus at 500% elongation (M500), a tensile strength (T.sub.B), and an elongation (E.sub.B) at room temperature were measured. In addition, the retention of tensile strength (T.sub.B) was obtained based on the following formula.

T.sub.B retention (%)=(T.sub.B of the X.sup.th prepared sample)/(T.sub.B of the 1.sup.st prepared sample)×100

[0119] Viscosity:

[0120] A test sample was poured into a 300 mL polypropylene beaker and bubbles included therein were completely eliminated. Using a B-type viscometer specified in JIS K7117-1:1999, viscosity was measured. Among the results obtained by continuous measurement, in which the measured value was within 5%, the viscosity of the second result was recorded.

[0121] Instrument: Viscometer, DV-E LVDVE115, produced by BROOKFIELD

[0122] Spindle: No. 1 spindle

[0123] Velocity: 60 rpm

[0124] Temperature: 20° C.

[0125] Tetrahydrofuran Insoluble Fraction:

[0126] Each of the isoprene polymer latexes in an amount of 1 g (water content: 35 to 65% by mass) was added dropwise to 100 mL of tetrahydrofuran, and was shaken with a shaker (SA300) produced by Yamato Scientific Co., Ltd., for 10 hours. The obtained mixture was thereafter subjected to centrifugal separation with a centrifuge (H-9R, produced by Kokusan Co., Ltd.) at 14,000 rpm for 60 minutes, and a supernatant dissolved phase was separated. Tetrahydrofuran was evaporated at a temperature of 100° C. for 1 hour to obtain a dry solid matter, and the dissolved amount was calculated and subtracted to obtain a tetrahydrofuran insoluble fraction (% by mass).

[0127] Molecular Weight:

[0128] The supernatant dissolved phase after the centrifugal separation at the time of measuring a gel content described above was separated, diluted with tetrahydrofuran, and subjected to molecular weight measurement in terms of polystyrene, by GPC (gel permeation chromatography). Thereby a weight average molecular weight (Mw) was measured. The GPC measurement conditions were determined such that LC-20AD produced by Shimadzu Corporation was used as a GPC measurement device, RID-10A (refractive index detector) produced by Shimadzu Corporation was used as a detector, the column type was PLgel 10 μm MiniMIX-B produced by Agilent Technologies Japan, Ltd., and tetrahydrofuran (for HPLC, produced by Kanto Chemical Co., Inc.) was used as an eluting solution, at a column temperature of 40° C., and an outflow rate of 0.4 mL/min.

[0129] pH Values:

[0130] Using a benchtop pH meter F-71 (produced by Horiba, Ltd.), pH values were measured at a sample temperature of 25° C.

[0131] Results are summarized in Tables 3 and 4.

TABLE-US-00001 TABLE 1 Components to be mixed Mixing ratio (parts by mass) Chloroprene polymer latex 100 Zinc oxide dispersion.sup.1) 5 Cross-linking accelerator ZDBC.sup.2) 0.5 Cross-linking accelerator ZMBT.sup.3) 0.5 Cross-linking accelerator DPG.sup.4) 0.25 Phenolic antioxidant dispersion.sup.5) 2 .sup.1)AZ-SW, produced by Osaki Industry Co., Ltd. .sup.2)Nocceler ® BZ, produced by Ouchi Shinko Chemical Industrial Co., Ltd. .sup.3)Nocceler ® MZ, produced by Ouchi Shinko Chemical Industrial Co., Ltd. .sup.4)Nocceler ® D, produced by Ouchi Shinko Chemical Industrial Co., Ltd. .sup.5)K-840, produced by Chukyo Yushi Co., Ltd.

TABLE-US-00002 TABLE 2 Components to be mixed Mixing ratio (parts by mass) Isoprene polymer latex 100 Zinc oxide dispersion.sup.1) 0.5 Sulfur.sup.6) 1.5 Cross-linking accelerator.sup.2) 0.5 Cross-linking accelerator.sup.3) 0.5 Cross-linking accelerator.sup.4) 0.25 Phenolic antioxidant dispersion.sup.5) 2 .sup.1) to .sup.5)are the same as described in Table 1. .sup.6)S-50, produced by Nippon Color Ind., Co., Ltd.

TABLE-US-00003 TABLE 3 Comparative Example 1 Example 1 Isoprene- Film forming rate (mm/min) 0.21 0.18 based Z-average particle size (nm) 190 130 polymer Tetrahydrofuran insoluble 94.1 37.2 latex fraction (%) Solid content (%) 52.9 50.5 BF viscosity (mPa .Math. s) 18 16

TABLE-US-00004 TABLE 4 Example 1 Comparative Example 1 Number of times of dipping 1.sup.st 3.sup.rd 7.sup.th 10.sup.th 1.sup.st 3.sup.rd 7.sup.th 10.sup.th time time time time time time time time Mixing ratio of 10:90 10:90 10:90 10:90 10:90 10:90 10:90 10:90 chloroprene polymer latex:isoprene polymer latex (mass ratio) Cross-linking 110 110 110 110 110 110 110 110 temperature (° C.) Cross-linking time 30 30 30 30 30 30 30 30 (min) M100 (MPa) 0.64 0.64 0.64 0.61 0.62 0.62 0.61 0.58 M300 (MPa) 1.10 1.13 1.20 1.10 1.20 1.10 1.20 1.10 M500 (MPa) 1.80 1.80 1.90 1.90 1.80 1.80 1.90 1.80 Eb (%) 1050 1050 1050 1050 1050 1050 1050 1050 Tb (MPa) 27.3 27.8 27.3 27.8 26.5 25.9 25.6 22.8 Tb retention relative 100 102 100 102 100 98 97 86 to the Tb of the 1.sup.st prepared sample (%)

[0132] Table 4 shows that in Comparative Example 1 in which the z-average particle size of the chloroprene polymer is smaller, the more times dipping is performed, the lower the retention of Tb relative to the Tb of the 1.sup.st-prepared sample is. Further shown is that dip-molded products retaining constant properties are not obtainable due to the compositional change in the chloroprene-based polymer composition.