Latex compositions and antistatic articles manufactured therefrom

Abstract

A method for making rubber films with improved ESD (electrostatic discharge) property relates to a method for making better ESD gloves using improved rubber composition with a precipitated CaCO.sub.3 filler. In addition, non-metallic filled organic pigment such as AZO compounds are suggested to make better ESD gloves. Additionally, other improved method steps such as chlorination and addition of Carbon Black in conjunction with chlorination are suggested to make better ESD gloves.

Claims

1. A process for making a static dissipative glove comprising: immersing a glove former in an aqueous coagulant solution to produce a coagulant coated former via a calcium salt; immersing the coagulant coated former into a rubber dispersion to coat the coagulant coated former with a rubber; washing the rubber coated on the coagulant coated former with water; curing the rubber coated on the coagulant coated former in an oven; chlorinating the rubber coated on the coagulant coated former by immersing the rubber coated on the coagulant coated former in an aqueous chlorine solution; washing the rubber coated on the coagulant coated former with water; drying the rubber coated on the coagulant coated former; obtaining a glove by removing the rubber from the coagulant coated former; and chlorinating the glove, wherein the rubber dispersion comprises an additive, the additive comprises a precipitated calcium carbonate hydrate and an Azo based non-metallic organic pigment, the precipitated calcium carbonate hydrate is in the range of 5% to 30% of total composition by weight, the Azo based non-metallic organic pigment is in the range of 0.1% to 4% of total composition by weight, the aqueous chlorine solution comprises chlorine from 1,000 to 10,000 ppm, and the Azo based non-metallic organic pigment being orange color and having CAS number 3520-72-7.

2. The process of claim 1 comprising: the aqueous coagulant solution comprising a polymer composition.

3. The process of claim 1 comprising: chlorinating the rubber coated on the coagulant coated former being occurred in-line; and chlorinating the glove being occurred off-line.

4. The process of claim 1 comprising: the rubber dispersion comprising a hydrophilic additive.

5. The process of claim 1 comprising: the rubber dispersion comprising a hydrophilic filler.

6. The process of claim 1 comprising: the additive being used for enhancing electrical conductivity.

7. The process of claim 6 comprising: the additive comprising a mineral additive with hydration molecules that acts as a filler.

8. The process of claim 1 comprising: the rubber dispersion being latex.

9. The process of claim 1 comprising: the rubber dispersion being nitrile rubber.

10. The process of claim 1 comprising: the rubber dispersion being a combination of latex and nitrile rubber.

Description

DETAIL DESCRIPTIONS OF THE INVENTION

(1) All examples are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention. The preferred embodiment of the present invention may be referred to hereinafter as The Antistatic Gloves or ESD gloves. The invention serves in increased productivity and enhance safety. Increased productivity is where the use of better ESD gloves in manufacturing, increasing static dissipation, preventing static discharge. The yield of production can be improved. Increased safety, where better ESD gloves can conduct and dissipate minor static sparks, discharge them and prevent explosions. The objective of the invention is to enable better productivity and safety. The present invention has to do with the medium of the rubber which include special fillers and pigments, in conjunction with a chlorination process.

(2) The objective of the present invention is to provide Elastomer articles with better ESD properties. In particular, the invention deals with natural latex gloves (called Latex) and with synthetic nitrile gloves (called Nitrile). It also referred to combination of latex and nitrile, and petroleum-based, cross-linked film. This includes better surface and better volume conductivity. The invention is improving the structure composition of the rubber in various dipped articles and gloves with special fillers, pigments and process. The preferred filler is precipitated calcium carbonate combined with orange color pigment having CAS No. 3520-72-7. The preferred process is chlorination. Another preferred filler is Carbon Black combined with chlorination. In a specific case, a specially filled rubber glove with added chlorination-resisted organic color pigments, are being used in order to distinguish an ESD glove, without heavy metal contamination, for sensitive electronic manufacturing. There are preferred three conditions: filler, pigment and chlorination. Such conditions can work separately or mutually to create a better ESD, elastomer glove.

Example 1. Preparation of a Static Dissipative Nitrile Rubber Glove

(3) A process of making a static dissipative nitrile rubber glove was shown as follows: (a) immersing a glove former in an aqueous coagulant solution and drying it. Such solution can include calcium stearate, a strong but oily electrolyte salt, capable of breaking latex and nitrile dispersions on contact and depositing the rubber as a uniform thin layer on the former. The process produces a coated former, where such oily salt covers the inside of the rubber film to prevent sticking. In some cases, the coagulant solution may also contain a polymer which prevents sticking too;

(4) (b) immersing the coated former into a nitrile rubber dispersion to coat the former with a nitrile rubber film, washing it with water to remove unneeded chemicals and then curing it in an oven;

(5) (c) chlorinating the nitrile rubber coated on the former, the chlorination also makes the surface of the rubber more inert to prevent sticking on removal;

(6) (d) washing the chlorinated nitrile rubber on the coated former with water and drying it in an oven;

(7) (e) removing the finished nitrile glove from the former; and optionally

(8) (f) chlorinating the nitrile gloves after removal.

(9) In step (b), an additive of precipitated CaCO.sub.3 as a filler, and an orange Azo pigment having CAS No. 3520-72-7 or Carbon Black pigment could be added.

(10) The level of the precipitated calcium carbonate hydrate is in the range of 1% to 40% or preferentially 10% to 30% of total composition by weight.

(11) The Azo pigment is between 0.05% to 8%, preferentially, between 0.15% to 4%.

(12) The level of Carbon Black is between 0.1% to 10%, preferentially between 1% to 5%.

(13) In step (c), an aqueous chlorine solution containing 500 to 15,000 ppm chlorine or 1,000 to 10,000 ppm was used.

Example 2. Preparation of a Static Dissipative Latex Glove

(14) A process of making a static dissipative latex glove was shown as follows: (a) immersing a glove former in an aqueous coagulant solution and drying it. Such solution can include calcium stearate, a strong but oily electrolyte salt, capable of breaking latex and nitrile dispersions on contact and depositing the rubber as a uniform thin layer on the former. The process produces a coated former, where such oily salt covers the inside of the rubber film to prevent sticking. In some cases, the coagulant solution may also contain a polymer which prevents sticking too;

(15) (b) immersing the coated former into a latex dispersion to coat the former with a latex film, washing it with water to remove unneeded chemicals and then curing it in an oven;

(16) (c) chlorinating the latex coated on the former, the chlorination also makes the surface of the rubber more inert to prevent sticking on removal;

(17) (d) washing the chlorinated latex on the coated former and drying it in an oven;

(18) (e) removing the finished latex glove from the former; and optionally

(19) (f) chlorinating the latex gloves after removal.

(20) In step (b), an additive of precipitated CaCO.sub.3 as a filler, and an orange Azo pigment having CAS No. 3520-72-7 or Carbon Black pigment could be added.

(21) The level of the precipitated calcium carbonate hydrate is in the range of 1% to 40% or preferentially 10% to 30% of total composition by weight.

(22) The Azo pigment is between 0.05% to 8%, preferentially, between 0.15% to 4%.

(23) The level of Carbon Black is between 0.1% to 10%, preferentially between 1% to 5%.

(24) In step (c), an aqueous chlorine solution containing 500 to 15,000 ppm chlorine or 1,000 to 10,000 ppm was used.

Experimental Results

(25) Testing results are presented for surface resistivity and volume resistivity. The testing methods include:

(26) (1) Surface Resistivity

(27) The results for surface resistivity are measured with a conventional resistivity meter. The one used is Monroe Electronic Resistivity Meter, Model 264A. The Monroe Instrument is built with two parallel wires, 5 CM long which are placed 5 CM apart. The range of testing is between 10 in the power of 5 and 10 in the power of 12 ohms. It is designated (10 e+5) to (10 e+12) Ohms.

(28) The tester measures in a span unit of 5, 6, 7, 8, 9, 10, 11 and 12 e values. The smaller is the e value, the better is the static dissipation. 0.1 mm thick rubber film is placed on a flat surface. The tester is placed on the rubber film and tested at 50+/5% relative humidity. The surface resistance is measured in Ohms units.

(29) (2) Volume Resistivity

(30) The testing for volume resistivity is made by an equipment, built from a 1507 FLUKA tester and an 850 ETS surface resistant probe. 0.1 mm thick rubber film is laid on an aluminum foil on a flat surface. The ETS probe is placed on it. Two electrodes are used. One is connected to the foil and one to the Fluka tester through the ETS probe. 500 DC volts are applied, and the resistance is measured with the Fluka Tester, at 50%+/5 relative humidity. The volume resistance is measured in Ohms units, across the film, from side to side.

(31) (3) ANSI ESD S20.20 Resistivity Test

(32) ANSI ESD S20.20 is a testing procedure, designed by the ESD association, used in the industry. This testing of resistivity, is measured in Ohms and made at 25+/2% relative humidity. We did not measure according to the ANSI ESD 520.20 protocol, only submitted to an outside lab. In order to pass the ANSI ESD S20.20 test, resistivity has to be less than 10 e+9 Ohms.

(33) Obviously measuring at 25% relative humidity overnight, dries the rubber and increases the resistivity a lot. It is therefore a very difficult test to pass but gives a good tool to distinguish between gloves.

(34) Kind of Gloves Tested

(35) Two kinds of gloves, a natural rubber, called Latex and synthetic NBR Rubber called Nitrile were used. In general, Nitrile gloves are more antistatic than natural Latex, it has a better ESD values. The natural Latex is built mostly of hydrocarbons which is an insulating material. It is difficult to make an ESD glove from Latex. The synthetic Nitrile is also a hydrocarbon material, but it has an electrical active chemical component, called acrylonitrile. The acrylonitrile section has nitrile groups which are relatively more conductive and gives this kind of rubber its name, Nitrile rubber. As a result, Nitrile rubber is known to be more antistatic than Latex and in general has lower e values, which indicates better ESD, antistatic properties.

(36) The improved nitrile and latex gloves, made with a filler of a precipitate calcium carbonate, combined with a pigment of an organic Azo compound having CAS No. 3520-72-7 pigment or a Carbon Black pigment, each of them along with chlorination, will grant such rubber elastomers a better electrostatic discharge (ESD) properties (See Tables 1-14).

Experimental Result

(37) As seen in the Tables below, in both elastomers, Latex and Nitrile, the precipitated CaCO.sub.3 filler, the two pigments AZO and Carbon Black and a chlorination treatment, helps to reduce surface and volume resistivity and make them a better ESD gloves.

(38) For nitrile rubber gloves, the combination of precipitated CaCO.sub.3 filler, orange Azo pigmentation and chlorination gave the best ESD properties. Such gloves were capable to pass the ANSI/ESD S20.20 STM test.

(39) Table 1. Evaluation of surface resistivity, in Ohms of various commercial Nitrile Glove types A, B and C, compared with Glove D, filled with precipitated CaCO.sub.3, pigmented with an orange Azo pigment and subjected to chlorination.

(40) Nitrile Glove A 1.0 e+10

(41) Nitrile Glove B 1.0 e+10

(42) Nitrile Glove C 1.0 e+09

(43) Nitrile Glove D 1.0 e+08

(44) The lower the e value, the better the ESD property of the glove is.

(45) Table 2. Evaluation of volume resistivity in Ohms of various commercial Nitrile Glove types A, B, C, compared with Glove D filled with precipitated CaCO.sub.3, pigmented with an orange Azo pigment and subjected to chlorination.

(46) Nitrile Glove A 3,500,000

(47) Nitrile Glove B 1,500,000

(48) Nitrile Glove C 1,000,000

(49) Nitrile Glove D 100,000

(50) Table 3. Evaluation of surface resistivity in Ohms of Nitrile Gloves, non-pigmented and pigmented with orange Azo pigment having CAS No. 3520-72-7.

(51) Nitrile Gloves, non-pigmented 1.0 e+10

(52) Nitrile Gloves, pigmented 1.0 e+09

(53) Table 4. Evaluation of volume resistivity in Ohms of Nitrile Gloves, non-pigmented and pigmented with orange Azo pigment having CAS No. 3520-72-7.

(54) Nitrile Glove, non-pigmented 1,000,000

(55) Nitrile Glove, pigmented 600,000

(56) Table 5. Evaluation of surface resistivity in Ohms of Nitrile Gloves, filled with a precipitated CaCO.sub.3 and subjected to a chlorination process.

(57) Nitrile Glove, non-chlorinated 1.0 e+09

(58) Nitrile Gloves, chlorinated 1.0 e+08

(59) Table 6. Evaluation of volume resistivity in Ohms of Nitrile Gloves, filled with precipitated CaCO.sub.3 filler and subjected to a chlorination process.

(60) Nitrile Glove, non-chlorinated 350,000

(61) Nitrile Gloves, chlorinated 100,000

(62) Table 7. Evaluation of surface resistivity in Ohms of Latex Gloves, filled with a mined CaCO.sub.3 filler and filled with a precipitated CaCO.sub.3 filler.

(63) Latex Glove, filled with mined CaCO.sub.3 1.0 e+12

(64) Latex Gloves, filled with precipitated CaCO.sub.3 1.0 e+10

(65) Table 8. Evaluation of volume resistivity in Ohms of Latex Gloves, filled with mined filler and with a precipitated CaCO.sub.3 filler.

(66) Latex Glove filled with mined CaCO.sub.3 30,000,000

(67) Latex Gloves filled with Precipitated CaCO.sub.3 900,000

(68) Table 9. Evaluation of surface resistivity in Ohms of Latex Gloves with an orange pigment (CAS No. 3520-72-7 pigment), filled and not filled with precipitated CaCO.sub.3 filler.

(69) Latex Gloves, not filled 1.0 e+10

(70) Latex Gloves, filled 1.0 e+09

(71) Table 10. Evaluation of volume resistivity in Ohms of Latex Gloves with an orange pigment (CAS No. 3520-72-7 pigment), filled and not filled with precipitated CaCO.sub.3 filler.

(72) Latex Gloves, not filled 900,000

(73) Latex Gloves, filled

(74) Table 11. Evaluation of surface resistivity in Ohms of Latex Gloves with and without Carbon Black pigment.

(75) Latex Gloves, non-pigmented 1.0 e+12

(76) Latex Gloves, Carbon Black pigmented 1.0 e+11

(77) Table 12. Evaluation of volume resistivity in Ohms of Latex Gloves with and without Carbon Black pigment.

(78) Latex Gloves, non-pigmented 590,000

(79) Latex Gloves, Carbon Black pigmented 260,000

(80) Table 13. Evaluation of surface resistivity in Ohms of Nitrile Gloves, pigmented with Carbon Black, and non-chlorinated or chlorinated.

(81) Nitrile Gloves, non-chlorinated, 1.0 e+10

(82) Nitrile Gloves, chlorinated 1.0 e+09

(83) Table 14. Evaluation of volume resistivity in Ohms of Nitrile Gloves, pigmented with Carbon Black and non-chlorinated or chlorinated.

(84) Nitrile Glove, non-chlorinated 33,000

(85) Nitrile Glove, chlorinated 1,300

(86) As seen in the Tables, the precipitated CaCO.sub.3 filler, pigments as orange Azo and Carbon Black pigment with added chlorination step, helps to reduce surface and volume resistivity, making a better ESD gloves.

(87) For using the invention in the industry, ESD type gloves are used in electronic or semi-conductor manufacturing, where sparks can damage the products. Such gloves are also used where vapors prone to combustion and flammable liquids are present. For example, in oil and gas facilities. They are also used in medicine production, where sterilization is performed by alcohol, resulting with vast amounts of vapors presence in the atmosphere.

(88) As used herein, a or an means one or more (or at least one).

(89) Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention.

REFERENCES

(90) Kimura, I; Nobori, K and Hikasa Methods of producing chlorinated rubber U.S. Pat. No. 5,143,980 (1992) Kishihara, H. and Ozawa, Y. Antistatic rubber latex composition and antistatic rubber glove JP2003321581A. Piesker, A. B. and Hansen, C. Chemical resistant mechanical resistant, anti-static glove. U.S. 2012/0090075 A1 Tsuwako, K.; Sasao; Y. Yamaguchi, K. and Yamamoto, H., Magnetic head handling glove U.S. Pat. No. 6,618,236 B1 (2003).