US20220386719A1

US20220386719A1 - Disposable vinyl acetate ethylene glove

Info

Publication number: US20220386719A1
Application number: US17/505,324
Authority: US
Inventors: Der-Lin Liou
Original assignee: Twolink Sdn Bhd
Current assignee: Twolink Sdn Bhd
Priority date: 2021-06-02
Filing date: 2021-10-19
Publication date: 2022-12-08

Abstract

A disposable glove has a thickness of 0.03-0.12 mm, tensile strength of at least 14 Mpa, and elongation of at least 350%. The disposable glove is made by dip-coagulating a glove former with a water-based latex compound consisting of or comprising a base latex which is a vinyl acetate ethylene latex or a blend of vinyl acetate ethylene latex and carboxylated acrylonitrile butadiene latex, a pH adjuster, an external crosslinker, and a process additive.

Description

FIELD

The disclosure relates to a disposable glove that has 0.03-0.12 mm thickness, at least 14 MPa tensile strength, and at least 350% elongation. The disposable glove is made by a glove former via dip-coagulating a water-based latex compound comprising or consisting of a base latex including vinyl acetate ethylene latex or a blend of vinyl acetate ethylene latex and a carboxylated acrylonitrile butadiene latex, a pH adjuster, an external crosslinker, and a process additive.

CITED PATENTS

U.S. Pat. Nos. 5,084,514, 7,001,941, 8,920,920B2, 9,090,793B2, 10,350,848B2, JP2001303329A, CN108102205B2,

BACKGROUND

The conventional disposable glove is made from polyvinyl chloride (abbreviated as PVC), nature rubber (abbreviated as NR), or carboxylated acrylonitrile butadiene (abbreviated as XNBR) by a dipping method. Because a PVC glove often contains an organic solvent, a phthalate, and chlorine, the PVC glove releases dioxins while manufacturing, burning, or landfilling, causing environmental pollution and health risks. Therefore, some countries banned PVC gloves. The NR glove contains proteins that may cause Type III allergy healthy risk, and it has been substituted by XNBR glove gradually since about two decades ago.
The glove industry has been continuously looking for a material to substitute PVC for a long time. Vinyl acetate ethylene (VAE) latex is a water-based emulsion made by emulsion polymerization. As VAE latex is eco-friendlier than PVC and cheaper than XNBR latex, it becomes one of the most potential glove materials, especially in the price-sensitive disposable glove market. VAE is not ethylene vinyl acetate (abbreviated as EVA). The industry defines VAE as a water-based emulsion or latex, in which the vinyl acetate is about 60-90%, and the ethylene is about 10-40% by weight. In contrast, the EVA is a solid resin, in which the vinyl acetate is about 10-40%, and ethylene is about 60-90% by weight.
Some natural or synthetic rubber latexes have been blended with VAE latex as the base material for making gloves. U.S. Pat. No. 5,084,514 disclosed a glove made from XNBR latex blended with at least one polymer latex selected from the group consisting of acrylics, butyl latex, ethylene-vinyl acetate, carboxylated butadiene styrene, polyurethane, neoprene, and natural rubber which is up to about 25% by weight of the total composition. JP2001303329A disclosed an acrylonitrile butadiene rubber household glove made by using a mixed latex prepared by mixing acrylonitrile butadiene rubber latex with 1-40% of a homopolymer or a copolymer of vinyl acetate by weight. U.S. Pat. No. 7,001,941 disclosed a styrene butadiene latex and/or a carboxylated styrene butadiene latex blending with thermoplastic ethylene-vinylacetate copolymer latex with a blending ratio of 95:5 to 40:60 as the base latex for making gloves. U.S. Pat. No. 10,350,848B2 disclosed a blend of polyurethane, XNBR, and ethylene-vinylacetate as the base material for making gloves, in which ethylene-vinylacetate is about 1-4% by weight of the base material. The above-mentioned references used a conventional rubber latex such as XNBR latex blended with VAE latex to either cost down or modify certain glove performances. Still, there is no disclosure or teaching to solve the latex blending incompatibility problems, and none of them uses VAE latex as the main base material for making gloves. U.S. Pat. No. 8,920,920B2 disclosed a blend of VAE as the first copolymer and a second styrene derivatives copolymer such as styrene butadiene, styrene butadiene acrylonitrile, or styrene acrylate used for paper coating. Still, there is no teaching of making gloves. U.S. Pat. No. 9,090,793B2 disclosed a blend of acrylic copolymer emulsion and VAE latex with a water-soluble compound crosslinker containing at least two hydrazine moieties used as a water-proof paint for construction, but there is no teaching of making glove. CN108102205B2 disclosed an EVA resin includes 10-20% by mass of vinyl acetate monomer as the main material. The EVA resin was blended with organic solvents and plasticizers to dissolve solid EVA resin into a liquid solution to be applied in the glove dipping process, which caused environmental pollution risks like a PVC glove.
Ordinary VAE latex is mainly used as an adhesive, water-proof coating or paint for paper, non-woven or construction industries. If VAE is used to make gloves, there are some deficiencies needed to address. The deficiencies include, for example, latex instabilities, short pot life, poor water and blocking resistance, etc.

SUMMARY

The disclosure herein provides a disposable, eco-friendly VAE glove with excellent physical performances by modifying conventional VAE latex compositions to suit the current disposable glove manufacturing process. The disposable VAE glove can substitute PVC disposable glove. The disclosure herein solves XNBR latex and VAE latex blending incompatibility problems, and provides a VAE glove that is free or with a reduced amount of protein, sulfur, accelerator, or zinc oxide to decrease allergy health risks, reduce environmental pollutions, and avoid harm to aquatic organisms.
The disclosure relates to a disposable glove made by a glove former via dip-coagulating a water-based latex compound consisting of or comprising a base latex, a pH adjuster, an external crosslinker, and a process additive. The base latex includes a VAE latex or a blend of VAE latex and XNBR latex. The VAE latex has a glass transition temperature (abbreviated as Tg) lower than 0° C. The VAE latex comprises or consists of 52-88% vinyl acetate, 10-40% ethylene, 2-8% crosslinkable functional group monomer by weight of the total monomer content, and 1-8% emulsifying agent by weight of the total copolymer content. Most of the conventional VAE latex either consists of vinyl acetate and ethylene monomer only or further includes additional third monomer and internal crosslinker during polymerization process to make a self-crosslinked type latex for easy operation and shortening operation time at ambient temperature to be applied as adhesive, water-proof coating or paint. However, the conventional VAE latex has a short pot life problem due to latex instability during the latex compounding and glove dipping process. Thus it is not suitable for use in continuous nonstop glove manufacturing.
The embodiments herein use a crosslinkable functional group monomer as the third monomer without containing an internal crosslinker in the polymerization process to make a post-crosslinking type VAE latex. The post-crosslinking type VAE latex can maintain latex stabilities during the compounding and dipping process, thus solving the problem of conventional self-crosslinked VAE latex not being suitable to use in the glove manufacturing process. The suitable crosslinkable functional group monomer of VAE latex is an ethylenically unsaturated monomer comprising one or more carboxyl, vinyl, and epoxy groups. The crosslinkable functional group monomer is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic anhydride, styrenesulfonic acid, ethenylphosphonic acid, allylglycidyl ether, glycidyl methacrylate, methacryloyl glycidyl ether, ethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 2,5-hexanediol dimethacrylate, 2,4-pentanediol diacrylate, 2,4-pentanediol dimethacrylate, dipropyleneglycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and a combination thereof.
The conventional VAE latex commonly used nonionic type surfactants or polyvinyl alcohols as an emulsifying agent or protective colloid, which is too stable for a cationic coagulant agent to coagulate latex particles and form a solid film. Most protective colloids such as polyvinyl alcohol and hydroxyethylcellulose increase VAE latex compound's viscosity and is prone to form air bubbles, leading to glove pinhole problem. To overcome the film formation and pinhole problems of conventional VAE latex, the emulsifying agent of the embodiments herein includes an anionic surfactant as a main component. The anionic surfactant is selected from the group consisting of ammonium lauryl sulfate, sodium lauryl sulfate, sodium lauryl sarcosinate, sodium myreth sulfate, sodium pareth sulfate, sodium decyl sulfate, sodium N-lauroyl-N-methyltaurate, sodium tetradecyl sulfate, sodium dodecylbenzene sulfonate (abbreviated as SDBS), sodium cetyl sulfate, sodium oleyl sulfate, sodium sulfosuccinate, and a combination thereof. The emulsifying agent can also optionally include a minor amount of nonionic surfactant or protective colloid selected from the group consisting of fatty alcohol ethoxylate, alkylphenol ethoxylate, fatty acid ethoxylate, sorbitan fatty acid ester, glycerol fatty acid ester, polyethylene glycol, polyvinyl alcohol, hydroxyethylcellulose, and a combination thereof.
The VAE latex of the embodiments can blend with a commercial XNBR latex at any ratio without compatibility problem. There is no gelation, sedimentation, lump, or poor film formation observed during the latex compounding and glove dipping process. The VAE latex is preferably blended with less than 50% of XNBR latex by weight of the total latex solid content to provide the VAE glove with certain beneficial properties, such as acrylonitrile component of XNBR can improve oil and grease resistance, and butadiene component of XNBR can improve softness.
To prepare a VAE latex compound for the glove dipping process, a proper amount of a pH adjuster is added to a VAE latex to increase pH to a range of about 6.0-9.0 to prevent too aggressive crosslinking reaction and latex instabilities. The pH adjuster is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, sodium acetate, potassium bicarbonate, potassium citrate, potassium acid phosphate, and a combination thereof. If a blend of VAE latex and XNBR latex is to be used as the base latex, XNBR is added to the pH-adjusted VAE latex, and then an external crosslinker is added at an amount of 0.5-4.0% by weight of the total latex solid content. The external crosslinker is selected from the group consisting of sulfur, accelerator, zinc oxide, aluminum oxide, sodium aluminate, aluminum hydroxide, adipic acid, lactic acid, oxalic acid, citric acid, glyceric acid, glycolic acid, gluconic acid, maleic acid, maleic anhydride, sodium citrate, sodium gluconate, polyethylene oxide, polyethylene glycol, glycerine, maltitol, sorbitol, xylitol, erythritol, glyoxal, glutaraldehyde, ammonium zirconium carbonate, potassium zirconium carbonate, ammonium zirconium lactate, polyamide epichlorohydrin, carbodiimide, and a combination thereof. In some cases, by selecting and hybridizing multivalent metal ionic and multifunctional crosslinkers to react with at least one or more crosslinkable functional groups of VAE copolymer chains, it is unnecessary to use sulfur, accelerator, and zinc oxide to decrease environmental pollutions and allergy health risks. Afterward, a proper amount of a process additive is added, and then a pH adjuster and water are added to adjust the pH to 7.0-11.0 and the total solid content to 10-30%. Continuous agitation is performed for about 10-24 hours for homogenization and maturation to obtain the VAE latex compound. The VAE latex compound can be used for making a disposable VAE glove by a dip-coagulating method. The resulting disposable VAE glove has a thickness of 0.03-0.12 mm, tensile strength of no less than 14 Mpa, elongation of no less than 350%. The resulting disposable VAE glove is free of organic solvent and plasticizer and has better physical performances than PVC glove according to ASTM D5250 test method.
The description herein provides a method of making a glove containing sulfur, accelerator, and zinc oxide, or a glove free of sulfur, accelerator and with a reduced amount of zinc oxide, or a glove free of sulfur, accelerator, and zinc oxide to decrease environmental pollutions, allergy health risks and the harmful of the aquatic organisms.

DETAILED DESCRIPTION

VAE latex is commonly used as an adhesive or water-proof coating or paint in paper, non-woven, textile, or construction industry. The composition of VAE latex is normally added an internal crosslinker monomer during polymerization to make a self-crosslinked or pre-crosslinked type latex for easy operation and shorten the operation process time at the ambient temperature condition. Unfortunately, this conventional VAE latex feature makes it difficult to use as a base material for making gloves. As most internal crosslinker monomers are more active in an acidic condition, to prevent too aggressive crosslinking reaction that causes so-called “latex instability,” normally a buffering agent is used to increase the pH value and slow down the crosslinking speed. However, the crosslinking reaction remains active even after polymerization and continues to be active during storage and transportation. Most self-crosslinked VAE latex has a short pot life. It is better to be used up within a short period to prevent early gelation, coagulation, or sedimentation. It is difficult and troublesome for the end-users of glove manufacturing to test and adjust the crosslinking degree of the received self-crosslinked VAE latex. Also, the current batch type latex compound process is prepared by a maximum of two operation shifts daily, which normally takes hours to prepare and at least 12 hours to consumed-up the prepared tons of latex compound. Thus it is not practical to use in a continuously nonstop running glove manufacturing process, and it is difficult to maintain the consistency of latex compound quality.
The embodiments herein use a crosslinkable functional group monomer only without an internal crosslinker during polymerization so that the VAE latex only reacts with an external crosslinker, resulting in the so-called “post-crosslinking” type latex. The post-crosslinking type latex allows the crosslinking reaction to be controlled in a slow speed condition to maintain latex compound stability during the compounding and glove dipping process. The crosslinking speed can be increased at a rising temperature to overcome deficiencies of a conventional self-crosslinked type VAE latex for not being suitable for use in a glove manufacturing process.
The preferred VAE latex disclosed herein has a Tg lower than 0° C. The VAE latex comprises about 52-88% vinyl acetate, 10-40% ethylene, and 2-8% crosslinkable functional group monomer by weight of the total monomer. The ethylene acts as an internal plasticizer. By increasing ethylene's content, the VAE copolymer's Tg decreases, and the formed film is softer with a better elongation. On the contrary, vinyl acetate acts as a hardener. By increasing vinyl acetate's content, the VAE copolymer's Tg increases, and the formed film is harder with better tensile strength. The crosslinkable functional group monomer is an ethylenically unsaturated monomer comprising carboxyl, vinyl, and/or epoxy groups. In an embodiment, the crosslinkable functional group monomer is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic anhydride, styrenesulfonic acid, ethenylphosphonic acid, allylglycidyl ether, glycidyl methacrylate, methacryloyl glycidyl ether, ethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 2,5-hexanediol dimethacrylate, 2,4-pentanediol diacrylate, 2,4-pentanediol dimethacrylate, dipropyleneglycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and the combination thereof. For example, methacrylic acid is commonly used in making carboxylated synthetic rubber such as acrylonitrile butadiene and styrene butadiene, where methacrylic acid is grafted to butadiene and crosslinked with multivalent metal to form metal ionic bond and other external crosslinkers containing amine, carboxyl, and/or polar hydroxyl groups to form covalent bond. Glycidyl methacrylate is an ester of methacrylic acid and glycidol with a dual-functionality of vinyl and epoxy groups which is commonly used in making epoxy resins. Glycidyl methacrylate's active vinyl and epoxy groups can be grafted with ethylene and react with a sulfur-based crosslinker and other external crosslinkers containing polar groups such amine, carboxyl, and hydroxyl groups to form double bond or covalent bond. The dip-coagulating method for making a glove employs a cationic calcium salt to act as a coagulant agent. The glove former is firstly coated with the cationic calcium salt and then dips in the latex compound. The latex compound becomes coagulated and forms a solid film on the glove former. During this process, some cationic calcium salts may penetrate the film and accumulate in the latex tank to cause latex instability and sediments or lumps phenomena. A suitable emulsifying agent in an appropriate amount is stable enough to maintain latex stability but not too stable to affect the film formation. Conventional VAE latex mainly used nonionic type surfactant or polyvinyl alcohol as an emulsifying agent or protective colloid; however, the nonionic type surfactant or polyvinyl alcohol is too stable for cationic coagulant agent to coagulate and cause difficulty in film formation. Polyvinyl alcohol tackified latex viscosity results in air bubbles formed, which are difficult to float out and break, which in turn causes pinholes problem during the glove dipping process. A purely anionic type surfactant such as SDBS has a low-cost advantage. But it is easy to foam, which causes a pinhole problem, and easy to react with calcium salt of coagulant agent to form solid calcium sulfonate derivatives, which are difficult to be leached out by water generate a high residue content to harm glove shelf life.
The VAE latex disclosed herein uses 1-8% emulsifying agent by weight of the total copolymer content to modify the nonionic type conventional VAE latex compositions and improve the defects of using anionic surfactant as an emulsifying agent for suitable use in the glove dipping process. The emulsifying agent is mainly an anionic surfactant selected from the group consisting of ammonium lauryl sulfate, sodium lauryl sulfate, sodium lauryl sarcosinate, sodium myreth sulfate, sodium pareth sulfate, sodium decyl sulfate, sodium N-lauroyl-N-methyltaurate, sodium tetradecyl sulfate, SDBS, sodium cetyl sulfate, sodium oleyl sulfate, sodium sulfosuccinate or their mixtures, and with additional minor amount of low-foam type nonionic surfactant or protect colloid selected from the group consisting of fatty alcohol ethoxylate, alkyl phenol ethoxylate, fatty acid ethoxylate, sorbitan fatty acid ester, glycerol fatty acid ester, polyethylene glycol, polyvinyl alcohol, hydroxyethyl cellulose, and a combination thereof. Many trials were conducted with various combinations of anionic type surfactants and/or with nonionic surfactants or cellulose, and some of them produced satisfactory results without a theoretical explanation. A preferred embodiment includes mainly an anionic surfactant and optionally a minor amount of nonionic surfactant or polyvinyl alcohol.
To prepare the VAE latex compound for glove dipping process, a water-diluted pH adjuster is first added into VAE latex to increase its pH value to about 6.0-9.0 to prevent the VAE latex from instability caused by too aggressive pH shocking or crosslinking reaction by the next added XNBR latex or external crosslinker. Another water-diluted pH adjuster is preferably added at the final latex compounding stage to adjust the latex compound to about 7.0-11.0. The pH adjuster acts as a stabilizer to control the crosslinking reaction speed and maintain VAE latex compound stabilities during the latex compounding and glove dip-coagulating process. The suitable pH adjuster is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, sodium acetate, potassium bicarbonate, potassium citrate, potassium acid phosphate, and a combination thereof. Some external crosslinkers such as glyoxal, polyamide epichlorohydrin, or carbodiimide are more active in acidity conditions; like internal crosslinker monomers, they have a short pot life. But the multivalent metal salts type external crosslinkers react with carboxyl functional groups to form metal ionic bond, which tends to be more active in an alkaline condition. Therefore, deciding the appropriate pH range of the VAE latex compound depends on the type of crosslinker selected and the actual practice.
After pH adjuster is added into the VAE latex compound, if the blend of VAE latex and XNBR latex is desired to use, then adding XNBR latex; otherwise, adding a water-diluted external crosslinker. The blend of VAE latex and XNBR latex can improve VAE glove properties or performances. For example, acrylonitrile of XNBR can improve glove oil and grease resistance; and butadiene can improve glove softness and elasticity. But the blending incompatibility problems of XNBR latex and VAE latex have not been disclosed and solved by the prior arts. The commercial XNBR latex suppliers seldom disclose their composition details. The commercial XNBR generally has a Tg from −10° C. to −30° C. and pH about 8.0 and comprises 20-40% acrylonitrile, 50-70% butadiene, 4-8% carboxylic acid by weight of the total monomer, and 1-5% anionic emulsifying agent by weight of the total copolymer. Normally, the blend incompatibility problems of XNBR latex and conventional VAE latex mostly occur when the VAE latex is in an acidity condition with a pH range of about 3.0-5.0, and when mainly nonionic type surfactant or protect colloid is used. When blending an acid-based VAE latex, the VAE latex releases cationic hydrogen react anionic surfactant of XNBR to cause copolymer particles coagulation or gelling conditions and further decrease XNBR latex pH value and stability. When blending nonionic base VAE latex into anionic base XNBR latex, the reaction speed with cationic coagulant agent is slowed down, which interferes with the film formation and causes uneven and thinner coating problems. After testing many VAE latex emulsifying agent compositions, it was found out that a satisfactory, even film can be obtained from the use of an emulsifying agent composition containing an anionic type surfactant and optionally a minor content of a nonionic surfactant or protect colloid, as this emulsifying agent can adjust the reaction speed with a cationic coagulant agent. After that, the VAE latex pH is adjusted to about 6.0-9.0 by a pH adjuster. The modified VAE latexes can freely blend with almost any ratio with various XNBR latex without incompatibility problems such as sedimentation, gelation, lump, or uneven film formation during the latex compounding and glove dipping process. The preferred blending ratio is less than 50% XNBR latex by weight of the total latex solid content.
Therefore, modifying compositions of conventional VAE latex and converting it to an anionic post-crosslinking type VAE latex with a pH of about 6.0-9.0 not only provide a VAE latex suitable to be used as the primary base material but also solve the blending incompatibility problems of VAE latex and XNBR latex as the base latex for making disposable glove.
The external crosslinker has an amount of 0.5-4.0% by weight to the total latex solid content. The external crosslinker is selected from the group consisting of sulfur, accelerator, zinc oxide, aluminum oxide, sodium aluminate, aluminum hydroxide, adipic acid, lactic acid, oxalic acid, citric acid, glyceric acid, glycolic acid, gluconic acid, maleic acid, maleic anhydride, sodium citrate, sodium gluconate, polyethylene oxide, polyethylene glycol, glycerine, maltitol, sorbitol, xylitol, erythritol, glyoxal, glutaraldehyde, ammonium zirconium carbonate, potassium zirconium carbonate, ammonium zirconium lactate, polyamide epichlorohydrin, carbodiimide, and a combination thereof. A conventional sulfur-based crosslinker consists of sulfur, accelerator, and zinc oxide. Sulfur causes environmental pollution; accelerators such as carbamates, thiurams, or thiazoles can cause type IV chemical allergy risks; and zinc oxide harms the aquatic organisms. As such, the EU suggests decreasing its amount in rubber. Because the sulfur base crosslinker can build up a strong double bond efficiently with a smooth crosslinking reaction at ambient temperature to keep the latex stability, it is still the most commonly used crosslinker in glove manufacturing. For example, the sulfur base crosslinker is applied in making NR glove, where zinc oxide acts as an activator to promote accelerator and sulfur to react with isoprene of NR copolymer chains. The sulfur-based crosslinker is also used to make an XNBR glove, where zinc oxide reacts with a carboxylic acid to form metal ionic bond, and the accelerator speeds up sulfur to react butadiene to form double bond. In some embodiments, the VAE latex comprises vinyl and epoxy functional monomer such as glycidyl methacrylate, which can react with a sulfur base crosslinker or other crosslinkers consisting of or comprising polar groups such amine, carboxyl, and hydroxyl groups to form a double bond or covalent bond. Many crosslinkers such as organic aluminum polyol complex, polyamide epichlorohydrin, maleic anhydride, and glyoxal can be used to substitute sulfur-based crosslinker. By selecting and hybridizing various crosslinkers, the resulting VAE glove is not only free of or with a reduced amount of sulfur, accelerator, and zinc oxide, which reduces the environmental pollutions, health allergy risks, and/or harm to the aquatic organisms, but also improves certain glove property and performance such as water or chemical resistance, softness, elongation or elasticity.
After adding the external crosslinker, then adding a proper amount of water-diluted process additives selected from the group consisting of antifoam agent, biocide agent, antioxidant, dispersing agent, emulsifying agent, thickener, wax, titanium dioxide, filler, color pigment, and a combination thereof, and then a pH adjuster and water to adjust the VAE latex compound pH to 7.0-11.0 and solid content to about 10-30%, followed by continuously agitating for about 10-24 hours for maturation. At this time, the VAE latex compound is ready to transport to a glove dipping production line for making gloves.
The following steps include: firstly dipping a cleaned ceramic glove former in a water-based coagulant solution comprising calcium nitrate, wetting agent, and releasing agent; drying the glove former in a heating chamber; dipping the dried glove former in a prepared VAE latex compound; coagulating to form a solid film on the glove former; drying the film in a heating chamber; then raising the film in warm water about 50° C. to leach out the chemical residues such as calcium nitrate and surfactants; then rolling the up-portion of film into a bead to obtain a glove; then sending the glove to a hot-air oven at about 100-130° C. for 15-25 minutes for crosslinking or curing; then dipping the glove in chlorine water for surface de-tacky and drying it, and finally striping the glove from the glove former and packing. The glove former is cleaned and back to the dipping process repeatedly. In an embodiment, the obtained VAE disposable glove has a thickness of 0.03-0.12 mm, a tensile strength of no less than 14 Mpa, an elongation of no less than 350%.
Hereinafter, the present invention will be explained in more detail with reference to the following examples. However, it should be understood that the examples are not intended to limit the scope of the invention.

Examples

The steps for preparing a VAE latex compound include: loading a pH-adjusted base VAE latex in a mixer and optionally adding XNBR latex if NBR latex is to be used as a second latex, followed by blending for homogenization; then slowly adding a pH adjuster solution to adjust the latex pH to about 8.0 and keeping agitating for about one hour; then adding an external crosslinker solution and agitating for another one hours; then adding process additives solution; then adding an additional pH adjuster solution and water to adjust to the final latex compound to the desired pH and a solid content of about 16%; continuing to agitate about 15 hours for maturation. To prevent too aggressive blending operation from causing latex instability, blending chemicals such as pH adjuster, external crosslinker and process additives are pre-diluted before adding or use. In some embodiments, the blending chemicals are pre-diluted to 5% solution with water. Adding the blending chemicals without pre-dilution and/or too quickly may cause side effects such as pH shocking or gelation, or poor dispersing problems.
The composition of the VAE latex compound is showing in TABLE 1. For convenience, the pH and the solid content of the VAE latexes are pre-adjusted to 6.5 and 50%, respectively. The process additives are not discussed in the examples. SDBS and polyvinyl alcohol are used as emulsifying agents. Glycidyl methacrylate and methacrylic acid are used as crosslinkable functional group monomers. Zinc dibutyldithiocarbamate (BZ) is used as an accelerator. The external crosslinker includes one or more selected from the group consisting of sulfur, zinc oxide, aluminum polyol complex, polyamide epichlorohydrin, carbodiimide, and ammonium zirconium carbonate(AZC).

TABLE 1

Example No.	1	2	3	4	5	6	7	8	9

VAE latex Tg (° C.)

−7

−14

% by weight of total monomer content of VAE latex

Vinyl Acetate	67	67	67	67	70	70	66	66	66
Ethylene	29	29	29	29	26	26	30	30	30
Methacrylic acid	4	4	4	4			2	2	2
Glycidyl methacrylate					4	4	2	2	2
SDBS	2.5	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0
Polyvinyl alcohol		0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5

% by weight of the total latex solid content

VAE latex	100	100	100	70	100	100	100	100	70
XNBR latex				30					30
Sulfur	1.0				1.0		1.0
BZ	0.8				0.8		0.8
Zinc oxide	1.2	0.5			1.2		1.2
Aluminum polyol		1.5						2.0	2.0
complex
polyamide						2.0
epichlorohydrin
Carbodiimide			1.2	1.2
AZC								0.3	0.3
KOH adjust latex	9.5	10.2	8.5	8.5	9.5	8.5	9.5	9.5	9.5
compound pH to

Water	Proper amount adjust total solid content to 16%

The gloves according to the compositions of latex compounds of TABLE 1 are made through a dip-coagulating process including the following steps:

A) Dipping a cleaned ceramic glove former in an about 50° C. water-based coagulant solution comprising 15% calcium nitrate and 1.2% calcium stearate as stripping agent and 0.3% nonionic surfactant as a wetting agent by weight of the total solution, and then drying the glove former in a heating chamber.
B) Dipping the glove former in the prepared VAE latex compound for about 15 seconds and then coagulating to form a film layer.
C) Drying the film and then dipping in about 50° C. warm water for about 60 seconds to leach out the water-soluble impurities such as calcium nitrate and surfactants, and then rolling the film up portion area into a bead.
D) Curing the film in a hot-air oven at 120° C. for about 20 minutes to obtain a VAE glove.
E) Treating the VAE glove by a chlorination process for de-sticky, and then drying and stripping the glove from the glove former.

The obtained glove examples have a thickness of about 0.065 mm and are tested after 24 hours stripped from formers. TABLE 2 shows the test results of wearing durability, water-resistance, and physical performances. The general market minimum requirements are 4 hours for wearing durability and 1 hour for water resistance. The wearing durability test is carried out by six persons wearing gloves and operating in room condition until the glove is broken, and then recording the average wearing time. The water resistance test is conducted by loading 1000 ml water into six gloves and hanging them on a rack until the gloves show water leaking, and then recording the average time. Physical performance test is conducted according to ASTM D6319 and ASTM D412 test methods.

	TABLE 2

	Before aging physical performance

				Stress
Example	Wearing	Water	Tensile	at 300%	Ultimate
No.	Durability	resistance	strength	elongation	elongation

1	<2 hours	<1 hour	23.3 Mpa	22.1 Mpa	371%
2	>4 hours	>1 hour	25.6 Mpa	23.3 Mpa	428%
3	>4 hours	>1 hour	26.3 Mpa	24.8 Mpa	397%
4	>6 hours	>2 hour	24.2 Mpa	19.7 Mpa	454%
5	>4 hours	>1 hour	23.7 Mpa	20.4 Mpa	436%
6	>4 hours	>1 hour	22.8 Mpa	18.7 Mpa	443%
7	>4 hours	>1 hour	25.3 Mpa	21.6 Mpa	457%
8	>6 hours	>2 hour	24.5 Mpa	20.6 Mpa	484%
9	>6 hours	>2 hour	23.2 Mpa	17.3 Mpa	562%

In Example 1, the VAE latex has a Tg of −7° C. and comprises 67% vinyl acetate, 29% ethylene, 4% methacrylic acid by weight of the total monomer, and 2.5% SDBS as an emulsifying agent by weight of the total copolymer content. The external crosslinker is 3.2% conventional sulfur-based crosslinker including 1.0% sulfur, 0.8% BZ, and 1.2% zinc oxide by weight to the total latex solid content. Potassium hydroxide is used to adjust the final latex compound's pH to 9.5. Water is used to dilute the final latex compound solid content to 16%. The obtained glove has a thickness of about 0.065 mm. The glove film was examined, which was in good condition without defects of uneven film thickness, flow marks, lumps, tears, or fisheyes. The glove of Example 1 failed in the wearing durability and water resistance tests caused by VAE latex-containing methacrylic acid, which only reacted with zinc oxide to form metal ionic bond. Although zinc metal ionic crosslinking bonds improve tensile strength enforcement, sulfur and BZ became reluctant chemicals and cannot build up a sufficient crosslinking network structure to pass the tests.
Example 2 and 3 used carboxylated VAE latex. The emulsify agent is 2.0% SDBS and 0.5% polyvinyl alcohol. The gloves' film formation was not obviously affected. The gloves have a thickness of less than 3% thinner than that of Example 1.
Example 2 used 0.5% zinc oxide and 1.5% aluminum polyol complex by weight to the latex solid content as the external crosslinker. The latex compound's pH was adjusted to 10.2 for promoting metal ionic bond formation. The glove of Example 2 has more than 4 hours wearing durability and one-hour water resistance, which are better than those of Example 1 because zinc ion and aluminum ion reacted with methacrylic acid to form metal ionic bond and polyol reacted methacrylic acid to form ester covalent bond which built up a crosslinking network structure with high enough density, resulting in wearing durability and water resistance improvements.
Example 3 used 1.2% carbodiimide by weight to the VAE latex solid content as the external crosslinker, which is a carbodiimide, to react with methacrylic acid to form N-acyl urea. The latex compound's pH was adjusted to 8.5 for maintaining latex compound stability. The test results of the gloves of Example 3 show that they had the highest tensile strength among all the Examples and the lowest dosage amount of crosslinker, which demonstrated carbodiimide is an effective crosslinker to react with the carboxyl functional group of methacrylic acid.
Example 4 used a blend of 70% VAE latex of Example 3 and 30% of XNBR latex having about −25° C. Tg as the base latex. The external crosslinker and latex compound's pH are the same as Example 3. No blending incompatibility phenomena such as sedimentation, gelation, or lumps during the latex compounding process were found. No poor film formation or latex incompatibility problems during the glove dipping process was observed. Example 4 gloves have better wearing durability of more than 6 hours and water resistance of more than 2 hours, compared to those of Example 3 gloves. Without any theory, it is believed that the two kinds of polymers are partially interlaced to form an interpenetrating network structure or partially form a covalent bond between the two carboxyl functional groups of the two carboxylated latexes and further mutually share and react with carbodiimide to form a covalent bond to strength crosslinking network structure during glove curing period result to wearing durability and water resistance improvements. Comparing the physical performances of Example 3 with those of Example 4, Example 4 glove is softer with a lower tensile strength, stress at 300% elongation, and higher elongation than Example 3 glove because the VAE latex in Example 4 was blended with additional lower Tg XNBR latex.
The VAE latex of Example 5 and 6 has a Tg of −14° C. and comprises 70% vinyl acetate, 26% ethylene, and 4% glycidyl methacrylate by weight of the total monomers. The pH of the latex compound of Example 5 is adjusted to 9.5. 3.2% sulfur-based crosslinker by weight to the total latex solid content is used as an external crosslinker, in which zinc oxide acted as an activator to active sulfur, and BZ as an accelerator to speed up the crosslinking reaction of sulfur and vinyl functional group of glycidyl methacrylate to form double bond. The pH of the latex compound of Example 6 was adjusted to 8.5. 2% polyamide epichlorohydrin by weight to the total latex solid content was used as the external crosslinker to react with an epoxy group of glycidyl methacrylate to form a covalent bond. A comparison of test results of Example 5 and 6 shows no obvious difference in wearing durability, water resistance, and physical performances. However, the glove of Example 5 has a slightly better tensile strength than that of Example 6.
The VAE latex of Example 7 and 8 has a Tg of −14° C. and comprises 66% vinyl acetate, 30% ethylene, 2% methacrylic acid, and 2% glycidyl methacrylate by weight of the total monomers. The pH of the latex compound of Example 7 is adjusted to 9.5. 3.2% sulfur-based crosslinker by weight to the total latex solid content was used as the external crosslinker. The zinc oxide reacted with methacrylic to form a metal ionic bond and BZ to speed up the reaction of sulfur and vinyl groups of glycidyl methacrylate to form double bond. The pH of the latex compound of Example 8 is adjusted to 9.5. 0.3% AZC and 2% Aluminum polyol complex are used as the external crosslinker by weight of the total latex solid content, in which zirconium and aluminum ions reacted with methacrylic acid to form metal ionic bond and polyol firstly grafted to aluminum ion to form an aluminum complex and then reacted with methacrylic acid and glycidyl methacrylate to form ester covalent bond. AZC also acted as an insolubilizer to improve glove water resistance, thereby extending the wearing durability of Example 8′s gloves from more than 4 hours to more 6 hours and the water resistance of Example 8′s gloves from more than 1 hour to more than 2 hours.
A blend of 70% of the VAE latex of Example 8 and 30% of XNBR latex was used as the base latex in Example 9. The external crosslinker and latex compound pH are the same as Example 8. No blending incompatibility problems and obviously different test performances were observed in Example 8 and 9. However, as Example 9 employed a lower Tg XNBR latex to soften the gloves, the gloves of Example 9 have a slightly lower tensile strength and stress at 300% elongation, and their elongation is above 500%. According to ASTM D5250, a PVC disposable medical glove shall fit the minimum physical requirements of the tensile strength of 9 Mpa and elongation of 300%. According to ASTM D6319, an XNBR examination glove has a minimum physical standard of before aging tensile strength of 14 Mpa and elongation of 500%. The VAE gloves of Example 9 have a tensile strength of no less than 14 Mpa, which is comparable to an XNBR glove, and an elongation of no less than 350%, which falls between those of the PVC and XNBR glove. Among the Examples, the gloves of Example 1, 5, and 7 contain sulfur, BZ, and zinc oxide. The glove of Example 2 is free of sulfur, BZ, and a reduced amount of zinc oxide. The gloves of Example 3, 4, 6, 8, and 9 are free of sulfur, BZ, and zinc oxide.
While the invention has been described with respect to preferred embodiments, variations, modifications would be apparent to one of ordinary skill in the art without departing from the spirit of the invention.

Claims

1. A disposable glove made by dip-coagulating a water-based latex compound comprising the composition of

a) a base latex,

b) an external crosslinker,

c) a pH adjuster,

d) a process additive,

wherein the disposable glove has a thickness of 0.03-0.12 mm, tensile strength of no less than 14 Mpa, elongation of no less than 350%.

2. The disposable glove according to claim 1, wherein the base latex comprises a vinyl acetate ethylene latex.

3. The disposable glove according to claim 1, wherein the base latex is a blend of vinyl acetate ethylene latex with less than 50% of a carboxylated acrylonitrile butadiene latex by weight of the total latex solid content.

4. The disposable glove according to claim 2, wherein the vinyl acetate ethylene latex has a Tg of lower than 0° C., and the vinyl acetate ethylene latex comprises 52-88% of vinyl acetate by weight of the total monomer content, 10-40% of ethylene by weight of the total monomer content, 2-8% of crosslinkable functional group monomer by weight of the total monomer content, and 1-8% emulsifying agent by weight of the total copolymer content.

5. The disposable glove according to claim 4, wherein the crosslinkable functional group monomer is an ethylenically unsaturated monomer comprising at least one or more carboxyl, vinyl, and epoxy groups, the crosslinkable functional group monomer is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic anhydride, styrenesulfonic acid, ethenylphosphonic acid, allylglycidyl ether, glycidyl methacrylate, methacryloyl glycidyl ether, ethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 2,5-hexanediol dimethacrylate, 2,4-pentanediol diacrylate, 2,4-pentanediol dimethacrylate, dipropyleneglycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and a combination thereof.

6. The disposable glove according to claim 4, wherein the emulsifying agent comprises an anionic surfactant selected from the group consisting of ammonium lauryl sulfate, sodium lauryl sulfate, sodium lauryl sarcosinate, sodium myreth sulfate, sodium pareth sulfate, sodium decyl sulfate, sodium N-lauroyl-N-methyltaurate, sodium tetradecyl sulfate, sodium dodecylbenzenesulfonate, sodium cetyl sulfate, sodium oleyl sulfate, sodium sulfosuccinate or their mixtures, and optionally with an additional amount of nonionic surfactant or protect colloid selected from the group consisting of fatty alcohol ethoxylate, alkyl phenol ethoxylate, fatty acid ethoxylate, sorbitan fatty acid ester, glycerol fatty acid ester, polyethylene glycol, polyvinyl alcohol, hydroxyethyl cellulose, and a combination thereof.

7. The disposable glove according to claim 1, wherein the external crosslinker is in an amount of 0.5-4.0% by weight to the total latex solid content, and the external crosslinker is selected from the group consisting of sulfur, accelerator, zinc oxide, aluminum oxide, sodium aluminate, aluminum hydroxide, adipic acid, lactic acid, oxalic acid, citric acid, glyceric acid, glycolic acid, gluconic acid, maleic acid, maleic anhydride, sodium citrate, sodium gluconate, polyethylene oxide, polyethylene glycol, glycerine, maltitol, sorbitol, xylitol, erythritol, glyoxal, glutaraldehyde, ammonium zirconium carbonate, potassium zirconium carbonate, ammonium zirconium lactate, polyamide epichlorohydrin, carbodiimide, and a combination thereof.

8. The disposable glove according to claim 1, wherein the pH adjuster is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, sodium acetate, potassium bicarbonate, potassium citrate, potassium acid phosphate, and a combination thereof, and the water-based latex compound has a pH in a range of 7.0-11.0.

9. The disposable glove according to claim 1, wherein the process additive is selected from the group consisting of antifoam agent, biocide agent, antioxidant, dispersing agent, emulsifying agent, thickener, wax, titanium dioxide, filler, color pigment, and a combination thereof.

10. A method for making the disposable glove according to claim 1, comprising:

a) dipping a glove former with a calcium nitrate solution as a coagulant agent and then dry it,

b) dipping and coagulating the vinyl acetate ethylene latex compound to form a solid film and then dry the solid film,

c) raising the solid film with warm water,

d) rolling the up-portion of the solid film into a bead,

e) curing a resulting glove in a hot-air oven at a temperature of about 100-130° C. for 15-25 minutes,

f) chlorinating the resulting glove for de-tacky,

g) stripping the disposable glove from the glove former.

11. The disposable glove according to claim 1, wherein the disposable glove contains sulfur, accelerator, and zinc oxide.

12. The disposable glove according to claim 1, wherein the disposable glove is free of sulfur and accelerator.

13. The disposable glove according to claim 1, wherein the disposable glove is free of sulfur, accelerator, and zinc oxide.

14. The disposable glove according to claim 3, wherein the vinyl acetate ethylene latex has a Tg of lower than 0° C., and the vinyl acetate ethylene latex comprises 52-88% of vinyl acetate by weight of the total monomer content, 10-40% of ethylene by weight of the total monomer content, 2-8% of crosslinkable functional group monomer by weight of the total monomer content, and 1-8% emulsifying agent by weight of the total copolymer content.

15. The disposable glove according to claim 7, wherein the disposable glove contains sulfur, accelerator, and zinc oxide.

16. The disposable glove according to claim 7, wherein the disposable glove is free of sulfur and accelerator.

17. The disposable glove according to claim 7, wherein the disposable glove is free of sulfur, accelerator, and zinc oxide.