CS245398B1 - Modified latex blend of natural or synthetic rubber - Google Patents

Abstract

The solution relates to modified filled mixtures based on natural or synthetic rubber latex containing vulcanizing agents, dispersants, stabilizers, accelerators and other auxiliary additives. Inorganic fillers are added to latex mixtures to adjust some properties of the products and, above all, to reduce their cost. However, their use is limited to relatively small amounts, otherwise their settling in production facilities makes the production process difficult or impossible. According to the present invention, the addition of 0.2 to 10 parts by weight of a surface-active alkyl ester of phthalic acid, e.g. dioctyl phthalate, improves sedimentation stability and allows for higher filling of latex mixtures. The solution also relates to a method of producing these mixtures by mixing a separately prepared dispersion of an inorganic filler with a dispersant and a surface-active substance and the latex mixture with other additives.

Description

The invention relates to modified latex mixtures based on natural or synthetic rubber containing vulcanizing agents, dispersants, stabilizers, accelerators, activators and other additives, as well as a process for preparing these mixtures.

The compositions according to the invention are intended for the production of rubber articles by dipping. This technology currently produces a number of rubber products such as gloves (for various technical uses, operational, household), protective equipment, advertising and meteorological balloons.

For most applications, latex mixtures based on natural or synthetic rubber, or mixtures thereof containing conventional additives such as vulcanizing agents, dispersants, stabilizers, accelerators, activators, antioxidants, pigments and other auxiliaries are used.

Inorganic fillers such as limestone, chalk, kaolin, lithopone, barium sulphate, which are commonly used in other technological processing of the latex to adjust hardness or stiffness, but especially to make latex mixtures cheaper, are used only to a limited extent. The fillers used cannot be added to the latex blends by direct mixing but must first be filled with the filler in water using suitable dispersants and then subjected to a particle dispersion process in one of the grinding equipment (ball, colloid and atritor mill).

Substances used as proven dispersants - ammonium, sodium or potassium oleate, sodium salts of alkylnaphthalenesulphonic acid and its various derivatives, or condensation product of oleyl chloride and methyltaurine sufficient for satisfactory dispersion of additives supplied to latex mixtures (colloidal sulfur, accelerators, antioxidants, vulcanizing agents, pigments) in small amounts, i.e. of the order of 1 to 5 parts per 100 parts of rubber (dsk). These dispersants allow wetting and dispersing of the inorganic fillers in water, but when the dispersed fillers are used in amounts of 10 dsk or more in latex mixtures, the filler particles are gradually sedimented. If the mixtures are not permanently mixed, the bottom of the vessels, pipes, hoses, and containers forms a hardly stirrable sediment, which makes it difficult to use fillers in the continuous production of dipped goods. Increasing the concentration of dispersants does not have a major effect on improving sedimentation stability. Other known dispersants of natural origin, such as casein, glue, gelatin, ammonium alginate, also exhibit low efficacy and, when used in large quantities, increase film wettability and coagulate latex due to their biodegradation.

Since it is not possible to ensure continuous mixing of the filled latex mixture at all stages of the soaking process, the use of inorganic fillers in the present process of making the mixture is completely unrealistic, although the physical-mechanical properties of the filled rubber products are satisfactory for most applications.

Suppression of sedimentation is possible by significantly reducing the particle size of fillers, but this affects the technical capabilities of filler manufacturers and suppliers. A second possibility of increasing sedimentation stability by increasing the viscosity of the latex composition by using various thickeners is very limited, apparently, since the soaking technology requires only a narrow viscosity range of the latex composition to achieve a uniform appearance and thickness of the articles.

It was an object of the present invention to provide a latex mixture filled with inorganic fillers of such a composition as to achieve long-term sedimentation stability allowing a continuous process of soaking. It has been found that a latex mixture based on natural or synthetic rubber containing vulcanizing agents, dispersants, stabilizers, accelerators, activators, antioxidants, fillers, pigments and other auxiliaries, characterized in that it contains 100 parts by weight of latex 5 up to 50 parts by weight of inorganic fillers such as limestone, chalk, barium sulfate or kaolin; and 0.2 to 10 parts by weight of a surfactant which is an alkyl ester of phthalic acid having 2 to 10 carbon atoms in the alkyl chain, preferably dioctyl phthalate.

To prepare a latex composition according to the invention, an aqueous dispersion of an inorganic filler with a dispersant and a surfactant is prepared on a suitable dispersing device, and the dispersion is added to the latex mixture containing vulcanizing agents, stabilizers, accelerators, activators, antioxidants, with stirring. pigments and other auxiliaries.

The combined use of an alkylnaphthalenesulfonic acid alkali salt dispersant and phthalic acid ester type organic materials in the preparation of a masterbatch of inorganic fillers makes it possible to form a protective layer on the surface of the filler particles. A probable mechanism for attaching the alkylnaphthalenesulfonic acid alkali salt molecules to the surface layer of the phthalic acid ester on the filler particle can be envisaged in such a way that an electronegative repellent coating of the particle towards the external environment is formed. The use of the treated filler in a latex mixture of natural or synthetic rubber then has a favorable sedimentation stability. In fact, the phthalic acid ester-like organic material here functions as a surfactant which requires a dispersion system.

In order to further elucidate the invention, the following examples of compositions of the invention are given:

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The dissolver mixer is used to prepare a master batch of the filler composition (in parts by weight):

Calcium carbonate precipitated 50.0 Water distilled 44.2 Disperser (based on condensate of sulphonated alkylnaphthalene with formaldehyde, 0.8 Dioctyl phthalate 5.0

The masterbatch is homogenized in an attritor mill filled with glass beads at 1000 rpm for 10 minutes. (Bead fill ratio and homogenized premix 1.5: 1.0). The prepared filler premix has a dry matter content of 56%, a viscosity of 12 s (FORD 0 4 mm) and does not contain particles larger than 10 ^-5 m.

Latex natural rubber 100,00

Disperser (condensate of sulfonated alkylnaphthalene with formaldehyde) 0.24

Sulfur ground 0,62

Zinc alkylthiocarbamate accelerator 0.62

Titanium dioxide - rutile 1.20

Silicone emulsion 0.07

Color premix 0.03

Distilled water 3,80

Precipitated calcium carbonate premix 30.00

This stuffed latex dipping mixture has a viscosity of 17 s (FORD 0 4 mm ,, good mechanical stability (KLAXON min. 1500 s), the filler in the mixture practically does not sediment after 7 days. mix slightly, the coagulability of the mixture is comparable to the latex-free filler.

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The mixture can be used for the production of dipped goods especially household and industrial gloves, technical gloves and advertising balloons.

Example 2

On the dlssolver mixer, a premix filler composition (in parts by weight) is prepared:

Kaolin 40,0 Water distilled 49,0 Disperser (based on condensate of sulphonated alkylnaphthalene with formaldehyde 1,0 Dlbutylphthalate 10,0

The mixture is dispersed in an attritor mill filled with steel or glass beads at 1000 rpm for 15 minutes. (Bead filling ratio and homogenized premix 1.5: 1.0). The prepared filler premix has a dry matter content of 51%, a viscosity of 19 s (FORD 0 4 mm).

Using this pre-mix, a steeped soaked composition (in parts by weight) was prepared with stirring:

Natural Rubber Latex (60%) 100.00 Disperser (based on sulphonated alkylnaphthalene condensate with formaldehyde 0.23 Sulfur ground 0.62 Accelerator (zinc alkylthiocarbamate) 0.62 Titanium dioxide - rutll 1.20 Silicone emulsion 0.07 Color masterbatch 0 , 03 Distilled water 3.80 Kaolin masterbatch 80.00

This stuffed latex dipping composition has a mechanical stability of min. 1000 s (KLAXON), the filler does not settle in the mixture. Slight turbidity can be easily mixed, the coagulability of the mixture is comparable to the latex-free filler.

The mixture can be used for the production of dipped goods, especially household and industrial gloves, technical gloves and advertising balloons.

Example 3

Using the masterbatch prepared according to Example 1, a filled soaked composition was prepared with the mixing (in parts by weight):

Butadiene acrylonitrile latex (dry matter content 45%) 100 Dispersing agent (based on condensate of sulphonated alkylnaphthalene with formaldehyde) 0,20 Sulfur ground 0,46 Accelerator (diethylditocarbamate zinc) 0,46 Titanium dioxide - rutile 0,90 Color masterbatch 0,0 Silicone emulsion Distilled water 2.05 Precipitated calcium carbonate premix 13.50

The soaked soaked latex mixture has satisfactory mechanical stability (min. 1000 with KLAXON), the filler does not sediment in the mixture. The low haze that is formed after 14 days of standing can be easily mixed, the coagulability of the mixture is comparable to a latex-free filler.

The mixture can be used for the production of dipped goods, especially technical gloves resistant to solvents and oils.

Claims (2)

1. A modified latex based natural or synthetic rubber composition containing vulcanizing agents, dispersants, stabilizers, accelerators, activators, antioxidants, pigments and other auxiliaries, characterized in that it contains from 5 to 50 parts by weight of inorganic filler such as limestone per 100 parts by weight of latex , kaolin, barium sulfate or chalk and 0.2 to 10 parts by weight of a surfactant which is an alkyl ester of phthalic acid having 2 to 10 carbon atoms in the alkyl chain, preferably dioctyl phthalate. 2. A process for the preparation of a latex composition according to claim 1, characterized in that an aqueous dispersion of an inorganic filler with a dispersant and a surfactant and a latex mixture containing stabilizers, accelerators, antioxidants, pigments and other auxiliaries are separately prepared. fillers into the latex mixture.