RU2454441C2 - Method of producing articles from cross-linked rubber - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing articles from cross-linked rubber. The method involves the following steps: a) depositing a sulphur-containing composition onto the surface of a pre-moulded article made from peroxide-containing cross-linked rubber and b) cross linking the rubber by heating the sulphur-coated article in the presence of air. Heating temperature ranges from 80 to 300°C.

EFFECT: method enables to obtain articles with a tack-free surface, sufficient strength and hardness; reduces smell, toxicity and inflammability.

11 cl, 2 tbl, 2 ex

Description

The present invention relates to a method for manufacturing an article from crosslinked rubber products and to rubber products obtained by this method.

Typically, crosslinking of rubbers is carried out using peroxide or sulfur as the crosslinking agent. Compared to crosslinking with sulfur, crosslinking with peroxide provides advantages in terms of heat resistance, permanent deformation under compression, electrical insulation properties and, when compounding with colored substances, dyeing and color fastness. However, oxygen prevents the formation of cross-links with peroxide. Thus, when crosslinking is carried out in the presence of air, this process is inadequate on the surface of the rubber, which leads to various problems, such as strong stickiness, reduced strength and insufficient stiffness. Consequently, the finished product has a sticky surface, is easily scratched, not sufficiently durable and slippery.

For this reason, peroxide-initiated crosslinking uses mainly airless techniques, such as compression molding, injection molding and melt vulcanization.

Another way to deal with the influence of oxygen is described in J. Groepper, Kautchuk + Gummi Kunststoffe, Vol. 36, 1983, pp. 466-470, which discloses the application to the surface of crosslinkable rubber products of boric acid before crosslinking in air. In addition, it is noted in this prior art that although dusting a rubber surface with sulfur or tetramethylthiuram disulfide (TMTD) also gives good results, the strong odor, toxicity and fire hazard of the vapors do not allow their practical use.

An object of the present invention is to provide a method for cross-linking preformed articles of crosslinkable rubber containing peroxide in the presence of air, which makes it possible to obtain articles of crosslinked rubber with a non-sticking surface, sufficient strength and rigidity. In addition, in comparison with dusting the surface of the rubber with sulfur, the method according to the present invention provides satisfactory results using less sulfur. In addition to economic advantages, this method also provides a reduction in odor, toxicity and fire hazard.

The present invention relates to a method for manufacturing crosslinked rubber products, comprising the steps of:

a) applying a sulfur-containing composition to the surface of a preformed product of crosslinkable rubber containing peroxide to provide a coated gray product; and

b) crosslinking the rubber by heating a gray coated article, optionally in the presence of air, at a temperature in the range of 80 to 300 ° C. to produce a crosslinked rubber article.

In addition, the present invention relates to a method for manufacturing products from crosslinked rubber, comprising the steps of:

a) applying a sulfur-containing aqueous suspension to the surface of a preformed article of peroxide-crosslinkable rubber to provide a sulfur-coated product, and

b) crosslinking the rubber by heating the gray coated article at a temperature in the range of 80 to 300 ° C., optionally in the presence of air, to produce a crosslinked rubber article.

The method of the present invention provides acceptable parameters for cross-linking even in the presence of air and, in turn, obtaining such mechanical properties of the finished cross-linked rubber that are comparable to those achieved with anaerobic cross-linking. In addition, the use of a sulfur-containing composition leads to a decrease in sulfur consumption compared to the application of powders consisting only of sulfur. Sulfur-containing compositions have improved wetting parameters and allow better distribution of sulfur particles on the surface of the crosslinkable rubber product.

In addition, sulfur-containing compositions and, in particular, sulfur-containing aqueous suspensions have improved organoleptic properties, that is, the present invention provides odor reduction. In addition, sulfur contained in aqueous suspensions ignites at higher temperatures than powdered sulfur.

In addition to sulfur particles, the sulfur-containing composition includes a distribution medium that improves wetting of the surface of the crosslinkable rubber product. The distribution medium may be another solid compound, such as a wax, or a suspending medium, such as an aqueous medium, or another solvent, in which sulfur particles can be dispersed. The sulfur-containing composition is preferably in the form of a sulfur-containing suspension, most preferably in the form of a sulfur-containing aqueous suspension.

The sulfur concentration in the composition is preferably at least 5% by weight, more preferably at least 15% by weight, most preferably at least 25% by weight. Said sulfur concentration is preferably not higher than 95% by weight, more preferably not higher than 75% by weight, most preferably not higher than 50% by weight, in all cases relative to the total weight of the suspension.

It is preferable to provide good wetting of the surface of the preformed rubber product with a sulfur-containing composition, preferably an aqueous sulfur-containing suspension. Therefore, it may be desirable and, as a rule, it is preferred that the aqueous suspension contains wetting agents. As wetting agents, cationic, anionic or nonionic surfactants can be used. Examples of suitable wetting agents include alkylbenzene sulfonate, arylbenzenesulfonate, ethoxylated alcohols, glycolic acid ethoxylate-4-nonylphenyl ether, and combinations thereof.

In addition, the suspension may contain stabilizers, such as clays (eg, bentonite), detergents and / or emulsifiers.

The suspension can be prepared by simply mixing the powdered sulfur with water and optional additives (for example, wetting agents, emulsifiers, detergents, stabilizers). The finished mixture is preferably milled, for example, in a ball mill or mill with high shear forces.

A sulfur-containing composition, in particular a sulfur-containing aqueous suspension, intended to be applied to the surface of a preformed rubber product, contains sulfur particles, of which preferably 90% have a diameter of less than 150 microns, more preferably less than 100 microns, even more preferably less than 80 microns, even more preferably less than 70 microns, even more preferably less than 60 microns, even more preferably less than 50 microns, most preferably less than 25 microns, measured in an aqueous suspension by laser diffraction Nia in accordance with ISO 9276-1 and ISO 9276-2.

The sulfur-containing composition can be applied to the surface of a preformed product from crosslinkable rubber containing peroxide in various ways: by immersing (dipping) the preformed product in suspension or by brushing or spraying the suspension on the surface of the product, for example, using a continuous coating device. This composition, in particular an aqueous suspension, is applied to the surface in an amount of preferably at least 0.005 mg S / cm ² , more preferably at least 0.01 mg S / cm ² , most preferably at least 0 , 1 mg S / cm ² . This composition or aqueous suspension is applied to the surface in an amount of preferably not more than 10 mg S / cm ² , more preferably not more than 1 mg S / cm ² .

Then, the sulfur-coated product is heated to a temperature of from 80 ° C, preferably from 120 ° C, more preferably from 140 ° C to 300 ° C, preferably to 230 ° C in the presence of air. Such heating can be carried out using a furnace (for example, a channel furnace), an autoclave, microwave, UV, steam or hot air, or a combination thereof. The gray coated article is heated for preferably at least 1 minute, more preferably at least 3 minutes, most preferably at least 5 minutes. This period of time preferably does not exceed 2 hours, more preferably does not exceed 60 minutes, most preferably does not exceed 30 minutes.

At the beginning of the heating step, the sulfur coating should still contain water, which means that before the heating step, the drying step is not carried out to remove water from the suspension.

Crosslinkable rubbers suitable for use in the method of the present invention include ethylene-propylene copolymers (EPM), ethylene-propylene-diene monomer copolymers (EPDM), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), natural rubber (cis-1,4-polyisoprene; NR), isoprene rubber (IR), ethylene-vinyl acetate (EVA) copolymers, acrylonitrile-butadiene-styrene (ABS) copolymers, styrene-isoprene-styrene (SIS) copolymers, chloroprene rubber (CR ), chlorinated polyethylene (CM), polyurethane rubber (AU), high density polyethylene (HDPE), olietilen low density (LDPE) and polimetanovy rubber.

Suitable peroxides that must be present in the crosslinkable rubber include perketals, perfers, dialkyl peroxides, diacyl peroxides, trioxepane compounds of the following formula:

where R ¹ , R ² and R ^{3 are} independently selected from each other as hydrogen and a substituted or unsubstituted alkyl group; and cyclic ketone peroxides with the structure represented by formulas I-III:

where R ₁ -R _{6 are} independently selected from the group consisting of hydrogen, C1-C20 alkyls, C3-C20 cycloalkyls, C6-C20 aryls, C7-C20 aralkyls, and C7-C20 alkylaryls, and these groups may include non-cyclic or branched alkyl moieties; each of R ₁ -R ₆ , optionally, may have one or more substituents in the form of a group selected from alkyl C1-C20, linear or branched, cycloalkyl C3-C20, aryl C6-C20, aralkyl C7-C20, hydroxyl, alkoxy C1-C20, aryloxy C6-C20, aralkoxy C7-C20, alkylaryloxy C7-C20, R ₁ C (O) O-, R ₁ OC (O) -, halogen, carboxy, nitrile and amido groups; or each of R ₁ / R ₂ , R ₃ / R ₄ and R ₅ / R ₆ together with the carbon atom to which they are attached, can form a cycloaliphatic ring of 3-20 atoms, which, optionally, may have one or more Deputy in the form of a group selected from alkyl C1-C20, linear or branched, cycloalkyl C3-C20, aryl C6-C20, aralkyl C7-C20, hydroxyl, alkoxy C1-C20, aryloxy C6-C20, aralkoxy C7-C20, alkylaryloxy C7 -C20, R ₁ C (O) O-, R ₁ OC (O) -, halogen, carboxy, nitrile and amido groups.

More preferred peroxides are selected from the following: dialkyl peroxides such as dicumyl peroxide (Perkadox® BC), tert-butyl cumyl peroxide (Trigonox® T), di-tert-butyl peroxide (Trigonox® B), di (tert-butyl peroxyisopropyl) benzene b meta-, para- or mixed meta / para-form (Perkadox 14), 2,5-dimethyl-2,5-di (tert-butyl peroxy) hexane (Trigonox® 101), 2,5-dimethyl-2,5-di (tert-butylperoxy) hexin-3 (Trigonox® 145), tert-butylisopropyl cumyl peroxide, di-tert-amyl peroxide (Trigonox® 201) and cumisopropyl cumyl peroxide; peroxyesters such as di (tert-butyl peroxy) phthalate, tert-butyl peroxybenzoate (Trigonox® C), tert-butyl peroxyacetate (Trigonox® F), tert-butyl peroxy isopropyl carbonate (Trigonox® BPIC), tert-butyl peroxy-2-niton-2-methyl ), tert-butyl peroxylaurate, tert-butyl peroxy diethyl acetate (Trigonox® 27), tert-butyl peroxy isobutyrate (Trigonox® 41), tert-butyl peroxy 3,5,5-trimethylhexanoate (Trigonox® 42), tert-amyl peroxybenzoate (Trigonox® 127) tert-amyl peroxyacetate; peroxyketals such as ethyl 3,3-di (tert-butylperoxy) butyrate, ethyl 3,3-di (tert-amylperoxy) butyrate, n-butyl-4,4-di (tert-butylperoxy) valerate, 2, 2-di (tert-amylperoxy) propane, 2,2-di (tert-butylperoxy) butane (Trigonox® D), 1,1-di (tert-butylperoxy) ceclohexane (Trigonox® 22), 1,1-di ( tert-butylperoxy) -3,5,5-trimethylcyclohexane (Trigonox® 29) and 1,1-di (tert-amylperoxy) cyclohexane (Trigonox® 122); trioxepanes such as 3,3,5,7,7-pentamethyl-1,2,4-trioxepane (Trigonox® 311); cyclic ketone peroxides such as 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxononan (Trigonox® 301).

The amount of peroxide that must be present in the preformed crosslinkable rubber containing peroxide product ranges from 0.1, preferably from 1.0, more preferably from 2.0 weight. parts to 10, preferably up to 8, most preferably up to 6 weight. parts of the weight of the rubber.

In addition to peroxides, the preformed crosslinkable rubber article may contain conventional additives in commonly used amounts. Examples of such additives include reinforcing components or fillers such as carbon black, silicon oxide, clay, chalk, talc, aluminum hydroxide, magnesium hydroxide and calcium carbonate, lubricants, tackifiers, waxes, antioxidants, pigments, UV-stabilizers, blowing agents , nucleating agents, accelerators, sulfur, ZnO, filling oils such as paraffin oils (e.g. stearic acid), voltage stabilizers, anhydrous inhibitors, metal deactivators, binders, coloring agents.

A preformed article of crosslinkable rubber containing peroxide is typically produced by introducing peroxide and optional additives into the rubber, followed by molding the mixture to form it.

Peroxide and optional additives can be introduced into the rubber by thorough mixing. If the peroxide is a heat-sensitive compound, the mixing is usually carried out at temperatures such that the half-life of the peroxide is more than 0.5 hours, preferably more than 1 hour, more preferably more than 2 hours. In practice, the rubber temperature is limited to 150 ° C. Mixing can be carried out in various ways known to those skilled in the art. For example, the components may be milled in various devices, including a multi-mill mill, a worm mill, continuous mixers, extrusion mixers and a Banbury mixer, or dissolved in a mutual or compatible solvent. If all the solid components of the composition are in powder form or in the form of fine particles, it is most convenient to prepare the composition by, firstly, mixing the components, for example, in a Banbury mixer or continuous extruder, and then plasticizing this mixture in a heated device, for example , a two-roll mill, continuing grinding until a homogeneous mixture of components is obtained. Alternatively, a masterbatch containing rubber and one or more antioxidants may be combined with peroxide and optional additives.

If the rubber cannot be obtained in powder form, mixtures can be made by introducing rubber into the mill, plasticizing it to form an array around one of the rollers (i.e., a batch of mixing), followed by adding the remaining components either in the form of a mixture or separately and plasticization to obtain a homogeneous mixture. The temperature of the rollers is maintained in the range of preferably about 25-150 ° C, more preferably 50-120 ° C and below the temperature of rapid decomposition of peroxide.

Then, the final peroxide-containing crosslinkable rubber is formed into a desired shape, for example by extrusion, in order to obtain a preformed article from the crosslinkable rubber containing peroxide. This preformed article of peroxide-containing crosslinkable rubber may be in the form of a sheet, tube (e.g., cable, pipe, hose), window, structure or automobile profile, or any other suitable shape.

In one embodiment, the method of the present invention is a continuous method for manufacturing a crosslinkable rubber product, comprising the steps of:

(i) shaping the peroxide crosslinkable rubber to form a preformed article of peroxide crosslinkable rubber,

(ii) applying a sulfur-containing composition to the surface of a preformed article of peroxide crosslinkable rubber to form a gray coated article; and

(iii) crosslinking the rubber by heating the gray coated article to a temperature in the range of 80 to 300 ° C., optionally in the presence of air, to obtain a crosslinked rubber article,

all stages are carried out continuously.

Crosslinked rubber products obtained by the method of the present invention can find various applications, for example, in tires such as a rolling surface, a subprotective layer, a side part, a reinforced layer, a sealing layer and a connecting material; in rubber compositions, such as hoses, belts, pipes, engine mounts, shock absorbers and insulators, gaskets, shaped material and car bumpers; in wires and cables as semiconductor and insulating compounds. They are especially well suited for use in building structures, windows and car profiles.

The present invention is illustrated by the following examples.

Examples

Example 1

Prepared a mixture containing 100 weight. parts of medium filled EPDM (containing 100 parts of Keltan®578 EPDM, 70 parts of black SRF, 70 parts of black FEF and 50 parts of Sunpar 2280), 6.3 weight. parts of di (tert-butylperoxyisopropyl) benzene (Perkadox® 14, ex-Akzo Nobel) and 8 wt. coated calcium oxide parts (Calaxol® CP2).

The resulting peroxide-containing rubber was compressed in a Mylar film to produce sheets of 0.2-0.3 mm. Both sides of these sheets were coated with approximately 0.5-0.7 mg / cm ^{2 of} various sulfur-containing compositions. Powders were applied to the surface with a brush; liquids were applied onto the surface with a foam roller.

The final coated sheets were then vulcanized for 5 minutes at 200 ° C. in a forced air circulation oven.

The final sheets were tested in a Zwick tensile testing machine in accordance with ISO 37. The test results are shown in table 1 below. For comparison, this table also shows the properties of an unvulcanized rubber product, a rubber product vulcanized without any surface treatment in the presence of air and a rubber product vulcanized without any surface treatment in the absence of air.

Table 1 Tensile strength, N / mm ² The modulus of elasticity is 100%, N / mm ² Elongation at break,% No vulcanization 4.6 1,6 700 No air, no surface treatment 13.6 5,0 250 Air, no surface treatment 4.8 2,3 330 Zinc Hexasulfide Powder 12.9 4,5 350 Tetramethyl-thiuramdisulfide powder 12.5 4,5 430 Dipentamethylene thiuramtetrasulfide powder 11,2 4.1 370 Powder S ¹ 14.0 4.7 370 90% weight. powder S ¹ + 10% weight. wax ² 15,2 6.4 320 Aqueous Suspension S
(40% wt. S) ³ 15.1 6.4 320 ¹ Crystex® HS OT20, ex Flexys
² Armid® HT, ex Akzo Nobel, for improved wetting
³ 50% by weight. Bayer® Garden Microsulfo Spuitzwavel in water + 1% by weight. sodium sec-alkanesulfonate (Armostat® 3002 ex Akzo Nobel), to improve wetting

The results of the tensile test clearly show that without surface treatment of the rubber, vulcanization with hot air does not lead to cross-linking on the surface of the rubber. Surface pretreatment with various sulfur-containing compounds improves cross-linking on the rubber surface. The best results are obtained when using sulfur, either in the form of a powder - preferably mixed with wax to improve wetting of the surface when melted in an oven - or in the form of an aqueous suspension. These results — tensile strength and modulus of elasticity — are even higher than vulcanization in the absence of air.

The amount of sulfur required to obtain the above results when using sulfur powder and an aqueous suspension of sulfur is 0.57 mg S / cm ² and 0.24 mg S / cm ² , respectively. This suggests that when sulfur is applied to the surface as an aqueous suspension rather than a powder, less sulfur is required. This is important not only from an economic point of view, but also because of toxicity. Additional benefits of using sulfur in the form of a suspension rather than a powder include the reduction of odor, fire hazard and dust formation.

In the examples described above, it is noted that when applying an aqueous suspension and a solid mixture containing wax, the smell is significantly less intense than when applying powdered sulfur. The smell of sulfur is also much less after vulcanization at 220 ° C.

It was also found that products on which sulfur powder was applied burned at 240 ° C for 5 minutes, while products on which an aqueous suspension or wax-containing composition was applied remained stable.

Example 2

Aqueous suspensions containing 50% by weight. S, were prepared as follows. 50 weight. parts of powdered sulfur was ground in a ball mill with 1 weight. part of the wetting agent (Tamol NN9104, ex-BASF), 1 weight. part of bentonite and 48 weight. parts of water.

Various sulfur powders were used, resulting in suspensions of d90 of 13, 16 and 17 μm, respectively. In other words, the size of 90% of the sulfur particles in these suspensions was less than the corresponding indicated values. Particle size was measured by laser diffraction in accordance with ISO 9276-1 and ISO 9276-2.

Two channel furnaces (each 1 m long) were placed in series with a distance of 5 cm between them. They were equipped with a conveyor belt and a drive unit. The furnaces were located along the process stream after the extruder, the distance between the extruder head and the first furnace was 10 cm.

An EPDM / peroxide mixture of Example 1 was extruded using this extruder. An aqueous sulfur-containing suspension was applied with a sponge to the surface of the tape exiting the extruder before entering the first furnace. The temperature in the furnaces was maintained equal to 220 ° C. The time spent in the ovens was 11 minutes.

The results are shown below in table 2. This table also shows the results of a control test performed similarly, but without surface treatment.

Scratch resistance was tested with a tailor's pin. The test surface was examined under a microscope (magnification: up to 400x). Under the microscope, the tailor's pin was pressed by hand to the rubber surface at an angle of about 45 °. Crossing lines were drawn on the surface. Penetration into the surface was evaluated as follows: the appearance of grooves on the surface was evaluated as negative (-) surface scratch resistance; if only lines were observed without penetration into the surface, scratch resistance was evaluated as positive (+). In addition, when the surface was well vulcanized, when pressed with a pin, it bent.

For each sample, a surface scratch test was performed several times.

table 2 d90 μm Tensile strength, N / mm ² The modulus of elasticity is 100%, N / mm ² Elongation at break,% Scratch resistant Control 12.0 4.4 246 - 13 13.9 4.1 292 - / + 16 13.7 4.3 281 + 17 14.0 4.1 285 +

These experiments show that the method of the present invention can be carried out continuously, including the steps of molding, surface treatment and vulcanization. From table 2 we can conclude that the scratch resistance of processed products compared with untreated is significantly increased.

Claims (11)

1. A method of manufacturing products from crosslinked rubber, including the stage at which:
a) applying a sulfur-containing composition to the surface of a preformed article of peroxide-crosslinkable rubber to provide a gray-coated product; and
b) crosslinking the rubber by heating a gray coated article, optionally in the presence of air, at a temperature in the range of 80 to 300 ° C. to produce a crosslinked rubber product, the sulfur containing composition containing sulfur particles and a distribution medium that improves wetting of the surface of the product made of crosslinked rubber. 2. The method according to claim 1, in which the sulfur-containing composition is a sulfur-containing aqueous suspension. 3. The method according to claim 2, in which 90% of the sulfur particles present in the sulfur-containing aqueous suspension, when measured in this suspension, have a diameter of less than 100 microns. 4. The method according to any one of the preceding paragraphs, in which the sulfur concentration in the sulfur-containing composition corresponds to a range from 5 to 95 wt.% Relative to the total weight of the composition. 5. The method according to any one of claims 1 to 3, in which the sulfur-containing composition also contains one or more additives selected from the group consisting of clay, stabilizers, emulsifiers and wetting agents. 6. The method according to any one of claims 2 and 3, in which a sulfur-containing aqueous suspension is applied to the surface of a preformed product containing peroxo crosslinkable rubber by immersing the specified product in the suspension or by brushing or spraying the suspension on the surface of the specified product. 7. The method according to any one of claims 1 to 3, in which the sulfur-containing composition is applied to the surface of a preformed article containing peroxide crosslinkable rubber in an amount of at least 0.005 mg S / cm ² . 8. The method according to any one of claims 1 to 3, in which between stages a) and b) do not carry out the drying stage. 9. A continuous process for the production of crosslinkable rubber products, comprising the steps of:
(i) shaping the peroxyd crosslinkable rubber to a preformed molded article of peroxo crosslinking rubber,
(ii) applying a sulfur-containing composition to the surface of a pre-molded article containing peroxo crosslinkable rubber to provide a gray-coated article; and
(iii) the rubber is crosslinked by heating the gray coated article to a temperature in the range of 80 to 300 ° C., optionally in the presence of air, to obtain a crosslinked rubber article,
moreover, all stages are carried out in a continuous mode, and the sulfur-containing composition contains sulfur particles and a distribution medium, which improves the wetting of the surface of the product from crosslinked rubber. 10. A crosslinked rubber product obtained by the method according to any one of the preceding paragraphs. 11. A sulfur-coated product obtained by applying a sulfur-containing composition, preferably a sulfur-containing aqueous suspension, to the surface of a pre-molded product containing peroxide crosslinkable rubber, the sulfur-containing composition containing sulfur particles and a distribution medium that improves wetting of the surface of the crosslinked rubber.