ITMI20002092A1 - PEROXIDE COMPOSITIONS WITH SCORCH RESISTANCE - Google Patents

Description

Description of the industrial invention

The present invention relates to peroxidic compositions usable for the crosslinking of elastomers and polyolefins in general having an improved resistance to scorch.

More particularly it relates to compositions having a longer time of scorch time.

It is well known that organic peroxides are used for the vulcanization of elastomers and polyolefins, however for the processing of compounds it is necessary to have the longest scorch times possible to avoid harmful pre-crosslinking.

To solve this technical problem, organic peroxides having a longer half-life could be used, however this has the disadvantage of requiring too long crosslinking times to achieve complete crosslinking, thus to the detriment of productivity.

It is also known to add additives to the peroxide compositions to increase the scorch time.

See for example the DE 2,553,145 and 2,553,094 patents in which peroxides with different scorch times are mixed but the disadvantage is that the crosslinking times are lengthened with the drawbacks indicated above.

Amine-based additives are also known, but today they can no longer be used because they are considered toxicologically dangerous due to their carcinogenic effects.

Hydroquinones are known, e.g. di-t-butyl or di-t-amyl, sulfur-based compounds, or antioxidants in general as burn retardants in peroxidic vulcanization, in this way, however, the final properties of the cured product are poor.

To solve the technical problem posed, as indicated above, numerous compounds already known in vulcanization with sulfur have been used, however the above-mentioned disadvantages have occurred. See USP 3,335,124.

Also known are peroxidic crosslinking systems containing promoters, such as TAIC (triallylisocyanurate) in combination with thiourea derivatives to increase the scorch time. (See GB patent 1,535,038).

USP 5,292,791 and 5,245,084 in the name of Elf Atochem North America discloses a peroxide composition having scorch retardant properties comprising

(a) a peroxide

(b) a derivative of hydroquinone

(c) a crosslinking promoter.

All examples of these patents and commercial products (Peroximon SR <(R)>, SR <(R)> G, SR <(R)> A, Luperox SR <{R)>, SR <(R)> G, SR <(R,> A are sold as blends containing the compounds listed above.

A col. 4, lines 26-29, it is stated that the mixtures are stable on storage.

The Applicant has unexpectedly and surprisingly found that the components of the mixture of USP '791 and' 084 if are used separately

(a) peroxides in powder form or in the form of granules or master batches, as defined below

(b) + (c) inhibitor and promoter in master batch,

results similar to those of the mixtures prepared by mixing the three components and used immediately for vulcanization are obtained.

It has been found that the separate mixtures formed by (a) and (b) + (c) can be stored for an indefinite time without giving rise to reactions which may possibly occur between the components during storage.

Compounds b) derived from hydroquinone have the following formulas

where R and R <1>, equal to or different from each other, have the meaning of hydrogen, tert-alkyl, tert-cycloalkyl or ary-t-alkyl; X = alkylene optionally substituted by alkyl, alkoxy, aromatic or cycloaliphatic groups. Preferably

have benzene ring, not containing the OH group, containing ethyl groups as substituents.

Component a) peroxide is used as is well known in the form of powder, granules or master batch. For powders the compositions in% weight are for example:

30-60% liquid or solid peroxide

40-70% inert filler inorganic powder, preferably

38-45% peroxide

62-55% inert filler;

more preferably 40% by weight of peroxide and 60% by weight of inert filler.

The inert fillers are well known and for example silica, calcium carbonate, kaolin, talc can be mentioned. The dimensions are those typical for these applications, for example of the micronized type or of a few microns.

Component a) can also be in the form of paste, or granules using the fillers indicated above and optionally, inert solvents and / or plasticizers such as for example paraffin oil.

(b) + (c) can be used formulated as mentioned for component a) in the form of powder, granule or master batch.

According to a preferred embodiment b) + c) it is used in the form of a master batch.

The master batch is obtained by adding b) and c) to a polymer, for example EVA, high or medium or low density PE, EPM, EPDM, HNBR, hydrogenated or non hydrogenated nitrile rubbers, SBR butadiene -styrene rubbers, PVC, silicone rubbers, fluorinated rubbers.

The polymers used for masterbatches are well known in the art. Component a) peroxide includes all peroxides well known for the vulcanization of elastomers and polyolefins. For example, the class of dialkyl peroxides, for example dicumyl peroxide (Peroximon DC), di-t-butyl peroxide (Luperox DI), t-butyl cumyl peroxide (Luperox 801), 2,5 dimethyl-2,5-bis (t -butylperoxy) hexane (Luperox 101),

2,5-dimethyl-2,5-bis (t-butyl peroxy) -exine (Luperox 130), a, a '-bis (t-butylperoxy-diisopropylbenzene (Peroximon F), a, a' -bis (t- amylperoxy-diisopropylbenzene (Peroximon 180) di-t-amyl-peroxide (Luperox DTA), etc .;

the class of perchetals:

1,1-bis {t-butylperoxy) -3,3-5-trimethylcyclohexane (Luperox 1, 1-bis (t-butylperoxy) cyclohexane,

2,2'-bis (t-butyl-peroxy) butane, etc.

The class of periesteri, for example perbenzoate (Luperox P).

It is also possible to use mixtures of the peroxides indicated above, or mixtures of the individual peroxides in the form of different isomers.

Compounds (b) are for example mono-t-butyl hydroquinone, mono -1-ami1-hydroquinone, 2-5 of t-ami1 hydroquinone, etc.

The promoters (c) are compounds that contain at least 2 polymerizable, bifunctional or polyfunctional C = C double bonds. For example, we can mention di and poly (meth) acrylates, vinyl monomers, allyl, TAC, TAIC, triallylphosphate, triallyltrimethylate, triallyl citrate, diallyl terephthalate, diallyladipate, trimethylolpropane trimethacrylate (TMPTM), ethylenglycol trimethylated -phenylene bismaleimide.

The amount of component (a) with respect to the polymer to be crosslinked varies from 0.1-15% by weight, preferably 1-8%; the amount of inhibitor (b) with respect to the polymer varies from 0.1-10% by weight, preferably 0.1-0.5% by weight; the amount of (c) with respect to the final polymer varies from 0.1-15% by weight, preferably 0.2-2% by weight.

The weight ratio between (a) and the sum of (b) + (c) is generally between 5: 1 and 1: 2, preferably 3: 1 and the weight ratio between components (b) and. c) in the mixture (b) + (c) it is generally comprised between 1: 2 and 0.5: 3, preferably 1: 2.

An advantage of the present invention with respect to the mixtures of components (a), (b) and (c) marketed as a single master batch lies in the fact that with the present invention the user can vary the ratio between the components of the two master batches to obtain the best results depending on the polymer you want to crosslincare.

Therefore the compositions of the present invention are endowed with greater flexibility in practical applications.

The following examples are given by way of non-limiting example of the present invention.

EXAMPLE 1 (comparison)

A master batch was prepared with the following components, such as parts by weight per 100 total parts,

(a) Peroximon F 40 parts, (b) 2-tert-amylhydroquinone 5.5

(c) triallyl cyanurate (TAC) 10

and with an EPM elastomer (see below) 44.5

in bambury leaving in agitation for 15 '.

6.9 phr of master batches are used to vulcanize an ethylene-propylene copolymer EPM rubber (Dutral (R) CO054).

The compound had the following formulation:

Dutral (R) CO054 100 parts

Smoke black HAF 50 phr

zinc oxide 5 phr.

Characterization was performed using a Monsanto rheometer and a Monsanto Mooney.

The data of the ODR curve at 170 ° C (oscillation arc = 3 °; oscillation frequency 100 cycles / minute) are:

The ODR (Oscillating Disc Rheométer) curve can be plotted with the aid of a rotating disc rheometer, according to the ASTM-D-2084-71T standards.

The times are reported on the abscissa and the twisting torque (pounds inches) measured with a dynamometer on the ordinate, opposed by the polymer to the rotation of the disc. The maximum crosslinking density was found to be at a maximum torque value (MH = 64.95 inch lbs) which no longer varies with time).

The expressions t10 and t90 respectively indicate the time it takes to reach a torque equal to 10% and 90% respectively of the maximum torque; ts2 and ts5 mean the time it takes to reach a level of 2 lb.inches and 5lb.inches, respectively, above the minimum of the ODR curve.

The characterization of the "scorching" times on the Mooney viscometer (135 ° C) gave the following results:

ts3 = 47 min and 48 sec

ts10 = 71 min and 3 sec.

By "scorching" we mean the premature vulcanization that occurs undesirably during the extrusion of the compound, before the extruder leaves the die; said premature vulcanization is a frequent cause of a stoppage of operations.

By scorching time ts2 and ts10 (at the Mooney viscometer) we mean the time required to reach an increase in the minimum viscosity value equal to 2 or 10 Mooney units respectively.

Viscosity was determined using a Mooney sharp disc viscometer (ASTM D 1646-81 standard).

EXAMPLE 2 (comparison)

Example 1 was repeated without adding components (b) and (c) and using a master with only component (a) peroxide in phr in the same quantities as in ex. 1.

6.9 phr of master are always taken and cross-linked with the formulation of the Es. 1.

The characterization gave the following results: The data of the ODR curve at 170 ° C (oscillation arc = 3 °; oscillation frequency 100 cycles / minute) are:

The characterization of the "schorching" times on the Mooney viscometer (135 ° C) gave the following results:

ts3 = 23 min and 39 sec

ts10 = 49 min and 15 sec.

EXAMPLE 2 BIS

Example 2 was repeated by taking 11 phr of master, in order to obtain a value of M4 similar to that obtained in Example 1, and it is cross-linked with the formulation of Example 1.

The characterization gave the following results: The data of the ODR curves at 170 ° C (oscillation arc = 3 °, oscillation frequency 100 cycles / minutes) are:

The characterization of the scorch times with the Mooney viscometer at 135 ° C gave the following results:

EXAMPLE 3

Example 1 was repeated, but using two master batches, the one containing component a) peroxide was prepared according to example 2 and 6.9 phr were taken to be used in the formulation for 100 parts of rubber.

The masterbatch of (b) + (c) was prepared as follows,

for 100 total parts of master:

(b) 24.8 parts

<c) 45.2 parts

EPM 30 parts.

(as defined above).

It is mixed in bambury for 15 'and then extruded in a Brabender extruder to obtain cylindrical granules of diameter = 4 min and length 4 mm.

1.7 phr of these granules are then taken for the formulation to be vulcanized.

The results obtained are the following:

the data of the ODR curve at 170 ° C (oscillation arc = 3 °; oscillation frequency 100 cycles / minute) are:

MH = 63.53 lbs * inches

ts2 - 64 seconds

ts5 = 83 seconds

ti0 = 100 seconds

^ 90 = 396 seconds.

The characterization of the "scorching" times on the Mooney viscometer (135 ° C) gave the following results:

ts3 = 47 min and 18 sec

ts10 = 74 min and 1 sec.

By comparing the results of Examples 1 (comparison) and 3 it can be seen that they are comparable.

EXAMPLE 4

Example 3 was repeated, using the two masters prepared there after 6 months of storage. The results obtained on the ODR curve and the scorching times with Mooney viscometer are similar to those of Example 3.

Claims (7)

CLAIMS 1. Peroxide compositions usable for crosslinking elastomers and polyolefins having scorch retardant properties comprising: (a) a peroxide in powder form or in the form of granules or master batches, (b) + (c) inhibitor and promoter in powder, granule or master batch, where (b) is a hydroquinone derivative inhibitor and (c) is a crosslinking promoter. 2. Peroxide compositions having retarding properties according to claim 1, wherein component (a) is a peroxide for the vulcanization of elastomers, component (b) is selected from hydroquinone derivatives having formula where R and R <1>, equal or different from each other, have the meaning of hydrogen, tert-alkyl, tert-cycloalkyl or aryl-talkyl; X = alkylene ^ -01β optionally substituted by alkyl, alkoxy, aromatic or cycloaliphasic groups are having the benzene ring, not containing the OH group, containing ethyl groups as substituents, component (c) is selected from the compounds that contain at least two C = C polymerizable, bifunctional or polyfunctional double bonds. 3. Peroxide compositions having scorch retardant properties according to claims 1 and 2, wherein component a) is used in the form of a master batch, the mixture (b) (c) in the form of a master batch. 4. Peroxide compositions having scorch retardant properties according to claims 1-3, wherein (a) is selected from the class of dialkylperoxides, perketals, periester. 5. Peroxide compositions having scorch retardant properties according to claim 4, wherein component (a) is selected from dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, 2,5 dimethyl-2,5-bis ( t-butylperoxy) hexane, 2,5-dimethyl-2,5-bis (t-butyl peroxy) -exino, a, a '-bis (t-butylperoxy-diisopropylbenzene, a, a' -bis (tamylperoxy-diisopropylbenzene, di-t-amyl-peroxide, 1,1-bis (t-butylperoxy) -3,3-5-trimethylcyclohexane, 1,1-bis (tbutylperoxy) cyclohexane, 2,2'-bis (t-butyl-peroxy) buta-no, perbenzoate. 6. Peroxide compositions having scorch retardant properties according to claims 1-3, wherein component (c) is selected from di and poly (meth) acrylates, vinyl, allyl monomers, TAC, TAIC, triallyl phosphate, triallyltrimethylate, triallyl citrate, diallyl terephthalate, diallyl adipate, trimethylolpropary trimethacrylate (TMPTM), ethylene glycol dimethacrylate, trimethylolpropantriacrylate, diallylite, diallyl fumarate, diallylmaleate, m-phenylene bismaleimide; compound (b) is selected from mono-t-butyl hydroquinone, mono-t-amyl hydroquinone, 2-5 of t-amyl hydroquinone. 7. Peroxide compositions having scorch retardant properties according to claims 1-6, wherein the amount of component (a) with respect to the polymer to be crosslinked varies from 1-8%, the amount of inhibitor (b) with respect to the polymer varies from 0 , 1-0.5% by weight, the amount of (c) with respect to the final polymer varies from 0.2-2% by weight; the weight ratio between (a) and the sum of (b) -f- (c) is between 5: 1 and 1: 2, the weight ratio between components (b) and (c) in the mixture (b ) + (c) is between 1: 2 and 0.5: 3.