JPS5853016B2 - Sankabo Shizaigan Yupolymer Soseibutsu - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to antioxidant-containing polymer compositions.

It is known that various thermoplastics undergo some degree of cross-linking upon irradiation, thereby substantially altering their plastic properties.

A special property that can be imparted to irradiated thermoplastics is heat-recovery.

Heat-recovery properties can be obtained by irradiation and subsequent heating can cause deformation of the polymer, causing contraction or expansion.

Methods of making heat-recoverable polymers by irradiation include, for example:
U.S. Patent No. 3597372.3396460 and 32
97819.

In a suitable ionizing radiation source, for example Van de
Mention may be made of the Graff high-energy electron accelerator; other suitable sources include X-rays and gamma-rays, such as cobalt-60 sources.

The dose required to achieve the required degree of cross-linking varies widely from material to material, but generally doses from 1 to 50 megarads give good results for most polymers.

Among the substances which are particularly suitable for cross-linking by radiation, one may enumerate, for example, olefin polymers such as polyethylene, polypropylene, ethylene/vinyl acetate copolymers, ethylene/acrylic ester copolymers, ethylene/propylene copolymers and saturated and ethylene/vinyl acetate copolymers.
Unsaturated olefin elastomers such as propylene/conjugated genter polymers.

Other thermoplastics that can be effectively cross-linked by irradiation include polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride and chlorinated polyethylene.

Mention may also be made of acrylic resins, polyethers and polyesters.

Unfortunately, although olefin polymers can be easily crosslinked by irradiation, they are also subject to severe degradation by the oxidizing effects of air at elevated temperatures, such as above 50°C.

They are also susceptible to degradation by ionizing radiation when exposed to large amounts of such radiation, such as 5×10 10 ergs per gram and more.

For this reason, the incorporation of antioxidants becomes necessary.

These generally serve to scavenge free radicals that would otherwise initiate oxidation of the polymer, and such radicals are exposed to various energy sources such as heat and light. Formation is possible by exposing.

When free radicals are formed, they are scavenged by the antioxidant before they can allow the oxidation reaction to propagate in the polymer.

However, irradiation of such polymers to produce cross-linking also proceeds through a free radical mechanism.

It has therefore hitherto been necessary to incorporate relatively large amounts of antioxidants into the polymer systems to be irradiated.

The incorporation of such large amounts of antioxidants creates a cross-linking effect as some of the polymer free radicals formed by irradiation are scavenged by the antioxidants before they can act as cross-linkers. This means that a larger amount of irradiation is required.

On the other hand, if smaller amounts of antioxidants are used, they are consumed or rendered ineffective during irradiation so that the formed polymer composition is easily oxidized during use at elevated temperatures. There will be.

Such oxidative loss or discoloration under elevated temperatures is manifested by surface cracks, crevices and eventually complete embrittlement of the material.

The present invention provides a polymer composition comprising at least one irradiated cross-linked polymer susceptible to oxidation and a minor amount of an organic phosphite.

The present invention also provides molded articles, particularly heat-recoverable articles, made from such polymeric compositions.

Organic phosphites are well known antioxidants, e.g. U.S. Pat.
Please refer to the issue.

Although certain organic phosphites do not prevent the formation of free radicals and subsequent reaction of such radicals under irradiation conditions to form cross-linkages; The present invention is based on the surprising discovery that, at elevated temperatures, the polymers nevertheless effectively serve as free radical scavengers to prevent oxidative degradation.

Therefore, it is not necessary to incorporate these substances in large quantities, which not only increases the cost but also reduces the overall strength of the plastic.

The organic phosphites used in this invention are effective when used in amounts up to 5% by weight of the polymer composition and can be conveniently used in amounts from 0.05 to 5%.

Desirable organic phosphites for use in the present invention are solid and substantially insoluble; in other words, during irradiation, a major portion of the organic phosphite is in a crystalline or glassy solid state, and even when irradiated, it remains insoluble. It will remain reactive and unaffected.

However, at temperatures above the temperature at which radiation cross-linking occurs, organic phosphites act to prevent the propagation of free radicals that cause oxidative degradation of plastic materials.

Organic phosphites suitable for use in the present invention may be found among those having the general formula R10P(OR)2.

where R' is an aliphatic, substituted aliphatic, aromatic or substituted aromatic group and the R groups can be the same or different, each being hydrogen or an aliphatic, substituted aliphatic, aromatic or substituted aromatic group. represents a group group or together forms a ring.

Both R' and R groups can be polymeric and/or further contain phosphite moieties.

A particularly suitable organic phosphite is U.S. Pat.
It is derived from pentaerythritol, dipentaerythritol and tripentaerythritol as described in No. 43.

It has also been found that in addition to organic phosphites, it may be advantageous in some cases to incorporate sulfur-containing hydroxyaromatic compounds.

Suitable hydroxyaromatic compounds generally consist of a phenol, fresol or naphthol group in which the sulfur is bonded, preferably to one cyclic unsaturated group; for example they can have the general formula R1-8-R2 ; where R1 and R2 can be the same or different and are substituted or unsubstituted phenol, fresol or naphthol groups.

However, the acetic unsaturated group to which the sulfur is attached need not be homoaromatic, but can be a heteronuclear unsaturated ring such as a triazine ring, in which case the sulfur is attached to a carbon atom in the ring.

Among the particularly suitable sulfur-containing compounds that may be mentioned are, for example, 4,4'-thiobis(6-tert-phthyl-meth-
4,4'-thiobis(6-tert-butyl-meta-fresol), a mixture of oligomers of 4,4'-thiobis(6-tert-butyl-meta-furesole) as disclosed in GB 1241582, 4,4'-thiobis(6-tert-butyl- ortho-talesol), ■・1'thiobis(2-naphthol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), phosphorus oxychloride and 4,4'-thiobis(
and 6-(4-hydroxy-3,5-tert-butylanilino)2,4-bis(n-octylthio)1,3.
5-triazine.

The optimum weight ratio of organophosphite to hydroxyaromatic sulfur-containing compound will vary depending on the particular compound used, but generally this ratio will be from 1:5 to 5:1, especially from 1:2 to 2:1.
within the range of

It is particularly preferred that the combination contains approximately equal amounts of phosphite moieties and sulfur-containing moieties.

Such mixed antioxidant compositions, when incorporated in amounts up to 5% based on the polymer composition, provide superior oxidation properties to the two-component mixture alone at the same total additive level. It appears to exhibit preventive properties.

They can also be used in highly filled flame retardant plastic systems.

The following examples illustrate the invention.

Example 1 1% by weight of various organic phosphite antioxidants were mixed in a mill at 160° C. with low density polyethylene (DFD 6005, Union Carbide Company, density 0.930, M, 1.0.2) and 6X6X0. at 170℃.
0.020 inch plates, cooled to room temperature and irradiated to give a radiation dose of 15 megarads.

The elastic modulus of the sample at 150°C is RoM, B 1ac
The Electrical Manufacture
ctrer, October 1957), but
This is directly proportional to the cross-linking density (A
, Char 1esby, Nuclear Radiation and Polymer Pe
rgamon Publishers, New York, 1960 151
(see page).

All the antioxidants evaluated were Unistone (Weston).
) An organic phosphite obtained from a chemical company and designated as: A, Uniston 243B phosphite is a polymeric phosphite of the general formula (both rings are saturated); B, Uniston 465, is a polymeric organic phosphite and is believed to be similar to A; C, Uniston 467, is a polymeric organic phosphite and is believed to be similar to A; D, Weston 625, is believed to be similar to A; The phosphate ester, dineodyl 25-pentaerythritol diphosphite (“Neodyl 25” is a trade name), has an average alkyl group of C14.
is believed to be a mixture of dialkyl pentaerythritol diphosphites; E, Unistone 618 phosphite; is distearyl pentaerythritol diphosphite; F, Unistone TP 24; G, Unistone 600;
is diisodecylpentaerythritol diphosphite; H, Unistone TPP, is triphenylphosphite.

The results in Table 1 indicate that organic phosphites A-G did not act to prevent cross-linking when irradiated and are therefore suitable for use in the present invention.

However, Sample H, triphenylphosphite, was unsuitable for use in the present invention because it was soluble and became active upon irradiation, preventing cross-linking of the polymer.

Example 2 The antioxidant of Example 1 was compounded into high density polyethylene at a level of 3% by weight and pressed into a board according to the procedure of Example 1.

The plate was irradiated with a dose of 15 megarads.

% inch conditions, 6 inch lengths were suspended in a hot air circulating oven at 200°C to evaluate antioxidant efficiency.

After varying elapsed times, the samples were removed from the oven, cooled to room temperature for at least 4 hours, and then stretched in an Instron tensile tester.

The initial jaw separation was 1 inch at a draw speed of 2 inches per minute.

The jaw field at break of the specimen was used to indicate the final elongation.

The number of hours of heat aging that resulted in failure of the sample at an elongation of 50% or less in the Instro tester was chosen as the failure point.

The results are summarized in Table 2.

Example 3 All of the phosphorous esters listed in Example 1 were added to CPE255.
2 (Dow Chemical Company), chlorinated polyethylene (approximately 25% chlorine content), at the 2% by weight level and subjected to irradiation of 20 megarads and tested and evaluated as in Example 1.

The composition containing phosphorous acid ester H melted and flowed when heated to 150°C.

With other phosphorous esters, no collapse or interference to radiation cross-linking was observed to any extent.

Moreover, phosphites A to G were effective stabilizers for the irradiated polymer.

Example 4 3 pph by weight of antioxidant A was added to Alathon 3170
(Typon), ethylene-hinyl acetate copolymer (density 0.94 M, 1.2) according to the procedure of Example 10.

The time to failure at 175° C. was evaluated as described in Example 1 after applying an irradiation dose of 20 megarads.

Sample failure occurred after more than 15 days at 175°C.

Comparable results were obtained for phosphites B to G and for all of these phosphites except H in the ethylene-acrylic ester copolymer.

Example 5 This example describes the incorporation of a sulfur-containing hydroxyaromatic compound into an organic phosphite.

Various amounts of distearyl pentaerythritol diphosphite (Sample E), other antioxidants, and their formulations were added to high density polyethylene (Sample E) on a mill at 160°C.
Marlex 6003, Phillips Oil Company, density 0.096, M, 1.2) and pressurized into 6 x 6 x 0.020 inch plates at 170°C with a hydraulic machine and cooled, then 20 megarads Irradiated with irradiation dose.

Antioxidant efficiency was evaluated by the method described in Example 2 and the results are summarized in Table 2.

As can be seen from Table 3, phosphorous ester alone (sample E)
Or the sulfur-containing hydroxyaromatic compound alone is generally 3
At the pph level, it broke in less than 13 days*.

However, the 3 pph level of the phosphite and sulfur-containing hydroxyaromatic blend gave substantially better results on the order of 25 days, indicating a synergistic outcome from the two-component blend.

Also, when evaluating phenols containing no sulfur (antioxidant K) and phenols with sulfur atoms not bonded to aromatic groups (antioxidant Q), there was little or no increase in time. I couldn't get it.

Therefore, a desirable system appears to be a blend of a phosphorous ester and a sulfur-containing hydroxyaromatic compound having at least one sulfur bonded to an unsaturated cyclic group.

Example 6 Various flame retardant plastic compositions according to the general formulation below were used to evaluate antioxidant efficiency.

Low density polyethylene 40% Ethylene ethylenemer ethyl acrylate copolymer Propylene diene terpolymer 7% 8% Flame retardant (brominated aromatic) Antimony oxide 1% ■ 0% Heat stabilizer 6% Trimethylolpropane Trimethylac 3% Lylate oxidation Inhibitor combination The 5% antioxidant combination is an organic phosphite, distearyl pentaerythritol diphosphite (sample E), and Unistone 243-B-phosphite (sample A), and a sulfur-containing hydroxyaromatic* compound. (Samples M and R).

M is as described in Example 5 and R is 3 moles of 4.
It is the reaction product of 4'-thiobis-(6-tert-butyl-meta-fresol) and 1.05 moles of phosphorus oxychloride.

This composition capable of cross-linking by irradiation was tested for oxidation resistance and the results are summarized in Table 4.

Example 7 A composition with the following formulation was used to evaluate antioxidant efficiency.

High density polyethylene 63 Ethylene/Hinyl acetate copolymer 14 Filler 10TiO
22 Irradiation cross-linking promoter 7 Total amount of antioxidant 4 In the above formulation various organic phosphite esters (Sample B from Example 1)
, C and F) with antioxidant M (Example 5) in a total amount of 4
% level and tested for oxidation resistance.

The test procedure was similar to that of Example 5, except that the test conditions were heat aging at 200°C.

4% Antioxidant M alone was used under these conditions and failed after 100 hours.

The results are given in Table 5 below.

The formulations tested are capable of cross-linking by irradiation.

Claims (1)

[Scope of Claims] 1 at least one irradiated cross-linked polymer susceptible to oxidation; an aliphatic substituted aliphatic group, an aromatic group, or a substituted aromatic group, R may be the same or different, and each is hydrogen or an aliphatic group, a substituted aliphatic group, an aromatic group, or a substituted aromatic group. or together form a ring), when the phosphorus atom of the phosphite moiety is bonded by oxygen to an aromatic or substituted aromatic A polymer composition further comprising a hydroxyaromatic compound having a sulfur atom.