JPS63137941A - Polyolefin composition - Google Patents

Abstract

PURPOSE:To obtain a polyolefin composition having excellent thermal stability and free from deterioration of color, by using vitamin E in combination with a specific phosphonite compound as stabilizers. CONSTITUTION:The objective composition is produced by compounding (A) 100pts.wt. of an alpha-olefin homopolymer or copolymer or a copolymer of an alpha-olefin and vinyl alcohol, vinyl acetate, maleic anhydride, etc., with (B) 0.005-0.5pts.wt., preferably 0.03-0.3pts.wt. of vitamin E, e.g. alpha-type, beta-type, gamma-type or delta-type tocopherol or their mixture and (C) 0.005-0.5pts.wt., preferably 0.03-0.3pts.wt. of a phosphonite compound of formula (R1-R6 are 1-30C alkyl or aryl; a and b are integer of 0-4), preferably tetrakis(2,4-di-t-butylphenyl)-4,4'- biphenylene diphosphonite.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polyolefin composition with excellent thermal stability and hue.

[Conventional technology]

Molding of polyolefin polymers is generally carried out at 200°C.
Since it is carried out at higher temperatures, the molecular weight decreases due to the effects of heat, oxygen, etc. Stabilizers are usually added to prevent this. The stabilizers used here are:
Sterically hindered phenols such as 2,6-di-t-butyl-4-methylphenol have been widely used. However, some of these phenols pose problems for the human body, and in cases where safety is particularly important, vitamin E, which has been shown to be somewhat effective as a heat stabilizer for polyolefins, has been substituted.

[Problem that the invention seeks to solve]

However, 5. When vitamin E is used, the hue of the polyolefin decreases, giving the product a yellowish tinge, which often impairs product value. In addition, reducing the amount added improves the hue, but it cannot be said that the thermal stability during molding is sufficient.

An object of the present invention is to provide a polyolefin composition that has excellent thermal stability and color during processing despite the use of vitamin E.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the present inventors found that when vitamin E and a specific phosphonite compound are used together as a stabilizer, no deterioration in hue is observed and the thermal stability is excellent. Heading, we arrived at the present invention.

That is, the present invention uses vitamin E as a stabilizer and the general formula l R2O, 0R4 (wherein R1-R6 are each independently an alkyl group or an aryl group having 1 to 30 carbon atoms, and a and b are 0 to 30).
It is an integer of 4. ) This is a polyolefin composition characterized by adding a phosphonite compound represented by:

The polyolefin used in the present invention includes α-
Olefin homopolymers, copolymers thereof, and α-
Examples include copolymers of olefins and vinyl alcohol, vinyl acetate, maleic anhydride, and the like.

What is vitamin E used in these polyolefins?
It is generally called tocopherol, and various α-type, β-type, T-type, and δ-type tocopherols and mixtures thereof are known.

The amount of vitamin E to be added is suitably from o, oos to 0.5 parts by weight, preferably from 0.03 to 0.3 parts by weight, per 100 parts by weight of the polyolefin. If the amount is less than 0.005 parts by weight, the improvement in thermal stability will not be sufficient, and if it exceeds 0.5 parts by weight, the hue will deteriorate.

The phosphonite compound used in combination with vitamin E is represented by general formula I, and particularly preferably tetrakis (
Examples include 2,4-di-t-butylphenyl)-4,4'-biphenylene diphosphonite.

The amount of these phosphonite compounds added is 0, Q
A range of O5 to 0.5 parts by weight is appropriate, preferably 0.
．． The range is 0.03 to 0.3 parts by weight. If it is less than 0.005 part by weight, the thermal stability will be poor, and if it is added in excess of 0.5 part by weight, there will be no difference in the effect and other physical properties will deteriorate, which is not preferable.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Examples 1 to 3 and Comparative Examples 1 to 3 To 100 parts by weight of polypropylene (manufactured by Mitsui Toatsu Chemical Co., Ltd., MI 0.5) powder, the compounds listed in Table 1 were added in the amounts listed in Table 1, and the mixture was prepared using a granulator. The mixture was pelletized at a granulation temperature of 230°C. The melt index (MI
) was measured according to ASTM D-1238-65T. The smaller the former, the better the thermal stability during molding.

Further, the pellets were hot-pressed to produce a pressed sheet with a thickness of 0.1 mm, and the whiteness was measured. The whiteness is defined by the following formula, and the higher the whiteness, the better the hue.

〔Effect of the invention〕

Although the polyolefin composition of the present invention uses vitamin E as a heat stabilizer, it has excellent color and heat stability, and after being thermoformed into various shapes, it can be used in food packaging, medical equipment, etc. , can be used in the field of toys, etc.

Claims (1)

[Claims] 1. Vitamin E as a stabilizer and general formula I ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (I) (In the formula, R_1 to R_6 each independently have a carbon number of 1 to 3
0 alkyl group or aryl group, and a and b are integers of 0 to 4. ) A polyolefin composition characterized by adding a phosphonite compound represented by: 2. The polyolefin composition according to claim 1, wherein the phosphonite compound is tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene diphosphonite.