JPS59219354A - Polyolefin resin composition for metal coating - Google Patents

Abstract

PURPOSE:To provide the titled resin compsn. having good adhesion to metal and excellent resistance to cathodic peeling and peeling by hot water on adhesive surfaces, by blending a rust-inhibiting pigment having a pH of 7 or below with an unsaturated carboxylic acid-modified polyolefin. CONSTITUTION:0.5-40pts.wt. rust-inhibiting pigment having a pH or 7 or below, e.g., aluminum dihydrogentripolyphosphate or aluminum phosphomolybdate (not more than 20wt% silica or zinc oxide may be used together) is mixed with 60- 99.5pts.wt. modified polyolefin obtd. by grafting 0.03-3wt% unsaturated carboxylic acid or anhydride such as maleic anhydride or a mixture consisting of at least 10wt% said modified polyolefin and not more than 90wt% unmodified polyolefin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyolefin composition for metal coating that has good cathodic peeling resistance. Techniques for coating the surface of metal plates or the inner and outer surfaces of metal tubes with various polymeric substances have been studied for the purpose of corrosion protection of metals, and numerous techniques have been disclosed in patents, literature, and the like. In particular, polyolefin resins have been extensively studied as coating resin materials because of their well-balanced resin properties. In particular, since polyolefin itself has poor affinity with metals, many techniques have been disclosed for the purpose of improving the adhesive strength between metals and polyolefins. For example, many methods have been proposed in which polyolefin resins modified by introducing carboxyl groups and copolymers of olefins, other polar monomers, and nil monomers are used as adhesives. In particular, the above-mentioned modified polyolefins, ie, polyolefins obtained by grafting unsaturated carboxylic acids or their anhydrides, have good initial adhesive strength with metals and have been put into practical use.

However, it has been pointed out as a major drawback that cathodic peel resistance, hot water resistance, etc., which are criteria for determining durable adhesive strength, deteriorate in a relatively short period of time, peeling occurs along the edges, and corrosion resistance deteriorates. Tokuko Sho 1 for improving water resistance, salt water resistance, etc.
! -7g; Publication No. 7 discloses a resin composition in which a modified polyolefin is blended with a phosphate at 0.0/~0.0%, but the present inventors found that the cathodic peeling resistance was not improved at all. This has been determined through a study of the following.

As a result of intensive studies aimed at improving cathodic peeling resistance, the present inventors found that (modified polyolefin grafted with Al unsaturated carboxylic acid or its anhydride or a mixture of the modified polyolefin and unmodified polyolefin 60~?? (B) A cathode-resistant composition in which o, s to qo parts by weight of an acidic rust-preventing pigment, particularly aluminum dihydrogen tripolyphosphate, and aluminum phosphomolybdate, having a pH of less than 7 according to the JISK 10/method are mixed with the weight part of the phosphor. The present invention was accomplished by discovering that a polyolefin resin composition for metal coating with good peelability can be provided.

To explain the present invention in detail, a modified polyolefin or a mixture of the modified polyolefin and an unmodified polyolefin [hereinafter referred to as component (A)] and a rust preventive pigment with pI (less than 7) [hereinafter referred to as (B) ) component] refers to the total amount of component (A) and component (B) (10θ parts by weight), (A + acid component 6O-99j parts by weight, component (B) in o, r to yo parts by weight) Preferably, component (A) is 70 to 99 parts by weight, particularly 73 parts by weight or more.
less than g parts by weight, component (B) is 7 to 30 parts by weight, especially 2
When the amount is more than 23 parts by weight and less than 23 parts by weight, the improvement effect is most exhibited within this range. If the amount of component (B) is less than 0.5 parts by weight, the effect of improving cathode peeling resistance will be small, and if it exceeds 10 parts by weight, the adhesive strength will decrease, which is not preferable.

When a mixture of a modified polyolefin and an unmodified polyolefin is used as component (A), it is preferable that component (A) contains at least 70% by weight of the modified polyolefin. The base polyolefin of the modified polyolefin and the unmodified polyolefin have a density of 0.97 o y
/d or less 0.9 / Of? High, medium, and low density polyethylene of /d or more, homo, random block polypropylene, density θ, q10y/cr/l or less o, g to
y 77 or more (copolymers of D-r-fV and α-olefins having 3 to 10 carbon atoms, and mixtures thereof, etc.). It can be produced by adding the anhydride and causing a grafting reaction according to a known method.The grafting reaction may be a solution method or a slurry method, but in terms of cost, a melt mixing method is preferable.This method In the case of polyolefin resin, 0.03 weight φ or more/less than weight % of unsaturated carboxylic acid or its anhydride and o, i weight %
Preferably, the method of blending 05% by weight of organic peroxide and melt-kneading at 20 to 3 ooc is advantageous because it has a high grafting efficiency, a good hue, and a small amount of gel-like substances. The content of one unit of graphite monomer in the modified polyolefin is preferably 0.03% by weight or more and less than 7M weight%.

Unsaturated carboxylic acids or their anhydrides used in the grafting reaction include acrylic acid, methacrylic acid, maleic acid,
Examples include maleic anhydride and itaconic anhydride. Among these, maleic anhydride can be preferably used.

The radical generator and organic peroxide added during the grafting reaction are not particularly limited, but it is preferably used that has a decomposition temperature of /jtOC or more and 300C or less in order to obtain a half-life of 7 minutes. For example, co,5-dimethylhexane-,2,A--
Civid robber oxide, λ, S-dimethylruco, S
-ditertiary-butylperoxyhexine-3,2,
di-dimethyl-u, 5-ditertiary-butylperoxyhexane, dicumyl peroxide, and the like.

Examples of the acidic antirust pigment having a pH of less than 7.0 as component (B) used in the present invention include aluminum dihydrogen tripolyphosphate, aluminum phosphomolybdate, mixtures thereof, and silica and zinc compounds such as zinc oxide. A mixture of these is used.

The mixing ratio of silica and zinc compound is less than 20% by weight with respect to the above rust preventive pigment. The particle size of the anti-rust pigment, silica, zinc compound, etc. is, for example,
Examples include those in which the sieve residue of 1Illμ measured according to the method of 1Illμ is less than or equal to 1Illμ.

Mixing of (A) component and (B) component is done using Banbury mixer 1.
This can be carried out by melt-kneading using a heated roll, extruder, or the like. At this time, additives such as antioxidants and stabilizers can also be added at the same time.

The resin composition thus obtained has good adhesion to metals, and the cathode peeling resistance and hot water peeling resistance of the adhesive surface are greatly improved. That is, steel products such as steel pipes and steel plates are coated by conventional methods (for example, T-die method, round die method, powder coating method, etc.). At this time, a primer (for example, epoxy type) may be used. Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto.

Test methods and equipment in Examples are shown below.

[Test sample preparation method]

When coating a layer with a polyolefin using the resin composition as an adhesive layer, two extruders were used to prepare a two-layer extruded sheet and the coating was carried out in the same manner.

A test piece of 15θ x 200 rrm was cut out from the coated steel pipe and the following tests were conducted.

(a) Cathode Peeling Test The test pieces were placed in a cathode peeling test device as shown in FIG. 1, and a cathode peeling test was carried out.

For evaluation, the maximum peeling distance from the hole was measured after 0 days of Testro.

(b) Hot water resistance test piece? j? The peel strength and maximum peel distance from the terminal after being immersed in a hot water bath for 7,000 hours were measured.

(/-1 Peel strength measurement test Measured according to Riko N30670.

) pH of anti-corrosion pigment Measurement was performed using 10IA on J.K. SK-.

Example-/Maleic anhydride in linear low density polyethylene with melt index x and oylio fractional density 0.9.2 dy/ctd! / 00 ppm grafted to 90 parts by weight pH! ;, 70 parts by weight of the sufficiently dried aluminum dihydrogen tripolyphosphate of 2 was mixed and pelletized.

A test piece was cut out from the steel pipe coated with the resin composition and subjected to a cathodic peel test and a hot water resistance test, and the results are summarized in Table 2.

Comparative Example 7 The results are summarized in Table 7 in the same manner as in Example 7 except that aluminum dihydrogen triboic acid was not added.

Examples - C, 3, G Comparative Examples - 2, 3 In Example -/, the content of aluminum dihydrogen tribo-1,11J was changed and the results were shown in Table 1 in the same manner as in Example -/. .

Comparative Example - As S phosphate compounds, 10 parts by weight of sodium phosphate and zinc phosphate, which have a large pH value, were added in the same manner as in Example -/, and the results are summarized in Table 7.

Example 3 The same procedure as in Example 3 was carried out except that aluminum phosphomolybdate was used instead of aluminum tripolyphosphate, and the results are summarized in Table 1.

Examples 6 and 7 Aluminum dihydrogen tripolyphosphate was fixed at 3 parts by weight, and the modified and unmodified polyolefin resins were varied in type and amount, and the results are summarized in Table 2.

[Brief explanation of the drawing]

FIG. 1 shows a partial longitudinal cross-sectional schematic diagram of the cathode peel test apparatus. /...Modified polyolefin resin layer or modified polyolefin and polyolefin resin layer, Co...Steel plate, 3...Drill hole (depth, t
ta, tmφ), da...Glass cylinder (
10 ownφ), 3...3% saline solution (koo'6
), 6...Platinum electrode, Ri... Constant voltage source (3■) Patent applicant Mitsubishi Chemical Industries, Ltd. Agent Patent attorney Necessity - Others/Names Figure 1 Mitsubishi Chemical Industries, Ltd. General Research Center, 1000 Kamoshida-cho, Midori-ku, Yayokohama City

Claims (1)

Scope of Claims: (1) (Bll)H7 for 60 to 5 parts by weight of a modified polyolefin grafted with an Al-unsaturated carboxylic acid or its anhydride or a mixture of the modified polyolefin and an unmodified polyolefin; Rust preventive pigment less than 0
．． Polyolefin resin composition for metal coating (2) with good cathodic peeling resistance, characterized by containing 5 to 0 parts by weight of
The composition (3) according to claim 1, wherein the rust preventive pigment is acuminium dihydrogen tripolyphosphate. The composition according to claim 1, wherein the rust preventive pigment is aluminum phosphomolybdate.