JPS5923742B2 - Polyethylene composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to polyethylene compositions suitable for powder coating.

More specifically, the present invention relates to a polyethylene composition for powder coating, which is made of polyethylene containing a specific ethylene/vinyl acetate copolymer and a modified polyolefin, and which imparts excellent coating properties to metal surfaces. Conventionally, powder coating methods such as fluidized dipping, electrostatic atomization, electrostatic dry spraying, thermal spraying, and spraying are known as methods for imparting anticorrosion properties, cosmetic properties, insulation properties, etc. to metals. .

Many resins such as thermoplastic resins and thermosetting resins are used as powder coating resins, but among these resins, polyethylene has excellent chemical resistance, flexibility, electrical insulation, processability, etc. It is an excellent material and widely used. However, conventional ones coated with polyethylene have the following problems. In other words, polyethylene has no polar parts, such as functional groups, in its molecular structure and is highly crystalline.
The conventional one simply covers the metal surface,
The adhesion between the metal and the resin is extremely weak, and the metal easily corrodes when placed in a corrosive atmosphere, so it has not been used in fields where particularly severe corrosion resistance is required.

There are many reports on methods for improving the adhesion between polyethylene and metals, and among them, methods of introducing polar groups into polyethylene, such as methods of introducing hydroxyl groups (
Japanese Patent Publication No. 47-30296), a method of introducing a carboxyl group (Japanese Patent Publication No. 50-84639), or a method of blending modified polyethylene having the polar group (Japanese Patent Publication No. 44-8728) are known. There is.

However, although these methods have strong adhesion immediately after coating the resin on a base material such as metal, they do not have the ability to maintain strong adhesion in a severely corrosive atmosphere, and the base material is made of steel. In this case, corrosion easily progresses. Another disadvantage of polyethylene coated products is that they are immersed in or come into contact with certain chemicals (e.g. detergents, surfactants, oils and fats, plasticizers, organic solvents, etc.) while the paint film remains under stress. Then, there is a phenomenon in which cracks occur from that part and the coating film is finally destroyed.

This phenomenon is generally known as environmental stress cracking, and is a significant obstacle to expanding the use of polyethylene coatings. There are several reports on methods for improving the resistance to environmental stress cracking, such as a method of blending polyisobutylene (Japanese Patent Publication No. 32-5447), a method of blending chlorsulfonated polyethylene (Japanese Patent Publication No. 32-5447), 36-1987) or a method of blending an ethylene/vinyl acetate copolymer (Japanese Patent Publication No. 46-29381) is known. However, sufficient environmental stress cracking resistance has not yet been obtained for objects with complex shapes and for painted products on large machines. The applicant previously proposed that (1) 100 parts by weight of polyethylene be selected from (2) carboxylic acid metal salts in which the hydrogens of 1 hydroxyl group, 2 epoxy group, 3 carpoxyl group, and 4 carboxyl group are replaced with metal. 1 to 100 parts by weight of an ethylene copolymer having one or more functional groups in the molecule; and (3) elastomer 1 to 100 parts by weight.
An ethylene-based resin composition for coating consisting of 100 parts by weight was provided (Japanese Patent Publication No. 12945/1983), which improved corrosion resistance in a severely corrosive atmosphere and improved environmental stress cracking resistance.

However, this ethylene-based resin composition for coating has
Furthermore, there are the following drawbacks.

When the coating ethylene resin composition is mixed with various additives such as grindability improvers, resin stabilizers, ultraviolet absorbers, pigments such as carbon black, and colorants, and used for powder coating, The problem is that sufficient adhesive strength cannot be obtained at normal painting temperatures. Although the desired adhesive strength can be obtained by increasing the painting temperature, the high appropriate temperature tends to cause the paint film to scorch, sag, etc., and the narrow allowable temperature range poses problems in painting workability. Particularly when painting large equipment, the heat capacity of the base material is large, so if it is heated to an appropriate temperature, it will overheat and cause phenomena such as discoloration and sagging of the paint film, resulting in poor surface conditions and loss of the original film properties of polyethylene. be exposed. For these reasons, a solution is desired. In addition, elastomers have problems such as poor compatibility with polyethylene and poor dispersibility, requiring special kneading methods, and poor heat resistance, such as the generation of a unique odor during painting. However, in the field of painting, this is by no means satisfactory in practice. As a result of intensive research into methods to improve these drawbacks, the present inventors have found that a powder coating obtained by blending polyethylene with a modified polyolefin obtained by grafting an ethylene/vinyl acetate copolymer or an ethylenically unsaturated carboxylic acid alone. Polyethylene compositions for use in polyethylene cannot be expected to simultaneously improve both corrosion resistance and environmental stress cracking resistance under severe corrosive atmospheres.
The polyethylene composition for powder coating, which contains a vinyl acetate copolymer and a modified polyolefin grafted with an ethylenically unsaturated carboxylic acid, provides sufficient adhesive strength at normal coating processing temperatures, and is resistant to corrosion and environmental stress cracking. The present invention was completed by paying attention to the fact that the composition has the effect of simultaneously improving That is, the present invention uses 1 to 50 parts by weight of an ethylene/vinyl acetate copolymer having a vinyl acetate content of 20 to 40% by weight and an ethylenically unsaturated carboxylic acid unit concentration of 0.01 to 40% by weight to 100 parts by weight of polyethylene. It is a composition containing 1 to 50 parts by weight of a modified polyolefin of 5% by weight, and the melt index of the polyethylene is 2 to 10.
0 (V/10 min) and a particle size of 20 mesh or less. The polyethylene referred to in this invention refers to the ordinary high pressure method,
The ethylene content in the polymer polymerized by medium and low pressure method is 9
α-olefin copolymers with 0% by weight or more of ethylene polymer and/or 10% by weight or less of propylene, butene-1, etc., vinyl copolymers with vinyl acetate, etc., acrylic copolymers with methyl methacrylate, etc., or these. Melt index (JISK6
76O) is 2 to 1007/10 minutes, preferably 5 to 50
y/10 minutes is preferred.

When the melt index of the polyethylene used in this invention is outside the above range, that is, 1007/10
If the melt index exceeds 27/10 minutes, the strength of the coating may decrease, the coating may sag during painting processing, or there may be problems with uniform dispersion with the modified polyolefin.On the other hand, if the melt index is less than 27/10 minutes, Since the smoothness is significantly deteriorated, a problem arises in painting processability, and a product that is practically satisfactory cannot be obtained.

The ethylene/vinyl acetate copolymer used in this invention contains 20 to 40% by weight of vinyl acetate, preferably 25 to 3% by weight.
It is contained in an amount of 5% by weight.

If the vinyl acetate content is less than 20% by weight, it is difficult to obtain the effects of the present invention, and if the vinyl acetate content exceeds 40% by weight, it will be difficult to handle it as a granular product, and this remaster batch will not be suitable for blending with polyethylene. Preliminary processes such as oxidation are required, which is economically disadvantageous. The modified polyolefin used in this invention is a polymer or copolymer mainly composed of α-olefin monomers such as ethylene, propylene, butene-1, and a monomer selected from ethylenically unsaturated carboxylic acids or their anhydrides. For example, it is modified by graft polymerization with acrylic acid, maleic acid, itaconic acid, fumaric acid, or anhydrides thereof, and the amount of grafting is 0.01 to 5% by weight, preferably 0.05 to 1% by weight. be.

In addition, the modified polyolefin has a substantial gel fraction (determined by wrapping the sample in a 200-mesh wire mesh, immersing it in a decalin solution at 135°C for 48 hours, and measuring the amount remaining in the wire mesh). It is good, but in reality it is 20% by weight.
The following are preferred. If the amount of grafting is less than 0.01% by weight, the desired adhesive strength cannot be obtained, whereas if it exceeds 5% by weight, unreacted monomer odor, resin coloring, and excessive crosslinking reaction occur, and the decalin insoluble content exceeds 20% by weight. If the amount exceeds the amount, the compatibility with polyethylene deteriorates, problems occur in uniform dispersion, and the surface of the paint film becomes uneven, making it impossible to obtain the effects of the present invention. The most preferred modified polyolefin is modified polyethylene obtained by graft polymerizing 0.1 to 1% by weight of maleic anhydride to polyethylene. The monomer grafting amount of the modified polyolefin is determined by forming the modified polyolefin into a sheet and using an infrared spectrophotometer (manufactured by JASCO Corporation, Model IR-G) based on the absorbance of 1710CTL-117900fL-1.

The method of blending the ethylene/vinyl acetate copolymer and modified polyolefin with polyethylene is not particularly limited, but the above three components are premixed in a blender, pen shell mixer, etc., and the mixture can be easily homogenized using a conventional kneading device such as an extruder. The mixture is melted and mixed.

At that time, for example, known additives such as antioxidants, resin stabilizers such as peroxide decomposers, ultraviolet absorbers, light stabilizers, grindability improvers, and organic and inorganic color pigments may be added as necessary. There is no problem even if they are combined at the same time. The preferred blending amount of these components is based on 100 parts by weight of polyethylene.
The ethylene/vinyl acetate copolymer and modified polyolefin are each in an amount of 1 to 50 parts by weight, most preferably 3 to 25 parts by weight each.

If the blending amount is less than 1 part by weight, the effect of the present invention cannot be obtained, and if it exceeds 50 parts by weight, the original excellent characteristics of polyethylene will deteriorate, for example, the smoothness of the coating film may be lost, or the smoothness of the coating may be lost. The rigidity of the coating is lost and the coating becomes soft, resulting in heat resistance.
Solvent resistance decreases and the effect cannot be expected to increase commensurate with the cost. The composition of this invention has a particle size of 20
Powder with a mesh size or less, particularly preferably 40 meshes or less.

The appropriate particle size of the powder varies depending on the coating method; if the particle size is large, uneven coating will occur, making it impossible to obtain a smooth coated surface and resulting in poor appearance. For example, in the electrostatic coating method, a powder with a relatively fine particle size is used, and powder with a particle size of 100 mesh or less is particularly preferably used. In thermal spraying, 8
Powders of 0 to 150 meshes are preferably used. In the scattering method and the fluidized dip coating method, relatively coarse powder of about 20 to 30 meshes can be used, but powder of 40 meshes or less is preferably used. Such powders can be produced by known methods, such as mechanically pulverizing them using a pulverizer, or dissolving them in a high temperature solvent and then adding a poor solvent to precipitate them. A powder composition produced by any method may be used. There are known methods for coating the powder composition of this invention, such as fluidized dipping, electrostatic coating, thermal spraying, and spraying, but the effects of the present invention can be obtained by any of these methods. .

Metal materials to be coated include aluminum, steel, zinc, tin, copper, brass, etc., and the effect is remarkable even in alloys of these or metal materials plated with these. The polyethylene composition for powder coating of the present invention provides sufficient adhesive strength at normal coating processing temperatures without substantially degrading the inherent excellent properties of polyethylene, and simultaneously exhibits corrosion resistance and environmental stress cracking resistance. It has an improving effect. Furthermore, even if various additives are added to the composition of the present invention, the effects of the present invention are not affected; the components of the composition of the present invention are well dispersed, kneading is easy, and there is no odor during painting. never occurs. Next, the present invention will be explained in more detail with reference to Examples.

The coating films in Examples and Comparative Examples were evaluated by the following method. Adhesion test: Make parallel cuts perpendicularly to the substrate with a thin sharp knife on the test piece (the interval is 10 mm).
), and the peel strength is measured and recorded using a tensile tester when the coating film between parallel lines is peeled from one end at a peeling rate of 200 mm/Mm in a direction of 90 degrees.

Corrosion resistance test: Using a sharp knife with a thin blade, make two intersecting cuts so as to reach the base material of the test piece, and place it in a wet tester (
After being exposed to JISZ-0228) for 500 hours, the spread of rust from the cut portion was observed.

Environmental stress crack test: A rigid ball of 10m71L is pressed against the test piece using an Erichsen tester, and this is
．． After being immersed in a 5% Igepearl solution for 100 hours, the condition of the coating film was observed.

Examples 1 to 5 and Comparative Examples 1 to 3 Low density polyethylene (melt index 28y/10
) Mix 0.4% by weight of maleic anhydride and 0.05% by weight of α・d-bistersyanbutylperoxy-p-diisopropylbenzene as an organic peroxide in the powder using a dry blend, and extrude to 40mmφ. 220 using a machine
The mixture was kneaded at 0.degree. C. to obtain maleic anhydride-modified polyethylene.

The absorption of maleic anhydride was measured using an infrared spectrophotometer using the modified polyethylene as a sheet. The melt tension of polyethylene (expressed as 7 is the force required to draw the melt extruded from an orifice with a diameter of 2.0 m77!φ at a constant speed under a load of 21607 at 190°C) is 3.57. The fraction is 3
It was in weight%. Low density polyethylene (manufactured by Asahi Tau Co., Ltd., melt index = 28y/10 minutes, density -0.9
16y/~) and an ethylene/vinyl acetate copolymer with a vinyl acetate content of 28% by weight (melt index 6y/10
) and the modified polyethylene obtained by the above method in the proportions shown in Table 1 and 2% carpon plaque, and the mixture was made into 407% polyethylene. Using a Tmφ extruder, extrusion kneading was carried out at 140°C, and after granulation, it was mechanically pulverized with a Victory Mill VP-1 type (manufactured by Hosokawa Iron Works) pulverizer, and passed through a 40-mesh sieve to obtain a polyethylene composition for powder coating. I adjusted things seven times.

This powder composition was applied to a 0.8 mm thick cold rolled steel plate (JI
SG3l4l) by fluidized dipping method, film thickness 350
A coated steel plate with a good μ appearance was obtained. The coating conditions were as follows: The steel plate was preheated for 5 minutes in an electric furnace preheated to 350°C.
Next, this was immersed for 3 seconds in a bath in which the powder was flowing, and after being pulled out of the bath, it was heated in an oven heated to 200° C. for 3 minutes. The coated steel sheet thus obtained was tested for the performance of its coating film, and the results are shown in Table 1. Example 6 A polyethylene composition for powder coating was prepared under the same conditions as in Example 2, except that low-density polyethylene with a melt index of -45y/10 minutes was used instead of the low-density polyethylene used in the formulation of Example 2. did.

This powder composition was coated under the same conditions and method as in Example 2,
A painted steel plate with good appearance was obtained. Table 2 shows the performance results of the coating film.
Shown below. Example 7 Same as Example 2 except that high density polyethylene (density -0.957/d, melt index -207/10 minutes) was used instead of the low density polyethylene used in the recipe of Example 2. A polyethylene composition for powder coating was prepared under the same conditions and coated using the same conditions and method as in Example 2 to obtain a coated steel plate with a good appearance.

The performance results of the coating film are shown in Table 2. Example 8 Instead of the modified polyethylene used in the formulation of Example 2, modified polyethylene containing 0.35% by weight of maleic anhydride and having a decalin insoluble content of 0.2% by weight at 135°C (Mitsubishi Yuka Co., Ltd.) was used. (Product name: MODETSUKU L-400H)
Coating was carried out under the same conditions and method as in Example 2, except that a coated steel plate with a good appearance was obtained.

The performance of the coating film is shown in Table-2. Comparative Examples 4-5 In the formulation of Example 2, melt index - 150y/10min and *{(0.6V
A polyethylene composition for powder coating was prepared under the same conditions as in Example 2, except that a polyethylene composition of /10 minutes was used.

Using this powder composition having a melt index outside the scope of the present invention, coating was performed under the same conditions and method as in Example 2 to evaluate coating film performance, and the results are shown in Table 2. Comparative Example 6 100 parts by weight of the low density polyethylene used in Example 1, 5 parts by weight of modified polyethylene and 10 parts by weight of vinyl acetate
A polyethylene composition for powder coating was prepared under the same conditions and method as in Example 1 by blending 20 parts by weight of ethylene monovinyl acetate copolymer and 2 parts by weight of carbon black.

This powder composition was coated in the same manner as in Example 1, and the coating film performance was evaluated. The results are shown in Table 2. Comparative Example 7 11 parts by weight of the modified polyethylene used in Example 8 and 2 parts by weight of carbon black were blended with 100 parts by weight of ethylene/vinyl acetate copolymer (vinyl acetate content 5% by weight, melt index 25y/10 min). A polyethylene composition for powder coating was prepared using the same conditions and method as in Example 1.

This powder composition was coated in the same manner as in Example 1, and the coating film performance was evaluated. The results are shown in Table 2. The obtained coated steel sheet has a good appearance, but has insufficient corrosion resistance and environmental stress cracking resistance. Example 9 Example 2
The extrusion granules obtained were frozen in liquid nitrogen, mechanically pulverized, and classified using a 100-mesh sieve to prepare a polyethylene composition for powder coating with a size of 100 mesh or less.

Using this powder composition, the thickness is 0.8m7! L polished steel plate, zinc plate, aluminum plate, brass plate and thickness 0.3
It was applied to a stainless steel plate (SUS43O), a tin plate, a galvanized iron plate, and a chromate-treated steel plate using an electrostatic coating method. For electrostatic coating, powder was applied using a Star Jet type electrostatic powder coating device manufactured by Sames under conditions of a voltage of 60 KV, a current of 150 tt, and a primary pressure of 0.5 kg/Cd from an A1 spray gun, and then in an oven heated to 200°C. A coated plate with a film thickness of 200 μm and a good appearance was obtained by heating for 15 minutes. The performance of the coating film was evaluated and the results are shown in Table 3. As is clear from these examples, the coating film obtained using the polyethylene composition for powder coating of the present invention has strong adhesion to the substrate, resistance to corrosion, and resistance to environmental stress cracking at the same time. However, no polyethylene composition for powder coating other than the present invention has been able to satisfy all of these properties at the same time.

Claims (1)

[Scope of Claims] 1. 1 to 50 parts by weight of an ethylene/vinyl acetate copolymer having a vinyl acetate content of 20 to 40% by weight and an ethylenically unsaturated carboxylic acid unit concentration of 0.01 to 100 parts by weight of polyethylene. A composition containing 1 to 50 parts by weight of modified polyolefin of ~5% by weight, characterized in that the polyethylene has a melt index of 2 to 100 (g/10 min) and a particle size of 20 mesh or less. Polyethylene composition for powder coating. 2. The composition according to claim 1, wherein the modified polyolefin is obtained by graft polymerizing maleic anhydride to polyethylene.