JPH06329954A - Polypropylene resin composition for powder coating - Google Patents

Abstract

PURPOSE:To obtain a polypropylene resin composition having excellent adhesiveness to metal, high surface hardness and excellent heat, chemical and hot-water resistances by mixing a polypropylene resin with a specified hydrogenated product and an acid-modified polypropylene. CONSTITUTION:The resin composition comprises 85-30wt.% polypropylene of an MFR of 5-200 or polypropylene resin of an MFR of 5-200 prepared by copolymerizing propylene with at most 20wt.% at least one alpha-olefin, 10-40wt.% hydrogenated vinylaromatic hydrocarbon/conjugated diolefin block copolymer and 5-30wt.% acid-modified polypropylene. As compared with a polyethylene coating film, a coating film made from this composition is more resistant to scratching. It has also impact strength, a high maximum service temperature, and durability markedly improved as compared with a coating film made from conventional polypropylene powder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene resin composition. More specifically, the polypropylene-based resin composition of the present invention has excellent adhesion to metals, high surface hardness, and excellent heat resistance, chemical resistance, ESCR resistance, and hot water resistance. Used for powder coating for painting

[0002]

2. Description of the Related Art Conventionally, metal products (for example, bicycle baskets, draining shelves, refrigerator shelving, etc.) are resistant to corrosion, chemicals,
In order to impart functions such as stain resistance and decorativeness, a method in which polyethylene powder is applied to the surface by a fluid immersion method, an electrostatic coating method, a rolling coating method, etc. has been widely adopted.
However, polyethylene has a problem in durability because it has low adhesion to metal.

As a means for solving this, a method of utilizing polyethylene modified with maleic anhydride or the like is disclosed in Japanese Patent Laid-Open No. 5-58200.
No. 8-2358, JP-A-58-142945, and JP-A-59-30841.
By thus improving the adhesion to metal and improving the durability, the polyethylene powder is used in the field of products such as fences which require durability, and the field of application is expanding. However, the surface of polyethylene coating is easily scratched,
It has drawbacks such as low usable temperature, and improvement is desired. Compositions using polypropylene, which is superior in heat resistance to polyethylene, are disclosed in JP-A-62-190265 and JP-A-01-297174. However, in both cases, the durability and low temperature impact resistance of the polypropylene coating film after coating are insufficient, and more improved products are desired.

[0004]

DISCLOSURE OF THE INVENTION The present invention has the same or higher level of corrosion resistance, chemical resistance, stain resistance, and decorativeness as a polyethylene coating film, and has a high surface hardness and heat resistance. A polypropylene resin composition capable of forming a coating film having excellent impact resistance on a metal product.

[0005]

That is, the present invention is as follows.
(A) Polypropylene having MFR of 5 to 200 or polypropylene resin in which propylene and 20% by weight or less of one or more α-olefins are copolymerized, 85 to 30% by weight, and (B) vinyl aromatic hydrocarbon and conjugated diolefin. A polypropylene resin composition for powder coating, comprising a hydrogenated product of a block copolymer, 10 to 40% by weight (C) acid-modified polypropylene, and 5 to 30% by weight.

(A) Polypropylene having an MFR of 5 to 200 or a polypropylene resin obtained by copolymerizing propylene with one or more kinds of α-olefin within 20% by weight,
Homopolymer of propylene homopolymer, random copolymer or block copolymer of propylene and ethylene, propylene, copolymer of ethylene and one or more other α-olefins, and combination of two or more thereof Used. The MFR of the polypropylene resin of the present invention is required to be 5 to 200, preferably 20 to 175, more preferably 25 to 1
A range of 30 is recommended. If the MFR is less than 5, the surface of the coated article will not be smooth due to poor fluidity during melting. On the other hand, when the MFR is higher than 200, the physical properties such as tensile strength and impact resistance of the coating film are extremely deteriorated, so that it cannot withstand long-term use. In the copolymer of propylene and ethylene, the ethylene content in the copolymer is preferably 0.1 to 25% by weight, more preferably 0.3 to 10% by weight.

From the viewpoint of impact resistance and low temperature resistance, it is recommended to use a block copolymer. Examples of the α-olefin used in the polypropylene-based copolymer include 1-butene, 1-hexene, 1-octene,
1-butene is preferable from the viewpoint of raw material price. Ethylene and α-olefin in the copolymer are preferably in the range of 0.1 to 20% by weight, preferably 0.3 to 10% by weight, and the ratio of ethylene and α-olefin is not particularly limited.

(B) As a hydrogenated product of a vinyl aromatic hydrocarbon and a conjugated diolefin block copolymer, a vinyl aromatic hydrocarbon polymer block X and at least one olefin having an unsaturation degree not exceeding 20% It is a block copolymer composed of a compound polymer block Y. Examples of the vinyl aromatic hydrocarbon polymer block X include those obtained by polymerizing one or more kinds of styrene, α-methylstyrene, vinyltoluene, etc., and preferably styrene is recommended. Here, as the olefin compound polymer block Y, monoolefin such as ethylene, propylene, 1-butene, isobutylene, or butadiene, isoprene, 1,3
One or more olefin compounds selected from conjugated diolefins such as pentadiene and non-conjugated diolefins such as 1,4 hexadiene, norbornene and norbornene derivatives are polymerized or copolymerized, and The degree of unsaturation is 20% or less. Specific examples of block copolymers include hydrogenated products of block copolymers of vinyl aromatic hydrocarbons and conjugated diolefins and block copolymers of vinyl aromatic hydrocarbons and monoolefins. Preferably, the degree of saturation of the conjugated diolefin moiety of the block copolymer composed of the vinyl aromatic hydrocarbon polymer block and the polymer block mainly containing the conjugated diolefin is not more than 20%. It is a hydrogenated product.

In the block copolymer, the weight ratio of the vinyl aromatic hydrocarbon polymer block X and the olefin compound polymer block Y is in the range of 60/40 to 90/10, preferably 65/35 to 85/15. . Further, it is possible to contain two or more polymer blocks, and the blocks may have the same structure or may have different structures. The number average molecular weight is 20,000 to 5
00000, preferably in the range of 40,000 to 400,000, and the molecular weight distribution of 1.05 to 10 is recommended. The double bond based on the conjugated diene contained in the olefin compound polymer block Y needs to have a degree of unsaturation in the block not exceeding 20%. When the degree of unsaturation contained in the block Y exceeds 20%, the weather resistance and heat resistance of the powder are adversely affected, which is not preferable.

As the acid-modified polypropylene (C), the content of the graft-copolymerized unsaturated carboxylic acid or its anhydride contained in the composition is suitably 0.01 to 5 parts by weight. If the graft content of the unsaturated carboxylic acid or its anhydride is less than 0.01 parts by weight, the adhesiveness will be insufficient, while if it exceeds 5 parts by weight, problems such as discoloration will occur. The MI of the acid-modified polypropylene is preferably in the range of 10-60.

The component (A) is 85 to 30% by weight. It is preferably 85 to 50% by weight. If it is less than 30% by weight, the features of the present invention such as heat resistance and high surface hardness cannot be achieved. On the other hand, if it is more than 85% by weight, the improvement of the adhesion and the elongation of the coating film is insufficient and the durability is lowered.
The component (B) is 10 to 40% by weight. Preferably 1
It is 0 to 30% by weight. If the amount is less than 10% by weight, as a result, the amount of the component (A) increases, the adhesion and the elongation of the coating film are insufficiently improved, and the durability decreases. On the other hand, when the amount of the component (B) is more than 40% by weight, the heat resistance and the surface hardness are low due to the relationship with the component (A).

The component (C) is 3 to 30% by weight. It is preferably 5 to 20% by weight. If it is less than 3% by weight, the adhesion is poor, and if it exceeds 30% by weight, it may be colored due to decomposition during molding. As a method for producing the composition, the components (A), (B) and (C) are melt-kneaded by a single-screw extruder, a twin-screw extruder or the like to obtain a uniform composition.

At the time of melt-kneading, it is advantageous to add a pigment or a master-batch of pigments and perform coloring at the same time in order to simplify the manufacturing process. Furthermore, antioxidants, weathering agents,
The polypropylene performance can be improved by a method of simultaneously adding a lubricant, a crystal nucleating agent, an antibacterial agent, an antifungal agent, an antistatic agent, a filler, a peroxide and the like. A suitable antioxidant formulation for polypropylene resin compositions is the combined use of phenolic antioxidants and phosphorus or sulfur antioxidants. Thermal stability can be obtained by adding 0.3% by weight to 0.9% by weight of this combination product.

As a polypropylene powder suitable for powder coating, it is important that the powder has good fluidity.
For this purpose, the average particle size of the powder is preferably 50 to 400 μ. The preferred particle size of the powder varies depending on the coating method, and is recommended to be 80 to 300 µ in the fluidized-bed method, 50 to 200 µ in the electrostatic coating method, and 80 to 400 µ in the rolling coating method.

The bulk density of the powder is 0.2 to 0.6 g /
The volume density is preferably 0.25 to 0.58 g / cm ^{3, and} more preferably 0.3 to 0.55 g / cm ^{3 in} order to obtain a good powder fluidity with a good range of cm ^{3. Is 3} . As a method for obtaining such a polypropylene-based powder, it is produced by various mechanical grinding methods at a temperature of 0 ° C or lower, preferably -10 ° C or lower. Further, it is also possible to improve the fluidity of the powder by stirring the powder after pulverization at a temperature below the melting point of the powder at a high speed. Furthermore, a method of mixing carbon black, a metal powder or the like for coloring by using a high speed mixer after pulverization, and a method of improving powder performance by mixing an inorganic substance such as finely divided silica or talc Is also possible.

[0016]

EXAMPLES Physical properties in the examples were measured by the following methods. 1) MFR: Measured under JIS K-6758 230 ° C and a load of 2.16 kg. 2) Average particle size: The powder was sieved with a shaking sieve, and 50% by weight of the particle size was determined as the average particle size from the integral curve for the particle size.

3) Tensile elongation: 2 by press molding of powder
mm flat plate is prepared, and the tensile test method (JIS K-676 is used.
It was measured in 0). 4) Surface hardness: Shore-D hardness was measured according to JIS K6760. 5) Adhesion strength: A metal test piece is coated by the fluidized-bed method, and 11 parallel cuts (the interval is 1 mm) and a cut perpendicular to this are formed on the coating film with a sharp blade of a thin blade to reach the base of the test piece. Eleven pieces (interval: 1 mm) were put in to form a grid (100 pieces), and a cello tape was attached on this and then peeled off, and the adhesion strength was indicated by the number of the peeled coating films.

6) Impact strength: DuPont impact test method (JI
SK-5400) 1kg steel ball is dropped from a height of 50cm, and a coating film without cracks is ◎, 40cm, 30c.
Items with a height of m and no cracks are ○, 20 cm, 10 cm
The thing which has no cracks at the height of Δ is indicated by Δ, and the thing which the coating film peeled off even at the height of 10 cm is indicated by x. 7) Anti-corrosion test: The coating film of a metal test piece was cut with a sharp blade of a thin blade so as to make two cuts so as to reach the base of the test piece, and the cut test piece was placed in a wetness tester (JISZ-0228).
After standing for 0 hour, the state of rust from the cut end was observed, and those with no rust expansion were represented by O, those with a little rust expansion were represented by Δ, and those with rust expansion were represented by X.

[0019]

Examples 1 to 5 and Comparative Examples 1 to 3 (1) Production of polypropylene-based powder Polypropylene and hydrogenated styrene-butadiene block copolymer shown in Table 1 (styrene content 30% by weight, hydrogenation rate 9
8%) and maleic anhydride modified PP (acid modification amount 0.76
%), And using a 30 mmφ twin-screw extruder, 220 ° C.
It knead | mixed on condition of and was made into the pellet. As antioxidants, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 2000 ppm and tetrakis (2,4-diene) were added to these resin components. -T-butylphenyl) -4,4'-
Biphenylene phosphonite 400 ppm was mixed. The pellets were cooled to -20 ° C or lower with liquid nitrogen, pulverized by mechanical pulverization, and the product that passed through a sieve having an opening of 250 µ was taken out to obtain a polypropylene powder having an average particle diameter of 200 µ. 2m of this powder by press molding
A flat plate of m was used to measure the physical properties. The results are shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2]

(2) Coating of polypropylene-based powder A 0.8 mm thick rolled steel plate was coated with the powder by a fluidized-bed method to form a coating film of 380μ. The results of measuring the physical properties of the coating film are shown in Table 2.

[0023]

[Effect of the Invention] The coating film of the polypropylene-based powder for coating metal products of the present invention has a coating film
The surface is hard to be scratched and also has impact resistance,
It has excellent properties such as a high usable temperature, and it has significantly improved durability compared to the coating film using conventional polypropylene powder.

Claims (1)

[Claims] 1. (A) Polypropylene having an MFR of 5 to 200 or propylene and at least one α within 20% by weight.
Polypropylene resin copolymerized with olefin, 85-
30% by weight and (B) hydrogenated product of vinyl aromatic hydrocarbon and conjugated diolefin block copolymer, 10 to 40% by weight
(C) A polypropylene resin composition for powder coating, which comprises 5 to 30% by weight of acid-modified polypropylene.