JP2681501B2 - Powder composition for coating - Google Patents

Description

TECHNICAL FIELD The present invention relates to a powder composition for coating a metal container such as a can for cans, especially the inner surface of a metal container used for foods, etc. The present invention relates to a powder composition for coating (seam part). More specifically, it has excellent impact resistance, particularly excellent impact resistance at low temperature, and, for example, heat sterilization treatment in the case of food containers, the process of filling the contents in the container and the processes accompanying them. The present invention relates to a powder composition which gives a coating film that can withstand the high temperature treatment conditions of 1.

(Prior Art) Metal containers such as cans for canning are coated in order to prevent metal corrosion and contamination of contents.
In particular, metal containers such as cans for canning usually have seams (seams) due to the manufacturing process, and in order to prevent leakage from those parts and contamination of the contents, the seams are coated. There is. For this coating, enamel was used for a long time, and in recent years, a solution of nylon resin or the like was used, and after coating the second time, heating is performed to evaporate the solvent, but this technology usually has the following drawbacks. is there.

(1) A solvent is required.

(2) Long-term heating is required.

(3) Uneven coating is likely to occur.

(4) It is necessary to prevent environmental pollution by organic vapor.

(5) It is often difficult to recover and reuse raw material resin components and the like.

Therefore, in order to eliminate these drawbacks, powder coating of an organic polymer system has been attempted.

For example, Japanese Examined Patent Publication (Kokoku) No. 48-4428 proposes powder coating with a resin on the second side of a metal container, which shortens the coating time, lowers the pollution, and protects the human body from the conventional methods using an organic solvent. Since it has advantages such as the safety of, the recovery of raw material resin, and the ease of reuse, various improvements have been tried.

As the organic polymer composition used in this method, an epoxy resin having a curing agent was widely tried at first, but there is a limit to productivity improvement such as time required for curing, and recently, the mainstream of the study has shifted to a thermoplastic resin. Recently, polybutylene terephthalate-based copolymers (hereinafter abbreviated as PBT-based copolymers) have been attracting attention particularly from the viewpoint of balance between heat resistance and moldability. However, even if powder coating is performed using this PBT-based copolymer, it is sufficiently satisfactory as a coating having impact resistance, particularly impact resistance at low temperature and resistance to high temperature operation such as retort resistance. The thing is not known, and various improvements have been tried.

For example, in order to obtain a PBT-based copolymer composition having these properties improved, an ethylene-ethyl acrylate copolymer (Plastics Engineering 44 (3), 47 (1988)), an ethylene-vinyl acetate copolymer (special Kosho 54-39429),
Polyether-based elastomer (JP-A-49-45150, etc.)
Although it has been tried to be added, it is sufficiently satisfactory that it is difficult to obtain a uniform coating film when used as a powder coating, or the impact resistance of the film at room temperature or low temperature after retort sterilization is significantly reduced. Things have not been obtained.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above problems by coating powder composition for metal containers such as cans for cans, especially the inner surface of a metal container used for food and the like. In particular, it is to provide a powder composition for a second coating.

That is, the present inventors have variously tried to improve a PBT-based copolymer composition as a powder composition for coating a metal container such as a can for canning, and have impact resistance, particularly impact resistance at low temperature. However, even if a high-temperature operation such as heat sterilization is performed, elongation and impact resistance do not deteriorate, and other properties such as adhesion can be satisfied, and there is no problem in safety when used for food etc. As a result of investigating the materials (for example, FDA §175,300 compliant product for the inner surface coating of food cans), we succeeded in obtaining a powder composition for coating a metal container satisfying the above-mentioned performance, and reached the present invention. did.

(Means for Solving Problems) The present invention provides a polybutylene terephthalate copolymer (PBT copolymer) 75 to 95 parts by weight, nitrile rubber (NBR)
3 to 20 parts by weight and 2 to 10 parts by weight of epoxy resin
A powder composition for coating, characterized in that 5 to 25 parts by weight of titanium dioxide is contained in 100 parts by weight, and by using this composition, a coating film solving the above problems can be obtained. it can.

The PBT-based copolymer used in the present invention is a polyester mainly composed of terephthalic acid and 1,4-butanediol, and in order to exert its characteristics, the terephthalic acid component in the constituent acid component is usually used. And 1,4-butanediol component in the constituent diol components are each 50 mol% or more,
Preferably, 75 mol% or more is used. In the present invention, it is often advantageous to use various copolymers obtained by adding a small amount of other components to the above-mentioned two main constituent components in order to improve workability and adhesion. Further, as shown in Examples described later, since the retort treatment test is performed at 130 ° C., it is preferable to use the PBT copolymer having the above composition, which has a softening point of higher than 130 ° C.

Examples of dicarboxylic acids that can be mixed with terephthalic acid include isophthalic acid, phthalic acid, 2,6-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 1,2-bis (phenoxy) ethane-p, Aromatic dicarboxylic acids such as p′-dicarboxylic acid, diphenyl-p, p′-dicarboxylic acid, etc., aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, 1,4-
Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, tetrahydrophthalic acid and chlorendic acid, and sulfonate derivatives of these dicarboxylic acids such as 5-sodium sulfoisophthalic acid And various other derivatives.

Examples of diols that can be mixed with 1,4-butanediol include ethylene glycol, 1,2- or 1,3-
Various butanediols other than propanediol and 1,4-
-Pentanediol, neopentanediol, etc., various pentanediols, 1,6-, etc., hexanediol, etc. alkylene glycols, diethylene glycol, triethylene glycol, tetra or higher polyethylene glycol, dipropylene glycol, tri or higher polypropylene glycol, etc. Of polyalkylene glycol, 1,4-cyclohexanedimethanol, alicyclic diol such as hydrogenated bisphenol A, aromatic diol such as paraxylylene diol, compound having two active hydrogens such as bisphenol A and hydrogenated bisphenol A Examples thereof include alkylene oxide adducts and various derivatives such as halogen compounds of these glycols such as dibromoneopentanediol.

The dicarboxylic acids and diols that can be used as a mixture thereof are not limited to the examples, and they can be used alone or in combination. As the polycarboxylic acid component, in addition to the above dicarboxylic acid, a trivalent or higher polyvalent carboxylic acid such as trimellitic acid or pyromellitic acid or a monovalent carboxylic acid can be used in a small amount, if necessary. is there. Further, as the polyhydric alcohol component, in addition to the glycol, a trihydric or higher polyhydric alcohol such as trimethylolethane, trimethylolpropane, and pentaerythritol, or a monohydric alcohol can be used in a small amount, if necessary. is there.
Furthermore, a small amount of hydroxycarboxylic acids such as p- (β-hydroxyethoxy) benzoic acid and p-hydroxymethylbenzoic acid can be used together. The method for producing these PBT-based copolymers is not particularly limited, and those produced by any method such as the transesterification method and the direct esterification method can be used.

However, when these PBT-based copolymers are used alone, their flexibility is lost at low temperatures, particularly at temperatures below the glass transition point, and the impact resistance is lowered as described above. Therefore, the present inventors have investigated the incorporation of an impact-absorbing elastomer having sufficient flexibility even at low temperatures into a PBT-based copolymer. In this case, the properties required for the elastomer include compatibility with the copolymer, adhesion between the copolymer and the elastomer interface, or safety (above FDA §175,300).
Compatible products).

As a result of diligent examination of these, nitrile rubber (NB
R), ethylene-ethyl acrylate copolymer (EEA),
Polyisobutylene (PIB), chloroprene rubber (CR),
Ethylene-propylene copolymer (EPM), polyethylene (PE), styrene-butadiene copolymer (SBR), ethylene-vinyl acetate copolymer (EVA), etc. are suitable,
It has been found that nitrile rubber (NBR ... Butadiene-acrylonitrile copolymer) gives the most preferable results from the viewpoint of safety. The NBR used in the present invention is used in an amount of 3 to 20 parts by weight based on 75 to 95 parts by weight of the PBT copolymer. If the amount is less than 3 parts by weight, the impact resistance improving effect is not sufficient,
When it is used in an amount of more than 20 parts by weight, the effect of improving impact resistance becomes large, but the powdering operation becomes difficult and it becomes difficult to obtain a powder composition.

As the NBR used in the present invention, any of ordinary commercial products containing 2 to 55% by weight of an acrylonitrile component can be used, and other unsaturated nitriles such as methacrylonitrile, acrylic acid, methacrylic acid, etc. A modified product obtained by copolymerizing a small amount of an unsaturated acid or an ester thereof, another diene such as isoprene or 1,2-pentadiene can also be used.
What contains by weight is preferable. NBR having an acrylonitrile component content in this range is the impact resistance of the PBT-based copolymer,
Greatly improves impact resistance, especially at low temperatures.

On the other hand, addition of an epoxy resin is effective for improving the adhesion between the metal and the coating film. Epoxy resin is PB
75 to 95 parts by weight of T-based copolymer, 3 to 20 parts by weight of NBR
Use ~ 10 parts by weight so that the total amount is 100 parts by weight. If the amount used is less than 3 parts by weight, the effect of improving the adhesion of the resulting coating film to the metal is not sufficient, and if it exceeds 10 parts by weight, the coating film becomes too hard and the impact resistance decreases.

The epoxy resin used in the present invention is a normal epoxy resin having two or more epoxy groups in one molecule, and is a glycidyl ether type, a glycidyl ester type, a glycidyl amine type, a linear aliphatic type, an alicyclic type. Any of these can be used. The main ones are bisphenol A,
An average molecular weight of about 300 to 10,000 made from polyphenols such as 3,5,3 ', 5'-tetrabromobisphenol A and epichlorohydrin, an epoxy equivalent of about 100 to 5,000,
Preferably, it is a bisphenol type compound having about 500 to 1500, a compound obtained by using an initial condensation product of phenol and formaldehyde as a raw material, an alicyclic group-containing epoxy compound and the like. Liquid products can be used, but solid products are often preferred. The epoxy hardener has an effect of improving the adhesive strength even when the epoxy hardener is added in a predetermined amount or is not added at all. As the curing agent, known substances such as dicyandiamide and aromatic amine can be used.

In the present invention, titanium dioxide is used in addition to the above three components. Titanium dioxide is usually used for coloring, but in the present invention, it is added for the purpose of improving the adhesive force between the metal and the coating film. As will be shown in Examples described later, it is surprising that titanium dioxide exhibits an adhesive strength improving effect in the present invention.

In the present invention, both anatase type and rutile type titanium dioxide can be used. Usually, a pigment grade product having an average particle size of 0.1 to 0.5 μ and a surface area of 5 to ²⁰ m ² / g is sufficient, but those having an oil absorption of 15 or less are effective for the purpose of the present invention. Titanium dioxide is a total of 10 components of PBT copolymer, NBR, and epoxy resin.
Use 5 to 25 parts by weight for 0 parts by weight. If it is less than 5 parts by weight, the adhesive force of the resulting coating film is not sufficient, and if it exceeds 25 parts by weight, the flowability (melt flow rate) of the resin during processing is lowered and it becomes difficult to use it for powder coating. .

 Embodiments of the present invention will be described below.

The composition of the present invention is produced by mixing the above four components, that is, the PBT copolymer, NBR, epoxy resin, titanium dioxide and, if necessary, predetermined amounts of the leveling agent in any order or at once, and pulverizing. Mixing is Banbury mixer,
A melt-kneading method using a pressure kneader, calendar, roll, extruder, etc. is used. At this time, PBT-based copolymer and N
In order to thoroughly mix BR and disperse NBR into sufficiently small fine particles, a predetermined amount of a PBT copolymer or a part thereof and NBR are sufficiently melt-mixed, and other components and the remaining PBT system are mixed. It is preferable to add each of the copolymers, or a mixture obtained by previously mixing by a dry method or a melting method, and further mixing by a melting method. Of course, it is also possible to granulate or grind after mixing in each stage of these melt-mixing, which has the advantage of improving the uniformity of the composition.

As the leveling agent, known acrylic additives such as Modaflow (manufactured by Monsanto Chemical Co., Ltd.), Polyflow S (manufactured by Kyoeisha Oil and Fat Chemical Co., Ltd.), and silicon-based additives such as Bacilon OL (manufactured by Bayer). , YF-
3818 (manufactured by Toshiba Silicon Co., Ltd.) can be used. The amount used is 0.1 to 1 with respect to 100 parts by weight as a total of the three resin components.
Parts by weight.

The PBT copolymer thus produced, NBR, epoxy resin, titanium dioxide and the molten mixture of the leveling agent are pulverized to obtain the coating powder composition of the present invention. Fillers, known crystal nucleating agents, facial dyes, plasticizers, flame retardants and the like can be added as necessary.

The crushing can be carried out by a usual crushing method, but it is preferable from the viewpoint of productivity that a so-called freeze crushing method, which is carried out under cooling using liquid nitrogen or the like, is used.

Further, in order to improve the powder physical properties such as the powder fluidity of the produced powder composition, it is preferable to add a powder fluidity improver during or after the pulverization.

As the fluidity improver, usually a main component is a metal oxide such as silicon dioxide, aluminum oxide, boron oxide, magnesium oxide, titanium dioxide or zirconium dioxide.
Fine powder of 0 micron or less, particularly about 0.01 to 200 micron is preferable. Of course, the surface of these metal oxide fine powders is directly bonded to an acyloxy group, an amide group, an amino group, an aminoxy group, an oxime group, an alkoxy group, a halogen atom or the like, silicon, aluminum, boron, magnesium,
Those treated with a compound having an atom such as titanium or zirconium, or those modified by adding a small amount of another metal oxide can be advantageously used.

The amount used is preferably 0.1 to 3 parts by weight based on 100 parts by weight of the total of three components of PBT copolymer, NBR and epoxy resin. 0.
If it is less than 1 part by weight, it is difficult to obtain sufficient powder fluidity, and even if an amount exceeding 3 parts by weight is added, there is almost no improvement in the fluidity improving effect, which may lead to poor leveling of the resulting coating film and deterioration of adhesiveness. . Thus, after being pulverized by the above-mentioned method, the composition for powder coating suitable for various methods can be obtained by classifying into various particle diameter ranges as needed.

The powder composition for coating of the present invention comprises a fluidized-bed method,
It is used for coating metal containers such as cans by conventional methods such as electrostatic coating and air jetting. In particular, it can be advantageously used for coating the inner surface of metal containers such as cans, especially seams, and the metal containers are subjected to high temperature treatment such as heat sterilization in the filling process of foods etc. In this case, it exhibits great characteristics such as no reduction in elongation and impact resistance of the coating film. For the coating in this case
Naturally, the coating method described in 48-4428 can be used.

Of course, if there is no high temperature treatment at the time of filling the contents, stable elongation and impact resistance can be expected for a longer period of time, so it is not limited to containers for food and liquid beverages, but various metal containers such as aerosol cans. It can be advantageously used as a coating on the inner surface of the steel, especially on the weld seam and the inner surface of a small metal tube.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The resin properties of the coating powder composition and the coating film were evaluated by the following methods.

MAR (melt flow rate): Measured by JIS K7210A method. (190 ° C, load 2.16kg) Surface hardness: Measured according to JIS K7215 and shown as shore D hardness.

Elongation and tensile strength: Performed according to JIS K713 (No. 2 test piece used) Adhesive strength: Comprehensively evaluated from JIS K5400 cross-cut test, forced peeling and whitening after impact test.

DnPont impact test: conducted according to JIS K5400 method. The impact strength is indicated by the maximum load height (cm) at which cracking does not occur. The test was conducted by leaving it at room temperature for 48 hours or more and retorting it (heating the test coating piece at 130 ° C for 30 minutes in an oven, putting it in boiling water, and then slowly cooling it) to the above room temperature and 5 ° C. Performed on the cooled one. In addition,
The load used was 1000 g at room temperature and 500 g at 5 ° C.

Oil absorption: Performed in accordance with JIS K5101.

Examples 1 to 3 65 mol% terephthalic acid and 35 isophthalic acid as acid components
A master batch was obtained by kneading 80 parts by weight of a PBT copolymer composed of 100% by mol of 1,4-butanediol as a diol component and 20 parts by weight of NBR (36% by weight of acrylonitrile component) with a Banbury mixer.

This is roughly crushed, and then PBT copolymer, epoxy resin, titanium dioxide, leveling agent, heat stabilizer, etc. are added so that the ratios shown in Table 1, A, B and C are obtained, and Henschel is added. After premixing with a mixer, the mixture was melt mixed using an extruder and pelletized. The pellets were finely pulverized by a freeze pulverization method, and the resulting powder was classified by a 100-mesh sieve. To 100 parts by weight of the obtained 100 mesh pass product, 0.5 parts by weight of the powder fluidity improver (Aerosil) was added and mixed with a Henschel mixer to obtain coating powder compositions A to C shown in Table 1. . Then the above composition 12
A 0 mm × 45 mm × 0.3 mm (thickness) tin-plated steel sheet was sprayed in a stripe shape with a width of 100 mm using an electrostatic coating device, and then heated to 300 ° C. for 15 seconds and baked. Part of the obtained test piece in an oven
It was heated at 130 ° C. for 30 minutes, then put in boiling water and gradually cooled, and the above-mentioned retort treatment was performed. Coating film evaluations were performed on various test pieces that were treated with or without retort, and the results are shown in Table 2 as Examples 1, 2, and 3.

Examples 4 to 7 The coating powder compositions shown in Tables 1 to D were obtained in the same manner as in Examples 1 to 3 except that 40% by weight of acrylonitrile component was used as NBR. The results of coating film evaluation are shown in Table 2 together with Examples 1 to 3.

Comparative Examples 1 to 7 In the same manner as in Examples 4 to 7, coating powder compositions H to N having the compositions shown in Table 3 were obtained.

Comparative Example 8 By using pigment grade zinc oxide in place of the titanium oxide used in the above Comparative Example, a powder composition O for coating having the composition shown in Table 3 was obtained.

Powder coating was performed using the above compositions H to O in the same manner as in Examples 1 to 3, and various tests were performed on the obtained test pieces. The results are shown in Table 4 as Comparative Examples 1 to 8.

From the comparison between the comparative example and the example, the impact resistance improving effect of NBR,
The effect of improving the adhesiveness of the epoxy resin and titanium dioxide is clear.

(Effects of the Invention) The coating powder composition of the present invention is applied to a metal surface with excellent impact resistance, adhesiveness, and surface hardness after being treated not only at room temperature but also at low temperature or high temperature (retort treatment). A film can be formed. By utilizing such characteristics, the composition of the present invention can be advantageously used for coating the inner surface of a metal container for canning and the like, particularly the seam (seams). Further not limited to such containers for food and liquid beverages, various metal containers, for example, the inner surface of the aerosol can,
In particular, it can be advantageously used as a coating for welding seams and the inner surface of small metal tubes.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C09D 163: 00)

Claims (5)

(57) [Claims] 1. A polybutylene terephthalate copolymer 75.
~ 95 parts by weight, nitrile rubber 3 to 20 parts by weight, and epoxy resin 2 to 10 parts by weight, a total of 100 parts by weight containing 5 to 25 parts by weight of titanium dioxide. 2. A polybutylene terephthalate-based copolymer, wherein the terephthalic acid component in the constituent acid component and the 1,4-butanediol component in the constituent diol component each account for 50 mol% or more. Composition. 3. The composition according to claim 1, wherein the acrylonitrile component in the nitrile rubber is 2 to 55% by weight. 4. The epoxy equivalent of the epoxy resin is 100 to 5000.
The composition according to claim 1, which is 5. The composition according to claim 1, wherein the oil absorption of titanium dioxide is 15 or less.