JPS59159860A - Thermosetting powder coating composition - Google Patents

Abstract

PURPOSE:To provide the titled compsn. which gives a uniform gloss coat without causing sagging during coating even when a large-sized article is subjected to fluidized bed coating at a high temp., by adding a given quantity of fine silica powder to a thermosetting resin paint powder having a specified particle size distribution. CONSTITUTION:A thermosetting powder coating compsn. comprises a dry mixture consisting of 0.3-1.7pts.wt. fine silica powder and 100pts.wt. thermosetting resin paint powder (e.g. epoxy resin paint pawder) having such a particle size distribution that the powder is composed of particles having a particle size of 350mu or below and not more than 20wt% thereof is composed of particles having a particle size of 88mu or below. By roughening the particle size distribution of the thermosetting resin powder to improve flow characteristics and dry-mixing a given quantity of fine silica powder therewith, there can be obtd. a powder coating compsn. which can form a uniform cured film without causing thick- wall deposition of the paint even when a large-sized article is coated at a high temp. of 200 deg.C or above, that is, without requiring after-cure after coating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermosetting powder coating compositions, particularly for large-sized coatings.
The present invention relates to a thermosetting powder coating *-1 composition that can be suitably used for fluidized dip coating of $, '17J products at a temperature of 200°C or higher.

Generally, in the fluidized dip coating method, the object to be coated is coated with 20%
] ``c-'' Pre-heat to a high temperature and run this.
'JA'! When immersed in 'no', coating 1'-1 or thickness <(=
Especially when it comes to large objects to be coated, a long immersion time or a long soaking time is required. It is difficult to form a uniform coating film over a long period of time.For this reason, especially large objects have traditionally been heated at 200°C.
Does it flow at temperatures below? l? The surface is coated with R4 paint, but in this case, it is essential to perform so-called after-cure, which involves heating after painting to completely cure the paint.

As a result of intensive research in order to solve the above-mentioned problems, the present inventors roughened the particle size distribution of thermosetting resin powder to improve its fluidity, and dry-mixed a predetermined amount of finely powdered silica to it. The thermosetting powder coating composition made of 5. High temperature 61 for large objects to be coated over 200°C! The present invention was developed based on the discovery that the paint does not build up even when applied with , and therefore a uniform cured film can be formed without the need for special after-curing after painting. .

The thermosetting powder coating composition according to the present invention has a particle size of 350
In μm! Dry process of 100 parts of a thermosetting resin coating powder consisting of the following powder, in which powder with a particle size of 88 μIn or less accounts for 20% by weight or more of -F, and 0.3 to 1.7 parts by weight of finely powdered silica. In FIG. 1, line C shows the relationship between the particle size of thermosetting resin coating powder commonly used in the past and the cumulative mfJJ% on the sieve. Consists of powder,
There is a large amount of fine powder throughout, and in particular, powder with a particle size of 88 μm or less accounts for more than 20% of the total.

In terms of this, the thermosetting resin coating powder used in the present invention is the same as C above in that it consists of powder with a particle size of 350 μm or less, as shown by the line and B, but the particle size is 88 μm or less.
Powders smaller than μm account for less than 20% of the total,
Contains a large amount of powder with large particle size throughout.

FIG. 2 shows the results of coatings using a conventional paint powder having a particle size distribution of line C (indicated by a broken line) and a paint powder according to the present invention having a particle size distribution of line A (indicated by a solid line). This is a graph showing the relationship between the immersion time of the paint powder in the fluidized bath and the mB'A thickness formed on the object when fluidized dip coating the object.
:The coating film thickness increases almost in proportion to the soaking time. For example, when the immersion time is 10 seconds, the coating film thickness is 800 μm in both cases.
That's all. In such a case, the paint drips when applied to the object, making it difficult to obtain a uniform coating.

However, the effect of adding fine powdered silica differs significantly due to the difference in particle size distribution of the coating powder as described above.

That is, as shown in FIGS. 3 to 5, in the case of a conventional paint powder having a particle size distribution of line C, even if finely powdered silica is added, the object to be coated cannot be immersed, as shown by the broken line. It is clear that the coating thickness still increases with time;
Therefore, dripping of the paint during painting is inevitable, the paint film is non-uniform, and the amount of paint required is unnecessarily large. However, in the case of the paint powder having a linear particle size distribution according to the present invention, as shown by the solid line, when finely powdered silica is added within a predetermined range, the thickness of the coating film can be kept extremely small.
Moreover, the tendency for the coating film thickness to increase due to the immersion time is also small. However, as shown in the line in Figure 1, even if the total powder with a particle size of 88, IIm or less accounts for 20% or less of the total, the powder with a particle size of 35
If coarse powder exceeding 0 μm is contained, the coating film will have irregularities, which is not preferable.

In the powder coating composition of the present invention, the additive amount of finely powdered silica is 0°3 to 1.7% per 100 parts by weight of the coating powder.
Parts by weight range. When the amount is less than 0.3 parts by weight, there is almost no effect of the addition, and the coating film may still be thick and sag in fluidized dip coating. On the other hand, 1.7
When added in an amount exceeding 1 part by weight, the coating film formed lacks gloss and has poor appearance, which is not preferable.

The thermosetting resin paint powder used in the present invention may be any of those conventionally used as powder paints, such as epoxy resins, phenol resins, xylene resins, urea resins, etc. , a material made of powder such as melamine resin is used, but ships 6. Preferably, it is made of Nieboxy resin powder.

The hardening resin paint 15) powder may contain various additives required depending on the resin used. Examples of hardening additives include curing agents, pigments, and fillers. , a flow control agent, etc., but are not limited to these. For example, engineering 2! In the case of mixi resin paint powder, curing agents include amines, polyamides, acid anhydrides, polysulfides, boron trifluoride, etc., and pigments include titanium oxide, chromium oxide, iron oxide, carbon black, etc. However, as a filler, for example, barium sulfate,
Calcium carbonate, aluminum oxide, calcium silicate, etc. are used, and as the flow control agent, for example, acrylic olicomer, silicone resin, etc. are used.

Paint powder containing these additives is usually prepared by adding the additives to a thermosetting resin and premixing, then melt-mixing, and then 15) crushing and classifying to have a predetermined particle size distribution.籏JJ is made.

The fine powder silica used in the present invention desirably has a particle diameter of 1 μm or less, and for example, Aerosil (manufactured by Hon Aerosil Co., Ltd.) can be preferably used as a commercially available product. The powder coating composition according to the present invention is produced by dry mixing finely powdered silica with a thermosetting resin coating having the particle size distribution as described above.

The dry mixing method is not particularly limited.

As described in 2 below, the thermosetting 4Lj fat powder coating composition according to the present invention is made by adding a predetermined amount of finely powdered silica to a thermosetting resin coating powder having a predetermined particle size distribution, and is suitable for coating large-sized objects. Even when objects are fluidized and coated at a high temperature of 200°C or higher, the paint does not adhere to the object thickly, so there is no dripping of the paint during painting, and there is no need for after-curing, resulting in a uniform and glossy finish. It is possible to obtain a certain coating +1A. Moreover, the amount of paint used can also be reduced.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, in the following, parts mean parts by weight.

Examples Hisfuconinol type A epoxy resin with an epoxy equivalent of 650, dicyandiamide, rutile titanium oxide, and acrylic flow control agent were mixed in 100 parts, 5 parts, 30 parts, and 1 part, respectively.
The mixture was blended in a proportion of 1.5 parts, and this was pre-mixed using a cylinder mixer, then melt-mixed using a co-kneader, and extruded.

Next, after pulverizing with a sample mill pulverizer, it is classified with 42 meshes with a rotary tube classifier, and as shown by line A or B in FIG.
An epoxy resin paint powder was obtained in which 15% of the total powder was 88 μm or less. Finely powdered silica (Aerosil manufactured by Nippon Aerosil Co., Ltd.) was added in various amounts as shown in the table to 100 parts by weight of this coating powder and dry mixed to obtain an epoxy resin powder coating composition according to the present invention (implemented). Examples 1-4).

For comparison, an epoxy resin powder coating composition was obtained in the same manner by adding finely powdered silica in an amount outside the range specified in the present invention to an epoxy resin coating powder having a particle size distribution of line B (Comparative Example 1 and 2) 6 In addition, an epoxy 4↓] fat paint 15) powder having the particle size distribution of the line C was prepared by using the same formulation as above as a stud, and finely powdered silica was added thereto to form an epoxy resin. A powder coating composition was obtained (Comparative Example 3). Furthermore, an epoxy resin paint powder having a particle size distribution indicated by a line containing coarse particles with a particle size of more than 400 μm was prepared in the same manner, and powder with a particle size of 88 μm or less was less than 20% of the total, but fine particles were added to the powder. An epoxy resin powder coating composition (14A) was prepared in the same manner by adding powder warping force and mixing.

A coating test was conducted on each of the powder coating compositions thus obtained as follows.

The results are shown in the table.

(]) Evaluation of coating film thickness Degreased 9X100X100+am steel plate with 210
After preheating in the dryer for 1 hour, the paint flowed 1i1.
1/10 seconds, and then allowed to cool to form a cured coating II. The thickness of this coating film was measured at an electromagnetic film thickness δ1, and the thickness was 600I1. ○ less than m, 600
Cases exceeding μm are indicated as × in the table.

(2) Write down the sag test (in the same manner as in 1 and 1, when the painted steel plate is taken out of the fluidized fluid tank, evaluate the presence or absence of sag with one eye. If sagging is not observed, mark ○, and if sag is observed, mark it as ○. It is shown in the table as ×.

)) Coating film (visual evaluation) In the same manner as in fl+ above, when the painted steel plate was taken out of the fluidized bath, visually observe the gloss of the coating film and the presence or absence of unevenness. It is shown in the table as ○ when it is not shiny, and as × when it is lack of gloss or unevenness is observed.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the particle size of the paint powder used in the present invention and the cumulative sieve percentage, together with a paint powder as a comparative example. Graphs showing the relationship between the immersion time and the coating thickness on the object to be coated during fluidized dip coating. Figures 3 to 5 show powders with different particle size distributions. 2 is a graph similar to FIG. 2 when a body paint composition is used. Figure 2, Figure 3; It's a cry against a tomb (lower figure 4, latitudinal hemorrhoid interval (seconds); Figure 5, a lower back)

Claims (1)

[Claims] (11 consists of powder with a particle size of 350 μm or less, and a particle size of 8
It consists of a dry mixture of 100 parts by weight of a thermosetting 41 oil paint powder containing 8μIn or less of 20% by weight or less of the total powder, and 0.3 to 1.7 parts by weight of 15% non-silica. Characteristic thermosetting powder coating composition.