JPS5830906B2 - Manufacturing method of thermosetting powder coating - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a method for producing a thermosetting powder coating with excellent weather resistance and chemical resistance using a twin-screw extruder equipped with co-rotating meshing screws. .

Conventionally, thermosetting powder coatings based on acrylic resins, polyester resins, and epoxy resins, and thermoplastic powder coatings based on polyethylene, nylon, and polyvinyl chloride have been produced and marketed, and these coatings do not require solvents. Because it is not used at all, it is used as a non-polluting paint.In particular, thermosetting powder paints require high thermal energy due to the molecular structure of the thermosetting resin, and low thermal energy due to the action of the curing agent contained in the compound. It changes into a macromolecular structure and has excellent weather resistance and chemical resistance, so it can be used for fences,
It is used in many applications such as guardrails, pipes, substation supplies, tanks, building materials, and motors.

However, thermosetting resins that contain hardening agents are very sensitive to heat, so it is important to consider how to cross-disperse the resin and other additives (such as pigments, viscosity, etc.) without causing the resin and hardening agent to react. The problem is to knead and disperse the additives (adjusting agents, brighteners, etc.) as uniformly as possible.

There are two conventional manufacturing methods: the tri-blend method and the melt-blend method.The tri-blend method melt-mixes pigments, fillers, flow control agents, etc. with resin, then finely powders the mixture, and then adds hardening agent powder. This is a mechanical dry mixing method at room temperature.

The melt blending method is a method in which the above-mentioned compound is melt-mixed with a curing agent using a hot roll, kneader, extruder, etc.

A melt blending method is generally used.

However, if this melt blending method is carried out using an extruder, for example, unlike batch methods such as heated rolls or kneaders, continuous production is possible and the quality is stable, but Since it was developed as a machine, there are various drawbacks when using one of the casings, as described below.

b) Unlike thermoplastic resin molding, the amount of additives other than plastics is extremely large, making it difficult to disperse crosstalk.

Furthermore, since the viscosity of the melt is much lower than that of thermoplastic resin, the conveyance efficiency is poor.

Ex) In order to improve the crosstalk dispersion, it is sufficient to increase L/D, but conversely, increasing L/D increases the residence time in the cylinder, causing a curing reaction and making extrusion impossible.

C) If the screw rotation speed is increased, the residence time will be shortened and L/D can be increased, but the heat generation of the resin will increase! However, as the rotation speed increases, curing reactions are more likely to occur.

2) In a single-screw extruder, the difference in friction between the cylinder and the screw is used to carry out conveyance and kneading, but as mentioned above, the melt has a low viscosity, so the conveyance force is not reliable, and the residence time is It is relatively difficult to make the material non-uniform, ensure a stable extrusion rate, and prevent put points.

e) The twin-screw extruder was developed to solve the above-mentioned drawbacks of the single-screw extruder, but the characteristic of the twin-screw extruder is that it rotates as slowly as possible to keep the resin temperature as uniform as possible. It is suitable for molding thermoplastic resins because it allows heat to be applied to the material, but it is not suitable for thermosetting resins because of its long residence time.

Furthermore, as the number of rotations increases, crosstalk becomes insufficient.

f) Because twin screw extruders are reliable in conveyance, they are generally used, although insufficiently, by reducing the L/D and increasing the rotational speed within the resin temperature range where curing reactions do not occur. There is.

In this case, since L/D is made small, crosstalk tends to be insufficient.

As mentioned above, we used a twin-screw extruder developed for thermoplastic resin molding, and trial settings had to be made to satisfy the mutually contradictory conditions of crosstalk and residence time. In fact, if the resin temperature rises too much, a curing reaction will occur, so it is impossible to solve the problem of kneading and residence time at the same time by increasing the rotation speed, and in fact, even if the rotation speed is increased, there is almost no dispersion. No improvement effect was obtained.

This invention was made based on the following new facts obtained as a result of various studies.

■ Using a current twin-screw extruder, the screw rotation speed is increased to give shear energy to the resin, and a certain temperature increase rate (
(extrusion resin temperature - powder composition temperature) / value expressed by residence time) or higher, a crosstalk dispersion effect that is incomparable to the conventional effect of increasing the rotation speed can be obtained, and this heating rate is 4℃/sec or more, preferably 5℃/s
Must be at least ee.

■ Determine the possible rotation speed, L/D, screw shape, extrusion amount, etc. within 30 seconds, preferably within 25 seconds, by melting and kneading the powder composition at the above heating rate and extruding it. It was found that no curing reaction occurred by doing so.

The powder composition is heated externally in the plasticizing section of the twin-screw extruder so that the temperature is lower than the temperature of the resin extruded through a nozzle installed at the tip of the extruder, and the mechanical energy generated by the rotational force of the screw is also applied. By converting it into thermal energy and giving it at a heating rate of 4° C./sec or more, preferably 5° C./sec or more, the resin temperature of the composition can be increased so that a curing reaction has already occurred in the conventional method. Despite reaching such a temperature at 1, extrusion was possible without any curing reaction occurring.

0 In order to obtain the above temperature increase rate, the shearing energy given by the screw to the resin must be 160 It has been found that the energy is converted into heat and given over a period of 200 sec or more, preferably 200 sec or more.

However, even if the shear rate was lowered and the external heating was increased to increase the heating rate, good crosstalk dispersion could not be achieved.

To explain these facts using Figure 3, if we plasticize and knead at a constant temperature increase rate and continue mixing in an isothermal state after complete melting, region A is the region that shows the degree of dispersion according to the weight method. However, the temperature increase rate is generally only 1° C./see or less, and even if the mixing time is long, the degree of dispersion cannot be expected.

Moreover, as the mixing time becomes longer, the rate of increase in the degree of dispersion decreases, and mixing longer than a certain amount of time is not only unnecessary, but also gives worse results.

Point a is the best point, and beyond point a' the quality begins to deteriorate.

On the other hand, when the temperature increase rate was increased to 2°C/see and 3°C/sec, a rapid improvement in dispersion was observed at 4°C/sec or higher.

This is the case in area B, but this improvement in dispersion is thought to be caused by a different dispersion mechanism than in area A.
It is thought that the mechanism is as shown in Figure 5 and Figures 5 to 5B.

This is completely new territory.

However, the rate of increase in dispersion is fine as long as it is within point b, but as it approaches point b', a rapid drop in dispersion is observed, clearly indicating that a curing reaction is occurring.

Region C indicates the maximum dispersion degree region obtained by the method in 1.

Note that the degree of dispersion expressed here is a relative indication of how little coarse particles such as aggregated pigment residue or cured product are present, and is as follows.

(This does not indicate the size of the particles) Number of coarse particles Dispersity O pieces/10i 100 coefficient 10 pieces/10i 90φ 100 pieces or more/10ffl Proceed to 5th A
Figures 5 to 5C show that the flow progresses from 5A to 5C in the case of high rising speed, where C is the cylinder and S (I'i screw).

P in FIG. 4A and FIG. 5A is an agglomerated pigment. In FIG. 4B, the agglomerated pigment P only rotates, but in FIG. 5B, the agglomerated pigment P collapses, so in FIG. Although the pigment P is included, it is considered that the dispersion is good because the dispersed pigment P' is included in the cured particles R in FIG. 5C.

In the following, the method of the invention will be explained with reference to a drawing showing a twin screw extruder in which it is carried out.

In Figures 1 and 2, a twin-screw extruder 1 is equipped with co-rotating meshing screws 2a and 2b, and mixes thermosetting resin, pigment, brightener, anti-flow agent, hardening agent, etc. supplied to a hopper 3. The product is transferred to twin screw extruder 1 by feed screw 4.
Screw 2a inside.

2b is supplied to the conveying section L1, and sent to the plasticizing section L2.

The plasticized portion L2 of the screws 2a and 2b has a screw diameter D.
, Distance between screw axes C1 Groove depth t, Screw non-meshing area S, Meshing area S', Average screw groove depth C
The relationship between the rotational speed and the shearing speed is set so that the shearing energy given to the resin is 160 sec or more as described above.

and the temperature of the plasticizing part is at least 1 higher than the melting temperature of the mixture.
By heating from the outside using the heating device 5, the temperature is set to create a thermal atmosphere that is 0°C1, preferably 15°C or more lower, so that the molten resin does not swallow the agglomerated pigment and break it up. Let's do it.

In this way, the temperature increase rate becomes 4° C./see or more.

At this time, the residence time in the cylinder tomoe of the extruder 1 at which the mixture supplied to the extruder 1 is extruded is the amount of the mixture supplied by the feed screw 4 (equal to the extrusion amount)
L/
Determine the size of D and the screw shape.

The temperature of the cylinder is controlled by the heating device 5 so that the temperature is lower than the extruded resin temperature at least in the plasticizing section L2.

The resin mixture kneaded and melted in the plasticizing section L2 is transferred to the degassing section L.
It is degassed in Step 3 and extruded from the nozzle 6 in an uncured state in the measuring section L4.

The temperature of the resin extruded from the nozzle 6 is slightly higher than that of the plasticizing part L2.

The resin extruded from the nozzle is cooled and solidified, and then pulverized.

Next, the production of a thermosetting powder coating will be described using the molding apparatus shown in the figure.

Example 1 Resin compound resin Epoxy Epicoat 1004 xoo part (manufactured by Shell Chemical Co., Ltd.) Pigment titanium oxide R-55080 parts (manufactured by 6 Hara Sangyo Co., Ltd.) Brightener Modaflow 5 parts (manufactured by Monsanto Chemical Co., Ltd.) Flow Erosil 200 4 parts Conditioner
(manufactured by Nippon Erosil Co., Ltd.) Curing agent: 4.5 parts of Ebicure 108 (manufactured by Shell Chemical Co., Ltd.) After mixing the above compounded resin materials in a Henschel mixer for 10 minutes, they were transferred to the hopper 3 of the co-rotating intermeshing twin-screw extruder 1 shown in Fig. 1. supplied.

The specifications of the twin screw extruder are as follows.

D-...85mm, C...75mm,
t...-10mm.

S...4260mrfi, S'...
450mrfi, R(S'/5X100)...
...10.6 tai, L/D...20. Vent hole position: L/D = 5°C from the screw tip
1...120°C2C2...1200
C2C3...130℃, Q (extrusion amount)...
...200 to 9/h A mixture of resin materials was supplied to the twin screw extruder 1 with the above specifications, and the screw rotation speed, shear rate, extruded resin temperature, residence time, temperature increase rate, and color change time were determined in Table 1.
The sample was extruded with the following changes as shown in .

After being extruded under the conditions shown in Table 1 above, the powder coating was cooled, solidified, and finely ground, and then baked on a steel plate at 160° C. for 30 minutes to a film thickness of 65 to 70 μm.

Table 2 shows test results showing the performance of this powder coating.

AI and A2 in the above samples had poor gloss and particle size because the external heating was too high.

A3 to I6.8 are excellent in gloss, orange beer, particle size, Erichsen and impact properties (especially A3 to A8).

Example 2 The same resin compounding and twin-screw extruder as in Example 1 were used, and the temperature and extrusion rate of the twin-screw extruder were set to C1...50.
℃ C2・・・75°CC3・・・90℃
Table 3 shows the extrusion conditions for extruding the resin compound material, with Q (extrusion rate) -.-=-300 kg/hr.

The resin compound material was extruded under the conditions shown in Table 3 above, cooled and solidified, and the powder coating powder was pulverized and baked onto a steel plate in the same manner as in Example 1**.

Table 4 shows test results showing the performance of this powder coating.

In sample A9, the temperature of the resin compound material was too low, resulting in insufficient crosstalk.

AIO has a slow heating rate, so coarse particles tend to form and the quality deteriorates.

Black 11 and Ni 12 have very good coating surface smoothness.

Example 3 Resin blended resin Acrylic Almatex P D 100
Part (manufactured by Mitsui Toatsu Chemical Co., Ltd.) Epoxy DER661-J 10 parts (manufactured by Dow Chemical Company) Pigment Titanium oxide R-82015 parts (manufactured by 6 Hara Sangyo Co., Ltd.) Phthalocyanine Blue 1 part (manufactured by BASF Company) Flow Erosil 200 5 parts Adjustment agent
(manufactured by Nippon Erosil Co., Ltd.) Brightener Modaclaw 3 parts (manufactured by Monsanto Cal Co., Ltd.) Curing agent Dodecane dioic acid 15 parts (manufactured by Toagosei Kagaku Co., Ltd.) The above compounded resin materials were mixed for 10 minutes in a Henschel mixer, as shown in Figure 1. , and supplied to the hopper 3 of the co-rotating intermeshing twin-screw extruder 1.

The specifications of extruder 1 are the same as in Example 1, and the temperature and extrusion amount are C1...600C2C2...110℃
, C3...130'C2Q (extrusion amount)...
Table 5 shows the extrusion conditions for extruding the above compounded resin material at a rate of 300 kg/h.

The blended resin material was extruded under the conditions shown in Table 5, cooled and solidified, and the finely pulverized powder coating was applied to a steel plate at a temperature of 200° C. for 20 minutes to obtain a film thickness of 50 to 60 μm.

Table 6 shows test results showing the performance of this powder coating.

Among the above samples, A, 13, and A14 had a low temperature increase rate, so the orange peel was somewhat poor.

The coated surfaces of R15 to A17 are very smooth and have good gloss.

Comparative example 1 Resin compound resin Epoxy Epigy) 1004 100 parts (manufactured by Shell Chemical Co., Ltd.) Pigment Titanium oxide R-55080 parts (manufactured by 6 Hara Sangyo Co., Ltd.) Brightener Modaclaw 5 parts (manufactured by Monsanto Chemical Co., Ltd.) Flow Erosil 200 4 parts Adjustment Agent (manufactured by Nippon Erosil Co., Ltd.) Curing agent Dicyandiamide 5 parts (manufactured by Nippon Carbide Co., Ltd.) The above compounded resin material was mixed for 1° in a Henschel mixer and then fed to the hopper 3 of the extruder 1 similar to Example 1.

At this time, the temperature and extrusion amount are C1...200'C, C2...200
0C2C3...Tune 200℃, Q (extrusion amount)...
Table 7 shows the extrusion conditions for extruding the above compounded resin material at a rate of 300 kg/h.

The blended resin material was extruded under the conditions shown in Table 7 above, and then cooled and solidified, and the finely ground powder coating was baked on a steel plate at 200° C. for 20 minutes to a film thickness of 50 to 60 μm.

Table 8 shows test results showing the performance of this powder coating.

Among the samples mentioned above, A18 did not form a coated surface at all because a slight curing reaction occurred in the twin-screw extruder.

In No. 19, the temperature increase rate was 4° C./sec or more, but the shear rate was low, the residence time was long, and the temperature of the extruded resin was high, so the coated surface was very poor.

Although 20 has a high shear rate and a high temperature increase rate, the external heating is too high, so the gloss is poor and the coating surface is poor.

Comparative Example 2 The blended resin material was the same as Comparative Example 1, and a conventional twin-screw extruder for molding thermoplastic resins was used*.

The specifications of the twin screw extruder are D--110mm, C-90
mm, t-20mm.

Sa-・-・・-11300tr+r? +, sb =
-...1720mr1M.

R(Sb/Sax 1o o ) -・-・・-1s
%, L/D----22, vent hole position...
・L/D=4゜C1...500C2 from the tip
C2...75°C2C5...90°C
2Q (extrusion rate)...Table 9 shows the extrusion conditions for extruding the blended resin material at 200 kg/h.

Example 1 After extruding the blended resin material under the conditions shown in Table 9 above, it was cooled and solidified, and the finely pulverized powder coating was baked on a steel plate.
A similar test was conducted.

Table 10 shows test results showing the performance of this powder coating.

The particle size of the above sample is very large because the shear rate and temperature increase rate are low.

Also, the gloss is poor. Color change time is very long.

As explained above, the present invention uses a twin-screw extruder equipped with co-rotating meshing screws to mix and melt compounded resin materials, kneads and melts compounded resin materials in a hot atmosphere lower than the extrusion resin temperature, Temperature increase rate of compounded resin material is 4℃/
See or more and the shear rate is 160 sec-1 or more, converting it into heat and applying shear energy within 30 seconds, extruding it, cooling it, solidifying it, and pulverizing it to produce a thermosetting powder coating will result in the following: It has a great effect.

■) The residence time of the compounded resin material is very short and the cross-wire melting is uniform, so the quality is stable.

Unlike traditional extrusion methods, which require shorter residence times, color change times are shorter and less resin material is lost.

2) Since the residence time of the compounded resin material is very short, even a curing agent with a fast curing reaction rate (generally referred to as a fast curing type) can be extruded before the curing reaction occurs, and it can be applied to any curing agent.

3) Due to the characteristics of a twin-screw extruder, even if the screw rotation speed is increased, the temperature of the compounded resin material hardly rises once it reaches a certain temperature, and because the residence time is short, it tends to decrease. No curing reaction occurs.

4) Since the residence time of the molten resin is very short, even if the extruder is operated for a long time, it can be extruded without causing a curing reaction.

Therefore, a coating film called orange peel, which is caused by the contamination of curing reactants, is less likely to occur.

5) Due to the high shear rate, the agglomerated pigment deliquesces in the screw flight and becomes very finely dispersed before being enveloped in the molten resin.The surface of the resulting coating film is smooth and no coarse particles are observed, and the pigment is Hidden payments will increase.

On the other hand, in the low shear rate range, the resin is melted by external heat and the aggregated pigment is wrapped in the resin before it deliquesces, so deliquescence within the screw flight is hardly expected and the residue is extruded. 1) The smoothness of the coating film deteriorates.

[Brief explanation of drawings]

Figure 1 is a sectional view of a twin screw extruder, Figure 2 is a sectional view showing screw engagement, Figure 3 is a graph showing mixing time and degree of dispersion, and Figures 4A to 4C are 5 person or 5
Figure C is an explanatory diagram of the melt-kneading mechanism at a high temperature increase rate. 1... Extruder, 2a, 2b... Screw 3... Hopper, 4... Feed screw 5... Heating device, 6...・・・・・・
nozzle.

Claims (1)

[Claims] 1. In a method for producing a thermosetting powder coating using a twin-screw extruder equipped with co-rotating meshing screws,
The temperature of the plasticizing section of the twin-screw extruder is heated from the outside so that the temperature is at least 10° C. lower than the temperature of the extruded resin, and the rate of temperature rise is controlled for the powder composition supplied into the twin-screw extruder. The powder composition is uniformly melted and kneaded by applying shearing energy such that the shear rate is 160 sec' or more using the screw so that the temperature is 4°C/sec or more and the residence time is 30 sec or less. 11. A method for producing a thermosetting powder coating, which comprises extruding, cooling, and pulverizing into fine powder.