KR100366005B1 - Color coating composition for manufacturing high gloss fluorinated coating agent - Google Patents

Abstract

The present invention relates to colored powder coating compositions for preparing high gloss fluorinated coatings.

Vinylidene fluoride copolymers having a melting temperature of about 160 ° C. or less are used to produce high gloss colored powder coating products. In addition, improved corrosion resistance is observed when the substrate with corrosion is coated.

Description

Colored coating compositions for preparing high gloss fluorinated coatings

The present invention relates to a colored powder coating composition for producing a high gloss fluorinated coating based on vinylidene fluoride copolymer (hereinafter referred to as VdFC) and to a process for coating a substrate as a high gloss colored powder coating composition. will be. In particular, the present invention relates to the use of vinylidene fluoride copolymers in coloring powder coating compositions to obtain high gloss VdFC-based protective coatings.

Conventionally, coatings based on vinylidene fluoride homopolymers (hereinafter referred to as PVdF) have been very useful as protective coatings for various types of substrates for excellent chemical and climatic resistance and for thermal stability of PVdF. The known technique used for its preparation was to disperse the PVdF in a suitable solvent and then heat-treat it in order to apply known means on the substrate.

Solvents used are known in the prior art as "latent solvents" and are described as organic solvents which do not have a significant effect at room temperature on PVdF, but do have significant solvent action at high temperatures.

However, while this known system provides good results, environmental protection laws throughout the world, particularly in Europe and the United States, make it increasingly difficult to handle solvent-based systems. Moreover, recovery of the solvent requires an expensive process. Thus, there is a need for PVdF-based coatings that do not require solvents. GB-2194539-A by Rabofina is a colored PVdF consisting of vinylidene fluoride homopolymer (or copolymer comprising almost 10% by weight comonomer), one or more suitable thermoplastics and one or more pigments -Based powder coating compositions are described. It also describes the process for producing the composition. However, the initial glossiness obtained is not very high.

Further, in EP-456018-A Elf Ato Chem furnace by Otsu America there are vinylidene fluoride / hexafluoro fluorine describes a colored powder coating composition of the propylene copolymer, the resin component at 100s ^-1 and 232 ℃ 1-4k poise [ 100-400 Pa.s] and 50-90% by weight of the copolymer and thermoplastic acrylic resin 50-10, characterized by a melting point in the range of about 160 ° C to 170 ° C (close to the melting point of PVdF). Weight percent by weight. The coating thus obtained is characterized by improved flexibility, crack resistance and smooth surface but does not require the addition of a flow improver. There is no reported information on gloss except that the thermoplastic acrylic resin is reliable for gloss durability.

U.S. Patent 5,229,460 to Evadex discloses a fluoropolymer-based powder coating based on PVdF or a copolymer of at least 80% by weight vinylidene fluoride and at least 20% by weight of at least one fluorine-based monomer It is describing. No information has been reported on gloss.

It is recognized in the art that it is impossible to use PVdF to produce high gloss coatings (see JOCA 1990 (4), 145).

Attempts have been made to produce high gloss fluorinated coatings.

U.S. Patent No. 3,944,689 to PPG describes a solvent-based coating composition which contains a gloss-increasing solvent as an essential element of the invention and is based on vinylidene fluoride copolymer.

It is an object of the present invention to provide colored VdFC-based powder coating compositions for producing high gloss coatings. The high gloss coating used herein is a coating having a gloss of at least 40, preferably at least 50 and most preferably at least 60 when measured at an angle of 60 ° by ISO 2813. It is yet another object of the present invention to provide a process for preparing a high gloss colored VdFC-based coating.

Surprisingly these compositions, when applied to corroded substrates, provide improved corrosion resistance compared to similar compositions based on PVdF.

Accordingly, in the present invention, the resinous bunnie and the resin component composed of 60 to 90% by weight of one or more vinylidene fluoride copolymers having a melting temperature of about 160 ° C. or less and 40 to 10% by weight of one or more suitable resins. A pigmented VdFC-based powder coating composition for producing a high gloss coating, consisting of 1 to 35 parts by weight or more of pigment, based on 100 parts by weight.

The present invention also provides the use of a vinylidene fluoride copolymer having a melting temperature of less than about 160 ° C. in a colored powder coating composition to provide a high gloss protective coating.

In the present invention,

(1) a resin component consisting of 60 to 90% by weight of one or more vinylidene fluoride copolymers having a melting temperature of about 160 ° C. or less and 40 to 10% by weight of one or more suitable resins and the resin component 100 Providing a colored polyvinylidene fluoride copolymer-based powder composition composed of 1 to 35 parts by weight of one or more pigments by weight;

(2) applying the powder composition to a substrate; And

(3) provides a process for producing a high gloss fluorinated coating, characterized in that the step of heat-treating the coating of the substrate.

The present invention also provides the use of vinylidene fluoride copolymers having a melting temperature of less than about 160 ° C. in colored powder coating compositions for application to corroded substrates.

The vinylidene copolymer used here is 1 such as tetra fluoroethylene (TFE), chlorotrifluoroethylene, vinyl fluoride, hexafluoropropene (HFP) and CF ₃ -CF ₂ -CF = CF ₂ It is prepared from from 30 to 30% by weight of one or more fluorinated comonomers and from 70 to 99% by weight of vinylidene fluoride (VdF) monomers, about 160 ° C. or less, preferably 150 ° C. or less, most preferably 140 ° C. It is a copolymer which has the following melting temperature.

Preferred copolymers are prepared from 75 to 95% by weight, preferably at least 80% by weight and most preferably at least 90% by weight of vinylidene fluoride monomer. Preferred comonomers are TFE and HFP.

As an example of a preferred embodiment, a VdF / HFP copolymer is used, which has a melting temperature T _M of about 107 + 68e ^-0.14x , where X is the method of Pianca ^et al. (Polymer 28, 224-). 30, 1987), the amount of HFP expressed in weight percent in the copolymer as calculated by NMR data.

Such copolymers are known in the art and are not described here.

Such copolymers are characterized by a lower melting point for the content given to the HFP comonomer. Although not constituted by one theory, it is understood that the high gloss is not the result from the lower melting temperature since the melt flow index representing the melt viscosity is not fundamentally dependent on the melting temperature. In any case, one skilled in the art could not expect lower melting points to exhibit higher gloss. In addition, according to U.S. Patent No. 4,179,542 to Penwalt, the use of fluxes (i.e. latent solvents such as high-boiling solvents for PVdF) lowers the melting point of PVdF measured at temperatures above 60 ° C, while EP-284996- Powder coating compositions containing more than 40% of the flux described in A have not been reported to possess high gloss.

In another preferred embodiment, a VdF / HFP copolymer is used having a polydispersity value Uz of less than or equal to 1.0, preferably about 0.9 and less than or equal to 1.7, preferably less than or equal to 1.6 and most preferably less than or equal to 1.5. Where Uz is equal to (Mz / Mw) -1 and Un is equal to (Mw / Mn) -1, where Mz is the Z-average molecular weight, Mn is the number-average molecular weight and Mw is the weight-average molecular weight All molecular weights are determined by GPC (gel permeation chromatography).

In a third embodiment, copolymers having a tensile modulus of 800 MPa or less, preferably 600 MPa or less and most preferably 400 MPa or less, as measured by ASTM D-638, are used.

In a fourth preferred embodiment, at least about 400 Pa.s measured at 100 sec ^-1 , 232 ° C. using an ASTM D3825 test method, preferably at least about 400 Pa.s at 100 sec ⁻¹ , 240 ° C., but at about 1300 Pa at 232 ° C. s or less, most preferably, a copolymer having a melting viscosity of about 600 Pa.s or more at 100 sec ^-1 and 240 ° C. but about 1000 Pa.s or less at 100 sec ^-1 and 232 ° C. is used.

Preferred VdFC resins have a weight-average molecular weight (determined by GPC) in the range 50,000 to 270,000, most preferably 90,000 to 160,000, and a melt flow index of 5 to 30 g / 10 min, most preferably 6 to 20 g / 10 min. (According to ASTM D-1238, weighing 5 kg at 230 ° C.).

The VdFC is mixed with one or several suitable resins, preferably acrylic resins. Acrylic resins are known in the art and will not be described here; FR-2,636,959-A by Atochem (line 18 on page 3 to line 14 on page 4). As examples of thermosetting acrylic resins, those described in U.S. Patent No. 4,659,768 by Desoto, in particular those described under the names "number of examples" and "resins in comparison" can be cited. However, it has been found that it is beneficial to use thermoplastic acrylic resins, and therefore it is most advantageous to use the preferred thermoplastic polymethylmethacrylate (PMMA) resins. As the thermoplastic PMMA resin, thermoplastic resins obtained by (co) polymerizing at least 75% by weight of alkylmethacrylate with one or several olefinically unsaturated comonomers, preferably alkyl (meth) acrylate types, can be used. The esters are formed by reacting acrylic- or methacrylic-acids with appropriate alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol and 2-ethylhexyl alcohol. In general, as the amount of alcohol in the ester increases, a softer and more flexible resin is obtained. In addition, the methacryl ester forms a film that is harder than the corresponding acrylic ester. Examples of such resins include polymethyl methacrylate, methyl methacrylate and ethyl acrylate, butyl methacrylate, isobutyl methacrylate, copolymers of acrylic acid or methacrylic acid, and the like. The most preferred PMMA resins are those which exhibit a viscosity of 7 to 17 P in a 40% solution of a 95: 5 weight ratio mixture of toluene and ethylene glycol methyl ether.

The weight ratio of VdFC to suitable resin can be broadly 90:10 to 60:40, preferably 75:25 to 65:35, most preferably about 70:30.

In order for the fluorinated coating to have an adjustable gloss, the amount of terpolymer must be included at least 60% by weight. If more than 90% by weight will increase the cost only no more effect. In addition, the acrylic resin should be included in an amount of at least 10% by weight or more, since it is the minimum amount necessary for dispersion of the pigment. However, if the amount of the acrylic resin is more than 40% by weight, high gloss and a bad effect on maintaining gloss after 200 hours of coating.

The resin composition may contain minor amounts of useful additives such as, for example, UV absorbers, adhesion promoters, flow promoters and / or antioxidants.

As suggested in US Pat. No. 5,229,460, antioxidants can increase thermal stability if necessary and provide protection against pyrolysis and discoloration due to excessive enzymatic temperatures. Another useful additive is a flow promoter, which is not essential to the present invention but helps to provide the high quality coating surface required in the art. As the flow promoter, acrylic resins having a relatively low molecular weight (for example, about 20,000) are generally used.

The amount of the flow promoter is broadly 0 to 3% by weight based on the total weight of the mixture, but the amount preferably used is about 1% by weight or less based on the total weight of the coating. The use of Kynar ADS ^™ as the flow promoter substrate is known from US Pat. No. 5,229,460.

It is preferable that a pigment is used for the coating composition. If no pigment is used, a clear film or varnish can be obtained. However, such coatings produce uneven milkiness and are undesirable. In addition, these transparent films reduce high temperature resistance, and most importantly, they do not sufficiently absorb ultraviolet rays, which in some cases contribute to the heat of the primer. However, the use of fine titanium dioxide to absorb ultraviolet light is already known in the art.

When using pigments, any one pigment or mixture of pigments can be used. The choice of pigments is made by those known in the art for PVdF-based coatings. The amount of pigment to be used may be used in various ways depending on the degree of its coloring power. For example, a white top film made only of titanium dioxide may require at least about 35% by weight of the pigment. Other pigments with better coloration may be needed in smaller amounts.

At least 1 part by weight or more of pigment per 100 parts by weight of resin is required for the powder coating to be colored. In addition, when the amount of the pigment exceeds 35 parts by weight per 100 parts by weight of the resin will cause problems in dispersion on the acrylic resin

The manufacturing process of the powder coating

(1) melt blending the VdFC, a suitable resin composition and a pigment,

(2) forming pellets, and

(3) grinding the pellets

It consists of.

Melt-mixing is generally carried out by injection. Injection and granulation can be carried out by a commercial process. The processes can be easily carried out by those skilled in the art. The treatment temperature is generally 150 ° C to 190 ° C. The size of the pellets is not limited and is generally about 3 mm diameter and 2 mm length.

Grinding the pellets can be carried out by means by which suitable particles can be obtained. Grinding techniques are already known to those skilled in the art and need not be described further. U. S. Patent No. 5,229, 460 discusses the milling techniques of fluoropolymer-based thermoplastic mixtures and the effects of the cooling step.

The powder consists mainly of particles of a size and shape suitable to pass through the device in a constant flow to obtain a constant coating thickness.

The type of particles is preferably as spherical as possible and their size is as uniform as possible, since the powder obtained has a better flow rate. Regarding the size of the particles, the milling step includes a sieving step to remove particles of the largest height, ie, particles larger than about three times the desired coating thickness. Excessively small particles, on the other hand, must be removed because these particles are harmful to health and block the transport line during use.

It is desirable to use a hammer mill, where one rotary shaft entails hammers that break through the sieve at the bottom of the hammer mill, breaking the pellets in a defined form within the casing of the hammer mill. In particular, a body hole of about 0.2 mm is used here.

The powder thus obtained is applied to the substrate by any means suitable for uniform distribution. In particular, by using an electrostatic disperser, charged particles can be dispersed on the oppositely charged substrate.

Other techniques include fog boxes, fluidized beds, and uniform triboelectric coating.

The VdFC-based powder is applied to primer coatings as known in the art as primers for suitable primer coatings, for example similar fluorinated coatings.

After the coating is applied to the substrate, heat treatment must be performed. The coated substrate is baked at a temperature of 150 to 220 ° C, preferably 160 to 190 ° C in a heated oven. The temperature used in this step should be higher than the melting point of the powder, which is easily determined experimentally, for example as an oven having a temperature gradient.

On the other hand, excessively high temperatures cause sulfidation in the finished coating.

The duration of the heating step is determined by any suitable method known in the art, with insufficient heating time damaging the surface strength and gloss.

One of the advantages of the present invention is that high gloss can be obtained without baking at significantly higher temperatures, contrary to the predictions of those skilled in the art.

Finally, the coating and its substrate may be slowly cooled in air or immersed in water.

It is surprising from the viewpoint known from US Pat. No. 3,944,689 described on the basis of gloss-increasing solvents that high gloss coatings can be obtained from VdFC-based powder coatings.

It has also been observed to exhibit better mechanical properties than the coatings obtained by the present invention.

To illustrate the invention in more detail, the following examples are described.

Example 1 and Comparative Example A

The following powder coating compositions were prepared.

64.8 parts by weight of fluorinated polymer

27.9 parts by weight of acrylic polymer

-0.7 parts by weight of flow improving agent

-6.6 parts by weight of pigment

100.0

The pigment mixture was chosen to obtain a red color corresponding to RAL 3004; It consists of 5.1 parts by weight of Bayferrox ^™ 130BM, 1.0 part by weight of Quindo ^™ Violet RV6951 (organic pigment) and 0.5 part by weight of Kronos ^™ 2160 (titanium dioxide).

The flow improver is a low molecular weight copolymer composed of 30% by weight ethyl acrylate monomer and 70% by weight 2-ethylhexyl acrylate monomer and having a viscosity of about 1.06 Pa · s at 98.9 ° C.

The acrylic polymer is a commonly available thermoplastic copolymer consisting of 70% by weight of methyl methacrylate monomer and 30% by weight of ethyl acrylate monomer, which is 40% of a mixture of toluene and ethylene glycol methyl ether mixed in a 95: 5 weight ratio. In solution has a viscosity of about 12P.

In Example 1, the fluorinated polymer is a copolymer of vinylidene fluoride and hexa fluoropropene having the following properties.

VDF / HFP molecular ratio: 93: 7 (NMR determination according to Pianca et al., Polymer 28, 224, 1987)

Melt Flow Index: 8.5g / 10min＼n (ASTM D-1238; 230 ℃, 2.16kg)

Melt Viscosity: 850 Pa.s (ASTM D-3835; 240 ℃, 100s ***)

Molecular Weight (GPC)

Mn = 49,000 Mw = 112,000 Mz = 217,000

Tensile properties (ASTM D-638 M for 2 mm thick compressed sheets):

Flexural Properties (ASTM D-790 for 4mm thick compressed sheets)

-DSC measurement value (ASTM D-3418)

Bushing point temperature (ASTM D-746 A): -23 ℃

The fluorinated polymer in Comparative Example A is a vinylidene fluoride homopolymer available from Atochem North America under the trademark KYNAR 710.

The resulting mixture is injected under the following conditions to provide pellets 3 mm in diameter and about 2 mm long:

-Pair of screw injection machines

Screw rotation speed: 200rpm

Load: 85%

-Temperature condition: It rises to 165 ℃ at the hopper exit, 190 ℃ at the center of screw, and more than 180 ℃ at the end of screw.

Material temperature at exit: 180 ℃

The pellet is cooled in liquefied nitrogen below about −150 ° C. and then milled to about −100 ° C. in a hammer mill to sieve to remove particles larger than about 150 μm. In a hammer mill, the rotating shaft involves a hammer that breaks the pellet into a fixed form, which allows particles to pass through the sifting lining at the bottom of the hammer mill. The particle size distribution is measured as follows; 99% of the particles are less than 90㎛. 40% of them are less than 32㎛. Only 5% is 15 μm.

The powder thus obtained is subjected to an electrostatic dispersion process on a 1 mm thick aluminum chromate plate which is preferentially covered with a 50 μm thick epoxy primer. The epoxy primer was prepared by Example 1 of DE-404752-A by the applicant.

The coated substrate was heated at 220 ° C. for 9 minutes to produce a 50 μm thick top coating.

Gloss measurements were measured at an angle of 60 ° according to ISO 2813:

Example 1: 60

Comparative Example A: 31

Additional measurements were taken with the coating of Example 1.

Example 2 and Comparative Example B

Example 1 and Comparative Example A are repeated except that the following white powder composition is prepared (RAL 9010).

54.9 parts by weight of fluorinated polymer

23.3 parts by weight of acrylic polymer

-0.7 parts by weight of flow improver

Titanium dioxide 21.1 parts by weight

100.0

Gloss measurement was made according to ISO 2813.

Examples 3 and 4 and Comparative Examples C and D

Example 2 is repeated except that vinylidene fluoride-hexafluoropropene copolymer having the following properties is used (the following properties are determined as mentioned in Example 1):

Other properties were found to be the same for Examples 3 and 4 and Comparative Examples C and D.

Example 5

Example 1 was repeated except that the following composition was prepared.

62.2 parts by weight of fluorinated polymer

26.5 parts by weight of acrylic polymer

-0.8 parts by weight of flow improver

10.5 parts by weight of pigment

Fluorinated polymers and pigments used are as follows.

The fluorinated polymer has the properties as indicated on the technical data sheet as a copolymer of vinylidene fluoride and tetra fluoroethylene.

Melting point 122-126 ° C (ASTM D-3418)

Melting calories 12.5-20.9 J / g (ASTM D-3417)

Tensile Properties (ASTM D-638 and D-1708 Temperature 25 ° C)

Yield tensile stress 14.5-18.6 MPa

Fracture Tensile Strength 32.4-44.8 MPa

Elongation at break 500-800%

Tensile coefficient 414-552 MPa

The pigment mixture was chosen to be brown. It is composed of 1.9 parts by weight of Flammruss ^™ 101 (carbon black), 2.5 parts by weight of Sheperd ^™ brown 49 (organic pigment), 3.4 parts by weight of Bayferrox ^™ 180 (iron oxide) and 2.7 parts by weight of Tipaque ^™ TY200 (chromium titanate).

Gloss was measured by ISO 2813 at an angle of 60 ° with a value of 56.

Examples 6 and 7 and Comparative Examples E and F

White powder coating composition is prepared as follows.

54.9 parts by weight of fluorinated polymer

23.3 parts by weight of acrylic polymer

-0.7 parts by weight of flow improving agent

Titanium dioxide 21.1 parts by weight

100.0

The fluorinated polymer, acrylic polymer and flow improver are the same as in Examples 1 and 5 (for Examples 6 and 7 respectively) and Comparative Example A (for Comparative Examples E and F).

These powders are prepared identically as described.

In Example 6 and Comparative Example E, the powders obtained were subjected to an electrostatic dispersion process on both sides of a 1 mm thick Sendzimir steel sheet covered with a 50 μm thick epoxy primer layer having a 25 μm thick zinc layer. The epoxy primer was prepared by Example 1 of DE-404752-A by Applicants.

In Example 7 and Comparative Example F, the powder coating agent was applied to both sides of a 1 mm thick tin plate covered with a 50 μm thick epoxy primer layer having a 40 μm thick zinc layer.

In Examples 6 and 7, the coated substrate was heated at 200 ° C. (air temperature) for 15 minutes to provide an 80 μm thick top coat.

The substrates coated in Comparative Examples E and F were heated at 230 ° C. (air temperature) for 15 minutes to provide a top coating of 80 μm thickness.

The coating thus obtained shows good corrosion resistance. These materials are determined in this field by the ASTM-B-117 (heat dissipation) test method using double coated panels measured by ASTM D-714 (bubble forming).

The panel, previously engraved with two intersecting lines, requires hydrochloric acid (50 g / 1NaCl) for 1000 hours at 35 ° C. Thus, the following result is obtained.

Example 8

Example 2 was repeated using a VDF-copolymer sold under the name Kimar RC 10062 to Elf-Atochem and possessing the following properties.

VDF-HFP Ratio (NMR) 94: 6

Melting Point 142-145 ℃

White Glossiness 65

Comparative Examples G, H and I

Example 2 was repeated except that vinylidene fluoride-hexafluoropropene copolymer having the following properties was used:

As can be seen, the coating obtained from the copolymer is very shiny due to the poor flowability reported by the ISO method.

Quantification of the flow rate of the VDF-copolymer at 220 ° C. was attempted by the method developed for phenolic resin (DIN 16916 Part 2):

41.7 mm copolymer of Example 1

Copolymer of Example 8 12.8 mm

Copolymer of Example 9 15.0 mm

Copolymer of Example 10 14.8 mm

Claims (9)

A resin component consisting of 60 to 90% by weight of vinylidene fluoride copolymer having a melting point of 160 ° C. or less and 40 to 10% by weight of an acrylic polymer, and pigments of 1 to 35 parts by weight based on 100 parts by weight of the resin component. Powder coating composition. The powder coating composition of claim 1, wherein the copolymer is made of 25 to 5% by weight of comonomer selected from tetrafluoroethylene and hexafluoropropene and 75 to 95% by weight of vinylidene fluoride monomer. . The powder coating composition of claim 1 or 2, wherein the copolymer has a melting point of 150 ° C or less. The powder coating composition of claim 1 or 2, wherein the copolymer has a tensile modulus of 800 MPa or less. 3. The powder coating composition of claim 1, wherein the copolymer has a melt viscosity of greater than 400 Pa · s and less than 1000 Pa · s at 100 sec ⁻¹ and 232 ° C. 4. The powder coating composition of claim 1 or 2, wherein the copolymer comprises hexafluoropropene and has a polydispersity value Uz of 1.0 or less and a polydispersity value Un of 1.7 or less. The copolymer of claim 1 or 2, wherein the copolymer comprises hexafluoropropene and ^has a melting point of 107 + 68e- ^0.141x , where x is in the copolymer calculated from NMR data by the method of ^Piannka . Powder percent by weight of hexafluoropropene). The powder coating composition of claim 1, wherein the acrylic polymer is a thermoplastic polymethylmethacrylate. The powder coating composition of claim 1 wherein the weight ratio of copolymer to acrylic polymer is 70:30.