JPH0138124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyvinylidene fluoride (PVDF) copolymers that can be directly adhered to metal surfaces without any other media such as primers or adhesives.

PVDF is known for its resistance to chemicals, UV radiation and abrasion. All of these properties make PVDF an ideal material for external use, especially for protecting metals used outdoors. However, this metal protection application has not been completely satisfactory because PVDF does not adhere directly to metal. The few known PVDF-based coatings always require the application of an intermediate bonding layer, such as a primer, between the metal and the PVDF.

Now, it is obtained by immobilizing 2 to 25% by weight of grafted moieties of acrylic acid or methacrylic acid polymers in the presence of water and a water-soluble chain inhibitor on a PVDF framework irradiated with at least 0.3 megarads. The product (polyvinylidene fluoride copolymerization is
It has been found that it not only retains the properties of PVDF, but also has the property of directly adhering to metal without any intermediate adhesive. This kind of graft polymer is
It is obtained by graft polymerizing acrylic acid or methacrylic acid onto a polymer chain of PVDF. These polyacrylic chains are typically grafted onto the backbone of the PVDF homopolymer. However, instead of PVDF homopolymer at least 90
Copolymers containing % vinylidene fluoride residues can be substituted, and these copolymers are PVDF
It still retains the properties of a homopolymer.

Accordingly, the present invention provides for irradiating a vinylidene fluoride homopolymer or copolymer with at least 0.3 megarads of radiation, and then applying a method to the irradiated vinylidene fluoride homopolymer or copolymer selected from acrylic acid or methacrylic acid. The acrylic monomer is graft-polymerized so that 2 to 25% of the weight of the graft produced from the acrylic monomer is fixed, and at this time,
A grafted polyvinylidene fluoride having a property capable of directly adhering to metal and containing at least 90% vinylidene fluoride remainder, wherein the graft polymerization is carried out in the presence of water and a water-soluble chain inhibitor; A method of making a copolymer is provided.

Graft polymerization is known per se. Graft polymerization consists of contacting PVDF having active sites on the PVDF backbone with an acrylic monomer for graft initiation at a temperature of 50-80° C. for 4-12 hours. The above reaction is carried out using water-soluble chain inhibitors such as CuSO ₄ or FeSO ₄ in order to prevent as much as possible the formation of acrylic homopolymers which increase the viscosity of the graft polymerization medium and which have to be separated and disposed of. It is usually carried out in the presence of water containing . Graft polymerization can also be carried out in the presence of a PVDF solvent. In order to obtain a graft polymer that has good adhesion to metals and retains the properties of PVDF, at least 2% by weight of the total weight of the graft polymer in the polyacrylic graft bond is added to PVDF.
It is recommended that it be fixed to the skeleton. If grafting conditions are used that yield a high degree of fixed methacrylic acid, the grafting compound can be mixed with the untreated polymer to obtain a solution that produces an adhesive coating. Advanced grafting, especially
25 of polyacrylic graft bonds on PVDF framework
Grafting in excess of % by weight can be obtained by using highly irradiated compounds, but is not of great utility. This is because PVDF is γ
This is because they are significantly degraded by excessive exposure to radiation.

One method of forming active sites on the PVDF backbone consists in irradiating the PVDF before graft polymerization. Irradiation of polyvinylidene fluoride is known and described in particular in US Pat. No. 4,137,137. Polyvinylidene fluoride is exposed to ionizing irradiation in air. In practice this ionizing radiation originates from a source of gamma or beta radiation. The dose required to ensure that effective grafting can occur is a minimum of 0.3 megarads to the polyvinylidene fluoride. The polyvinylidene fluoride can be irradiated in the form of a raw polymer or in the form of a polymer that has already been converted to a greater or lesser extent. Usually, for maximum availability of active sites, polyvinylidene fluoride is irradiated in the form of a powder, where the particle size of the powder can vary from about 0.2 to 100 microns, or else in the form of filaments of at least 200 microns. After irradiation, the polyvinylidene fluoride can be brought into direct contact with monomers for the purpose of graft polymerization or else stored at temperatures typically below 10° C. until the grafting operation is carried out.

Protecting metals with graft polymers is carried out in a conventional manner for coating metal parts with thermoplastic resins. The graft polymer coating layer is
For example, a solution of grafted PVDF in a solvent such as dimethylformamide or a plastisol of grafted PVDF in a latent solvent such as dimethyl phthalate, diisobutyl ketone, isophorone, cyclohexanone or mixtures thereof is dried at high temperature (a suitable temperature is 200°C). can be obtained by making This coating layer has a thickness of about 280 to 380
It can also be obtained by injecting grafted PVDF powder onto the surface of the metal heated to ℃; the thickness of the coating layer can be adjusted by making multiple applications, alternating with periods in a drying chamber. can. The resulting coating layer adheres particularly well to steel sheets, galvanized steel sheets and aluminum. For this aluminum, the coating resists immersion in water at 120° C. for 70 hours without any obvious decomposition.

Before applying the above-mentioned coating layer, the metal sheet is preferably subjected to a surface treatment which is suitable for the respective metal and which is generally carried out before the application of any coating layer or paint, such as degreasing, sanding, phosphorous and chrome treatment. It is preferable to perform a combination treatment with compounds, etc.

The method of the invention is illustrated by the following example.

Example 1 Obtained from latex and 0.8 Megarad (M
−rad) Irradiated powdered polyvinylidene fluoride
50 g, 93 g of water containing 7 g of methacrylic acid and 0.030 g of dissolved CuSO ₄ .5H ₂ O are placed in a stirred 500 cm ³ vessel under nitrogen atmosphere. The resulting mixture is heated to 60° C. for 6 hours. The grafted solid is separated by filtration, centrifuged, washed with water on a filter, and the product is then dried at 100° C. in a drying cabinet.

Dry polymer 54 containing 9.8% methacrylic acid
Collect g. The acid content was determined by alkaline titration using a solution of methanol-potassium, the graft polymer was dissolved in dimethylformamide, and the
Add 25% water to the solution. The completion of neutralization is monitored using a PH meter.

Example 2 50 g of powdered polyvinylidene fluoride obtained from latex and irradiated with 0.5 megarads;
Dissolved in 100g of water containing methacrylic acid.
and 0.03 g of CuSO ₄ .5H ₂ O into the same reactor as in Example 1. The mixture is heated to 85° C. for 6 hours.

The grafted solids are separated by filtration, centrifuged, then washed by redispersing the product in water and filtered again. The product is then dried in a drying cabinet at 120°C.

53.2 g of polymer containing 7.45% methacrylic acid
Collect. The amount of residual methacrylic acid is determined from the wash water by acid titration and 0.74 g of methacrylic acid is found. By titrating the double bonds, 0.72 g of methacrylic acid is found.

Example 3 Each of the two graft polymers obtained in Examples 1 and 2 and the non-irradiated raw material polyvinylidene fluoride are dissolved in dimethylformamide to form a 20% by weight solution. A fourth solution is also prepared by mixing equal amounts by weight of a portion of the solution of the unirradiated raw polymer, the polymer of Example 2, and the polymer of Example 2. Small iron and aluminum plates, previously degreased, cleaned with a phosphorous-chromium mixture, rinsed and dried, are coated with these four aforementioned solutions by immersion and then dried in an oven at 210° C. for 15 minutes. All of the coating layers, with the exception of the coating layer containing only polyvinylidene fluoride, adhere and the polyvinylidene fluoride-containing coating layer can be removed from the substrate by simply scratching with a fingernail.

The other six metal plates were placed in an autoclave half-filled with water and heated to 120°C for 72 hours. After this treatment it is not possible to even begin to remove the coating layer by scratching the plate with a knife blade.

Example 4 500 g of polyvinylidene fluoride obtained by suspension polymerization and in the form of a powder of 40 to 100 μm and having an apparent density of about 0.7 are introduced into two stirred reactors under a nitrogen atmosphere. This polyvinylidene fluoride is irradiated with 1 megarad. 0.3g _{of CuSO4.5H2O} and 70g
of distilled methacrylic acid and 930 g of water are also added. The mixture is heated to 60°C for 6 hours.

The resulting grafted solid was separated by filtration, centrifuged, washed with water on the filter, and then
Dry in an oven at 120°C. A graft polymer with a methacrylic acid content of 12% is recovered.

The iron plate that has been degreased and cleaned as described above is heated in a furnace for 300 min.
℃ and coated by sprinkling with a non-irradiated powdered raw polyvinylidene fluoride and a powdered graft copolymer containing 12% methacrylic acid. A number of cycles of spreading and placing in the oven are carried out until a coating layer with a thickness of approximately 200 μ is obtained. Finally, the iron plate is placed in the oven for 15 minutes and immersed in cold water when it is removed from the oven. When scratched with a knife and thus pried open, the unirradiated raw PVDF coating is fairly easily removed, whereas the graft polymer coating is removed.
Fully adhered even after 72 hours of immersion in water at 100°C.

Example 5 100 g of PVDF obtained from latex and irradiated with 1 megarad, 200 g of water containing 10 g of acrylic acid and 0.05 g of dissolved CuSO ₄ .5H ₂ O are placed in the reactor used in Example 1. the mixture for 6 hours
Heat to 83°C.

The obtained graft polymer was separated by filtration.
After centrifugation and water washing on a filter, the product is then dried in an oven at 100°C.

101.5 g of dry polymer containing 4.9% acrylic acid is recovered by acidity measurement.

As described in Example 3, the graft polymer described above is used to prepare a 20% solution in dimethylformamide and used to coat aluminum and steel sheets fired in an oven at 210 DEG C. for 15 minutes. This coating of polymer grafted with acrylic acid was found to have the same good boiling water resistance as the methacrylic acid graft used in Example 3.

Example 6 50 g of powdered polyvinylidene fluoride obtained from latex and irradiated with 3 megarads, 75 g of water containing 25 g of methacrylic acid and dissolved _SuSO4 .
0.025 g of 5H ₂ O in a 500 cm ³ stirred vessel under nitrogen atmosphere. The mixture is heated to 60° C. for 6 hours. The resulting grafted solid is separated by centrifugation, redispersed in water, centrifuged again and the product is then dried in an oven at 100°C.

62g dry polymer containing 24% methacrylic acid
Collect.

1 g of this product is dissolved in 30 g of dimethylformamide along with 5 g of pure, non-irradiated PVDF. A degreased aluminum plate is coated with the solution by dipping and then dried at 210° C. for 15 minutes. The same quality of the other coating layers of grafted polyvinylidene fluoride used in Examples 3 and 5 was found in boiling water.

Claims (1)

[Claims] 1. A vinylidene fluoride homopolymer or copolymer is irradiated with at least 0.3 megarads of radiation, and then an acrylic monomer selected from acrylic acid or methacrylic acid is applied to the irradiated vinylidene fluoride homopolymer or copolymer. Graft polymerization is carried out so that 2 to 25% by weight of the graft generated from the acrylic monomer is fixed, and at this time, the graft polymerization is carried out in the presence of water and a water-soluble chain inhibitor. 1. A process for producing a grafted polyvinylidene fluoride or copolymer having properties that allow direct adhesion to a metal and containing at least 90% vinylidene fluoride with the remainder being vinylidene fluoride.