FR2478649A1 - VINYLIDENE POLYFLUORIDE TREATED FOR METAL ADHESION, PROCESSING METHOD - Google Patents

Abstract

VINYLIDENE POLYFLUORIDE ADHESIVE TO METALS CHARACTERIZED IN THAT POLYACRYLIC GRAFTS ARE FIXED ON ITS SKELETON. THIS POLYMER GRAFT IS OBTAINED BY POLYMERIZATION GRAFTING OF AN ACRYLIC MONOMER ON THE SKELETON OF A VINYLIDENE POLYFLUORIDE PREIRRADIATED UNDER AT LEAST 3.10 RADS. THIS PRODUCT IS PARTICULARLY RECOMMENDED FOR THE PROTECTION OF METALS IN THE EXTERIOR.

Description

The present invention relates to a polyfluoride of

  vinylidene (PVDF) treated in such a way that no other

  intermediate, it adheres directly to metal surfaces.

  The invention also relates to the method of manufacturing such a polymer. PVDF is known for its resistance to agents

  ultraviolet light as well as abrasion.

  All these qualities make it an ideal material for use in

  outdoor and especially for the protection of metals. This last use could not, however, give

  entirely satisfying because of the lack of

  the PVDF on metals. The only known PVDF-based coatings always require the application of a layer

  intermediate adhesion between the metal and the PVDF.

  It has been found that the product obtained by

  polyacrylate grafts on a PVDF skeleton not only retains the qualities of PVDF but

  the property of adhering directly to metals without

  collage. Such a graft polymer is obtained by

  graft polymerization of an acrylic monomer on the chain

macromolecular PVDF.

  The acrylic monomers particularly recommended

  Dice for the graft polymerization and to obtain a grafted PVDF having the best characteristics are acrylic acid or methacrylic acid. The grafting of polyacrylic chains is usually carried out on a homopolymer PVDF backbone. However, a copolymer containing at least 90% of the homopolymer can be assimilated to the homopolymer

  residues of vinylidene fluoride, such copolymers

  the properties of PVDF homopolymer.

  The graft polymerization is known in itself.

  It consists in putting in contact the PVDF possessing

  assets on its skeleton with the initial acrylic monomer

  - 2 - graft tiator for 4 to 12 hours at a temperature

  between 50 and 80BC. The reaction usually takes place

  in the presence of water containing a hydrosolu-

  Such as CuSO4 or FeSO4, in order to avoid as much as possible the formation of acrylic homopolymer which increases the viscosity of the grafting polymerization medium and which must be separated and rejected. The graft polymerization can also be carried out in the presence of PVDF solvent. In order to obtain a graft polymer having good adhesion

  metals and retaining the properties of PVDF, it is necessary to

  ordered to fix on the PVDF skeleton at least 2% by weight

  of the total weight of graft polymer of polyacrylic grafts.

  If grafting conditions leading to high levels of fixed methacrylic acid are used, it is possible to

  mix this grafted product with untreated polymer to

  hold solutions giving adherent coatings. The high levels of grafting, in particular those exceeding 25% by weight of polyacrylate grafts on the PVDF skeleton, being obtained with highly irradiated products are not very interesting because the PVDF is strongly degraded by

  too much exposure to gamma radiation.

  One of the ways to create active sites on the sque-

  lette consists in irradiating the PVDF before the polymer

  grafting. Irradiation of polyvinylidene fluoride

  dene is known, it is in particular described in United States Patent 4,137,137. Polyfluoride

  of vinylidene is exposed to ionizing radiation.

  These ionizing radiation come in practice from a source of gamma or beta radiation. The dose required for

  effective grafting can be carried out is irradiation

  minimum of polyvinylidene fluoride to at least 3.105

  rads. Polyvinylidene fluoride can be irradiated with

  state of raw polymer or already more or less transformed. Habi-

  In order to obtain the maximum accessibility of the active sites, the polyvinylidene fluoride in the form of a powder whose particle size can vary from about 0.2 to 100 9 or in the form of filaments can be irradiated.

  less than 200 p. After irradiation, the polyvinyl fluoride

  dene can be immediately brought into contact with the monomer

  for graft polymerization, or stored at a time

  usually below 100C until

  grafting. The protection of metals by means of the graft polymer is carried out conventionally and habitually with the coatings

  metal parts by thermoplastics. The dreams-

  may be obtained by hot drying, a temperature

  200 C may be suitable, of a solution of PVDF

  in a solvent, such as dimethylformamide,

  or a plastisol of the same PVDF grafted in solvents la-

  such as dimethylphthalate, diisobutylketone, isotope

  phorone, cyclohexanone or their mixtures. Coatings can also be obtained by spraying grafted PVDF powder onto the previously heated metal surface at about 280-3800C; several projections alternating with passages in an oven can be made to adjust

  the thickness of the coating. The coatings obtained are

  particularly adherent on steel, galvanized steel

  or on aluminum. On the latter metal the coatings

  carry a passage of 70 hours in water at 1200C without

apparent degradation.

  Prior to application of the coating, the plates are preferably subjected to clean surface treatments to each metal and generally performed prior to application.

  any coating or paint such as: degreasing

  sanding, blasting, combined treatments with phos-

  phoric and chromic, etc. The following examples illustrate the object process

of the invention.

EXAMPLE 1

  500 g of polyvinylidene fluoride in powder obtained from a latex and irradiated with 0.8 Mrad, 93 g of water containing 7 g of water are introduced into a vessel of 500 cm 3 stirred under a nitrogen atmosphere. methacrylic acid and 0.030 g of CuSO 4, 5H 2 O dissolved. The mixture is heated for 6 hours at 60 ° C. The grafted solid is filtered off, filtered off with suction and washed with water and the product is dried in an oven at 1000 ° C. 54 g of dry polymer containing 9.8% of methacrylic acid are collected. The acid content is determined by alkalimetry with a solution of methanolic potassium hydroxide, the graft polymer is dissolved in dimethylformamide,

  the solution being supplemented with 25% of water before titration.

  The end of neutralization is located at the pH meter.

EXAMPLE 2

  In the same reactor as in Example 1,

  50 g of polyvinylidene fluoride powder obtained from a latex irradiated at 0.5 Mrad, 100 g of water containing g of methacrylic acid and 0.03 g of CuSO 4 5H 2 O dissolved.

The mixture is heated for 6 hours at 85 ° C.

  The grafted solid is separated by filtration, filtered and washed, redispersing the product in water and filtering.

  again. It is then dried in an oven at 1200C.

  53.2 g of polymer containing 7.45% of methacrylic acid are collected. On washing water is determined

  the amount of residual methacrylic acid by acid

  the acid content is 0.74 g and the double

  0.72 g of methacrylic acid.

EXAMPLE 3

  20% by weight is dissolved in dimethyl

  formamide each of the two graft polymers obtained in the

  Examples 1 and 2 as well as polyvinylidene fluoride

  non-irradiated tial. A fourth solution is also made by mixing, in even-bodied quantities, a portion of the solutions of the initial non-irradiated polymer and the polymer of

  Example 2. Blocks of iron and aluminum degreasing

  - 5 - seeds, pickled with a phosphochromic mixture, rinsed and

  dried, are covered with these four solutions by trem-

  page, then dried in an oven for 1 hour at 210 ° C. All coatings adhere except for the one containing only polyvinylidene fluoride which separates from its support

by simply scratching the nail.

  The other six platelets are placed in a

  toclave half filled with water and heated 72 hours at 120 C.

  After this treatment it is impossible to start

  coating even by scraping it with a knife blade.

EXAMPLE 4

  500 g of polyvinylidene fluoride are introduced into a stirred 2-liter reactor under a nitrogen atmosphere.

  obtained by suspension polymerization, its appearance is

  - it a powder of 40 to 100 P of apparent density 0.7

  viron. It was irradiated at 1 Mrad. 930 g of water containing 0.3 g of CuSO 4 5H 2 O and 70 g of acid are also introduced.

  methacrylic distilled. It is heated for 6 hours at 600C.

  The grafted solid is separated by filtration, it is

  Wash and wash with water on a filter and then dry in an oven at 1200C. A graft polymer is collected whose content in

Methacrylic acid is 12%.

  Degreased and etched iron plates as previously are heated in an oven at 3000C, coated with powder of non-irradiated initial polyvinylidene fluoride powder and polymer powder grafted with 12% methacrylic acid. Several powdering cycles are carried out and

  in an oven until it has a thickness of

  approximately 200 9. We end with a passage in an oven for 15 minutes and quenching in the cold water of the piece leaving the oven. The initially unirradiated PVDF coating is scratched with a knife and thus primed, but the grafted polymer coating adheres perfectly even after 72 hours in the water.

at 1o00c.

EXAMPLE 5

  100 g of PVDF obtained from a latex and irradiated with 1 Mrad, 200 g of water containing 10 g of acrylic acid are introduced into the reactor used for Example I and

  0.05 g CuSO4, 5H2 dissolved. It is heated for 6 hours at 83 ° C.

  The grafted polymer is separated by filtration, drained and washed with water on a filter and the product is then dried.

an oven at 100 C.

  101.5 g of dry polymer containing

  4.9% acrylic acid according to the acidity dosage.

  As indicated in Example 3, a 20% solution in dimethylformamide is made with the graft polymer, coated with an aluminum plate and a plate.

  of steel that is cooked for 15 minutes in an oven at 2100C. We build

  tate for this acrylic acid graft polymer coating the mime good resistance to boiling water than for the

  grafted methacrylic acid used in Example 3.

EXAMPLE 6

  500 g of powdered vinylidene polyfluoride obtained from a latex and irradiated with 3 Mrads, 75 g of water containing 25 g of methacrylic acid and 50 g of polyvinylidene fluoride are introduced into a stirred vessel of 500 cm3 under a nitrogen atmosphere. 0.025 g CuSO4 H20 dissolved. It is heated for 6 hours at 600C. The grafted solid is separated by centrifugation, redispersed in water and centrifuged again, then the product is dried in an oven

at 1000C.

  62 g of dry polymer containing 24% are collected.

of methacrylic acid.

  We put 1 g of this product with 5 g of pure PVDF not

  irradiated in solution in 30 g of dimethylformramide. Plac-

  degreased aluminum strips are covered with the solution by soaking and then dried for 15 minutes at 2100C. We observe the

  even held in boiling water than for the other revolts

  vinylidene polyfluoride grafts used in

Examples 3 and 5.

- '8 -

R E V E N D I C A.T I 0 N S

_R .__.______ N_i ___ __ A! _____ N____

  1. Polyvinylidene fluoride adhering to the metals

  terized in that are fixed on its skeleton

polyacrylic grafts.

  2. Polyvinylidene fluoride according to claim 1, characterized in that the grafts are acid polymers.

  acrylic or methacrylic acid.

  3. Polyvinylidene fluoride according to one of the claims

  I to 2, characterized in that it contains on its sque-

  from 2 to 25% by weight of polyacrylic grafts.

  4. Probed of manufacturing a grafted vinylidene polyfluoride adhering to metals by graft polymerization of a

  monomer on an IR vinylidene polyfluoride skeleton

  at least 3.105 rads, characterized in that the

is a monomer acrylic.

  5. Method according to claim 4 characterized in that

  the monomer is acrylic acid or methacrylic acid.

  6. Method according to one of claims 4 to 5

  in that the polyvinylidene fluoride backbone is grafted onto the vinylidene fluoride backbone by polymerization of the

  2 to 25% by weight of polyacrylic grafts.

  7. Metal coating obtained from a solution in a solvent of a polyvinylidene fluoride having

  on his skeleton of polyacrylic grafts.

  8. Coating on metals obtained by hot spraying a polyvinylidene fluoride having on its skeleton

polyacrylic grafts.