Method of joining metal with plastic

FIELD: shaping or joining of plastics.

SUBSTANCE: method comprises applying adhesive polymeric composition on the metallic surface, molding a plastic covering on the metallic surface, and heating and pressing the metallic surface. The surface is pressed during five seconds or less, the pressure ranging from 0.01 MPa to 5 MPa.

EFFECT: enhanced adhesion between the polymeric and metallic surfaces.

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The present invention relates to a method for joining metal parts with plastic. In particular, the invention relates to a method of applying metal coatings of plastics by injection moulding and to the products obtained by this method.

The number of parts used in many areas, characterized by the presence of the connection pane of plastic with the surface of metal parts. To obtain such products use the method of the present invention. The reasons for creating such connections are different. For example, the coating on the metal parts is sometimes necessary to prevent contacting the metal surface with food or exposure to chemical substances during use. Examples of products obtained by the method of the present invention, are covers. The lid of the plastic bottle attached to a metal material, such as aluminum, in order to prevent the diffusion of oxygen in the bottle.

In industry it is also necessary to connect the various parts, such as metal valves, metal fittings or metal pipes, with the pipes or fittings made of plastic.

Known methods for joining plastics to the surfaces of metals. In particular, the known method of connection is to be placed metal parts with plastic by injection molding. This method is described in international patent application WO 96/14533. In accordance with the described invention the method includes the stage of applying to a metal tube or pipe fittings of organic or inorganic primer coating, then the effects of heat on the end part of the metal pipe or the fitting and then immersing the metal tube or pipe fittings in a hot state in a fluidized bed of plastic. The next and last stage consists in forming on the surface of the metal tube or pipe fittings plastic by injection molding.

The problem is in the way described in the aforementioned patent application, is that the adhesion strength between the metal pipe and plastic are small.

Currently discovered the way in which the adhesion strength between the metal surface and the plastic increases.

In addition, due to the method of the present invention are higher values of the adhesion forces without damage to the plastic coating. In fact, the chemical degradation of the polymer does not occur or is minimized.

Moreover, this method does not even lead to loss of form formed on the surface of the plastic cover under the action shall eat the heat.

Accordingly, the present invention provides a method of connection between the plastic and the surface of metal parts (metal surface), which includes stages:

a) applying the adhesive resin composition on the surface of the metal;

b) forming on the metal surface coating of plastic material by injection molding; and

c) applying heat to a metal surface.

The metal surface may be the entire surface of the metal part or a part of it depending on the manufactured product containing this compound.

The item is intended for connection to plastic, and can refer to any type of metal or metal alloy. Examples of suitable metals and metal alloys are iron, aluminum, copper, steel and brass.

The part exposed to the method of the present invention may not necessarily be applied to the electrolytic coating, or it can be processed by the surface treatment, generally used in modern technology. So, for example, acceptable and also details with electrolytic chromium or zinc coating.

Adhesive resin composition used in stage (a), preferably compatible with the polymer used for forming the surface of the metal is at the stage (b). For example, the polymer adhesive may be the same polymer as the polymer used for forming the coating on the metal surface.

Adhesive resin composition preferably contains a polymer modified by grafting on him modifiers containing functional group. Can be used adhesive resin composition, known in modern technology. The modification of the polymer is achieved, in accordance with known methods by mixing a polymer and a modifier (such as maleic anhydride or isophorone-bismaleimides or acrylic acid) or in the molten state or in solution, preferably in the presence of free-radical initiators such as organic peroxides. Is a partial or complete graft modifier in amounts in the range from 0.5 to 10%.

Examples of suitable modified polymers are the following (all percentages by weight):

I) a random copolymer of propylene with from 0.5 to 10% of the olefin CH2=CHR, where R is chosen from H and linear or branched C2-C4is an alkyl radical, modified with polar groups in amounts of from 0.002 to 10%;

II) polyolefin composition comprising in weight percent:

a) 30-94%, preferably 54-85%, polypropylene or polite the ene (HDPE, LDPE or LLDPE) or propylene/ethylene or propylene/ethylene/C4-C10- α-olefinic crystalline statistical copolymer;

b) 0-70%, preferably 5-40%, ethylene-propylene or ethylene/1-butenova elastomeric copolymer; and

C) 0.5 to 10%, preferably 2-6%, of polypropylene or of polyethylene (HDPE, LDPE or LLDPE), modified with polar groups in amounts from 0.5 to 10%.

Preferably, the adhesive polymer composition also contains from 0.1 to 0.5% (wt.) nucleating agent, such as dibenzylidene or talc, and from 0.1 to 10% (wt.) titanium dioxide.

Preferably, α-olefin selected from 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene. Particularly preferred 1-butene.

Polymer composition (II) can be obtained by mixing the components or by sequential polymerization of monomers in the presence of stereospecific catalysts of the Ziegler - Natta supported on dihalogenide magnesium in the active form, as described, for example, in EP-A-483523.

Method of applying adhesive resin composition on the surface of metal parts is not critical. For example, the adhesive polymer composition may be applied by injection molding or dipping parts in a fluidized bed of polymer powder. Other coming is their ways of applying a polymer adhesive in powder form are flame spraying or coating on a pre-heated parts or using a spray, equipped with a system for electrostatic charging of powders. Alternatively can be used extrusion method, if the item has a simple form. Depending on the way the metal surface is heated prior to or after application of the adhesive resin composition.

Plastic coating which is formed on the metal surface, can include thermoplastics, such as polyolefins, for example Homo - or copolymers of ethylene, propylene and 1-butene and polyamides. Examples of polyolefins is heterophase polymeric composition comprising (in weight percent):

- 30-90% of a crystalline propylene homopolymer when the content of fraction insoluble in xylene at room temperature greater than 90, or a crystalline statistical copolymer of propylene with ethylene and/or olefin CH2=CHR, where R represents a C2-C6is an alkyl radical containing more than 85% of propylene and containing insoluble fraction in excess of 85%;

- 0-40% polymer fraction containing ethylene, insoluble in xylene at room temperature (i.e. at about 23°C); and

- 10-60% of an amorphous ethylene-propylene copolymer, optionally containing minor quantities of a diene, soluble in xylene at room temperature and containing 10-70% ethylene.

The use of the s heterophase polymer compositions are described in published European patent applications No. 400333 and 472946.

The plastic may include other components commonly used in contemporary art, such as fillers and pigments.

At the stage (C) heat is applied to the metal surface, for example, under the action of induction. Way to supply the induction of heat is carried out in an induction furnace.

The metal surface is heated up to a temperature which causes softening or melting formed on the metal surface coating of plastic material in contact with the metal. Therefore, the temperature depends on the type of used plastics. For example, if the plastic is a propylene polymer, the metal surface can be heated to a temperature of 180-220°C.

In order to determine how much energy is needed for heating the metal surface with the coating at the required temperature, you can define it to a metal surface without coating.

The method of the present invention for selecting includes a step of applying to the surface of the metal organic or inorganic primer coating before the stage of application to the surface of the metal adhesive resin composition. Examples of suitable primers are epoxy resin and chromates.

When at the stage (C) warm, to increase the adhesion between the surface of metal and plastic to detail is whether and/or laminated on the metal surface plastic coating possible application of pressure. Pressure is applied, for example, by rolling or by using the mold. On the magnitude of the pressure applied is influenced by the type of part and the types of the used polymers. Applied pressure can be selected in the range from 0.01 to 5 MPa. If pressure is applied through the mold, pressure is preferably applied within 5 seconds or less.

The following examples are provided to illustrate but not to limit the present invention.

Data relating to compositions and samples from examples, determine using the following methods:

the melt index (MIL): ASTM D 1238, condition L.

the solubility in xylene: (see note below).

the characteristic viscosity: defined in tetrahydronaphthalene at 135°C.

test for exfoliation: NF 49 711 at room temperature.

Note.

Determine the percentage of fraction soluble in xylene: prepare a sample solution with a concentration of 1% (wt.), maintaining the temperature at 135°C and stirring the solution for one hour and then cooling the solution to room temperature. After that, the solution is filtered, and a portion of the filtrate add acetone for precipitation of the dissolved polymer. After that, the polymer is extracted, washed, dried and weighed in order to define the th percentage fraction, soluble in xylene.

The polymers used in examples.

- Adhesive polymer composition comprising (in weight percent):

a) 74% crystalline poly(propylene-co-butene-1-co-ethylene)containing approximately 8% and 2% of recurring units derived from butene-1 and ethylene, respectively, containing a small amount of fraction soluble in xylene at room temperature;

b) 20% of the statistical copolymer of propylene with 15% of recurring units derived from ethylene, containing the fraction soluble in xylene at 23°C, 50%;

c) 5% polypropylene with 1.5% grafted maleic anhydride; and

d) 1% TiO2.

The polymers obtained in the polymerization of olefinic monomers in the presence of a catalyst of Ziegler - Natta, providing a high polymer yield.

The polymer composition stabilized against thermal ageing and ageing under the action of ultraviolet rays, using the known additives, and the composition is subjected to slight cracking under the action of peroxides up to MIL equal to 140 DG/min. and the average particle size of 250 μm, which is achieved by using cryogenic grinding.

- Heterophase polymeric composition, characterized by the value MIL of 3.5 DG/min and consisting of the following polymers (in weight percent):

- 79% of kristallicheskogo propylene homopolymer, containing 2.5% of a fraction soluble in xylene at 23°C; and

- 21% statistical elastomeric copolymer consisting of 87% of recurring units derived from propylene, and 13% of ethylene.

Fraction soluble in xylene at 23°C for heterophase composition is characterized by the value of the characteristic viscosity of 3 DL/g

Composition was prepared by sequential polymerization with use of providing a high yield of polymer and vysokotehnicheskoe catalyst of Ziegler - Natta supported on magnesium chloride.

Comparative example 1C.

Sandblasted plate carbon steel with dimensions 124×124×1.5 mm connect with plastic in accordance with the following method.

Stage (a): the plate is heated in a furnace at 250°C and then immersed in a fluidized bed (for 5 seconds), containing the powder adhesive resin composition. The plate coated with the thus coated is allowed to cool in the open air. The coating has a thickness of 300-400 microns. The adhesion of the plastic coating to the metal belongs to the class 5 In accordance with method ASTM D 3359.

Stage (b): plate coated with the thus coated is introduced into the apparatus for injection moulding. The cavity in the form was the size of 126 mm × 126 mm and a thickness of 4 mm

The coating layer g is therianos polymeric composition is formed over the surface of the plate with a coating of the modified polymer in the injection heterogeneous composition in the mold at a temperature of 260°C. The resulting layer has a thickness of 2-2,2 mm.

The strength otder plastics from carbon steel sheet is 0-2 N/mm

Example 1

The plate obtained in stage (b) of comparative example 1C was processed at the next stage.

Stage (C): plate connected with plastic, heated to a temperature of 180-220°C, using an induction furnace, and simultaneously subjected to rolling. Applied pressure is approximately 0.1 MPa.

The strength otder plastic from the plate carbon steel at room temperature is 6.5-7 N/mm

1. The method of connection of plastic with a metallic surface, comprising the following stages:

a) applying an adhesive polymer composition on the metal surface,

b) forming on the metal surface coating of plastic material by injection molding,

c) application of heat and pressure to a metal surface, the pressure is chosen in the range from 0.01 to 5 MPa and put it in 5 seconds or less.

2. The method according to claim 1, comprising a stage of heating the metal surface before or after application of the adhesive polymer composition.

3. The method according to claim 1 or 2, comprising a stage of applying organic or inorganic underlayer coating on the metal surface prior to application to the surface of the metal powder is dhesives polymeric composition.

4. The product obtained by the method according to PP. 1-3.



 

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