TECHNICAL FIELD

The present invention concerns the bonding of plastics, particularly relates to a method for bonding polyolefins.

BACKGROUND ART

It is known that it is relatively difficult to bond plastics such as polyolefins, omopolymers, copolymers, either thermoplastic or crosslinked, expanded or not expanded, alone or properly compounded with plasticizers, extender, fillers, organic or inorganic fibres, stabilizers, chemical additives, to other organic and inorganic, natural or synthetic materials, such as leather, hide, polyvinylchloride and polyurethane, metal, concrete, ceramics. The principal reason of such a weak and unsufficient bond comes from the low polarity and surface energy of these kind of plastic materials, especially when the bond is carried out with traditional adhesive systems.

Moreover, it is known that the bond of the above mentioned polyolefins, can be improved subjecting their surfaces to chemical and physical _, treatments fit to increase their surface energy and polarity. Normally this is reached by using technics such as the corona-discharge treatment, plasma treatment, exposure to ultraviolet radiations, flame treatment, surface chemical grafting.

Nevertheless, these surface treatments are not sufficient or not suitable in practice, when a very high bond resistance is required, similar in value to the cohesion of the bonded materials, for example in bonding shoe components, such as soles or midsoles, in bonding waterproofing or fluid-tight membranes, slabs for wall-paneling or for flooring, or insulating panels, fluid transport piping, to substrates of different nature as metal, concrete, plastics, ceramics, or in structural bonding on rigid or semirigid plastic structures in several industrial applications.

It is to be emphasized that it is practically impossible to implement flame treatments in a shoe factory due to safety reasons. Most of the shoes are realized with soles of synthetic materials including, for example, styrenebutadiene rubber, styrene-butadiene-styrene o

CONFIRMATION COFΫ

styrene-isoprene-styrene rubbers, ethylenevinylacetate, polyurethane, polyvinylchloride, polyolefins.

For example the known methods for bonding soles to natural or synthetic uppers, for example with polyurethane adhesives, involve a previous treatment of the soles with a specific solution of a chlorine donor compound and then, after the application of the polyurethane adhesive onto both the soles and the uppers, the assembly of the parts under pressure.

The main disadvantage of the known methods is that very often the bond obtained does not satisfy the requirements of the bond itself. In fact in the case of soles or midsoles made with polyolefins, omopolymers, copolymers, either thermoplastic or crossiinked, expanded or not expanded, based on polypropylene, polyethylene, ethylenevinylacetate, the bond values reached with the known methods are very low and not sufficient.

Further disadvantage of such a known methods is the resulting chlorine emission which is noxius for the environment.

The known methods for bonding polyolefins in fields other than footwear, include a previous chemical and physical treatments fit to increase their surface energy and polarity. Normally this is reached by using technics such as the corona-discharge treatment, plasma treatment, exposure to ultraviolet radiations, flame treatment, surface chemical grafting.

Each method then involves the subsequent application of an adhesive, more frequently of a paint to polyolefins so treated.

Besides the mentioned methods, it is known that polyolefins can be bonded also by applying a primer based on polychloroolefins dissolved in organic solvents that, after dry' ⁿ g _> leaves a polar film that makes the surface fit to receive the subsequent application of polychloroprene or polyurethane adhesives, more frequently than paints.

The main disadvantage of these known methods is that, although in painting operations they could be useful for obtaining a good and durable adhesion of the paint film,

howewer in bonding polyolefin plastic materials, often they do not meet the requirements of the whished bonding.

DISCLOSURE OF THE INVENTION

The main aim of the present invention is to provide a bonding method fit to improve, compared with the known art, the bond value obtainable on polyolefinic plastic materials, omopolymers, copolymers, either thermoplastic or crosslinked, expanded or not, alone or properly compounded with plasticizers, extender, fillers, mineral or organic fibres, stabilizers, chemical additives.

Further aim of the present invention is to provide a bonding method and a usage of adhesive compositions that, when implemented, are such as to release insignificant chlorine amounts to the einvironment. The aims as above are achieved according to the content of the claims.

BEST MODE OF CARRYING OUT THE INVENTION

Each used surface is made by polyolefinic plastic materials, omopolymers, copolymers, either thermoplastic or crosslinked, expanded or not expanded, alone or properly compounded with plasticizers, extender, fillers, mineral or organic fibres, stabilizers, chemical additives. For ease of reference each of such surfaces shall be henceforth called SURFACE S.

Plastic materials are mainly shoe components, e.g. soles and midsoles, waterproofing or fluid-tight membranes, slabs for wall-paneling or for flooring, insulating panels and rigid or semirigid plastics structures, fluid transport pipes.

These materials, especially waterproofing and fluid-tight membranes, slabs for wall- paneling or for flooring, insulating panels and rigid or semirigid plastics structures, pipes, are bonded with each other or with substrates of different nature, such as metals, concrete, plastics or ceramics.

The method for bonding polyolefins basically includes the following steps:

- the application onto each SURFACE S of a coat of a solution containing 0.5% up to 10% of a chlorinated organic compound dissolved into an organic solvent blend in the ratio of 99.5% to 90 %;

- a first evaporation of solvents contained in said solution; - the exposure to ultraviolet radiations of the SURFACE S treated with said solution;

- the cooling of the SURFACE S;

- the application of an adhesive, in solution of organic solvents or in water dispersion, with or without crosslinker, both onto the SURFACE S and the surface of another substrate to which said SURFACE S has to be bonded, this application being followed by a second evaporation of the organic solvents or water contained in the adhesive, or the application of a melted 100% not volatile adhesive both onto the SURFACE S and the other material to be bonded thereto:

- the coupling , applying pressure, of the treated surfaces of said materials.

The application of the adhesive to the SURFACE S it coul be followed by a heat reactivation of the treated surfaces of said SURFACE S to be bonded together.

The method may also include solvent cleaning of the SURFACES S, this being often required for removing from these surfaces release agents or contaminants which may be onto it, the cleaning is carried out by using a solvent belonging to the group of ketone, or esters, or chlorinated, aromatics or aliphatics hydrocarbons, such as methyl ethyl ketone, acetone, ethyl acetate, trichloroethylene, toluene, or their blends.

The composition, henceforth referred to as PRIMER, of the preferred embodiment, includes organic compounds based on chlorinated natural rubber, e.g. of the Pergut S20 (Bayer trademark) or Alloprene (ICI trademark) and formulated as follows: -chlorinated natural rubber in the ratio of 0.5% up to 10%; -organic solvent blend in the ratio of 99.5% to 90%.

The solvent blend contains solvent such as toluene, methyl ethyl ketone, ethyl acetate, acetone and other organic solvents in various proportions, as necessary to dissolve the chlorinated natural rubber. A favorite blend is the following:: - toluene 10%

- methyl ethyl ketone 20%

- ethyl acetate 35%

- acetone 35%

In the PRIMER, the chlorinated natural rubber can be replaced by vinylchloroacetate resins, e.g. Vinylite VMCH (trademark of the Union Carbide Chemicals), or by chlorinated polyethylene, e.g. Hypalon (trademark of Du Pont Dow Elastomers), by acrylic polymers and copolymers, e.g. chlorovinylacrylic resin like Haloflex (marchio della ZENECA Resins), by polychloroprene polymers, e.g Neoprene (marchio DuPont Dow Elastomers) and by phenolic resins.

The application of a very thin layer of PRIMER to the area of SURFACE S to be subsequently bonded is made by means of a brush or of a spreading machine or roller spreader, or by a spray equipment.

The first evaporation or drying of solvents contained in the solution takes a few minutes, preferably 5 to 6 minutes.

The source of ultraviolet radiations is a ultraviolet rays lamp having, for example, the following characteristics: a high to medium vapour pressure mercury light having total power ranging from 400 to 4000 Watt.

For example it is preferable to use a tube 35 cm long having a power of 100 Watt/cm. Such a lamp can emit the complete range of ultraviolet wavelenghts from 184nm to 366nm, this with different strenghts but with prevailing presence of wavelenghts included from 210nm to 336nm, and significant presence of wavelenghts included from 210nm to 254nm.

The exposition to the ultraviolet radiation lamp of the SURFACE S area treated with the PRIMER for a time from 5 up to 30 seconds depending on the condition in which the distance of the radiation source from the SURFACE S can vary from 0.1 to 0.3 metres.

The adhesive is, for example, based on polymers such as polyurethane, polycloroprene, styrene-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) block copolymers, styrene-butadiene rubber, nitrile rubber, acrylic resins, cyanoacrylate, vinyl resins, epoxy

resins dissolved in a blend of organic solvents, or in water dispersion, or in a 100% non volatile composition, with or without curing agent.

The application of said adhesive to SURFACE S takes place after cooling of this surface.

Having allowed a second drying time as necessary for evaporation of solvents contained in the adhesive, then the adhesive films coated onto the surfaces are reactivated at a temperature ranging from 20°C to 80 °C.

Finally, adhesive coated areas of SURFACE S can be positioned and assembled to the other surface, and then a pressure which can indicatively range from 3 to 5 bar, is applied to the assembly.

It is to point out that second evaporation does not take place when the adhesive composition is 100% non volatile and that heat-reactivation is not always required with this kind of adhesives, or anyway when the adhesive at room temperature has a tackiness sufficient to carry out the bond, as the most polychoroprene adhesives.

It follows examples concerning different formulation of the PRIMER solution.

EXAMPLE 1.0: a chlorinated natural rubber, e.g. Pergut (Bayer AG trademark) preferably having viscosity of 20 mPa.s at 20°C in 20% toluene, such as Pergut S20 (trademark of Bayer AG), is dissolved in a blend of organic solvents preferably as follows:

PRIMER 1

Pergut S20 (Bayer AG trademark) 2,16 toluene 10,29 methyl ethyl ketone 18,47 ethyl acetate 34,88 acetone 34,20

TOTAL 100,00

The method of the present invention, using the above mentioned PRIMER, is hereafter disclosed and called PROCESS P.O.

This solution is applied to the SURFACE S of ethylenevinylacetate, crosslinked and expanded, wiped with methyl ethyl ketone for removing from the surface the release agents used in moulding process.

After 2 to 5 minutes drying time the SURFACE S is exposed to UV rays preferably passing the same through an oven provided in its upper side with ultraviolet rays tubular lamps 35 cm long and 100 Watt/cm power, set with a reflecting shelter fit to focus up to a certain extent the rays to an area of above 20 centimetres distant from the lamp. At such distance the SURFACE S is transported onto a conveyor so that to be treated inside the oven. Dwelt time in the oven is about 30 seconds, though the effective dwell time in the focus area is about 5 to 12 seconds.

Then SURFACE S is allowed to cool for a few minutes, about 5 minutes, and next bonded to PVC with a polyurethane heat reactivable adhesive, for example by using EN 1392 standard method.

Bond values (Kg/cm) achieved with PROCESS P.O by using PRIMER 1 are shown in the following TABLE 1.0.

The SURFACES S of ethylenevinylacetate will be hereinafter referred to as EVA, the ones of polypropylene as PP, and the ones of low density polyethylene as PE LD. "Initial strenght" means here the resistance of the adhesive to peel taken immediately after pressing of parts as described in EN 1392 standard method. Such a resistance is expressed in Kg/cm.

TABLE 1.0

SURFACE S Initial strenght type of failure Final streng type of failure

EVA not expanded 2-3 adhesion 5-6 adhes /cohesion EVA

EVA expanded 2-3 adhesion 5-6 adhes. /cohesion EVA pp . 3-S adhesion 5-9 adhes /cohes on surface

PE LD * 3-7 adhesion 9-15 adhes /cohes on surface wiped con Napparό (EXXON trademark)

EXAMPLE 1.1 : Process P.l : the composition PRIMER 1 is applied on SURFACE S of polypropylene wiped with methyl ethyl ketone for removing from surface the release agents used in moulding process.

After 2 to 5 minutes drying time SURFACE S is exposed to UV rays preferably letting the same through an oven provided in its upper side with ultraviolet rays tubular lamps 35 cm long and 100 Watt cm power, set with a reflecting shelter able to focus up to a certain extent the rays to an area of about 20 cm distant from the lamp. At such distance SURFACE S is conveyed on a belt so that to be treated inside the oven. Dwell time in the oven is about 30 seconds, though the effective dwell time in the focus area is about 5 to 12 seconds.

Then SURFACE S is allowed to cool for a few minutes, about 5 minutes, and next bonded to previous abraded leather, by using solvent based or water based adhesives. Bond values Kg cm obtained with PROCESS P.l by using PRIMER 1 are shown in the following TABLE 1.1.

TABLE 1.1 bond on leather (peel values at 72 hours from the bond following EN 1392, Kg/cm) SURFACE S- PP* Final strenght type of failure acrylic adhesive in water dispersion 5-6 leather cohesion nitrite adhesive in organic solvent blend 5-6 leather cohesion polychloroprene adhesive in organic solvent blend 5-6 leather cohesion SBS adhesive in organic solvent blend 5-6 cohes of adhesive /leather vinyl adhesive in water dispersion 5 leather cohesion

* wiped with methyl ethyl ketone

EXAMPLE 1.2: Process P.2: the composition PRIMER 1 is applied on SURFACE S of polypropylene wiped with methyl ethyl ketone for removing from surface the release agents used in moulding process.

After 2 to 5 minutes drying time SURFACE S is exposed to UV rays preferably letting the same through an oven provided in its upper side with ultraviolet rays tubular lamps 35 cm long and 100 Watt cm power, set with a reflecting shelter able to focus up to a certain extent the rays to an area of about 20 cm distant from the lamp At such distance SURFACE S is conveyed on a belt so that to be treated inside the oven. Dwel time in the

oven is about 30 seconds, though the effective dwell time in the focus area is about 5 to 12 seconds.

Then SURFACE S is allowed to cool for a few minutes, about 5 minutes, and next bonded to wood by using solvent based or water based adhesives or a 100% non volatile adhesive in melted phase.

Bond values obtained with PROCESS P.2 by using PRIMER 1 are shown in the following TABLE 1.2.

TABLE 1.2: bond to wood (shear strenght as Kg/cm2 following UNI-EN205)

SURFACE S= PP* Final strenght type of failure polychloroprene adhesive in organic solvent blend 20-30 cohesion of adhesive nitrile adhesive in organic solvent blend 20-30 cohesion of adhesive vinyl adhesive in water dispersion 40-50 cohesion on wood surface acrylic adhesive in water dispersion 40-50 cohesion on wood surface cyano-acrylic liquid adhesive 50-60 wood cohesion moisture-curing polyurethane liquid adhesive 50-60 wood cohesion epoxy bicomponent liquid adhesive 60-80 wood cohesion

* wiped with methyl ethyl ketone

EXAMPLE 2: a chloroacetovinyl resin, e.g Vinylite VMCH (trademark of the UNION CARBIDE CHEMICALS) is dissolved in a blend of organic solvents preferably as follows: PRIMER 2 VMCH (trademark UNION CARBIDE CHEMICALS) 1 ,98 Toluene 9,17 methyl ethyl ketone 22,21

Napparό (trademark of EXXON) 66,50

TOTAL 100,00

Bond values Kg/cm obtained with PROCESS P.O by using PRIMER 2 are shown in the following TABLE 2. TABLE 2

SURFACE S Initial strenght type of failure Final strenght type of failure

PE LD * 8-10 Adhesion 15-17 adhes /cohes on surface

* wiped con Napparό (EXXON trademark)

EXAMPLE 3: a chlorosulphonated polyethylene, e.g. Hypalon48 (trademark of

DuPONT DOW ELASTOMERS), is dissolved in a blend of organic solvents preferably as follows:

PRIMER 3

Hypalon48 (DuPONT DOW ELASTOMERS trademark) 2,45

Methylmetacrylate 0,98

4-chlorobenzophenone 0,49 toluene 73,41 acetone 22,68

TOTAL 100,00

Bond values Kg cm obtained with PROCESS P.O by using PRIMER 3 are reported in the following TABLE 3. TABLE 3

SURFACE S Initial strenght type of failure Final strenght type of failure

EVA expanded 1-2 adhesion 4-5 Adhesion pp . 4-5 adhesion 8-12 adhcs./cohcs on surface

PE LD * 8-10 adhesion 15-17 adhes /cohes on surface

* wiped con Napparό (EXXON trademark)

pXAMPLE 4: a chlorinated polyethylene acid copoiymer, e.g Hypalon 337 (trademark of DuPONT DOW ELASTOMERS) is dissolved in a blend of organic solvents preferably as follow:

PRIMER 4

Hypalon337 (DuPONT DOW ELASTOMERS trademark) 2,50 toluene 97,50

TOTAL 100,00

Bond values Kg/cm obtained with PROCESS P.O by using PRIMER 4 are reported in the following TABLE 4. TABLE 4

SURFACE S Initial strenght type of failure Final strenght type of failure

PE LD * 3-4 adhesion 10-15 ades /coes superficiale

* wiped con Napparό (EXXON trademark)

EXAMPLE 5: Haloflex 208 (trademark of teh Firm ZENECA Resins) dispersion is diluted with water in order to obtain a dry content of about 2%, then wetting agents are added to improve the application, preferably as follows:

PRIMER 5 Haloflex 208 (ZENECA Resins trademark) 4,73

Carbopol E21 (BF Goodrich trademark) 0,39 water 93,09

NaOH 20% 0,74

Lutensit AFK (B.A.S.F. trademark) 1,05 TOTAL 100,00

Bond values Kg/cm obtained with PROCESS P.O by using PRIMER 5 are shown in the following TABLE 5 TABLE 5 SURFACE S Initial strenght type of failure Final strenght type of failure

PE LD * adhesion 3-4 6-15 Adhesion

* wiped con Napparό (EXXON trademark)

EXAMPLE 6: a chlorinated natural rubber, e.g. Pergut S20 (Bayer AG trademark) and preferably having viscosity of 20 mPa.s at 20°C in toluene 20% and a phenolic resin are dissolved in a blend of organic solvents preferably as follows:

PRIMER 6

Pergut S20 (Bayer AG trademark) 1,10

Alresen PA 565 (HOECHST trademark) 1 ,22 methyl ethyl ketone 1,42 toluene 90,30 acetone 5,96

TOTAL 100,00

Bond values Kg/cm obtained with PROCESS P 0 by using PRIMER 6 are shown in the following TABLE 6. TABLE 6

SURFACE S Initial strenght type of failure Final strenght type of failure pp. 4-5 Adhesion 8-12 ades /coes superficiale

PE D * 1-2 Adhesion 15-17 Adhesion wiped con Napparό (EXXON trademark)

E.XAMPLE 7: a polychloroprene water dispersion, e.g NPX 9368 (trademark of Du

PONT DOW ELASTOMERS) , is diluted in order to obtain a dry content of about 2%, then wetting agents are added to improve the application, preferably as follows:

PRIMER 7

NPX 9368 (DuPONT DOW ELASTOMERS trademark) 2,50

Water 94,72

Carbopol E21 (BF Goodrich trademark) 0,35

NaOH 20 % 0,66

TOTAL 100,00

Bond values Kg cm obtained with PROCESS P.O by using PRIMER 7 are reported in the following TABLE 7. TABLE 7

SURFACE S Initial strenght type of failure Final strenght type of failure

PE LD * 1-2 Adhesion 5-6 adhesion

*wiped con Napparό (trademark of EXXON)

Experimental data here reported evidence that the main advantage achieved by using this method consists of improving bond of plastic materials of the polyolefin family, omopolymers, copolymers, either thermoplastic o crosslinked, expanded or not expanded, alone or properly compounded with plasticizers, extender, fillers, organic or inorganic fibres, stabilizers, chemical additives, as for example ethylenevinylacetate, crosslinked or not crosslinked.

The use of this method for example in shoe manufacturing, allows to obtain very good bonds both onto polyolefin based soles, crosslinked or not, and onto ethylenevinylacetate based soles as well, crosslinked or not, reaching bond values close to cohesion values of materials and anyhow complying, with or depassing minimum requisites set by EN 1391 standards.