Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/51—One specific pretreatment, e.g. phosphatation, chromatation, in combination with one specific coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
  • B05D3/102—Pretreatment of metallic substrates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies

Definitions

• This invention relates to laminated metal strip for use especially, but not exclusively, in the packaging industry and to methods of manufacturing such metal strip. More especially, the invention relates to a method of chemically treating metal strip prior to lamination with a thermoplastic material.
• Organic-coated metal substrates for example thermoplastic resin- coated tinplate or blackplate
• thermoplastic resin- coated tinplate or blackplate are used, inter alia, in the production of packaging materials, for example, food and beverage cans.
• organic coatings so used are required to conform with strict performance criteria.
• the coating must exhibit good stain resistance, corrosion resistance and resistance to delamination.
• Organic coatings have traditionally comprised solvent or water-based lacquers. Recently however, the use of laminated polymer films and coatings, such as thermoplastic resins, has been recognised as a viable alternative.
• organic coatings are not applied directly onto metal strip, such as mild steel or blackplate, because for packaging applications the metal surface is too reactive and underfilm corrosion can spread rapidly.
• metal strip such as mild steel or blackplate
• metallic-coated mild steels such as tinplate or eiectrolytically chromium-coated steel (ECCS) as substrates for organic coatings.
• ECCS eiectrolytically chromium-coated steel
• a surface-treated mild steel strip may comprise a chrome/CrO x or tin layer electrochemically deposited so that the final substrate has either a metallic chromium layer of typically from 50 to 1 50 mg/m 2 and a chromium oxide/hydroxide layer of typically from 10 to 30 mg/m 2 , or a layer of metallic tin of typically between 5 and 1 0 g/m 2 .
• tinplate is additionally subjected to chromate solution treatment, the amount of oxidisable chromium being between 1 and 10 mg/m 2 .
• electro-plating pre-treatment is a costly and time consuming process. Not only are materials expensive, but the electro-plating process itself consumes large quantities of energy. In addition, this conventional pre-treatment adds an additional production step in the process line, which adds costs in terms of line-time, manpower and through yield.
• any such pre-treatment should be capable of application under the present day metal strip coating and lamination line conditions.
• a process for producing laminated metal strip which comprises the steps of chemically treating the strip to form on at least one of its surfaces a non- metallic coating, and applying to that coated surface a coating of a thermoplastic resin to form a layer thereon.
• non-metallic coatings refers to coatings which despite optionally including metal ions, differ from what is conventionally described as a metallic layer in that there is no native metal. Unlike a metal layer wherein metal atoms, through metallic bonding, solely form a crystalline structure, in the non-metallic coatings of the present invention, both metallic and non-metallic ions are distributed within an amorphous network.
• the invention provides a process for manufacturing laminated metal strip, the process comprising the steps of:
• the metal strip may be cold-rolled metal strip.
• the metal strip has a gauge of between 0.08 and 0.50mm.
• a preferred gauge is 0.18mm.
• the metal strip comprises mild steel (conventionally referred to as blackplate) .
• the metal strip is cleaned to remove all traces of contamination which may be present as a result of previous cold rolling and annealing processes.
• the metal strip is cleaned electrolytically using a caustic-based solution, although the nature of the cleaner does not influence the subsequent chemical treatment. After cleaning, the strip may be rinsed with water to remove all traces of the cleaning solution.
• the chemical coating may be applied to the metal strip using a conventional application method such as immersion, spraying, roller coating, or a combination thereof.
• the chemical coating is applied by immersing the cleaned metal strip in chemical contained in one or more treatment vessels.
• the metal strip is chemically treated for less than 60 seconds; in other embodiments, the chemical treatment times are less than 30 seconds or less than 1 5 seconds.
• the metal strip is chemically treated for less than 1 0 seconds; typically, 5 seconds.
• the metal strip is chemically treated at a temperature of less than 100°C, most preferably at less than 30°C.
• the metal strip is chemically treated to form a chemical coating which prevents subsequent underfilm corrosion of the metal strip and promotes adhesion between the metal strip and thermoplastic resin.
• the chemical coating may be referred to as a coupling agent since it forms a strong and durable chemical bridge at the interface between the metal substrate and the final organic resin coating.
• the chemical bridge has a dual role; it interacts with receptive inorganic surfaces to form tenacious chemical bonds at the interface with the metal substrate and at the interface with the organic resin coating.
• the chemical coating may comprise an oxyanion such as phosphate, chromate, oxalate or arsenate.
• the coating may comprise yttrium, elements in the lanthanum series of the periodic table, silanes or azoles.
• the surface of the metal develops a naturally occurring surface oxide layer.
• the oxide layer on blackplate at ambient temperature will have an average thickness of between 2 and 20 mm.
• the chemical coating may be applied to the metal oxide layer on the surface of the metal substrate.
• the chemical coating comprises silanes.
• Silanes are a family of organosilicon monomers that are characterised by the formula R-SiX 3 , where R is an organofunctional group linked to silicon by a hydrolytically stable bond and X denotes hydrolyzable groups, such as alkoxy groups, which are converted to silanol groups on hydrolysis.
• the chemical coating comprises CH 2 CH 2 CH 2 Si(OCH 3 ) 3 , where R is a reactive functional group and X is the methoxy group.
• the chemical coating in order to react with the metal strip, the chemical coating may be converted to an active silanol by hydrolysis.
• the hydrolysed silane may react with the inorganic surface hydroxyl groups on the metal oxide layer.
• organic chemistry predicts the formation of chemical covalent bonds between the organofunctional group of the silane and the reactive species in the organic resin matrix.
• formation of an interpenetrating polymer network of the silane and the organic polymer may involve the formation of a "diffused" polymer at the silane-polymer interface.
• the chemical treatment may comprise phosphates, for example zinc orthophosphates, manganese phosphates or iron phosphates, thereby producing crystalline phosphate coatings on the metal substrate.
• phosphates for example zinc orthophosphates, manganese phosphates or iron phosphates, thereby producing crystalline phosphate coatings on the metal substrate.
• the metal strip is chemically coated with a composition comprising less than 5% atomic chromium.
• the chemical coating may comprise a commercially available chemical treatment comprising chromium, silicon and organic active species.
• the chemical coating may comprise a commercially available chemical treatment comprising a two component organic polymer i.e. an acrylic polymer and (NH 3 )Cr 2 O 6 .
• the metal strip may be rinsed and/or dried, for example with hot air, prior to treatment with organic resin.
• thermoplastic resin may be applied to one or both sides of the chemically-treated metal strip.
• the layer or layers of thermoplastic resin may be melted and rapidly quenched to attain the required degree of crystalline structure.
• thermoplastic resin may be co-extruded with the chemically-treated metal strip to form laminated metal strip.
• the film of thermoplastic resin may be bonded to chemically-treated metal strip under conditions of elevated temperature and pressure.
• the chemically-treated metal strip may be coated with a thermoplastic resin together with a bonding layer.
• the bonding layer may comprise a polyester, or an acid or acid-anhydride polyolefin resin containing carboxyl or anhydride groups. Typically, the bonding layer is between 1 and 10 ⁇ m thick.
• the chemically-treated metal strip may be extrusion coated with at least one thermoplastic resin.
• thermoplastic resins comprise polypropylene (PP), polyethyieneteraphthalate (PET) or a combination thereof.
• the thickness of the layer, or layers, of thermoplastic resin are between 3 and 50 ⁇ m.
• the chemical treatment has two functions; firstly it provides corrosion protection and inhibits underfilm corrosion, and secondly, it promotes good adhesion between the organic resin coating and the metal strip. These properties combined with the barrier properties of the organic coating provide a laminated metal strip product which can be formed into components for a range of applications whilst maintaining adequate performance criteria with regard to corrosion resistance and inter layer adhesion during the lifetime of the products.
• the invention provides a laminated metal strip produced by a process which comprises the steps of chemically treating the strip to form on at least one of its surfaces a non-metallic coating, and applying to that coated surface a coating of a thermoplastic resin to form a layer thereon.
• the invention provides a laminated metal strip produced by a process which comprises the steps of:-
• the invention provides a packaging container comprising such laminated metal strip.
• Figure 1 is a histogram showing the performance rating of food-filled cans made from PET-laminated and chemically treated blackplate;
• Figure 2 is a histogram showing the performance rating of food-filled cans made from PP-laminated and chemically treated blackplate.
• a process line for producing laminated blackplate comprises a plurality of guide rollers for transporting a strip of blackplate continuously from a coiled roll to an exit coil via a multiplicity of vertical tanks. These tanks include a cleaning tank, rinsing tanks and a chemical treatment tank. The line speed is typically 10 to 100 metres per minute with a treatment dwell time of between 1 to 10 seconds.
• organic polymeric resin e.g. a thermoplastic resin such as PET at elevated temperature and pressure.
• the laminated metal strip is then rapidly quenched to produce an essentially amorphous organic outer coating.
• chemicals A and B were evaluated as potential alternatives to the conventional electroplating step in the production of an organically coated mild steel strip.
• Chemical A comprised a commercially available chemical treatment comprising chromium, silicon and organic active species.
• Chemical B comprised a commercially available chemical treatment comprising a two component organic polymer i.e. an acrylic polymer and (NH 3 )Cr 2 0 6 .
• blackplate of 0.08 to 0.50mm thickness was subjected to an electrolytic cleaning process using a commercial cleaning solution at a temperature not exceeding 1 00° C, by passing a current of 20A for 5 seconds. This treatment is considered to return current densities to approximately 10 Adm '2 .
• the nature of the cleaner employed on the blackplate does not influence any subsequent chemical treatment. It is important that the metal strip is clean and free of contamination from prior processing. Before dipping in the chemical treatment vessels, the samples were washed in two ambient water rinse tanks. The concentrations of the cleaner and chemical treatments were those recommended by the respective suppliers. A batch of samples exposed only to electrolytic cleaning were also prepared as a control sample group, identified in Figures 1 and 2 as B- plate.
• an ECCS control sample group was also laminated. Samples of both 15 ⁇ m PET and/or 40 ⁇ m PP were laminated at elevated temperature and pressure. The hot samples were plunged into cold water just as the current was switched off. Instant quenching of this nature has the effect of retaining the amorphous nature of the thermoplastic coating at ambient temperature. Table 1 illustrates the concentrations, dip times and treatment section temperatures for evaluated chemicals A and B.
• 8oz cans (73 x 63mm) were filled with either rabbit cat food or cut green beans in salt brine under standard filling conditions. The cans were stored on their sides at an elevated temperature (37°C). Cans with scored ends were stored with the score running vertically so that it entered the head space area. Four cans of each variable were opened after 2, 5, and 15 weeks. Opened cans were evaluated for sulphide staining, delamination and corrosion (on and off the score line) .
• the can end performance was judged on three main criteria (sulphide staining, delamination and corrosion (on and off the score line)) using a points system. Three points were awarded if the defect was obviously present and two points if the defect was only minor. No points were allocated if the defect was absent. All points were totalled for each category of defect over the three openings, for both polymer film types and for each chemical pre-treatment. The results are illustrated in Figure 1 and Figure 2.
• the trials show that chemical pre-treatment in accordance with the invention provides an effective alternative to metallic electroplated coatings prior to coating of metal strip with organic resins.
• blackplate can undergo chemical pre-treatment "off-line" with transfer to the lamination line post treatment.
• this is less cost effective due to the necessity for a separate coating facility and any associated transportation or storage costs.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Laminated Bodies (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=10827778

Family Applications (1)

Country Status (14)

Cited By (1)

Families Citing this family (7)

Family Cites Families (16)

• 1998
  • 1998-03-02 GB GB9804297A patent/GB2334906A/en not_active Withdrawn
• 1999
  • 1999-03-02 EP EP99937821A patent/EP1060032B1/de not_active Expired - Lifetime
  • 1999-03-02 KR KR1020007009643A patent/KR20010041481A/ko not_active Application Discontinuation
  • 1999-03-02 RU RU2000124868/12A patent/RU2220789C2/ru not_active IP Right Cessation
  • 1999-03-02 DE DE69901797T patent/DE69901797T2/de not_active Expired - Lifetime
  • 1999-03-02 CA CA002322533A patent/CA2322533A1/en not_active Abandoned
  • 1999-03-02 AT AT99937821T patent/ATE218930T1/de not_active IP Right Cessation
  • 1999-03-02 AU AU32596/99A patent/AU741976B2/en not_active Ceased
  • 1999-03-02 BR BR9908396-5A patent/BR9908396A/pt not_active IP Right Cessation
  • 1999-03-02 PL PL99343020A patent/PL343020A1/xx unknown
  • 1999-03-02 ES ES99937821T patent/ES2178453T3/es not_active Expired - Lifetime
  • 1999-03-02 WO PCT/GB1999/000567 patent/WO1999044756A2/en not_active Application Discontinuation
  • 1999-03-02 ID IDW20001982A patent/ID28089A/id unknown
  • 1999-03-02 CN CN99803547A patent/CN1291918A/zh active Pending
• 2003
  • 2003-08-06 RU RU2003124575/02A patent/RU2003124575A/ru not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events