Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/22—Addition to the formed paper
  • D21H23/52—Addition to the formed paper by contacting paper with a device carrying the material
  • D21H23/64—Addition to the formed paper by contacting paper with a device carrying the material the material being non-fluent at the moment of transfer, e.g. in form of preformed, at least partially hardened coating
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/02—Metal coatings
  • D21H19/08—Metal coatings applied as vapour, e.g. in vacuum
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H5/00—Special paper or cardboard not otherwise provided for
  • D21H5/0005—Processes or apparatus specially adapted for applying liquids or other fluent materials to finished paper or board, e.g. impregnating, coating
  • D21H5/0025—Processes or apparatus specially adapted for applying liquids or other fluent materials to finished paper or board, e.g. impregnating, coating by contact with a device carrying the treating material
  • D21H5/004—Processes or apparatus specially adapted for applying liquids or other fluent materials to finished paper or board, e.g. impregnating, coating by contact with a device carrying the treating material the treating material being non-fluent at the moment of transfer, e.g. in form of preformed, at least partially hardened, coating

Definitions

• the present invention is directed to the manufacture of a high gloss coating onto a paper substrate and to the highly reflective vacuum metallized paper produced therefrom.
• paper includes sheet-like masses made from fibrous cellulosic materials which may be derived from both natural sources as well as from synthetics such as polyamides, polyesters, and polyacrylic resins, and from mineral fibers such as asbestos and glass. In addition, papers made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is also included within the broad term "paper”.
• metal foils have been laminated to paper using solvent-based or curing adhesives.
• the process requires that the metal foil be of a thickness of more than 1 micron (0.0001 mil).
• the foil laminates are glossy since the finish of the final product is not dependent upon the paper surface but only on the gloss and finish of the foil itself. Foil laminates, even using very thin foils, are expensive.
• the foil/paper laminates also present handling and application problems (i.e. they tend to curl and crease).
• Metallized papers have also been prepared by the direct metallization method where a metallic laden, high solids coating composition is employed.
• Useful compositions have included ultraviolet curing coatings, electron beam or radiation curing coatings, and high solids aqueous emulsion coatings. By employing high solids coatings, penetration into the porous paper stock is prevented. The gloss and finish of the metallized surface are dependent upon the smoothness of the paper as well as the smoothness of the coating that has been applied.
• the paper's surface is typically pre-coated with a base coating which fills minor surface imperfections and provides a smooth surface to receive the metal deposit.
• a vacuum metallized paper substrate will have a Specular gloss which is very similar to that of the substrate prior to metallization, it is generally understood that the smoother the surface is of the paper substrate employed, the better the resultant gloss will be of the substrate after metallization.
• substrates having a 75° Specular gloss of at least 80 are required for vacuum metallization.
• Glossy coated paper suitable for subsequent vacuum metallization has been prepared by the wet casting method which involves pressing a paper substrate carrying a layer of wet coating against the surface of a heated drum having a highly polished finishing surface. This method is slow and, as such, is not advantagous for economic reasons. Moreover, the critical balance of useful temperatures, pressures and speeds which may be employed in order to prevent a coating from sticking to the casting drum is difficult to maintain during manufacture.
• the process described in the British patent involves coating a backing (e.g. a plastic film or sheet) with a carrier vehicle having a metallic powder dispersed therein, applying an adhesive to the surface of the substrate, combining the backing and substrate, and maintaining the laminated combination at ambient temperature for a time sufficient to permit the adhesive to cure (i.e. absorb the metallic powder and bond it to the surface of the substrate) before the backing is separated.
• a backing e.g. a plastic film or sheet
• a carrier vehicle having a metallic powder dispersed therein
• the transfer technique involves coating a carrier web of a synthetic plastic material with a release layer, forming a metal film on the release layer using vacuum deposition techniques, coating either the surface of the substrate or the metallized layer with an adhesive, combining the substrate and web, conveying the substrate/web combination through hot or cold pressure rollers (depending upon the nature of the adhesive layer) to effect bonding, and then stripping away the carrier. Since the metallic particles are embedded in the release coating and since the release layer only superficially adheres to the carrier web, the carrier web can be readily stripped away without disturbing the metallic particles. The metallic surface, after transfer, is smooth and glossy and covered with a top coating of the plastic used to form the release layer.
• the transfer technique of this patent due to the multiplicity of steps and coatings required to achieve a glossy surface, is not recognized as being economically advantageous.
• U.S. Pat. Nos. 4,153,494 and 4,215,170 disclose a transfer technique which involves depositing a metal film onto a transfer agent (i.e. carrier) which does not contain a release coating.
• the transfer agent e.g. untreated polypropylene
• the transfer agent must be smooth since it imparts the final surface to the metallized substrate, and it must have an adherence to the metallic particles less than that of the varnish employed to transfer the metallic particles to the substrate.
• the transfer agent is metallized by any known method; the substrate or metallized transfer agent is coated with the varnish (e.g. polyurethane varnish); and, before the varnish can cure, the transfer agent and substrate are laminated together by conventional means (a single roll under slight pressure).
• the varnish absorbs the metallic particles and takes on the smooth surface characteristics of the transfer agent once exceed.
• the laminate must be cured prior to stripping away the transfer agent.
• the curing step may be natural or accelerated by heat or exposure to radiation. Due to the cure times required, this process has the economic disadvantage that significant quantities of unacceptable product may be manufactured without any means for determining the cureability of the varnish employed prior to stripping away the transfer agent.
• the similar transfer metallization process of U.S. Pat. No. 4,382,831 involves forming a metal film onto a plastic transfer agent (e.g. polyester or polyolefin), coating either the surface of a paper support member or the metallized layer with an aqueous-based thermoplastic adhesive and combining the paper support number and transfer agent. By application of pressure and/or heat the thermoplastic layer is caused to flow. The plastic transfer agent is subsequently removed from the composite leaving a transferred metallic film of high reflectivity on the paper.
• a plastic transfer agent e.g. polyester or polyolefin
• the present invention provides an improved process for the manufacture of paper having high gloss which is suitable for vacuum metallization comprising the steps of:
• the thermal resin adhesives useful herein comprise a thermoplastic resin having a Tg of greater than 0 to less than +50°C.
• the resin-coated paper substrate prepared have a 75° specular gloss of at least about 85, and preferably have a gloss of 90 or above.
• paper having similarly high gloss may also be manufactured by the process comprising the steps of:
• a paper substrate is directly coated with a thin layer of a thermal resin coating using a medium suitable for the particular resin selected (e.g. aqueous emulsion or aqueous solution or organic solvent solution.)
• a medium suitable for the particular resin selected e.g. aqueous emulsion or aqueous solution or organic solvent solution.
• the lamination step takes place.
• the resin-coated surface of the paper substrate is brought in contact with a suitable interleaving film and laminated through a nip roller at a temperature and pressure sufficient to render the thermal resin flowable.
• the interleaving film may be immediately stripped. Cooling to ambient temperature prior to stripping is not required because the slight temperature drop which occurs in the period between laminating and stripping is adequate to harden the thermal resin adhesives used herein.
• the interleaving film which possesses a smooth, high gloss surface, acts as a template for the thermal resin once it is rendered flowable.
• the interleaving film unaffected by the above process, may be employed in web form or in the form of a reuseable continuous loop.
• a transfer film is coated with the thermal resin coating.
• the resin-coated surface (either wet or dried) is thereafter similarly laminated with a paper substrate.
• the thermal resin coating will adhere to the paper substrate such that subsequent to lamination, the transfer film (which is also suitable for reuse) may be stripped away leaving a paper substrate coated with the resin which exhibits a significantly high gloss suitable for metalli­zation.
• the transfer film (which is also suitable for reuse) may be stripped away leaving a paper substrate coated with the resin which exhibits a significantly high gloss suitable for metalli­zation.
• the laminant has a moisture content above about 4-6% subsequent to lamination, it may be necessary to further dry it prior to stripping away the transfer film.
• the dry transfer process is particularly useful for coating light weight porous base paper stock such as tissue, while the wet transfer process is not generally suitable for such light weight materials.
• the thermal resin coatings useful herein contain a thermoplastic resin capable of forming a continuous, smooth, hard but flexible film having good block resistance.
• Thermoplastic resins are those which require no cure (i.e. hardening or crosslinking at room temperature or with heat or irradiation). Moderately hard resins are preferred; however, those which have a slight tack may be used herein.
• Useful resins herein have a theoretical Tg (glass transition temperature) within the range of greater than 0 to less than +50°C., preferably +3 to +45°C, and most preferably +10 to +40°C. Resins having a theoretical Tg less than 0°C provide coated papers with soft coatings and poor block resistance making them unsuitable for metallization. Resins having a theoretical Tg greater than about +50°C provide coated surfaces which are generally brittle, an undesirable property making such coated paper also unsuitable for metallization.
• thermoplastic resins particularly useful herein include the following: polymers and copolymers of styrenes, acrylates and methacrylates, vinyl acetate, maleates, acrylonitrile, acrylamides, acrylic acid and methacrylic acid, and ethylene.
• the useful concentrations of the comonomers employed in order to provide a thermoplastic resin within the useful Tg range may be easily determined by one skilled in the art.
• One preferred coating is a blend of styrene/butyl acrylate and styrene/acrylic acid resins having a theoretical Tg of +40°C.
• Another preferred coating comprises a modified polyvinyl acetate copolymer described in U.S.
• crosslinking agents may be employed in the coating composition in order to provide improved water or chemical resistance to the paper substrate.
• Other optional coating components include, for example, viscosity modifiers, defoamers, and non-blocking additives.
• coalescing solvent When practicing the wet transfer process, the use of a coalescing solvent may in some instances be advantageously employed to solvate a resin employed in aqueous emulsion in order to provide improved film formation.
• a coalescing solvent typically used and well known in the art.
• coalescing solvents include, in general, hydrocarbons, alcohols, esters, ethers and ketones.
• useful coalescents include ethylene glycol monoethylether, ethylene glycol monobutylether, diethylene glycol monobutylether, ethylene glycol monohexylether and the acetates thereof, ethanol, and isopropanol.
• thermoplastic resins may be applied directly onto the paper substrate or onto the transfer film (depending on whether the direct or transfer coating process is employed) by any conventional technique capable of depositing a continuous film. Suitable coating techniques include rotogravure, reverse roll, wire-wound bar, and the like.
• the coating weight required to form a suitable resin film will vary depending on the paper substrate which is to be employed. Typically for an uncoated paper substrate from 1-4 lbs. (.45-1.81 kg.) dry resin per ream (3000 ft.2 or 278.7 m.2) is required, with the optimum being about 1.5-2.5 lbs. (.68-1.13 kg.) per ream for a light weight, machine glazed paper substrate.
• the useful percent solids of the resin medium employed will typically range from about 20-50%, preferably 20-40% solids and will vary depending on the resin composition employed, the resin medium (aqueous or organic solvent), the desired coating weight, coating viscosity and the paper coating process employed.
• the interleaving films useful in the direct coating method are also generally useful as transfer films when practicing the transfer coating methods herein.
• the films should be heat resistant, dimensionally stable, and exhibit low adhesion to the resin coating employed for easy stripability. Due to the low adhesion of the film to the coating, the film is capable of being reused one or more times in the absence of a buildup of coating on the film.
• Suitable materials useful for the films include, for example, coated and uncoated polyolefins, coated and uncoated polyesters, and cellulose esters. Films which have been treated (e.g. corona dischared) have found some utility in the practice of the processes herein. However, untreated films are generally preferred.
• a particular film will vary depending, for example, on the coating process (direct v.s. transfer) and lamination temperature as well as on the thermal resin coating employed.
• Particularly preferred interleaving films for the direct coating process as well as transfer films used in the dry or wet transfer processes include cellulose acetate and a polyester film obtained from Dupont referred to as 92A Mylar.
• the lamination of the combined paper and film may be achieved by conventional lamination techniques.
• the nip roller employed may consist of one or more pairs of heated metal/pressure rubber roller combinations. Generally only one pair is necessary to effect satisfactory lamination with the paper substrate preferably in contact with the rubber roller.
• the metal roller is heated to about 160-270°F (71-132°C), preferably 180-­250°F (82-121°C), and most preferably 210°F (99°C), the temperature used depending upon the resin selected.
• the pressure applied by the rubber roller should be sufficient to bring the surfaces into intimate contact (at least about 40-200 psi).
• the minimum amount of pressure required will also vary depending on the resin and lamination temperature employed. As shown herein, one may be able to employ lower lamination temperatures as the pressure is increased.
• Other suitable lamination apparatus for practicing the present invention include calendar rolls.
• Suitable paper substrate for use herein include both heavy and thin paper stocks, for example, bleached and unbleached sulfate (kraft), bleached and unbleached sulfite, bleached and unbleached soda, neutral sulfite, semi-chemical and chemical groundwood, groundwood and the like.
• the preferred substrates for metallized bottle labels include those with a clay coating or wet strength.
• the paper substrate does not need to be pre-coated prior to practicing the present invention; however, depending on the ultimate end use of the paper after metallization, a pre-coating may advantageously be employed in order to provide improved water resistance or strength to the paper.
• Vacuum metallization is well-known and the detailed procedures will be apparent to those skilled in the art. A review of vapor deposition techniques may be found in Vapor Deposition, C. F. Powell, J. H. Oxley, and J. M. Blocker, Jr., eds., John Wiley and Sons, Inc., New York (1966).
• the coated paper substrate is unwound, exposed to the metallizing source under high vacuum, and rewound.
• the optimum vacuum level will depend upon the coating material and most often is 10 ⁇ 4 Toor or less.
• the particular metal chosen will vary with the requirements of the practitioner. Suitable metals include zinc, cadmium, copper, silver, gold, and for bottle labels preferably aluminum.
• Evaporation sources which can be used in single or multiple chambers include an oven with indirectly heated crucibles, an intermetallic boat heated by direct current inductive evaporation, electron beam evaporation, and sputtering.
• resin denotes 3000 ft.2 (278.7 m.2). All resins exemplified were employed as 20-40% solids solutions or dispersions unless otherwise noted and were applied directly to a paper substrate or transfer film with a #6 or #8 wire-wound rod.
• the test used to measure the gloss of the resin-coated paper substrates before and after metallization was the ASTM Standard Test Method For Specular Gloss (ASTM D 523 - 80) using the 75° geometry. Higher readings indicate better gloss which is the ratio of reflected light to incident light.
• This example describes the preparation of a high gloss paper substrate by the direct coating method of the present invention employing an interleaving film.
• One surface of a paper substrate was coated with various solvent-borne or aqueous-borne thermoplastic resins.
• the coating weight was 2.5 pounds (1.13 kg.) of resin per ream.
• the coated surface was dried for 2 minutes at 200°F (93°C).
• a 1.0 mil (.025 mm.) thick interleaving film of polyester having a basis weight of 12 lb. (5.44 kg.)/ream (92A Mylar obtained from DuPont and referred to herein as PES) was placed on top of the resin coated surface of the paper substrate.
• the paper/film laminate was run through a nip roller set at 210°F (99°C).
• the nip roller consisted of a metal/rubber nip with the metal roller being heated to the indicated temperature. During passage through the nip, the interleaving film was in contact with the heated steel roller and the paper substrate was in contact with the rubber roller. After exit from the nip, the interleaving film was subsequently peeled away.
• Part A The process of Part A was repeated by coating Resins A and B onto the 60# Paper or the clay coated side of 279# Paper (279 lb. (126.55 kg.)/ream clay coated news back board having a 75° Specular gloss of 24).
• the interleaving films employed during lamination were: PE - 1.0 mil (.025 mm.) thick polyethylene having a basis weight of 19 lb. (8.62 kg.)/ream obtained from Visqueen. PE/PES - 0.5 mil (.012 mm.) thick polyethylene-coated polyester having a basis weight of 19 lb. (8.62 kg.)/ream obtained from DuPont (500 L).
• the 38# Paper described in Example 1 having an initial gloss of 58 was coated with Resin A (described above) or Resin A ⁇ (Resin A containing 3% polyfunctional aziridine, a crosslinker obtained from Cordova Chemical as XAMA-2).
• Resin A Resin A containing 3% polyfunctional aziridine, a crosslinker obtained from Cordova Chemical as XAMA-2).
• the crosslinking additive in Resin A ⁇ aids in providing water resistance to the coated paper substrate.
• the coating weight was 2.5 lbs. (1.13 kg.) resin per ream.
• the coated surfaces were oven dried for two minutes at 200°F. (93°C).
• the 75° Spectral gloss of the coated papers measured 76-78.
• thermoplastic resins within the useful Tg range of greater than 0 to less than 50°C. Suitable laminating temperatures and pressures will depend on the Tg of the resin employed.
• This example describes the preparation of a high gloss paper substrate by the dry transfer method of the present invention.
• thermoplastic resins A-D
• the coating weight was 2.5 lbs. (1.13 kg.) of resin per ream.
• the coated surface was dried 2 minutes at 200°F (93°C).
• a paper substrate was placed on top of the resin-coated surface of the transfer film.
• the paper/film laminate was run through a nip roller described in Part A of Example 1 which was set at 210°F (99°C). During passage through the nip the uncoated surface of the transfer film was in contact with the heated steel roller and the paper substrate was in contact with the rubber. After exit from the nip, the transfer film was easily peeled away.
• the three paper substrates employed are described in Example 1.
• the transfer films employed were PES, CA, LSPP, HSPP and HSPP-CD.
• the gloss results are given in Table IV. In all cases, except where indicated, the transfer film was easily peeled from the paper substrate.
• Table IV show the excellent gloss provided in general to the paper substrates by the transfer coating method employing the exemplified resins and the PES, CA, and untreated HSPP transfer films. While unsatisfactory gloss and/or difficult pull was exhibited when LSPP was employed as a transfer film, LSPP was shown to be useful when employed in conjunction with Resin D on the two lower basis weight paper stocks. Varying results were also obtained when corona discharged HSPP was employed as a transfer film. The treated film was as useful as the untreated film in some instances providing excellent transfer and gloss with Resins B and D; poor transfer was exhibited with Resins A and C.
• Part A The process of Part A was repeated by transferring various resins from polyester (coated at 2.5 lb. (1.13 kg.)/ream) to the 38# ground wood paper. Unless otherwise noted the coatings were transferred employing a nip temperature of 225°F (107°C). The gloss results are given in Table VI.
• thermoplastic resins of varying Tg's Resin M (Tg +55°C) provided excellent gloss but was unacceptably brittle. Lower Tg (0° or less) resins H and P were transferrable, however the gloss values provided were low. Such low Tg resins also provide poor block resistance. Resins I and J provided unacceptable gloss, however, by adjusting the coating weight and/or nip temperature, acceptably high gloss may be obtained.
• This example illustrates the correlation which exists between the gloss of a paper substrate before and after metallization.
• the dry transfer method described in Part A of Example 3 was repeated by transferring a thermoplastic resin from polyester (coated with 2.5 lb. (1.13 kg.)/ream of the resin) to the 38# ground wood paper. Thereafter the coated papers were vacuum metallized by conventional laboratory methods.
• the resins employed were Resin A (previously described) and Resin S (described below): Resin S - Styrene/butyl acrylate/N-methylol acrylamide/methacrylic acid resin (Tg +40 C.) in aqueous emulsion .
• This example illustrates the effect the Tg of the resin coating to be transferred has on the temperatures and pressures required for lamination in order to practice the dry transfer method of the present invention.
• Resins having Tg's of +5 to +40°C were coated at 2.5 lb (1.13 kg.)/ream on polyester, dried for 2 minutes at 200 F (93°C) and then laminated with 18# paper (18 lb. (8.2 kg.)/ream machine glazed bleached groundwood) employing a Faustel laminator at varying temperatures and pressures. After lamination the polyester transfer film was pulled away from the paper. The transfer efficiency was then evaluated as follows: NT - no transfer PT - partial transfer T - complete transfer The results may be found in Table VIII.
• This example illustrates the recyclable use of a transfer film in the dry transfer process of the present invention.
• PES was coated with 2 lb. (.91 kg.)/ream of Resin A and laminated with the 38# paper at 210°F (99°C) according to the dry transfer process of Example 3. The process was repeated ten times with the same piece of PES used each time. After 10 recycles, no appreciable build up of coating residue was present on the PES and the papers all exhibited acceptably high gloss.
• This example describes the preparation of a high gloss paper substrate by the wet transfer method of the present invention.
• Resin A Resin A containing 7% ethylene glycol momobutyl ether acetate obtained from Union Carbide as Butyl Cellosolve® Acetate.
• the coating weight was 2.5 dry lb. (1.13 kg.) resin/ream.
• a paper substrate was placed on top of the wet resin-coated surface of the transfer film.
• the paper/film laminate was run through a nip roller at 210°F (99°C) according to the procedure of Example 3.
• the three paper substrates as well as the seven transfer films employed are described in Example 1. In all cases the resin coatings were not dried prior to or subsequent to lamination. The gloss results are given in Table IX. In all cases, except where indicated, the transfer film was easily peeled from the paper substrate.
• the transfer film, nip temperature and basis weight of the paper will all affect the optimimum conditions for obtaining a high gloss paper. Given that the process was successful for a resin and one basis weight paper would indicate that by adjusting the lamination conditions, other paper substrates may be successfully coated.
• This example directly compares the gloss of paper substrates coated by the dry and wet transfer coating methods with a given resin.
• transfer film was coated with a resin at a coating weight of 2 lb. (0.91 kg.)/ream.
• the 38# paper substrate was placed on top of the resin-coated PES immediately or after the coating had dried for 2 minutes at 200°F (93°C).
• the paper/film laminate was run through a steel on felt-covered steel nip roller set at 270°F (132°C) and 5000 psi with the uncoated side of the transfer film in contact with the heated steel roll. After exit from the nip, the transfer film was immediately peeled away.
• Resin T was also evaluated: Resin T - Vinyl acetate/vinyl alcohol (Tg +32°C) resin in aqueous emulsion.
• the coating contained 7% of the coalescent Butyl Cellosolve® Acetate.
• this invention is seen to provide high gloss papers suitable for vacuum metallization.

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• 1987
  • 1987-09-23 EP EP87113933A patent/EP0267395A3/de not_active Withdrawn
  • 1987-10-15 AU AU79796/87A patent/AU580725B2/en not_active Ceased
  • 1987-10-15 JP JP25848387A patent/JPS63112792A/ja active Pending

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