Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G9/00—Other accessories for paper-making machines
  • D21G9/009—Apparatus for glaze-coating paper webs

Definitions

• This invention relates to a process for treating paper and other flexible supports or substrates so as to produce in a single working step a coated product which can be printed by any known processes such as offset, letterpress, intaglio, etc.
• the product also has a very smooth surface and a gloss greater than can be obtained by conventional processes for making stucco paper; also the conventional processes do not provide the same uniformity of coating as does this invention.
• the present process resides in applying to one side or surface the substrate by some conventional means (air blade, rollers, etc.) an aqueous suspension basically comprising one or more mineral pigments, such as kaolin, calcium carbide, satin white and titanium dioxide, and an adhesive such as casein or starch or latex, and While still Wet-i.e., mouldablepressing the coated surface lightly against a heated polished metal surface, such as a cylinder or endless belt, and then allowing it to dry, to produce in the coated surface an exact mirrorimage copy of the polished metal surface on which it dries. It is left in contact with the polished surface long enough to be removed therefrom without tearing.
• aqueous suspension basically comprising one or more mineral pigments, such as kaolin, calcium carbide, satin white and titanium dioxide, and an adhesive such as casein or starch or latex
• the function of the adhesive is to bind the pigment to the substrate and lessen the tendency of the coating to stick to the polished surface during the finishing step. Separation agents can cooperate to the same purpose.
• a synthetic adhesive having elastomeric and thermoplastic properties can be a single resin or a combination of resins; in the latter case, a hard plastic or plastics is usually combined with an elastomer to provide the required flexibility.
• An aim of this invention is to produce a coating composition basically being an aqueous suspension of mineral pigments (kaolin, calcium carbonate, satin white and titanium dioxide) andan adhesive (starch, casein, latex, etc.) from which most of the air introduced during preparation has been removed.
• mineral pigments kaolin, calcium carbonate, satin white and titanium dioxide
• an adhesive starch, casein, latex, etc.
• Another aim of this invention is to provide a method to increase stuccoing operation efi'iciency, more particularly during the phase of drying the water contained in the coating composition.
• Another aim of this invention is to produce, in coating compositions comprising mineral pigments and adhesives, a state of not sticking to a chromium-plated and polished metal surface.
• Another aim of this invention is to provide a stucco paper which when out into sheets presents as a flat surfacei.e., it has no tendency to cockling or corrugate in a manner making it difficult to handle subsequently.
• Another aim of this invention is to provide a coated paper whose specific volume is greater and more uniform than can be achieved by conventional processes.
• a strip of paper or flexible material from a reel goes to a conventional section in which one of its sides has a coating composition applied to it, whereafter, and while the coated paper surface is still wet-i.e., mou1dableit is pressed by a rubber-clothed roller against a polished heated metal surface, such as a cylinder or endless belt; as such surface rotates, the water contained in the coating evaporates and the paper. when sufliciently dry, does not stick to the metal surface, and when the paper spontaneously disengages from the surface it contains a mirror image thereof.
• the coating composition in the tube supplying the applicator section goes through a deaerator of the kind used in the cosmetic paste and cream and foodstuffs industries; a low-speed, low-centrifuged-acceleration and moderate-vacuum device provides from to elimination of the occluded air in the coating composition.
• This step automatically obviates the associated defects in the stuccoed surface of the paper, since the coating composition used is substantially bubble-free in the manner essential for the process.
• a flaw can be produced in the glossy stuccoed surface by any solid particle vehicled along on the uncoated side of the paper or coming from anywhere else in the installation, such as coating composition which has dried on the edges of the metal surface not covered by the paper and which has been deposited on the rubber-clothed roller pressing the paper against the metal surface at the first place of contact. Since it is substantially impossible to prevent such impurities from entering this section, an extra facility which continuously cleans the pressing roller has been used satisfactorily.
• the paper ceases to stick to the metal surface and disengages on its own, so that a mirror image of the metal surface is obtained on the stuccoed surface of the paper.
• the metal surface is a chromiumplated polished material
• the papers manufactured by this process have the disadvantage that when the coating has dried, the coated paper does not completely disengage from the metal surface, some particles of coating being attracted by and sticking tightly to the chromium surface, with detriment to the quality of the paper due to the resulting surface defects.
• Various solutions of the problem were studied but none was fully satisfactory.
• a non-sticking state must be produced in the chromium-plated metal surface; the chromium can exist in an active state--i.e., chemically active and in a neutral state, and it has been found that to ensure that coating compositions including aqueous suspensions of mineral pigments and adhesives do not stick to a chromium-plated metal surface, the same must be in this neutral state--i.e., a state of inertia and inactivity in respect of chemical agents.
• a periodic polishing operation can be given using felt discs to which a paste consisting of a mixture of chromium oxide and fatty substances such as disclosed in Pat. 3,014,833, has been applied.
• Rates of output may vary from 15 to 40 metres/min; endeavours to improve output by increasing the temperature of the metal surface and therefore the drying capacity leads to a reduced tion of quality (less gloss) and the frequent appearance of irregularities in the coated surface, due to the dispersion agent of the coating boiling.
• the improvement according to this invention is to eliminate the vapour buffer arising from evaporation of the water contained in the coating and in the paper moisture content, such vapour accompanying the paper strip during the passage thereof around the metal surface; also, in the zone near the paper there is a vapour-saturated atmosphere which reduces the evaporation rate and impairs drying.
• a stream of hot air is directed on the uncoated side of the paper across the whole width thereof; the stream vehicles away the water vapour accompanying the strip and thus helps to speed up the drying of the coating; output can be improved by from 15 to 25%, according to paper and the applied weight of coating.
• the uncoated side of the paper is treated with a compensating layer in an amount and of a nature depending upon paper weight, the compensating layer basically comprising a solution of natural adhesive mixed with hygroscopic substances which facilitate conditioning of the paper.
• the treatment is given in a special filter press in a way so that the glossy coated surface does not lose any of its properties; such press is disposed in the same machine between the drying section and the rolling section.
• the manufacturing process also comprises further subsequent steps usually performed outside the coating machine;
• the paper goes through glazing or dofrering calenders to give it the required surface finish for presentation and as technically necessary for subsequent use.
• the specific volume is reduced considerably and there is an increased risk of irregularities being formed across and along the paper strip.
• the stucco paper is given its final state in the same coating machine and requires no further finishing step; also, since the water contained in the mineral coating is evaporated through the base paper, the fibres thereof swell and help to increase the specific volume.
• the difference from papers stuccoed by other processes can vary from '15 to 25%, an increase which, taken together with the improved regularity, for the reasons hereinbefore given, represents a considerable advantage in the operations which users of such papers need to perform.
• a process for mould coating a flexible substrate, such as paper, with a pigment and binding composition comprising:

Landscapes

• Paper (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8448252

Family Applications (1)

Country Status (11)

Cited By (1)

• 1968
  • 1968-03-15 ES ES351667A patent/ES351667A1/es not_active Expired
  • 1968-12-18 BE BE725631D patent/BE725631A/xx unknown
  • 1968-12-18 FR FR1602984D patent/FR1602984A/fr not_active Expired
  • 1968-12-30 AT AT1270268A patent/AT301327B/de not_active IP Right Cessation
• 1969
  • 1969-01-06 NO NO00044/69A patent/NO128593B/no unknown
  • 1969-02-21 NL NL6902725A patent/NL6902725A/xx unknown
  • 1969-02-24 BR BR206605/69A patent/BR6906605D0/pt unknown
  • 1969-03-06 US US805014A patent/US3687711A/en not_active Expired - Lifetime
  • 1969-03-09 IL IL31766A patent/IL31766A/xx unknown
  • 1969-03-13 DK DK135669AA patent/DK138705B/da unknown
  • 1969-03-15 GB GB61849/68A patent/GB1267360A/en not_active Expired

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