FI77183C - Process for finishing color-developing paper - Google Patents

Description

Method for finishing color-developing paper - Förfarande för färdigbehandling av färgframkallande papper 771 83 This method relates to a method for finishing the type of color-developing paper used in pressure-sensitive 5 and, in particular, transfer-type reproduction systems.

In such a transfer system, the topsheet (hereinafter referred to as a CB sheet) is coated on its lower surface with microcapsules containing an oily solution of at least one colorless color-forming agent and the lower sheet (hereinafter referred to as a CF sheet) is coated on its top surface with a color-developing co-reactive agent such as acidic clay, phenolic resin or certain organic acid salts. When more than one copy is desired, one or more intermediate sheets (hereinafter referred to as CFB sheets) coated on the lower surface with microcapsules and on the upper surface with a color-developing co-reactive agent are used. When the sheets are subjected to pressure during writing or typing, the microcapsule-20 liters rupture, releasing the color-forming solution with a color-developing co-reactive agent, which causes a chemical reaction that develops a color former to produce a trace.

One of the main applications of pressure sensitive ice systems is business forms. It is important that the coated paper used for business forms is easy to print and should be easy to handle for easy feeding to a printing or printing machine. In particular, the color-developing paper should be smooth and have a certain stiffness and specific volume to achieve the desired processability.

2 77183

To achieve the required smoothness, the color-developing paper is usually cold calendered (although the calender rolls may become warm as the hot paper web passes between them, such as when the web comes directly from the drying section).

5 However, satisfactory smoothness is often achieved only at the expense of stiffness and specific volume.

It is an object of the present invention to provide a color-developing paper which has excellent smoothness but also good processability.

According to a first object of the present invention, there is provided a method of finishing a color-developing paper for use in a pressure-sensitive annealing system comprising passing a web of paper with a surface layer of an inorganic color-developing co-reactive agent through a nip between two calender rolls. that both calender rolls are heated to a temperature higher than that of the web.

According to another object, the present invention relates to a color-developing paper finished in accordance with the first object.

A third object of the invention is a pressure-sensitive frosting system using color-developing paper finished according to the first object.

The temperature of the calender rolls is preferably at least 50 ° C, most preferably at least 80 ° C and in particular at least 110 ° C. The heating can take place, for example, by means of any of the following media, high-pressure steam, pressurized water or oil. The heating medium can pass either through the central tank 30 in the calender roll or around the annular space 3 77183 in the roll (this type of roll is called a transfer roll and provides a more uniform temperature across the roll).

Suitable rollers can generally be any rolls commonly used in the paper industry, for example hardened iron rolls.

This method is particularly suitable for use in paper in which the color-developing co-reactant is an acid clay or other inorganic substance, but in principle it could alternatively be a phenolic resin or certain organic acid salts, both of which are well known in the pressure sensitive process. therefore not explained in more detail in this context.

The color-developing co-reactant is preferably an acid-washed dioctahedral montmorillonite clay, such as "Silton" sold under the trademark Mizusawa Industrial Chemicals of Japan or ^ Copisil sold under the trademark Siid-Chemie AG of the Federal Republic of Germany.

The color developing coating may further comprise an excipient such as kaolin or calcium carbonate. The coating may also include a binder such as latex.

While the present invention provides improved smoothness without the corresponding deterioration in stiffness and specific volume generally encountered herein, the present invention also provides significant cost savings in that more filler can be added to the base paper, reducing the need for expensive fiber without affecting the color obtained. the stiffness and specific volume of the developing sheet at a certain smoothness.

4 77183 For a better understanding of the present invention, reference is now made to the accompanying drawing, which schematically and by way of example illustrates an embodiment of the invention and schematically shows an apparatus for finishing color-developing paper in a side view.

In general, the paper web is denoted 1 in which the surface 3 is provided with a color-developing agent layer is unwound from a reel 4 to indicate the direction of the arrow and then passes around the guide rollers 2. Thereafter, the web passes between two calender rolls 6. The fish blade rolls are hardened iron and are supplied with high-pressure steam so that their surface temperature is about 105 ° C. The rollers 6 form a pressure nip 9 at their point of contact. The nip 9 is protected by a nip cover 8.

The web 1 then passes around the other two guide rollers 2 before being wound into a roll 5.

Instead of unwinding the paper web from the roll 4, it may alternatively come directly from the coating compartment where it has just been coated and dried on the calender rolls.

The invention is explained in the following by means of an example.

Example

A web of clay-coated color-developing paper ("Idem" CF 57, supplied by Wiggins Teape) was passed through a hot calender nip as shown in the drawing with the coated surface facing down. The surface temperature of the calender rolls was maintained at 105 ° C. The nip pressure was varied as was the speed at which the web passed through the hot calender nip.

At the same time, the control was already performed by passing a similar web through a cold calender nip, whereby the surface temperature of the calender rolls was 18 ° C.

5 77183 The specific volume and stiffness of the paper were then measured to determine the conceptuality of the paper obtained. Bendtsen and Parker roughness were also measured to determine the smoothness of the color-developing coating. Stiffness was measured in Taber-5 units using International Standard (IS) No. 2493 in both the concave direction (MD) and the transverse direction (CD) of the web. The specific volume was measured according to the British standard BS 3983. Bendtsen roughness was measured according to British Standard BS 4420: 1969 for both the surface of a paper web coated with a color-developing agent and the surface of an uncoated paper web.

Parker roughness was measured in the same manner as in the method proposed by the British Paper and Board Industry Federation (BPBIF) No. PP 59.

15 Parker roughness can be measured under different conditions. In this case, Parker roughness was measured on a standard type soft background (Neoprene Litho blanket 85 ° Shore) at a compression pressure of 20 kg / cm. This is shown in the scoreboards under S-20.

20 For both Bendtsen and Parker roughness, a high value indicates a rough surface, i.e. the lower the value the smoother the surface. All values shown are averages from multiple readings. To illustrate that hot calendering does not interfere with the functional properties of the color developing paper, a calender intensity test was also performed. The calender strength test (CI) consisted of placing paper strips coated with an encapsulated dye-forming solution on top of the coated paper strip to be tested, passing the superimposed strips through a laboratory calender to break the capsules to produce color on the test strip, thus dyeing the test strip. Expression of the result (I / IQ) as a percentage of the unused control strip (IQ). That is, the lower the intensity value (I / I0) of the lantern, the stronger the developed color. CI values were recorded after 2 minutes and again after 48 hours.

The results are shown in Table 1, where the nip pressures are reported as linear pressures because it is difficult to report an absolute value, as is well understood.

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It can be seen from the results that the main effect of hot calendering was to reduce the characteristic volume and improve the smoothness at a certain line pressure. Stiffness also increased with a certain smoothness.

5 Hot calendering does not appear to have any significant effect on the functional properties of CF as evidenced by the CI values obtained. The CI values obtained for hot calendered paper do not differ significantly from those obtained for cold calendered paper.

10 Although the results suggest that the absolute values obtained when calendering at 105 ° C would be different from those obtained at 120 ° C, the relative advantages of hot calendering are the same in both cases. These differences are likely due to variations in web moisture content prior to calendering or small variations in basis weight.

Claims (8)

A method for finishing a color-developing paper, for use in a pressure-sensitive copying system, according to which a paper web carrying a coating of an inorganic color-forming co-reacting material is passed through the nip between two calender rolls characterized therefrom, each of the calender rolls. heated to a temperature above the web temperature. 2. A process according to claim 1, characterized in that the temperature of the rollers is above 50 ° C. 3. A process according to claim 2, characterized in that the temperature of the rollers is at least 80 ° C. 4. A process according to claim 3, characterized in that the temperature of the rollers is at least 110 ° C. Process according to claim 1 or 2, characterized in that the color-developing co-reacting material is an acidic clay. Process according to any of the preceding claims, characterized in that the color-developing co-reacting material is an acid-washed dioctahedral montmorillonite. A color-inducing paper which is finished with the method of claim 1. 8. Pressure-sensitive copying system using a color-developing paper which has been finished with the method of claim 1.