ITRM20060004A1 - PROCEDURE FOR THE PRODUCTION OF PATINATED PAPER WITHOUT GLOSSY HIGH WOOD, SPECIFIC AND IMPROVED STAMPABILITY - Google Patents

Description

DESCRIPTION

accompanying a patent application for an invention entitled "Process for the production of glossy woodfree coated paper with high specific volume and improved printability"

The present invention relates to a process for the production of high specific volume glossy woodfree coated paper and improved printability.

In particular, the object of the invention is a process for the production of glossy woodfree coated paper, with the same mechanical characteristics (thickness, stiffness) and paper gloss> = 65 (Caps 480) of a corresponding conventional gloss paper having however a grammage from 10% to 15% higher, without resorting to the aid of polishing machines (calender, brushing machines, etc.), thus managing to solve the problem of the loss of thickness and stiffness of the paper due to the mechanical action to which it is subjected to obtain polishing.

The object of the invention also requires a quantity of virgin cellulosic fibers less than 20-25% and allows you to set the same or higher production speeds of normal glossy coated papers.

The standard procedure for the production of glossy coated paper (gloss) generally includes in addition to the normal phases of preparation of the mixtures and manufacture of the fibrous support, two other subsequent phases such as the coating phase and the finishing phase.

To achieve a glossy finish effect, the paper is generally calendered.

It is known from the state of the art that in general the coating phase has the purpose of smoothing the surface of the fibrous support through the application of different layers of patina and maximizing the printing quality while the subsequent and last processing phase depends on the desired finish of the paper itself.

Therefore assuming a primary role in its simplest form, the patina consists of a dispersion in water of a pigment and an adhesive necessary to bind the pigment particles together and anchor them to the paper support.

The raw materials generally used are calcium carbonate and kaolin (pigments), synthetic latexes and starches as binders, thickeners, optical brighteners, dyes and anti-fermentation agents.

Once the mixture has been prepared, it is applied on the fibrous support, through coating systems commonly known as "coating machines" both mounted in direct succession with the continuous machine (ie the part of the plant that produces the fibrous support) "on line" coating machines, both mounted separately, “off line coating machines”, which allow you to apply one or more layers of coating on each side of the paper web.

Glossy coated paper is currently used mainly due to its properties of surface uniformity and gloss which highlight certain printing details found above all in photographic images.

Among the procedures already known for the production of glossy paper, the one defined as "cast coating" can be distinguished, which allows to obtain a glossy coated paper by applying the patina and subsequent, immediate drying by contact with a chromed and heated cylinder. This method is substantially slower in production than conventional coating processes and normally applied to only one side of the paper. The method allows to obtain very high paper transparencies (normally beyond the normal range in which the glossy coated paper is positioned) with the front of the transparency after printing at the most equal to that of the unprinted paper, therefore with an effective level print yield mediocre.

Another method consists in subjecting the paper, on which the layer (s) of patina has been affixed, to the action of brushing rollers whose surface is made up of horsehair. This allows to obtain a particularly glossy paper (generally higher than the normal market target of wood-free gloss coated papers) while keeping the thickness losses in the calender passage contained (however this cannot be eliminated) to guarantee a surface that is not too delicate that can be damaged. by the action of the bristles of which the cylinders of the brushes are made.

The productivity of these machines is very limited since the speeds allowed by this technique are contained between 200 and 500 m / min.

An alternative system, better known as soft calender, consists of a series of rollers, (from 2 to 6), alternately deformable (soft) and non-deformable (hard), arranged vertically or horizontally, of which the hard ones are made of metal while the soft ones can be of compressed elastomeric or fibrous materials.

The passage of the paper through the rollers produces a compression of the material and leads to a loss of thickness and stiffness of the paper and does not reach the gloss values required for gloss coated papers.

It is a technique comparable to "supercalanders" with the advantage of being online and the disadvantage of not allowing the achievement of adequate gloss values for wood-free gloss coated papers.

The system that adopts the so-called “supercalender” is the most widely used method for the production of wood-free gloss coated paper.

It consists of a series of rollers (from 10 to 14), alternately deformable (soft) and non-deformable (hard) arranged vertically.

Hard rollers are made of metal while soft rollers can be made of elastomeric materials or compressed fibrous materials.

By exerting a pressure and a reciprocal slipping, they allow to orient the particles of the material applied to the paper surfaces during the coating phase, with the result of obtaining a considerably improved specular reflection of light and a high level of smoothness.

It is a process carried out off the machine as the rollers are easily damaged and force frequent machine stops.

The productivity of these machines is lower than that obtainable from a modern coating machine since the calendering speed is lower than that of the coating process.

The passage of the paper through the rollers produces an elevation of the gloss and an excellent sanding but however the major disadvantage of this process is the loss of thickness, stiffness, opacity and whiteness due to the compression action exerted by the rollers. To reduce the intensity of the pressure necessary to obtain the desired effect on the particles constituting the patina layer, alternative systems have been identified over the years that resort to the use of particular thermoplastic materials (e.g. plastic pigments), which having greater polishing of the classic inorganic pigments (kaolin and calcium carbonate) allow to reach higher values of the paper gloss or ultimately require lower pressures for the same gloss obtained, allow to limit the negative effect of the passage in the calender, without, however, for this delete it.

The use of these materials is also very expensive both economically and technologically due to the difficulty of reusing the scraps and production waste within the same production cycle.

It is therefore evident, on the basis of what already exists in the state of the art, the need to be able to have a gloss paper, in the scale of common commercial weights, which guarantees yields in thickness, rigidity, opacity and white unaltered with respect to the characteristics conferred. with the coating and normally impaired in the passage in the calender, and which contributes, avoiding loss of thickness and rigidity, to the saving in the use of fibrous support material and therefore to the reduction of the environmental impact on forest resources, compared to classic gloss papers.

In order to satisfy this need, according to the invention, a process is proposed for obtaining wood-free, glossy, high specific volume coated paper in which the calendering step and therefore the drawbacks connected to it are eliminated, providing instead for the affixing on the support of four successive layers of patina, of specific composition and particularly accurate application system, starting from the third layer of patina.

Therefore, the specific object of the present invention is a process for the production of wood-free coated paper, of the gloss type, comprising the steps of preparing the fibrous support and coating characterized by the fact that said coating step involves the application of four layers successive layers for each side of the paper and that said successive layers constitute the final surface of the paper itself, requiring no further passage through calender means to obtain the required level of surface gloss.

Furthermore, a further specific object of the invention is the glossy coated woodfree paper obtained with the above method.

The formulations use the "% parts" which correspond to the dry quantity of the component in relation to the total dry quantity of pigments present.

Example: if in a formula I have 1000 kg of dry pigments (kaolin carbonates) these correspond to 100 parts%. If I add 100 kg to the dry latex this will correspond to an additional 10 parts%.

The process according to the invention involves the application of successive layers (up to 4) of patina for each of the faces of the fibrous substrate (fibrous support) of the paper, with particular regard to the last two layers.

According to a preferred embodiment of the invention, in table 2 it will be understood:

C60 +: family of products based on calcium carbonate with particle distribution in which at least 60% (starting from 60% onwards) the weight of the particles has an equivalent hydrodynamic diameter of less than 2 pm. Eg. Hydrocarb60®, Hydrocarb75®,

C90 +: a family of products based on calcium carbonate with particle distribution in which at least 90% (starting from 90% onwards) by weight of the particles has an equivalent hydrodynamic diameter of less than 2 pm. Eg. Hydrocarb90®, Hydrocarb99®.

C99 +: a family of products based on calcium carbonate with particle distribution in which at least 99% (starting from 99% onwards) the weight of the particles has an equivalent hydrodynamic diameter of less than 2 pm. Eg, HydrocarbHG®, F-14115®.

Ultrafine clay: a family of kaolins characterized by a particle distribution in which at least 95% by weight of the particles has an equivalent hydrodynamic diameter of less than 2 pm ex. Hydragloss 90®, Amazon 90®.

In fact, according to the invention, the penultimate layer is characterized by the presence of a mixture of "fine" pigments belonging to the C90 + or C99 + class in proportions ranging from 70 to 100 parts%, preferably Hydrocarb 90®, plus percentages ranging from 30 to 0 % of kaolin belonging to the "ultrafine clay" class preferably Hydragloss 90®, Amazon 90®.

Again according to the invention, advantageously the last layer is characterized by the presence of a mixture of "ultrafine" mineral pigments belonging to the C99 + class in proportions ranging from 70 to 100 parts% (natural calcium carbonate, precipitated calcium carbonate) eg. commercial Omya F-14115® plus variable percentages from 30 to 0% of kaolin belonging to the "ultrafine clay" class, preferably Hydragloss 90® which make the surface of the paper sufficiently shiny and smooth to make it fall into the commercial "gloss" type without having to resort to the conventional polishing means discussed above.

According to the invention, the coating process takes place using both roller coating machines (eg GRIC®) and blade coating machines (eg Beloit S-Matic®, Jagenberg CombiBlade®), with both roller (applicator roll) and fountain patina applicators. (eg Jet-flow F®, S-Flow®). The patina leveling phase (doctoring) can be obtained both with a smoothing blade configuration (bent biade) characterized by working angles from 0 + 15 °, and in a scraping blade configuration (stiff biade) typically characterized by an angle greater than 30 °.

The production of this paper requires a review of the parameters and settings (targets) of the production of the fibrous support and of the modalities, quality and quantity of applied coating.

In fact, to obtain the product according to the invention with a final weight of 305 g / m <2>, equivalent to a "standard" product with a weight of 350 g / m <2>, the fibrous support must be reduced from 256 g / m <2 > at 205 g / m <2>; it is foreseen to carry out a succession of 4 layers of patina instead of three and the total quantities of patina applied in the various passages vary. In the product according to the invention, a total of about 90 g / m <2> of patina is applied while previously in the old type 76 g / m <2> of patina were applied, consequently changing the individual quantities applied for each layer of patina.

This global revision is necessary to give the paper, in addition to the necessary qualitative characteristics, a good runnability free from defects such as eg. the presence of lines due to the ever increasing smoothing of the paper from one pass to the next, especially in the application of the last layer. It should be noted that the degree of finish of the third layer of patina is already equivalent to a normal matt coated paper and therefore capable of being marketed "as it is". The choice of the components of the last two layers of patina, especially the pigments, is fundamental for obtaining the final characteristics.

The present invention will now be described for illustrative but not limitative purposes with reference also to the tables and examples reported below.

The process according to the invention consists in preparing an adequate fibrous support in rolls respecting the new weight standards (see tables 1, 2 and 3 and in the examples below) and preparing it for the coating phase which, as reported in the table 2, in a preferred embodiment it adopts a roller system (eg GRIC®) and / or a blade system (eg Beloit S-Matic® or Jagenberg Combi-Blade®) and a wiper type adjustment system / smoothing.

According to a preferred embodiment, the components used in the four subsequent coating steps are those reported in table 2, bearing in mind that the process according to the invention is applied substantially only to examples 1 to 7 while with STD 1, 2, 3 and 4 describes the parameters of conventional gloss paper of different weights and thicknesses treated with the calendering process and used for the comparison of the parameters as shown in table 3.

Table 1: sequence and typology of the coating and calendering processes

Table 2: methods and quantity and quality of the applied patinas

Comparison parameter 1 named STD1

Corresponds to a conventional (normally commercially available) three-coated gloss paper in which a cellulosic fiber support of suitable weight is repeatedly coated on both sides using both roller and blade coating machines (see table 2) with patinas specially designed to obtain the final characteristics of gloss, thickness, stiffness and printability.

Final weight (5.2% humidity) 150 g / m <2>

The passage in the grille includes the following settings:

N ° of rollers 12

No. nip 11

Max speed 500 m / min

Max pressure 130 kg / cm

Temperature 40 ° C

Comparison parameter 2 called STD2

Corresponds to a conventional (normally commercially available) three-coated gloss paper in which a cellulosic fiber support of suitable weight is repeatedly coated on both sides using both roller and blade coating machines (see table 2) with patinas specially designed to obtain the final characteristics of gloss, thickness, stiffness and printability.

Final weight (5% moisture) 250 g / m <2>

The passage in the grille includes the following settings:

N ° of rollers 12

No. nip 11

Max speed 500 m / min

Max pressure 130 kg / cm

Temperature 40 ° C

Comparison parameter 3 called STD3

Corresponds to a conventional (normally commercially available) three-coated gloss paper in which a cellulosic fiber support of suitable weight is repeatedly coated on both sides using both roller and blade coating machines (see table 2) with patinas specially designed to obtain the final characteristics of gloss, thickness, stiffness and printability.

Final weight (5% moisture) 300 g / m <2>

The passage in the grille includes the following settings:

N ° of rollers 12

No. nip 11

Max speed 500 m / min

Max pressure 130 kg / cm

Temperature 40 ° C

Comparison parameter 4 called STD4

Corresponds to a conventional (normally commercially available) three-coated gloss paper in which a cellulosic fiber support of suitable weight is repeatedly coated on both sides using both roller and blade coating machines (see table 2) with patinas specially designed to obtain the final characteristics of gloss, thickness, stiffness and printability.

Final weight (5% moisture) 350 g / m <2>

The passage in the grille includes the following settings:

N ° of rollers 12

No. nip 11

Max speed 500 m / min

Max pressure 130 kg / cm

Temperature 40 ° C

Example 1 called Es 1 Final weight (4.2% humidity) 250 g / m <2>

Example 2 called Es 2 Final weight (4.2% humidity) 215 g / m <2>

Example 3 called Es 3 Final weight (4.2% humidity) 215 g / m <2>

Example 4 called Ex 4 Final weight (4.2% humidity) 215 g / m <2>

Example 5 called Es 5 Final weight (4.5% humidity) 265 g / m <2>

Example 6 called Ex 6 Final weight (4.5% humidity) 305 g / m <2>

Example 7 called Ex 7

Final weight (4.2% moisture) 215 g / m <2>

The data reported in the examples were examined and processed with the following methods:

Weight: ISO 536: 1995 method was used

Dry weight: ISO 287-1985 method was used

Sepssore: the method ISO 534-1988 point 8.2 "sheet thickness" was used

Apparent specific volume: the ISO 534: 1988 method point 10.3.2 "apparent sheet densisty" was used by calculating the reciprocal, that is <1⁄2 / g where 02 is the thickness of the single sheet in pm and g the grammage in g / m < 2>.

Stiffness: The TAPPI 489-om92 method was used.

Paper gloss: TAPPI 480om-92 method was used, using a 75 ° Lehman instrument

Glossy print: the TAPPI 480om-92 method was used, using a Lehman instrument at 75 ° on paper printed for 24 hours with HORIZON MACH2 ICIFICIS BLACK ink on Prufbau Smooth (PPS) machine: the ISO 8791-4 method was used.

Pick resistance: this test gives indications on the resistance of the paper surface to stress during the printing phase. The printing was done on a Prufbau printing machine using a BLACK HORIZON MACH2 ICIFICIS ink, the picking level is visually assessed.

Evaluation criteria: A = no picking; B = light picking; C = high picking.

CO π X ωI co I-

From the analysis of the data summarized in Table 3 it appears that:

1. The calendering of STD1, STD2, STD3, STD4 involves a reduction in thickness of just over 20% compared to the initial value regardless of the initial weight and the number, modality and quality of the applied coating layers.

Consequently, as already widely known in the literature, both the rigidity and the opacity of calendered paper significantly decrease.

2. The Es1 prototype demonstrates that the passage of the last top layer T3 alone without adequate preparation through the previous layers, as in the Es 3, Es 4, Es5 prototypes cannot reach the desired gloss values (> = 65% ) therefore the final layer alone does not allow the achievement of the objectives if not combined with an appropriate preparation of the previous layers.

3. The Es2 prototype demonstrates that just passing the T5 top coat layer with the F-14115 pigment alone without the presence of other specially dosed components fails to meet the requirements.

4. The example prototype Es3 meets all the required requirements.

indeed:

- the thickness of Es3 is the same as that of STD2 even with 35 g / m <2> less

- the stiffness of Es3 is the same as that of STD2 even with 35 g / m <2> less

- the paper gloss of Es3 without pass through the calender is 65% - the print gloss of Es3 of 89% is better in absolute terms and significantly better in relative terms of Delta gloss than STD2

- the dry pick resistance test shows an equivalence between Es3 and STD2

- the smooth PPS value of Es3 is within the normal range for common gloss papers (0.70 -1, 0 pm) 5. The prototype example Es4 meets all the required requirements.

indeed:

- the thickness of Es4 is the same as that of STD2 even with 35 g / m <2> less

- the stiffness of Es4 is the same as that of STD2 even with 35 g / m <2> less

- the paper gloss of Es4 without pass through the calender is 65% - the print gloss of Es4 of 89% is better in absolute terms and significantly better in relative terms of Delta gloss than STD2

- the dry pick resistance test shows an equivalence between Es4 and STD2

- the smooth PPS value of Es4 is within the normal range for common gloss papers (0.70 -1, 0 pm) 6. The example prototype Es5 meets all the required requirements, in fact:

- the thickness of Es5 is the same as that of STD3 even with 35 g / m <2> less

- the stiffness of Es5 is the same as that of STD3 even with 35 g / m <2> less

- the paper gloss of Es5 without pass through the calender is 65% - the print gloss of Es5 of 89% is better in absolute terms and significantly better in relative terms of Delta gloss than STD3

- the dry pick resistance test shows an equivalence between Es5 and STD3

- the smooth PPS value of Es5 is within the normal range relative to common gloss papers (0.70 -1, 0) 7. The example prototype Es6 reaches all the required requirements, in fact:

- the thickness of Es6 is the same as that of STD4 even with 45 g / m <2> less

- the stiffness of Es6 is the same as that of STD4 even with 45 g / m <2> less

- the paper gloss of Es6 without pass through the calender is 65% - the print gloss of Es6 of 89% is better in absolute terms and significantly better in relative terms of Delta gloss than STD4

- the dry pick resistance test shows an equivalence between Es6 and STD4

- the smooth PPS value of Es6 is within the normal range relative to common gloss papers (0.70 -1, 0) 8. The example prototype Es7 meets all the required requirements. indeed:

- the thickness of Es7 is the same as that of STD2 even with 35 g / m <2> less

- the stiffness of Es7 is the same as that of STD2 even with 35 g / m <2> less

- the paper gloss of Es7 without calender pass is 69% - the print gloss of Es7 of 87%

- compared to Es3 it has a better paper gloss development but a lower print gloss development (due to the lower quantities of latex used), so you can adjust the relative ratio between paper gloss and print gloss by varying the quantities of latex between 10 and 16 parts% - dry pick resistance test shows equivalence between Es7 and STD2

- The smooth PPS value of Es7 is within the normal range relative to common gloss papers (0.70 -1, 0). A preferred embodiment of the invention also relates to the paper obtained with the procedure described above. above and equipped with the characteristics of weight, thickness, apparent specific volume, longitudinal stiffness, transverse stiffness, PPS smooth, paper gloss, print gloss, Dry Pick, highlighted in the previous examples and shown in table 3.

Claims (10)

CLAIMS Rev. 1 Process for the production of highly printable glossy woodfree coated paper comprising the step of preparing the fibrous support and the coating step characterized in that said coating step comprises: the application of a first layer of patina on both sides; the application of a second layer of patina on both sides; the application of a third layer of patina on both sides; the application of a fourth layer of patina on both sides; and by the fact that after the application of said fourth layer, the paper is passed to the preparation phase, skipping the calendering phase. Rev. 2 Process according to claim 1 characterized by the fact that said first layer of patina is applied both by means of a roller and blade coating machine with a roller applicator (appiicator roll) with a leveling phase both in a smoothing (bent biade) and scraping (stiff biade) configuration. ). Rev. 3 Process according to claims 1 and 2 characterized in that said second layer of patina is applied both by means of a blade coating machine with roller applicator (appiicator roll) and with fountain applicator (jet flow) with leveling phase and in smoothing configuration ( bent fodder) than scraping (stiff fodder). Rev. 4 Process according to claims 1, 2 and 3 characterized in that said third layer of patina is applied both by means of a blade coating machine with a roller applicator (appiicator roll), and with a fountain applicator (jet flow), e.g., Jet-Flow F ®, Beloit S-Flow®) with leveling phase in both smoothing and scraping configuration. Rev. 5 Process according to claims 1, 2, 3 and 4 characterized in that said fourth layer of patina is applied both by means of a blade coating machine with roller applicator (applicator roll), and with a fountain applicator (jet flow), with leveling both in smoothing (bent biade) and scraping (stiff biade) configuration. Rev. 6 Process according to claims 1 and 3 wherein said first layer of patina comprises a combination of components consisting of a mixture of pigments of the type 100 parts% of C60 +. Rev. 7 Process according to claims 1 and 4 wherein said second layer of patina comprises a combination of components consisting of a mixture of pigments of the 100 parts% C60 + type. Rev. 8 Process according to claims 1 and 4 wherein said third layer of patina comprises a combination of components consisting of a mixture of pigments of the type from 70 to 100 parts% of C90 + and from 30 to 0 parts% of "ultrafine clay". Rev. 9 Process according to claims 1 and 4 wherein said fourth layer of patina comprises a combination of components consisting of a mixture of pigments of the type 70 at 100 parts% of C99 + and from 30 to 0 parts% of "ultrafine clay". Rev. 10 Paper obtained according to claim 1 and having the characteristics of weight, thickness, apparent specific volume, longitudinal stiffness, transverse stiffness, PPS smooth, paper gloss, print gloss, dry pick, as described in table 3.