Printable glazed paper article and its production process

Description

[0001] The present invention relates to a printable glazed paper article and the relative production process.

[0002] The use of glazing compositions for coating the surface of sheets of paper has been known for some time in the paper industry. The glazing compositions are applied to one or both sides of a sheet of paper in order to modify its external appearance, the mechanical properties, the feel and/or to make its surface more suitable for printing processes.

[0003] In the specific field of glazed paper production there is a constant search for compositions and processes which allow the production of paper products, such as paper and cardboard, characterized by new external aspects and/or particular finishings.

[0004] The application of coating glazes known in the state of the art for obtaining a certain aesthetic effect, however, often jeopardizes other qualities of the paper to which the glaze is applied, such as the feel that this can transmit when it is handled or its suitability for printing (printability). In particular, in the case of paper coated with matted glazes (opaque paper), the surface is not smooth and has the disadvantage of a high ink absorbance, giving a low shining printing yield. A further drawback is the high scratchability of the surface of the paper.

[0005] With traditional glazing methods, it is possible to make the lines on opaque paper less visible, by producing less rough glazes which, however, has the disadvantage of being much less opaque and making fingerprints much more evident.

[0006] An objective of the present invention is to overcome the drawbacks of the state of the art.

[0007] A first object of the present invention relates to an printable glazed paper article comprising a paper support in a sheet or bobbin having at least one side coated with a layer of glaze, characterized in that said layer of glaze comprises

a) an organic matting agent,

b) a mineral pigment,

c) a polymeric binder and

in that said side of said support, before being coated with said layer of glaze, has a smooth index ranging from 100 ml/min. to 180 ml/min.

[0008] A second object of the present invention relates to an aqueous-based glazing composition for preparing a printable glazed paper article, said composition comprising

a. an organic matting agent,

b. a mineral pigment,

c. a polymeric binder.

[0009] A further object of the present invention relates to a process for the production of a printable glazed paper article, in a sheet or bobbin, comprising the following operative steps:

i) applying an aqueous-based glazing composition comprising:

a. an organic matting agent,

b. a mineral pigment,

c. a polymeric binder
on at least one side of a paper support in a sheet or bobbin, said side having a smooth index ranging from 100 ml/min to 180 ml/min,

ii) subjecting the paper article obtained in step i) to heating to evaporate the water and fix the layer of glaze onto the paper article.

[0010] The Applicant has surprisingly found that the particular combination of ingredients of the above glazing composition suitably applied to a paper support allows white, black or coloured glazed paper articles to be obtained, which have a surface with a high degree of opacity and at the same time a good printing yield, a pleasant feel, in addition to a good scratch resistance, whereas fingerprints deriving from contact with the hands of the user are almost invisible.

[0011] The paper articles, object of the present invention, comprise a paper support of the type commonly used for graphic printing. The paper support is generally produced in the form of a strip on a continuous machine for paper manufacturing. For the purposes of the present invention, the paper support can be used either in sheets or bobbins. The support preferably has a grammage ranging from 80 g/m² to 400 g/m², more preferably from 110 g/m² to 320 g/m².

[0012] The paper support must have a composition and surface structure as homogeneous as possible.

[0013] The layer of glaze can be present on only one side or on both sides of the paper support.

[0014] Before being coated with the layer of glaze, the side of the support must have a smooth index ranging from 100 ml/min. to 180 ml/min. The best results in terms of opacity and pleasantness of feel, in particular softness, of the surface of the paper article are obtained using a paper support having a smooth index value, determined on its surface before application of the layer of glaze, preferably within the range of 120 ml/min. to 150 ml/min. The smooth index values indicated in the present description are intended as being determined according to the Bendtsen method (method ISO 8791-2).

[0015] Before application of the layer of glaze, the paper support preferably has a water absorption index value lower than 40 g/m², preferably lower than 30 g/m². The water absorption index values in the present description are intended as being determined according to the Cobb method (method ISO 535).

[0016] The layer of glaze which coats the paper support is a homogeneous and uniform layer which is applied by means of industrial glazing processes of paper materials known in the state of the art.

[0017] The layer of glaze which coats the paper support comprises at least one organic matting agent.

[0018] Organic matting agents which can be used for the purposes of the present invention are compounds known in the state of the art and used, for example, in the field of solvent-based or aqueous-based varnishing products. The organic matting agent is preferably selected from the group consisting of polymethylurea, precipitated polyethylene, ground polytetrafluoroethylene (PTFE - Teflon®), micronized polyurethane and/or mixtures thereof. The organic matting agent is more preferably polymethylurea.

[0019] The layer of glaze which coats the paper support also comprises a mineral pigment of the type normally used in the glazing field of paper materials. The mineral pigment is preferably selected from the group consisting of precipitated calcium carbonate, calcined kaolin, talc and/or mixtures thereof. The mineral pigment is more preferably precipitated calcium carbonate.

[0020] A further essential component of the layer of glaze of the paper article, object of the present invention, consists of the polymeric binder. The polymeric binder is preferably selected from styrene-butadiene latex, polyurethane latex, acrylic-vinyl acetate latex and/or mixtures thereof. The polymeric binder is more preferably styrene-butadiene latex or polyurethane latex.

[0021] The above ingredients can be present in the layer of glaze in variable weight ratios depending on the type of aesthetical effect and feel properties to be obtained, and in relation to the colour intensity to be conferred to the surface of the paper article.

[0022] In the layer of glaze of the paper article, object of the present invention, the "a:b:c" weight ratio of the ingredients "a" (organic matting agent), "b" (mineral pigment) and "c" (polymeric binder), in the dry state, varies within the range of 1:1:2 ≤ a:b:c ≤ 1:4:5, more preferably within the range 1:1:3 ≤ a:b:c ≤ 1:3.5:3.5.

[0023] In a first preferred embodiment, the layer of glaze of the paper article object of the present invention comprises:

a) polymethyl urea,

b) precipitated calcium carbonate,

c) polyurethane latex,

in a weight ratio a:b:c, in the dry state, equal to 1:1:3.

[0024] In a second preferred embodiment, the layer of glaze of the paper article, object of the present invention comprises

a) polymethyl urea,

b) precipitated calcium carbonate and/or kaolin,

c) styrene-butadiene latex,

in a weight ratio a:b:c, in the dry state, equal to 1:3.1:3.

[0025] The layer of glaze is carried out on the paper support by means of glazing processes known in the state of the art which comprise the application of a glazing composition on one or both sides of a paper support. The layer of glaze is generally applied to the paper support in bobbin, which at the end of the processings can be cut to produce sheets having the desired dimensions. In the description of the present invention, the terms "bobbin" and "sheet" are therefore used alternatively.

[0026] The application of the glazing composition can be effected by means of a glazing machine of the type known in the state of the art (for example, with an air blade or threaded rod) capable of uniformly distributing layers having a variable thickness of a glazing composition on one or both surfaces of a paper support.

[0027] The glazing composition, object of the present invention, is an aqueous dispersion comprising, in addition to the ingredients described above (organic matting agent, natural pigment and polymeric binder), other possible additive compounds of the type known to experts in the field, such as for example thickening compounds, dispersing agents, insolubilizing agents, wetting agents, dyes, bleaches, pH regulators.

[0028] In order to obtain a uniform layer of glaze on the paper article, it is necessary to use glazing compositions as homogeneous as possible.

[0029] The ingredients of the glazing composition, object of the present invention, are mixed with each other in both the solid state (in granules, flakes or powder) and in the form of solutions or aqueous dispersions, for example, with the help of a high-velocity disperser of the type known to experts in the field.

[0030] The glazing composition preferably has a viscosity varying within the range of 300-500 cps (determined with Brookfield viscosimeters, according to the method ISO 2555) and a dry residue value varying from 30% to 40% by weight with respect to the overall weight of the glazing composition.

[0031] The pH of the glazing solution preferably ranges from 7.5 to 9.5, more preferably from 8 to 9. In order to obtain a glazing composition having the above pH values, it may be necessary to add pH regulator compounds, such as caustic soda or ammonia, to the glazing composition.

[0032] The glazing composition is generally prepared by dispersing the organic matting agent in water. The mineral pigments and a dispersing agent are added to the dispersion thus obtained and mixing is then effected until the total homogenization of the fillers.

[0033] Possible pH regulators, if necessary, thickening compounds and other additives (dyes, insolubilizing agents, etc.) are added to the mixture thus homogenized. Finally, the polymeric binder (latex) is added to the mixture thus obtained, and the mixing is continued until the complete homogenization of the glazing composition.

[0034] The application of the layer of glaze can be effected in the same production line as the paper support, for example, in a processing unit situated at the end of the continuous machine itself which produces the paper support wound in bobbins.

[0035] Before spreading the glazing composition, the paper support can be subjected to possible pretreatment processings such as, for example, calendering, to obtain the most adequate smoothness degree for the surface of the support to be glazed.

[0036] The glazing composition is then spread on a surface of the paper support, or on both of its surfaces, in such a quantity as to have from 5 g/m² to 15 g/m² of glaze, in the dry state, per glazing side.

[0037] The paper support on which a homogeneous and uniform layer of glazing composition has been applied is then subjected to heating in order to evaporate the water contained in the glazing composition and crosslink the polymer binder, thus fixing the layer of glaze to the paper support.

[0038] The heating of the paper support and layer of glaze is preferably effected in two consecutive and continuous heating phases.

[0039] In the first phase (drying), the paper support with the layer of glazing composition applied is heated using a hot air flow at a temperature of about 100-120°C. Heating at this temperature causes the removal of most of the water contained in the glazing composition.

[0040] In the second phase (polymerization), the paper support leaving the first heating phase is heated to a temperature ranging from 250°C to 300°C, in order to complete the evaporation of the water and obtain the cross-linking (polymerization) of the polymeric binder. At the end of this heating phase, the layer of glaze is permanently fixed to the paper support.

[0041] The overall duration of the two heating phases can vary from 5 seconds to 2 minutes approximately, in relation to the quantity of water to be eliminated and the thickness of the layer of glaze applied, in addition to the performance of the drying and polymerization ovens.

[0042] At the end of the second heating phase, the glazed paper article thus obtained is cooled, for example by passage on cooling cylinders of the type generally used in the production industry of glazed paper.

[0043] Once the paper has been cooled, it is available for the subsequent operations, such as for example, winding into rolls (bobbins), cutting and packaging.

[0044] The glazed paper article which can be obtained with the process described above has a Bendtsen smooth index value of the glazed surface varying within the range of 100-240 ml/min, preferably 150-220 ml/min.

[0045] The Cobb index value relating to the water absorption is lower than 25 g/m², preferably lower than 20 g/m², more preferably lower than 18 g/m².

[0046] The glazed paper articles, object of the present invention, can be produced in various colours, white and black. The surface of the layer of glaze has a high opacity degree and contemporaneously a pleasant feel. The specific composition of the layer of glaze, in fact, makes the surface of the article smooth and velvety.

[0047] The particular glazing composition prepared by the Applicant also has the property of guaranteeing a high printing quality with the usual printing techniques known in the state of the art.

[0048] The layer of glaze obtained is scratch-resistant and, if touched with the hands, shows fingerprints less evidently than the highly opaque glazed paper known in the state of the art.

[0049] Furthermore, the surface of the glazed paper article obtained with the present invention has a good sliding degree (low entrainment resistance), which facilitates its preparation on an industrial scale and use in printing.

[0050] The following embodiment examples are provided for purely illustrative purposes of the present invention and should not be considered as limiting the protection scope defined by the enclosed claims.

EXAMPLE 1

[0051] A first deep black glazing composition (CP1) according to the present invention was prepared by mixing the following ingredients in the following weight ratios (parts by weight referring to each component in the dry state)

• Polymethylurea 100
• Precipitated calcium carbonate 100
• Polyurethane latex 300
• Insolubilizing agents 15
• Dispersing and wetting agents 4
• Thickening agents 10
• Ammonia 3
• Black dye (carbon black) 30

[0052] A second white glazing composition (CP2) according to the present invention was prepared by mixing the following ingredients in the following weight ratios (parts by weight referring to each component in the dry state)

• Polymethylurea 100
• Precipitated calcium carbonate 350
• Styrene-butadiene latex 350
• Dispersing and wetting agents 5
• Thickening agents 7
• Ammonia 1
• Optical bleaches 4

[0053] A third ivory-coloured glazing composition (CP3) according to the present invention was prepared by mixing the following ingredients in the following weight ratios (parts by weight referring to each component in the dry state)

• Polymethylurea 100
• Precipitated calcium carbonate 220
• Calcined kaolin 90
• Styrene-butadiene latex 300
• Insolubilizing agents 15
• Dispersing and wetting agents 5
• Thickening agents 6
• Ammonia 1
• Optical bleaches 4

[0054] The compositions CP1, CP2 and CP3 also contain water in such a quantity as to have a dry residue value of the composition equal to 35% by weight and their pH values were regulated to a value of 8.5.

[0055] All of the above glazing compositions were prepared by mixing the ingredients in a high-velocity disperser (of the Kedymill type) until complete homogenization.

[0056] The compositions were applied by means of an air-blade spreading machine on one or both sides of four paper supports having variable grammages from 120 g/m² to 340 g/m².

[0057] Before being coated with the layer of glaze, the sides of the paper supports have a smooth value (Bendtsen) as indicated in the fourth column of Table 1.

[0058] The paper articles obtained were characterized by determining the Bendtsen smooth value and the Cobb index value for the water absorption. The results are indicated in Table 1 below.

TABLE 1

Glazing comp.	Gramm age(*) (g/m2)	Sides coated	Bendtsen Smooth index ml/min(*)	Cobb Index g/m2(*)	Bendtsen Smooth index ml/min(**)	Cobb Index g/m2(**)
CP1	120	1	120	-	170	15
CP1	130	2	120	28	210	15
CP2	260	2	140	-	220	18
CP3	340	2	150	30	210	20

(*) Value determined on the surface of the support (**) Value determined on the surface of the glazed paper article

[0059] All the paper articles of Table 1 had a high opacity degree, a soft surface and a pleasant feel. They also proved to be particularly suitable as supports for high-quality printing.

Claims

1. A printable glazed paper article, comprising a paper support in a sheet or bobbin having at least one side coated with a layer of glaze, characterized in that said layer of glaze comprises

a. an organic matting agent,

b. a mineral pigment,

c. a polymeric binder and

said side of said support, before being coated with said layer of glaze has a smooth index ranging from 100 ml/min. to 180 ml/min.

2. The article according to claim 1, wherein said side of said support, before being coated with said layer of glaze, has a smooth index ranging from 120 ml/min to 150 ml/min.

3. The article according to claim 1 or 2, wherein said paper support has a grammage ranging from 80 to 400 g/m², preferably from 110 to 320 g/m².

4. The article according to any of the previous claims, wherein said side of said support, before being coated with said layer of glaze, has a water absorption index lower than 40 g/m², preferably lower than 30 g/m².

5. The article according to any of the previous claims, wherein in said layer of glaze the weight ratio a:b:c of the dry ingredients varies within the range of 1:1:2 ≤ a:b:c ≤ 1:4:5, more preferably within the range of 1:1:3 ≤ a:b:c ≤ 1:3.5:3.5

6. The article according to any of the previous claims, wherein the organic matting agent a) is selected from the group consisting of polymethylurea, precipitated polyethylene, ground polytetrafluoroethylene, micronized polyurethane and/or mixtures thereof, preferably polymethylurea.

7. The article according to any of the previous claims, wherein the mineral pigment b) is selected from the group consisting of precipitated calcium carbonate, calcined kaolin, talc and/or mixtures thereof, preferably precipitated calcium carbonate.

8. The article according to any of the previous claims, wherein the polymeric binder c) is selected from the group consisting of styrene-butadiene latex, polyurethane latex, acrylic-vinyl acetate latex and/or mixtures thereof, preferably styrene-butadiene latex or polyurethane latex.

9. The article according to any of the claims from 1 to 5, wherein said layer of glaze comprises

d. polymethyl urea,

e. precipitated calcium carbonate,

f. polyurethane latex,

in a weight ratio d:e:f, in the dry state, equal to 1:1:3.

10. The article according to any of the claims from 1 to 5, wherein said layer of glaze comprises

g. polymethyl urea,

h. precipitated calcium carbonate and/or kaolin,

i. styrene-butadiene latex,

in a weight ratio g:h:i, in the dry state, equal to 1:3.1:3.

11. The article according to any of the previous claims, wherein the surface of the glazed side has a smooth index ranging from 100 ml/min to 240 ml/min, preferably from 150 ml/min to 220 ml/min.

12. The article according to any of the previous claims, wherein the surface of the glazed side has a water absorption index lower than 25 g/m², preferably lower than 20 g/m², more preferably lower than 18 g/m².

13. An aqueous-based glazing composition for preparing a printable glazed paper article, said composition comprising

a. an organic matting agent,

b. a mineral pigment,

c. a polymeric binder.

14. A process for the production of a printable glazed paper article, in a sheet or bobbin, comprising the following operative steps:

i) applying an aqueous-based glazing composition comprising:

a. an organic matting agent,

b. a mineral pigment,

c. a polymeric binder

on at least one side of a paper support in a sheet or bobbin, said side having a smooth index ranging from 100 ml/min to 180 ml/min,

ii) subjecting the paper article obtained in step i) to heating to evaporate the water and fix the layer of glaze onto the paper article.