FI116087B - Base paper, process for its manufacture and release paper - Google Patents

Description

1 116087

Base paper, process for its manufacture and release paper

The invention relates to a release paper base paper having a backing layer of fibrous material having a surface sizing comprising a binder and a pigment on its release surface. The invention also relates to a release paper having a base paper of the above quality and to a process for making such a base paper.

Release papers are used as backing papers for various labels, whereby they are provided with a release agent, which is a layer of material based on silicone polymers, which is easily detached from the adhesive layer on the surface of the label.

Most of the base paper currently on the market is used for silicon-15 machine coating with a solvent-free silicone system. The increasing popularity of this method has highlighted the importance of the surface properties of the release paper base paper in achieving good siliconized surface quality. Due to its silicone properties, low porosity, low water and oil absorption and high smoothness of the 20-key keys have increased.

The release requirements for release liner base paper are complex due to their wide range of applications and difficult applications. The key (> base paper properties are: strength properties (including after heat treatment), dimensional stability, high density, barrier properties, chemical suitability for silicone, high transparency, low porosity and good smoothness. processing machine, requires little silicone for good silicone coverage, works with laminate: ... '· without any problems in stamping and does not cause any difficulty in labeling.

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In order to improve the quality of the base paper, it is known to provide at least its release agent receiving surface with a suitable material. Thus, U.S. Patent 4,859,511 discloses a layer of a hydrophobic polymer between a base paper and a release agent. Further, it is known to coat base paper with a latex binder-pigment mixture prior to application of the release agent, as disclosed in U.S. Patent No. 4,609,589 (Example No. 47), corresponding to European Patent Application 150,772, International Publication No. WO 96/31651. , and Japanese Patent Application Laid-Open No. 2 116087 JP-6-264038. The surface adhesive of the latter publication contains 100 parts by weight of pigment, 10 to 30 parts by weight of styrene-butadiene latex as a hydrophobic binder and 0.5 to 5 parts by weight of oxidation-modified starch and / or starch phosphate as a hydrophilic binder. The amount of application of the surface adhesive 5 is typically about 3 g per square meter according to the prior art.

A mixture of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) is a commonly used surface adhesive for papers. This has also been used in the surface sizing recipe for release agent 10 receiving base paper. Providing a sealed surface with either a high sealing thin film of adhesive or a large amount of adhesive results in a release liner having good properties. However, it has been found that the PVA / CMC alloy is unable to fill the pores of varying sizes on the surface of the paper.

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It is an object of the invention to provide a new base paper which, by virtue of its surface sizing, has better silicone resinability, meaning a reduction in the amount of silicone required for good silicon machine coverage. The improved properties of the base paper that accomplish this include low porosity and hydrophobicity of the paper.

To accomplish this purpose, the invention is essentially characterized in that the pigmented surface sizing binder comprises at least a mixture of polyvinyl alcohol (PVA) and a latex dispersion. TA; 25 he based blend has achieved, through appropriate interrelationships, "better values in many properties that are important for silicone compatibility.

Y · 'According to a preferred embodiment, the binder also contains carboxymethylcellulose (CMC), preferably 10-50% by weight of the total amount of PVA and CMC, more preferably 15-25% by weight.

Em. binder-based combinations also provide good results. with very small application rates. According to a preferred embodiment, the amount of 35 surface sizing as dry matter is up to 2 g / m 2, preferably 0.7-2.0 g / m 2, more preferably 0.7-1.5 g / m 2, which increases the base paper. Y: economical manufacturing, and transparency remains good.

3, 116087

The invention will now be described with reference to the accompanying drawing, in which Figure 1 is a schematic sectional view of one possible 5 label product in which release paper can be used, and Figure 2 is a schematic sectional view of release paper.

The illustrations are provided to illustrate the scope of the invention, and the relative sizes of their parts are not intended to represent the actual situation.

As shown in Figure 1, the label product consists of a surface paper P having an adhesive layer 4 and a release paper R having a release agent layer 3 facing the adhesive layer 4. Text and / or patterns can be printed on one surface of the surface paper 2 by various printing methods.

Figure 2 shows the base paper 1 of the release paper R for the label product of Figure 1. The base paper 1 has a backing layer 1a, 20 formed of a suitable fibrous raw material, e.g. cellulose-based paper pulp. On top of the base layer 1a, at least on the side receiving the release agent layer, is a surface sizing 1b.

The following describes, by way of example, the process for preparing a label product:. 25 which is not limiting of the invention.

In the manufacture of a label product, the label paper of the label product and the base paper of the release paper are brought to the production line in rolls of a certain width and length.

Iina. The base paper is first coated with a layer of silicone 30 in a roll coating unit, which is polymerized and cured in an oven at 140 ° C. The application rate for Sili-Kon is about 1 g / m2. This produces a release paper having a layer of release agent on its surface. Next, the release paper is coated with an adhesive layer on its siliconized side. Usually the adhesive is'. an aqueous dispersion from which excess water is evaporated in a drier. After drying, the web passes through a wetting unit to achieve a suitable moisture level. The backing paper and the backing paper are laminated together by running them between the rolls which press the layers together. The finished laminate is collected on a roll. The laminate can be further processed 4 116087 in many different ways, such as printing on a printing press. Laminates can also be cut to size labels after printing. A release liner with a release liner can also be brought to the manufacturing line as a finished product and combined with the label product surface paper.

The following are non-limiting tests of the invention.

10 The known PVA / CMC surface adhesive, the known barrier coating for paper and board based packaging materials and mixtures thereof were used in the surface sizing tests. In the first series, known surface adhesive and coating compositions were tested separately, and in the second series, mixtures of these compositions were tested.

15

The known surface adhesive (hereafter surface adhesive) was a water-soluble mixture of polyvinyl alcohol and carboxymethylcellulose (PVA / CMC) with a ratio of PVA to CMC of 80:20 by weight.

The known barrier coating (hereinafter barrier) was a water-based pigment paste for barrier paper and paperboard packaging, the main components being 2 parts by weight of talc and 1 part by weight of a styrene-butadiene-latex dispersion based on dry substance. Additives and excipients are the same as in the paper industry:. . 25 pastas used.

The surface sizing was performed on the paper with a film adhesive press, after which the coating was dried and the paper was calendered.

30 First tests:

The known barrier coating used in the comparative experiments of the first set of experiments gave poorer results e.g. In Bekk porosity, '. 35 IGT stain correlation with surface smoothness and unger oil absorption compared to known surface adhesives at those coatings (less than 3 g / m 2) that can be used without loss of transparency. The poor result of the Unger oil absorption indicates that the silicone is absorbed by 5116087 excess paper. On the other hand, in the shirlastain test, which is commonly used to test the surface hydrophobicity of siliconized papers based on the absorption of an aqueous test solution, the known barrier coating achieved a clear improvement over the known surface adhesive.

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Other tests

Better results were obtained with a topical adhesive composition in which the known topical adhesive and the known barrier coating were mixed in a ratio in which they were equal in dry weight (hereinafter "mixture").

Bekk porosities (s / 100ml) with 1.5 g / m2 coatings:

Surface glue: approx. 190 15 Barrier: approx

900: Approx

Bekk porosities (s / 100ml) with 0.7 g / m2 coatings:

Surface glue: approx. 210 20 Barrier: approx

280: Approx

Unger Oil Absorption (g / m 2) with 1.5 g / m 2 coating amounts:

Surface adhesive: about 0.85 25 Barrier: about 2.5

Mixture: about 0.65

Silicone Absorption (g / m2, Unger test with silicone),: '1.5 g / m2 Coating Amounts: 30 Surface Adhesive: Approx. 0.9

0.7: '': 0.7 g / m2 coating amounts:

Surface Adhesive: 1.0 1.0 35 Mixture: 0.8 6 116087

Shirlastain test (solution absorption g / m2) with 1.5 g / m2 coatings: Adhesive: approx. 16 Barrier: 12

Mixture: Approx. 14 5

Shirlastain test (solution absorbance in g / m2) with 0.7 g / m2 coatings: Adhesive: approx. 18 Barrier approx. 14 Mixture: approx. 15 10 IGT stain length (cm) with 1.5 g / m2 coatings:

Surface Adhesive: Approx. 13.7 Mixture: Approx. 14.1 15 With a 50:50 mixture, there was a clear improvement in oil absorption and a significant improvement in Bekk porosity compared to both references. Similarly, absorption of the shirlastain test fluid was better than known surface adhesive.

In addition, the results were better than the known surface adhesive, with ratios of surface adhesive to barrier ranging from 40:60 to 60:40. Taking into account the compositions of the above materials and the fact that good results at least for some properties can be achieved even outside the above mentioned limits, the amount of pigment in the total adhesive is about 20-45 wt.% And the latex is 20-55 parts by weight. Per 100 parts.

It can be assumed that the components of the composition work together to achieve an op: ·· * 'effect with the PVA / CMC adhesive acting as a film-maker, the fine pigment (preferably having an average particle size of less than 2 µm equivalent (esd)) blocking pores and styrene butadiene. water-sealing:

Other fine micronutrient fillers or mixtures of mineral fillers may be used instead of talc as pigment. The mineral filler is preferably hydrophobic in nature, which is typical of talc. (e.g. US 5,229,094).

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It is also possible to use other homo- and copolymer latex dispersions as a latex binder. Examples are acrylate, styrene acrylate and polyvinyl acetate latexes.

In addition to the latex dispersion and PVA or PVA / CMC blend, the binder component may contain up to 10 wt.% Of the total amount of binder.

The paper surface is made denser and more water resistant by using small amounts of the coating according to the invention, e.g. up to 2 g / m2. Only coatings of about 1 g / m 2 are sufficient to provide sufficient surface properties of the base paper.

The top adhesive mixture may be applied as an aqueous composition in which the latex binder, polyvinyl alcohol, optionally carboxymethyl cellulose, and pigment are well mixed, by suitable coating methods over the backing layer. The backing layer is preferably an uncoated paper made from chemical pulp, e.g. a mixture of softwood pulp and hardwood pulp. With surface sizing, the backing layer can be glued on one side to prevent warping.

The base paper obtained typically has a basis weight of between 50 and 90 g / m2.

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Claims (15)

116087 A release paper base paper having a fibrous material backing layer (1a) having a surface adhesive (1b) comprising a binder and a pigment on the surface thereof, and wherein the pigment-containing binder of the surface adhesive (1b) comprises at least polyvinyl alcohol (PVA) and a latex dispersion. Base paper according to claim 1, characterized in that the binder also contains carboxymethylcellulose (CMC). Base paper according to claim 2, characterized in that the ratio by weight of polyvinyl alcohol to CMC is in the range from 15:50 to 50:90, preferably from 75:25 to 85:15. Base paper according to one of the preceding claims, characterized in that the pigment is talc. Base paper according to one of the preceding claims, characterized in that the amount of pigment is 10-50% by weight, preferably 25-40% by weight, based on the dry weight of the surface sizing (1b). Base paper according to claim 5, characterized in that the amount of pigment is 30-37% by weight. A base paper according to any one of the preceding claims, characterized in that the ratio of the latex dispersion to polyvinyl alcohol or, if the binder contains CMC, to a mixture of PVA and CMC is 20: 100-30 55: 100. Base paper according to claim 7, characterized in that f 1 »; * * ': The ratio is 30: 100-40: 100. »> · * Base paper according to one of the preceding claims, characterized in that the amount of surface sizing (1b) is less than 2 g / m 2, preferably: Y: 0.7-1.5 g / m 2. «* 116087 Base paper according to any one of the preceding claims, characterized in that: It is claimed that the backing layer (1a) is a chemical pulp, e.g. a mixture of softwood pulp and hardwood pulp. ! ? | A base paper according to any one of the preceding claims, characterized in that: Its weight is 50-90 g / m2. A method for producing base paper for release liner (R), wherein the backing layer (1a) of fibrous raw material is surface-bonded with a adhesive containing a binder and a pigment, characterized in that the binder of the surface adhesive comprises at least polyvinyl alcohol (PVA) and a latex dispersion. 13. A method according to claim 12, characterized in that the surface adhesive is prepared by mixing an aqueous mixture of a latex dispersion and a pigment and an aqueous solution of polyvinyl alcohol, optionally also containing carboxymethyl cellulose. Method according to claim 12 or 13, characterized in that the surface adhesive is applied on the backing layer (1a) at a maximum of 2 g / m2, preferably 7-1.5 g / m2. 15. A release paper having a release layer (3) on its surface facing the adhesive layer of the label product, applied to the base paper (1), characterized in that the release layer (3) is applied to one of the preceding claims. -11 (1b). ♦ · 1 * · 116087