JP6236353B2 - Multi-layer paper - Google Patents

Description

  The present invention relates to multilayer paper. More particularly, the present invention relates to a multilayer paper that has excellent printability and is not easily torn in a high temperature and humidity environment.

  2. Description of the Related Art Conventionally, paper cards have been used in order to sort or manage machine parts and the like in the manufacturing process of cars and machines. This type of paper card is often used in the form of being inserted into a card insertion part such as a pallet, directly fixed by a clip or the like, or suspended. In the manufacturing process of cars and machines, there are painting process, washing process, hot air drying process, etc., and the working environment is hot and humid, so these paper cards can be used without tearing even in hot and humid environment Needed. At the same time, information necessary for sorting and management is printed on paper cards, and characters, barcodes, designs, etc. are printed by various printing methods such as thermal transfer, letterpress printing, and gravure printing. High surface smoothness is required to satisfy these printability.

  As a paper that can be used without tearing even in a hot and humid environment, Patent Document 1 discloses a wet paper strength agent having an epoxy group in a paper layer, a polyacrylamide-based dry paper strength enhancer, and a filler comprising aluminum hydroxide. Added heat-resistant paper is disclosed. Patent Document 2 discloses a thermal transfer recording paper obtained by smoothing a coated paper with a super calendar as a paper having high surface smoothness. Patent Document 3 discloses a thermal transfer image receiving paper in which husk fibers and straw pulp are blended in a paper layer.

JP-A-7-229088 JP2003-276348 JP 5-32077

  However, although the paper described in Patent Document 1 is satisfactory in water resistance and heat resistance, since the surface layer has too much NBKP, the paper surface has low smoothness, and the thermal transfer method causes printing unevenness such as white spots. In letterpress printing, however, there is a problem in that characters are crushed or missing lines, and in gravure printing, shading unevenness is likely to occur in the printed part. In addition, since the thermal transfer recording paper of Patent Document 2 uses a water-soluble binder such as starch that is easy to adjust to water in the coating layer, it is easy to be curled and corrugated and easily torn in a high-temperature and high-humidity environment. There's a problem. In addition, the thermal transfer image receiving paper of Patent Document 3 is characterized by a unique texture and toughness. However, since a large amount of scabbard fibers are blended, white spots and printing in a thermal transfer system that requires surface smoothness are required. There is a problem that unevenness cannot be suppressed.

  The present invention has been made in view of such problems, and the object of the present invention is to the extent that it is difficult to break even in a high-temperature and high-humidity environment and satisfies printability such as a thermal transfer method, letterpress printing, and gravure printing. An object of the present invention is to provide a multilayer paper having surface smoothness.

  Other objects and effects of the present invention will be easily understood by those skilled in the art by referring to the following description of the present specification.

The multilayer paper of the present invention is a multilayer paper consisting of two or more paper layers containing a pulp as a main component and including a surface layer and a back layer, and 70 to 100 mass of the pulp contained in the surface layer. % Is LBKP, 40 to 70% by mass of NBKP among pulps contained in the entire multilayer papermaking, basis weight is 100 to 300 g / m ² , and a wet paper strength enhancer is included. And

  According to such a configuration, the surface layer has a relatively uniform surface formation, high smoothness, and good surface cushioning, so that it is suitable for printing such as thermal transfer, letterpress printing, and gravure printing. It will have. Moreover, since the total amount of NBKP is relatively large as a whole multilayer paper, it is excellent in strength and can be made into a multilayer paper that is not easily torn even in a high temperature and high humidity environment.

In a preferred embodiment of the present invention, when the surface of the surface layer is pressed against the flat surface of the prism with a pressing pressure of 3.4 MPa, the contact includes a minute non-contact portion having an area of less than 0.16 mm ^2. And a non-contact part having an area of 0.16 mm ² or more, the “total area ratio of the non-contact part” indicating the ratio of the total area of the non-contact part to the measurement part area is 3.0. % May be sufficient.

  According to such a configuration, the surface texture of the surface layer is uniform, the cushioning property of the surface layer is uniform and can be easily crushed, and a multilayer paper having a surface layer having good printability is obtained. It is done.

  In preferable embodiment of this invention, 0.3-2 mass% wet paper strength enhancer may be contained with respect to the pulp of the said multilayer papermaking whole.

  According to such a configuration, the strength of the multi-layered paper as a whole is higher, and the paper can be more difficult to tear even in a high-temperature and high-humidity environment.

In a preferred embodiment of the present invention, at least the surface on the surface side is coated with a coating liquid containing an emulsion binder such as polyacrylamide and / or an acrylate copolymer, and 1 to 2. Size press treatment may be performed in the range of 5 g / m ² .

  According to such a structure, it can be set as the multilayer paper which was excellent in intensity | strength.

  In preferable embodiment of this invention, the range of 300-600 ml (CSF) may be sufficient as the freeness of the pulp mix | blended with the said surface layer.

  According to such a structure, it can be set as the multilayer paper which has high intensity | strength and is hard to tear.

  In a preferred embodiment of the present invention, the tear strength may be 2000 mN or more and the wet tear strength may be 2400 mN or more in the CD direction (lateral direction) of the multilayer paper.

  According to such a configuration, it is possible to make it difficult to tear even in a hot and humid environment, and a multilayer paper having sufficient strength can be obtained.

  The multilayer paper of the present invention is not easily torn even in a hot and humid environment, and can satisfy printing aptitudes such as a thermal transfer system, letterpress printing, and gravure printing.

It is a graph (the 1) which shows the structure of an Example, and a physical-property evaluation result. It is a graph (the 2) which shows the structure of an Example, and a physical-property evaluation result. It is a graph which shows the structure and physical-property evaluation result of a comparative example.

  Hereinafter, the present invention will be described, but the present invention is not construed as being limited to these embodiments.

The multilayer paper of the present invention is a multilayer paper consisting of two or more paper layers containing a pulp as a main component and including a surface layer and a back layer, and 70 to 100 mass of the pulp contained in the surface layer. % Is LBKP, 40 to 70 mass% of the pulp contained in the entire multilayer paper is NBKP, the basis weight is 100 to 300 g / m ² , and a wet paper strength enhancer is included. .

  As the pulp used in the multilayer paper of the present invention, LBKP (hardwood bleached kraft pulp) made of hardwood such as eucalyptus and poplar and NBKP (softwood bleached kraft pulp) made of softwood such as fir and pine are mainly used. Other pulps include chemical pulp such as sulfite pulp (SP), mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP), and non-wood pulp such as straw, bagasse, reed and kenaf. It can be used as long as the effect is not impaired. Moreover, as long as it is a range which does not impair the target effect as LBKP and NBKP, you may use waste paper pulp.

  When comparing LBKP and NBKP, the fibers of LBKP are finer and shorter, so that paper containing a large amount of LBKP tends to have a good texture and surface smoothness, and it is easy to satisfy printability. On the other hand, NBKP has a longer and thicker fiber than LBKP, and thus a paper containing a large amount of NBKP is a paper having a relatively high paper strength. Therefore, in the multilayer paper of the present invention, a relatively large amount of LBKP is blended in the surface layer to improve the surface smoothness of the surface layer and satisfy the printability, while the multilayer paper as a whole has a blending ratio of NBKP. By increasing the height, the structure is excellent in strength and is not easily broken even in a hot and humid environment.

  In the multilayer paper of the present invention, 70 to 100% by mass, preferably 80 to 100% by mass of the pulp to be blended in the surface layer is LBKP. Moreover, 40-70 mass% among the pulp mix | blended with the whole multilayer papermaking, Preferably 50-60 mass% is NBKP.

  When the blending amount of LBKP in the surface layer is less than 70% by mass, there is a possibility that sufficient printability such as printing unevenness and printing unevenness may not be obtained by a thermal transfer method, letterpress printing, gravure printing or the like. If the blending amount of NBKP in the entire multilayer paper is less than 40% by mass, the strength is insufficient, and there is a possibility that it cannot be used in a hot and humid environment. Moreover, when the compounding amount of NBKP in the entire multilayer paper exceeds 70% by mass, a high strength can be obtained, but there is a possibility of adversely affecting the printability of the surface layer.

  The multi-layer paper of the present invention has a structure of three or more layers in which one or more intermediate layers are provided between the surface layer and the back layer, even if it has a structure of two layers consisting of a surface layer and a back layer. Also good. Further, the surface layer, the back layer, and the intermediate layer may have different thicknesses and basis weights.

  As described above, the multilayer paper according to the present invention increases the ratio of LBKP in the pulp to be blended in the surface layer to 70 to 100% by mass, while the multilayer paper as a whole contains the pulp to be blended. Among them, 40 to 70% by mass of NBKP makes it possible to achieve both printing suitability and tear strength. For this reason, if it is a two-layer structure of the front layer and the back layer, it is necessary to increase the ratio of NBKP in the back layer, and if it is a configuration consisting of a surface layer, a back layer, one or more intermediate layers, The above conditions can be satisfied by increasing the ratio of NBKP between the intermediate layer or the back layer and the intermediate layer. In the case of a two-layer structure consisting of a surface layer and a back layer, increasing the basis weight of the back layer compared to the surface layer makes it easier to control the proportion of NBKP blended in the entire multilayer paper, It becomes easy to secure the strength of the entire paper. Moreover, when it is set as the structure of three or more layers which consist of a surface layer, a back layer, and an intermediate | middle layer, it is good also as a different raw material for each of a surface layer, a back layer, and an intermediate | middle layer. The NBKP blending amount of the entire multilayer paper may be adjusted by adjusting the raw material blending and basis weight of the intermediate layer. In addition, when the front layer and the back layer are made of the same raw material, both the front and back surfaces have high smoothness and can be a multilayer paper that satisfies printability.

The basis weight of the multilayer paper of the present invention is 100 to 300 g / m ² . When the basis weight is less than 100 g / m ² , the strength of the multilayer paper as a whole is insufficient and cannot be used in a hot and humid environment. On the other hand, if the basis weight exceeds 300 g / m ² , the thickness increases, making it difficult to pass paper with a printer.

Moreover, although the basic weight for each surface layer, back layer, and intermediate layer is not particularly limited, the basic weight of the surface layer is preferably 35 g / m ² or more. When the basis weight of the surface layer is less than 35 g / m ² , the influence of the surface property of the back layer or the intermediate layer tends to appear on the surface layer, and the smoothness of the surface of the surface layer is lowered, which may lead to deterioration of printing suitability. The upper limit of the basis weight of the surface layer is not particularly limited, but it is generally considered that it is generally up to about 180 g / m ² . In addition, when the back layer is made of the same raw material as the surface layer and the back layer also has printing suitability, the basis weight of the back layer is preferably 35 g / m ² .

  Although the freeness of the pulp mix | blended with a surface layer is not specifically limited, It is preferable to set it as 300-600 ml (CSF). By setting the freeness within this range, the surface smoothness of the surface layer can be increased. If it is less than 300 ml (CSF), the cushioning property of the paper surface layer is lowered, and the printability may be impaired. If it exceeds 600 ml (CSF), the smoothness of the surface may decrease. The freeness of the pulp blended in the back layer or intermediate layer is not particularly limited, and can be set according to the desired paper strength and the like. Preferably, it is 300 to 700 ml (CSF).

  In the present invention, it is preferable to increase the smoothness of the surface of the surface layer in order to increase the printability. Here, the smoothness of the paper surface is defined by the non-contact area ratio at the time of constant pressurization. The smoothness of the surface of the surface layer is defined by the non-contact area ratio at constant pressure. This measurement method makes it easier to reproduce the smoothness during printing such as thermal transfer, letterpress printing, and gravure printing. This is because the surface state can be grasped more directly than the so-called air leak method smoothness measurement method such as surf (PPS) or Beck smoothness. Here, PST2600 (manufactured by FIBRO system AB) was used as a means for measuring the non-contact area ratio at the time of constant pressurization, and the clamping time was set to 1.0 seconds as a measurement condition. Hereinafter, the measurement method will be described.

First, the paper is clamped by the prism and the backing plate at a specific clamping pressure (pressing pressure) and a specific time (the pressing pressure is 3.4 MPa and the clamping time is 1.0 second). Next, light is applied to the surface of the paper obliquely from above through a prism pressed against the surface of the paper, and the reflected light is read by the upper CCD camera. Then, the contact / non-contact portion between the prism surface and the paper surface is calculated from the measured image by the dedicated image analysis platform and dedicated program of PST2600 attached to a commercially available personal computer. Here, the contact portion is a portion where the area of the micro non-contact portion between the prism surface and the paper surface is less than 0.16 mm ² , and the non-contact portion is the area of the micro non-contact portion between the prism surface and the paper surface. It is a portion of 0.16 mm ² or more. Since the non-contact portion is classified according to the area, data correlating with the lack of the image portion due to poor walling can be obtained. If there are many non-contact portions with a large area, the printing ink is difficult to fix and tends to cause chipping of the print portion. Based on the above principle, it is possible to perform surface state measurement more directly than the so-called air leak method smoothness measurement method. In the present invention, the “total area ratio of the non-contact portion (hereinafter sometimes referred to as“ MA value ”)” indicating the ratio of the total area of the non-contact portion to the measurement portion area is the measurement portion area (10 mm). × 13 mm) is the ratio of the total area of non-contact portions having an area of 0.16 mm ² or more, and is obtained from the following (Equation 1).
MA value [%] = (total area of non-contact part having an area of 0.16 mm ² or more [mm ² ] ÷ measurement part area [mm ² ]) × 100 (Equation 1)
In Equation 1, the measurement part area is an area of an actual measurement part to which light is applied in the pressing surface of the prism. The measurement conditions are a pressing pressure of 3.4 MPa and a clan pink time of 1.0 seconds.

  The fact that there are few non-contact parts between the prism and the paper surface when pressure is applied also means that there are few non-contact parts between the head and the paper surface during printing, and printing pressure is applied to the head for gravure printing and letterpress printing. This means that the printing method is high in printability. That is, if the cushioning property (elasticity) of the paper surface is good and there are few non-contact parts when pressure is applied, even if the smoothness in the normal state is low, the unevenness of the paper surface is reduced in the state where printing pressure is applied, Good printing suitability can be obtained for gravure printing and letterpress printing. For example, newsprint paper has low smoothness on the paper surface, but because of its cushioning property, printing suitability by letterpress printing is good.

  In the multilayer paper of the present invention, the MA value obtained by the above (Equation 1) is preferably less than 3.0%. If the MA value is less than 3.0%, the formation of the surface layer and the cushioning property of the surface layer are uniform, and the unevenness of the surface of the paper is reduced when printing pressure is applied. It can be a surface layer. On the other hand, when the MA value is 3.0% or more, there are many large dents on the surface of the surface layer, and sufficient printability such as printing unevenness and printing unevenness is caused by the thermal transfer method, letterpress printing, gravure printing and the like. May not be obtained. In addition, as a control method of MA value, the method of performing a calendar process, selecting a pulp, preparing so that it may become a bulky paper etc. can be considered.

  In the present invention, the specific means for setting the MA value to less than 3.0% is not particularly limited, but examples thereof include a method of calendering multilayer paper. Since the multilayer paper of the present invention contains 70-100% by mass of LBKP in the surface layer, the surface smoothness of the surface layer can be made relatively high, but a soft calender treatment is performed at the time of making the multilayer paper. For example, the MA value can be made less than 3.0%. When the multilayer paper of the present invention has a structure of three or more layers and the raw material for the surface layer and the back layer is the same, the MA values of the surface of the surface layer and the surface of the back layer are both less than 3.0%. It is also possible to do. In this case, a multilayer paper having good printability on both the front and back sides can be obtained.

  The multilayer paper of the present invention has a tear strength in the CD direction (transverse direction) of 2000 mN or more and a wet tear strength in the CD direction (transverse direction) in consideration of the difficulty of tearing in a high temperature and humidity environment. Is preferably 2400 mN or more. A multilayer paper that satisfies these conditions is guaranteed to have sufficient tear strength even under high-temperature and high-humidity environmental conditions. The method of setting the tear strength to 2000 mN or more is not particularly limited, and can be achieved by using 40 to 70% by mass of NBKP among the pulp contained in the entire multilayer paper described above. This can be achieved more easily by using a paper strength enhancer and / or an external paper strength enhancer.

Here, as the internal paper strength enhancer, polyvinyl alcohol, cationic starch, amphoteric starch, cationic polyacrylamide, amphoteric polyacrylamide, carboxymethylcellulose, graft-polymerized starch and the like can be used. Examples of the external paper strength enhancer include various polyvinyl alcohols, cellulose derivatives such as hydroxyethyl cellulose and carboxymethyl cellulose, polyacrylamide, polyethylene oxide, polypropylene oxide, starch, modified starch, polyacrylic acid, sodium polyacrylate, and casein. Water-soluble binder such as polyethylene, polypropylene, polyisobutylene, polystyrene, polyacrylamide, ethyl polyacrylate, polymethyl methacrylate, polyacrylonitrile, polybutadiene, polyisoprene, polyethylene terephthalate, melamine resin, epoxy resin, alkyd resin, unsaturated Polyester resin, styrene-butadiene copolymer, modified styrene-butadiene copolymer, acrylonitrile-butadiene copolymer Body, an emulsion type binder such as a methyl methacrylate-butadiene copolymer, an acrylate ester-methacrylate ester copolymer, or an urethane resin binder that is an emulsion type. It can be applied or impregnated using a size press, a gate roll coater or the like. Among these, it is preferable to externally add an emulsion type binder such as polyacrylamide and / or an acrylate copolymer for the purpose of increasing the internal bond strength. If it is applied by a size press, it is preferably applied in the range of 1 to 2.5 g / m ² per side in terms of solid content.

Further, the method of setting the wet tear strength to 2400 mN or more is not particularly limited, but it is preferable to use a wet paper strength enhancer. As the wet paper strength enhancer, polyamide-polyamine epichlorohydrin resin, urea-formaldehyde resin, epoxidized polyamide resin, melamine-formaldehyde resin, urea-formaldehyde resin, etc. can be used, and among these, polyamine epichlorohydrin-based wet paper strength It is preferred to use an enhancer. As an example, when the multilayer paper of the present invention has a basis weight of 200 g / m ² , the polyamine epichlorohydrin-based wet paper strength enhancer is 0.3 to 2 mass based on the pulp of the entire multilayer paper. By making it contain in%, the wet tear strength can be easily made 2400 mN or more.

  The tear strength and wet tear strength can also be improved by adjusting the freeness of the pulp blended in the back layer or intermediate layer. The drainage degree of the pulp is preferably 300 ml (CSF) or more. When the freeness is less than 300 ml (CSF), the bond between fibers becomes strong, but the strength of the pulp itself becomes weak, which is not preferable. If the freeness of the pulp is 300 ml (CSF) or more, the strength of the pulp itself can be maintained, so that it becomes easy to set the tear strength to 2000 mN or more and the wet tear strength to 2400 mN or more.

  In addition to pulp and the above-mentioned paper strength enhancer and wet paper strength enhancer, the multilayer paper of the present invention includes a filler, a sizing agent, a bulking agent, a yield improver, a drainage improver, a sulfuric acid band, and a coloring dye. Various auxiliary agents such as a color pigment, a fluorescent brightening agent, a fluorescent decoloring agent, a pH adjusting agent, an antifoaming agent, a pitch control agent, and a slime control agent can be contained as necessary. Here, when adding a sizing agent, it is preferable to add in 0.05-0.5 mass% with respect to 100 mass% of pulp. In addition, various surface paper strength agents such as starch, polyvinyl alcohol, polyacrylamide, and surface sizing agents such as rosin sizing agents, synthetic sizing agents, and neutral sizing agents can be applied using a two-roll size press, a gate roll coater, etc. It may be impregnated.

  The method for producing the multilayer paper of the present invention is not particularly limited, and a known paper making method such as a circular net paper machine, a long net paper machine, a short net paper machine, or an inclined wire paper machine can be used.

  The multilayer paper of the present invention can be subjected to a calendar process. Various printability can be improved by performing calendar processing to further increase the smoothness of the surface. In particular, in printing by the thermal transfer method, printing unevenness such as white spots is suppressed. The calendar processing method for the multi-layer paper is not particularly limited, and a known calendar processing method can be used, and a multi-stage calendar such as a machine calendar or a super calendar, a soft calendar, or the like can be used. . The linear pressure at the time of calendar processing is not particularly limited, but if it is a machine calendar, the linear pressure is 50-100 kg / cm at 3 nips (3 passes), and 2 nips (2 passes) if it is a soft calendar. The linear pressure is preferably about 50 to 100 kg / cm.

  Examples of the multi-layer paper according to the present invention will be specifically described below, but the present invention is not limited to these examples. In the examples, “parts” and “%” indicate “parts by mass” and “% by mass” in dry solids unless otherwise specified.

Example 1
<Preparation of surface paper>
100 parts of LBKP (freeness 500 ml CSF) is dispersed in water to obtain a pulp slurry. To this pulp slurry, 0.5 part of talc (manufactured by Taihei Talc Co., Ltd.) is used, and an alkyl ketene dimer sizing agent (trade name: SE-2360). 0.1 parts by Seiko PMC) and 0.5 parts polyamine epichlorohydrin resin (trade name: WS-4010, produced by Seiko PMC) as a paper strength enhancer were added to prepare a surface stock. .
<Preparation of backing material>
100 parts of LBKP (freeness 500 ml CSF) is dispersed in water to obtain a pulp slurry. To this pulp slurry, 0.5 part of talc (manufactured by Taihei Talc Co., Ltd.) is used, and an alkyl ketene dimer sizing agent (trade name: SE-2360). 0.1 parts of Seiko PMC) and 0.5 parts of polyamine epichlorohydrin resin (trade name: WS-4010, Seiko PMC) as a paper strength enhancer are added to prepare a backing paper stock. did.
<Preparation of middle layer paper stock>
100 parts of NBKP (freeness 500 ml CSF) is dispersed in water to obtain a pulp slurry. To this pulp slurry, 0.5 part of talc (manufactured by Taihei Talc Co., Ltd.) is used, and an alkyl ketene dimer sizing agent (trade name: SE-2360). 0.1 parts by Seiko PMC) and 0.5 parts polyamine epichlorohydrin resin (trade name: WS-4010, produced by Seiko PMC) as a paper strength enhancer were added to prepare an intermediate layer stock. .
<Making of multi-layer paper>
Using the above three types of paper stock, a four-ply paper making was performed with a circular net type paper machine so as to have a surface layer / middle layer / middle layer / back layer structure to obtain a multi-layer paper. At the time of papermaking, a double roll size press is used to apply a 6.0% aqueous solution of a modified polyacrylamide resin (trade name: ST-5000, manufactured by Seiko PMC) as an external paper strength agent to both sides of the multilayer paper. After coating and drying so as to be 40 ml / m ² , calendering was performed under conditions of 4 steps, 3 nips, and a linear pressure of 100 kg / cm. The basis weight of each layer are each 50 g / m ^2, the basis weight of the multilayer-made paper was 202.4g / m ^2.

(Example 2)
In the preparation of the surface layer and the back layer, the composition of the pulp was changed from 100 parts LBKP (freeness 500 ml CSF) to 20 parts NBKP (freeness 500 ml CSF) and 80 parts LBKP (freeness 500 ml CSF). A multilayer paper was obtained in the same manner as in Example 1.

(Example 3)
In the preparation of the stock for the front and back layers, the composition of the pulp was changed from 100 parts of LBKP (freeness 500 ml CSF) to 30 parts of NBKP (freeness 500 ml CSF) and 70 parts of LBKP (freeness 500 ml CSF). Example 1 except that the surface layer / middle layer / back layer was formed by combining three layers and the basis weight of the surface layer and the back layer was 50 g / m ² and the basis weight of the middle layer was 100 g / m ^2. In the same manner, a multilayer paper was obtained.

Example 4
A multilayer paper was obtained in the same manner as in Example 2 except that the basis weight of the surface layer and the back layer was 38 g / m ² and the basis weight of the middle layer was 62 g / m ² .
(Example 5)
In the preparation of the middle layer stock, the composition of the pulp was changed from 100 parts NBKP (freeness 500 ml CSF) to 60 parts NBKP (freeness 500 ml CSF) and 40 parts LBKP (freeness 500 ml CSF), and the basis weight of the surface layer and the back layer was 35 g / and m ^2, and obtain a multilayer paper making paper, except that the basis weight of the middle layer were respectively 65 g / m ² in the same manner as in example 2.

(Example 6)
In the preparation of the middle layer paper, the pulp composition was changed from 100 parts of NBKP (freeness 500 ml CSF) to 60 parts of NBKP (freeness 500 ml CSF) and 40 parts of LBKP (freeness 500 ml CSF). I got paper.

(Example 7)
In the preparation of the surface and back layer stocks, the pulp composition was changed from 100 parts LBKP (freeness 500 ml CSF) to 10 parts NBKP (freeness 500 ml CSF) and 90 parts LBKP (freeness 500 ml CSF). was a 35 g / m ^2, to obtain a multi-layer made paper basis weight of the middle layer except that the 40 g / m ^2, respectively in the same manner as in example 1.

(Example 8)
A multilayer paper was obtained in the same manner as in Example 1 except that the basis weight of the surface layer and the back layer was 45 g / m ² and the basis weight of the middle layer was 45 g / m ² .

Example 9
In the preparation of the back layer stock, the composition of the pulp was changed from 100 parts LBKP (freeness 500 ml CSF) to 50 parts NBKP (freeness 500 ml CSF) and 50 parts LBKP (freeness 500 ml CSF). Multi-layer papermaking was carried out in the same manner as in Example 2 except that paper was formed by two-layer papermaking so as to form the back layer, the basis weight of the surface layer was 60 g / m ² , and the basis weight of the back layer was 160 g / m ^2. I got paper.

(Example 10)
In the preparation of the surface layer and the back layer, the composition of the pulp was changed from 100 parts of LBKP (freeness 500 ml CSF) to 15 parts of NBKP (freeness 500 ml CSF) and 85 parts of LBKP (freeness 500 ml CSF). The composition of the pulp was changed from NBKP (freeness 500 ml CSF) 100 parts to NBKP (freeness 500 ml CSF) 65 parts, LBKP (freeness 500 ml CSF) 35 parts, the surface layer basis weight was 65 g / m ² , and the middle layer basis weight was 125 g / m. m ^2, and obtain a multilayer paper making paper except that the basis weight of the backing layer and 60 g / m ² in the same manner as in example 3.

(Example 11)
The basis weight of the surface layer and the back layer is 30 g / m ² , the basis weight of the middle layer is 90 g / m ^2, and the three layers are laminated by a circular net type paper machine so that the structure of the surface layer / middle layer / back layer is obtained. A multilayer paper was obtained in the same manner as in Example 1 except that the paper was made.

(Comparative Example 1)
In the preparation of the surface layer and the back layer, the composition of the pulp was changed from 100 parts of LBKP (freeness 500 ml CSF) to 40 parts of NBKP (freeness 500 ml CSF) and 60 parts of LBKP (freeness 500 ml CSF). A multilayer paper was obtained in the same manner as in Example 1 except that the composition of the pulp was changed from 100 parts NBKP (freeness 500 ml CSF) to 40 parts NBKP (freeness 500 ml CSF) and 60 parts LBKP (freeness 500 ml CSF).

(Comparative Example 2)
In the preparation of the surface layer and the back layer, the composition of the pulp was changed from 100 parts of LBKP (freeness 500 ml CSF) to 60 parts of NBKP (freeness 500 ml CSF) and 40 parts of LBKP (freeness 500 ml CSF). A multilayer paper was obtained in the same manner as in Example 1 except that the composition of the pulp was changed from 100 parts NBKP (freeness 500 ml CSF) to 60 parts NBKP (freeness 500 ml CSF) and 40 parts LBKP (freeness 500 ml CSF).

(Comparative Example 3)
In the preparation of the middle layer paper, the pulp composition was changed from 100 parts NBKP (freeness 500 ml CSF) to 40 parts NBKP (freeness 500 ml CSF) and 60 parts LBKP (freeness 500 ml CSF). I got paper.

(Comparative Example 4)
In the preparation of the middle layer paper, the pulp composition was changed from 100 parts NBKP (freeness 500 ml CSF) to 50 parts NBKP (freeness 500 ml CSF) and 50 parts LBKP (freeness 500 ml CSF). I got paper.

(Comparative Example 5)
In the preparation of the surface layer and the back layer, the composition of the pulp was changed from 100 parts of LBKP (freeness 500 ml CSF) to 40 parts of NBKP (freeness 500 ml CSF) and 60 parts of LBKP (freeness 500 ml CSF). The composition of the pulp was changed from 100 parts NBKP (freeness 500 ml CSF) to 85 parts NBKP (freeness 500 ml CSF) and 15 parts LBKP (freeness 500 ml CSF), and the basis weight of the surface layer and the back layer was 25 g / m ² , respectively. A multilayer paper was obtained in the same manner as in Example 3 except that the amount was 150 g / m ² .

(Comparative Example 6)
A multilayer paper was obtained in the same manner as in Example 1 except that the pulp composition was changed from 100 parts NBKP (freeness 500 ml CSF) to 100 parts LBKP (freeness 500 ml CSF) in preparation of the middle layer paper stock.

(Comparative Example 7)
A multilayer paper was obtained in the same manner as in Example 1 except that the pulp composition was changed from 100 parts of LBKP (freeness 500 ml CSF) to 100 parts of NBKP (freeness 500 ml CSF) in the preparation of the surface layer and the back layer. .

(Comparative Example 8)
In the preparation of the surface layer stock, the composition of the pulp was changed from 100 parts LBKP (freeness 500 ml CSF) to 35 parts NBKP (freeness 500 ml CSF) and 65 parts LBKP (freeness 500 ml CSF). The blending was changed from 100 parts of LBKP (freeness 500 ml CSF) to 70 parts of NBKP (freeness 500 ml CSF) and 30 parts of LBKP (freeness 500 ml CSF). Paper making was performed by combining, and a multilayer paper was obtained in the same manner as in Example 1 except that the basis weight of the surface layer was 80 g / m ² and the basis weight of the back layer was 150 g / m ² .

  The multilayer papers obtained in Examples 1 to 11 and Comparative Examples 1 to 8 were conditioned under conditions of 23 ° C. × 50% RH, and then the tear strength, wet tear strength, thermal transfer printing suitability by the following methods. The printability was evaluated. The results are shown in FIGS. 1 to 3, “N” in the “pulp blend ratio” column indicates NBKP, “L” indicates LBKP, and “N blend ratio in all layers” accounts for pulp contained in all layers. The percentage of NBKP is shown.

<Tear strength>
In accordance with JIS P8116, the CD direction (lateral direction) of the paper was measured.
<Wet tear strength>
The sample was immersed in water at 20 ° C. for 5 minutes and then measured in the CD direction (lateral direction) of the paper according to JIS P8116.

<Thermal transfer aptitude>
Using a thermal transfer printer (MD5500, manufactured by ALPS), an arbitrary design was printed on the surface of the surface layer, and the printing unevenness was visually evaluated.
◎ Excellent with no printing unevenness such as white spots and passed.
○ There are few printing unevenness such as white spots and it passes.
△ In rare cases, the print is missing, but there is little uneven printing such as white spots, and it passes.
× Printing unevenness such as white spots is noticeable and rejected.

<Printability (MA value)>
The MA value of the surface of the surface layer was measured using PST-2600 (manufactured by FIBRO System AB).
Measurement conditions: clamping pressure 3.4 MPa, unit% (non-contact area ratio after 1 second of measurement time)

As is clear from the results shown in FIGS. 1 and 2, the multilayer papers obtained in Examples 1 to 10 are all excellent in thermal transfer suitability and good because the MA value is less than 3.0%. Presumably having printability. Further, the tear strength and the wet tear strength were sufficient, and the strength was not easily torn even in a high temperature and high humidity environment. The multilayer paper obtained in Example 11 had a MA value of 3.1% because the basis weight of the surface layer was relatively low at 30 g / m ^2, and the thermal transferability was slightly inferior, It was possible. From a comparison between Examples 1 to 10 and Example 11, it is presumed that the MA value is preferably less than 3.0 from the viewpoint of thermal transfer suitability.

  On the other hand, as shown in FIG. 3, the multilayer papers obtained in Comparative Examples 1, 2, 5, 7, and 8 have a poor surface texture due to the small amount of LBKP in the surface layer. It became uniform and the MA value was 3% or more, so that the surface cushioning property was inferior and the thermal transfer suitability was not satisfactory. On the other hand, the multi-layer papers obtained in Comparative Examples 3, 4, and 6 have insufficient NBKP content in all layers, so that sufficient strength cannot be obtained and tear strength and the like are reduced. For this reason, there is a possibility that problems such as tearing may occur when used in a hot and humid environment.

  Since the multilayer paper according to the present invention has high strength and printability, it can be suitably used without being torn even in a high-temperature and high-humidity environment such as a car or machine manufacturing process. .

Claims (5)

A multilayer paper made of two or more paper layers containing pulp as a main component and including a surface layer and a back layer,
70-100 mass% of the pulp contained in the surface layer is LBKP,
40 to 70 mass% of the pulp contained in the entire multilayer paper is NBKP,
At least the surface on the surface side is subjected to size press treatment in the range of 1 to 2.5 g / m ² per side using a coating liquid containing polyacrylamide and / or acrylate copolymer as an emulsion type binder. Is given,
A multi-layer paper having a basis weight of 100 to 300 g / m ² and containing a wet paper strength enhancer. When the surface of the surface layer is pressed against the flat surface of the prism with a pressing pressure of 3.4 MPa, a contact portion including a minute non-contact portion having an area of less than 0.16 mm ^{2 and} an area of 0.16 mm ² or more The total area ratio of the non-contact portion, which indicates the ratio of the total area of the non-contact portion to the measurement portion area, is less than 3.0%. Item 2. The multilayer paper according to item 1.   The multilayer papermaking according to claim 1 or 2, wherein a wet paper strength enhancer of 0.3 to 2% by mass is contained with respect to the pulp of the whole multilayer papermaking. The multi-layer paper according to any one of claims 1 to 3 , wherein the freeness of the pulp blended in the surface layer is in the range of 300 to 600 ml (CSF). The multilayer papermaking according to any one of claims 1 to 4 , wherein the tearing strength is 2000 mN or more and the wet tearing strength is 2400 mN or more in the CD direction (lateral direction) of the multilayer paper. paper.

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