JP7765236B2 - Patterned paper and its manufacturing method - Google Patents

Description

The present invention relates to patterned paper and its manufacturing method.

One type of handmade washi paper is a patterned paper called Unryu paper, which incorporates long fibers such as kozo. Industrially, machine-made "rayon paper" is produced to resemble the texture of handmade Unryu paper. Rayon paper is made from a mixture of bleached kraft pulp and rayon fiber, to which a binder such as polyvinyl alcohol (PVA) is added.

For example, Patent Document 1 describes Unryu paper, which is made by papermaking from a raw material that is a mixture of a rayon flock slurry containing rayon fibers, a cationic styrene-based resin, and an anionic polyacrylamide-based resin, and a cellulosic raw material slurry containing NBKP, rayon fibers, and PVA binder fibers.

Patent Document 2 also describes a patterned paper with luminous properties, which is made by papermaking raw materials containing hollow flat rayon fibers, luminous oral powder, and a fibrous vinylon binder.

Patent No. 4662252 Patent No. 4787810

In recent years, overseas markets have been demanding patterned paper with a Japanese paper-like appearance, such as the rayon paper mentioned above, as packaging for food products made in Japan or for food products that imitate Japanese cuisine. However, in some countries, the use of PVA is restricted by law, so there is a demand for patterned paper that does not contain PVA, with export and overseas use in mind. It is also predicted that similar regulations will be imposed in Japan, and this has been raised as one of the required qualities.

Therefore, the object of the present invention is to provide patterned paper that does not use PVA-based resin and a method for producing the same.

The patterned paper according to the present invention contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm to 20 mm, contains no PVA-based resin, and has a surface PPS smoothness of 2.0 to 4.0 μm in the patterned portion of the patterned paper . Another embodiment contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm to 20 mm, contains no PVA-based resin, and contains 0.05% by mass to 2.0% by mass of a wet strength agent. Yet another embodiment contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm to 20 mm, contains no PVA-based resin, and has a thickness of 15 μm to 71 μm.

The first method for producing patterned paper according to the present invention includes a step of making a raw material containing pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, but not containing a PVA-based resin. In another embodiment, the method includes a step of wet-laid papermaking a raw material containing pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, but not containing a PVA-based resin, and a step of drying the obtained wet paper without a step of subjecting the wet paper to a high-pressure water jet treatment.

The second method for producing patterned paper according to the present invention includes the steps of: making a first raw material containing pulp fibers but no PVA-based resin; making a second raw material containing hollow flat rayon fibers with a fiber length of 10 mm or more and 20 mm or less and no PVA-based resin; and laminating a layer made from the first raw material and a layer made from the second raw material.

The present invention provides patterned paper that does not use PVA-based resins and a method for producing the same.

The patterned paper according to the present embodiment contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm to 20 mm, and does not contain a PVA-based resin as a binder. In this specification, PVA-based resin refers to polymers and copolymers having the structural unit _-CH2CH (OH)- derived from vinyl acetate, and includes PVA, PVA-derived synthetic resins such as vinylon, PVA-based resin fibers, and vinylon fibers. The patterned paper according to the present embodiment may be a single-layer mixed paper, or a laminate of two or more layers.

(pulp fiber)
As the pulp fibers, for example, kraft pulp, non-wood pulp, recycled paper pulp, mercerized pulp, a combination of these pulps, etc. can be used.

Examples of kraft pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), semi-bleached hardwood kraft pulp (LSBKP), semi-bleached softwood kraft pulp (NSBKP), hardwood sulfite pulp, and softwood sulfite pulp; and mechanical pulps (MP) such as stone ground pulp (SGP), pressed stone ground pulp (TGP), chemi-ground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP). These can be used alone or in combination.

Examples of non-wood pulp that can be used include hemp pulp, kenaf pulp, abaca pulp, cotton linter pulp, straw pulp, and bamboo pulp.

Lyocell fiber and other materials can also be used as recycled pulp.

Examples of waste paper pulp that can be used include disintegrated waste paper pulp, disintegrated and deinked waste paper pulp (DIP), and disintegrated, deinked, and bleached waste paper pulp, which are produced from brown paper, kraft envelope paper, magazine paper, newspaper paper, flyer paper, office paper, corrugated cardboard, white paper, Kent paper, imitation paper, and land tax paper, and can be used alone or in combination.

The freeness of the pulp fiber is not particularly limited, but is preferably 300 to 650 ml. The freeness is a value based on JIS P 8121 (2012). Having the freeness of the pulp fiber within this range improves printability.

(hollow flat rayon fiber)
Hollow flat rayon fibers have fine irregularities on their surfaces, which function like fibrils. Furthermore, hollow flat rayon fibers can form hydrogen bonds with each other and with pulp fibers (cellulose fibers). Rayon fibers that do not have a hollow flat shape cannot be fixed to pulp fibers without the use of a binder, resulting in the rayon fibers falling off after papermaking. However, hollow flat rayon fibers are fixed to pulp fibers even after papermaking due to hydrogen bonding with the rayon fibers and cellulose fibers. By using hollow flat rayon fibers as the rayon fibers, it is possible to make patterned paper with a texture similar to that of Unryu paper without using binders such as PVA or vinylon. Here, examples of hollow flat rayon fibers that can be used include Corona SBH and SBR manufactured by Daiwabo Rayon Co., Ltd.

The fiber length of the hollow flat rayon fibers used to form the patterned layer is preferably 10 mm or more and 20 mm or less. If the fiber length of the hollow flat rayon fibers is less than 10 mm, the dragon pattern will be too small and the texture of Unryu paper will not be obtained, which is undesirable. Also, if the fiber length of the hollow flat rayon fibers exceeds 20 mm, the hollow flat rayon fibers will not form the dragon pattern and will bond together to form clumps, which will not provide the texture of Unryu paper, which is undesirable.

(Fiber blending ratio)
Of the total amount of pulp fiber and hollow flat rayon fiber, the pulp fiber content is 30.0% by mass or more and 99.5% by mass or less, and the hollow flat rayon fiber content is 0.5% by mass or more and 70.0% by mass or less. By using pulp fiber and hollow flat rayon fiber in this blending range, it is possible to make patterned paper with a dragon pattern similar to Unryu paper. If the hollow flat rayon fiber content is less than 0.5% by mass, the amount of hollow flat rayon fiber is too small, resulting in a less pronounced dragon pattern and the texture of Unryu paper being lost, which is undesirable. A higher hollow flat rayon fiber content improves surface smoothness and is therefore preferable in terms of printability, but if the hollow flat rayon fiber content exceeds 70.0% by mass, the shives become noticeable and the pattern is impaired, which is undesirable.

(Internal additives)
Furthermore, internal additives such as pigments, surfactants, waxes, sizing agents, fillers, rust inhibitors, conductive agents, antifoaming agents, dispersants, viscosity adjusters, flocculants, coagulants, paper strength improving components, wet strength improvers, retention aids, paper dust prevention agents, bulking agents, etc. may be added to the papermaking raw materials.

Wet strength agents that can be used include epichlorohydrin resins such as polyamide-epichlorohydrin resin, polyamine resins, urea resins, acid colloid-melamine resins, and thermally crosslinked polyacrylamides (thermally crosslinked PAM). Unless otherwise noted, the amount of agent used in this application refers to the solids content.

When a wet strength agent is added, the amount of wet strength agent added is preferably 0.05% to 2.0% by mass of the combined pulp fiber and hollow flat rayon fiber, and particularly preferably 0.10% to 0.50% by mass. As mentioned above, the hollow flat rayon fibers are fixed by hydrogen bonding with the pulp fiber or between the hollow flat rayon fibers. However, since the hollow flat rayon fibers do not contain a binder, the hydrogen bonds are broken when the fibers become wet with water, reducing the self-fixing ability of the hollow flat rayon fibers. Adding a wet strength agent within the above range is preferable because it can compensate for the reduced self-fixing ability of the hollow flat rayon fibers when wet and also imparts water resistance to hollow flat rayon fibers, which are weak in water resistance.

(Surface PPS smoothness)
The surface PPS smoothness of the pattern portion of the patterned paper according to this embodiment is preferably 2.0 to 4.0 μm. The surface PPS smoothness of the pattern portion is a value measured by selecting a measurement site across the pattern. Having the surface PPS smoothness within the above numerical range improves printability. In addition, the bond between fibers is maintained, preventing the hollow flat rayon fibers from falling off.

Surface PPS smoothness is measured as Parker Print Surf smoothness (μm) in accordance with Appendix A of JIS-P8151 (2004). Parker Print Surf smoothness is measured using a device that determines smoothness from the amount of air flow, but by applying pressure to the measuring head, it is possible to measure smoothness under pressure. Parker Print Surf smoothness is measured using a soft backing at a clamping pressure of 1.0 MPa, and can be used to evaluate microscopic surface smoothness.

(Beck smoothness)
The Beck smoothness of one side of the patterned paper according to this embodiment is preferably 20 seconds or more. The Beck smoothness is a value measured in accordance with "Paper and paperboard - Smoothness test method using a Beck smoothness tester" JIS P 8119 (1998). If the Beck smoothness of one side of the patterned paper is 20 seconds or more, this is preferable because the printability of that side is excellent. The measurement was performed on a blank part of the paper, without selecting a pattern.

(Basic weight)
The basis weight (US basis weight) of the patterned paper according to this embodiment is not particularly limited, but is preferably 8.0 to 60.0 g/ ^m² . The basis weight is a value measured in accordance with "Paper and paperboard - Method of measuring basis weight" JIS P8124 (2011). If the basis weight is less than 8.0 g/ ^m² , the strength of the patterned paper will be low and it may not be suitable for use as a packaging material. If the basis weight is more than 60.0 g/ ^m² , the stiffness will be too high and it may not be suitable for use as a packaging material. The basis weight is the value for the entire patterned paper, regardless of whether the patterned paper is a single layer or a laminate.

(Thickness)
The thickness of the patterned paper according to this embodiment is not particularly limited, but is preferably 15 to 80 μm. The density is a value measured in accordance with JIS P 8118 (2014).

(density)
The density of the patterned paper according to this embodiment is not particularly limited, but is preferably 0.20 to 1.00 g/cm ^3. The density is a value measured in accordance with JIS P 8118 (2014).

(Tensile strength)
The tensile strength in the machine direction of the patterned paper according to this embodiment is not particularly limited, but is preferably 0.20 kN/m or more. The tensile strength is a value measured based on "Paper and paperboard -- Testing methods for tensile properties" JIS P 8113 (2006).

(Manufacturing method)
When producing the patterned paper according to this embodiment as a single-layer mixed paper, the patterned paper can be produced by wet-laid papermaking using raw materials containing pulp fibers and hollow flat rayon fibers but not containing PVA-based resin, and then drying the resulting wet paper.

When patterned paper is constructed as a laminate of two or more layers, it can be produced by wet-laid papermaking a first raw material containing pulp fibers but not PVA-based resin, and wet-laid papermaking a second raw material containing hollow flat rayon fibers but not PVA-based resin, and then overlapping and pressing the layer made from the first raw material and the layer made from the second raw material, followed by drying. The first raw material may contain hollow flat rayon fibers with a fiber length of less than 10 mm in addition to the pulp fibers. The second raw material may contain pulp fibers in addition to the hollow flat rayon fibers.

The paper is preferably dried using a Yankee dryer. When dried in a Yankee dryer, one side of the resulting patterned paper becomes glossy, and the increased smoothness improves its printability.

After the drying process, calendering can be performed to increase the smoothness of the patterned paper and improve its printability. However, calendering is not always necessary and can be omitted.

The calendering process can be carried out using calendering equipment such as a hard nip calender, soft calender, or super calender. The drying process can also be carried out using calendering equipment that combines metal rolls and elastic rolls. The metal roll is a heated calender roll made of cast steel. The elastic roll is a calender roll on the non-heated side made of materials such as cotton, epoxy resin, special polyester, or aramid. The Shore hardness of the elastic roll is preferably D60 or more and D95 or less.

The linear pressure in the calendaring process is preferably 30 kg/cm or more and 350 kg/cm or less. From the perspective of improving the uniformity of the thickness of the wrapping paper to be laminated, the linear pressure in the calendaring process is more preferably 80 kg/cm or more and 180 kg/cm or less.

The surface temperature (heating temperature) of the metal roll in the calendaring process is preferably 70°C or higher and 200°C or lower. From the perspective of preventing a decrease in the tensile strength of the wrapping paper to be laminated, the surface temperature of the metal roll in the calendaring process is more preferably 80°C or higher and 180°C or lower.

As explained above, the patterned paper according to this embodiment contains pulp fibers and hollow flat rayon fibers with a fiber length of 10 mm to 20 mm, and does not contain binders such as PVA resin, PVA-derived fibers, or vinylon fibers. However, the hollow flat rayon fibers can be fixed to the patterned paper by hydrogen bonding with the pulp fibers or between the hollow flat rayon fibers. Furthermore, by setting the fiber length of the hollow flat rayon fibers to 10 mm to 20 mm, a dragon pattern can be formed, and patterned paper with a texture similar to that of cloud dragon paper can be obtained.

The following describes specific examples of patterned paper according to the present invention. However, the present invention is not limited to these examples. Furthermore, the parts by weight, % by weight, and % shown in the examples indicate values of dry solids or substantial components.

Each internal additive was added to a raw material slurry containing fibers in the formulation shown in Table 1 (0.2% by mass for the wet strength agent), which was then fed into a cylinder paper machine for wet papermaking. The wet-made paper was then dried in a Yankee dryer to produce the papers of Examples 1 to 12 and Comparative Examples 1 to 6.

The basis weight, thickness, density, tensile strength (longitudinal and transverse), surface PPS smoothness and Beck smoothness of the obtained paper were measured by the following methods.
The basis weight was measured in accordance with JIS P8124 (2011) "Paper and paperboard - Method for measuring basis weight."
The thickness and density were measured in accordance with JIS P 8118 (2014) "Paper and paperboard - Test methods for thickness, density and specific volume."
The tensile strength was measured based on JIS P 8113 (2006) "Paper and paperboard - Testing methods for tensile properties."
The surface PPS smoothness was measured based on Appendix A of JIS-P8151 (2004) "Paper and paperboard - Surface roughness and smoothness test method (air leak method) - Print surf tester method."
Beck smoothness was measured in accordance with "Paper and paperboard - Smoothness test method using a Beck smoothness tester" JIS P 8119 (1998).

The surface of the resulting paper was visually inspected, and the state of formation of the Unryu paper-like dragon pattern was visually evaluated according to the following criteria.
○: A dragon pattern is formed, and the paper has an excellent texture as Unryu paper.
△: The dragon pattern is a little small, but it has a texture similar to Unryu paper.
×: The dragon pattern is not formed, and the texture is different from that of Unryu paper.

Table 2 shows the above measured values and the evaluation values for packaging suitability.

As shown in Table 2, the papers of Examples 1 to 12 were made from raw materials containing pulp fibers and hollow flat rayon fibers, but no rayon fibers other than hollow flat rayon fibers or vinylon fibers, and all had a dragon pattern similar to that of Unryu paper. Furthermore, although the papers of Examples 1 to 12 did not contain a binder, they did not fall off due to the self-fixing properties of the hollow flat rayon fibers.

In contrast, the papers in Comparative Examples 1 and 2 used rayon fibers that did not have a hollow flat structure, so the addition of vinylon fibers as a binder was essential to fix the rayon fibers, which did not have a hollow flat structure.

The paper in Comparative Example 3 used hollow flat rayon fibers, but because the fiber length of the hollow flat rayon fibers was too long, the hollow flat rayon fibers were bound together and did not form a dragon pattern.

The paper in Comparative Example 4 was made from hollow flat rayon fibers and rayon fibers without a hollow flat structure, so the addition of vinylon fibers as a binder was essential to fix the rayon fibers without a hollow flat structure.

The paper in Comparative Example 5 was made using only hollow flat rayon fibers, but the dragon pattern was not formed.

The paper in Comparative Example 6 contains hollow flat rayon fibers as well as rayon fibers that do not have a hollow flat structure. Therefore, the addition of vinylon fibers as a binder was essential to fix the rayon fibers that do not have a hollow flat structure.

This invention can be used to create patterned paper with a texture similar to Unryu paper, and a method for manufacturing the same.

Claims (7)

The patterned paper contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, does not contain a PVA-based resin, and has a surface PPS smoothness of 2.0 to 4.0 μm in the patterned portion of the patterned paper . The patterned paper contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, does not contain a PVA-based resin, and contains 0.05% by mass or more and 2.0% by mass or less of a wet strength agent. The patterned paper contains pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, does not contain a PVA-based resin, and has a thickness of 15 μm or more and 71 μm or less. The patterned paper according to any one of claims 1 to 3, wherein the content of the pulp fibers is 30.0% by mass or more and 99.5% by mass or less, and the content of the hollow flat rayon fibers is 0.5% by mass or more and 70.0% by mass or less . A method for producing patterned paper according to any one of claims 1 to 4 , comprising a step of making paper from a raw material containing pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, and not containing a PVA-based resin. A step of making a first raw material containing pulp fibers and not containing a PVA-based resin;
a step of making a second raw material containing hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less and not containing a PVA-based resin;
and laminating a layer made from the first raw material and a layer made from the second raw material. a step of wet-laid papermaking using a raw material containing pulp fibers and hollow flat rayon fibers having a fiber length of 10 mm or more and 20 mm or less, and not containing a PVA-based resin;
and drying the obtained wet paper without subjecting it to a high-pressure water jet treatment.