Dyeing process of bleached sulfate paper pulp and paperboard containing bleached sulfate paper pulp layer

Abstract

The invention provides a dyeing process of bleached sulfate paper pulp and a paperboard containing a bleached sulfate paper pulp layer, and the dyeing process is as follows: under certain conditions, bleached sulfate paper pulp and direct dye are subjected to a circulating contact dyeing reaction in water, and coloring pulp is obtained through forming. The dyeing process can achieve a specific coloring effect, and is short in dyeing time, good in color fastness, small in dye consumption, small in dye loss after dyeing and environment-friendly. The paperboard is provided with more than two layers of layered structures, and the coloring paste obtained by the dyeing process is distributed in one layer or a plurality of layered structures of the paperboard. The paperboard can be composed of dyed and bleached sulfate chemical pulp and undyed and bleached sulfate chemical pulp, can be made with paper according to the color and form of the dyed pulp, can be used for counterfeiting prevention, decoration and other personalized use, and is safe and environment-friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and in particular relates to a dyeing process for bleached kraft pulp and a cardboard containing a bleached kraft pulp layer. Background Art

[0002] Paper dyeing is usually a technique for decorating paper, which can endow paper with rich and colorful colors. The traditional dyeing method is to immerse the formed base paper in a dye solution, and the color depth is controlled by the soaking time, which is mainly suitable for the effect of single-color dyeing. In addition, the paper can be directly given a uniform background color by in-pulp dyeing, reducing the secondary processing cost.

[0003] In-pulp dyeing of pulp mainly uses basic dyes, acid dyes and other types, and the dye dry powder or dye solution can be added to the auxiliary materials for dyeing. However, the existing pulp dyeing process has poor environmental protection, and the produced colored pulp mainly plays a decorative role with single functionality. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a dyeing process for bleached kraft pulp, and a cardboard with anti-counterfeiting function formed by papermaking based on this process, which has the characteristics of safety, environmental protection and good anti-counterfeiting performance.

[0005] The present invention provides a dyeing process for bleached kraft pulp, comprising the following steps:

[0006] Carrying out a cyclic contact dyeing reaction between the bleached kraft pulp and a direct dye in water, and obtaining a colored pulp through forming; the total dosage ratio of the direct dye is less than 250 ppm, and the total time of the cyclic contact dyeing reaction is within 5 hours.

[0007] In an embodiment of the present invention, the total dosage ratio of the direct dye is 50-200 ppm.

[0008] In an embodiment of the present invention, the total time of the cyclic contact dyeing reaction is 2-5 hours, and the dyeing concentration of the bleached kraft pulp is 3-5.5%.

[0009] In an embodiment of the present invention, 1-10 wt% of the bleached kraft pulp slurry is short-circuited 5-7 times during the cyclic contact dyeing reaction.

[0010] In an embodiment of the present invention, the bleached kraft pulp is bleached hardwood kraft pulp and / or bleached softwood kraft pulp; the bleached kraft pulp is also ground before the cyclic contact dyeing reaction.

[0011] In an embodiment of the present invention, after the process steps of the cyclic contact dyeing reaction and before the process steps of forming, dilution, screening, and slag removal are further included.

[0012] The present invention provides a cardboard containing a bleached sulfate pulp layer, having a layered structure of two or more layers, and the colored pulp obtained by the dyeing process as described above is distributed in one or several layered structures of the cardboard.

[0013] In an embodiment of the present invention, the mass proportion of the colored pulp in the cardboard is 0.5 - 20%.

[0014] In an embodiment of the present invention, the basis weight of the cardboard containing the bleached sulfate pulp layer is 160 - 320 g / m 2 .

[0015] In an embodiment of the present invention, the density of the cardboard containing the bleached sulfate pulp layer is 0.5 - 0.7 g / cm 3 .

[0016] White cardboard generally refers to a single-layer or multi-layer combined paper product made entirely of bleached chemical pulp and fully sized, which is suitable for printing and packaging of some products. Among them, anti-counterfeiting white cardboard mainly has functions such as photosensitive change, which can meet the anti-counterfeiting requirements.

[0017] Compared with the prior art, the present invention provides a simple and efficient dyeing process for bleached sulfate chemical pulp, mainly using bleached sulfate pulp and direct dyes to carry out a cyclic contact dyeing reaction in water. The total dosage ratio of the direct dyes is less than 250 ppm, and the total time of the cyclic contact dyeing reaction is within 5 hours, and a colored pulp is obtained through forming. In this dyeing method process, the direct dye with an anionic group can directly carry out a dyeing reaction with the bleached sulfate chemical pulp to achieve specific coloring and color fixation effects. The colored pulp obtained by the present invention can not only be used for personalized applications such as anti-counterfeiting and decoration, but also has good color fastness, short dyeing time, less dye consumption, less dye loss after dyeing, is environmentally friendly, and is safe to use.

[0018] The present invention provides a cardboard containing a bleached sulfate pulp layer, which can be composed of a dyed bleached sulfate chemical pulp (the colored pulp described above, or called dyed pulp), and an undyed bleached sulfate chemical pulp. This cardboard can be made according to the color and form of the dyed pulp, is safe and environmentally friendly, and can be used for personalized applications such as anti-counterfeiting and decoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the cardboard containing a bleached sulfate pulp layer according to some embodiments of the present invention;

[0020] Figure 2Process flow chart for manufacturing cardboard containing bleached kraft pulp layers according to some embodiments of the present invention;

[0021] Figure 3 Photograph of cardboard containing blue bleached kraft pulp according to Embodiment 1 of the present invention;

[0022] Figure 4 Photograph of cardboard containing red bleached kraft pulp according to Embodiment 3 of the present invention. Detailed implementation manners

[0023] In order to more clearly understand the technical features, objectives, and effects of the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0024] The present invention provides a dyeing process for bleached kraft pulp, comprising the following steps:

[0025] Subject the bleached kraft pulp and a direct dye to a dyeing reaction by circulating contact in water, and obtain a colored pulp through forming;

[0026] The total dosage ratio of the direct dye is less than 250 ppm, and the total time of the circulating contact dyeing reaction is within 5 hours.

[0027] The colored pulp obtained by the dyeing process provided by the present invention can be used as decorative cardboard and anti-counterfeiting white cardboard, and has characteristics such as safety, environmental protection, good decoration, and good anti-counterfeiting performance.

[0028] In the dyeing process of the bleached kraft pulp according to the embodiments of the present invention, the dye used is a direct dye, and its charge property is anionic, which can be called an anionic direct reaction type dye.

[0029] Direct dyes usually have water-soluble group molecular structures such as sulfonic acid groups (-SO3H) or carboxyl groups (-COOH), and are arranged in a linear shape. They are dyes that can be heated and boiled in neutral and weakly alkaline media and can dye fibers without the help of a mordant. The coloring of direct dyes is mainly achieved by the combination of dye molecules and cotton fibers through hydrogen bonds and van der Waals forces, and is mainly applied to industries such as cotton spinning, silk, and leather. Direct dyes can be classified into azo, stilbene, etc. types according to their structures, and are mainly classified into ordinary direct dyes, direct lightfast dyes, and direct azo dyes according to their cotton spinning applications.

[0030] Preferably, the dyeing of the bleached kraft pulp according to the embodiments of the present invention is implemented according to the following process:

[0031] The bleached sulfate chemical pulp is disintegrated, and after beating and refining, it is sent to the paper machine pulp chest. At this time, the pulp concentration is about 3.0 - 5.5%, preferably 3.0 - 5.0% or 3.5 - 4.5%. Under this concentration cycle, an anionic direct dye is added, and the addition amount is preferably 50 - 200 ppm. The direct dye contacts and undergoes a chemical reaction with the bleached sulfate chemical pulp in water, which can produce a specific dyeing and fixing effect; for example, according to the reaction effect of the anionic direct dye, the addition amount of the blue anionic direct dye can be about one-third of that of the purple anionic direct dye.

[0032] The bleached sulfate pulp described in the specific embodiments of the present invention is sulfate chemical pulp, which can be bleached hardwood sulfate pulp or bleached softwood sulfate pulp, or can also include a certain proportion of bleached hardwood sulfate pulp and bleached softwood sulfate pulp; in the embodiments of the present invention, commercially available conventional bleached sulfate chemical pulp products can be used. The sulfate pulping method is generally a chemical pulping method with sodium hydroxide and sodium sulfide as the main components of the cooking liquor; the English abbreviation of bleached softwood sulfate pulp is NBKP, which is a chemical pulp prepared by cooking and bleaching softwood with the sulfate method, while bleached hardwood sulfate pulp is a sulfate chemical pulp with hardwood as the raw material. In addition to chemical pulp, chemimechanical pulp is the name of an intermediate product pulp in the paper manufacturing process, and its pulping method uses chemical pretreatment and mechanical refining post-treatment.

[0033] As a preferred technical solution of the present invention, the dyeing process of the bleached sulfate pulp includes the following steps:

[0034] The bleached chemimechanical pulp and the bleached sulfate chemical pulp are respectively disintegrated by a pulper and refined by a disk refiner, and then sent to the paper machine pulp chest; at this time, the pulp concentration in the pulp chest can be 3.5 - 5.5%, preferably an anionic direct dye is added at the outlet of the paper machine pulp chest, and the color type can be one or more of red dye, yellow dye, purple dye, blue dye, etc., and a dyeing reaction is carried out through cyclic contact; the obtained pulp is further diluted, screened, and de - slagged, and dehydrated and formed in the paper machine.

[0035] In the embodiments of the present invention, the cyclic contact dyeing reaction is that after the pulp and the direct dye are mixed and contacted, they remain in contact reaction in the wet part of the paper machine and before forming in the dry part. The total time of this process is 2 - 5 hours, and the dyeing concentration of the bleached sulfate pulp can be 3 - 5%; during the cyclic contact dyeing reaction process, 1 - 10 wt% of the bleached sulfate pulp slurry is short - cycled 5 - 7 times. Short - cycling means that the pulp goes from the paper machine pulp chest to the headbox, and then from the headbox through a pressure screen to the headbox, and part of the pulp in the headbox flows back to the paper machine pulp chest, and so on; the short - cycled pulp concentration is 3.0 - 3.5%.

[0036] Before the bleached kraft pulp undergoes a cyclic contact dyeing reaction, it also undergoes beating; the beating is to beat the prepared pulp with a disk refiner, which can defiber and fibrillationize the fibers in the pulp to meet the requirements of the forming process.

[0037] After the process step of the cyclic contact dyeing reaction and before the forming process step, it also includes dilution, screening, and slag removal, which mainly serve to remove impurities such as slag.

[0038] Correspondingly, the present invention provides a cardboard containing a bleached kraft pulp layer, having a layered structure of two or more layers. The colored pulp obtained by the dyeing process as described above is distributed in one or several of the layered structures of the cardboard. Embodiments of the present invention are based on the above dyeing process to perform composite papermaking of the cardboard, so that the dyed bleached kraft pulp layer is distributed in one or more layers of the cardboard.

[0039] The cardboard provided by the embodiments of the present invention can be composed of dyed bleached kraft chemical pulp and undyed bleached kraft chemical pulp. The cardboard can be made according to the color and form of the obtained colored pulp and can be used for personalized security purposes such as anti-counterfeiting and decoration.

[0040] Some embodiments of the present invention provide a cardboard containing dyed bleached kraft chemical pulp and a papermaking method thereof, including a base paper layer, a core paper layer, and a face paper layer stacked in sequence; the base paper is single-layer or multi-layer and contains dyed bleached kraft wood pulp.

[0041] The composition of the face paper layer in the embodiments of the present invention is the same as that well-known to those skilled in the art and is not particularly limited. In terms of raw material types, the pulp of the face paper layer in some embodiments of the present invention preferably includes 65 - 85 wt% of bleached hardwood kraft pulp and 15 - 35 wt% of bleached softwood kraft pulp; the bleached hardwood kraft pulp in the pulp of the face paper layer is preferably wet pulp with a pulp concentration of 10%; the bleached softwood kraft pulp in the pulp of the face paper layer is preferably wet pulp with a pulp concentration of 10%.

[0042] According to the present invention, a coating layer is preferably further stacked on the surfaces of the face paper layer and the base paper layer; the coating layer is preferably single-layer coated; the coating amount of the coating layer is preferably 4 - 8 g / cm 2 ; the coating amount of the coating layer on the face paper layer is preferably 5 - 7 g / cm 2 .

[0043] Please refer to Figure 1 , Figure 1Schematic structural diagram of the cardboard containing a bleached sulfate paper layer according to some embodiments of the present invention. The base paper in the cardboard includes: a top paper layer 103, a core paper layer 102, and a bottom paper layer 101 stacked in sequence. One or more of the coloring slurries may be included in these three layers; a first coating layer 104 is further coated on the top paper layer 103, and / or a second coating layer 105 is further coated on the bottom paper layer 101.

[0044] Further, the wood pulp components and weight percentages of the top paper layer 103 are: 65 - 85 wt% of bleached hardwood sulfate pulp, 15 - 35 wt% of bleached softwood sulfate pulp, and both may be the coloring slurries.

[0045] Further, the wood pulp components and weight percentages of the core paper layer 102 are: 40 - 60 wt% of bleached chemimechanical pulp, 5 - 25 wt% of bleached hardwood sulfate pulp, and 25 - 35 wt% of broke (dry broke and wet broke generated during the production process, whose composition is a mixture of bleached softwood pulp, bleached hardwood pulp, and thermomechanical pulp, that is, the formed paper is broken up, reground, and then enters the pulp system).

[0046] Further, the wood pulp components and weight percentages of the bottom paper layer 101 are: 65 - 85 wt% of bleached hardwood sulfate pulp, 15 - 35 wt% of bleached softwood sulfate pulp, and both may be the coloring slurries.

[0047] Further, the first coating layer is denoted as the pre - coating layer 104, and the second coating layer is denoted as the back - coating layer 105. The coating amounts of both may be 4 - 8 g / m² and 4 - 8 g / m² respectively. The coating can be carried out using the coatings in traditional processes, and there are no special limitations in the embodiments of the present invention.

[0048] The basis weight of the cardboard containing the dyed bleached sulfate chemical pulp (paper layer) is preferably 160 - 320 g / m 2 , and more preferably 200 - 290 g / m 2 ; the cardboard is composed of the above - mentioned three - layer pulp composite. One or more layers of the cardboard contain dyed bleached sulfate chemical pulp fibers. As a preference, the mass proportion of the coloring slurry in the cardboard is 0.5 - 20%, and it can be 1 - 20%, 3 - 10%, for example, 0.5 - 5%, 4 - 9%, 5 - 8%, 6 - 7%, etc. And, the density of the cardboard containing the bleached sulfate paper layer in the embodiments of the present invention can be 0.5 - 0.7 g / cm 3 .

[0049] In some embodiments of the present invention, the papermaking method of this kind of cardboard containing a bleached sulfate paper layer includes:

[0050] Carry out the pulping and refining procedures according to the conventional papermaking process of white cardboard. Add anionic direct dyes in the thick pulp area. After a short-cycle reaction for 2-5 hours, dyed bleached sulfate chemical pulp fibers can appear on the paper surface.

[0051] The present invention also provides a method for preparing the above cardboard, including:

[0052] Mix the pulp of the base paper layer, the pulp of the core paper layer, and the pulp of the surface paper layer. The pulp of the base paper layer and / or the pulp of the core paper layer contains dyed bleached chemical pulp fibers. After dewatering, forming, laminating, pressing, and drying by a paper machine, cardboard is obtained.

[0053] According to the present invention, after drying, it is preferably also subjected to sizing, coating, and calendering, all of which can be conventional process operations in the art.

[0054] See Figure 2 , Figure 2 For the schematic diagram of the papermaking process flow. In the embodiment of the present invention, the bleached sulfate chemical pulp board raw material is disintegrated by a pulper and sent to a disc refiner for refining; while the bleached mechanical pulp board raw material is disintegrated by a pulper and sent to a defibrator for treatment.

[0055] In the embodiment of the present invention, mixing is carried out according to a certain wood pulp ratio respectively. According to the different structures of the surface paper layer, the core paper layer, and the base paper layer, they enter the surface layer, core layer, and bottom layer paper machine pulp tanks respectively. At the inlet of the pump at the outlet of each pulp tank, a certain proportion of anionic direct reaction dyes (anionic direct dyes) can be optionally added for cyclic contact dyeing reaction; then after the pulp is further diluted, screened, and slag removed, it enters a paper machine with a three-layer long wire forming, that is, after dehydration by the long wire paper machine and three-layer superimposed composite forming treatment, a wet paper sheet with a 103 surface paper layer, a 102 core paper layer, and a 101 base paper layer can be produced. The wet paper sheet is obtained after pressing, drying, and surface sizing; then coating is carried out, a pre-coating layer 104 is coated on the surface layer, a back coating layer 105 is coated on the bottom layer, and finally, after calendering, winding, rewinding, and packing into finished products, cardboard containing dyed bleached sulfate paper layers is obtained. The color of the dyed bleached sulfate pulp is red, yellow, blue, purple, or black.

[0056] The cardboard described in the embodiment of the present invention can be made according to the color and form of the dyed pulp, which is safe and environmentally friendly and can be used for anti-counterfeiting, decoration, and other personalized uses.

[0057] In order to further understand the present invention, the present invention will be described in detail below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments. In the embodiments, all the original reagents and materials can be obtained commercially, and the experimental methods without specific experimental conditions are conventional methods and conditions well known in the art.

[0058] Example 1

[0059] According to Figure 2 the shown technological process, the bleached kraft chemical pulp board and the bleached mechanical pulp board are disintegrated by a pulper, and the specific process is as follows.

[0060] Bleached hardwood kraft pulp: Dilute the bleached hardwood kraft pulp with a concentration of 10 wt%, that is, dilute the wet pulp with a concentration of 10% of the pulp to a concentration of 5 wt%, and send it to a disk refiner for refining.

[0061] Bleached softwood kraft pulp: Dilute the bleached hardwood kraft pulp with a concentration of 10 wt% to a concentration of 5 wt%, and send it to a disk refiner for refining.

[0062] Bleached chemi-mechanical pulp: Dilute and disintegrate the air-dried bleached chemi-mechanical pulp board to a concentration of 5 wt%, and send it to a dissolver for treatment.

[0063] Waste paper: The dry waste paper and wet waste paper generated during the production process are concentrated by a waste paper concentrator and then sent to a waste paper disk refiner for treatment.

[0064] Facing paper layer pulp: Wood pulp (weight percentage: 80% bleached hardwood kraft pulp, 20% bleached softwood kraft pulp) enters the pulp pool of the facing paper machine after mixing and refining.

[0065] Core paper layer pulp: Wood pulp (weight percentage: 80% bleached chemi-mechanical pulp, 10% bleached hardwood kraft pulp, 10% waste paper) enters the pulp pool of the core paper machine after mixing and refining.

[0066] Back paper layer pulp: Wood pulp (weight percentage: 80% bleached hardwood kraft pulp, 20% bleached softwood kraft pulp) enters the pulp pool of the back paper machine after mixing and refining.

[0067] At the inlet of the pump at the outlet of the pulp pool of the facing paper machine, anionic direct reaction dye blue is added, and the addition amount is 50 ppm. Anionic direct reaction dye purple is added, and the addition amount is 150 ppm. During the circulating contact dyeing reaction process, 1-10 wt% of the pulp is short-circuited 5-7 times. Short-circuiting means that the pulp goes from the pulp pool of the paper machine to the high-level tank, and then from the high-level tank through a pressure screen to the headbox. Part of the pulp in the high-level tank flows back to the pulp pool of the paper machine, and so on; the concentration of the short-circuited pulp is 3.0-3.5%.

[0068] Debris removal and screening, and then through a fourdrinier paper machine for three-layer superposition forming treatment to produce a wet paper sheet with a 103 facing paper layer, a 102 core paper layer, and a 101 back paper layer with identification fibers added. The wet paper sheet is dried, surface-sized to obtain the base paper, and then coated. A precoat 104 is coated on the facing layer, and the coating amount is 5 g / m 2 and a backcoat 105 is coated on the back layer, and the coating amount is 5 g / m 2, finally, through calendering, coiling, rewinding, and packing, the finished products are obtained.

[0069] Among them, the coating ratio of the pre - coating and the surface - coating is carried out according to the traditional coating process.

[0070] After 2 hours, blue - violet bleached sulfate chemical fibers appear on the paper surface, as Figure 3 shown.

[0071] The basis weight of the manufactured cardboard is 200 g / cm 2 , and the density is 0.69 g / cm 3 .

[0072] Comparing various indicators of the produced cardboard with ordinary cardboard of the same basis weight on the market, the results show that the cardboard containing dyed bleached sulfate wood pulp fibers of the present invention can be repulped and recycled, which is superior to ordinary cardboard. The cardboard containing dyed bleached sulfate pulp of the present invention can obviously observe the dyed fibers on the front side, which is significantly different from ordinary cardboard.

[0073] The following table shows the comparison of the physical index detection between the ordinary cardboard on the market with a basis weight of 200 grams and the cardboard obtained in Example 1 of the present invention.

[0074] Table 1 Physical property detection results of the cardboard obtained in Example 1 and ordinary cardboard

[0075]

[0076] Example 2

[0077] According to the Figure 2 shown technological process, the bleached sulfate chemical pulp board and the bleached mechanical pulp board are disintegrated by a pulper, and the specific process is as follows.

[0078] Bleached hardwood sulfate pulp: Dilute the bleached hardwood sulfate pulp with a concentration of 10 wt% to a concentration of 5 wt%, and send it to a disk refiner for refining treatment.

[0079] Bleached softwood sulfate pulp: Dilute the bleached hardwood sulfate pulp with a concentration of 10 wt% to a concentration of 5 wt%, and send it to a disk refiner for refining treatment.

[0080] Bleached chemimechanical pulp: Dilute and disintegrate the air - dried bleached chemimechanical pulp board to a concentration of 5 wt%, and send it to a defiberator for treatment.

[0081] Waste paper: The dry waste paper and wet waste paper generated during the production process are concentrated by a waste paper concentrator and then sent to a waste paper disk refiner for treatment.

[0082] Facing - paper layer pulp: Wood pulp (weight percentage: 80% bleached hardwood sulfate pulp, 20% bleached softwood sulfate pulp) enters the pulp pool of the facing - paper machine after mixing and refining.

[0083] Core paper layer pulp: Wood pulp (weight percentage: 80% bleached chemi-thermomechanical pulp, 10% bleached hardwood kraft pulp, 10% broke) enters the core layer paper machine pulp tank after mixing and refining.

[0084] Base paper layer pulp: Wood pulp (weight percentage: 80% bleached hardwood kraft pulp, 20% bleached softwood kraft pulp) enters the bottom layer paper machine pulp tank after mixing and refining.

[0085] Anionic direct reactive dye blue is added at the inlet of the pump at the outlet of the core layer paper machine pulp tank, with an addition amount of 100 ppm, and anionic direct reactive dye purple is added, with an addition amount of 200 ppm.

[0086] After removing impurities and screening, and then through the three-layer superposition forming process of a fourdrinier paper machine, a wet paper sheet with 103 surface paper layers, 102 core paper layers, and 101 base paper layers added with identification fibers is produced. The wet paper sheet is dried, surface sized to obtain the base paper, and then coated. A precoat layer 104 is coated on the surface layer, with a coating amount of 5 g / m 2 , and a backcoat layer 105 is coated on the bottom layer, with a coating amount of 5 g / m 2 , and finally finished products are obtained through calendering, winding, rewinding, and packing.

[0087] Among them, the coating ratio of the precoat and the topcoat is carried out according to the traditional coating process.

[0088] After 3 hours, blue-violet bleached sulfate chemical fibers appear on the paper surface.

[0089] The basis weight of the manufactured cardboard is 250 g / cm 2 , and the density is 0.67 g / cm 3 .

[0090] The cardboard produced is compared with ordinary cardboard of the same grammage on the market in terms of various indicators. The results show that the cardboard containing dyed bleached sulfate wood pulp fibers of the present invention can be repulped and recycled, which is superior to ordinary cardboard. The cardboard containing dyed bleached sulfate pulp of the present invention can clearly observe the dyed fibers on the front side, which is significantly different from ordinary cardboard.

[0091] The following table shows the comparison of the physical index detection between the ordinary cardboard on the market with a basis weight of 250 g and the cardboard obtained in Example 1 of the present invention.

[0092] Table 2 Physical property detection results of the cardboard obtained in Example 2 and ordinary cardboard

[0093]

[0094] Example 3

[0095] According to Figure 2For the shown process flow, the bleached kraft chemical pulp board and the bleached mechanical pulp board are disintegrated by a pulper. The specific process is as follows.

[0096] Bleached hardwood kraft pulp: Dilute the bleached hardwood kraft pulp slurry with a concentration of 10 wt% to a concentration of 5 wt%, and send it to a disk refiner for refining.

[0097] Bleached softwood kraft pulp: Dilute the bleached hardwood kraft pulp slurry with a concentration of 10 wt% to a concentration of 5 wt%, and send it to a disk refiner for refining.

[0098] Bleached chemi-thermomechanical pulp: Dilute and disintegrate the air-dried bleached chemi-thermomechanical pulp board to a concentration of 5 wt%, and send it to a defiberator for treatment.

[0099] Waste paper: The dry waste paper and wet waste paper generated during the production process are concentrated by a waste paper concentrator and then sent to a waste paper disk refiner for treatment.

[0100] Facing paper layer slurry: Wood pulp (weight percentage: 70% bleached hardwood kraft pulp, 30% bleached softwood kraft pulp) enters the facing paper machine pulp tank after mixing and refining.

[0101] Core paper layer slurry: Wood pulp (weight percentage: 70% bleached chemi-thermomechanical pulp, 20% bleached hardwood kraft pulp, 10% waste paper) enters the core paper machine pulp tank after mixing and refining.

[0102] Backing paper layer slurry: Wood pulp (weight percentage: 70% bleached hardwood kraft pulp, 30% bleached softwood kraft pulp) enters the backing paper machine pulp tank after mixing and refining.

[0103] Add anionic direct-reacting dye red at the inlet of the outlet pump of the facing paper machine pulp tank, with an addition amount of 50 ppm, and add anionic direct-reacting dye violet, with an addition amount of 100 ppm.

[0104] Add anionic direct-reacting dye red at the inlet of the outlet pump of the core paper machine pulp tank, with an addition amount of 100 ppm, and add anionic direct-reacting dye violet, with an addition amount of 200 ppm.

[0105] Then, it undergoes three-layer superposition forming treatment on a fourdrinier paper machine to produce a wet paper sheet with a 103 facing paper layer, a 102 core paper layer, and a 101 backing paper layer with identification fibers added. The wet paper sheet is dried, surface sized, and calendered to obtain the base paper, and then coated; coat a precoat layer 104 on the facing layer, with a coating amount of 7 g / m 2 , coat a backcoat layer 105 on the backing layer, with a coating amount of 8 g / m 2 , and finally, it is calendered, wound, rewound, and packed into finished products.

[0106] The coating ratio of the precoat and the topcoat is carried out according to the traditional coating process.

[0107] After 2.5 hours, blue-violet bleached sulfate chemical fibers appear on the paper surface.

[0108] The basis weight of the manufactured board is 290 g / cm 2 , and the density is 0.66 g / cm 3 .

[0109] The produced board is compared with ordinary boards of the same grammage on the market in terms of various indicators. The results show that the board containing dyed bleached sulfate wood pulp fibers of the present invention can be repulped and recycled, which is superior to ordinary boards. The board containing dyed bleached sulfate pulp of the present invention can obviously observe dyed fibers on the front side, which is significantly different from ordinary boards.

[0110] The following table shows the comparison of the physical index tests between the ordinary board on the market with a basis weight of 290 g and the board obtained in Example 1 of the present invention.

[0111] Table 3 Physical property test results of the board obtained in Example 3 and the ordinary board

[0112]

[0113]

[0114] Figure 3 is a photo of the board containing blue bleached sulfate wood pulp in Example 1 of the present invention; Figure 4 is a photo of the board containing red bleached sulfate wood pulp in Example 3 of the present invention. In the examples of the present invention, bleached sulfate pulp and direct dyes are mainly used to carry out a cyclic contact dyeing reaction in water. The total dosage ratio of the direct dyes is less than 250 ppm, and the total time of the cyclic contact dyeing reaction is within 5 hours to obtain a colored pulp through forming. In this dyeing method process, the direct dye with an anionic group can directly carry out a dyeing reaction with the bleached sulfate chemical pulp to achieve a specific coloring and color fixation effect. The colored pulp obtained by the present invention can not only be used for personalized applications such as anti-counterfeiting and decoration, but also has good color fastness, short dyeing time, less dye dosage, less dye loss after dyeing, is environmentally friendly and safe to use.

[0115] The present invention provides a board containing a bleached sulfate pulp layer, which can be composed of dyed bleached sulfate chemical pulp (the colored pulp described above, or called dyed pulp) and undyed bleached sulfate chemical pulp. The board can be manufactured according to the color and form of the dyed pulp, is safe and environmentally friendly, and can be used for personalized applications such as anti-counterfeiting and decoration.

[0116] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A dyeing process for bleached kraft pulp, characterized in that: The following steps are involved: The bleached kraft pulp and direct dye are subjected to a cyclic contact dyeing reaction in water, and then formed into a colored pulp; the total usage ratio of the direct dye is less than 250 ppm, and the total time of the cyclic contact dyeing reaction is within 5 hours.

2. The dyeing process according to claim 1, characterized in that: The total usage ratio of the direct dye is 50-200ppm.

3. The dyeing process according to claim 1, characterized in that: The total time of the cyclic contact dyeing reaction is 2-5 hours, and the dyeing concentration of the bleached kraft pulp is 3-5.5%.

4. The dyeing process according to any one of claims 1 to 3, characterized in that: During the cyclic contact dyeing reaction, 1-10 wt% of bleached kraft pulp is short-circuited 5-7 times.

5. The dyeing process according to claim 4, characterized in that: The bleached kraft pulp is bleached broadleaf kraft pulp and / or bleached coniferous kraft pulp; the bleached kraft pulp is also refined before the cyclic contact dyeing reaction.

6. The dyeing process according to claim 4, characterized in that: After the process step of the cyclic contact dyeing reaction and before the molding process step, it also includes dilution, screening and deslagging.

7. A paperboard containing a bleached kraft pulp layer, having a layered structure of two or more layers, characterized in that: The coloring pulp obtained by the dyeing process according to any one of claims 1 to 6 is distributed in one or more layers of the paperboard.

8. The paperboard according to claim 7, characterized in that: The coloring pulp accounts for 0.5-20% by weight in the paperboard.

9. The paperboard according to claim 7, characterized in that: The basis weight of the paperboard containing the bleached kraft pulp layer is 160-320 g / m 2 .

10. The paperboard according to claim 7, characterized in that: The density of the paperboard containing the bleached kraft pulp layer is 0.5-0.7 g / cm 3 .

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