Raw white two-side offset paper and preparation method thereof

Abstract

The invention discloses raw white two-side offset paper and a preparation method thereof, and belongs to the technical field of papermaking, and the method comprises the following steps: taking long-fiber paper pulp with ISO whiteness of 89-90%, short-fiber paper pulp with ISO whiteness of more than or equal to 89% and chemithermomechanical pulp with ISO whiteness of more than or equal to 77% as fiber raw materials, pulping, mixing 10-30wt% of long-fiber paper pulp, 55-80wt% of short-fiber paper pulp and 15-30wt% of chemithermomechanical pulp, and carrying out extrusion molding to obtain the raw white two-side offset paper. Mixed slurry is obtained; adding a purple dye, a blue dye, a yellow dye and a red dye into the mixed slurry according to a color mixing principle and a preset formula to obtain the mixed slurry added with the dyes; and sequentially carrying out sizing, net part forming, dehydration, pre-drying, surface sizing and post-drying on the mixed slurry added with the dye to obtain the raw white two-side offset paper. According to the method, the raw white two-side offset paper meeting the national standard eye protection requirement can be prepared, the pulp supply is more stable, and the product quality is more stable.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and more specifically to a natural white offset paper and a preparation method thereof. Background Art

[0002] Offset paper is a paper made by coating the adhesive on both sides of the paper during the papermaking process. It has good smoothness and absorbs ink evenly. The general basis weight is 60-120g / m 2 . The current market demand for offset paper is still mainly concentrated in the student group. At present and in the future, its use in textbooks and various teaching materials will remain the mainstream of the market. According to GB40070-2021 "Hygiene Requirements for Myopia Prevention and Control of Children and Adolescents' Learning Supplies", the D65 brightness of textbooks, teaching aids, workbooks, reading materials, examination papers and other learning papers is greater than 55% and less than 85%, and the fluorescence value is less than 5%. At this hue value, the impact on the vision of teenagers is relatively low. Therefore, it is particularly important to develop a natural white offset paper with a soft color and non-glaring. Summary of the invention

[0003] In view of this, the present invention provides a white offset paper and a preparation method thereof. The method of the present invention can prepare white offset paper that meets the national standard eye protection requirements, and the pulp supply is more stable and the product quality is more stable.

[0004] The present invention provides a method for preparing white offset paper, comprising the following steps:

[0005] Taking long fiber pulp with ISO brightness of 89-90%, short fiber pulp with ISO brightness ≥89% and chemical mechanical pulp with ISO brightness ≥77% as fiber raw materials, after beating, 10-30wt% of long fiber pulp, 55-80wt% of short fiber pulp and 15-30wt% of chemical mechanical pulp are mixed to obtain mixed pulp;

[0006] Adding purple dye, blue dye, yellow dye and red dye to the mixed slurry according to the toning principle and a preset formula to obtain a mixed slurry with added dyes;

[0007] Then, the mixed pulp with added dye is subjected to sizing, web forming, dehydration, pre-drying, surface sizing and post-drying in sequence to obtain natural white offset paper.

[0008] In an embodiment of the present invention, the beating is performed with the assistance of beating enzyme.

[0009] In an embodiment of the present invention, fillers and cationic starch are added after pulping.

[0010] In an embodiment of the present invention, the mass concentration of the purple dye is 0.1-0.5%, the mass concentration of the red dye is 0.01-0.03%, and the mass concentrations of the blue dye and the yellow dye are 0.1-0.3% respectively; the dye content per ton of paper is: 0-50g of purple dye, 0-30g of blue dye, 10-60g of yellow dye, and 0-10g of red dye.

[0011] In an embodiment of the present invention, the pulping further comprises pulping by a pulper before the pulping.

[0012] In an embodiment of the present invention, the concentration of the sizing is 1-1.2 wt %.

[0013] In an embodiment of the present invention, the dehydration is squeezing dehydration; and the surface sizing is double-sided coating using a sizing agent.

[0014] The present invention provides a natural white offset paper obtained by the above-mentioned preparation method, and the CIE whiteness is 55-85%.

[0015] In the embodiment of the present invention, the L value of the natural white offset paper is 93 to 96, the a value is -0.1 to -0.5, the b value is 0.5 to 6.5, and the fluorescence value is 0.4 to 2.0.

[0016] In the embodiment of the present invention, the weight of the white offset paper is 60-120 g / m 2 The natural white offset paper does not contain any additional fluorescent brightener.

[0017] The raw materials for producing natural white offset paper on the market are natural white or low white unbleached pulp, which has low whiteness, and its ISO whiteness is generally 79-83%. However, the existing technology is easily affected by the supply of pulp and the stability of product quality.

[0018] Compared with the prior art, the present invention mainly uses high-whiteness pulp to produce white offset paper, wherein the ISO whiteness of the raw material is generally above 89%; and a suitable dye is selected to adjust the color of the mixed pulp, and after various papermaking processes, a paper product is obtained. The fiber raw material of the present invention has a high whiteness. After the production of high-white paper is completed, there is no need to replace the pulp, and white offset paper can be directly produced. The pulp supply is relatively stable, the quality fluctuation of the finished product is small, and there is no need to add fluorescent brighteners, which is more environmentally friendly and healthy. The white offset paper described in the present invention has a unique product hue, and the hue has a better eye protection effect under the premise of meeting the requirements of national standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic diagram of the preparation process of natural white offset paper according to some embodiments of the present invention;

[0020] Figure 2A schematic diagram of a dye addition process in some embodiments of the present invention;

[0021] Figure 3 This is a product photo of the natural white offset paper prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as those skilled in the art generally understand. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0023] The present invention provides a method for preparing white offset paper, comprising the following steps:

[0024] Taking long fiber pulp with ISO brightness of 89-90%, short fiber pulp with ISO brightness ≥89% and chemical mechanical pulp with ISO brightness ≥77% as fiber raw materials, after beating, 10-30wt% of long fiber pulp, 55-80wt% of short fiber pulp and 15-30wt% of chemical mechanical pulp are mixed to obtain mixed pulp;

[0025] Adding purple dye, blue dye, yellow dye and red dye to the mixed slurry according to the toning principle and a preset formula to obtain a mixed slurry with added dyes;

[0026] Then, the mixed pulp with added dye is subjected to sizing, web forming, dehydration, pre-drying, surface sizing and post-drying in sequence to obtain natural white offset paper.

[0027] The method of the present invention can prepare natural white offset paper that meets the eye protection requirements of national standards, and the pulp supply is more stable, which is beneficial to improving the stability of product quality.

[0028] See also Figure 1 The papermaking process of the white offset paper in the embodiment of the present invention generally includes: pulping, beating, pulping, sizing, fiber dispersion in the headbox, dehydration and forming in the wire section, dehydration in the press section, pre-drying, surface sizing, post-drying and calendering, calendering and curling (and rewinding).

[0029] The production of paper in some embodiments of the present invention includes the following production scheduling process: firstly produce a high white paper with a CIE whiteness of 145 to 158, and after the production of the high white paper is completed, produce a natural white offset paper with a CIE whiteness of 55 to 85. In the past, low whiteness pulp (referred to as low white pulp) was used to produce natural white offset paper, and high whiteness pulp (referred to as high white pulp) was used as raw material to produce high white paper. After the production of high white paper is completed, the raw material pulp needs to be replaced with low white pulp. The pulp replacement leads to unstable pulp quality, large fluctuations in the quality of the finished product, and an additional fluorescent brightener needs to be added to stabilize the color of the finished product.

[0030] The embodiment of the present invention directly adopts high white pulp to produce white offset paper, and the pulp supply is more stable. The embodiment of the present invention also includes a pulp preparation step: long fiber pulp with high whiteness of 89%-90% ISO whiteness, short fiber pulp with high whiteness of ≥89% ISO whiteness, and chemical mechanical pulp with ISO whiteness ≥77% can be provided respectively.

[0031] Among them, the long fiber pulp fiber length is generally 2-3mm, the fiber width is 22-30μm, and the tensile index is ≥95Nm / g at 300ml freeness; the short fiber pulp fiber length is generally 0.7-2mm, the fiber width is 8-16μm, and the tensile index is ≥75Nm / g at 300ml freeness, and the L, a, and b values ​​are 97~97.5, -0.5~-0.6, and 3~4.5 respectively.

[0032] The chemimechanical pulp is the full name of chemical mechanical pulp, which is generally a pulp formed by chemical treatment and mechanical pulping of wood chips, with a yield of more than 85%; its fiber length is generally 0.5-0.7mm, fiber width is 25-26μm, tensile index after thermal decomposition is ≥25Nm / g, L, a, b values ​​are 95~96, -1~-2, 8~11 respectively.

[0033] In the embodiment of the present invention, the fiber raw material is pulped by a pulper and then beaten; thereafter, 10% to 30% of the high-whiteness long-fiber pulp, 55% to 80% of the high-whiteness short-fiber pulp and 15% to 30% of the chemical-mechanical pulp are evenly mixed by weight to obtain a mixed pulp.

[0034] The beating is to use physical methods to mechanically or fluidly treat the pulp fibers in water, so that the fibers are subjected to shear force, the fiber morphology is changed, and the pulp acquires certain characteristics to ensure that the paper produced meets the expected quality requirements. In a preferred embodiment of the present invention, the beating is assisted by a beating enzyme.

[0035] After beating, fillers are added in the embodiment of the present invention, and cationic starch is added in the pulping step (commercially available conventional papermaking starch products can be used). Specifically, a conical mill can be used for beating, and the freeness of long fibers is controlled at 250-350ml, the freeness of short fibers is controlled at 350-420ml, and the freeness of chemical mechanical pulp is controlled at 280-320ml. Before beating, a beating enzyme is used to pretreat long fibers and short fibers. The beating enzyme is a cellulase, which can "react" with cellulose and hemicellulose in the cell wall, promote the relaxation and softening of the cell wall structure, increase permeability, promote swelling, reduce fiber cohesion, and make the fiber softer; the mechanical force of beating causes the fiber cell wall to be stratified and collapsed, accelerates the destruction of the cell wall and performs fibrillation, so that there are more bonding points between the fibers and improves the strength.

[0036] In the embodiment of the present invention, the filler used may be heavy calcium carbonate or light calcium carbonate, and the addition ratio of light calcium carbonate is 10%-30% of the mass of all fillers.

[0037] After obtaining the mixed pulp, the embodiment of the present invention performs a dye adding step: first prepare a purple dye with a mass concentration of 0.1%-0.5%, a blue dye with a mass concentration of 0.1%-0.3%, a yellow dye with a mass concentration of 0.1%-0.3%, and a red dye with a mass concentration of 0.01%-0.03%; for natural white offset paper with different CIE whiteness, add the above dyes to the mixed pulp according to a preset formula to obtain a mixed pulp with added dyes. In the specific formula, the dyes contained per ton of paper are: 0-50g of purple dye, 0-30g of blue dye, 10-60g of yellow dye, and 0-10g of red dye; in some embodiments, 1-45g of purple dye, 0.1-28g of blue dye, 11-50g of yellow dye, and 0.1-9g of red dye.

[0038] The application of colorimeter in paper color difference defect detection includes: measuring the color of paper and surface color difference, objectively evaluating and quantifying the depth of color and the size of color difference, etc.

[0039] After the colorimeter is used for measurement, the three stimulus values ​​XYZ of the sample color can be directly calculated, and these values ​​can also be converted into color parameters of other uniform color spaces, such as Lab color space, LCh color space, Hunter Lab color space, etc. The most commonly used one is the Lab color space, which uses three different coordinate axes, L, a*, and b, to indicate the position and code of the color in the geometric coordinate diagram.

[0040] Based on the color representation method established by this theory, when a color is represented by CIE, L, a, b, the L axis represents lightness, black is at the bottom and white is at the top; +a represents red, -a represents green; +b represents yellow, -b represents blue. The color change of any color can be represented by the a and b values, and the level change of any color can be represented by the L value. The three values ​​of L, a, and b can describe any color in nature. When giving these chromaticity values, the colorimeter can also give color difference values ​​such as ΔE, ΔL, Δa, Δb after colorimetry. By analyzing these color difference values, you can know whether there is color difference in the paper, and then effectively control the color quality of the paper to ensure color consistency between batches.

[0041] The following are the effects of different dyes on hue involved in the embodiments of the present invention:

[0042] Table 1 Comparison of the effects of different dyes and brightener OBA on hue

[0043] dye L a b CIE D65 F Yellow Dye ↓ ↓ ↑ ↓ ↓ Red Dye ↓ ↑ ↑ ↓ ↓ Blue Pigment ↓ ↓ ↓ ↑ ↓ Purple Pigment ↓ ↑ ↓ ↑ ↓ Brightener OBA ↑ ↑ ↓ ↑ ↑ ↑

[0044] In Table 1, a downward arrow represents a decrease in value, and an upward arrow represents an increase in value, and D65 and F are both corresponding light sources.

[0045] According to Table 1, adding purple dye: L value decreases, a value increases, and b value decreases; adding blue dye: L value decreases, a value decreases, and b value decreases. Adding yellow dye: L value decreases, a value decreases, and b value increases; adding red dye: L value decreases, a value increases, and b value decreases. Adding whitening agent OBA: L value increases, a value increases, and b value decreases.

[0046] See also Figure 2 In the embodiment of the present invention, the dye enters the dilution tank to adjust the concentration, and then enters the storage tank; when preparing the pulp, the dye in the storage tank can be added through the inlet of a first-stage pulp pump. Because the whiteness of high white pulp and low white pulp is quite different, the embodiment of the present invention selects a suitable dye and adjusts the formula of the dye without adding additional fluorescent brighteners, thereby producing natural white offset paper that meets the eye protection requirements (natural and soft color, not dazzling).

[0047] After the slurry is prepared in the embodiment of the present invention, papermaking is carried out, and the papermaking steps include sizing, fiber dispersion in the flow box, mesh forming, dehydration in the press section, pre-drying, surface sizing, post-drying, calendering, curling and rewinding, which are all common knowledge in the field and will not be repeated here. Among them, the concentration of the sizing may be 1wt%, 1.1wt% or 1.2wt%. In addition, the present invention has no special restrictions on papermaking machine equipment and other steps and processes. The sizing agent is a mixture of surface starch, alkyl ketene dimer (AKD) and styrene acrylic acid (SAE) surface sizing agent, which is added to the sizing machine through the sizing feeding trough and transferred to the paper through the sizing roller for sizing, and the single-sided sizing amount is ≥1g / m 2 , which can increase the water resistance of paper, prevent ink from bleeding when writing, and make fonts clear and non-spreading. In some embodiments, the mixed pulp with added dye and the surface sizing do not add fluorescent brightener, which is more environmentally friendly.

[0048] The embodiment of the present invention provides a white offset paper obtained by the preparation method as described above, wherein the weight of the white offset paper can be 60-120 g / m 2 ; CIE whiteness is 55-85% (different products produced by different paper mills have different standards for hue). CIE whiteness is the visual whiteness of the human eye under the D65 light source, which is widely used in the papermaking industry. ISO whiteness uses C light source to reflect the brightness of paper, which is difficult to reflect the color or hue characteristics of the sample. CIE whiteness is more in line with the human eye's evaluation of whiteness than ISO whiteness.

[0049] In a specific embodiment of the present invention, the L value of the white offset paper is 93 to 96, the a value is -0.1 to -0.5, the b value is 0.5 to 6.5, and the fluorescence value is 0.4 to 2.0. In addition, the white offset paper has no additional fluorescent brightener and is more environmentally friendly.

[0050] The embodiment of the present invention uses high white pulp as the main raw material, which can remove the restriction that low white pulp must be used to produce natural white offset paper, and provide more choices and more stable product quality and environmental protection for the domestic market. The natural white offset paper of the present invention has a unique product hue, and the hue meets the requirements of national standards and has a better eye protection effect.

[0051] In order to better illustrate the present invention, the following examples are further illustrated. Unless otherwise specified, the various reagents and raw materials used in the present invention are all commercially available products or products that can be prepared by recognized methods.

[0052] The long fiber pulp involved has a fiber length of 2-3 mm, a fiber width of 22-30 μm, and a tensile index of ≥95 Nm / g at a freeness of 300 ml; the short fiber pulp has a fiber length of 0.7-2 mm, a fiber width of 8-16 μm, and a tensile index of ≥75 Nm / g at a freeness of 300 ml, and L, a, and b values ​​of 97 to 97.5, -0.5 to -0.6, and 3 to 4.5, respectively. The chemical mechanical pulp fiber has a fiber length of 0.5-0.7 mm, a fiber width of 25-26 μm, and a tensile index of ≥25 Nm / g after thermal decomposition, and L, a, and b values ​​of 95 to 96, -1 to -2, and 8 to 11, respectively.

[0053] Example 1

[0054] (1) Slurry preparation steps:

[0055] ① Provide high white long fiber pulp with ISO brightness of 89%-90%, high white short fiber pulp with ISO brightness of 89%, and chemical mechanical pulp with ISO brightness of 77%;

[0056] ② After pulping with a pulper, add a pulping enzyme for pulping; add filler after pulping, the filler addition amount is 25% ash, 10% high white long fiber pulp, 70% high white short fiber pulp and 20% chemical mechanical pulp are mixed evenly by weight percentage, and 7kg of cationic starch is added to prepare the pulp to obtain a mixed pulp; the pulping can use a conical mill, the long fiber freeness is controlled at 250-350ml, the short fiber freeness is controlled at 350-420ml, and the chemical mechanical pulp freeness is controlled at 280-320ml. Before pulping, use a pulping enzyme to pretreat the long fiber and short fiber, and the pulping enzyme is cellulase. The fillers used are heavy calcium carbonate and light calcium carbonate, and the addition ratio of light calcium carbonate is 20% of the mass of all fillers.

[0057] (2) Dye addition steps:

[0058] ① Prepare in a dilution tank a purple dye with a mass concentration of 0.1%-0.5%, a blue dye with a mass concentration of 0.1%-0.3%, a yellow dye with a mass concentration of 0.1%-0.3%, and a red dye with a mass concentration of 0.01%-0.03%;

[0059] ② For white paper with different CIE whiteness, add the above dyes to the mixed pulp according to the following formula. The content per ton of paper is calculated as: purple dye 42g, blue dye 10g, yellow dye 15g, red dye 3g.

[0060] (3) Copying steps:

[0061] Sizing, fiber dispersion in headbox, dehydration and forming in the wire section, dehydration in the press section, pre-drying, surface sizing, post-drying and calendering, curling and rewinding. The sizing concentration is 1%; the sizing agent involved is a mixture of surface starch, alkyl ketene dimer (AKD) and styrene acrylic acid (SAE) surface sizing agent, which is added to the sizing machine through the sizing feeder trough and transferred to the paper through the sizing roller for sizing. The single-sided sizing amount is 1g / m 2 .

[0062] See the product photos of the natural white offset paper produced Figure 3 Its CIE whiteness is 81.2, L value is 93.8, a value is -0.2, b value is 1.0, and fluorescence value is 0.4. The product has a hue that meets the requirements of national standards and has a better eye protection effect.

[0063] Comparative Example 1

[0064] 1. Pulping step: preparing high white long fiber pulp with ISO brightness of 89% to 90%, low white short fiber pulp with ISO brightness of 75% to 85%, and chemical mechanical pulp with ISO brightness of 79% to 83% respectively;

[0065] 2. Slurry preparation step: 5% to 30% of high white long fiber pulp, 55% to 80% of low white short fiber pulp and 5% to 30% of chemical mechanical pulp are mixed evenly according to weight percentage to obtain a mixed pulp;

[0066] 3. Adding chemicals: adding fluorescent brightener with a mass concentration of 0.1%-5%, purple pigment with a mass concentration of 0.1%-0.5% and blue pigment with a mass concentration of 0.1%-0.5% to the mixed pulp; the addition amount is calculated according to the content per ton of paper: fluorescent brightener 0.01-0.1kg; purple pigment and blue pigment are both 5-20g;

[0067] 4. Papermaking steps: The papermaking steps usually include sizing, fiber dispersion in the headbox, dehydration and forming in the wire section, dehydration in the press section, pre-drying, surface sizing, post-drying and calendering, curling, and rewinding.

[0068] 5. The paper production method includes the following production process:

[0069] 5.1. Produce high white paper with CIE whiteness of 145-158;

[0070] 5.2. After the production of the high-white paper is completed, produce natural white offset paper with a CIE whiteness of 55-85;

[0071] 6. Pulping process: Change from high white paper to natural white offset paper, and change short fiber pulp from high white pulp to low white pulp.

[0072] The difference between low white pulp and high white pulp: low white pulp whiteness 81%, high white pulp whiteness 89%; low white pulp needs 2500 revolutions to be beaten to 300ml freeness, high white pulp needs 2100 revolutions to be beaten to 300ml freeness, and the beating is unstable; the tear index of low white pulp at 300ml freeness is 7.2mN.m 2 / g, the tear index of high white pulp at 300ml freeness is 8.5mN.m 2 / g; low white pulp loose thickness is 1.3cm 3 / g, high white pulp bulk thickness is 1.37cm 3 / g, the fine fiber content of low white pulp is 8.1%, and the fine fiber content of high white pulp is 5.5%; the pulp changing process causes fluctuations in the dehydration and operation of the paper machine, and the quality of the finished product such as thickness, strength, smoothness, etc. also becomes unstable.

[0073] According to the remaining order volume of high-white paper grades, calculate the time for switching to the production of raw white offset paper, control the liquid level of the staple fiber (high white pulp) pulp tower in advance, lower the liquid level of the staple fiber pulp tower, and according to the time for switching to the production of raw white offset paper, shred the low white staple fiber pulp in advance to ensure that the low white staple fiber pulp can be put online when switching to the production of raw white offset paper.

[0074] 7. Dye preparation process: prepare violet pigment and blue pigment with mass concentration of 0.1%-0.5% and fluorescent brightener of 0.1%-5%.

[0075] In the process of preparing low white offset paper, the fluorescence value of the low white offset paper is controlled at 0.4-2. Specifically, when the fluorescence value is close to the lower limit range, start adding fluorescent brightener with a mass concentration of 0.1%-5% into the paper machine; when the fluorescence value is too low in the later stage, the mass concentration of the fluorescent brightener can be controlled according to the hue requirements, so that the fluorescence value of the low white offset paper reaches the target hue.

[0076] According to the above production process, the CIE whiteness of the white offset paper produced from the low white short fiber pulp is 55-85, the L value is 93-95.5, the a value is -0.5-0.5, the b value is 0.5-6.5, and the fluorescence value is 0.4-2.

[0077] Example 2

[0078] (1) Slurry preparation steps:

[0079] ① Provide high white long fiber pulp with ISO brightness of 89%-90%, high white short fiber pulp with ISO brightness of 89%, and chemical mechanical pulp with ISO brightness of 77%;

[0080] ② After pulping with a pulper, a pulping enzyme is added for pulping; after pulping, a filler is added, wherein the filler addition amount is 27% of ash, 30% of high white long fiber pulp, 55% of high white short fiber pulp and 15% of chemical mechanical pulp are mixed uniformly by weight percentage, and 7.5 kg of cationic starch is added to prepare the pulp to obtain a mixed pulp;

[0081] (2) Dye addition steps:

[0082] ① Prepare in a dilution tank a purple dye with a mass concentration of 0.1%-0.5%, a blue dye with a mass concentration of 0.1%-0.3%, a yellow dye with a mass concentration of 0.1%-0.3%, and a red dye with a mass concentration of 0.01%-0.03%;

[0083] ② For white paper with different CIE whiteness, add the above dyes to the mixed pulp according to the following formula. The content per ton of paper is calculated as: 5g purple dye, 2g blue dye, 30g yellow dye, and 5g red dye.

[0084] (3) Copying steps:

[0085] The papermaking steps are as follows: sizing, fiber dispersion in the headbox, dehydration and forming in the wire section, dehydration in the press section, pre-drying, surface sizing, post-drying and calendering, curling, and rewinding.

[0086] The CIE whiteness of the produced natural white offset paper is 62.2, the L value is 95.5, the a value is -0.3, the b value is 6.7, and the fluorescence value is 0.7.

[0087] As can be seen from the above embodiments, the present invention mainly uses high-whiteness pulp to produce white offset paper, wherein the ISO whiteness of the raw material is generally above 89%; and a suitable dye is selected to adjust the color of the mixed pulp, and after various papermaking processes, a paper product is obtained. The whiteness of the fiber raw material in the present invention is relatively high. After the production of high-white paper is completed, there is no need to replace the pulp, and white offset paper can be directly produced. The pulp supply is relatively stable, the quality fluctuation of the finished product is small, and there is no need to add additional fluorescent brighteners, which is more environmentally friendly and healthy. The white offset paper described in the present invention has a unique product hue, and the hue has a better eye protection effect under the premise of meeting the requirements of the national standard.

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing white offset paper, characterized in that: The following steps are involved: Taking long fiber pulp with ISO brightness of 89-90%, short fiber pulp with ISO brightness ≥89% and chemical mechanical pulp with ISO brightness ≥77% as fiber raw materials, after beating, 10-30wt% of long fiber pulp, 55-80wt% of short fiber pulp and 15-30wt% of chemical mechanical pulp are mixed to obtain mixed pulp; Adding purple dye, blue dye, yellow dye and red dye to the mixed slurry according to the toning principle and a preset formula to obtain a mixed slurry with added dyes; Then, the mixed pulp with added dye is subjected to sizing, web forming, dehydration, pre-drying, surface sizing and post-drying in sequence to obtain natural white offset paper.

2. The preparation method according to claim 1, characterized in that: The beating is performed with the assistance of beating enzyme.

3. The preparation method according to claim 1, characterized in that: Fillers and cationic starch are added after the beating.

4. The preparation method according to claim 1, characterized in that: The mass concentration of the purple dye is 0.1-0.5%, the mass concentration of the red dye is 0.01-0.03%, and the mass concentrations of the blue dye and the yellow dye are 0.1-0.3% respectively; each ton of paper contains: 0-50g of purple dye, 0-30g of blue dye, 10-60g of yellow dye, and 0-10g of red dye.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The pulping process also includes pulping by a pulper before the beating.

6. The preparation method according to any one of claims 1 to 4, characterized in that: The sizing concentration is 1-1.2 wt %.

7. The preparation method according to any one of claims 1 to 4, characterized in that: The dehydration is squeezing dehydration; the surface sizing is double-sided coating using a sizing agent.

8. The white offset paper obtained by the preparation method according to any one of claims 1 to 7, having a CIE whiteness of 55 to 85%.

9. The white offset paper according to claim 8, characterized in that: The L value of the natural white offset paper is 93 to 96, the a value is -0.1 to -0.5, the b value is 0.5 to 6.5, and the fluorescence value is 0.4 to 2.

0.

10. The white offset paper according to claim 8, characterized in that: The weight of the white offset paper is 60-120g / m 2 The natural white offset paper does not contain any additional fluorescent brightener.

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