Natural color thin sheet packaging paper and preparation method thereof

Abstract

The invention relates to a natural color thin sheet wrapping paper and a preparation method thereof, and belongs to the field of thin sheet wrapping paper in the papermaking industry, wherein: the whiteness of the natural color thin sheet wrapping paper is 35-50%, and the pulp used in the preparation of the natural color thin sheet wrapping paper comprises 20-30% of wood pulp and 70-80% of unbleached straw pulp, and the beating degree of the unbleached straw pulp is 42-53°SR. Since the natural color thin sheet wrapping paper of the invention is mainly made of unbleached straw pulp with low beating degree, the technical prejudice that the thin sheet wrapping paper made of straw pulp needs a high beating degree is overcome, and the prepared paper has high strength, low cost, environmental friendliness, no toxic substances, and a wide range of applications. The preparation method thereof overcomes the problem of high difficulty in preparing thin sheet wrapping paper using straw pulp, and the prepared thin sheet wrapping paper has uniform texture, good transparency and high physical strength.

Description

Technical Field

[0001] The invention relates to a natural color thin sheet packaging paper, belonging to the field of thin sheet packaging paper in the papermaking industry, and in particular to a natural color thin sheet packaging paper produced by using wood pulp and unbleached pulp and a preparation method thereof. Background Art

[0002] Thin wrapping paper, also known as Sydney paper, is 22g / m 2 The following is a general term for a type of wrapping paper, which is used to wrap fruits, clothing, shoes, leather goods, hardware, porcelain, wine, handicrafts, etc. It has the functions of moisture-proof, protection and shaping, and can greatly improve the packaging grade of products. With the development of economy and the improvement of people's living standards, enterprises pay more and more attention to product packaging. Thin sheet wrapping paper is increasingly widely used and is closely related to daily consumer goods. The consumption demand for thin sheet wrapping paper is also gradually expanding.

[0003] Thin wrapping paper is a high-grade wrapping paper that is very difficult to produce. It is generally required to be thin and soft, with excellent uniformity and transparency, high physical strength, and good surface properties. It should be fine, flat, smooth, free of foam and sand, and have good printability. At present, thin wrapping paper is mainly produced with bleached wood pulp, but my country's wood resources are scarce, and currently my country's wood resources are far from meeting the needs of the growing pulp and paper industry. In order to make up for the shortage of raw materials, a considerable amount of pulp must be imported from abroad every year. By 2009, the import volume of wood pulp had reached 73% of the total wood pulp consumption. The high dependence on wood pulp imports has led to a continuous increase in production costs.

[0004] my country is a large agricultural country. The annual output of wheat, rice, cotton and corn straw used for pulping and papermaking is about 490 million tons. Grass fiber resources are abundant. Using straw pulp to make thin wrapping paper can greatly reduce the production cost of thin wrapping paper. Compared with wood pulp, straw pulp has short average fiber length, small fiber diameter, appears stiff, thick fiber cell wall, small cell cavity, and high content of miscellaneous cells. Therefore, when straw pulp is used for papermaking, the beating degree of straw pulp increases quickly, but it is not easy to achieve external fine fiberization.

[0005] The structure of straw pulp fiber can be divided into the intercellular layer, primary wall, secondary wall outer layer, secondary wall middle layer and secondary wall inner layer. The primary wall is a porous film similar to plastic, with a thickness of 0.1-1 micron, and its fine fibers are arranged in a network. From a structural point of view, it is isotropic and has a high lignin content, so it can only permeate water but not swell. On the contrary, it will limit the swelling of the secondary wall middle layer during pulping. The physical structure and chemical composition of the secondary wall outer layer are similar to those of the secondary wall. The secondary wall middle layer and the secondary wall inner layer are the main parts of the fiber and have a low lignin content. The outer layer of the secondary wall of straw pulp fiber is thicker and is tightly bonded to the secondary wall middle layer. It is difficult to remove it during the pulping process. Therefore, it is very difficult for the fiber to absorb water, swell and fibrillate.

[0006] The common bleaching method is strong oxidative bleaching, which can degrade lignin, fragment it and dissolve it, and also has an oxidative effect on cellulose and hemicellulose. Cellulose and hemicellulose are severely degraded under the action of bleaching agents, resulting in shorter fiber length and smaller fiber size in the straw pulp after bleaching, more fine fibers, and a lower water filtration rate. At the same time, there are many thin-walled cells in plant cells, which are easily broken during the pulping process, which leads to a rapid increase in the beating degree of straw pulp. The fibers do not have obvious longitudinal splitting until 80-90°SR, but at this time the fibers have been cut quite short, resulting in excessive fiber cutting, which not only affects the strength of the finished paper, but also makes it difficult to filter water during papermaking.

[0007] Since thin wrapping paper has a low basis weight and generally has low strength, a high beating degree is usually required to obtain a higher paper strength. In addition, while thin wrapping paper meets the quality standard requirements, it also has high requirements for the appearance quality such as paper uniformity. A well-formed thin wrapping paper should have uniform fiber structure and uniform distribution. Therefore, the pulp used in the production of thin wrapping paper requires longitudinal fiber splitting, a large number of fine fibers, and good brooming. The pulp beating degree required in the production of thin paper is above 80°SR, which is a high-viscosity pulp. (See Zhang Shengli, "Application of Table Tilting in the Production of High-grade Thin Paper", Heilongjiang Papermaking, 2003 (2): 39-39).

[0008] "Discussion on the pulp technology of thin paper using bamboo and awn pulp on a circular paper machine" (See Xiao Delin "Discussion on the pulp technology of thin paper using bamboo and awn pulp on a circular paper machine", Guangdong Papermaking, 1989 (3): 31-35) Thin paper packaging paper is made by mixing awn pulp with a certain amount of wood pulp. After bamboo and awn pulp are cooked, bleached, washed and beaten, the paper quality parameters of the thin paper packaging paper are as follows: Bamboo weight 21g / m 2 , tightness 0.6g / cm 3 , whiteness 77.1%, average tear length 4.15km, tear strength 78mN, dust degree 0 / m2 The requirements for pulping quality are: the fiber fully absorbs water and swells, has good softness and plasticity, the brooming rate should be more than 20%, the hydration degree is 5-8°SR, the average fiber length is 1.0-1.2mm, the beating degree is more than 80°SR, and the wet weight is 4-6g.

[0009] "Color Type II Thin Wrapping Paper Production Process" (see Wang Zengguo "Color Type II Thin Wrapping Paper Production Process", Northern Papermaking, 1994 (4): 38-39) uses reed pulp to make color type II thin wrapping paper. The reed pulp is boiled, washed, screened, purified, bleached, beaten, filled, and dyed before papermaking. The quality parameters of the prepared paper are as follows: Quantity 21.5g / m 2 The average breaking length is 2.92 km, and the longitudinal tear strength is 78 mN. In the beating step, the medium-viscous beating method is used for beating, the beating concentration is 6.8-6.9%, and the beating degree of the pulp is 60-62°SR.

[0010] Both methods use straw pulp to produce thin wrapping paper with low basis weight and quality that meets the standard. However, in order to improve the strength, uniformity and smoothness of the paper, the pulp used in the preparation has a high beating degree. It can be seen that it is generally believed that a high beating degree is required to produce thin wrapping paper with quality that meets the standard using straw pulp.

[0011] However, there are the following problems with high pulp beating degree: First, increasing the beating degree of straw pulp will lead to longer beating time, increased power consumption, and reduced production capacity; second, it will cause poor water filtration of straw pulp during the papermaking process, sticking to the pressing rollers and drying cylinders, causing paper sheets to break and increase paper defects, which directly affects the speed and productivity of the paper machine; third, due to the shearing action of the roller knife and bottom knife of the pulping equipment, increasing the beating degree will cause the straw pulp fibers to be excessively cut, greatly reducing the strength of the paper, especially the tear resistance.

[0012] In order to solve the above problems and overcome the technical prejudice that straw pulp needs a high beating degree to make thin packaging paper, it is necessary to use straw pulp with a low beating degree and capable of achieving fine fiberization to prepare thin packaging paper that meets quality standards. At present, thin packaging paper made from unbleached straw pulp and wood pulp with a low beating degree has not been found. Moreover, a preparation method for thin packaging paper made from unbleached straw pulp and wood pulp with a low beating degree has not been found. Summary of the invention

[0013] One of the purposes of the present invention is to provide a natural color thin wrapping paper. The pulp used in the natural color thin wrapping paper is mainly low-beating degree unbleached straw pulp, which has a short beating time, reduces the power consumption of pulping, improves the strength and quality stability of the thin wrapping paper, and the natural color thin wrapping paper has a smooth and uniform surface, can withstand considerable tensile strength, and can adapt to high-speed mechanical production operations.

[0014] In order to achieve the above object, the technical solution adopted by the present invention is:

[0015] Disclosed is a natural color tissue wrapping paper, the whiteness of which is 35-50%. The pulp used in the preparation of the natural color tissue wrapping paper comprises 20-30% of wood pulp and 70-80% of unbleached straw pulp, preferably 22-28% of wood pulp and 72-78% of unbleached straw pulp, and the beating degree of the unbleached straw pulp is 42-53°SR.

[0016] It is much more difficult to make thin paper with straw pulp than to make general cultural paper because straw pulp has its own characteristics. It is well known to those skilled in the art that straw pulp has shorter fiber length, smaller fiber diameter, and appears stiffer than wood pulp. It has thicker cell walls, smaller cell cavities, and more miscellaneous cells. Therefore, the production of thin paper with straw pulp has higher requirements for pulping quality. "A Study on the Pulp Technology of Making Thin Paper with Small Bamboo and Ion Cane Pulp on a Garden Wire Paper Machine" (see Xiao Delin's "A Study on the Pulp Technology of Making Thin Paper with Small Bamboo and Ion Cane Pulp on a Garden Wire Paper Machine", Guangdong Papermaking, 1989 (3): 31-35) puts forward the following requirements for pulping quality: the fiber fully absorbs water and swells, has good softness and plasticity, the brooming rate should reach more than 20%, the hydration degree is 5-8°SR, the average fiber length is 1.0-1.2mm, the beating degree is more than 80°SR, and the wet weight is 4-6g. It can be seen that the prior art generally believes that the pulping degree in the production of straw pulp tissue paper is required to be above 80°SR.

[0017] The present invention proposes to use unbleached straw pulp with low beating degree to prepare thin packaging paper with excellent performance parameters in all aspects, thus overcoming the prejudice of the prior art. The unbleached straw pulp used in the present invention has low beating degree, short beating time, reduced grinding power consumption, reduced cost, and improved production capacity, thus having huge economic and social benefits; the present invention adds a small amount of wood pulp to the pulp to overcome the problem of low strength of thin packaging paper prepared with straw pulp alone, thereby improving the quality of thin packaging paper; the pulp of the thin packaging paper of the present invention mostly uses unbleached straw pulp, thus eliminating the pollution to the environment caused by waste gas and waste liquid released in bleached straw pulp, thereby reducing the pollution to the environment caused by the preparation of natural color thin packaging paper.

[0018] The unbleached straw pulp may also be straw pulp treated with oxygen delignification, and the straw pulp has a beating degree of 42-50°SR, preferably 43-49°SR, more preferably 44-48°SR, and most preferably 45-47°SR.

[0019] The natural color thin sheet packaging paper of the present invention has a density of 0.46-0.70 g / cm 3 The average tearing length is 2.8-4.0km in both vertical and horizontal directions, and the average tearing strength is 40-70mN in both vertical and horizontal directions.

[0020] The density of the natural color thin sheet packaging paper of the present invention is 0.46-0.64g / cm 3 , preferably 0.46-0.60g / cm 3 , more preferably 0.46-0.49 g / cm 3 The tear length of the natural color thin sheet wrapping paper is 2.9-3.8 km on average in both longitudinal and transverse directions, preferably 3.0-3.5 km, more preferably 3.1-3.3 km; the tear strength of the thin sheet wrapping paper is 50-68 mN on average in both longitudinal and transverse directions, preferably 55-67 mN, more preferably 56-66 mN.

[0021] The basis weight of the natural color thin sheet packaging paper of the present invention is 14-18g / m 2 , preferably 16-18g / m 2 .

[0022] The air permeability of the unbleached thin sheet packaging paper of the present invention is 14-41 μm / Pa·s, preferably 15-20 μm / Pa·s; the moisture content of the unbleached thin sheet packaging paper is 7.0-12.0%, preferably 7.0-8.8%; the brightness of the unbleached thin sheet packaging paper is 30-60%; the dustiness of the unbleached thin sheet packaging paper is 0.3-1.5 mm 2 0-2 pieces / m 2 , 0.5-1.5mm 2 0pcs / m 2 , ≥1.5 mm 2 0pcs / m 2 .

[0023] The unbleached thin sheet packaging paper of the present invention is obtained by using unbleached straw pulp with a beating degree of 42-53°SR as the main raw material, and adding a certain amount of wood pulp when necessary, and then beating and papermaking. Since the straw pulp used is an unbleached straw pulp with a low beating degree that has been subjected to oxygen bleaching lignin, it has excellent properties such as fast water filtration speed and high strength. The obtained unbleached thin sheet packaging paper has a smooth surface, uniform paper fiber structure, high strength and good quality.

[0024] Thin wrapping paper has a small basis weight and a thin thickness; the paper requires uniform fiber structure, smooth appearance, fine paper and high paper strength. It is generally believed that the pulping degree required in the production of straw pulp thin paper is above 80°SR. The present invention overcomes the prejudice of the prior art and proposes to use low-beating straw pulp to prepare thin wrapping paper with excellent performance parameters in all aspects. It is a low-cost, green and environmentally friendly product with better quality than the thin wrapping paper of the prior art.

[0025] Since the straw pulp used has been oxygen delignified, the crystallization index of cellulose and hemicellulose is reduced, and the fiber structure is loose, so that the straw pulp is easy to be fine-fibered and easy to be beaten, thereby improving the water filtration performance of the pulp, reducing the beating degree, and reducing the energy consumption of pulping; compared with the bleached straw pulp, the fiber strength of the unbleached straw pulp is increased by 30-50%, the fiber yield is increased by 10%, and the breaking length (average vertical and horizontal) is increased by 2-5%, thereby greatly improving the strength of the natural color thin sheet packaging paper, such as the breaking length and tear strength; the amount of straw pulp used is large, which reduces the cost and saves wood resources; at the same time, adding a small amount of wood pulp overcomes the problem of low strength of thin sheet packaging paper prepared with straw pulp alone, and improves the quality of thin sheet packaging paper.

[0026] In addition, with the increasing attention paid to protecting the ecological environment around the world, wastewater pollution generated by the pulp bleaching process has been recognized by people. Pulp bleaching wastewater and its sludge contain highly toxic substances, such as dioxins, which are extremely toxic, have strong carcinogenicity, mutagenicity and teratogenicity, can feminize males, affect the growth and development of children, and cause multiple brain neuropathy and acute toxicity, especially acute toxicity to aquatic organisms, which is extremely destructive to the environment. In addition, the bleached pulp also contains residual toxic substances, which limits the use of the packaging paper, such as it cannot be used for food packaging. The unbleached thin sheet packaging paper described in the present invention removes the complicated bleaching steps during the preparation process, which not only further simplifies the preparation process, but also fundamentally eliminates the pollution caused to the environment by the waste gas and waste liquid released in the bleached straw pulp, thereby reducing the pollution caused to the environment when preparing the unbleached thin sheet packaging paper. In addition, the prepared unbleached thin sheet packaging paper does not contain toxic substances generated during the bleaching process, which expands the scope of application, such as for food packaging.

[0027] Another object of the present invention is to provide a method for preparing the natural color thin sheet packaging paper of the present invention, wherein the preparation method has a simple process and the prepared natural color thin sheet packaging paper is of high quality.

[0028] In order to achieve the above object, the technical solution adopted by the present invention is:

[0029] A method for preparing the natural color thin wrapping paper comprises:

[0030] 1) The grass raw material is steamed, squeezed, washed and deflated to obtain the unbleached straw pulp; or the unbleached straw pulp is obtained by oxygen delignification after deflation;

[0031] 2) beating the wood pulp and the unbleached straw pulp respectively, wherein the beating concentration of the wood pulp is 2.0-3.0%, and the beating concentration of the unbleached straw pulp is 2.5-4.0%. After the beating, the obtained wood pulp has a beating degree of 48-55°SR, and a beating wet weight of 7.0-9.0g, and the obtained unbleached straw pulp has a beating degree of 42-53°SR, and a beating wet weight greater than 1.5g;

[0032] 3) Mixing 20-30% of the above-mentioned wood pulp and 70-80% of the above-mentioned unbleached straw pulp after beating until the pulp is uniform;

[0033] 4) The slurry obtained in step 3) is paper-made to obtain the natural color thin sheet packaging paper.

[0034] The grass raw material of the present invention comprises one or a combination of rice straw, wheat straw, cotton stalk, bagasse, reed or Phragmites australis.

[0035] The cooking, squeezing, washing and debonding in step 1) of the present invention all adopt existing technologies.

[0036] The oxygen delignification in step 1) of the present invention comprises: pumping the straw pulp obtained after cooking to an oxygen delignification reaction tower, and adding sodium hydroxide, magnesium sulfate and oxygen; the straw pulp undergoes a delignification reaction in the oxygen delignification reaction tower to obtain unbleached straw pulp.

[0037] The unbleached straw pulp described in the present invention refers to straw pulp that has not been subjected to conventional chlorine-containing bleaching.

[0038] The unbleached straw pulp of the present invention is prepared by oxygen delignification after cooking straw pulp, and a large amount of lignin remaining after cooking is removed by using oxygen and alkali, so that the crystallinity index of cellulose and hemicellulose is reduced, the fiber structure is loose, and the straw pulp is easy to be fine-fibered; at the same time, the degradation and damage of cellulose and hemicellulose useful for papermaking in the straw pulp raw material are reduced as much as possible, and the inherent length of straw pulp fibers is maintained. The straw pulp fibers are cellulose and hemicellulose.

[0039] The oxygen delignification process has the following effects on the fibrillation of straw pulp at low beating degree: (1) The hydrogen bonds between the straw pulp fibers are broken, making it easy to split and separate longitudinally. Cellulose and hemicellulose swell significantly in alkaline solution. Due to the swelling pressure and the action of oxygen dissolved in the alkali solution, the hydrogen bonds between the straw pulp fibers are oxidized and broken, which reduces the crystallinity index of cellulose and hemicellulose, destroys the cellulose crystallization area, makes the fiber structure loose, and makes the fiber surface fluffy. (2) Oxygen delignification removes part of the lignin, which reduces the restriction of lignin on the swelling of cellulose and hemicellulose. Under the action of alkali solution and oxygen, the lignin in the outer layer of the primary wall and secondary wall is degraded in large quantities, and the oxygen dissolved in the alkali solution can easily pass through the swollen fiber surface and enter the fiber interior, reacting with the lignin mixed in cellulose and hemicellulose or tightly bound to cellulose and hemicellulose. The removal of lignin is conducive to the swelling of straw pulp fibers during beating, and longitudinal splitting occurs to produce fine fibers; (3) The transverse cutting effect of the beating process on straw pulp fibers is reduced. After oxygen delignification, the straw pulp fibers are fully swollen, and the fibers become flexible and elastic, and deformation, curling and kinking occur, which makes the straw pulp fibers less susceptible to transverse cutting during the pulping process; (4) the purity of cellulose and hemicellulose is improved. During the oxygen delignification process, organic matter on the surface of straw pulp fibers and impurities between fibers will also dissolve into the alkali solution under the action of oxygen, reducing the content of impurities and fine cells in the straw pulp, increasing the purity of cellulose and hemicellulose in the straw pulp that are useful for papermaking, and increasing the water filtration rate of the straw pulp. The above factors make the straw pulp fibers fully swell and bend after oxygen delignification, and the fiber surface begins to fluff, which is conducive to the fine fiberization of cellulose and hemicellulose in the subsequent pulping step.

[0040] The oxygen delignification preferably described in the present invention is single-stage oxygen delignification, using an oxygen delignification reaction tower; the straw pulp concentration is 8-18%, the temperature of the straw pulp at the inlet of the reaction tower is 90-100°C, and the pressure is 0.9-1.2MPa; the temperature at the outlet is 95-105°C, and the pressure is 0.2-0.4MPa; the amount of alkali used in the oxygen delignification treatment is 2-4% of the absolute dry pulp amount in terms of sodium hydroxide, the amount of magnesium sulfate used is 3-5% of the absolute dry pulp amount, and the amount of oxygen added is 20-40kg / ton of pulp; the reaction time of the straw pulp in the reaction tower is 60-90 minutes.

[0041] The present invention adopts single-stage oxygen delignification mainly to further ensure the strength of pulp. Compared with multi-stage oxygen delignification, single-stage oxygen delignification has less degradation effect on cellulose. The preferred process parameters of the present invention for single-stage oxygen delignification are generally lower temperature and relatively longer time, mainly to carry out the delignification reaction more gently and avoid the degradation of cellulose as much as possible. Adding magnesium sulfate as a protective agent during the oxygen delignification process can successfully control the degradation of cellulose and protect the damage of cellulose and hemicellulose to the oxygen delignification process to the greatest extent.

[0042] The preferred concentration of straw pulp before oxygen delignification treatment in the present invention is 8-18%. The main advantages of oxygen delignification under medium-consistency conditions are: low investment; due to the success of medium-consistency mixing and pumping technology, the pulp treatment is much easier than high-consistency pulp; the pulp concentration is low, the equipment is less corroded, and there is no danger of burning in oxygen. The beating degree of unbleached straw pulp after oxygen delignification is 32-36°SR. The straw pulp after oxygen delignification only needs light beating to achieve fine fiberization, meeting the requirements of papermaking thin sheet packaging paper.

[0043] The beating described in the present invention is carried out in a double-disc refiner.

[0044] The unbleached straw pulp and the wood pulp are beaten separately, and the beating quality is easy to control, so that each type of pulp reaches the best strength, and the situation of uneven beating, excessive beating of some fibers and insufficient beating of some fibers is avoided.

[0045] The papermaking described in the present invention is carried out in a fourdrinier multi-cylinder paper machine.

[0046] In step 2) of the present invention, the pulping concentration of the wood pulp is 2.2-2.5%, and the pulping concentration of the unbleached straw pulp is 2.5-2.9%. After the pulping is completed, the pulping degree of the wood pulp obtained is 50-53°SR, and the wet weight of the pulp is 7.2-7.8g; the pulping degree of the unbleached straw pulp obtained is 42-50°SR, and the wet weight of the pulp is 1.5-2.0g.

[0047] In the step 3) of the present invention, additives are added to the mixed slurry, and the additives include starch in the slurry, a dispersant in the slurry, an alkyl ketene dimer and a drying cylinder peeling agent.

[0048] The additives added in the present invention are 6-13 kg / ton of starch in the slurry, 1-5 kg / ton of dispersant in the slurry, and 8-12 kg / ton of alkyl ketene dimer.

[0049] The starch in the pulp can improve the bursting resistance and tensile strength of natural thin paper packaging paper, increase stiffness and resist powdering and hair loss. The dispersant in the pulp can effectively disperse the pulp fibers, increase the retention rate of fine fibers and additives, improve the uniformity of the pulp and the softness of the paper, so that the paper can avoid holes, have high uniformity and good hand feel, and can also increase the papermaking speed. The alkyl ketene dimer (AKD) is a synthetic glue commonly used in papermaking. AKD is a kind of reactive neutral sizing agent, which has an active group that directly reacts with the hydroxyl group in cellulose, and directly reacts with the hydroxyl group of cellulose to achieve the purpose of sizing. The drying cylinder stripping agent can completely solve the problem of sticking to the cylinder in papermaking, keep the system clean, and the paper sheets free of oil spots, and can play a good stripping, lubrication and glossing effect; at the same time, it can also reduce the phenomenon of paper breakage, hair loss and powder loss, greatly improve the smoothness and glossiness of the paper, do not affect the strength of the paper, improve the quality of the finished paper, and have a good lubrication and protection effect on the drying cylinder wrinkling scraper, extending the service life of the scraper.

[0050] In the test for detecting harmful substances in the natural color thin sheet packaging paper of the present invention, neither dioxins nor adsorbable organic halides were detected.

[0051] The natural color tissue wrapping paper of the present invention can be transformed into tissue wrapping paper of various colors by adding dyes commonly used in the prior art into the pulp according to product requirements. The tissue wrapping paper does not contain dioxins, adsorbable organic halides and other substances harmful to the body.

[0052] In order to clearly explain the content and technical solutions of the present invention, some terms used in the present invention are defined as follows. In the event of any inconsistency between the definitions in any other document and the present invention, the definitions in the present invention shall prevail, as follows:

[0053] The unbleached straw pulp described in the present invention refers to the straw pulp obtained by using one or more combination raw materials of annual plants, including but not limited to wheat straw, rice straw, cotton stalks, corn stalks, reeds, etc., without any bleaching.

[0054] The wood pulp described in the present invention is bleached wood pulp or unbleached wood pulp.

[0055] The natural color thin sheet packaging paper of the present invention refers to the thin sheet packaging paper which is mainly made of grass pulp obtained by using grass plants as raw materials and not subjected to any bleaching and a small amount of wood pulp.

[0056] Since the thin wrapping paper of the present invention is made of low-beating degree unbleached straw pulp and wood pulp, the unbleached straw pulp has a low beating degree and a short beating time, which reduces the power consumption of pulping, reduces the cost, and improves the production capacity, thus having huge economic and social benefits. The present invention is beneficial in that:

[0057] (1) The natural color thin wrapping paper of the present invention mainly adopts unbleached straw pulp with low beating degree, which overcomes the technical prejudice of the prior art that straw pulp needs a high beating degree to make thin wrapping paper, reduces the excessive cutting effect of beating on fibers, reduces the influence on the tear length and tear resistance, and improves the strength of paper.

[0058] (2) The method for preparing natural color thin wrapping paper of the present invention overcomes the prejudice that straw pulp has a high beating degree in preparing thin wrapping paper, and solves the problems of poor water filtration, sticking to the pressing rollers and drying cylinders, and paper breakage caused by the high beating degree in the papermaking process. The prepared thin wrapping paper has uniform texture and smooth surface.

[0059] (3) The use of unbleached straw pulp can avoid the generation of harmful chemicals during the bleaching process, reduce papermaking wastewater, benefit environmental protection and greatly reduce the cost of enterprise sewage treatment. The natural color thin sheet packaging paper of the present invention does not contain toxic substances generated during the bleaching process, thereby expanding the scope of application, such as for food packaging, etc. DETAILED DESCRIPTION

[0060] The present invention will be described in more detail below in conjunction with the embodiments. It should be noted that the embodiments given below are only illustrative and do not limit the scope of protection of the present invention. Those of ordinary skill in the art may make various improvements and changes without violating the spirit of the present invention, and these changes and changes all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0061] In the following examples, various quality indicators were measured under the following conditions: temperature: 23.1° C., relative humidity: 50.9% (after equilibrium).

[0062] Example 1

[0063] The wheat straw raw material is cooked by conventional methods, and then squeezed, washed and deflated. The 10% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 20kg / ton of oxygen, 5% magnesium sulfate for absolute dry pulp and 4% alkali solution for absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed through the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 90°C and the pressure is 0.9MPa. It stays for 75 minutes to allow the pulp to undergo sufficient delignification reaction. The temperature at the outlet is 100°C and the pressure is maintained at 0.3MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 34°SR.

[0064] Unbleached wood pulp and unbleached straw pulp are beaten respectively, the unbleached wood pulp beating concentration is 2.5%, the unbleached straw pulp beating concentration is 2.5%, the beating is carried out in a double disc refiner, and the pulp quality standard obtained after beating is: unbleached wood pulp beating degree 53°SR, wet weight 7.5g, unbleached straw pulp beating degree 43°SR, wet weight 1.5g. The unbleached wood pulp is the unbleached wood pulp of the prior art, including unbleached sulfate coniferous wood pulp, unbleached sulfite coniferous wood pulp, etc.

[0065] 30% of the above-mentioned unbleached wood pulp and 70% of the above-mentioned unbleached straw pulp are mixed until the pulp is uniform, 6kg / ton of starch, 3kg / ton of dispersant, 10kg / ton of alkyl ketene dimer and 0.5kg / ton of drying cylinder stripping agent are added and mixed evenly, and then papermaking is carried out according to conventional processes to obtain the natural color thin sheet packaging paper.

[0066] The quality indicators of the natural color thin wrapping paper are as follows:

[0067] Basis weight: 17.0g / m 2 ;

[0068] Whiteness: 38.0%;

[0069] Tightness: 0.49g / m 3 ;

[0070] Fault length (average vertically and horizontally): 2.91km;

[0071] Tear strength (average vertical and horizontal): 57mN;

[0072] Air permeability: 18μm / (Pa·s);

[0073] Dust degree: 0.3-1.5mm 2 :2pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0074] Moisture: 7.4%;

[0075] Brightness: 40%.

[0076] Example 2

[0077] The bagasse raw material is cooked by conventional methods, and then squeezed, washed and deflated. The 8% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 20kg / ton of oxygen, 3% magnesium sulfate for the absolute dry pulp and 3% alkali solution for the absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed through the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 95°C and the pressure is 0.9MPa. It stays for 75 minutes to allow the pulp to undergo sufficient delignification reaction. The temperature at the outlet is 100°C and the pressure is maintained at 0.4MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 36°SR.

[0078] The unbleached wood pulp and unbleached straw pulp were pulped separately, with the unbleached wood pulp beating concentration of 2.5%, and the unbleached straw pulp beating concentration of 2.5%. The pulping was carried out in a double-disc refiner, and the quality standards of the pulp obtained after beating were: unbleached wood pulp beating degree 53°SR, wet weight 7.5g, unbleached straw pulp beating degree 42°SR, wet weight 1.5g.

[0079] 20% of the unbleached wood pulp and 80% of the unbleached straw pulp are mixed until the pulp is uniform, 13 kg / ton of starch, 5 kg / ton of dispersant, 12 kg / ton of alkyl ketene dimer and 0.8 kg / ton of drying cylinder stripping agent are added, mixed evenly and then papered according to conventional process to obtain the natural color thin sheet packaging paper.

[0080] The quality indicators of the natural color thin wrapping paper are as follows:

[0081] Basis weight: 17.2g / m 2 ;

[0082] Whiteness: 35.0%;

[0083] Tightness: 0.47g / m 3 ;

[0084] Fault length (average vertically and horizontally): 3.16km;

[0085] Tear strength (average vertically and horizontally): 56mN;

[0086] Air permeability: 14μm / (Pa·s);

[0087] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2:0pcs / m 2 ;

[0088] Moisture: 7.8%;

[0089] Brightness: 30%.

[0090] Example 3

[0091] The raw material of Phragmites australis is boiled by conventional methods, and then squeezed, washed and deflated. The 13% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 30kg / ton of oxygen, 4% magnesium sulfate for absolute dry pulp and 2% alkali solution for absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed into the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 100°C and the pressure is 1.02MPa. It stays for 90 minutes so that the pulp can undergo sufficient delignification reaction. The temperature at the outlet is 105°C and the pressure is maintained at 0.4MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 35°SR.

[0092] The unbleached wood pulp and unbleached straw pulp were pulped separately, with the unbleached wood pulp beating concentration of 3.0% and the unbleached straw pulp beating concentration of 3.7%. The pulping was carried out in a double-column refiner. The quality standards of the pulp obtained after pulping were: unbleached wood pulp beating degree 48°SR, wet weight 8.8g, unbleached straw pulp beating degree 50°SR, wet weight 2.0g.

[0093] 22% of the above-mentioned unbleached wood pulp and 78% of the above-mentioned unbleached straw pulp are mixed until the pulp is uniform, 5kg / ton of starch, 5kg / ton of pulp, 12kg / ton of pulp, and 0.5kg / ton of pulp are added to the pulp, and after mixing evenly, papermaking is carried out according to conventional processes to obtain the natural color thin sheet packaging paper.

[0094] The quality indicators of the natural color thin wrapping paper are as follows:

[0095] Basis weight: 17.1g / m 2 ;

[0096] Whiteness: 45.6%;

[0097] Tightness: 0.55g / m 3 ;

[0098] Fault length (average vertically and horizontally): 2.89km;

[0099] Tear strength (average vertical and horizontal): 57mN;

[0100] Air permeability: 30μm / (Pa·s);

[0101] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0102] Moisture: 11.2%;

[0103] Brightness: 40%.

[0104] Example 4

[0105] The straw raw material is cooked by conventional methods, and then squeezed, washed and deflated. The straw pulp with a concentration of 15% obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 30kg / ton of oxygen, 3% magnesium sulfate for the absolute dry pulp and 2% alkali solution for the absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed through the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 98°C and the pressure is 1.2MPa. It stays for 90 minutes so that the pulp can undergo sufficient delignification reaction. The temperature at the outlet is 95°C and the pressure is maintained at 0.4MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 33°SR.

[0106] The unbleached wood pulp and unbleached straw pulp were pulped separately, with the unbleached wood pulp beating concentration of 2.0% and the unbleached straw pulp beating concentration of 4.0%. The pulping was carried out in a double-column refiner. The quality standards of the pulp obtained after pulping were: unbleached wood pulp beating degree 48°SR, wet weight 9.0g, unbleached straw pulp beating degree 53°SR, wet weight 1.5g.

[0107] 25% of the unbleached wood pulp and 75% of the unbleached straw pulp are mixed until the pulp is uniform, 8 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, and after mixing evenly, papermaking is carried out according to conventional processes to obtain the natural color thin sheet packaging paper.

[0108] The quality indicators of the natural color thin wrapping paper are as follows:

[0109] Basis weight: 14.0g / m 2 ;

[0110] Whiteness: 36.8%;

[0111] Tightness: 0.46g / m 3;

[0112] Fault length (average vertically and horizontally): 2.80km;

[0113] Tear strength (average vertically and horizontally): 49mN;

[0114] Air permeability: 14μm / (Pa·s);

[0115] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0116] Moisture: 9.5%;

[0117] Brightness: 50%.

[0118] Example 5

[0119] The reed raw material is boiled by conventional methods, and then squeezed, washed and deflated. The 12% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 40kg / ton of oxygen, 5% magnesium sulfate for absolute dry pulp and 3.5% alkali solution for absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed into the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 95°C and the pressure is 0.9MPa. It stays for 70 minutes to allow the pulp to undergo sufficient delignification reaction. The temperature at the outlet is 95°C and the pressure is maintained at 0.3MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 36°SR.

[0120] The unbleached wood pulp and unbleached straw pulp were pulped separately, the unbleached wood pulp had a pulping concentration of 2.0%, and the unbleached straw pulp had a pulping concentration of 4.0%. The pulping was carried out in a double-disc refiner, and the quality standards of the pulp obtained after pulping were: unbleached wood pulp had a beating degree of 50°SR, a wet weight of 7.0g, and unbleached straw pulp had a beating degree of 44°SR, and a wet weight of 2.0g.

[0121] 28% of the unbleached wood pulp and 72% of the unbleached straw pulp are mixed until the pulp is uniform, 13 kg / ton of starch, 1 kg / ton of dispersant, 8 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, mixed evenly and then papered according to conventional process to obtain the natural color thin sheet packaging paper.

[0122] The quality indicators of the natural color thin wrapping paper are as follows:

[0123] Basis weight: 18.0g / m 2 ;

[0124] Whiteness: 36.5%;

[0125] Tightness: 0.64g / m 3 ;

[0126] Fault length (average vertically and horizontally): 3.57km;

[0127] Tear strength (average vertically and horizontally): 68mN;

[0128] Air permeability: 32μm / (Pa·s);

[0129] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0130] Moisture: 7.0%;

[0131] Brightness: 38%.

[0132] Example 6

[0133] The cotton stalk raw material is cooked by conventional methods, and then squeezed, washed and deflated. The 15% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 40kg / ton of oxygen, 3% magnesium sulfate for absolute dry pulp and 4% alkali solution for absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed into the pipeline to heat the pulp. After that, the pulp is fully mixed and enters the oxygen delignification reaction tower. The temperature at the inlet of the reaction tower is 95°C and the pressure is 0.9MPa. It stays for 60 minutes to allow the pulp to undergo sufficient delignification reaction. The temperature at the outlet is 95°C and the pressure is maintained at 0.2MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 32°SR.

[0134] The bleached wood pulp and unbleached straw pulp were pulped separately, the bleached wood pulp was pulped at a concentration of 2.2%, and the unbleached straw pulp was pulped at a concentration of 2.9%. The pulping was carried out in a double-disc refiner. The quality standards of the pulp obtained after pulping were: bleached wood pulp beating degree 50°SR, wet weight 7.2g; unbleached straw pulp beating degree 45°SR, wet weight 1.8g.

[0135] 30% of the bleached wood pulp and 70% of the unbleached straw pulp are mixed until the pulp is uniform, 10 kg / ton of starch, 3 kg / ton of dispersant, 10 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, mixed evenly and then papered according to conventional process to obtain the natural color thin sheet packaging paper.

[0136] The quality indicators of the natural color thin wrapping paper are as follows:

[0137] Basis weight: 14.2g / m 2 ;

[0138] Whiteness: 36.0%;

[0139] Tightness: 0.47g / m 3 ;

[0140] Fault length (average vertically and horizontally): 3.19km;

[0141] Tear strength (average in longitudinal and transverse directions): 62mN;

[0142] Air permeability: 34μm / (Pa·s);

[0143] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0144] Moisture: 7.8%;

[0145] Brightness: 54%.

[0146] Example 7

[0147] The rice straw, wheat straw and reed raw materials with a mass ratio of 1:3:1 are cooked by conventional methods, and then squeezed, washed and deflated. The 18% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 20kg / ton of oxygen, 4% magnesium sulfate for the absolute dry pulp and 4% alkali solution for the absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed into the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 100°C and the pressure is 1.15MPa. It stays for 75 minutes to allow the pulp to undergo sufficient delignification reaction. The temperature at the outlet is 100°C and the pressure is maintained at 0.4MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 33°SR.

[0148] The bleached wood pulp and unbleached straw pulp were pulped separately, the bleached wood pulp had a pulping concentration of 2.9%, and the unbleached straw pulp had a pulping concentration of 2.7%. The pulping was carried out in a double-disc refiner. The quality standards of the pulp obtained after pulping were: bleached wood pulp had a beating degree of 50°SR, wet weight of 8.1g, and unbleached straw pulp had a beating degree of 49°SR, wet weight of 2.0g.

[0149] 20% of the bleached wood pulp and 80% of the unbleached straw pulp are mixed until the pulp is uniform, 10 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, and papermaking is carried out according to conventional technology. After mixing evenly, the natural color thin sheet packaging paper is obtained.

[0150] The quality indicators of the natural color thin wrapping paper are as follows:

[0151] Basis weight: 17.8g / m 2 ;

[0152] Whiteness: 50.0%;

[0153] Tightness: 0.55g / m 3 ;

[0154] Fault length (average vertically and horizontally): 3.52km;

[0155] Tear strength (average vertically and horizontally): 54mN;

[0156] Air permeability: 21μm / (Pa·s);

[0157] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0158] Moisture: 9.0%;

[0159] Brightness: 48%.

[0160] Example 8

[0161] The wheat straw raw material is cooked by conventional methods, and then squeezed, washed and deflated. The 12% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 20kg / ton of oxygen, 3% magnesium sulfate for absolute dry pulp and 4% alkali solution for absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed through the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 100°C and the pressure is 1.05MPa. It stays for 75 minutes so that the pulp can undergo sufficient delignification reaction. The temperature at the outlet is 100°C and the pressure is maintained at 0.3MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 33°SR.

[0162] The bleached wood pulp and unbleached straw pulp were pulped separately, the bleached wood pulp had a pulping concentration of 2.5%, and the unbleached straw pulp had a pulping concentration of 2.5%. The pulping was carried out in a double-disc refiner. The quality standards of the pulp obtained after pulping were: bleached wood pulp had a beating degree of 52°SR, a wet weight of 7.8g, and unbleached straw pulp had a beating degree of 48°SR, and a wet weight of 2.0g.

[0163] 22% of the bleached wood pulp and 78% of the unbleached straw pulp are mixed until the pulp is uniform, 10 kg / ton of starch, 3 kg / ton of dispersant, 10 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, mixed evenly and then papered according to conventional process to obtain the natural color thin sheet packaging paper.

[0164] The quality indicators of the natural color thin wrapping paper are as follows:

[0165] Basis weight: 17.0g / m 2 ;

[0166] Whiteness: 44.6%

[0167] Tightness: 0.59g / m 3 ;

[0168] Fault length (average vertically and horizontally): 3.49km;

[0169] Tear strength (average vertically and horizontally): 67mN;

[0170] Air permeability: 18μm / (Pa·s);

[0171] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2:0pcs / m 2 ;

[0172] Moisture: 7.2%;

[0173] Brightness: 53%

[0174] Example 9

[0175] The rice straw and wheat straw raw materials with a mass ratio of 1:1 are cooked by conventional methods, and then squeezed, washed and deflated. The 10% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 30kg / ton of oxygen, 4% magnesium sulfate for the absolute dry pulp and 4% alkali solution for the absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed into the pipeline to heat the pulp. After that, the pulp is fully mixed and enters the oxygen delignification reaction tower. The temperature at the inlet of the reaction tower is 100°C and the pressure is 0.9MPa. It stays for 80 minutes so that the pulp can undergo sufficient delignification reaction. The temperature at the outlet is 100°C and the pressure is maintained at 0.3MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 34°SR.

[0176] The bleached wood pulp and unbleached straw pulp were pulped separately, the bleached wood pulp had a pulping concentration of 2.3%, and the unbleached straw pulp had a pulping concentration of 2.9%. The pulping was carried out in a double-disc refiner. The quality standards of the pulp obtained after pulping were: bleached wood pulp had a beating degree of 50°SR, a wet weight of 7.4g, and unbleached straw pulp had a beating degree of 47°SR, and a wet weight of 1.5g.

[0177] 28% of the bleached wood pulp and 72% of the unbleached straw pulp are mixed until the pulp is uniform, 10 kg / ton of starch, 3 kg / ton of dispersant, 10 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, mixed evenly and then papered according to conventional process to obtain the natural color thin sheet packaging paper.

[0178] The quality indicators of the natural color thin wrapping paper are as follows:

[0179] Basis weight: 16.0g / m 2 ;

[0180] Whiteness: 38.6%;

[0181] Tightness: 0.49g / m 3 ;

[0182] Fault length (average vertically and horizontally): 3.16km;

[0183] Tear strength (average vertically and horizontally): 66mN;

[0184] Air permeability: 15μm / (Pa·s);

[0185] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0186] Moisture: 7.4%;

[0187] Brightness: 60%.

[0188] Example 10

[0189] The raw material of Phragmites australis is boiled by conventional methods, and then squeezed, washed and deflated. The 12% straw pulp obtained after deflation is pumped to the oxygen delignification reaction tower for oxygen delignification treatment. Before entering the reaction tower, the pulp is mixed with 30kg / ton of oxygen, 3% magnesium sulfate for the absolute dry pulp and 3% alkali solution for the absolute dry pulp in terms of sodium hydroxide in the pipeline, and steam is passed through the pipeline to heat the pulp. After that, the pulp enters the oxygen delignification reaction tower after being fully mixed. The temperature at the inlet of the reaction tower is 95°C and the pressure is 0.9MPa. It stays for 80 minutes so that the pulp can undergo sufficient delignification reaction. The temperature at the outlet is 105°C and the pressure is maintained at 0.4MPa. After the treatment is completed, the pulp is sprayed into the pulp pool and diluted to obtain the unbleached straw pulp. The beating degree of the unbleached straw pulp is 34°SR.

[0190] The bleached wood pulp and unbleached straw pulp were pulped separately, with the bleached wood pulp pulping concentration of 2.2% and the unbleached straw pulp pulping concentration of 2.9%. The pulping was carried out in a double-disc refiner. The quality standards of the pulp obtained after pulping were: bleached wood pulp beating degree 50°SR, wet weight 7.2g, unbleached straw pulp beating degree 46°SR, wet weight 1.8g.

[0191] 25% of the bleached wood pulp and 75% of the unbleached straw pulp are mixed until the pulp is uniform, 10 kg / ton of starch, 3 kg / ton of dispersant, 10 kg / ton of alkyl ketene dimer and 0.5 kg / ton of drying cylinder stripping agent are added, mixed evenly and then papered according to conventional process to obtain the natural color thin sheet packaging paper.

[0192] The quality indicators of the natural color thin wrapping paper are as follows:

[0193] Basis weight: 17.0g / m 2 ;

[0194] Whiteness: 48.7%;

[0195] Tightness: 0.46g / m 3 ;

[0196] Fault length (average vertically and horizontally): 3.26km;

[0197] Tear strength (average in longitudinal and transverse directions): 65mN;

[0198] Air permeability: 21μm / (Pa·s);

[0199] Dust degree: 0.3-1.5mm 2 :0pcs / m 2 , 0.5-1.5mm 2 :0pcs / m 2 , ≥1.5mm 2 :0pcs / m 2 ;

[0200] Moisture: 7.4%;

[0201] Brightness: 49%.

Claims

1. A method for preparing natural color thin wrapping paper, characterized in that: The method for preparing the natural color thin wrapping paper comprises the following steps: 1) The grass raw material is steamed, squeezed, washed and deflated to obtain unbleached straw pulp; or after deflation, oxygen delignification is performed to obtain unbleached straw pulp; 2) beating the wood pulp and the unbleached straw pulp respectively, wherein the beating concentration of the wood pulp is 2.0-3.0%, and the beating concentration of the unbleached straw pulp is 2.5-2.9%. After the beating, the obtained wood pulp has a beating degree of 48-55°SR, and a beating wet weight of 7.0-9.0g. The obtained unbleached straw pulp has a beating degree of 43-49°SR, and a beating wet weight of 1.5-2.0g. 3) Mix 22-28% of the wood pulp and 72-78% of the unbleached straw pulp after beating until the pulp is uniform; 4) Papermaking the slurry obtained in step 3) to obtain the natural color thin sheet packaging paper; The natural color thin sheet packaging paper has a whiteness of 35-50% and a basis weight of 14-18 g / m 2 ; The density of the natural color thin sheet packaging paper is 0.46-0.70g / cm 3 The average tear length is 2.8-4.0km in both vertical and horizontal directions, and the average tear strength is 40-70mN in both vertical and horizontal directions; The air permeability of the natural color thin sheet wrapping paper is 14-41µm / Pa·s; the moisture content of the natural color thin sheet wrapping paper is 7.0-12.0%; the brightness of the natural color thin sheet wrapping paper is 30-60%; the dustiness of the natural color thin sheet wrapping paper is 0.3-1.5mm 2 0-2 pieces / m 2 , 0.5-1.5mm 2 0pcs / m 2 , ≥1.5 mm 2 0pcs / m 2 ; Step 3) Adding additives to the mixed slurry, wherein the additives include starch in the slurry, a dispersant in the slurry, an alkyl ketene dimer and a drying cylinder release agent.

2. The preparation method according to claim 1, characterized in that: The basis weight of the natural color thin sheet packaging paper is 16-18 g / m 2 .

3. The preparation method according to claim 1, characterized in that: The pulp comprises 22% wood pulp and 78% unbleached straw pulp, or 25% wood pulp and 75% unbleached straw pulp, or 28% wood pulp and 72% unbleached straw pulp.

4. The preparation method according to claim 1, characterized in that: The beating degree of the unbleached straw pulp is 44-48°SR.

5. The preparation method according to claim 4, characterized in that: The beating degree of the unbleached straw pulp is 45-47°SR.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The density of the natural color thin sheet wrapping paper is 0.46-0.64 g / cm 3 The tear length of the natural color thin sheet wrapping paper is 2.9-3.8 km on average in both longitudinal and transverse directions; the tear strength of the thin sheet wrapping paper is 50-68 mN on average in both longitudinal and transverse directions.

7. The preparation method according to claim 6, characterized in that: The density of the natural color thin sheet wrapping paper is 0.46-0.60 g / cm 3 The tear length of the natural color thin sheet wrapping paper is 3.0-3.5 km on average in both longitudinal and transverse directions; the tear strength of the thin sheet wrapping paper is 55-67 mN on average in both longitudinal and transverse directions.

8. The preparation method according to claim 7, characterized in that: The density of the natural color thin sheet wrapping paper is 0.46-0.49 g / cm 3 The tear length of the natural color thin sheet wrapping paper is 3.1-3.3 km on average in both longitudinal and transverse directions; the tear strength of the thin sheet wrapping paper is 56-66 mN on average in both longitudinal and transverse directions.

9. The preparation method according to claim 8, characterized in that: The air permeability of the natural color thin sheet packaging paper is 15-20 μm / Pa·s; the moisture content of the natural color thin sheet packaging paper is 7.0-8.8%.

10. The preparation method according to claim 9, characterized in that: The pulping concentration of the wood pulp in step 2) is 2.2-2.5%; after the pulping is completed, the obtained pulp has a pulping degree of 50-53°SR and a wet weight of 7.2-7.8g.

11. The preparation method according to claim 10, characterized in that: The additives are added in amounts of 6-13 kg / ton of slurry starch, 1-5 kg / ton of slurry dispersant, and 8-12 kg / ton of slurry alkyl ketene dimer.