阅读说明：本技术 一种制备可膨胀微球的方法及得到的微球与应用 (Method for preparing expandable microspheres, microspheres obtained by method and application of microspheres ) 是由 沈后平 徐新连 于 2019-04-30 设计创作，主要内容包括：本发明公开了一种制备可膨胀微球的方法及得到的可膨胀微球与应用,其中,采用悬浮聚合技术制备以聚合物为壳、发泡剂为核的可膨胀微球,在聚合物壳体制备时,引入了蒙脱土,得到气密性非常优异的聚合物外壳。得到的可膨胀微球可以直接用于造纸工艺中,所述微球在造纸的干燥过程中直接发泡,而无需改变现有造纸工艺,得到轻质纸。(The invention discloses a method for preparing expandable microspheres, the expandable microspheres obtained by the method and application of the expandable microspheres, wherein the expandable microspheres with a polymer as a shell and a foaming agent as a core are prepared by a suspension polymerization technology, and montmorillonite is introduced during preparation of a polymer shell to obtain a polymer shell with excellent air tightness. The obtained expandable microspheres can be directly used in a papermaking process, and the microspheres are directly foamed in the drying process of papermaking without changing the existing papermaking process to obtain the lightweight paper.)

1. The method for preparing the expandable microspheres is characterized in that polymerizable monomers, a cross-linking agent, an initiator, montmorillonite and a foaming agent are used as raw materials, and suspension polymerization is carried out to obtain the expandable microspheres.

2. The method according to claim 1, wherein the polymerizable monomer is selected from one or more compounds having a polymerizable double bond; and/or

The montmorillonite is organic modified montmorillonite; and/or

The blowing agent is selected from two or more alkanes.

3. The method of claim 2,

the polymerizable monomer is selected from one or more of styrene, acrylate, vinylidene chloride, (meth) acrylamide, (meth) acrylonitrile and acrylic acid; and/or

The organic modified montmorillonite is selected from montmorillonite modified by one or more of Dodecyl Trimethyl Ammonium Bromide (DTAB), hexadecyl trimethyl ammonium bromide (CTAB), Octadecyl Trimethyl Ammonium Bromide (OTAB) and hexadecyl trimethyl ammonium chloride (CTAC); and/or

The cross-linking agent is a compound containing at least two double bonds, and is preferably selected from one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and allyl-terminated hyperbranched polyether polyol.

4. The method according to one of claims 1 to 3,

the molecular weight of the allyl-terminated hyperbranched polyether polyol is 200-2000 g/mol; and/or

When the allyl-terminated hyperbranched polyether polyol is used as a cross-linking agent, the modified montmorillonite and the allyl-terminated hyperbranched polyether polyol are subjected to composite treatment, such as ball milling treatment, before suspension polymerization is carried out, so as to obtain a composite; and/or

The dosage ratio of the modified montmorillonite to the cross-linking agent is (0.2-1): 1.

5. expandable microspheres, preferably obtainable by the process according to any one of claims 1 to 4.

6. Use of expandable microspheres according to claim 5 for the preparation of lightweight paper.

7. A method of making lightweight paper, the method comprising the steps of:

step 1, mixing the expandable microspheres of claim 5, a surfactant and water to obtain a precursor slurry;

step 2, adding water into the fiber raw material, cooking and smashing to form fiber slurry, and adding the precursor slurry obtained in the step 1 into the fiber slurry to obtain paper pulp;

step 3, placing the paper pulp on a spray net for dehydration treatment to obtain wet paper sheets;

and 4, sequentially carrying out squeezing dehydration and heating drying treatment on the wet paper to obtain the light paper.

8. The method of claim 7,

in the slurry in the step 1, the weight concentration of the expandable microspheres is 10-40%; and/or

In step 1, a dispersant and a preservative are also mixed in the precursor slurry; and/or

In step 1, the precursor slurry is also mixed with other papermaking fillers, such as calcium carbonate.

9. The method of claim 8,

in the slurry in the step 1, the weight concentration of the expandable microspheres is 10-60%; and/or

In step 1, a dispersant and a preservative are also mixed in the precursor slurry;

preferably, the dispersant is present in the precursor slurry in a concentration of (0.1 to 2)% by weight and the preservative is present in the precursor slurry in a concentration of (0.01 to 1)% by weight.

10. The method according to claims 7 to 9,

in the step 2, the dosage ratio of the fiber raw material to the expandable microspheres is (1.5-6): 1; and/or

In step 4, the temperature of the drying treatment is 95-135 ℃.

Technical Field

The invention relates to the field of microspheres, in particular to expandable microspheres, and particularly relates to a method for preparing the expandable microspheres, the microspheres obtained by the method and application of the expandable microspheres.

Background

Paper has been popularized in various fields of life and work, and at present, one of the problems faced in the preparation of paper is how to improve the performance of paper while reducing the amount of cellulose used.

The prior art discloses that the hollow microspheres obtained by thermally expanding expandable microspheres can be applied to papermaking to reduce the density of paper and reduce the consumption of fiber raw materials.

However, the expandable microspheres disclosed in the prior art have the disadvantages of poor toughness, poor air tightness and the like. And, when applied to papermaking, it has poor binding with pulp.

Disclosure of Invention

In order to solve the above problems, the present inventors have made intensive studies to prepare expandable microspheres having a polymer shell and a blowing agent core by using a suspension polymerization technique, wherein montmorillonite is introduced during the preparation of the polymer shell to obtain a polymer shell having excellent airtightness. The obtained expandable microspheres can be directly used in a papermaking process, and the microspheres are directly foamed in the drying process of papermaking without changing the existing papermaking process to obtain light paper, thereby completing the invention.

In one aspect, the present invention provides a method for preparing expandable microspheres, which is embodied in the following aspects:

(1) the method for preparing the expandable microspheres comprises the steps of taking polymerizable monomers, a cross-linking agent, an initiator, montmorillonite and a foaming agent as raw materials, and carrying out suspension polymerization to obtain the expandable microspheres.

(2) The method according to the above (1), wherein the polymerizable monomer is selected from one or more compounds having a polymerizable double bond; and/or

The montmorillonite is organic modified montmorillonite; and/or

The blowing agent is selected from two or more alkanes.

(3) The method according to the above (2), wherein,

the polymerizable monomer is selected from one or more of styrene, acrylate, vinylidene chloride, (meth) acrylamide, (meth) acrylonitrile and acrylic acid; and/or

The organic modified montmorillonite is selected from montmorillonite modified by one or more of Dodecyl Trimethyl Ammonium Bromide (DTAB), hexadecyl trimethyl ammonium bromide (CTAB), Octadecyl Trimethyl Ammonium Bromide (OTAB) and hexadecyl trimethyl ammonium chloride (CTAC); and/or

The cross-linking agent is a compound containing at least two double bonds, and is preferably selected from one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and allyl-terminated hyperbranched polyether polyol.

(4) The method according to one of the above (1) to (3), wherein,

the molecular weight of the allyl-terminated hyperbranched polyether polyol is 200-2000 g/mol; and/or

When the allyl-terminated hyperbranched polyether polyol is used as a cross-linking agent, the modified montmorillonite and the allyl-terminated hyperbranched polyether polyol are subjected to composite treatment, such as ball milling treatment, before suspension polymerization is carried out, so as to obtain a composite; and/or

The dosage ratio of the modified montmorillonite to the cross-linking agent is (0.2-1): 1.

in a second aspect the present invention provides expandable microspheres, preferably obtainable by a process according to the first aspect of the invention.

In a third aspect the present invention provides the use of expandable microspheres according to the second aspect of the invention for the preparation of lightweight paper.

The fourth aspect of the invention provides a method for preparing lightweight paper, which comprises the following steps:

step 1, mixing expandable microspheres according to the second aspect of the invention, a surfactant and water to obtain precursor slurry;

step 2, adding water into the fiber raw material, cooking and smashing to form fiber slurry, and adding the precursor slurry obtained in the step 1 into the fiber slurry to obtain paper pulp;

step 3, placing the paper pulp on a spray net for dehydration treatment to obtain wet paper

And 4, sequentially carrying out squeezing dehydration and heating drying treatment on the wet paper to obtain the light paper.

Detailed Description

The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.

The invention provides a method for preparing expandable microspheres, wherein polymerizable monomers, a cross-linking agent, an initiator, montmorillonite and a foaming agent are used as raw materials, and the expandable microspheres are obtained through suspension polymerization.

According to a preferred embodiment of the present invention, the polymerizable monomer is selected from one or more compounds having a polymerizable double bond.

In a further preferred embodiment, the polymerizable monomer is selected from one or more of styrene, acrylates, vinylidene chloride, (meth) acrylamide, (meth) acrylonitrile and acrylic acid.

The polymerizable monomer is oil-soluble, and is easy to form suspension droplets after being mixed with water in which a dispersing agent is dispersed. Wherein the polyhedral oligomeric silsesquioxane containing double bonds can be copolymerized with other polymerizable monomers to form the polymer shell of the microsphere.

According to a preferred embodiment of the invention, the montmorillonite is an organically modified montmorillonite.

The reason for introducing the montmorillonite in the invention is that the montmorillonite has a lamellar interlayer structure, and the lamellar structure among different layers has excellent barrier property, so that the montmorillonite applied to the foaming microsphere can effectively block the escape of the internal foaming agent (especially under the heating condition), so that the internal foaming agent can fully play a role, and the hollow microsphere with higher expansion factor is obtained.

In a further preferred embodiment, the organically modified montmorillonite is selected from montmorillonite modified with one or more of dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (CTAB), octadecyltrimethylammonium bromide (OTAB) and hexadecyltrimethylammonium chloride (CTAC).

Wherein, the unmodified montmorillonite is not easy to disperse in the oil phase because the interlayer contains a large amount of inorganic ions, therefore, the invention adopts the organic modified montmorillonite to improve the lipophilicity of the montmorillonite, so that the montmorillonite can be uniformly dispersed in the oil phase. Specifically, the modified organic matter is inserted between the sheets of the montmorillonite to obtain the modified montmorillonite. In the present invention, the preparation of the organically modified montmorillonite is not particularly limited, and may be carried out by techniques disclosed in the prior art.

In a still further preferred embodiment, the organically modified montmorillonite is selected from montmorillonite modified with one or more of dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (CTAB), octadecyltrimethylammonium bromide (OTAB), such as hexadecyltrimethylammonium bromide (CTAB) modified montmorillonite.

Compared with unmodified montmorillonite, the organically modified montmorillonite has larger interlayer spacing, and the larger the interlayer spacing is, the stronger the barrier property to gas is.

According to a preferred embodiment of the invention, the crosslinking agent is a compound containing at least two double bonds.

In a further preferred embodiment, the cross-linking agent is selected from one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and terminal allyl hyperbranched polyether polyol.

In a still further preferred embodiment, the cross-linking agent is an allyl-terminated hyperbranched polyether polyol.

The allyl-terminated hyperbranched polyether polyol has a hyperbranched structure and contains a plurality of extended molecular chains, and the tail end of the molecular chain is allyl or hydroxyl, so that the hyperbranched structure contains a plurality of allyl and hydroxyl groups at the tail end of the molecular chain, and the allyl groups can be used as crosslinking sites to crosslink in a polymerization reaction.

According to a preferred embodiment of the present invention, the allyl-terminated hyperbranched polyether polyol is prepared as follows: and adding epoxypropane and glycidol to carry out anionic polymerization by using a polyol compound as an initiator to obtain the hydroxyl-terminated hyperbranched polyether polyol.

Wherein, a plurality of hydroxyl groups in the polyol compound are initiation sites, so as to construct the hyperbranched structure. The molecular chain ends of the hydroxyl-terminated hyperbranched polyether polyol obtained in the first step are all hydroxyl groups.

In a further preferred embodiment, the obtained hydroxyl-terminated hyperbranched polyether polyol is used as an initiator, and propylene oxide and Allyl Glycidyl Ether (AGE) are added to carry out anionic polymerization to obtain allyl-terminated hyperbranched polyether polyol.

And modifying partial hydroxyl at the tail end of the molecular chain of the hydroxyl-terminated hyperbranched polyether polyol obtained in the first step to be of an allyl structure, so that the tail end of the obtained allyl-terminated hyperbranched polyether polyol not only contains a plurality of double bonds, but also contains a plurality of hydroxyl groups, and is also of a hyperbranched structure.

Compared with the traditional cross-linking agent, the allyl-terminated hyperbranched polyether polyol has a hyperbranched structure, can endow the obtained microsphere shell with better toughness, and is not easy to crack when heated and expanded. Meanwhile, the allyl-terminated hyperbranched polyether polyol is also a polyether polyol, and can play a role of a surfactant during suspension polymerization, so that adjacent liquid drops are not easy to adhere to each other, suspended emulsion drops with more uniform particle sizes are obtained, and the uniformity of the particle sizes of the microspheres is finally realized.

Meanwhile, due to the special structure of the allyl-terminated hyperbranched polyether polyol, a plurality of remote claw type hydroxyl structures are endowed on the surface of the microsphere after polymerization. Thereby endowing the expandable microspheres with various further-modified characteristics, for example, hydroxyl on the surface can be further reacted with other functional groups for further modification.

According to a preferred embodiment of the present invention, the molecular weight of the allyl-terminated hyperbranched polyether polyol is 150 to 1000 g/mol.

In a further preferred embodiment, the allyl-terminated hyperbranched polyether polyol has a molecular weight of 200 to 500 g/mol.

The molecular weight of the allyl-terminated hyperbranched polyether polyol is not easy to be too large, and the molecular weight of the allyl-terminated hyperbranched polyether polyol is used as a cross-linking agent, so that if the molecular weight is too large, the cross-linking density is too low, and the phenomenon that gas gasified inside is likely to escape when the microspheres are thermally expanded is likely to occur; another reason why the molecular weight should not be too large is that: it is necessary to complex with the modified montmorillonite in the latter stage, and if the molecular weight is too large, it is not preferable to insert the interlayer structure of the modified montmorillonite (see below for details).

According to a preferred embodiment of the present invention, the weight ratio of the crosslinking agent to the polymerizable monomer is 1.2 to 6%, preferably 1.5 to 4%, and more preferably 1.8 to 2%.

The cross-linking agent dosage is too small, otherwise, the cross-linking density is too small, the foaming agent in the microsphere is easy to escape during thermal expansion, and the expansion effect of the microsphere is further influenced.

According to a preferred embodiment of the present invention, when the allyl-terminated hyperbranched polyether polyol is used as the cross-linking agent, the modified montmorillonite and the allyl-terminated hyperbranched polyether polyol are subjected to a compounding treatment before the suspension polymerization is performed.

In a further preferred embodiment, the modified montmorillonite and the allyl-terminated hyperbranched polyether polyol are placed in a ball milling tank and subjected to ball milling treatment to obtain the composite.

The modified montmorillonite and the allyl-terminated hyperbranched polyether polyol are subjected to ball milling treatment, the allyl-terminated hyperbranched polyether polyol can be intercalated into a lamellar structure of the montmorillonite, and the lamellar spacing of the montmorillonite can be further increased due to the hyperbranched structure, so that the gas barrier performance between different lamellar layers is further enhanced.

In the invention, the pretreatment is carried out by adopting the organic modified montmorillonite and the terminal allyl hyperbranched polyether polyol, rather than directly adopting the montmorillonite, which is considered for reasons. Firstly, as shown above, the organically modified montmorillonite has better compatibility with oil phase substances (including organic substances such as allyl-terminated hyperbranched polyether polyol); secondly, the interlayer spacing of the untreated montmorillonite is small, and the hyperbranched structure is not easy to be directly inserted into the montmorillonite, so that in the invention, the montmorillonite is modified by using the organic modifier, the interlayer spacing is pre-increased, and then the montmorillonite is subjected to ball milling treatment with the crosslinking agent with the hyperbranched structure on the basis of the increased interlayer spacing, so that the crosslinking agent with the hyperbranched structure is easier to be inserted into the interlayer structure of the montmorillonite.

According to a preferred embodiment of the invention, the dosage ratio of the modified montmorillonite to the cross-linking agent is (0.2-1): 1.

in a further preferred embodiment, the dosage ratio of the modified montmorillonite to the cross-linking agent is (0.2-0.6): 1.

in the invention, the modified montmorillonite and the cross-linking agent are pretreated before suspension polymerization, so that the interlayer spacing of the montmorillonite is further increased, and after the montmorillonite with larger interlayer spacing is mixed with other raw materials, such as monomers, initiators and the like, the monomers are also inserted between the layers of the montmorillonite, and polymers are carried out in the layers.

According to a preferred embodiment of the invention, the initiator is an oil-soluble free radical initiator.

Wherein, the oil-soluble initiator refers to a free radical initiator which can be mutually soluble with a polymerizable monomer.

In a further preferred embodiment, the initiator may be selected from initiators commonly used in the art, such as azobisisobutyronitrile, dibenzoyl peroxide, and the like.

According to a preferred embodiment of the present invention, the weight ratio of the initiator to the polymerizable monomer is 0.05 to 0.5 wt%.

In a further preferred embodiment, the weight ratio of the initiator to the polymerizable monomer is 0.1 to 0.3 wt%.

According to a preferred embodiment of the invention, the blowing agent is selected from two or more alkanes.

In a further preferred embodiment, the alkane comprises isobutane, n-butane, isopentane, n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, isoheptane, n-octane, isooctane, and petroleum ether.

In a further preferred embodiment, the two or more alkanes have a difference in boiling point of 10 to 100 ℃, preferably 20 to 90 ℃, more preferably 30 to 80 ℃.

The two or more foaming agents have a synergistic effect in the heating foaming process of the microspheres, so that the pressure generated by the foaming agents above the boiling points of the foaming agents is buffered along with the temperature change.

According to a preferred embodiment of the present invention, the weight ratio of the blowing agent to the polymerizable monomer is 20 to 60 wt%.

In a further preferred embodiment, the weight ratio of the blowing agent to the polymerizable monomer is 30 to 50 wt%.

In a further preferred embodiment, the weight ratio of the blowing agent to the polymerizable monomer is 35 to 45 wt%.

In the invention, the dosage of the foaming agent is higher than that in the prior art, and because the crosslinking agent with a hyperbranched structure is adopted, the obtained polymer shell can be endowed with better toughness, so that the polymer shell with better toughness is not easy to crack when the microspheres are heated and expanded. And the foaming degree is improved when the using amount of the foaming agent is increased, and finally the hollow microspheres with thinner shell walls are obtained.

According to a preferred embodiment of the present invention, a dispersion stabilizer and optionally an auxiliary stabilizer are dispersed in the aqueous dispersion.

Wherein, the addition of the dispersion stabilizer and the auxiliary stabilizer is beneficial to the dispersion of the oil phase droplets in the water phase. In the invention, when the allyl-terminated hyperbranched polyether polyol is used as the cross-linking agent, the auxiliary stabilizing agent can be optionally added, because the allyl-terminated hyperbranched polyether polyol can also play an auxiliary stabilizing role to a certain extent.

In a further preferred embodiment, the dispersion stabilizer is selected from colloidal titanium dioxide and/or colloidal silicon dioxide and the like.

In a further preferred embodiment, the weight concentration of the dispersion stabilizer in the aqueous dispersion medium is 5 to 15 wt%.

In the present invention, the aqueous phase may be pH-controlled depending on the selection of the dispersion stabilizer and the auxiliary stabilizer, and an inorganic salt may be optionally added to the aqueous phase.

According to a preferred embodiment of the invention, the polymerization is carried out in a protective atmosphere at 50 to 90 ℃.

In a further preferred embodiment, the polymerization is to N₂Is carried out at 65-80 ℃ in the atmosphere.

According to a preferred embodiment of the invention, the thermal polymerization is followed by a post-treatment.

In a further preferred embodiment, the post-treatment comprises, in order, water washing, filtration, drying and grinding.

In a second aspect, the present invention provides expandable microspheres obtained according to the method of the first aspect of the invention.

The expandable microspheres have a core-shell structure, the polymer is used as a shell, the foaming agent is used as a core, and after heat treatment, the internal foaming agent is gasified to obtain the hollow microspheres with the polymer as the shell.

In a third aspect the present invention provides the use of expandable microspheres according to the second aspect of the invention for the preparation of lightweight paper.

The expandable microspheres form a hollow structure through heat treatment, and when the expandable microspheres are applied to paper preparation, the weight of the paper can be reduced, and meanwhile, the surface touch feeling of the paper is improved.

In the invention, when the expandable microspheres are applied to papermaking, the expandable microspheres are directly added in the form of an auxiliary agent without changing the original papermaking process, and the microspheres are directly foamed in the heating process of a drying roller of paper without heat treatment in advance.

The fourth aspect of the invention provides a method for preparing lightweight paper, which comprises the following steps:

step 1, mixing the expandable microspheres of the second aspect of the invention, a surfactant and water to obtain a precursor slurry.

According to a preferred embodiment of the invention, the surfactant is selected from cationic surfactants and/or anionic surfactants.

Wherein, the common surfactant is selected to promote the dispersion of the expandable microspheres in water. On the other hand, the surfactant can play a role of a retention aid in later-stage spraying, so that the retention rate of fine components on the spraying net in later stages is improved, the components are ensured to be fully retained in paper, and the utilization rate of raw materials is improved.

In a further preferred embodiment, the ratio of the amount of the surfactant to the expandable microspheres is (0.1-0.5): 1, preferably (0.2-0.3): 1.

The invention adopts the expandable microspheres with special structures, and the surfaces of the expandable microspheres contain a plurality of telechelic hydroxyl structures, thereby improving the water insolubility of the traditional microspheres. The surface of the expandable microsphere disclosed by the prior art is generally not modified by functional groups, so that the expandable microsphere is poor in water miscibility, but a plurality of remote claw type hydroxyl structures are distributed on the surface of the expandable microsphere adopted by the invention, so that the microsphere is endowed with certain water compatibility.

According to a preferred embodiment of the present invention, in the slurry of step 1, the concentration of the expandable microspheres is 10 to 60% by weight.

In a further preferred embodiment, the slurry in step 1 has a concentration of expandable microspheres of 10-40% by weight.

In a further preferred embodiment, the slurry of step 1 has a concentration of expandable microspheres of 10 to 20% by weight.

According to a preferred embodiment of the present invention, in step 1, a dispersant and a preservative are further mixed in the precursor slurry.

The dispersant is selected from common papermaking dispersants, mainly polyacrylamide, carboxylate such as LBD-1 dispersant, starch modification and the like, and is used for promoting good dispersion of fibers and/or other auxiliaries in water so as to improve the viscosity of subsequently prepared paper pulp. The preservative is selected from commonly used papermaking preservatives such as chlorine-based preservatives (represented by chloramine), bromine-based preservatives, peroxides (such as peracetic acid), phenolic compounds, aldehyde compounds (such as glutaraldehyde), and the like.

In a further preferred embodiment, the dispersant is present in the precursor slurry in a weight concentration of (0.1 to 2)%, preferably (0.5 to 1)%; the weight concentration of the preservative in the precursor slurry is (0.01-1)%, preferably (0.1-0.5)%

In a further preferred embodiment, in step 1, the precursor slurry is also mixed with other papermaking fillers, such as calcium carbonate.

Wherein, the added calcium carbonate can ensure that the paper has good brightness, solid structure and the like.

And 2, adding water into the fiber raw material, cooking and smashing to form fiber slurry, and adding the precursor slurry obtained in the step 1 into the fiber slurry to obtain paper pulp.

In the present invention, the fiber material is not particularly limited, and fibers that can be used for papermaking disclosed in the prior art are used, and may be selected according to the purpose.

The telechelic hydroxyl distributed on the surface of the expandable microsphere can be bonded with the hydroxyl in the fiber, so that the acting force between the telechelic hydroxyl and the hydroxyl in the fiber is increased, and the retention rate of paper pulp is improved. At the same time, the resulting tough tension of the paper is enhanced due to the interaction with each other.

According to a preferred embodiment of the present invention, in step 2, the ratio of the fiber raw material to the expandable microspheres is (1.5-6): 1.

in a further preferred embodiment, in the step 2, the usage ratio of the fiber raw material to the expandable microspheres is (1.5-2.5): 1.

in the invention, the expandable microspheres are adopted, so that the consumption of fiber raw materials is greatly reduced on the premise that the obtained paper has the same thickness.

And 3, placing the paper pulp on a spray net for dehydration treatment to obtain wet paper sheets.

Wherein the pulp is dewatered and formed on a wire. In the present invention, the expandable microspheres of the first aspect of the present invention are used, and the surface of the expandable microspheres contains a large number of hydroxyl groups, and when the expandable microspheres are mixed with paper fibers (also containing terminal hydroxyl groups), the hydroxyl groups of the paper fibers and the paper fibers can interact with each other, such as hydrogen bonds, so that the retention rate of the pulp on the screen can be further improved.

And 4, sequentially carrying out squeezing dehydration and heating drying treatment on the wet paper to obtain the light paper.

The pressing treatment can further dewater the paper, improve the dryness of the paper, increase the tightness and strength of the paper and improve the surface smoothness of the paper.

In the invention, the expandable microspheres do not need to be foamed in advance, and the expandable microspheres can be directly foamed in the heating and drying treatment of the wet paper sheet. Therefore, the original papermaking process is not changed, and the expandable microspheres directly start to foam in the heating and drying process of the drying roller.

According to a preferred embodiment of the present invention, in the step 4, the temperature of the drying process is 95 to 135 ℃.

In a further preferred embodiment, in the step 4, the temperature of the drying treatment is 100 to 125 ℃.

Meanwhile, the addition of the expandable microspheres improves the vacuum drying speed of the paper after net spraying, and can shorten the vacuum-pumping time by 20 percent.

The heating and drying of the paper are generally carried out by adopting a drying roller, and in the drying process, the microspheres are foamed to increase the thickness of the paper, so that the paper has larger thickness under the condition of the same gram weight. The paper that has dried, the microballon has realized the foaming, and after the pinch roller is passed, because the special obturator structure and the resilience performance of microballon for the paper can trace back original thickness fast after the pinch roller, reduces the loss of paper thickness.

The invention has the following beneficial effects:

(1) the polymer shell of the expandable microsphere prepared by the method has better air tightness due to the introduction of the montmorillonite, and the escape of an internal foaming agent is effectively prevented;

(2) according to the method, the allyl-terminated hyperbranched polyether polyol is used as a special cross-linking agent, so that the obtained polymer shell can have better toughness. Meanwhile, the allyl-terminated hyperbranched polyether polyol is also a polyether polyol and can be used as a surfactant during suspension polymerization;

(3) The expandable microspheres prepared by the method can be applied to papermaking, so that the bulk and the surface touch of paper are improved;

(4) when the expandable microspheres are applied to papermaking, a special microwave drying and foaming process is not needed, and the expandable microspheres are directly foamed in a paper drying process, so that the production efficiency is improved;

(5) meanwhile, the addition of the expandable microspheres improves the vacuum drying speed of the paper after net spraying, and can shorten the vacuum-pumping time by 20 percent;

(6) the thickness of paper can be remarkably increased by adding the expandable microspheres into a papermaking process, and the thickness is increased by about 10-40%; similarly, the weight of the paper sheet is reduced by 10-40% under the same thickness.