阅读说明：本技术 一种预发泡热膨胀微球、其制备方法及应用 (Pre-foaming thermal expansion microsphere, preparation method and application thereof ) 是由 潘仕荣 周小三 于 2020-12-31 设计创作，主要内容包括：本发明提供了一种预发泡热膨胀微球、其制备方法及应用,所述预发泡热膨胀微球包括热塑性树脂外壳和包封在所述外壳中的沸点不高于所述热塑性树脂外壳软化点的发泡剂,其中,所述热塑性树脂外壳包括聚合单体组分,其中,所述聚合单体组分包括：按重量份计,丙烯酸类单体25-40；丙烯腈类单体60-75。其中,所述预发泡热膨胀微球的空隙率为70-95％。本发明的预发泡热膨胀微球粒径达到3-10微米,由于预发泡后微球外壳为超薄热塑性树脂壳体薄膜,内部包封烷烃气体,从而形成具有高空隙率的预发泡热膨胀微球。该预发泡热膨胀微球可以添加在热敏纸的热敏涂层中,起到良好的隔热效果,提高热敏打印的清晰度。(The invention provides a pre-foaming thermal expansion microsphere, a preparation method and application thereof, wherein the pre-foaming thermal expansion microsphere comprises a thermoplastic resin shell and a foaming agent which is encapsulated in the shell and has a boiling point not higher than the softening point of the thermoplastic resin shell, wherein the thermoplastic resin shell comprises a polymerized monomer component, and the polymerized monomer component comprises: 25-40 parts by weight of acrylic monomers; 60-75 parts of acrylonitrile monomers. Wherein the pre-foamed thermal expansion microspheres have a porosity of 70-95%. The particle size of the pre-foaming thermal expansion microspheres reaches 3-10 microns, and the shell of the pre-foaming microspheres is an ultrathin thermoplastic resin shell film, and alkane gas is encapsulated inside the shell film, so that the pre-foaming thermal expansion microspheres with high porosity are formed. The pre-foaming thermal expansion microspheres can be added into a thermal sensitive coating of thermal sensitive paper, so that a good thermal insulation effect is achieved, and the definition of thermal sensitive printing is improved.)

1. A pre-expanded thermally-expandable microsphere comprising a thermoplastic resin shell and a foaming agent having a boiling point not higher than the softening point of the thermoplastic resin shell encapsulated in the shell, wherein,

the thermoplastic resin shell includes a polymerized monomer component, wherein,

the polymerized monomer component includes: based on the weight portion, the weight portion of the material,

25-40 parts of acrylic monomers;

60 to 75 parts of acrylonitrile monomers, namely,

wherein the pre-foamed thermal expansion microspheres have a porosity of 70-95%.

2. The pre-expanded thermally-expandable microspheres according to claim 1, wherein the particle diameter of the pre-expanded thermally-expandable microspheres is 3 to 10 μm.

3. The pre-expanded thermally-expandable microspheres according to claim 1, wherein the acrylic monomer comprises methacrylic acid, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate or methyl acrylate, preferably methyl methacrylate, methyl acrylate or isobornyl methacrylate.

4. The pre-expanded thermally-expandable microspheres according to claim 1, wherein the acrylonitrile-based monomer comprises acrylonitrile or methacrylonitrile or the like, preferably acrylonitrile.

5. A method for producing pre-expanded thermally expandable microspheres according to any one of claims 1 to 4, wherein the method comprises:

(1) preparation of oil phase: mixing and stirring 30-100 parts by weight of foaming agent, 100 parts by weight of polymerized monomer component, 0.01-2 parts by weight of initiator and 0.05-0.6 part by weight of cross-linking agent at 20 ℃ for 10-15min to form uniform oil phase;

(2) preparation of the aqueous phase: adding 10-50 parts by weight of dispersion stabilizer into 300 parts by weight of 150-one-phase dispersion medium, adding 0.5-1.0 part by weight of water-soluble compound, continuously adding 0.1-0.2 part by weight of inhibitor, uniformly stirring, and adding hydrochloric acid to adjust the pH value to 3-5 to form a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homogeneous mixer at 8000-;

(4) preparation of thermally expanded microspheres: reacting the suspension for 20-24h at 50 ℃ and 0.5-0.6MPa in nitrogen atmosphere to obtain the thermal expansion microspheres;

(5) preparation of pre-expanded thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and performing spray drying to obtain pre-foamed thermal expansion microspheres, wherein the drying temperature is 160-180 ℃.

6. The preparation method according to claim 5, wherein the foaming agent is one or a combination of isobutane, isopentane, n-pentane, isohexane, isooctane or n-octane, preferably isopentane.

7. The method of claim 5, wherein the initiator is azobisisobutyronitrile or dibenzoyl peroxide, preferably azobisisobutyronitrile.

8. The production method according to claim 5, wherein the crosslinking agent is a trifunctional or higher crosslinking agent.

9. The production method according to claim 8, wherein the crosslinking agent is triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanate, or trimethylolpropane trimethacrylate, preferably trimethylolpropane trimethacrylate.

10. The production method according to claim 5, wherein the dispersion medium is water containing an electrolyte.

11. The preparation method according to claim 10, wherein the electrolyte is one or a combination of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate or potassium sulfate, preferably sodium chloride or potassium chloride.

12. The production method according to claim 5, wherein the dispersion stabilizer is colloidal silica.

13. The method according to claim 5, wherein the inhibitor is an alkali nitrite.

14. The production method according to claim 13, wherein the alkali nitrite is sodium nitrite or potassium nitrite.

15. The method according to claim 5, wherein the water-soluble compound is sodium lauryl sulfate or disodium ethylenediaminetetraacetate.

16. The production method according to claim 5, wherein the diameter of the thermally expandable microspheres produced in step (4) before being expanded is 0.5 to 4 μm.

17. The preparation method according to claim 5, wherein the expansion starting temperature of the thermally expandable microspheres prepared in the step (4) is 110-130 ℃.

18. Use of the pre-expanded thermally-expandable microspheres of any one of claims 1 to 4 for the production of thermal paper.

Technical Field

The invention relates to a preparation method, in particular to a pre-foaming thermal expansion microsphere, a preparation method and application thereof.

Background

Thermal paper (also called thermal fax paper, thermal recording paper or thermal copy paper) is a processed paper, and is produced by coating a layer of thermal paint (thermal discoloration layer) on a high-quality base paper. Although the color-changing layer uses more than ten chemicals, the color-changing layer at least comprises the following compounds: leuco dyes (most commonly fluorescent compounds) are a wide variety of dyes; the developer (such as bisphenol and p-hydroxybenzoic acid) is less than about 20%; the sensitizer (such as benzene sulfonic acid amide compounds) accounts for less than 10 percent; fillers (e.g., calcium carbonate (microparticles)) present at less than about 50%; less than about 10% of a binder (e.g., polyvinyl acetate); stabilizers, such as dibenzoyl terephthalate; lubricants, and the like. When the thermal paper is placed in an environment above 70 ℃, the thermal coating begins to change color. The thermosensitive components in the thermosensitive paper coating mainly comprise: leuco dyes (or leuco dyes) and developers and this type of thermal paper is also called two-component chemical type thermal recording paper, which also includes dispersants, topcoat layers, and undercoat layer auxiliaries. The leuco dye mainly comprises Crystal Violet Lactone (CVL) of a triphenylmethyl phthalide system, a fluorane system, colorless benzoyl methylene blue (BLMB) or a spiropyran system and the like; the dispersant mainly comprises polyvinyl alcohol L-3266, polyvinyl alcohol GL-05 or polyvinyl alcohol KL-03 (produced by Japanese synthetic chemistry); the auxiliary agents of the top coating and the bottom coating mainly comprise gohsefimer Z-200, polyvinyl alcohol T-350 or polyvinyl alcohol N-300; the developer mainly comprises p-hydroxybenzoic acid and esters thereof (PHBP, PHB), salicylic acid, 2, 4-dihydroxybenzoic acid or aromatic sulfone, etc.

The colorless dye and the color developing agent generate chemical reaction to generate color after the thermal sensitive paper is heated, so that the pictures and texts are displayed when the thermal sensitive paper is used for receiving signals on a fax machine for printing or is directly used for printing by a thermal printer. Further, since there are a plurality of leuco dyes, the colors of the displayed handwriting are different, such as blue, magenta, black, and the like. The thermal expansion microspheres with small particle size and high porosity are added into the thermal sensitive coating, so that the thermal insulation effect is achieved, the printing area and the non-printing area of the thermal sensitive head can be well isolated and heated, and the definition of the thermal sensitive printing font can be obviously improved.

The thermally expandable microspheres (thermoplastic hollow polymeric microspheres) consist of a thermoplastic polymer shell and an encapsulated blowing agent (liquid alkane) having an average diameter ranging from 10 to 50 μm and a true density of 1000 to 1300kg/m³. Upon heating, the gas pressure within the shell increases and the thermoplastic outer shell softens, thereby causing the volume of the thermally expanded microspheres to increase significantly; when cooled, the shell of the thermally expandable microspheres stiffens again and the volume is fixed. Thermoplastic polymer shells typically include vinylidene chloride-based copolymers, acrylonitrile-based copolymers, and acrylate copolymers; the foaming agent is alkane. The great expansion capacity of the thermally expandable microspheres makes them useful in a wide variety of fields, for example, to reduce the mass of products, to change the properties of products (such as thermal, acoustic and electrical insulation properties) and to save the amount of materials used; the thermal expansion microsphere also has the advantages of excellent solvent resistance, wear resistance, good mechanical property, no toxicity, no pollution and the like.

Disclosure of Invention

The invention provides a pre-foaming thermal expansion microsphere, a preparation method and application thereof. The particle size of the pre-foaming thermal expansion microsphere reaches 3-10 microns, so that the pre-foaming thermal expansion microsphere with high porosity is formed. The pre-foaming thermal expansion microspheres can be added into a thermal sensitive coating of thermal sensitive paper, so that a good thermal insulation effect is achieved, and the definition of thermal sensitive printing is improved.

In order to realize the purpose of the invention, the technical scheme of the invention is as follows:

the present invention provides a pre-expanded thermally-expandable microsphere comprising a thermoplastic resin shell and a foaming agent encapsulated in the shell having a boiling point not higher than the softening point of the thermoplastic resin shell, wherein,

the thermoplastic resin shell includes a polymerized monomer component, wherein,

the polymerized monomer component includes: based on the weight portion, the weight portion of the material,

25-40 parts of acrylic monomers;

60 to 75 parts of acrylonitrile monomers, namely,

wherein the pre-foamed thermal expansion microspheres have a porosity of 70-95%.

In a preferred embodiment of the present invention, the particle size of the pre-expanded thermally-expansible microballs is 3 to 10 μm.

In a preferred embodiment of the present invention, the acrylic monomer comprises methacrylic acid, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate or methyl acrylate, preferably methyl methacrylate, methyl acrylate or isobornyl methacrylate.

In a preferred embodiment of the present invention, the acrylonitrile-based monomer includes acrylonitrile, methacrylonitrile, or the like, and acrylonitrile is preferred.

The invention also provides a preparation method of the pre-foaming thermal expansion microspheres, wherein the method comprises the following steps:

(1) preparation of oil phase: mixing and stirring 30-100 parts by weight of foaming agent, 100 parts by weight of polymerized monomer component, 0.01-2 parts by weight of initiator and 0.05-0.6 part by weight of cross-linking agent at 20 ℃ for 10-15min to form uniform oil phase;

(2) preparation of the aqueous phase: adding 10-50 parts by weight of dispersion stabilizer into 300 parts by weight of 150-one-phase dispersion medium, adding 0.5-1.0 part by weight of water-soluble compound, continuously adding 0.1-0.2 part by weight of inhibitor, uniformly stirring, and adding hydrochloric acid to adjust the pH value to 3-5 to form a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homogeneous mixer at 8000-;

(4) preparation of thermally expanded microspheres: reacting the suspension for 20-24h at 50 ℃ and 0.5-0.6MPa in nitrogen atmosphere to obtain the thermal expansion microspheres;

(5) preparation of pre-expanded thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and performing spray drying to obtain pre-foamed thermal expansion microspheres, wherein the drying temperature is 160-180 ℃.

In a preferred embodiment of the present invention, the blowing agent is one or a combination of isobutane, isopentane, n-pentane, isohexane, isooctane, or n-octane, preferably isopentane.

In a preferred embodiment of the present invention, the initiator is azobisisobutyronitrile or dibenzoyl peroxide, preferably azobisisobutyronitrile.

In a preferred embodiment of the present invention, the crosslinking agent is a trifunctional or higher crosslinking agent.

In a preferred embodiment of the invention, the crosslinker is triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanate or trimethylolpropane trimethacrylate, preferably trimethylolpropane trimethacrylate.

In a preferred embodiment of the present invention, the dispersion medium is water containing an electrolyte.

In a more preferred embodiment of the present invention, the electrolyte is one or a combination of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate or potassium sulfate, preferably sodium chloride or potassium chloride.

In a preferred embodiment of the present invention, the dispersion stabilizer is colloidal silica.

In a preferred embodiment of the present invention, the inhibitor is an alkali metal nitrite.

In a more preferred embodiment of the present invention, the alkali metal nitrite is sodium nitrite or potassium nitrite.

In a more preferred embodiment of the present invention, the water-soluble compound is sodium lauryl sulfate or disodium edetate.

In a preferred embodiment of the present invention, the diameter of the thermally expandable microspheres produced in step (4) before being expanded is 0.5 to 4 μm.

In a preferred embodiment of the present invention, the expansion initiation temperature of the thermally expandable microspheres prepared in step (4) is 110-130 ℃.

The invention also provides application of the pre-foamed thermal expansion microspheres in manufacturing thermal sensitive paper.

Drawings

FIG. 1 is an optical microscopic view of the pre-expanded thermally-expandable microspheres of example 4.

Detailed Description

The following are more specific examples to develop the present invention, but the present invention is not limited to the scope of these examples. The particle size of the pre-foaming thermal expansion microspheres reaches 3-10 microns, and the shell of the pre-foaming microspheres is an ultrathin thermoplastic resin shell film, and alkane gas is encapsulated inside the shell film, so that the pre-foaming thermal expansion microspheres with high porosity are formed. The pre-foaming thermal expansion microspheres can be added into a thermal sensitive coating of thermal sensitive paper, so that a good thermal insulation effect is achieved, and the definition of thermal sensitive printing is improved.

The present invention provides a pre-expanded thermally-expandable microsphere comprising a thermoplastic resin shell and a foaming agent encapsulated in the shell having a boiling point not higher than the softening point of the thermoplastic resin shell, wherein,

the thermoplastic resin shell includes a polymerized monomer component, wherein,

the polymerized monomer component includes: based on the weight portion, the weight portion of the material,

25-40 parts of acrylic monomers;

60 to 75 parts of acrylonitrile monomers, namely,

wherein the pre-foamed thermal expansion microspheres have a porosity of 70-95%.

In the description of the present invention, the thickness of the thermoplastic resin shell of the pre-expanded thermally-expansible microballs is 0.1 to 0.3 μm.

In the description of the present invention, the particle size of the pre-expanded thermally-expansible microballs is 3 to 10 μm.

In the description of the present invention, the acrylic monomer includes, but is not limited to, methacrylic acid, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate or methyl acrylate, preferably methyl methacrylate, methyl acrylate or isobornyl methacrylate.

In the description of the present invention, the acrylonitrile-based monomer includes, but is not limited to, acrylonitrile or methacrylonitrile, etc., with acrylonitrile being preferred.

The invention also provides a preparation method of the pre-foaming thermal expansion microspheres, wherein the method comprises the following steps:

(1) preparation of oil phase: mixing and stirring 30-100 parts by weight of foaming agent, 100 parts by weight of polymerized monomer component, 0.01-2 parts by weight of initiator and 0.05-0.6 part by weight of cross-linking agent at 20 ℃ for 10-15min to form uniform oil phase;

(2) preparation of the aqueous phase: adding 10-50 parts by weight of dispersion stabilizer into 300 parts by weight of 150-one-phase dispersion medium, adding 0.5-1.0 part by weight of water-soluble compound, continuously adding 0.1-0.2 part by weight of inhibitor, uniformly stirring, and adding hydrochloric acid to adjust the pH value to 3-5 to form a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homogeneous mixer at 8000-;

(4) preparation of thermally expanded microspheres: reacting the suspension for 20-24h at 50 ℃ and 0.5-0.6MPa in nitrogen atmosphere to obtain the thermal expansion microspheres;

(5) preparation of pre-expanded thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and performing spray drying to obtain pre-foamed thermal expansion microspheres, wherein the drying temperature is 160-180 ℃.

In the description of the present invention, the blowing agent is one or a combination of isobutane, isopentane, n-pentane, isohexane, isooctane, or n-octane, preferably isopentane.

In the description of the present invention, the initiator is azobisisobutyronitrile or dibenzoyl peroxide, preferably azobisisobutyronitrile.

In the description of the present invention, the crosslinking agent is a trifunctional or higher crosslinking agent.

In the context of the present invention, the crosslinker is triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanate or trimethylolpropane trimethacrylate, preferably trimethylolpropane trimethacrylate.

In the description of the present invention, the dispersion medium is water containing an electrolyte.

In a more preferred embodiment of the present invention, the electrolyte is one or a combination of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate or potassium sulfate, preferably sodium chloride or potassium chloride, and the electrolyte is not particularly limited, and may be selected by one skilled in the art according to the need, and the amount of the electrolyte is preferably 10 to 30 parts.

In the description of the present invention, the dispersion stabilizer is colloidal silica.

In the description of the present invention, the inhibitor is an alkali metal nitrite.

In the description of the present invention, the alkali metal nitrite is sodium nitrite or potassium nitrite.

In the description of the present invention, the water-soluble compound is sodium dodecyl sulfate or disodium ethylene diamine tetraacetate.

In the description of the present invention, the diameter of the thermally expandable microspheres produced in step (4) before being expanded is 1 to 4 μm.

In the description of the present invention, the temperature of the initiation expansion of the thermally expandable microspheres prepared in step (4) is 110-130 ℃.

The preparation method comprises the following steps: in an aqueous dispersion medium, the polymerizable components are subjected to medium-low temperature suspension polymerization in the presence of an initiator. The polymerization monomer component adopts acrylonitrile and acrylic monomer composition, a shell with high barrier property and micro-expansion property is formed after polymerization, the average grain diameter of the thermal expansion microsphere is 0.5-4 microns, and the grain diameter reaches 3-10 microns after pre-foaming expansion, so that the pre-foaming thermal expansion microsphere with high void ratio is formed. The pre-foaming thermal expansion microspheres can be added into a thermal sensitive coating of thermal sensitive paper, so that a good thermal insulation effect is achieved, and the definition of thermal sensitive printing is improved.

The invention also provides application of the pre-foamed thermal expansion microspheres in manufacturing thermal sensitive paper.

The invention also provides application of the pre-foamed thermal expansion microspheres in a thermal sensitive coating of thermal sensitive paper.

The thickness of the thermoplastic resin shell of the thermally expandable microspheres of the present invention (before foaming) is 0.5 to 1 μm.

The average particle diameter of the thermally expandable microspheres of the present invention (before foaming) is 1 to 4 μm.

In the description of the present invention, "temperature to initiate expansion" refers to the temperature at which the microspheres begin to expand when heated;

in the description of the present invention, "spray drying" refers to a drying method in which a raw material liquid is dispersed into mist droplets by using an atomizer, and the mist droplets are dried with hot gas (air, nitrogen gas, or superheated steam) to obtain a product.

In the description of the present invention, "porosity" means a ratio of the internal void volume of the pre-expanded microsphere to the volume of the whole pre-expanded microsphere, and is referred to as porosity.

Determination of the "average particle size" in the following examples: the volume average particle size was measured by a laser particle size distribution analyzer (model: Bettersize 2600, Dendon.) and D50 particle size was defined as the average particle size;

determination of the "onset expansion temperature" in the following examples: shimadzu TMA-60 was used as a measuring apparatus, microspheres were put in an aluminum cup having a diameter of 6.0mm and a depth of 4.8mm, and an aluminum cap having a diameter of 5.6mm and a thickness of 0.1mm was placed on the upper part of the microsphere layer to prepare a sample. The height of the sample was measured in a state where a force was applied to the sample from above by the pressurizing head. The sample was heated from 20 ℃ at a temperature rising rate of 10 ℃/min to 400 ℃ in a state of applying a force by the pressure head, and the amount of displacement in the vertical direction of the pressure head was measured. The displacement start temperature in the positive direction is set as the expansion start temperature, and the temperature indicating the maximum displacement amount is set as the maximum expansion temperature.

Measurement of "average expansion Rate" in the following examples: observing the change of radius R value before and after the expansion of the scale microsphere through an optical detection microscope (model: Shanghai rectangular optical instrument CCM-900E), and calculating a formula V through the microsphere volume＝(4/3)πr³Calculating the ratio, i.e. V_{Mean expansion ratio}＝V_{(volume after microsphere expansion)}/V_{(volume before expansion of microspheres)}；

Determination of "void fraction" in the following examples: observing the inner void radius R value and the overall radius R value of the scale pre-foamed microspheres by a scanning electron microscope (model: Taisiken MIRA 3XMH scanning electron microscope), and calculating the formula V ═ 4/3 (pi R) by the microsphere volume³The porosity, i.e., the porosity ═ V (V) was calculated_{(internal void volume of Pre-expanded microspheres)}/V_{(Pre-expanded microsphere volume)})x100％。

Example 1

1. Preparation of pre-foamed thermal expansion microsphere

(1) Preparation of oil phase: 27g of isopentane, 3g of methyl acrylate, 7g of methyl methacrylate, 14g of isobornyl methacrylate, 41g of acrylonitrile, 0.15g of trimethylolpropane trimethacrylate and 0.6g of azobisisobutyronitrile are mixed and stirred at the temperature of 20 ℃ for 10-15min to form a uniform oil phase;

(2) preparation of the aqueous phase: dissolving 40g of sodium chloride in 200g of deionized water, then adding 25g of a colloidal silicon dioxide solution with the mass concentration of 25%, adding 0.5g of sodium dodecyl sulfate and 0.2g of disodium ethylene diamine tetraacetate, adding 0.15g of sodium nitrite, stirring uniformly, adding hydrochloric acid, adjusting the pH value to 3, and taking the formed solution as a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homomixer (such as a homogenizer and an electric stirrer) at 12000rpm for 10min to obtain a suspension;

(4) preparing the thermal expansion microspheres by reaction: transferring the suspension into a high-pressure reaction kettle, reacting for 20 hours at 50 ℃ and 0.6MPa in the atmosphere of nitrogen to obtain milky liquid, performing suction filtration and deionized water washing, and drying to obtain thermal expansion microspheres, wherein the average particle size of the thermal expansion microspheres is 2 microns, the initiation expansion temperature is 124 ℃, and the average expansion ratio is 2-4 times;

(5) preparation of pre-expanded thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and then carrying out spray drying and pre-foaming to obtain pre-foamed thermal expansion microspheres with high void ratio (the void ratio is 80%) by spray drying, wherein the drying temperature is 160 ℃;

the average particle diameter of the pre-expanded thermal expansion microspheres is 4-6 microns.

2. Preparation method of thermal sensitive paper containing prefoamed thermal expansion microspheres of the embodiment

The thermal sensitive paper of the embodiment is compounded by bottom layer base paper, a pre-foaming thermal expansion microsphere transition layer, a thermal sensitive coating and a protective coating, wherein a color developing agent in the thermal sensitive coating is p-hydroxybenzoic acid and esters thereof (PHBB, PHB) and salicylic acid, and the pre-foaming thermal expansion microsphere transition layer is pre-foaming microspheres: styrene-butadiene latex 10: 2 (oven dry ratio) to prepare a coating solution with a solid content of 10%. The pre-foaming thermal expansion microsphere transition layer is coated on the bottom layer base paper, dried at 65 ℃ and then coated with the thermosensitive coating and the protective coating to form the thermosensitive paper.

3. The effect of using the thermal paper containing the prefoamed thermal expansion microspheres of the embodiment is as follows: the thermal sensitive paper added with the pre-foaming thermal expansion microspheres has the optical density of 1.1, and is clear in printing, and due to the addition of the pre-foaming thermal expansion microspheres, the thermal insulation effect is improved, the thermal sensitive printing speed is improved, and the handwriting is still clear.

Example 2

1. Preparation of pre-foamed thermal expansion microsphere

(1) Preparation of oil phase: mixing 31g of isopentane, 5g of methyl acrylate, 6g of methyl methacrylate, 13g of isobornyl methacrylate, 44g of acrylonitrile, 0.15g of trimethylolpropane trimethacrylate and 0.6g of azobisisobutyronitrile at 20 ℃ and stirring for 10-15min to form a uniform oil phase;

(2) preparation of the aqueous phase: dissolving 40g of sodium chloride in 200g of deionized water, then adding 23g of a colloidal silicon dioxide solution with the mass concentration of 25%, adding 0.5g of sodium dodecyl sulfate and 0.25g of disodium ethylene diamine tetraacetate, adding 0.15g of sodium nitrite, stirring uniformly, adding hydrochloric acid to adjust the pH value to 3, wherein the formed solution is a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homomixer (such as a homogenizer and an electric stirrer) at 12000rpm for 12min to obtain a suspension;

(4) preparing the thermal expansion microspheres by reaction: and transferring the suspension into a high-pressure reaction kettle, reacting for 20 hours at 50 ℃ and 0.6MPa in the atmosphere of nitrogen to obtain milky white liquid, performing suction filtration and deionized water washing, and drying to obtain the thermal expansion microspheres. The average grain diameter of the thermal expansion microsphere is 1-2.5 microns, the initiation expansion temperature is 115 ℃, and the average expansion multiplying power is 2-5 times;

(5) preparation of pre-expanded thermal expansion microspheres: dispersing the thermal expansion microspheres prepared in the above step into water, and then carrying out spray drying and prefoaming to obtain prefoamed thermal expansion microspheres with high porosity (the porosity is 82%)), wherein the drying temperature is 175 ℃.

The average particle diameter of the pre-foaming thermal expansion microspheres is 3-10 microns.

2. Preparation method of thermal sensitive paper containing prefoamed thermal expansion microspheres of the embodiment

The thermal sensitive paper of the embodiment is compounded by bottom layer base paper, a pre-foaming thermal expansion microsphere transition layer, a thermal sensitive coating and a protective coating, wherein, a color developing agent in the thermal sensitive coating is para-hydroxybenzoic acid and esters thereof (PHBB, PHB) and salicylic acid, and the pre-foaming thermal expansion microsphere transition layer is pre-foaming microspheres: styrene-butadiene latex 10: 2 (oven dry ratio) to prepare a coating solution with a solid content of 10%. The pre-foaming thermal expansion microsphere transition layer is coated on the bottom layer base paper, dried at 65 ℃ and then coated with the thermosensitive coating and the protective coating to form the thermosensitive paper.

3. The effect of using the thermal paper containing the prefoamed thermal expansion microspheres of the embodiment is as follows: the thermal sensitive paper added with the pre-foaming thermal expansion microspheres has the optical density of 1.07, and is clear in printing, and due to the addition of the pre-foaming thermal expansion microspheres, the thermal insulation effect is improved, the thermal sensitive printing speed is improved, and the handwriting is still clear.

Example 3

1. Preparation of pre-foamed thermal expansion microsphere

(1) Preparation of oil phase: mixing 32g of isopentane, 6g of methyl acrylate, 9g of methyl methacrylate, 7g of isobornyl methacrylate, 42g of acrylonitrile, 0.17g of trimethylolpropane trimethacrylate and 0.6g of azobisisobutyronitrile at 20 ℃ and stirring for 10-15min to form a uniform oil phase;

(2) preparation of the aqueous phase: dissolving 42g of sodium chloride in 200g of deionized water, then adding 20g of a colloidal silicon dioxide solution with the mass concentration of 25%, adding 0.55g of sodium dodecyl sulfate and 0.15g of disodium ethylene diamine tetraacetate, adding 0.20g of sodium nitrite, stirring uniformly, adding hydrochloric acid to adjust the pH value to 3, wherein the formed solution is a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homomixer (such as a homogenizer and an electric stirrer) at 11000rpm for 13min to obtain a suspension;

(4) preparing the thermal expansion microspheres by reaction: and transferring the suspension into a high-pressure reaction kettle, reacting for 24 hours at 50 ℃ and 0.6MPa in the atmosphere of nitrogen to obtain milky white liquid, performing suction filtration and deionized water washing, and drying to obtain the thermal expansion microspheres. The average grain diameter of the thermal expansion microsphere is 0.5-3 microns, the initiation expansion temperature is 118 ℃, and the average expansion multiplying power is 2-4 times;

(5) preparation of pre-expanded thermal expansion microspheres: dispersing the thermal expansion microspheres prepared in the above step into water, and then carrying out spray drying and prefoaming to obtain prefoamed thermal expansion microspheres with high void ratio (the void ratio is 72%), wherein the drying temperature is 165 ℃.

The average particle diameter of the pre-expanded thermal expansion microspheres is 2-7 microns.

2. Preparation method of thermal sensitive paper containing prefoamed thermal expansion microspheres of the embodiment

The thermal sensitive paper of the embodiment is compounded by bottom layer base paper, a pre-foaming thermal expansion microsphere transition layer, a thermal sensitive coating and a protective coating, wherein, a color developing agent in the thermal sensitive coating is para-hydroxybenzoic acid and esters thereof (PHBB, PHB) and salicylic acid, and the pre-foaming thermal expansion microsphere transition layer is pre-foaming microspheres: styrene-butadiene latex 10: 2 (oven dry ratio) to prepare a coating solution with a solid content of 10%. The pre-foaming thermal expansion microsphere transition layer is coated on the bottom layer base paper, dried at 65 ℃ and then coated with the thermosensitive coating and the protective coating to form the thermosensitive paper.

3. The effect of using the thermal paper containing the prefoamed thermal expansion microspheres of the embodiment is as follows: the thermal sensitive paper added with the pre-foaming thermal expansion microspheres has the optical density of 0.99, and is clear in printing, and due to the addition of the pre-foaming thermal expansion microspheres, the thermal insulation effect is improved, the thermal sensitive printing speed is improved, and the handwriting is still clear.

Example 4

1. Preparation of pre-foamed thermal expansion microsphere

(1) Preparation of oil phase: mixing 29g of isopentane, 3g of methyl acrylate, 6g of methyl methacrylate, 16g of isobornyl methacrylate, 39g of acrylonitrile, 0.17g of trimethylolpropane trimethacrylate and 0.6g of azobisisobutyronitrile at 20 ℃ and stirring for 10-15min to form a uniform oil phase;

(2) preparation of an aqueous phase: dissolving 42g of sodium chloride in 200g of deionized water, then adding 20g of a colloidal silicon dioxide solution with the mass concentration of 25%, adding 0.55g of sodium dodecyl sulfate and 0.15g of disodium ethylene diamine tetraacetate, adding 0.15g of sodium nitrite, stirring uniformly, adding hydrochloric acid to adjust the pH value to 3, wherein the formed solution is a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homomixer (such as a homogenizer and an electric stirrer) at 11000rpm for 13min to obtain a suspension;

(4) preparing the thermal expansion microspheres by reaction: and transferring the suspension into a high-pressure reaction kettle, reacting for 24 hours at 50 ℃ and 0.6MPa in the atmosphere of nitrogen to obtain milky white liquid, performing suction filtration and washing with deionized water, and drying to obtain the thermal expansion microspheres. The average grain diameter of the thermal expansion microsphere is 1-2 microns, the initiation expansion temperature is 128 ℃, and the average expansion multiplying power is 1-4 times;

(5) preparing pre-foaming thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and then carrying out spray drying and prefoaming to obtain the prefoamed thermal expansion microspheres with high void ratio (the void ratio is 89%), wherein the drying temperature is 183 ℃.

The pre-expanded thermally-expansible microballs had an average particle diameter of 2 to 8 μm (see FIG. 1).

2. Preparation method of thermal sensitive paper containing prefoamed thermal expansion microspheres of the embodiment

The thermal sensitive paper of the embodiment is compounded by bottom layer base paper, a pre-foaming thermal expansion microsphere transition layer, a thermal sensitive coating and a protective coating, wherein a color developing agent in the thermal sensitive coating is p-hydroxybenzoic acid and esters thereof (PHBB, PHB) and salicylic acid, and the pre-foaming thermal expansion microsphere transition layer is pre-foaming microspheres: styrene-butadiene latex 10: 2 (oven dry ratio) to prepare a coating solution with a solid content of 10%. The pre-foaming thermal expansion microsphere transition layer is coated on the bottom layer base paper, dried at 65 ℃ and then coated with the thermosensitive coating and the protective coating to form the thermosensitive paper.

3. The effect of using the thermal paper containing the prefoamed thermal expansion microspheres of the embodiment is as follows: the thermal sensitive paper added with the pre-foaming thermal expansion microspheres has the optical density of 1.12, and is clear in printing, and due to the addition of the pre-foaming thermal expansion microspheres, the thermal insulation effect is improved, the thermal sensitive printing speed is improved, and the handwriting is still clear.

Example 5

1. Preparation of pre-foamed thermal expansion microsphere

(1) Preparation of oil phase: mixing 29g of isopentane, 4g of methyl acrylate, 6g of methyl methacrylate, 11g of isobornyl methacrylate, 45g of acrylonitrile, 0.13g of trimethylolpropane trimethacrylate and 0.7g of azobisisobutyronitrile at 20 ℃ and stirring for 10-15min to form a uniform oil phase;

(2) preparation of an aqueous phase: dissolving 42g of sodium chloride in 200g of deionized water, then adding 20g of a colloidal silicon dioxide solution with the mass concentration of 25%, adding 0.45g of sodium dodecyl sulfate and 0.35g of disodium ethylene diamine tetraacetate, adding 0.15g of sodium nitrite, stirring uniformly, adding hydrochloric acid, adjusting the pH value to 3, and taking the formed solution as a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homomixer (such as a homogenizer and an electric stirrer) at 8000rpm for 16min to obtain suspension;

(4) preparing the thermal expansion microspheres by reaction: and transferring the suspension into a high-pressure reaction kettle, reacting for 24 hours at 50 ℃ and 0.6MPa in the atmosphere of nitrogen to obtain milky white liquid, performing suction filtration and washing with deionized water, and drying to obtain the thermal expansion microspheres. The average grain diameter of the thermal expansion microsphere is 4 microns, the initiation expansion temperature is 116 ℃, and the average expansion multiplying power is 1-2 times;

(5) preparing pre-foaming thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and then carrying out spray drying and prefoaming to obtain the prefoamed thermal expansion microspheres with high void ratio (the void ratio is 70%), wherein the drying temperature is 155 ℃.

The average particle diameter of the pre-expanded thermally-expansible microballs was 10 μm.

2. Preparation method of thermal sensitive paper containing prefoamed thermal expansion microspheres of the embodiment

The thermal sensitive paper of the embodiment is compounded by bottom layer base paper, a pre-foaming thermal expansion microsphere transition layer, a thermal sensitive coating and a protective coating, wherein a color developing agent in the thermal sensitive coating is p-hydroxybenzoic acid and esters thereof (PHBB, PHB) and salicylic acid, and the pre-foaming thermal expansion microsphere transition layer is pre-foaming microspheres: styrene-butadiene latex 10: 2 (oven dry ratio) to prepare a coating solution with a solid content of 10%. The pre-foaming thermal expansion microsphere transition layer is coated on the bottom layer base paper, dried at 65 ℃ and then coated with the thermosensitive coating and the protective coating to form the thermosensitive paper.

3. The effect of using the thermal paper containing the prefoamed thermal expansion microspheres of the embodiment is as follows: the thermal sensitive paper added with the pre-foaming thermal expansion microspheres has the optical density of 0.88, and is clear in printing, and due to the addition of the pre-foaming thermal expansion microspheres, the thermal insulation effect is improved, the thermal sensitive printing speed is improved, and the handwriting is still clear.

Comparative example 1

1. Preparation of pre-foamed thermal expansion microsphere

(1) Preparation of oil phase: mixing 29g of isopentane, 1g of methyl acrylate, 9g of methyl methacrylate, 5g of isobornyl methacrylate, 53g of acrylonitrile, 0.13g of trimethylolpropane trimethacrylate and 0.7g of azobisisobutyronitrile at 20 ℃ and stirring for 10-15min to form a uniform oil phase;

(2) preparation of an aqueous phase: dissolving 42g of sodium chloride in 200g of deionized water, then adding 20g of a colloidal silicon dioxide solution with the mass concentration of 25%, adding 0.435g of sodium dodecyl sulfate and 0.25g of disodium ethylene diamine tetraacetate, adding 0.15g of sodium nitrite, stirring uniformly, adding hydrochloric acid to adjust the pH value to 3, and taking the formed solution as a water phase;

(3) homogenizing the water phase and the oil phase: pouring the oil phase into the water phase, and dispersing the mixed liquid in a homomixer (such as a homogenizer and an electric stirrer) at 5000rpm for 10min to obtain suspension;

(4) preparing the thermal expansion microspheres by reaction: and transferring the suspension into a high-pressure reaction kettle, reacting for 24 hours at 50 ℃ and 0.6MPa in the atmosphere of nitrogen to obtain milky white liquid, performing suction filtration and washing with deionized water, and drying to obtain the thermal expansion microspheres. The average grain diameter of the thermal expansion microsphere is 10 microns, the initiation expansion temperature is 136 ℃, and the average expansion multiplying power is 2-3 times;

(5) preparing pre-foaming thermal expansion microspheres: dispersing the prepared thermal expansion microspheres into water, and then carrying out spray drying and prefoaming to obtain the prefoamed thermal expansion microspheres with high void ratio (the void ratio is 50%), wherein the drying temperature is 180 ℃.

The average particle diameter of the pre-expanded thermally-expansible microballs was 20 μm.

2. Preparation method of thermal sensitive paper containing prefoamed thermal expansion microspheres of the embodiment

The thermal sensitive paper of the embodiment is compounded by bottom layer base paper, a pre-foaming thermal expansion microsphere transition layer, a thermal sensitive coating and a protective coating, wherein a color developing agent in the thermal sensitive coating is p-hydroxybenzoic acid and esters thereof (PHBB, PHB) and salicylic acid, and the pre-foaming thermal expansion microsphere transition layer is pre-foaming microspheres: styrene-butadiene latex 10: 2 (oven dry ratio) to prepare a coating solution with a solid content of 10%. The pre-foaming thermal expansion microsphere transition layer is coated on the bottom layer base paper, dried at 65 ℃ and then coated with the thermosensitive coating and the protective coating to form the thermosensitive paper.

3. The effect of using the thermal paper containing the prefoamed thermal expansion microspheres of the embodiment is as follows: the thermal sensitive paper added with the pre-foaming thermal expansion microspheres has the optical density of 0.5, and has light leakage in printed characters due to large particle size and low porosity.