CN108178818A - Reversed core-shell emulsion of NMA modified polyvinyl acetate bases and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of emulsion adhesive preparation, and specifically relates to an NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion and a preparation method thereof. The emulsion is mainly made of vinyl acetate, styrene and functional monomer NMA The composite latex particles in the emulsion have a strawberry-shaped core-shell structure, with polyvinyl acetate as the core and small polystyrene particles as the shell, and functional monomer NMA is added on the surface of the composite latex particles. The emulsion adhesive of the present invention can effectively improve the bonding wet strength of the emulsion adhesive by utilizing the self-crosslinking properties of NMA while maintaining good bonding performance and the excellent hydrothermal resistance of the reverse structure composite latex particles, and at the same time can improve The initial tack of the emulsion adhesive, and because NMA is a hydrophilic group, can greatly improve the wettability of the emulsion adhesive to the objects to be bonded. The emulsion adhesive provided by the invention is non-toxic, harmless and pollution-free, and can be widely used in the fields of paper packaging, furniture manufacturing, interior decoration, floor laying, gluing wood and the like.

Description

NMA modified polyvinyl acetate based reverse core-shell structure emulsion and preparation method thereof

technical field

The invention belongs to the field of emulsion adhesive preparation, and in particular relates to an NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion and a preparation method thereof.

Background technique

The construction of polyvinyl acetate (PVAc)-based core-shell structure emulsion can maintain the film-forming and adhesive properties of the original emulsion film, and at the same time introduce styrene (St) and other modified monomers that are difficult to carry out traditional copolymerization and have excellent performance. Body, improve the water resistance, heat resistance and creep resistance of the emulsion. Constructing a reverse core-shell structured emulsion with polyvinyl acetate as the core and polystyrene as the shell can improve the compressive shear strength, water resistance, and freeze-thaw stability of the emulsion, but styrene is a rigid monomer. There are no active functional groups in the body. After compounding to the surface layer of polyvinyl acetate particles, although the strength and water resistance of the latex film can be improved, the bonding performance of the emulsion will be affected. In addition, hot and humid conditions can greatly damage the emulsion adhesive layer, which affects the bonding wet strength of the adhesive layer, which greatly limits the practical application of emulsion adhesives.

Contents of the invention

In order to solve the above-mentioned deficiencies in the prior art, the present invention provides an NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion and a preparation method thereof.

Technical scheme of the present invention:

An NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion, mainly made of vinyl acetate, styrene and functional monomer NMA, the composite latex particles in the emulsion have a strawberry-shaped core-shell structure, with poly Vinyl acetate is the core, small polystyrene particles are the shell, and functional monomer NMA is added on the surface of the composite latex particles.

A kind of preparation method step of NMA modified polyvinyl acetate base reverse core-shell structure emulsion is as follows:

Step 1. Add the pH buffer and compound emulsifier into deionized water of a certain quality, raise the temperature to 60°C, stir for a certain period of time, add vinyl acetate monomer accounting for 10-20% of the total weight of vinyl acetate monomer, stir and emulsify After a certain period of time, add an aqueous initiator solution accounting for 30-50% of the total weight of the initiator, heat up to 65°C to continue the reaction, and continue to heat up to 80°C after the blue light appears, and react for a certain period of time to prepare a nuclear seed emulsion;

Step 2. Maintain the reaction temperature of the nuclear seed emulsion prepared in step 1 at 80°C, and dropwise add the mixture of the remaining vinyl acetate monomer and butyl acrylate monomer to the above-mentioned nuclear seed emulsion. , add the remaining initiator in batches in equal amounts; after the dropwise addition of the core monomer mixture is completed, the grafted monomer is added dropwise into the reaction system, and the styrene shell monomer is added dropwise immediately after the addition of the grafted monomer is completed. After the styrene shell monomer is added dropwise, the temperature is raised to 85°C, and after holding for a certain period of time, the temperature of the emulsion is lowered to 60°C. At this time, a certain proportion of NMA functional monomer is added dropwise. The temperature was raised to 80°C, and after a certain period of time, the reaction system was naturally cooled to room temperature and filtered to obtain an NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion.

Further, based on the total amount of vinyl acetate monomer and styrene monomer reacted, the weight ratio of each raw material used is as follows:

Further, the pH buffering agent is NaHCO3; the composite emulsifier is composed of emulsifier PCA507 and emulsifier PCA078, wherein the weight ratio of PCA507 and PCA078 is (1～2):(1～2); the initiator It is ammonium persulfate, and the initiator aqueous solution is prepared by dissolving ammonium persulfate in deionized water accounting for 10% to 15% of the total weight of deionized water; the graft monomer is maleic anhydride, maleic anhydride monomer It is prepared by dissolving maleic anhydride in deionized water accounting for 5-10% of the total weight of deionized water.

Further, the stirring time after adding the pH buffer and the composite emulsifier into the deionized water and raising the temperature to 60°C in step 1 is 30 minutes; the stirring and emulsifying time after adding vinyl acetate monomer is 30 minutes; the blue light appears Afterwards, the temperature was continued to rise to 80° C. for 30 minutes for the reaction.

Further, the dropping rate of the mixture of the remaining vinyl acetate monomer and butyl acrylate monomer described in step 2 is 0.3-0.5 mL/min.

Further, the interval between batch addition of the initiator described in step 2 is 30 minutes.

Further, the addition rate of the grafted monomer in step 2 is 0.7-0.8 mL/min.

Further, the dropping rate of the styrene shell monomer in step 2 is 0.1-0.4 mL/min; the holding time after the temperature is raised to 85° C. is 10 min.

Further, the dropping rate of the NMA functional monomer in step 2 is 0.1-0.2 mL/min, and the holding time after the temperature is raised to 80° C. is 30 min.

Beneficial effects of the present invention:

One, the composite latex particles in the NMA modified polyvinyl acetate base reverse core-shell structure emulsion provided by the present invention take polyvinyl acetate as the core, and the small polystyrene particles are the shells, and add function on the surface of the composite latex particles Monomer NMA, the emulsion adhesive of the present invention, while maintaining the good bonding performance of the polyvinyl acetate emulsion and the excellent hydrothermal resistance of the reverse structure composite latex particles, greatly improves the compression shear of the emulsion bonding test piece. wet strength.

Two, the preparation method of NMA modified polyvinyl acetate base reverse core-shell structure emulsion provided by the invention adopts N-methylolacrylamide (NMA) as functional monomer, by graft copolymerization, in polyvinyl acetate ( The shell layer of PVAc-based core-shell composite latex particles introduces cross-linkable groups. Due to the presence of highly active hydroxymethyl groups on the nitrogen atoms in the NMA structure, the PVAc-based core-shell composite latex particles have cross-linking ability, and their molecular chains are in Under certain conditions, a methylol reaction occurs, and a molecule of water is removed to form an interpenetrating network structure. The self-crosslinking property of NMA itself can effectively improve the bonding wet strength of the emulsion, and at the same time improve the initial tack of the adhesive. , and because NMA is a hydrophilic group, it can greatly improve the wettability of the emulsion to the glued object.

3. The NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion-type adhesive provided by the present invention is non-toxic and harmless, has no pollution to the environment, can be stored and cured at room temperature, and can be directly used as a water-based adhesive , Widely used in paper packaging, furniture manufacturing, interior decoration, floor laying and glued wood and other fields.

Four, the preparation process of NMA modified polyvinyl acetate base reverse core-shell structure emulsion provided by the present invention is simple, and raw material price is cheap, and preparation and production use cost are low, and the prepared composite latex particles are uniform in size and regular in appearance, which is beneficial to Provide better bonding properties of emulsion adhesives and facilitate actual sizing.

Description of drawings

Fig. 1 is the TEM figure of the NMA modified polyvinyl acetate base reverse core-shell structure emulsion sample that embodiment 2 makes;

Fig. 2 is the SEM figure of the NMA modified polyvinyl acetate base reverse core-shell structure emulsion sample that embodiment 2 makes;

Fig. 3 is the particle size distribution figure of composite latex particle in the modified polyvinyl acetate base reverse core-shell structure emulsion of the different NMA content that embodiment 2-4 makes;

Fig. 4 is the infrared spectrogram of the NMA modified polyvinyl acetate base reverse core-shell structure emulsion sample that embodiment 2 makes;

Fig. 5 is the shear wet strength comparative figure of the polyvinyl acetate-based reverse core-shell structure emulsion of the different NMA content that embodiment 2-4 and comparative example 1 make;

Fig. 6 is a comparison chart of compressive shear strength of modified polyvinyl acetate-based reverse core-shell structure emulsions with different NMA contents prepared in Examples 2-4 under different boiling water treatment conditions.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the examples, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered by the present invention within the scope of protection.

Example 1

An NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion, mainly made of vinyl acetate, styrene and functional monomer NMA, the composite latex particles in the emulsion have a strawberry-shaped core-shell structure, with poly Vinyl acetate is the core, small polystyrene particles are the shell, and functional monomer NMA is added on the surface of the composite latex particles.

A kind of preparation method step of NMA modified polyvinyl acetate base reverse core-shell structure emulsion is as follows:

The total amount of vinyl acetate monomer and styrene monomer by reaction is based on the basis, and each raw material is prepared according to the following weight ratio:

Step 1. Add NaHCO3 and composite emulsifier to a certain quality of deionized water, wherein the composite emulsifier is composed of emulsifier PCA507 and emulsifier PCA078, wherein the weight ratio of PCA507 to PCA078 is (1～2):(1～2) , heat up to 60°C, stir for 30 minutes, add vinyl acetate monomer accounting for 10-20% of the total weight of vinyl acetate monomer, stir and emulsify for 30 minutes, add ammonium persulfate aqueous solution accounting for 30-50% of the total weight of ammonium persulfate , the ammonium persulfate aqueous solution is prepared by dissolving 10-15% of the total weight of deionized water. It is heated to 65°C to continue the reaction. After the blue light appears, continue to heat up to 80°C. seed emulsion;

Step 2. Maintain the reaction temperature of the nuclear seed emulsion prepared in step 1 at 80° C., dropwise add the mixture of the remaining vinyl acetate monomer and butyl acrylate monomer to the above-mentioned nuclear seed emulsion at a rate of 0.3- 0.5mL/min, during this dropping process, add the remaining ammonium persulfate in equal amounts in batches, and the interval between adding in batches is 30min; Add dropwise into the reaction system. The maleic anhydride monomer is prepared by dissolving 5-10% of the total weight of deionized water. The dropping rate is 0.7-0.8mL/min. Immediately after the addition of the styrene shell monomer, start to drop the styrene shell monomer. The dropping rate of the styrene shell monomer is 0.1-0.4mL/min. Cool down to 60°C, start to drop a certain proportion of NMA functional monomers at this time, the dropping rate of NMA functional monomers is 0.1-0.2mL/min, after the addition of NMA functional monomers, raise the temperature to 80°C, and keep warm for 30min. The reaction system was naturally cooled to room temperature, and filtered to obtain an NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion.

Example 2

An NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion, mainly made of vinyl acetate, styrene and functional monomer NMA, the composite latex particles in the emulsion have a strawberry-shaped core-shell structure, with poly Vinyl acetate is the core, small polystyrene particles are the shell, and functional monomer NMA is added on the surface of the composite latex particles.

A kind of preparation method step of NMA modified polyvinyl acetate base reverse core-shell structure emulsion is as follows:

The total amount of vinyl acetate monomer and styrene monomer by reaction is based on the basis, and each raw material is prepared according to the following weight ratio:

Step 1. Add NaHCO3 and composite emulsifier to a certain quality of deionized water, wherein the composite emulsifier is composed of emulsifier PCA507 and emulsifier PCA078, the weight ratio of PCA507 and PCA078 is 1:1, heat up to 60°C, and stir for 30 minutes Add vinyl acetate monomer accounting for 10% of the total weight of vinyl acetate monomer, stir and emulsify for 30 minutes, then add ammonium persulfate aqueous solution accounting for 30% of the total weight of ammonium persulfate, the ammonium persulfate aqueous solution is the total weight of deionized water It is prepared by dissolving 12% of deionized water, and the temperature is raised to 65°C to continue the reaction. After the blue light appears, the temperature is continued to rise to 80°C, and the nuclear seed emulsion is prepared after 30 minutes of reaction;

Step 2, the nuclear seed emulsion that step 1 is made maintains reaction temperature to be 80 ℃, the mixture of remaining 90% vinyl acetate monomer and butyl acrylate monomer is added dropwise in the above-mentioned nuclear seed emulsion, and the rate of addition is 0.3mLmin, during this dropwise addition process, add the remaining 70% ammonium persulfate in equal amounts in batches, and the interval between adding in batches is 30min; Add the maleic anhydride monomer dropwise to the reaction system. The maleic anhydride monomer is prepared by dissolving 6% of the total weight of the deionized water. The dropping rate is 0.7mL/min. After the maleic anhydride monomer is added dropwise Immediately start adding the styrene shell monomer dropwise at a rate of 0.2mL/min. After the dropwise addition of the styrene shell monomer is complete, raise the temperature to 85°C, keep the temperature for 10 minutes and cool the emulsion down to 60°C, then start adding NMA dropwise Functional monomer, make NMA content be 1.0% of vinyl acetate monomer and styrene monomer gross weight, the rate of addition of NMA functional monomer is 0.1mL/min, be warming up to 80 ℃ after NMA functional monomer is added dropwise, After 30 min of heat preservation, the reaction system was naturally cooled to room temperature, and filtered to obtain a modified polyvinyl acetate-based reverse core-shell structure emulsion (CSN1) with an NMA content of 1.0%.

Example 3

An NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion, mainly made of vinyl acetate, styrene and functional monomer NMA, the composite latex particles in the emulsion have a strawberry-shaped core-shell structure, with poly Vinyl acetate is the core, small polystyrene particles are the shell, and functional monomer NMA is added on the surface of the composite latex particles.

A kind of preparation method step of NMA modified polyvinyl acetate base reverse core-shell structure emulsion is as follows:

The total amount of vinyl acetate monomer and styrene monomer by reaction is based on the basis, and each raw material is prepared according to the following weight ratio:

Step 1. Add NaHCO3 and composite emulsifier to a certain quality of deionized water, wherein the composite emulsifier is composed of emulsifier PCA507 and emulsifier PCA078, the weight ratio of PCA507 and PCA078 is 1:2, heat up to 60°C, and stir for 30 minutes Add vinyl acetate monomer accounting for 15% of the total weight of vinyl acetate monomer, stir and emulsify for 30 minutes, then add ammonium persulfate aqueous solution accounting for 40% of the total weight of ammonium persulfate, the ammonium persulfate aqueous solution is the total weight of deionized water It is prepared by dissolving 13% of deionized water, and the temperature is raised to 65°C to continue the reaction. After the blue light appears, the temperature is continued to rise to 80°C, and the nuclear seed emulsion is prepared after 30 minutes of reaction;

Step 2, the nucleus seed emulsion that step 1 is made maintains reaction temperature to be 80 ℃, the mixture of remaining 85% vinyl acetate monomer and butyl acrylate monomer is added dropwise in the above-mentioned nucleus seed emulsion, and the rate of addition is 0.4mL/min, during this dropping process, add the remaining 60% ammonium persulfate in equal amounts in batches, and the interval between adding in batches is 30min; The acid anhydride monomer is added dropwise in the reaction system. The maleic anhydride monomer is prepared by dissolving 7% of the total weight of deionized water in deionized water. The dropping rate is 0.75mL/min. Immediately after the addition of the styrene shell monomer, start dropping the styrene shell monomer at a rate of 0.3mL/min. After the addition of the styrene shell monomer is completed, raise the temperature to 85°C, keep the temperature for 10 minutes, and then cool the emulsion down to 60°C. Add NMA functional monomer, make NMA content be 2.0% of vinyl acetate monomer and styrene monomer total amount, the dropping rate of NMA functional monomer is 0.15mL/min, be warming up to 80 after NMA functional monomer is added dropwise ℃, after 30 min of heat preservation, the reaction system was naturally cooled to room temperature, and filtered to obtain a modified polyvinyl acetate-based reverse core-shell structure emulsion (CSN2) with an NMA content of 2.0%.

Example 4

An NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion, mainly made of vinyl acetate, styrene and functional monomer NMA, the composite latex particles in the emulsion have a strawberry-shaped core-shell structure, with poly Vinyl acetate is the core, small polystyrene particles are the shell, and functional monomer NMA is added on the surface of the composite latex particles.

A kind of preparation method step of NMA modified polyvinyl acetate base reverse core-shell structure emulsion is as follows:

The total amount of vinyl acetate monomer and styrene monomer by reaction is based on the basis, and each raw material is prepared according to the following weight ratio:

Step 1. Add NaHCO3 and composite emulsifier to a certain quality of deionized water, wherein the composite emulsifier is composed of emulsifier PCA507 and emulsifier PCA078, the weight ratio of PCA507 and PCA078 is 2:1, heat up to 60°C, and stir for 30 minutes Add vinyl acetate monomer accounting for 20% of the total weight of vinyl acetate monomer, stir and emulsify for 30 minutes, then add ammonium persulfate aqueous solution accounting for 50% of the total weight of ammonium persulfate, the ammonium persulfate aqueous solution is the total weight of deionized water It is prepared by dissolving 14% of deionized water, and the temperature is raised to 65°C to continue the reaction. After the blue light appears, the temperature is continued to rise to 80°C, and the nuclear seed emulsion is prepared after 30 minutes of reaction;

Step 2, the nuclear seed emulsion that step 1 is made maintains reaction temperature to be 80 ℃, the mixture of remaining 80% vinyl acetate monomer and butyl acrylate monomer is added dropwise in the above-mentioned nuclear seed emulsion, and the rate of addition is 0.5mL/min, during this dropwise addition process, add the remaining 50% ammonium persulfate in equal amounts in batches, and the interval between additions in batches is 30min; The acid anhydride monomer is added dropwise in the reaction system, and the maleic anhydride monomer is prepared by dissolving in deionized water accounting for 8% of the total weight of deionized water, and the dropping rate is 0.8mL/min. Immediately after the addition of the styrene shell monomer, drop the styrene shell monomer at a rate of 0.4mL/min. After the addition of the styrene shell monomer is complete, raise the temperature to 85°C, keep the temperature for 10 minutes, and cool the emulsion down to 60°C. Add NMA functional monomer, make NMA content be 3.0% of vinyl acetate monomer and styrene monomer total amount, the dropping speed of NMA functional monomer is 0.2mL/min, be warming up to 80 after NMA functional monomer is added dropwise ℃, after 30 min of heat preservation, the reaction system was naturally cooled to room temperature, and filtered to obtain a modified polyvinyl acetate-based reverse core-shell structure emulsion (CSN3) with an NMA content of 3.0%.

Comparative example 1

A polyvinyl acetate-based reverse core-shell structure emulsion, mainly made of vinyl acetate and styrene, the composite latex particles of the emulsion have a strawberry-shaped core-shell structure, with polyvinyl acetate as the core, polystyrene The small particles are shells.

A kind of preparation method step of polyvinyl acetate-based reverse core-shell structure emulsion is as follows:

The total amount of vinyl acetate monomer and styrene monomer by reaction is based on the basis, and each raw material is prepared according to the following weight ratio:

Step 1. Add NaHCO3 and composite emulsifier to a certain quality of deionized water, wherein the composite emulsifier is composed of emulsifier PCA507 and emulsifier PCA078, the weight ratio of PCA507 and PCA078 is 1:1, heat up to 60°C, and stir for 30 minutes Add vinyl acetate monomer accounting for 10% of the total weight of vinyl acetate monomer, stir and emulsify for 30 minutes, then add ammonium persulfate aqueous solution accounting for 30% of the total weight of ammonium persulfate, the ammonium persulfate aqueous solution is the total weight of deionized water It is prepared by dissolving 12% of deionized water, and the temperature is raised to 65°C to continue the reaction. After the blue light appears, the temperature is continued to rise to 80°C, and the nuclear seed emulsion is prepared after 30 minutes of reaction;

Step 2, the nuclear seed emulsion that step 1 is made maintains reaction temperature to be 80 ℃, the mixture of remaining 90% vinyl acetate monomer and butyl acrylate monomer is added dropwise in the above-mentioned nuclear seed emulsion, and the rate of addition is 0.3mL/min, during this dropwise addition process, add the remaining 70% ammonium persulfate in equal amounts in batches, and the interval between batch additions is 30min; An acid anhydride monomer is added dropwise into the reaction system. The maleic anhydride monomer is prepared by dissolving 6% of the total weight of deionized water in deionized water. The dropping rate is 0.7mL/min. Immediately after the completion of the dropwise addition of the styrene shell monomer, the dropping rate was 0.2mL/min. After the dropwise addition of the styrene shell monomer was completed, the temperature was raised to 85°C, and after 10 minutes of heat preservation, the reaction system was naturally cooled to room temperature. Polyvinyl acetate-based reverse core-shell structure emulsion (CS) modified by NMA.

Morphological characterization of NMA-modified polyvinyl acetate-based reverse core-shell emulsion:

One, adopt the transmission electron microscope (TEM) to analyze the morphology of the modified polyvinyl acetate base reverse core-shell structure emulsion sample of 1.0% to the NMA content that embodiment 2 makes, carry out fumigation and dyeing to the emulsion sample by heavy metal, Further verify the composition of the core layer and the shell layer of the composite latex particle. Polystyrene is easily stained by heavy metals, so it appears dark under the transmission electron microscope, and polyvinyl acetate, which is not easily stained by heavy metals, appears light. It can be seen from Figure 1 that the core layer is light-colored, while the shell layer is dark-colored, and the dark-colored part is discontinuous and distributed on the surface of the core layer in the form of dots, which shows that the core is polyvinyl acetate, and the outer part is made of polyvinyl acetate. The small particles are polystyrene, thus proving that the composite latex particles prepared by the present invention take polyvinyl acetate as the core and polystyrene as the reverse core-shell structure of the shell. It can be seen from Figure 1 that the particle size distribution of the composite latex particles is between 150 and 300 nm, and there is adhesion between the composite latex particles, which increases the particle size of the composite latex particles.

Two, the morphology of the modified polyvinyl acetate-based reverse core-shell structure emulsion sample with 1.0% NMA content prepared in Example 2 is analyzed by scanning electron microscope (SEM), as shown in Figure 2, it is diluted 10000 times Scanning electron micrograph of the composite latex particle after. It can be seen from Figure 2 that the composite latex particles in the emulsion have a strawberry-shaped structure, with polyvinyl acetate as the core, and its surface is covered by hemispherical polystyrene particles with a diameter of 50-70 nm.

Three, Fig. 3 is the particle size distribution figure of composite latex particle in the modified polyvinyl acetate base reverse core-shell structure emulsion of the different NMA content that embodiment 2-4 makes, abscissa represents particle size, and ordinate represents Light intensity; As can be seen from Figure 3, when the NMA content was 1.0%, the average particle diameter of the composite latex particles was about 157nm, and the polydispersity coefficient of the emulsion was 0.078, showing a narrow distribution; When the content of NMA is further increased to 3.0%, the particle size of latex particles increases sharply, the average particle size is 307.6nm, the polydispersity coefficient becomes 0.111, and the particle size distribution becomes wider.

Combined with the TEM morphology characterization of the composite latex particles in the emulsion sample in Figure 1, it can be shown that adding a small amount of NMA to the emulsion system can cause polymerization in the shell of the composite latex particles, increasing the particle size of the composite latex particles. When the NMA content is too high, it will cause the adhesion and agglomeration between the composite latex particles, so that the particle size of the composite latex particles will increase sharply, and the larger particle size of the emulsion will have a greater impact on the stability of the emulsion and the compactness of the latex film. Influence, directly affect the glue quality of glued products. Therefore, the NMA content of the present invention is 1.0-3.5% when preparing the modified polyvinyl acetate-based reverse core-shell structure emulsion.

Four, adopt Fourier transform infrared spectrum to analyze the chemical structure of the NMA modified polyvinyl acetate base reverse core-shell structure emulsion sample that embodiment 2 makes, and Fig. 4 is the NMA modified polyvinyl acetate that embodiment 2 makes Infrared spectrogram of base reversed core-shell structure emulsion sample; NMA unique structural primary amide double absorption peaks appear at 3542cm ^-1 and 3456cm ^-1 ; C=O stretching vibration characteristic absorption peak on vinyl acetate appears at 1739cm ^-1 ; 1244cm Obvious absorption peaks of CO stretching vibration appear on vinyl acetate and butyl acrylate at ^-1 . Out-of-plane bending vibration peaks belonging to the adjacent five hydrogens in styrene appear at 758 cm ⁻¹ and 694 cm ⁻¹ . The sharp peak at 836cm ^-1 is the out-of-plane bending vibration absorption peak of the -CH-CH- structure formed by the opening of the double bond of the maleic anhydride monomer. Through the comparison of the above infrared spectra, it can be clearly demonstrated that the composite occurred between vinyl acetate, butyl acrylate, maleic anhydride monomer, styrene and NMA.

The performance analysis of the modified polyvinyl acetate-based reverse core-shell structure emulsion of different NMA contents prepared in Examples 2-4 and the non-NMA-modified polyvinyl acetate-based reverse core-shell structure emulsion of Comparative Example 1:

One, Fig. 5 is the shear wet strength contrast figure of the polyvinyl acetate-based reverse core-shell structure emulsion of the different NMA content that embodiment 2-4 and comparative example 1 make; As can be seen from Fig. 5, comparative example 1 does not have The wet shear strength of the blank control emulsion modified by NMA is 0.90MPa, and the wet shear strength of the polyvinyl acetate-based reverse core-shell structure emulsion with 1.0% NMA content is 1.05MPa, when the NMA content is increased to 2.0% The wet shear strength rose to 1.7MPa; when the NMA content continued to increase to 3.0%, the wet shear strength rose to 2.6MPa, and the wet shear strength of the emulsion after introducing NMA in Example 4 increased by 188.89% compared with Comparative Example 1. The self-crosslinked network structure of dehydration and formaldehyde removal between NMA itself improves the water resistance of the emulsion; at the same time, the hydroxymethyl structure in NMA can form hydrogen bonds with -COOH, -OH in wood to improve the shear wet strength of the emulsion .

Two, Fig. 6 is the compression shear strength comparison figure of the modified polyvinyl acetate base reverse core-shell structure emulsion of the different NMA content that embodiment 2-4 makes under different boiling water treatment conditions; After the specimen was boiled in boiling water for 30 minutes, when the NMA content was 0, the compressive shear strength was 0.04MPa; when the NMA content was 1.0%, the compressive shear strength was 0.07MPa; when the NMA content increased to 2.0%, the compressive shear strength to 0.043MPa; continue to increase the NMA content to 3.0%, the compressive shear strength increased to 0.13MPa. After the transfer specimens were boiled in boiling water for 180 minutes, as the NMA content increased, the compressive shear strength maintained the same law as that in the boiling water treatment for 30 minutes, showing a trend of first decreasing and then increasing. It can be shown that the bonded specimens still maintain a certain bonding strength after boiling water treatment. Tg represents the temperature at which the molecular chain segment thaws and starts to move. Temperatures above Tg make the polymer transform into a highly elastic state, and the chain segment can move relatively freely. The Tg of polyvinyl acetate is between 30 and 40°C, and it will creep under high temperature conditions. Due to the synergistic effect of the monomer structure and the core-shell structure and other conditions under the condition of boiling water for a short time, the glue layer is not completely destroyed. Therefore, the specimens bonded by NMA-modified polyvinyl acetate-based emulsion adhesive still retain a certain bonding strength after boiling water treatment, and when the NMA content is 3.0%, its compressive shear strength is relatively high , which proves that the modified polyvinyl acetate-based reverse core-shell structure emulsion of the present invention can still maintain good compressive shear strength after being treated with boiling water.

Claims (10)

1. a kind of reversed core-shell emulsion of NMA modified polyvinyl acetates base, it is characterised in that the NMA is modified poly-vinegar acid second The reversed core-shell emulsion of enester base is mainly made of vinylacetate, styrene and function monomer NMA, answering in the lotion Emulsion particle is closed in strawberry type nucleocapsid, using polyvinyl acetate as core, polystyrene little particle is shell, in the composite emulsion Grain surface is added with function monomer NMA.

A kind of 2. preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base, it is characterised in that the method Step is as follows：

Step 1: pH buffer and compound emulsifying agent are added in the deionized water of certain mass, 60 DEG C are warming up to, stirring is certain Added in after time and account for the Vinyl Acetate Monomer of Vinyl Acetate Monomer total weight 10~20%, stirring and emulsifying after a certain period of time, The initiator solution for accounting for initiator total weight 30~50% is added in, being warming up to 65 DEG C, the reaction was continued, continues after blue light to appear 80 DEG C are warming up to, semi-conducting materia lotion is made in reaction after a certain period of time；

Step 2: it is 80 DEG C that semi-conducting materia lotion made from step 1 is maintained reaction temperature, remaining vinyl acetate is added dropwise dropwise In the mixture of ester monomer and Butyl Acrylate Monomer to above-mentioned semi-conducting materia lotion, during this dropwise addition, equivalent is added surplus in batches Remaining initiator；After nuclear monomer mixture is added dropwise, grafted monomers are added dropwise in reaction system, monomer dropping to be grafted After start that styrene shell monomer is added dropwise at once, after styrene shell monomer is added dropwise, be warming up to 85 DEG C, one timing of heat preservation Between after lotion is cooled to 60 DEG C, start that a certain proportion of NMA function monomers are added dropwise at this time, after NMA function monomers are added dropwise 80 DEG C are warming up to, reaction system cooled to room temperature, filtering are obtained into NMA modified polyvinyl acetates after held for some time The reversed core-shell emulsion of ester group.

3. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 2, It is characterized in that based on the basis of the Vinyl Acetate Monomer of reaction and styrene monomer total amount, the weight proportion of each raw material used is such as Under：

4. a kind of preparation side of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to Claims 2 or 3 Method, it is characterised in that the pH buffer is NaHCO₃；The compound emulsifying agent is by emulsifier PCA507 and emulsifier PCA078 The weight ratio of composition, wherein PCA507 and PCA078 are (1~2):(1~2)；The initiator be ammonium persulfate, initiator water Solution is to be formulated ammonium persulfate with 10~15% deionized water dissolving for accounting for ionized water total weight；The grafting is single Body is maleic anhydride, and maleic anhydride monomer is that maleic anhydride is water-soluble with 5~10% deionization for accounting for ionized water total weight Solution is formulated.

5. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 4, It is characterized in that adding in pH buffer and compound emulsifying agent in deionized water described in step 1 and is warming up to the mixing time after 60 DEG C For 30min；The time of stirring and emulsifying is 30min after the addition Vinyl Acetate Monomer；It is described the subsequent temperature of continuing rising of blue light occur The time reacted to 80 DEG C is 30min.

6. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 5, The rate of addition for being characterized in that the mixture of remaining Vinyl Acetate Monomer and Butyl Acrylate Monomer described in step 2 is 0.3 ~0.5mL/min.

7. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 6, It is characterized in that initiator described in step 2 adds institute's interlude as 30min in batches.

8. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 7, The rate of addition for being characterized in that grafted monomers described in step 2 is 0.7~0.8mL/min.

9. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 8, The rate of addition for being characterized in that styrene shell monomer described in step 2 is 0.1~0.4mL/min；The guarantor being warming up to after 85 DEG C The warm time is 10min.

10. a kind of preparation method of the reversed core-shell emulsion of NMA modified polyvinyl acetates base according to claim 9, It is characterized in that the rate of addition of NMA function monomers described in step 2 be 0.1~0.2mL/min, it is described be warming up to 80 DEG C after Soaking time is 30min.