Vinyl-based copolymer, waterproofing composition containing the same, and use thereof

Abstract

This invention discloses a vinyl copolymer, a waterproof composition containing the vinyl copolymer, and its applications. The vinyl copolymer is obtained by free radical polymerization of monomers; based on a total monomer weight of 100 parts, it includes 40-60 parts of monomer a, 30-50 parts of monomer b, 5-10 parts of monomer c, and 0.1-5 parts of monomer d; monomer a is a vinyl monomer with a homopolymer glass transition temperature (Tg) below 0°C; monomer b is a vinyl monomer with a homopolymer glass transition temperature greater than or equal to 0°C; monomer c is a cationic vinyl monomer; and monomer d is a crosslinked vinyl monomer. The presence of cationic monomers in the vinyl copolymer makes it cationic; simultaneously, the copolymer contains crosslinking units, which react with hydroxyl groups on the fibers during the drying process of paper products to form a network structure, improving the adhesion of the waterproof membrane and imparting better mechanical properties to the paper products.

Description

Technical Field

[0001] This invention relates to the field of polymers, and more specifically to a vinyl copolymer, a waterproof composition containing the vinyl copolymer, and its applications. Background Technology

[0002] Pulp molding products (paper-plastic composites) are currently the most ideal alternative to disposable foamed plastics. They are characterized by a wide range of raw material sources, a virtually pollution-free production process, easy biodegradability, and recycling from waste paper. Their application scope is gradually expanding, from their initial use in fast food containers to industrial packaging, medical devices, and other industries, with a very optimistic application prospect. The main component of paper products is cellulose fiber, whose surface is rich in hydroxyl groups. Since hydroxyl groups are polar groups, they easily adsorb polar water molecules and form hydrogen bonds with the adsorbed water molecules. This is the inherent reason why cellulose adsorbs water. At the same time, there are many pores between the fibers that make up paper. Liquids can diffuse through these pores via capillary action and gradually permeate the entire paper. Therefore, paper products have a certain degree of water absorption and are easily affected by moisture during storage. Pulp molding products used in fast food containers and packaging require a certain degree of waterproofing, especially in situations where they are easily exposed to water, even hot water, such as using fast food containers to hold hot soup or packaging cartons exposed to short-term rain during transportation. These applications place high demands on the waterproof performance of paper products.

[0003] Currently, the industry mainly uses two methods. One method is to coat paper products with plastic film, varnish, or wax to protect them. However, plastic film is expensive, non-biodegradable, and easily causes environmental pollution. It also compromises the breathability of paper products, making it unsuitable for packaging requiring breathability (such as fruits and vegetables). Varnishing and waxing are essentially micro-coatings, which are more environmentally friendly, economical, and aesthetically pleasing than traditional coatings, but they also compromise breathability and their waterproof performance is insufficient to replace plastic film. Furthermore, wax layers have temperature limitations. The other method involves adding waterproofing or water-resistant agents to the fibers during paper and paperboard manufacturing, either through internal pulping or surface coating. This alters the surface tension (surface energy) of the paper, reducing the wetting effect of liquids. Alternatively, hydrophobic fillers can be added to block the capillary channels formed by interwoven fibers, achieving waterproofing or water resistance. This method is convenient, inexpensive, and does not affect the biodegradability of paper products or waste paper recycling, and is gradually becoming the mainstream approach.

[0004] Water-repellent agents for paper mainly include paraffin wax, rosin gum, stearic acid chromium chloride complex, organosilicon, chitosan, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA). These are generally used as sizing agents, applied internally or surface-sizing to impart certain water and ink resistance properties to paper. However, to achieve specific liquid resistance for particular fluids or applications, the type and performance of the sizing agent must be adjusted accordingly. Pulp molded products, whether paper lunch boxes or paper products in the packaging industry, face contact with large amounts of water and even immersion, requiring high water resistance. General water-repellent agents often fail to meet these requirements or necessitate increased dosages, inevitably increasing production costs and emission reduction burdens for enterprises. Therefore, developing water-repellent agents for pulp molded products with excellent waterproof performance, low dosage, and ease of use is of great significance.

[0005] CN102720093A discloses an oxidized polyethylene wax emulsion water-resistant agent and its preparation method. It is formulated into an emulsion by oxidized polyethylene wax and silica nanoparticles in a composite emulsifier. When applied to cardboard boxes and high-grade paper products, it provides waterproofing, moisture resistance, and flame retardancy. CN103711033A discloses a waterproof water-based varnish and its preparation method. It mainly consists of a room-temperature cross-linked polypropylene emulsion, a styrene-acrylate resin liquid, and a waterproof wax emulsion, suitable for varnishing the surface of printed paper products requiring waterproofing. CN104594118A discloses a waterproof coating for paper products, composed of a polymeric silicone oil emulsion and a nano-wax emulsion. By coating or printing onto the surface of paper products, a silicone oil-nano composite layer is formed, producing a waterproof effect and exhibiting transparency. These published documents all involve coating the surface of paper products with a waterproof substance. The inner fibers of the paper products do not have waterproofing properties. Furthermore, since paraffin wax has a melting point of around 50°C, paper products cannot be used at high temperatures. CN103866615A discloses a paper waterproofing agent and its preparation method. The waterproofing agent is composed of polyacrylonitrile fiber, polyethylene, polyethylene wax, N-isopropylacrylamide, potassium lauryl ether phosphate, vinyl acetate, and sodium bicarbonate. It can be added to the papermaking stage in the existing paper production process to give the paper waterproof properties. The waterproofing agent introduces recalcitrant polyacrylonitrile fiber and polystyrene, and is compounded in an emulsifier. Phase separation and instability may occur during use. CN104452453A discloses a water-based waterproof and oil-repellent agent for special paper and its preparation method. The method involves grafting hydrogen-containing silicone oil, vinyl polyether, perfluoroacrylate, glycidyl methacrylate, and long-chain acrylates under the catalysis of chloroplatinic acid. Then, a polyisocyanate compound is added to partially block the hydroxyl groups on the polymer chain, thus obtaining the waterproof and oil-repellent agent. This agent can be compounded with starch aqueous solution for sizing paper surfaces, improving the paper's waterproofness, oil resistance, mechanical strength, and softness. The key component of this waterproof and oil-repellent agent is the perfluoroacrylate, a monomer that is expensive. Using this monomer would increase costs for enterprises if the goal is simply to impart waterproofing to paper products. Summary of the Invention

[0006] To address the shortcomings and deficiencies of the prior art, the present invention aims to provide a vinyl copolymer containing cationic monomers, making the copolymer cationic; simultaneously, the copolymer contains crosslinking units that react with hydroxyl groups on the fibers during the paper drying process to form a network structure, thereby improving the adhesion of the waterproof membrane and imparting better mechanical properties to the paper product.

[0007] Another object of the present invention is to provide a method for preparing the vinyl copolymer.

[0008] Another object of the present invention is to provide applications of the vinyl copolymer.

[0009] Another object of the present invention is to provide a waterproof composition containing the aforementioned vinyl copolymer.

[0010] Another object of the present invention is to provide a method of using the waterproof composition.

[0011] Another object of the present invention is to provide a pulp molded article containing the vinyl copolymer.

[0012] The above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0013] A vinyl copolymer, said vinyl copolymer being obtained by free radical polymerization of monomers; calculated based on 100 parts by total monomer weight, comprising 40-60 parts of monomer a, 30-50 parts of monomer b, 5-10 parts of monomer c, and 0.1-5 parts of monomer d;

[0014] The monomer a is a vinyl monomer with a glass transition temperature (Tg) below 0°C; the monomer b is a vinyl monomer with a glass transition temperature (Tg) greater than or equal to 0°C; the monomer c is a cationic vinyl monomer; and the monomer d is a crosslinked vinyl monomer.

[0015] The methyl ethyl ketone (MEK) insoluble component of the vinyl copolymer is 90% or more by mass;

[0016] The weight-average molecular weight (Mw) of the butanone-soluble fraction of the vinyl copolymer is 10,000 to 100,000, and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), expressed as Mw / Mn, is 2.0 to 4.0.

[0017] The vinyl copolymer of this invention contains soft monomers (monomer a), hard monomers (monomer b), and functional monomers (monomer c and monomer d), which endow the vinyl copolymer with better film-forming properties, bonding with paper substrates, and solubility in aqueous media. Monomers a and b are hydrophobic monomers, which impart waterproof properties to the copolymer. Monomers c and d are functional monomers, which improve the copolymer's solubility, stability, and bonding with fibers in aqueous media. Copolymerizing monomers a, b, c, and d forms a polymer molecule with a polar hydrophilic group at one end and a non-polar hydrophobic group at the other end. During use, the hydrophilic groups adsorb onto the surface of the paper fiber through electrostatic attraction, while the hydrophobic groups arrange themselves on the outer side of the fiber, forming a hydrophobic barrier that reduces the surface tension of the fiber, thus giving it a certain degree of waterproof performance.

[0018] The homopolymer of monomer a has a low glass transition temperature, and its long-chain side groups can mitigate the interaction between polymer chains, thus achieving a plasticizing effect. The strength of the polymer of the soft monomer is not high, and it generally needs to be used in combination with the hard monomer.

[0019] Preferably, monomer a is one or more of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, isooctyl acrylate, or lauryl methacrylate.

[0020] Monomer b has a high glass transition temperature and can be copolymerized with soft monomers to produce copolymers with good cohesive strength and high service temperature.

[0021] Preferably, monomer b is one or more of styrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, or acrylonitrile.

[0022] Monomer C is a cationic vinyl monomer that contains cations or can generate cations under suitable conditions (cationic precursors). It can impart good dispersibility of the copolymer in aqueous media and good adhesion between the waterproof product and paper fibers. However, monomer C has a certain impact on the waterproof performance of the copolymer. Excessive monomer C will increase the hydrophilicity of the copolymer, thereby reducing its waterproof performance.

[0023] The cationic vinyl monomer can be selected based on the polymerization method of the vinyl copolymer. For example, when solution polymerization is used, a cationic precursor is usually selected, and after polymerization, the cationic precursor is converted into a cationic precursor. When emulsion polymerization is used, a monomer containing a cationic precursor is usually selected directly.

[0024] Preferably, monomer c is a vinyl-containing ammonium salt or a precursor of a vinyl-containing ammonium salt. Vinyl-containing ammonium salts or precursors of vinyl-containing ammonium salts are common cationic vinyl monomers.

[0025] Specifically, the vinyl-containing ammonium salt is selected from (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxypropyltrimethylammonium chloride, dimethyldiallylammonium chloride, and (meth)acryloyloxyethyldimethylbenzylammonium chloride.

[0026] The vinyl-containing ammonium salt precursor is selected from one or more of dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, diethylaminoethyl methacrylate, diethylaminopropyl methacrylate, or diisopropylaminoethyl methacrylate.

[0027] Monomer d is a monomer that can produce crosslinks. By introducing crosslinking units into the polymer molecule, the copolymer molecular chains are crosslinked to form a three-dimensional network structure, which better combines with paper-based fibers and improves the mechanical strength of the product.

[0028] In addition to vinyl groups, the cross-linked vinyl monomer also has at least one functional group that can undergo a cross-linking reaction, such as a hydroxyl group or a carbon-carbon double bond.

[0029] Preferably, the monomer a4 is one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, N-hydroxymethylacrylamide, divinylbenzene, ethylene glycol di(meth)acrylate, allyl methacrylate, trimethylolpropane tri(meth)acrylate, or triallyl cyanurate.

[0030] Preferably, the weight-average molecular weight Mw of the butanone-soluble portion of the vinyl copolymer is 20,000 to 100,000, and the ratio of weight-average molecular weight Mw to number-average molecular weight Mn, expressed as Mw / Mn, is 2.0 to 4.0.

[0031] The method for preparing the vinyl copolymer of the present invention preferably employs a free radical polymerization method, specifically conventional emulsion polymerization and solution polymerization.

[0032] In emulsion polymerization or solution polymerization, the reaction takes place in the presence of a polymerization medium, and an initiator is added to allow the polymerization to proceed. If emulsion polymerization is used, an emulsifier must also be added to the reaction medium.

[0033] The emulsifier may be one or more of the following: fatty alcohol polyoxyethylene ether, alkyl polyoxyethylene ether, alkylphenyl polyoxyethylene ether, alkyl polyoxyethylene polyoxyethylene ether, alkyl trimethyl ammonium chloride, dialkyl dimethyl ammonium chloride, alkyl dimethylamine hydrochloride, and dialkyl methylamine hydrochloride.

[0034] In the free radical polymerization process of the vinyl copolymer described in this invention, the amount of emulsifier used is 0.5 to 2 parts by mass relative to 100 parts by mass of the total amount of monomers a, b, c and d added.

[0035] The initiator can be at least one of inorganic peroxides, organic peroxides, and azo initiators. Examples of inorganic peroxides include hydrogen peroxide, potassium persulfate, and ammonium persulfate. Examples of organic peroxides include benzoyl peroxide, dicumyl peroxide, isocumyl hydroperoxide, tert-butyl hydroperoxide, and tert-butyl peroxypentanoate. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobisisoheptanenitrile, 4,4'-azobis(4-cyanopentanoic acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride, and 2,2'-azobis[N-(2-carboxymethyl)-2-methylpropanediamine] hydrate. In the free radical polymerization process of polymer A according to the present invention, the amount of initiator is 0.5 to 1 part by mass relative to the total amount of monomers a, b, c and d added, which is 100 parts by mass.

[0036] In the process of forming vinyl copolymers, a chain transfer agent is preferably added to control the molecular weight of the resulting vinyl copolymer. Examples of chain transfer agents include alkyl thiols, such as dodecyl thiols, butyl thiols, and octyl thiols, and at least one of these can be used. In the free radical polymerization process of the vinyl copolymers described in this invention, the amount of the chain transfer agent used is 0.3 to 0.5 parts by mass relative to 100 parts by mass of the total amount of monomers a, b, c, and d added.

[0037] In the step of forming the vinyl copolymer, the polymerization medium is selected according to the polymerization method and the type of initiator. The polymerization medium can be an aqueous medium or an oil-based medium. As an aqueous medium, deionized water can be used. As an oil-based medium, it can be one or a mixture of ketones, alcohols, ethers, esters, or solvents thereof, preferably propylene glycol, propylene glycol methyl ether, propylene glycol ethyl ether, or a mixture thereof, which are miscible with water. In the free radical polymerization process of the vinyl copolymer of the present invention, the amount of the polymerization medium used is 65 to 500 parts by mass relative to 100 parts by mass of the total amount of monomers a, b, c, and d added.

[0038] The application of the vinyl copolymer in the preparation of waterproof compositions.

[0039] A waterproof composition comprising the following components: the vinyl copolymer and an aqueous medium.

[0040] The pH value of the waterproof composition is 6 to 7.

[0041] Preferably, the content of the vinyl copolymer in the waterproof composition is 20-22% of the total weight of the waterproof composition.

[0042] The method of using the waterproof composition is to apply the waterproof composition to the surface of a pulp molded product or to add it into the pulp.

[0043] In this invention, the coating can be carried out according to the processes commonly used in the art, including various printing methods, such as spin coating, casting, bar coating, roller coating, wire bar coating, dip coating, slot coating, microgravure coating, gravure coating, capillary coating, spraying, nozzle coating, screen printing, gravure printing, offset printing, and flatbed printing.

[0044] A pulp molded article having the vinyl copolymer contained on its surface or inside.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention provides a vinyl copolymer. One end of the vinyl copolymer contains a polar hydrophilic group, imparting good dispersibility to the waterproof composition in an aqueous medium, while the other end contains a non-polar hydrophobic group, imparting low surface tension to the paper-based product and thus enabling it to be waterproof. The cationic monomer introduced into the vinyl copolymer carries a positive charge, allowing it to be adsorbed onto negatively charged fibers via electrostatic attraction during use. It then combines with the hydroxyl groups on the cellulose molecules, forming a hydrophobic film on the fiber surface, achieving excellent retention. The crosslinking groups introduced into the vinyl copolymer react with the hydroxyl groups on the fibers during the paper drying process, forming a network structure that improves the adhesion of the waterproof film and simultaneously imparts better mechanical properties to the paper product. The vinyl copolymer can be mixed with an aqueous medium to prepare a waterproof composition, which can be used for surface coating or intramolecular addition to molded pulp products to form molded pulp products with good waterproof properties. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only for explaining the present invention and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials. Regarding "parts" and "%" in this specification, unless otherwise specified, they respectively represent "parts by mass" and "% by mass". The embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

[0048] The physical properties of this invention are measured using the following methods.

[0049] (1) Weight-average molecular weight / Number-average molecular weight

[0050] Vinyl copolymers were collected and refluxed with methyl ethyl ketone (MEK) in a Soxhlet extractor for 8 hours. The MEK-insoluble components were then separated by filtration, and the MEK-insoluble components were calculated. Simultaneously, the MEK-soluble components were collected and dried under vacuum at 80°C for 24 hours. The weight-average molecular weight / number-average molecular weight of the obtained vinyl copolymers was determined using gel permeation chromatography (GPC). The eluent for GPC was tetrahydrofuran (THF), and the temperature was 23±2°C.

[0051] (2) Stability test

[0052] To observe the dispersion stability of vinyl copolymers in water: Adjust the solid content of the waterproof composition to 20% by weight in an aqueous dispersion solution, centrifuge at 3000 rpm / min for 5 min, and then observe the amount of precipitation. Evaluate its stability performance according to the following criteria.

[0053] Good: Almost no sediment;

[0054] Generally: A small amount of sediment may be present;

[0055] Poor: There is a lot of sediment.

[0056] (3) Waterproofing test

[0057] The bagasse board is soaked in water until it is fully swollen. Then, it is loosened using a fiber standard dissociator and refined using a pulper. The pulp is then beaten and polished. The waterproof composition of the vinyl copolymer prepared in this invention is added to the polished pulp, stirred evenly, and then molded, demolded, dried, and shaped to make pulp molded products (paper lunch boxes) for testing.

[0058] Pour 100℃ hot water into the dried test sample, let it stand for 30 minutes, and observe whether there is any penetration.

[0059] No penetration: Good;

[0060] No penetration, but some discoloration: average;

[0061] Possible penetration: poor.

[0062] Example 1

[0063] In a four-necked flask equipped with an electric stirrer, a constant-pressure dropping funnel, a thermometer, and a condenser, 250 parts of propylene glycol methyl ether were added as a solvent. The stirrer was turned on, and 40 parts of monomer a isooctyl acrylate, 50 parts of monomer b styrene, 8 parts of monomer c dimethylaminoethyl methacrylate, and 2 parts of monomer d N-hydroxymethylacrylamide were weighed to form the monomer component. The monomer component was mixed with 1 part of 2,2'-azobisisobutyronitrile and 0.5 parts of dodecyl mercaptan and added to the four-necked flask under a nitrogen atmosphere. The reaction was carried out at 65°C for 10 hours to complete the polymerization. After cooling to room temperature, a vinyl copolymer solution was obtained. The pH was adjusted to 6-7 with acetic acid, and finally diluted with deionized water to form a water-dispersible waterproof composition with a solid concentration of 20%.

[0064] Example 2

[0065] In a four-necked flask equipped with an electric stirrer, a constant-pressure dropping funnel, a thermometer, and a condenser, 250 parts of propylene glycol methyl ether were added as a solvent. The stirrer was turned on, and 50 parts of monomer a (butyl acrylate), 40 parts of monomer b (styrene), 8 parts of monomer c (dimethylaminoethyl methacrylate), and 2 parts of monomer d (N-hydroxymethylacrylamide) were weighed to form the monomer component. The monomer component was mixed with 1 part of 2,2'-azobisisobutyronitrile and 0.5 parts of dodecyl mercaptan and added to the four-necked flask under a nitrogen atmosphere. The reaction was carried out at 65°C for 10 hours to complete the polymerization. After cooling to room temperature, a vinyl copolymer solution was obtained. The pH was adjusted to 6-7 with acetic acid, and finally diluted with deionized water to form a water-dispersible waterproof composition with a solid concentration of 20%.

[0066] Example 3

[0067] In a four-necked flask equipped with an electric stirrer, a constant-pressure dropping funnel, a thermometer, and a condenser, 250 parts of propylene glycol methyl ether were added as a solvent. The stirrer was turned on, and 60 parts of monomer a (ethyl acrylate), 30 parts of monomer b (methyl methacrylate), 8 parts of monomer c (dimethylaminoethyl methacrylate), and 2 parts of monomer d (N-hydroxymethylacrylamide) were weighed to form the monomer component. The monomer component was mixed with 1 part of 2,2'-azobisisobutyronitrile and 0.5 parts of dodecyl mercaptan and added to the four-necked flask under a nitrogen atmosphere. The reaction was carried out at 65°C for 10 hours to complete the polymerization. After cooling to room temperature, a vinyl copolymer solution was obtained. The pH was adjusted to 6-7 with acetic acid, and finally diluted with deionized water to form a water-dispersible waterproof composition with a solid concentration of 20%.

[0068] Example 4

[0069] Weigh out 50 parts of monomer a butyl acrylate, 40 parts of monomer b styrene, 8 parts of monomer c methacryloyloxyethyl trimethylammonium chloride, and 2 parts of monomer d hydroxyethyl methacrylate to form a monomer component. Mix the monomer component with 0.4 parts dodecyl polyoxyethylene ether, 0.5 parts dodecyl mercaptan, and 100 parts deionized water evenly, and pre-emulsify at high speed using a homogenizer to prepare a monomer emulsion.

[0070] Weigh 0.8 parts of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride and dissolve it in 20 parts of deionized water to prepare an initiator solution.

[0071] In a four-necked flask equipped with an electric stirrer, a constant-pressure dropping funnel, a thermometer, and a condenser, 280 parts of deionized water were added as solvent. The stirrer was turned on, and 0.8 parts of dodecyl polyoxyethylene ether and 0.4 parts of hexadecyltrimethylammonium chloride were weighed and added to the four-necked flask to dissolve. Under a nitrogen atmosphere, 1 / 5 of the monomer emulsion and 1 / 5 of the initiator solution were added to the four-necked flask, and the reaction was carried out at 70°C. After the reaction liquid in the flask showed blue light, the remaining monomer emulsion and initiator solution were added dropwise simultaneously. The addition was completed in 3 hours, and the mixture was kept at this temperature for 2 hours. After cooling to room temperature, a vinyl copolymer solution was obtained.

[0072] Example 5

[0073] In Example 4, monomer b (styrene) was replaced with 41.5 parts, and monomer d was replaced with 0.5 parts of ethylene glycol dimethacrylate. The rest was the same as in Example 4.

[0074] Example 6

[0075] In Example 4, monomer b (styrene) was replaced with 41.9 parts, and monomer d was replaced with 0.1 parts of trimethylolpropane trimethacrylate. The rest was the same as in Example 4.

[0076] Comparative Example 1

[0077] In Example 4, monomer a (butyl acrylate) was replaced with 53 parts, monomer b (styrene) with 45 parts, and monomer c with 0 parts; all other parts were the same as in Example 4.

[0078] Comparative Example 2

[0079] In Example 4, monomer b was replaced with 42 parts and monomer d was replaced with 0 parts, while everything else remained the same as in Example 4.

[0080] Comparative Example 3

[0081] Replace the dodecyl mercaptan in Example 4 with 0 parts, and everything else is the same as in Example 4.

[0082] Preparation and evaluation of paper-plastic products

[0083] The molecular weight of the vinyl copolymers prepared in the examples and the stability of the water-dispersible waterproof compositions were determined. The waterproof compositions were then added to paper-plastic products via pulp addition at a rate of 3% (relative to dry pulp), and their waterproof performance was measured. The test results are shown in Table 1.

[0084] Table 1

[0085]

[0086] As shown in Table 1, in Examples 1 to 6, waterproof compositions were prepared by using different monomer ratios based on the differences in the glass transition temperature of the monomer homopolymers. When applied to paper and plastic products, they all achieved good waterproof effects while ensuring stability.

[0087] Comparative Example 1 shows that the waterproof performance is very poor when no cationic vinyl monomer is added to the system. This is because no positive charge is introduced into the polymer, so it cannot combine with the hydroxyl groups on the fiber, making it impossible for the polymer to adhere to the paper-based products.

[0088] Comparative Example 2 shows that the waterproof performance is very poor when no cross-linked vinyl monomer is added to the system. This is because although the polymer may have been attached to the fiber, a dense film layer has not been formed on the fiber surface through cross-linking functional groups. When in contact with water, water will penetrate into the interior of the paper-based product.

[0089] Comparative Example 3 shows that when the molecular weight of the methyl ethyl ketone (MEK) soluble component in the system is too high, both stability and waterproof performance are poor. This is because a high polymer molecular weight leads to poor dispersion in aqueous solutions and the formation of a large amount of gel during polymerization, resulting in poor waterproof performance.

[0090] The above embodiments are preferred embodiments of the present invention. However, the present invention is not limited to these embodiments. Any changes, modifications, substitutions, combinations, or simplifications made to the above embodiments without departing from the spirit and principle of the present invention are considered equivalent substitution methods and are included within the protection scope of the present invention.

[0091] Industrial availability

[0092] The vinyl copolymers and waterproof compositions containing the vinyl copolymers involved in this invention can be widely used in the papermaking industry.

Claims

1. A vinyl copolymer, characterized in that, The vinyl copolymer is obtained by free radical polymerization of monomers; calculated based on a total monomer weight of 100 parts, it includes 40-60 parts of monomer a, 30-50 parts of monomer b, 5-10 parts of monomer c, and 0.1-5 parts of monomer d. The monomer a is a vinyl monomer with a homopolymer glass transition temperature (Tg) below 0°C; the monomer a is one or more of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, isooctyl acrylate, or lauryl methacrylate; the monomer b is a vinyl monomer with a homopolymer glass transition temperature greater than or equal to 0°C; the monomer b is one or more of styrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, or acrylonitrile; the monomer c is a cationic vinyl monomer; the monomer d is a crosslinked vinyl monomer. The methyl ethyl ketone (MEK) insoluble component of the vinyl copolymer is 90% or more by mass; The weight-average molecular weight (Mw) of the butanone-soluble fraction of the vinyl copolymer is 10,000 to 100,000, and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), expressed as Mw / Mn, is 2.0 to 4.

0.

2. The vinyl copolymer according to claim 1, characterized in that, The monomer c is a cationic monomer that is a vinyl-containing ammonium salt or a vinyl-containing ammonium salt precursor.

3. The vinyl copolymer according to claim 1, characterized in that, The monomer d is one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, N-hydroxymethylacrylamide, divinylbenzene, ethylene glycol di(meth)acrylate, allyl methacrylate, trimethylolpropane tri(meth)acrylate, or triallyl cyanurate.

4. A method for preparing the vinyl copolymer according to any one of claims 1 to 3, characterized in that, Includes the following steps: Monomers a, b, c, and d are mixed with an initiator and a chain transfer agent, and then heated in an inert atmosphere to obtain the vinyl copolymer.

5. A method for preparing the vinyl copolymer according to any one of claims 1 to 3, characterized in that, Includes the following steps: Monomer a, monomer b, monomer c, monomer d, emulsifier, chain transfer agent and water are mixed evenly and pre-emulsified to obtain monomer emulsion; Preparation of initiator solution; In an emulsifier and an inert atmosphere, a portion of the monomer emulsion and a portion of the initiator solution were added, and the mixture was heated until blue light appeared in the system. The remaining monomer emulsion and initiator solution were then added dropwise, and the mixture was kept at a constant temperature to obtain the vinyl copolymer.

6. A waterproof composition, characterized in that, It includes the following components: The vinyl copolymer and aqueous medium according to any one of claims 1 to 3.

7. The method of using the waterproof composition according to claim 6, characterized in that, The waterproof composition is used to coat the surface of molded pulp articles or to add it into the pulp.

8. A pulp molded product, characterized in that, Its surface or interior contains the vinyl copolymer as described in any one of claims 1 to 3.

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