RU2315062C1 - Method for preparing acrylic copolymer aqueous dispersion for pressure-sensitive glues - Google Patents

Abstract

FIELD: chemistry of polymers.

SUBSTANCE: invention relates to emulsion method for co-polymerization of acrylic monomers. Invention proposes a method involving preliminary emulsification of mixture of butyl acrylate with (meth)acrylic and/or vinyl monomer in water in the following mass ratio co-monomer : water = 1:(0.2-0.3) in the presence of 3.4-4.0 wt.-% of sulfooxyethylated alkylphenol ammonium salt wherein (C₈-C₁₀)-alkyl has the alkylation degree 18-26 wt.-%, the following emulsion co-polymerization at temperature 78-82°C for 3-10 h at continuous dosing of preliminary prepared co-monomers emulsion and 0.3-0.6 wt.-% of ammonium or potassium persulfate in the total ratio to the reaction mass co-monomer : water = 1:(0.4-0.5) followed by additional polymerization of the reaction mixture in addition of 0.1 wt.-% of ammonium or potassium persulfate after keeping the reaction mixture for 0.5 and 1.5 h and its final temperature keeping for 2 h. Invention provides increasing concentration of acrylic copolymer aqueous dispersion at low content of coagulum and improving its adhesion properties. Invention provides the development of a method for preparing highly concentrated aqueous dispersion with the content of acrylic copolymer 60 wt.-%, not less, for glues showing sensitivity to pressure.

EFFECT: improved preparing method, improved and valuable properties of dispersion.

2 cl, 1 tbl, 13 ex

Description

The invention relates to the chemistry of polymers, in particular to an emulsion method for the polymerization of acrylic monomers, which allows to obtain highly concentrated aqueous dispersions for pressure sensitive adhesives used in the manufacture of self-adhesive materials.

The concept of self-adhesive materials includes various kinds of polymer films, textile, foamed polymeric materials, paper products, on one or two sides of which an adhesive layer is protected, protected by an adhesive coating. They are used as finishing coatings, labels and markings, heat-, noise-, vibration-proofing materials, packing tape, medical plasters, etc.

The use of such materials is based on the preliminary removal of the protective release material, if any, and gluing to the surface due to light short-term pressing or rolling, resulting in a strong bond between the material and the surface. Such conditions of “instant bonding” are provided by a special group of adhesives called adhesives with constant stickiness or pressure sensitive adhesives. They do not provide structural strength, however, they glue almost all materials, including those having a low-energy surface - polyethylene, polypropylene, fluoropolymers.

Significant advantages of adhesives based on aqueous dispersions are determined by the absence of toxic, combustible and expensive organic solvents. However, the use of adhesives with a water content of about 50% increases energy costs during their processing, reduces the productivity of equipment, which does not always compensate for their lower cost. Reducing these costs becomes possible with the production of highly concentrated aqueous dispersions. In this case, the cost of transportation and storage of adhesives is also reduced.

The inventors were faced with the task of obtaining a highly concentrated aqueous dispersion of an acrylic copolymer (copolymer content of at least 60 wt.%) For a pressure sensitive adhesive with a low coagulum content and improved adhesive properties.

A known method of producing an acrylic copolymer for medical adhesive films (USSR author's certificate No. 1171470, C08F 220/18, 1985), comprising radical emulsion copolymerization of butyl acrylate with acrylic acid and processing the reaction mixture with aqueous ammonia. The method includes dosing into the reactor monomers, an aqueous solution of sulfated hydroxyethylated nonylphenol, ammonium persulfate, then heating to 65-70 ° С and, when 4-10% conversion of monomers is achieved, adding aqueous ammonia in an amount of 0.5-1.0 equivalent in relation to acrylic acid. At the end of the dosing of the monomers, the polymerization is continued for 4 hours with continuous stirring and purging with nitrogen. The finished dispersion has a dry matter content of 59-60 wt.%, A viscosity of 4.0-8.7 Pa · s. The content of coagulum in the description is missing. Reproduction of this copyright certificate shows that the dispersion has a coagulum content of 5 to 8 wt.%. In addition, the adhesive based on the dispersion obtained in this way does not provide sufficient adhesion properties.

The closest in technical essence to the present invention is a method for producing aqueous dispersions of (co) polymers according to the patent of the Russian Federation No. 2076109, C08F 2/24, 1997 - prototype. The method for producing aqueous dispersions of (meth) acrylic or (meth) acryl vinyl polymers according to the prototype includes radical emulsion polymerization of pre-emulsified (meth) acrylic monomers or mixtures thereof with vinyl monomers. At the stage of preliminary emulsification, an emulsion is prepared at a mass ratio of monomer: water equal to 1: (0.1-0.7), an ionic compound of the formula RO (CH ₂ CH ₂ O) _n -XO ₃ Me (1) is used as an emulsifier, where X-S, P, Me = Na, K, NH ₄ , when R is alkyl n = 1-13, when R is alkyl phenyl, dialkyl phenyl n = 6-30 or a mixture thereof with a nonionic compound of the general formula: RO (CH ₂ CH ₂ O) _n -H (2), where R is alkylphenyl, dialkylphenyl n = 6-100, containing at least 0.4% by weight of the monomers of the compounds of formula (1) with a total emulsifier content of at least 0.5% by weight monomers. The prepared emulsion of monomers is metered into the reactor for 1.5-2.0 hours and at the same time, the entire amount of the polymerization initiator is dosed. As the polymerization initiator, potassium or ammonium persulfate is used. The polymerization temperature of 75-80 ° C. After the dosage of the monomers is completed, the reaction mass is maintained for 30 minutes at a temperature of 80 ± 2 ° C and cooled. As acrylic monomers, methyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylic acid are used, and methacrylic monomers are methyl methacrylate, methacrylic acid. As vinyl monomers: styrene, vinyl acetate.

The main disadvantage of the prototype aqueous dispersion of (meth) acrylic copolymers is the low concentration of the copolymer. The concentration of the copolymer in the patent is not shown. It is obtained by calculation from the examples described in the description and is 50-55 wt.%. The description also does not provide data on the content of coagulum in the dispersion and its adhesive characteristics. The method of example 10 of the description of the prototype was reproduced, which is the closest in composition of the polymerizable mixture to the claimed one, and the necessary data were obtained for comparison. The content of coagulum upon receipt of the dispersion was 0.1 wt.%, And the strength when peeling glue on its basis in accordance with GOST 289666.2-91 - 0.51 kN / m.

The aim of the invention is to increase the concentration of an aqueous dispersion of an acrylic copolymer with a low content of coagulum and to improve its adhesive properties.

To achieve this goal, the following method is proposed for producing an aqueous dispersion of an acrylic copolymer.

An emulsion of comonomers in water is preliminarily prepared at a mass ratio of comonomer: water equal to 1: (0.2-0.3), in the presence of 3.4-4.0 wt.% Ammonium salt of sulfooxyethylated alkyl phenol, where C ₈ -C ₁₀ alkyl , with a degree of sulfation of 17-26 wt.%. Butyl acrylate, vinyl acetate, acrylic and methacrylic acids are used as comonomers.

The finished emulsion of monomers is metered into the reactor for 3-10 hours and, in parallel, 0.3-0.6 wt.% Of ammonium or potassium persulfate is supplied at a total weight ratio in the reaction mass of comonomer: water equal to 1: (0.4-0 ,5). The polymerization proceeds at a temperature of 78-82 ° C.

After completion of dosing of the emulsion and the polymerization initiator, the residual monomers are additionally polymerized by feeding 0.1 wt.% Potassium or ammonium persulfate after holding the reaction mass for 0.5 and 1.5 hours at a temperature of 78-82 ° C. Next, the reaction mass is kept at a temperature of 78-80 ° C for 2 hours and cooled.

The result is a dispersion of acrylic copolymer with a copolymer content of 69.5-70.2 wt.%.

The essence of the invention is illustrated by the following examples.

Example 1

In a reactor equipped with a reflux condenser, a stirrer and a funnel for dosing the components, 30 g of water are charged and the temperature is raised to 80 ± 2 ° C. Preliminarily, an emulsion of monomers with water and an emulsifier is prepared as follows: 114 g of water, 31 g of 79% ammonium salt of sulfooxyethylated nonylphenol with a degree of sulfation of 26 wt.% (3.4 wt.%) And the whole monomer mixture - 465.5 g are placed in a glass (64.0%) butyl acrylate (TU 2435-002-52460063-2003) and 24.5 g (3.4 wt.%) Methacrylic acid (TU 6-02-59-89). After stirring for 30 minutes, a white viscous mass formed. Next, a initiator solution is prepared - 2.94 g of ammonium persulfate (GOST 20478) (0.4 wt.%) Is dissolved in 60 g of water. 50 g of initiator solution was used for dosing.

The total water content in the reactor is 28.8 wt.%.

Upon reaching a temperature of 80 ± 2 ° C, dosing of the emulsion and initiator solution within three hours begins in the reactor. At the end of the dosage, the emulsions are allowed to stand for 0.5 hours, after which the initiator solution is added - 5 g, after one and a half hours the remaining initiator solution is added - another 5 g. The reaction mixture is kept at 78-80 ° С for two hours and cooled to 20-30 ° C, filtered through a nylon sieve and poured into a dry clean container.

Next, determine the properties of the resulting dispersion.

The concentration of the copolymer is determined through the mass fraction of non-volatiles according to GOST 17537. To do this, take a portion of the dispersion weighing 0.5-1.0 g.

Drying of the sample is carried out for 3 hours at a temperature of (110 ± 2) ° С in an oven to a constant weight.

The coagulum content obtained during the polymerization is determined in dry form from the total amount of coagulum remaining on the filter, the walls of the reactor and the stirrer.

The granularity of the dispersion is determined visually. To do this, the dispersion is applied in a thin layer (~ 20-30 μm dry) on a glass plate or polymer film and in the light the granularity is determined on a scale from 0 (very good, no microcoagulum) to 10 (very poor, numerous microcoagulums).

The neutralization of the resulting dispersion is carried out by introducing ammonia water to a pH of 6.5-7.5. A uniform adhesive composition is obtained, which is used to evaluate the adhesive properties.

Adhesive properties are characterized by an indicator of strength when peeling PET-stainless. steel, which is determined according to GOST 28966.2-91. The thickness of the adhesive layer was 60 μm.

The degree of sulfation of hydroxyethylated alkyl phenol (OP-10) (mass fraction of the ammonium salt of the sulfated substance) was determined by the titrimetric method in acetone with the thymol blue indicator according to the method developed by the Federal State Unitary Research Institute of Polymers.

The test results of the obtained dispersion are shown in the table.

Examples No. 2-4

The polymerization is carried out analogously to example No. 1, only use the ammonium salt of sulfooxyethylated nonylphenol with varying degrees of sulfation: example No. 2 - 17 wt.%; example No. 3 - 19 wt.%; example No. 4 - 21 wt.%. The properties of the obtained dispersions are shown in the table.

Example No. 5

The polymerization is carried out analogously to example No. 1, with the difference that 420.4 g (57.4 wt.%) Butyl acrylate, 70.0 g (9.6 wt.%) Vinyl acetate, 9.8 g (1, 3 wt.%) Of methacrylic acid, and as an emulsifier, 32.9 g of 82% of the ammonium salt of sulfooxyethylated nonylphenol with a degree of sulfation of 19 wt.% (3.7 wt.%). The amount of initiator was 4.9 g of ammonium persulfate (0.7 wt.%). The properties of the resulting dispersion are shown in the table.

Example No. 6

The polymerization is carried out analogously to example No. 1, with the difference that 445.0 g (60.7 wt.%) Butyl acrylate, 11.5 g (1.6 wt.%) Acrylic acid and 11.5 g (1 , 6 wt.%) Methacrylic acid, 35.3 g of 79% ammonium salt of sulfooxyethylated nonylphenol with a degree of sulfation of 17 wt.% (3.8 wt.%). The properties of the resulting dispersion are shown in the table.

Example No. 7 (prototype)

168 g (40.7 wt.%) Of butyl acrylate, 28 g (6.8 wt.%) Of vinyl acetate, 4 g (1.0 wt.%) Of methacrylic acid, 80 g of water, 10 g (2.6 wt. %) ammonium salt of sulfooxyethylated nonylphenol. Since the degree of sulfation was not indicated, we used an emulsifier with a degree of sulfation of 17 wt.%. Stir until a stable, uniform emulsion is formed. The resulting emulsion is metered into a reactor containing 100 g of water for 1.5 hours at 75 ° C. At the same time, ammonium persulfate is supplied in an amount of 2.0 g (0.5 wt.%) Dissolved in 20 g of water. At the end of the dosage, the mixture was incubated for 30 minutes at 80 ± 2 ° C and chilled. The properties of the resulting dispersion are shown in the table.

The total water content in the reactor is 48.4 wt.%.

Examples No. 8-13 (for comparison)

The production conditions and properties of the dispersions are shown in the table.

Table Production conditions and properties of dispersions used as pressure sensitive adhesives No pp The composition of the reaction mixture, wt.% Dispersion Conditions Properties of dispersion and adhesive based on it Monomer mixture Water Emulsifier - ammonium salt of sulfo-hydroxyethylated alkyl phenol (degree of sulfation) Initiator Monomer / Water Phase Ratio Emulsion dosing time, hour The temperature exposure time, hour Mass fraction of non-volatiles, wt.% The content of coagulum, wt.% Grain, points Peeling strength, kN / m one 2 3 four 5 6 7 8 9 10 eleven 12 one. BA 64.0 IAC 3.4 28.8 3.4 (26) ammonium persulfate 0.4 1: 0.43 3 0.5, 1.5 and 2.0 69.5 0.1 0-2 0.70 2. BA 63.7 MAK 3.4 28.8 3.7 (17) ammonium persulfate 0.4 1: 0.43 3 0.5, 1.5 and 2.0 69.8 0 four 0.74 3. BA 63.7 MAK 3.4 28.8 3.7 (19) ammonium persulfate 0.4 1: 0.43 3 0.5, 1.5 and 2.0 70,2 0 3 0.70 four. BA 63.7 MAK 3.4 28.8 3.7 (21) potassium persulfate 0.4 1: 0.43 10 0.5, 1.5 and 2.0 70.0 0 0-2 0.67 5. BA 57.4 VAC 9.6 MAK 1.3 27.3 3.7 (19) ammonium persulfate 0.7 1: 0.4 3 0.5, 1.5 and 2.0 69.5 0.4 3 0.67 6. BA 60.7 MAK 1.6 AK 1.6 31.7 4.0 (17) ammonium persulfate 0.4 1: 0.5 5 0.5, 1.5 and 2.0 69.6 1.3 four 0.60 For comparison Prototype persulfate 7. BA 40.7 48,4 2.6 ammonium 1: 0.43 1,5 0.5 50,0 0.1 6 0.51 VAC 6.8 (17) 0.5 MAK 1.0 8. BA 63.7 28.8 3,7 persulfate 1: 0.43 3 0.5, 1.5 63.5 28.6 8 0.43 IAC 3.4 (fifteen) ammonium and 2.0 0.4 9. BA 63.7 28.8 3.7 persulfate 1: 0.43 3 0.5, 1.5 70.3 2,3 four 0.52 MAK 3.4 (28) ammonium and 2.0 0.4 10. BA 64.4 29.1 2.7 persulfate 1: 0.43 3 0.5, 1.5 100% coagulum MAK 3.4 (17) ammonium and 2.0 0.4 eleven. BA 63.1 28.5 4.7 persulfate 1: 0.43 3 0.5, 1.5 71.0 1,1 four 0.55 MAK 3.3 (17) ammonium and 2.0 0.4 12. BA 69.8 22.0 4.1 persulfate 1: 0.3 3 0.5, 1.5 73.1 12.1 5 0.54 MAK 3.7 (17) ammonium and 2.0 0.4 13. BA 63.7 39.8 3,1 persulfate 1: 0.7 3 0.5 and 2.0 41.2 0 0 0.34 MAK 3.4 (17) ammonium 0.4

From the data in the table it follows that the proposed method for producing an aqueous dispersion of an acrylic copolymer allows one to obtain a dispersion having a copolymer concentration of 69.5-70.2 wt.%, With a coagulum content of 0-1.3 wt.% And strength when peeling glue on its basis of 0.60-0.74 kN / m (see examples No. 1-6). These figures are significantly higher than the prototype, which has a copolymer concentration of 50-55 wt.% And a peeling strength of ~ 0.51 kN / m. The content of coagulum in the prototype is ~ 0.1 wt.% (See example No. 7).

Changing the conditions of the proposed method for producing dispersion leads to a deterioration in the quality of the dispersion.

The data in the table show that only the use of the ammonium salt of sulfooxyethylated alkyl phenol, where C ₈ -C ₁₀ alkyl, with a degree of sulfation of 17-26 wt.% Allows to obtain a dispersion with improved properties. The use of sulfooxyethylated alkyl phenol with a degree of sulfation outside the claimed, for example 15 wt.% And 28 wt.%, Results in a dispersion with a high coagulum content (28.6 wt.%) And low adhesive properties (0.43-0.52 kN / m) (see examples No. 8-9).

The use of the ammonium salt of sulfooxyethylated alkyl phenol with a degree of sulfation of 17-26 wt.% In an amount outside the claimed leads to an increase in the coagulum content and to a decrease in adhesive properties (see examples No. 10-11).

The polymerization of monomers in the present method is carried out with continuous dosing of the emulsion of monomers and initiator for 3-10 hours. Reducing the dosing time, for example, to 2 hours leads to an increase in the coagulum content to ~ 2-3% and a decrease in adhesive properties to 0.4-0.5 kN / m. Increasing the dosing time also reduces the adhesion properties of the dispersion to ~ 0.5 kN / m.

According to the claimed method, preliminary emulsification is carried out with a mass ratio of comonomer: water, equal to 1: (0.2-0.3). Going beyond the specified ratios affects the quality of the aqueous dispersion.

The implementation of the polymerization with a mass ratio in the reaction mass of comonomer: water, equal to 1: (0.4-0.5), is also an essential sign of the proposed method. Going beyond the limits of the claimed ratios, for example 1: 0.3 or 1: 0.7, increases the content of coagulum in the dispersion and reduces its adhesive properties (see examples No. 12-13).

The increase in exposure time at the stage of prepolymerization compared with the prototype is necessary for the complete exhaustion of residual monomers in obtaining a highly concentrated copolymer.

Thus, only a combination of all the above essential features of the proposed method allows to obtain an aqueous dispersion of an acrylic copolymer for pressure sensitive adhesives, with a high polymer concentration, with a low coagulum content and high adhesive properties. The exclusion of any of the above signs of the proposed method significantly degrades the quality of the aqueous dispersion and limits its use as a pressure sensitive adhesive.

Claims (2)

1. A method of obtaining an aqueous dispersion of an acrylic copolymer for pressure-sensitive adhesives by pre-emulsifying a mixture of butyl acrylate with a (meth) acrylic and / or vinyl monomer with water and an emulsifier — an ammonium salt of sulfoxylated alkyl phenol, followed by its emulsion copolymerization at a temperature of 78-82 ° C in the presence of a radical initiator and temperature exposure of the dispersion, characterized in that the preliminary emulsification of the comonomers in water is carried out in a mass ratio of comonomer : water, equal to 1: (0.2-0.3), in the presence of 3.4-4.0 wt.% the ammonium salt of sulfooxyethylated alkyl phenol, where alkyl is C ₈ -C ₁₀ , with a degree of sulfation of 17-26 wt.% and emulsion polymerization is carried out for 3-10 hours with continuous dosing of the previously obtained emulsion of comonomers and 0.3-0.6 wt.% ammonium or potassium persulfate with a total mass ratio in the reaction mass of comonomer: water equal to 1: (0, 4-0.5), followed by depolymerization of the reaction mixture with the introduction of 0.1 wt.% Ammonium or potassium persulfate after 0.5 and 1.5 hours of exposure of the reaction This mixture and its final temperature exposure for 2 hours 2. The method according to claim 1, characterized in that the depolymerization of the reaction mixture and the final exposure of the resulting dispersion is carried out at a temperature of 78-82 ° C.