Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/50—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by form
  • D21H21/52—Additives of definite length or shape
  • D21H21/54—Additives of definite length or shape being spherical, e.g. microcapsules, beads
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/02—Making microcapsules or microballoons

Definitions

• the present invention relates to a process for preparing latexes having polymer particles with a hollow structure. More specifically, the present invention relates to a process for preparing latexes with hollow particles having positive charge and high heat resistance.
• Cationic hollow particle latexes with high thermal stability of the hollow polymer are useful as opacifying agents, fillers, binders and extenders in coating and impregnating applications, particularly when positive charge and high thermal stability of the hollow polymer particles are required.
• the cationic hollow particle latexes are very useful for acid-catalyzed thermosetting coatings cured at high temperatures.
• the cationic hollow particle latexes can be used in pulp and paper industry as multifunctional additives (white pigments; fillers; density decreasing, retention aids etc.)
• the cationic hollow particle latexes are useful in the production of filled antistatic latex coatings on the basis of amine containing polymers.
• the Finnish patent application FI 991050 discloses a process for the preparation of cationic hollow particle latexes by recharging of anionic hollow particles with cationic surfactants selected from quartemary ammonium salts.
• the main drawback of this mode is connected with low heat stability of the hollow polymer prepared since the glass transition temperature is no higher than
• US patent 4,489,825 discloses a method for the preparation of latexes with cationic hollow polymeric particles consisting of the core comprising crosslinked copolymer of methyl methacrylate and amino-monomer and the shell comprising poly(iso-butyl methacrylate).
• an additional external shell comprising up to 50% wt. of a crosslinking monomer such as divinyl benzene can be obtained.
• a crosslinking monomer such as divinyl benzene
• the method has the following disadvantages: 1. In accordance with an example a large coagulate amount (higher than 50% wt.) is formed at the synthesis.
• Too high cationic surfactant concentrations (about 10% wt.) are used at the stage of latex particle core formation.
• the solids of the final latex is low (about 8% wt.).
• the present invention comprises a process for making cationic hollow particle latex useful for opacifying characterized in that an anionic hollow particle latex is recharged by addition into said latex of an acid colloid of melamine-formaldehyde resin, the weight ratio of said acid colloid of melamine-formaldehyde resin/anionic hollow particle latex based on dry weight of components being equal to from 0.1 to 0.7.
• the process for making a cationic hollow particle latex characterized in that said acid colloid of melamine-formaldehyde resin is prepared in aqueous medium at molar ratio melamine/formaldehyde/hydrochloric acid as
• the invention comprises a composition for coating and/or impregnating characterized in that said cationic hollow particle latex and water-soluble melamine-formaldehyde resin are mixed at weight ratio based on dry weight of components in the range from 0.05 to 0.70, preferably 0.30, curing being carried out at elevated temperatures up to 130-200°C.
• the cationic hollow particle latex is prepared by mixing of an anionic hollow particle latex and acid colloid of melamine-formaldehyde resin at ambient temperature, said acid colloid of melamine-formaldehyde resin being added fast into anionic hollow particle latex at intensive agitation. During this procedure anionic hollow particles are recharged and converted into cationic ones. The fast mixing of the components makes it possible to avoid the coagulation because the system passes through the isoelectric state quickly.
• the recharged hollow particle latexes have positive ⁇ -potential in the range from +5 mV to +70 mV, preferably from +20 to +40 mV. Solids of the cationic hollow particle latexes is from 15% wt. to 30% wt., preferably from 20 to 25% wt.
• the weight ratio of the said acid colloid of melamine-formaldehyde resin/anionic hollow particle latex based on dry weight of components is equal to from 0.1 to 0.7, preferably from 0.3 to 0.5. At low values of said weight ratio (below 0.3) the cationic hollow particle latex is too viscous. At high value of the weight ratio the shelf life of cationic hollow particle latexes is too low because the latex gelation or coagulation occurs.
• hollow particle latexes of Rohm & Haas Co. or hollow particle latexes prepared according to well-known procedures disclosed e.g. in US patent 4,427,836 or PCT patent application WO 98/39372 are used as anionic hollow particle latexes.
• a hollow polymer comprises styrene, methyl methacrylate and small amounts of other monomer units such as acrylonitrile, (me h)acrylic acid, crosslinking monomer etc.
• Negative charge of the hollow particles is provided with the application of usual anionic surfactants and persulfate initiators.
• the ⁇ -potential of anionic hollow particle latexes is in the range from -20 mV to -65 mV.
• Anionic hollow particle latexes have particles from 400 nm to 950 nm in size. Solids of the latexes are in the range from 30% wt. to 46% wt.
• Acid colloids of melamine-formaldehyde resins are prepared in aqueous medium at molar ratio melamine / formaldehyde / hydrochloric acid as 1 : (2-12) : (0.3-1.5), preferably as 1 : (4.0-7.0) : (0.4-0.7) at 70-97°C. The process temperature depends on the amount of hydrochloric acid (the larger this amount the lower the temperature).
• the procedure of the acid colloids of melamine-formaldehyde resins preparation is as follows. First water and melamine are charged into a reactor. The amount of water charged depends on formalin concentration and is selected so that the final product concentration should be in the range from 10 to 15% wt. The reaction mixture is heated to 70-97°C at agitation. Then concentrated hydrochloric acid (30-35% wt.) is added. When melamine is dissolved completely formalin is charged and the process is carried out for 50-60 min.
• a composition for coating and/or impregnating is prepared by mixing of cationic hollow particle latex and water soluble alkyl-etherified melamine-formaldehyde resin as a binder at weight ratio based on dry weight of components in the range from 0.05 to 0.30.
• the composition may or may not comprise a water-thinnable alkyd resin or aqueous dispersion of a soft polymer, e.g. vinyl acetate-dibutyl maleate copolymer, for plasticization.
• Curing of the composition is carried out at 150-200°C. Depending on the temperature the curing time varies from several minutes to several hours.
• the heat resistance of the hollow polymer is evaluated according to the following test.
• a coating on a glass plate is prepared on the basis of hollow particle latex and melamine binder.
• the coating is dried at ambient temperature for 24 hrs and opacity of the coating is measured.
• the coating is cured for 75 min when temperature is elevated gradually from ambient to 170°C and opacity is measured again.
• Simultaneously opacity of the coating prepared with usual hollow particle latex free of cationic colloid of melamine-formaldehyde resin treatment is measured.
• the hollow polymer is considered as heat resistant when opacity of the coating does not decrease or drops slightly after curing at elevated temperature. A significant decrease of opacity after curing is an evidence of destruction of hollow particles and consequently low heat resistance of a hollow polymer.
• Opacity is defined as a contrast ratio of the coatings determined by photometric method.
• First the reflection coefficient of a glass plate with coating placed on a black surface with reflection coefficient of less than 1% is determined.
• the glass plate with the coatings is placed on a white surface with the reflection coefficient 82% and the reflection coefficient is determined again.
• the contrast ratio is calculated as the ratio of reflection coefficients.
• the ⁇ -potential of the latexes is estimated by macroelectrophoresis technique at Barton installation using latexes with the concentration 7% and 0.025 N KC1 solution as a side liquid.
• the ⁇ -potential was calculated using the Helmholtz-Smolukhovsky equation
• the process is carried out in a glass 100 cm J reactor equipped with a stirrer. reflux condenser, inlet for inert gas and necks for charge of the components.
• Distilled water 57.5 g This step is carried out as a batch process. 57.5 g of distilled water is charged into the reactor and heated up to 80°C with stirring and inert gas flow. Then SDBS solution is charged. In 5 min PP solution and monomer mixture 1 are added. The process period (after the monomer mixture charge) is 105 min. The latex prepared is cooled, discharged and filtered. The following stages are carried out in the only glass 350 cm reactor equipped with stirrer, reflux condenser, inlet for inert gas and a device for feeding of the components as a number of successive steps.
• Stage B Highly carboxylated core polymer preparation.
• the seed latex and 48.86 g of water are charged into the reactor.
• the reactor content is heated in the inert gas flow up to 80°C.
• the solution of PP (0.027 g in 5.0 g of water) is added followed by monomer mixture 2 and aqueous mixture 2 feeding. Feeding of the both components is carried out with a constant rate for 180 min. Then the process is continued for 25 min.
• Latex prepared at stage B 1 11.79 g
• Stage C starts straight away after completing stage B.
• PP solution (0.28 g in 10.0 g of water) is added followed by monomer mixture 3 and aqueous mixture 3 feeding.
• the feeding of the both mixtures is carried out with a constant rate for 134 min.
• the process continues for 10 min followed by addition of 0.62 g of SDBS in 2.38 g of water.
• Stage D Neutralization and swelling of the core-shell particles.
• Ammonia aqueous solution (cone. 14% wt.) 6.94 g
• Ammonia solution is added into the latex dropwise within 4-5 min and the reaction mixture is heated up to 97-98°C within the next 10-15 min and maintained for 60 min. Then the latex is cooled and filtered. The final diluted latex is examined with an electron microscope. A single void can be observed inside each particle.
• the process is carried out in 200 cm glass reactor equipped with stirrer, reflux condenser and neck for charge of components.
• First water and melamine are charged into the reactor and the reaction mixture is heated to 70-97°C at agitation.
• concentrated hydrochloric acid (cone. 31.8 % wt.) is added.
• melamine is dissolved completely formalin (formaldehyde cone. 36.0% wt.) is charged and the process is carried out for 60 min. Conditions of the process are listed in Table 2.
• the process is carried out in 200 cm glass vessel equipped with stirrer at ambient temperature. Anionic hollow particle latex and water are placed into the vessel and then an acid colloid of melamine-formaldehyde resin is charged fast within 20-30 s with intensive agitation.
• a methyl-etherified melamine-formaldehyde resin only or in combination with aqueous dispersion of vinyl acetate-dibutyl maleate copolymer are used as a water-thinnable binder.
• a water soluble methyl-etherified melamine-formaldehyde resin is prepared according to the following procedure.
• Example 4B Preparation of a combined binder methylated melamine-formaldehyde resin - vinyl acetate-dibutyl maleinate copolymer
• Combined binder is prepared by addition of vinyl actetate - dibutyl maleate copolymer aqueous dispersion into methylated melamine-formaldehyde resin with stirring at ambient temperature.
• methylated melamine-formaldehyde resin prepared according to example 4 A is placed into 200 cm glass vessel. Then the resin is diluted with 49.35 g distilled water followed by addition of 21.61 g vinyl acetate-dibutyl maleate copolymer dispersion (solids 51.3% wt.) at stirring. Stirring continues for 10 min.
• Example 5 Composition preparation, casting and curing of the coatings
• compositions are prepared by incorporation of a cationic hollow particle latex into a binder produced according to examples 4A and 4B at agitation.
• the cationic hollow particle latex is introduced dropwise into the binder at stirring.
• Coatings are prepared by casting of the compositions prepared onto glass plates followed b drying at ambient temperature for 24 hrs and curing at gradual temperature increase from ambient temperature to 170°C for 75 min
• the contrast ratio for the coatings is measured before and after the curing.
• the composition recipes and opacity of the coatings prepared therefrom characterized by contrast ratio are listed in Table 4.
• Table 4 illustrates that opacity of the coatings after curing practically does not change This result can be considered as an evidence of high heat resistance of the hollow particles incorporated into the coating.
• Example 1 17 4 Example 2L 32 6 0 5 22 2 +33
• Example 4A 26 1 Example 3A 23 9 0 976 0965
• Example 4A 27 6 Example 3E 22 4 0 718 0725
• Example 4A 29 8 Example 3F 20 2 0 933 0930
• Example 4B 34 6 Example 3A 15 4 0 923 0928

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Paper (AREA)
• Paints Or Removers (AREA)

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Citations (8)

• 2000
  • 2000-02-18 FI FI20000367A patent/FI20000367A/fi unknown
• 2001
  • 2001-02-14 AU AU2001237460A patent/AU2001237460A1/en not_active Abandoned
  • 2001-02-14 WO PCT/FI2001/000135 patent/WO2001060510A1/en active Application Filing

Patent Citations (8)

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