Composite Resin Particles, Its Preparation and Resinous Composition for Coating Use Containing the Same

The present invention relates to composite resin particles and a dispersion of said particles in an organic solvent medium.

Heretofore proposed resins for coating compositions are divided, from the morphological point of view, into three classes, i.e. soluble type resins (including a water soluble resin), colloidal dispersion resins and granular resins. A soluble type resin is very useful for coating purpose because of its capabilities to act as a binder as well as a pigment dispersing agent and its excellent film-forming property. Therefore, such a resin has been practically and widely used as a resinous vehicle for an oil paint. However, with the increased demands for such social needs as economization of natural resources, energy-saving and conservation of good surroundings, the use of oil paints is decreasing and public attentions are mostly directed to the use of high quality aqueous paints, high solids coating compositions and powder paints, in place of the oil paints. Neverthless, a soluble type resin is hardly applicable to such paints because of its comparatively poor application characteristic and insufficient film performance. Colloidal dispersion resins had once been tried for use in aqueous paints, and however, the application characteristics and the stabilities of the paints were not yet up to the mark and such resins had failed to be the main current of the resinous vehicles of the coating compositions.

Granular resins are supplied in the forms of emulsions, microgels, non-aqueous dispersions and powder resins, and have been watched with keen interest in paint industries, because of their capabilities of resulting ideal aqueous paints, high solids paints and powder paints which may fulfill the requirements of economization of natural resources, energy-saving and conservation of good surroundings.

They are used singularly or in combination form with other soluble type resins and are believed to act as a binder, a rheology regulator or a polymer filler. Thus, a high quality film can be obtained therewith.

However, when the granular resin is used alone, it is unable to get a uniform or excellent film and the resulting film has a serious drawback of being deficient in film appearance. Even when the granular resin is combined with a soluble type resin, there is a case wherein the viscosity of the combined system is greatly increased as compared with that of the soluble type resin alone due to the considerable interaction between the surfaces of granules and soluble type resin. Therefore, a great care is often required in the actual use of such combined resins.

An object of the invention is, therefore, to provide novel composite resin particles which are free from the drawbacks of the abovementioned coating use resins.

Additional objects of the invention are to provide novel composite resin particles which are able to be used either singularly or in combination form with any other resins customarily used in paint industry, to give excellent coating compositions with good application characteristics and storage slability, and capable of giving a uniform film with an excellent appearance, and a dispersion composition comprising said resin particles and an organic solvent.

The present inventors have now found that the composite resin particles each of which comprises a crosslinked granular body portion and a number of linear polymer chains, a part of the respective chains penetrating into the inside of said granular body portion and the remaining part extending outwardly therefrom, are quite useful in paint industries because of having comparatively lower solution viscosities, capability of forming a uniform coating, and being excellent in compatibility with other resins, and on the basis of these findings, the inventors have succeeded in coming to the present invention.

Thus, according to the present invention, there are provided composite resin particles each of which comprises a granular body portion of a crosslinked polymer having a mean diameter of 0.01 to 10.mu., and a number of linear polymer chains, a part of the respective chains penetrating into said body portion and the remaining part extending outwardly therefrom, the process for the preparation of such particles and a resinous composition for coating use containing the same.

The novel composite resin particles of the present invention are characterized in that each particle comprises a granular body portion of a crosslinked polymer and a number of linear polymer chains and has a larger grain size as compared with that of the original particle of the crosslinked polymer, the grain size being at most 2.5 times the original size of said crosslinked polymer particle.

Also, the solution viscosity of the resinous composition is significantly lower as compared with that of the mere blend of the cross-linked polymer particles and the linear polymer concerned.

The granular body portion is composed of a crosslinked polymer and has a mean diameter of 0.01 to 10.mu., the polymer being of polycondensation type as polyester resin, epoxy resin and amino resin or of addition polymerization type as acrylic resin and vinyl resin. Such resin particles may be advantageously prepared by any of the known processes as, for example, an emulsion polymerization, a non-aqueous dispersion polymerization or a solution polymerization, and the product may be, according to the method of preparation, used as it is, or after separation and pulverization as desired.

The linear polymer chain is characterized by being composed of a linear polymer prepared by the addition polymerization of (a) polymerizable ethylenic compound(s). Examples of such polymerizable ethylenic compounds are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and their esters, styrene, vinyl toluene, acrylonitrile, vinyl acetate, acrylamide, N-methylol acrylamide and other similar monomers.

Employable acrylic or methacrylic esters may be represented by the formula: ##STR1## wherein R.sub.1 is H or CH.sub.3 and R.sub.2 is a saturated hydrocarbon having 1 to 15 carbon atoms, including methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate and the like. Other esters may include the members represented by the abovesaid formula wherein R.sub.2 is a saturated hydrocarbon bearing hydroxyl group. Examples of such members are hydroxy propyl acrylate, hydroxy propyl methacrylate, 2-hydroxy ethyl acrylate, and 2hydroxy ethyl methacrylate.

The present composite resin particles are, as already stated, characterized in that each particle has a specific structure such that a part of the respective linear chain penetrates into the inside of the crosslinked polymer particle and the remaining parts extend outwardly therefrom.

Such composite resin particles may be easily and advantageously prepared by the method wherein addition polymerizable ethylenic compound(s) is (are) polymerized by a solution polymerization in the presence of crosslinked polymer particles.

That is, any of the known solution polymerization techniques may be advantageously used as, for example, by adding into a reaction vessel a radical polymerization initiator (e.g. organic peroxide or organic azo compound), solvent(s), crosslinked polymer particles and polymerizable monomer(s) and heating the mixture to effect polymerization, or by placing, in a reaction vessel, organic solvents and adding, under heating, dropwise a polymerization initiator, crosslinked polymer particles and monomers, or by the combination of said techniques.

The present composite resin particles are, owing to the specific preparation method used, characterized by having the specific structure of the so-called semi-interpenetrating polymer network, wherein a part of the respective polymer chain penetrates into the inside of the crosslinked polymer particle and the remaining part extends outwardly therefrom. The said composite resin particles are strictly distingushed from the mere blend of crosslinked polymer particles and linear polymer, in which case a number of linear polymer chains are merely attached to the respective crosslinked polymer particle, in respect of, inter alia, viscosity behavior or the like.

Though the weight ratio of crosslinked polymer/linear polymer in the present composite resin particle may considerably vary with the intended use, the kind of polymer and the like, it is generally determined in a range of 100 parts by weight of the crosslinked polymer/5 to 1000 parts by weight of the linear polymer.

It is, of course, possible to increase or decrease the amount of the linear polymer than the abovesaid range. The present composite resin particles are, after being dispersed in an organic solvent, used in a paint industry. As the organic solvent, any of the members customarily used in coating compositions may satisfactorily be used, including aromatic hydrocarbons (e.g. toluene, xylene), aliphatic hydrocarbons, alcohols, ethers, esters, ketones and the like. The thus obtained dispersions may be used as they are or in combination with the other resinous vehicles, in either conventional or novel type coating compositions.

In the present invention, crosslinked polymer particles and linear polymer are closely bound together by the adoption of solution polymerization technique, thereby forming composite resin particles of the novel structure hereinbefore stated. The inventors have also succeeded in having a novel coating composition with said resin particles, which has excellent properties in regard to viscosity, film appearance, application characteristic, stability and film-forming property.

The invention shall be now more fully explained in the following examples. Unless otherwise being stated, all parts are by weight.

Into a glass reactor fitted with a thermometer, a reflux condenser, a nitrogen gas inlet tube and a stirrer, were placed 200 parts of deionized water, 3 parts of sodium lauryl sulfate and 1 part of ammonium persulfate and the mixture was, while introducing a nitrogen gas, heated to 80.degree. to 85.degree. C. To this, a monomer mixture of 40 parts of methyl methacrylate, 20 parts of styrene, 20 parts of isopropyl acrylate and 20 parts of ethyleneglycol dimethacrylate was, while continuing stirring, dropwise added over 1 hour and after completion of said addition, the mixture was further reacted for 1 hour under stirring.

From the thus obtained emulsion, water was removed off in vacuo to obtain 100 parts of crosslinked polymer particles (1) having a mean diameter of 110 nm and a crosslinking density of 1.01.times.10.sup.-3 mol/g. The grain diameter was determined by a quasi-elastic light-scattering photometer with a laser beam. The crosslinking density was determined by the following equation. ##EQU1##

Preparation of dispersion-stabilizing resin:

Into a glass reactor fitted with a thermometer, a reflux condenser, a nitrogen gas inlet tube, a stirrer and a decanter, were placed 191 parts of hydroxyl ethyl taurine, 140 parts of ethyleneglycol, 170 parts of triethyleneglycol, 331 parts of adipic acid, 168 parts of phthalic anhydride and 40 parts of xylene, and the mixture was heated. The thus formed water was azeotropically removed off with xylene. The content's temperature was raised to 190.degree. C in about 2 hours from the commencement of reflux, and stirring and dehydration were continued until the acid value (equivalent to carboxylic acid) reached to less than 10. At this stage, the reaction was stopped to obtain a dispersion-stabilizing polyester resin having an acid value of 79, hydroxyl number of 79 and Mnof 708.

Preparation particles (2):

Into a glass reactor fitted with a thermometer, a reflux condenser, a nitrogen gas inlet tube and a stirrer, were placed 150 parts of deionized water, 15 parts of the abovementioned dispersion-stabilizing polyester resin and 2 parts of dimethyl aminoethanol, and the mixture was heated to 80.degree. C. under stirring to obtain a solution.

To this, was dropwise added a solution of monomer mixture comprising 20 parts of n-butyl acrylate, 40 parts of styrene and 40 parts of ethyleneglycol dimethacrylate, and 1 part of azo-bis-cyanovaleric acid in 20 parts of deionized water and 0.7 part of dimethyl ethanol amine, in 1 hour. Thereafter, the mixture was stirred for additional 1 hour. From the thus obtained emulsion, water was removed off in vacuo to obtain 110 parts of crosslinked polymer particles (2) having a mean diameter of 40 nm and a cross linking density of 2.02.times.10.sup.-3 mol/g.

Into the similar reaction vessel as used in Manufacturing Example 1, were placed 170 parts of deionized water, 5 parts of the dispersion-stabilizing polyester resin prepared in Manufacturing Example 2 and 2 parts of dimethyl aminoethanol, and the mixture was, under stirring, maintained at 80.degree. to 85.degree. C. to obtain a solution.

Next, was added dropwise a solution of the monomer mixture comprising 30 parts of methyl methacrylate, 20 parts of n-butyl acrylate, 40 parts of styrene and 10 parts of eythylene glycol dimethacrylate, and 1 part of azo-bis-cyanovaleric acid in deionized water and 0.7 part of dimethyl aminoethanol, in 1 hour and the mixture was further stirred for additional 1 hour.

From the thus obained emulsion, water was azeotropically removed off with xylene, and the solvent was substituted with xylene to obtain 330 parts of a xylene dispersion (solid 30%) of crosslinked polymer particles (3) having a mean diameter of 150 nm and a crosslinking density of 5.05.times.10.sup.--4 mol/g.

Into the similar reaction vessel as used in Manufacturing Example 1, were placed 98 parts of maleic anhydride and 106 parts of diethylene glycol and the mixture was, while stirring and introducing a nitrogen gas thereto, heated at 190.degree. to 200.degree. C. for 6 hours to obtain diethylene glycol maleate having an acid value of 30.

On the other hand, 1 part of benzoyl peroxide was dissolved in 50 parts of 1,4-butanediol divinyl ether, and to this solution, was uniformly added the abovementioned diethyleneglycol maleate and the mixture was heated at 70.degree. C. for 1 hour to obtain a hard gelation product (unsaturated polyester resin). After completion of the reaction, the thus obtained gelation product was pulverized in a ball mill, and shieved to obtain 150 parts of crosslinked polymer particles having a mean diameter of 6.mu. and a crosslinking density of 1.39.times.10.sup.-3 mol/g.

Into the similar reaction vessel as used in Manufacturing Example 1, were placed 300 parts of the xylene dispersion of crosslinked polymer particles (3) obtained in Manufacturing Example 3, 3 parts of styrene, 5 parts of n-butyl acrylate, 2 parts of 2-hydroxyethyl methacrylate and 0.15 part of isobutyronitrile and the mixture was heated at 110.degree. C. for 5 hours to obtain a dispersion of composite resin particles. The thus obtained particles had a mean grain diameter of 152 nm, which was bigger than the grain diameter of the original, crosslinked polymer particles (3). Upon subjecting to a spray drying, composite resin part-cleis were obtained.

Into the similar reaction vessel as used in Example 1, were placed 10 parts of the crosslinked polymer particles (1) obtained in Manufacturing Example 1, 27 parts of styrene, 18 parts of n-butyl acrylate, 27 parts of 2-ethyl hexyl acrylate, 13.5 parts of 2-hydroxyethyl methacrylate, 4.5 parts of acrylic acid and 100 parts of xylene. Next, 6 parts of azobis-isobutyronitrile were added, and the mixture was stirred and heated at 125.degree. C. for 3 hours to obtain a xylene dispersion of composite resin particles, having a resinous acid value of 35 and a solid content of 50%.

For comparison sake, an acrylic resinous varnish was prepared following the abovesaid procedures but omitting the crosslinked polymer particles (1). The thus obtained varnish was added with 10 parts of the crosslinked polymer particles (1) prepared separately, and mixed well by means of a laboratory mixer to obtain a comparative composition.

Characteristic properties of the abovesaid two compositions were examined and the results were shown below.

From the above, it is clear that the present composite resin particles do have a large grain diameter as compared with those of the original, crosslinked polymer particles and that the viscosity of said dispersion is considerably lower than the viscosity of the comparative composition.

The abovesaid viscosity was determined by using E-type viscometer at 20.degree. C.

The similar procedures as stated in Example 2 were repeated with 50 parts of crosslinked polymer particles (2), 10 parts of styrene, 10 parts of methyl methacrylate, 21 parts of n-butyl acrylate, 8 parts of 2-hydroxyethyl acrylate, 1 part of acrylic acid, 100 parts of xylene, and 5 parts of azobis-isobutyronitrile, to obtain a dispersion of composite resin particles. A comparative composition was also prepared following the procedures of Example 2 but using the aforesaid raw materials.

It was found that the mean grain diameter of the composite resin particles was 1.2 times bigger than that of the crosslinked polymer particles used as the starting material and that the viscosity of the present dispersion is lower than the viscosity of the comparative composition.

Using the same procedures as stated in Example 2 but substituting 80 parts of crosslinked polymer particles (4), 6 parts of styrene, 4 parts of n-butyl acrylate, 6 parts of 2-ethyl hexyl acrylate, 3 parts of 2-hydroxyethyl methacrylate, 1 part of acrylic acid, 100 parts of xylene and 1 part of azobis-isobutyronitrile for the disclosed starting materials, a xylene dispersion of composite resin particles and a comparative composition were prepared.

The former was found to have a bigger grain diameter and a lower viscosity as compared with those of the latter.

Into a glass reaction vessel fitted with a thermometer, a reflux condenser, a nitrogen gas inlet tube and a stirrer, were placed 400 parts of deionized water, 25 parts of the dispersion-stabilizing polyester resin stated in Manufacturing Example 2, and 3.5 parts of dimethylaminoethanol and the mixture was heated to a temperature of 50.degree. to 55.degree. C. under stirring to obtain a solution. To this, were added 150 parts of Sumimal M-50W (melamine resin, trade mark of Sumitomo Chem. Co. ) and the mixture was stirred for 20 minutes, heated to 90.degree. C. and continued reaction at the same temperature for 90 minutes. From the thus obtained emulsion, water was removed off in vacuo to obtain crosslinked melamine resin particles (5) having a mean diameter of less than 5.mu..

Into a glass reaction vessel fitted with a thermometer, a reflux condenser, a nitrogen gas inlet tube and a stirrer, were added 400 parts of deionized water, 25 parts of the dispersion stabilizing polyester resin as shown in Manufacturing Example 2, and 3.5 parts of dimethylaminoethanol and the mixture was stirred at a room temperature to obtain a solution. To this, were added 120 parts of ERL-4221 (trade mark of Union Carbide alicyclic epoxy resin) and the mixture was stirred for 30 minutes. Thereafter, 30 parts of triethylene tetramine were added and the combined mixture was stirred for 40 minutes.

The thus formed granular precipitates were separated, washed well with water to remove the adhered triethyl tetramine therefrom, dried and pulverized by an atomizer to obtain crosslinked epoxy resin particles (6) having a mean diameter of less than 5.mu..

The similar procedures as stated in Example 2 were repeated with 50 parts of the crosslinked melamine resin particles (5), 100 parts of xylene, 50 parts of n-butyl alcohol, 20 parts of methyl methacrylate, 16 parts of ethyl acrylate, 8 parts of n-butyl methacrylate, 6 parts of hydroxy propyl methacrylate, and 1 part of t-butyl peroxy-2-ethyl hexanoate, to obtain a dispersion of composite resin particles in xylene/n-butyl alcohol.

The same procedures as stated in Example 2 were repeated with 20 parts of the crosslinked epoxy resin particles (6), 80 parts of xylene, 20 parts of methylisobutyl ketone, 23 parts of styrene, 12 parts of isobutyl methacrylate, 38 parts of n-butyl acrylate, 5 parts of 2-hydroxyethyl acrylate, 2 parts of methacrylic acid and 1.5 parts of azo-bis-isobutyronitrile to obtain a dispersion of composite resin particles in xylene/methylisobutyl ketone.

A xylene dispersion of composite resin particles was prepared by dispersing 50 parts of the composite resin particles (1) in 75 parts of xylene. While stirring in a disper, the dispersion was added with 15 parts of U-ban 20SE-60 (trade mark of Mitsuitohatu, melamine resin) and mixed well. To the thus obtained disperion of composite resin particles--melamine resin, were added, while stirring in a disper, 60 parts of Dianal HR-595 (trade mark of Mitsubishi Rayon, acrylic resin) and the combined mixture was stirred well to obtain a clear coating composition. The composition was then adjusted to a #4 Ford cup viscosity of 25 to 30 sec. and applied, by means of an air-spray gun, to a tin plate held vertically so as to give a wet thickness of 35.mu.. After setting for 5 minutes, the coating was baked at 140.degree. C. for 25 minutes. The thus obtained coating had a PGD value of 0.9 and had an excellent smoothness measured by a visual observation. PGD value is a measure of the distinctness of the coating and becomes bigger in proportion to the goodness of the same. In these experiments, the said value was determined by using a Portable Distinctness of Image Grossmeter (manufactured by Nippon Shikisai Kenkyusho).

Into a disper, 80 parts of the xylene dispersion of the composite resin particles obtained in Example 2, 30 parts of U-ban 128 (trade mark of Mitsuitohatu, melamine resin) and 70 parts of Beckosol 1307-60-EL (trade mark of Dainippon Ink, alkyd resin) were added and the mixture was stirred to obtain a clear coating composition. This was adjusted to a #4 Ford cup viscosity of 25 to 30 sec. and applied, by means of an air-spray gun, to a tin plate held vertically so as to give a a wet thickness of 30.mu.. After setting for 5 minutes, the coating was baked at 140.degree. C. for 25 minutes. The thus obtained coating had a PGD value of 0.8 and had an excellent smoothness measured by a visual observation.

Clear coating compositions were prepared according to the procedures of Example 7 with the prescriptions as given in Table 1. The respective composition was then applied to a tin plate and baked, and the thus obtained coating was evaluated as in Example 7. The test results are shown in Table 1.