A PRIMER PAINT OR PRIMER SURFACER COMPOSITION

Abstract: A plastic article, in particular highly crystalline, can be effectively coated with a paint by using a primer composition comprising (A) a polyurethane, (B) a spiro-­ ortho-ester resin being capable of the ring-opening expansion, (C) a cellulose derivative and (D) a surfactant having a hydroxy group.

Description: The present invention relates to a primer paint or a primer-surfacer paint for use in plastics showing a superior adhesion to a surface of plastics having a high crystallinity and a small surface polarity and a superior interlayer adhesion to various kinds of final coating of paint. (Prior Art) Since an adhesive capacity of paints to plastics having a high crystallinity or a small surface polarity, such as polyacetal resins and polyester resins (polyethylene terephthalate, polybutylene terephthalate, complete aromatic polyesters and the like, is inferior, in general the plastics have been subjected to physical or chemical surface treatments prior to painting. The physical methods include a method of mechanically roughing a surface, the chemical methods including a method of treating with solvents, and the physico-chemical methods including a method of treating with a flame, a method of treating with ultraviolet rays, a corona-discharging treatment, a plasma treatment and the like. According to these methods, a surface of the plastics is changed in quality to improve the adhesive capacity of paints. As above described, the methods, in which the surface of the plastics is physically or chemically treated and then painted, have shown vital difficult points in that not only considerable trouble and a large amount of money are required for the surface treatment but also the surface-treated portions are deteriorated. In view of the above described, a primer paint or a primer-surfacer paint exhibiting a superior adhesive capacity by merely directly painting without requiring any surface treatment has been being developed. Some materials have been already put into practice. The following characteristics are required for this primer paint or primer surfacer paint: (1) A surface and an interior of the plastics are not injured. (2) An interlayer adhesive capacity of a coated paint to the plastics is superior (for example, no separation in the tape-separation test using 100 meshes of 1 mm). (3) The coated film is tough (a small shrinkage and a small internal strain are produced in the formation thereof). (4) A wet-on-wet final coating is possible due to a fast drying capacity. (5) The coated film exhibits a high flexibility and is resistant to physical shocks (shocks and chipping). (6) The coated film is solvent-resistant, water-resistant (superior in adhesive capacity) and heat-resistant (including a heat-resistant cycle capacity). However, since the above described plastics having a high crystallinity and a small polarity exhibit a small affinity to almost materials, it is not easy to give them a high adhesive capacity without any heat treatment. Actually, no primer paint or primer surfacer paint exhibiting a satisfactory adhesive capacity to for example polyacetal- and polyester molded products without any surface treatment has been on the market. The above shown prior arts are disclosed in (1) T. Endo et al., J. Polym. Sci., Polym. Lett. Ed., 13 , 193(1975), (2) J. Polym. Sci., Polym. Chem. Ed., 13 , 2525(1975), (3) Makromol. Chem., 176 , 2897(1975), (4) J. Polym. Sci., Polym. Chem. Ed., 14 , 1735(1976), (5) Makromol Chem., 177 , 3231(1976), (6) J. Polym. J., 13 , 715(1981), (7) J. Polym. Sci., Polym. Chem. Ed., 19 , 1283(1981), (8) Polym. J., 14 , 485(1982), (9) J. Polym. Sci., Polym. Chem. Ed., 20 , 2935(1982), (10) M. Shimbo, M. Ochi, Y. Shigeta, J. Appl. Polym. Sci., 22 , 2265(1981), (11) M. Shimbo, M. Ochi. T. Inamura, M. Inoue, J. Mater. Sci., 20 , 2965(1985), (12) S.P. Thimoshenko, J.N. Goodier, Theory of Elasticity, by McGrow-Hill, New York, 1970, (13) J. Polym. Sci., Polym. Lett. Ed., 18 , 457(1900) and (14) ibid., 18 , 771(1980). The present invention was achieved in view of the above described matters. Thus, it is an object of the present invention to provide a primer paint or a primer surfacer paint capable of suficiently meeting the above described characteristical requirements for use in plastics having a high crystallinity and a small surface polarity. In order to solve the above described problems, a primer paint or primer surfacer composition according to the invention is characterised in that it comprises as essential ingredients for forming a paint film (A) polyurethane resins, (B) spiro-ortho-ester resins which are capable of ring-opening expansion, (C) cellulose derivatives and (D) hydroxyl group-containing surfactants. A primer paint or primer surfacer composition according to the invention thus comprises (A) a polyurethane having a number-average molecular weight of 2000 to 10000, (B) a spiro-ortho-ester resin being capable of ring-opening expansion, (C) a cellulose derivative and (D) a surfactant having a hydroxy group, in which the proportions of ingredients, based on the total weight of (A), (B), (C) and (D), are at least 50 wt % of (A), 2 to 40 wt % of (B), 1 to 9 wt % of (C) and 0.05 to 1 wt % of (D). It is preferable that the polyurethane (A) has a number-average molecular weight of 4000 to 7000, the resin (B) has a spiro-ortho-esterification degree of 250 to 500 g/eq and an epoxy value of zero to 5.0 g/eq and (C) the cellulose derivative has a hydroxy group content of 1 to 3 per 4 glucose units and a viscosity of 0.01 to 20.0 sec. From the practical point of view, it is preferable that it further comprises a solvent and contains the unsoluble ingredients, if any, having a particle size of 10 µm or smaller, uniformly dispersed in the solvent. The invention moreover provides a method for coating a plastic article with a paint, which comprises firstly coating the article with the composition as defined above and secondly with the paint. The ingredients for forming a paint film of a primer paint or a primer surfacer paint according to the present invention are described. The ingredient (A) is characterized by a high adhesive capacity and a high elasticity and has a function of simultaneously enhancing an adhesive capacity to an article to be painted and a shock-resistance of the paint film. According to the present invention, polyurethane resins are used as the ingredient (A). The polyurethane resins include thermoplastic polyurethane resins and thermosetting polyurethane resins. In addition, the polyurethane resins include also very modified polyurethane resin as far as it mainly comprises polyurethane resins. However, in order to give a high adhesive capacity and a high elasticity to a paint film, thermoplastic polyurethane resins having a mean molecular weight ( M n) of 2,000 to 10,000, preferably 4,000 to 7,000, are used. The ingredient (B) mainly gives to the paint film a non-shrinking capacity. The ingredient (B) shows a bridged structure due to an inner-molecular irreversible ring-opening in the presence of cationic catalysts to be expanded, whereby playing a part in the reduction of the shrinkage of paint film during the formation thereof, so that it exhibits an effective plasticizing effect even under the ring-closed condition in addition to the effect of simultaneously reducing an external stress and a residual strain (internal stress) of the film due to the shrinkage thereof. This ingredient comprises spiro-ortho-ester resins including 2, 2 - bis [4 - (2, 3 - epoxypropoxy) phenyl] propane · 6-hexanolyd poly-addition product having the below shown formula. In addition, a compound having the below shown formula may be used. Moreover there may be used 8, 10, 19, 20-tetraoxatrispiro [5.2.2.5.2.2.] heneicosan - 2, 14 - dien and the like as typical examples. Of them, spiro-ortho-ester resins having a spiro-esterification degree of 250 to 500 g/eq, preferably 300 to 400 g/eq, and an epoxy value of 0 to 5.0 g/eq, preferably about 4.65 g/eq, are preferably used. The ingredient (C) aims at the provision of a film-forming capacity (thermal fluidity) to paints and a hardness to a paint film and consists of cellulose derivatives. Of them, cellulose esters, such as cellulose acetate, cellulose propyonate, cellulose butylate, cellulose acetate propyonate, cellulose acetate butylate and cellulose nitrate, are suitable for the object of the present invention. In particular, cellulose acetate butylate and cellulose acetate propyonate having a butylation degree or a propyonation degree of 17 to 55 %, a hydroxyl group-concentration of 1.0 to 3.0, preferably about 1.0 (per four units of glucose anhydride) and a viscosity of 0.01 to 20.0 sec, preferably about 0.2 sec (standardized falling ball viscosity), are preferably used. The ingredient (D) aims at the adjustment of film surface and the provision of interlayer adhesive capacity to a final coating of paint. Hydroxyl group-contained reactive surfactants of fluorine system and silicone system having a capacity of adjusting a film surface and a reactive capacity are preferably used as the ingredient (D). The concrete examples of hydroxyl group-contained reactive surfactants of fluorine system include hydroxyl group-introduced perfluoroalkyls while the concrete examples of hydroxyl group-contained reactive surfactants of silicone system include a hydroxyl group-introduced organocyloxane. Both hydroxyl group-contained reactive surfactants of fluorine system and those of silicone system having higher hydroxyl group values are more effective. A part of these hydroxyl groups is exposed on a surface of paint film under an uncombined state to give an excellent adhesive capacity to a final coating of paint. These ingredients (A), (B), (C) and (D) lead to the formation of a paint film having excellent performances as a paint film and a superior adhesive capacity to an article to be painted and a final coating of paint in co-operation. According to the present invention, it is necessary that a primer paint or a primer surfacer paint comprises the ingredients for forming a paint film - (A) polyurethane resins, (B) spiro-ortho-ester resins, (C) cellulose derivatives and (D) hydroxyl group-contained surfactants - at the following ratios: (A) polyurethane resins : at least 50% (by weight) (B) spiro-ortho-ester resins (containing catalysts) : 2.0 to 40 % (by weight) (C) cellulose derivatives : 1.0 to 9.0 % (by weight) (D) hydroxyl group-contained surfactants : 0.05 to 1.0 % (by weight) The reasons that the above described composition was selected are as follows: (A) If polyurethane resins are comprised at ratios below 50 % by weight, an adhesive layer for giving a high adhesive capacity is wanting, whereby an adhesive capacity becomes insufficient while if polyurethane resins are comprised at ratios exceeding 97 % by weight, the corpusculization when sprayed, the surface flatness and the surface hardness are extremely deteriorated. (B) If spiro-ortho-ester resins are comprised at ratios below 2.0 % by weight, not only the expanding capacity but also the plasticizing effect can not be obtained at all and a primer paint or a primer surfacer paint becomes difficult to arrive at an edge (corner and side) portion of a molded product while if they are comprised at ratios exceeding 40 % by weight, the adhesive capacity is deteriorated. Now, the opening of a ring in spiro-ortho-ester resins are carried out by cationic ingredients in a system. Although usually the ring-opening reaction is promoted by the presence of catalysts such as methyl-hexahydrophthalic anhydride and di-n-butyl tin dilaurate, in some cases the opening of a ring is carried out by an action of - COOH group, - SO₃H group and the like in the system or fillers (aluminium silicate, magnesium silicate, surface carboxyl type organic micro gel and the like) having acidic hydroxyl groups contained therein. Also a superior plasticizing effect under the ring-closed state appears. Since this ring-opening reaction is difficult to take place at room temperature, usually said paint is preferably subjected to a heat treatment at about 100°C after the application thereof or the ring-opening reaction is preferably promoted utilizing a heat during the baking of a final coating of paint. The above shown ring-opening reaction using an anhydride is illustrated below. (C) If cellulose derivatives are comprised at ratios below 1.0 % by weight, the effects of giving the thermal fluidity and the surface hardness are insufficient while if they are comprised at ratios exceeding 9.0 % by weight, the adhesive capacity is deteriorated. (D) If hydroxyl group-contained reactive surfactants are comprised at ratios below 0.05 % by weight, the surface-adjusting effect does not appear whereby the surface of a paint film is inferior in flatness while if they are comprised at ratios exceeding 1.0 % by weight, defects (craters and the like) are generated in the resulting paint film and the adhesive capacity to the final coating of paint is deteriorated. In addition, said primer paint or primer surfacer paint comprising the above described four kinds of ingredient can form a paint film meeting the above described requirements by thermally treating after the application thereof to put particularly the ingredients (B), (C) and (D) into reaction. In this sense it is most advantageous to use said ingredients for forming a paint film in combination with thermosetting type final coatings of paint, such as baking paints and use a heat during the baking whereby promoting the bridging (cross-linkage) of said ingredients for forming a paint film. However, it goes without saying that said primer paint or a primer surfacer paint can be subjected to a heat treatment after the application thereof and then coated with a final coating of paint of such type that is set at the normal temperature. Besides, said four kinds of ingredient can be combined with the final coating of paint of such type that is set at the normal temperature within the above described range of composition to use as such type that is set at the normal temperature. Pigments, fillers and various kinds of additive may be added to usual paint compositions to improve physical properties, an ultraviolet ray permeability, an electrical conductivity, a coloring capacity and the like of a paint film if necessary. Also in the present invention such a third group of ingredients can be added to enhance the performance of the paint film. However, it goes without saying that the kind and the quantity to be added of pigments, fillers and the like must be determined so that they may be stably mixed with said ingredients (A), (B), (C), (D) for forming a film of a primer paint or a primer surfacer paint. Said ingredients for forming a paint film and other additives, such as pigments, added if necessary are diluted with solvents and blended to obtain the primer paint or primer surfacer paint. It goes without saying that the solvents must not injure the surface of plastics, which are articles to be painted, and preferably have a fast drying capacity. Although the solvents are selected according to the kind of articles to be painted, the most popular ones are shown in the left column of Table 2 and mixtures thereof. In addition, in the preparation of the paint it is desired that insoluble ingredients of the ingredients for forming a paint film, pigments and other additives have grain sizes of 10 µm or less so as to be uniformly dispersed in the solvent. The primer paint or primer surfacer paint according to the present invention can be provided in the form of solution type paint or dispersion type paint by suitable controlling the kind and the quantity to be added of the solvents. Painting methods, such as an air spray painting, an immersion painting, an electrostatic painting, an airless painting, a roller painting, a curtain painting and a shower painting, can be used by adjusting a viscosity, an electric conductivity and the like of said paint. After painting, the resulting paint film is hardened by drying at the normal temperature and drying with a hot wind for an optional time. It is suitable that the drying with a hot wind is carried out for 5 to 20 minutes at 40 to 140°C and a thickness of the dried paint film is 15 to 30 µm. It may be thought that the standard thickness is 22 ± 2 µm. The above shown airless painting is conducted by forcing a paint through an orifice at a high pressure to atomize it. (Preferred Embodiments) A primer paint or a primer surfacer paint having the compositions as shown in the following Table 1 was prepared and then diluted with a solvent mixture having compositions as shown in Table 2. The diluted paint was applied on a plate made of polyacetal, polyethylene terephthalate, polybutylene terephthalate and complete aromatic polyesters (constituent monomer unit: = 70/30) in a dried film thickness of 22 ± 2 µm and then dried with a hot wind for 20 to 30 minutes at paint film temperatures of 80 to 140°C to thermally set the ingredients for forming a paint film. Subsequently, a melamine-alkyd paint (AMILAC manufactured by Kansai Paint Co., Ltd.) on the market as a final coating of paint for use in an outside plating or cars was applied on the thermally set primer paint or primer surfacer paint in a dried film thickness of 30 to 40 µm by spraying, set for 10 minutes and then dried with a hot air for 30 minutes at 140°C. The ingredients shown in the left column of Table 1 are the following substances. VERNOC: (A) polyurethane resin (manufactured by Dainihon Ink Chemical Co., Ltd.) exp-101 : (B) spiro-ortho-ester resin (catalyst: di-n-butyl tin dilaurate) (manufactured by Toa Gosei Chemical Co., Ltd.) CAB-551-0.2 : (C) cellulose acetate butylate (manufactured by Eastman Kodack Co., Ltd.) Difenser MCF-312 : (D) hydroxyl group-contained fluorine reactive surfactant (manufactured by Dainihon Ink Chemical Co., Ltd.) BYK No-370: (D) hydroxyl group-contained silicon reactive surfactant (manufactured by BYK Chemie AG) The primer paint or the primer surfacer paint having the above described compositions satisfied the following requirements: (1) It does not injure the surface and the interior of plastics. (2) It is superior in interlayer adhesive capacity after finally coated (there is no separation in the tape-separation test using 100 meshes of 1 mm). (3) It forms a tough paint film (the shrinkage and the internal strain during the formation of film are small). (4) It is fast dried and can be finally coated in a wet-on-wet manner. (5) It forms a paint film having a high flexibility and a high physical shock-resistance (shock-resistance and chipping-resistance). (6) It forms a paint film superior in water-proofness (adhesive capacity) and heat-resistance (heat cycle-resistance). (Comparative Example) A polyacetal resin plate was subjected to only a final coating in the preferred embodiment without using the primer according to the present invention and tested on adhesive capacity (the tape-separation test using 100 meshes of 1 mm) in the same manner as in the preferred embodiment, for reference. 100 meshes were all separated. In addition, the primers, which were obtained by removing any one of the ingredients A, B, C, D from the primer (Preferred Embodiment 1) comprising the ingredients A, B, C, D according to the present invention were tested on separation in the same manner as in the preferred embodiment. Average residual adhesion coefficients (average numbers of residual adhesion meshes of 100 meshes tested on adhesive capacity by the tape-separation test) were as follows: In the case where the ingredient A is not contained 0/100 meshes In the case where the ingredient B is not contained 20/100 meshes In the case where the ingredient C is not contained 32/100 meshes In the case where the ingredient D is not contained 7/100 meshes As above described, the primer paint or the primer surfacer paint comprises (A) polyurethane resins, (B) open-ring expansion spiro-ortho-ester resins, (C) cellulose derivatives and (D) hydroxyl group-contained reactive surfactants as essential ingredients for forming a paint film according to the present invention exhibits a superior adhesive capacity to a surface of plastics having a high crystallinity and or a small surface polarity without requiring the conventional chemical and physical surface treatment processes and a superior interlayer adhesive capacity to various kinds of final coating of paint. Thus, the primer paint or the primer surfacer paint according to the present invention is remarkably useful for polyacetal resins, polyester resins (polyethylene terephthalate, polybutylene terephthalate, complete aromatic polyesters and the like) and the like.

Claims: A primer paint or primer surfacer composition which comprises (A) a polyurethane having a number-average molecular weight of 2000 to 10000, (B) a spiro-ortho-ester resin being capable of ring-opening expansion, (C) a cellulose derivative and (D) a surfactant having a hydroxy group, in which the proportions of ingredients, based on the total weight of (A), (B), (C) and (D), are at least 50 wt % of (A), 2 to 40 wt % of (B), 1 to 9 wt % of (C) and 0.05 to 1 wt % of (D). A composition as claimed in claim 1, in which the polyurethane (A) has a number-average molecular weight of 4000 to 7000. A composition as claimed in claim 1 or claim 2, in which the resin (B) has a spiro-ortho-esterification degree of 250 to 500 g/eq and an epoxy value of zero to 5.0 g/eq. A composition as claimed in any of claims 1 to 3, in which the cellulose derivative (C) has a hydroxy group content of 1 to 3 per 4 glucose units and a viscosity of 0.01 to 20.0 sec standardized falling ball viscosity. A composition as claimed in any preceding claim, which further contains a solvent and in which any insoluble ingredients having a particle size of 10 µm or less are uniformly dispersed in the solvent. A composition as claimed in any preceding claim, which further contains (E) an electrically conductive material. A composition as claimed in any preceding claim in which the spiro-ortho-ester resin (B) has a degree of spiro ortho esterification of 300 to 400 g/eq. A composition as claimed in any preceding claim, in which the spiro-ortho-ester resin (B) has an epoxy value of about 4.65 g/eq. A composition as claimed in any preceding claim, in which the electrically conducting material (E) is zinc oxide. A composition as claimed in any preceding claim, which includes, as a catalyst for promoting the ring opening of the spiro-ortho-ester resin (B), one or more components selected from methyl hexahydrophthalic anhydride, di-n-butyl-tin dilaurate and fillers having acidic hydroxyl groups contained therein. A method of coating a plastic article with paint, which comprises first coating the article with a composition as claimed in any preceding claim and second with the paint.

Inventors: ITO, HARUYASU, SUZUKI, YOSHIHARU, TAKAHASHI, KATSUHIKO
Applicants: POLYPLASTICS CO. LTD.
Application year: 1987
Main classification: C08L75
IPC codes: C09D175