JPS6345420B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a polypropylene resin molded article which has excellent mechanical properties, particularly flexural modulus and impact strength at low temperatures, and has excellent coating film adhesion. Polypropylene resin is widely used in industrial parts and miscellaneous goods because of its excellent balance of mechanical properties and relatively low price, but it is difficult to paint because it has no polar groups in its molecules and has low surface tension. In addition, it is difficult to hot stamp, and at present, it is hardly used for secondary processing that requires adhesiveness on the surface of a molded product. Various attempts have been made to improve the surface characteristics of polypropylene resin molded articles. For example, a method of activating the surface of a molded product by flame treatment, corona treatment, chromic acid immersion treatment, organic solvent treatment, etc.
A method of introducing polar groups into polypropylene resin through chemical bonding (Japanese Patent Publication No. 43-27421, Japanese Patent Publication No. 44-15422), a method of mixing inorganic fillers and wood flour with polypropylene resin (Japanese Patent Publication No. 53-9619), or Add wood flour and inorganic filler to
Method of adding ABS resin or atactic polypropylene (Special Publication No. 53-6013;
19346) Furthermore, a method of mixing polypropylene with a surface-treated inorganic filler and a styrene-butadiene block copolymer (Japanese Patent Publication No. 54-124050), etc.
An endless variety of methods have been tried. However, looking around at this point,
Although an infinite number of various methods have been discovered, they are hardly used in the world. Even if it is used, it is only used in very limited fields. The reason is simple. From an industrial perspective,
This is because it has little utility value. In other words, the conventional method is difficult to work with,
There are hygienic problems, it is not worth the cost, it is not possible to obtain adhesive strength sufficient for the purpose of use, and even if it can be obtained, the most important characteristic of polypropylene resin, mechanical This is because the industrial value of properties and relatively low cost would be lost, and there would be no need to use polypropylene resin. The present inventors have aimed to improve the coating performance of polypropylene resin without losing its excellent mechanical properties and industrial utility value, and to improve the mechanical properties conventionally possessed by polypropylene resin, and to improve the performance of automobiles. This is an alternative to interior and exterior parts or light electrical parts, where ABS resin or other resins have traditionally been used mainly because of their good paintability, even though they are more expensive than polypropylene resins. As a result of intensive studies to make this possible, the present invention has been developed, and its industrial value is extremely high. The present invention will be explained in detail below. In order to produce the coated molded product of the present invention, the resin composition of the molded product must be 93 to 60% by weight of polypropylene resin (hereinafter abbreviated as PP resin) and styrene thermoplastic elastomer (hereinafter abbreviated as TPS). The content of vinyl acetate (hereinafter referred to as VA) is 2 to 10% by weight in the resin composition of the molded product. Must be in range. Both TPS and EVA have very good coating performance compared to PP resin, and coating molded products obtained by molding a composition obtained by melt-kneading PP resin and TPS or PP resin and EVA. Performance is TPS,
It improves as the mixing ratio of EVA increases. When TPS is mixed with PP resin, the adhesion of the coating film is improved and the impact resistance is improved, but on the other hand, the flexural modulus decreases, and the balance of the mechanical properties of the PP resin is lost. On the other hand, when EVA is mixed with PP resin, the adhesion of the coating film improves, but the impact resistance and flexural modulus decrease, and the properties of PP resin are lost. In order to improve the strength of PP resin, ethylene-propylene rubber (hereinafter abbreviated as EPR) has traditionally been used.
and olefin thermoplastic elastomers (hereinafter referred to as
The method of mixing TPO (abbreviated as TPO) is often used, but
Even in the case of this mixture, EPR or TPO
As the mixing ratio increases, the degree of improvement in impact resistance and the degree of decrease in flexural modulus increase, while the adhesion of the coating film tends to improve. The present inventors added TPS to the above-mentioned PP resin.
As a result of mixing EVA, TPO, etc. individually,
Even if EPR or TPO, which do not inherently have polar groups, is mixed, the adhesion of the coating film to molded products made of PP resin as a main component tends to improve as the mixing ratio increases. We found that it is very closely related to the flexural modulus of the molded product, and that there is a certain relationship, although there are differences depending on the substance mixed with the PP resin, the type of paint, and the coating method (Figure 1). ~See Figure 2). Therefore, the present inventors aimed to minimize the decrease in the bending elastic modulus that would occur when molded with PP resin alone, which is the main component of the molded product, in the relationship between the adhesion of the coating film and the bending elastic modulus. As a result of studying ways to improve the adhesion of paint films by improving impact resistance, we found that only when molded products were manufactured using the resin composition of the present invention and painted, TPS and EVA were combined with PP resin individually. The inventors have discovered that a synergistic effect can be produced in the relationship between the adhesion and bending elasticity of the coating film, which could not be obtained when the mixture is mixed and molded.This led to the present invention. The PP resin referred to in the present invention is a polymer mainly composed of polypropylene, and can be an essentially crystalline polypropylene homopolymer, or a random or block copolymer containing polypropylene as the main component and ethylene or other α-olefins. A polymer that is essentially crystalline. Furthermore, the homopolymer or copolymer may contain currently known EPR or TPO.
PP resins also include compositions in which impact resistance is improved by adding 25% by weight or less of The PP resin used in the present invention is preferably an ethylene-propylene block copolymer, but PP resins having other compositions may also be used without any loss in the effects of the present invention. The significance of the present invention is to minimize the decrease in the flexural modulus of molded products made from PP resin alone as the main component, to significantly improve the adhesion of the coating film, and to improve impact resistance. This is because it improves the In addition, the melt flow index of the PP resin used in the present invention is 0.5 to 20 g/ A time range of 10 minutes is preferable, and more preferably 1.0 to 10 minutes.
10g/10 minutes. If a melt flow index of 20 g/10 minutes or more is used, good results cannot be obtained for the low-temperature impact strength of the molded product obtained by the present invention, and the sheet molded product When used for other purposes, problems arise in processability and the like, which is not preferable. on the other hand,
If the melt flow index is 0.5 g/10 minutes or less, there will be no problem in sheet molded products, but there will be problems with molding processability in injection molded products.
Insufficient fluidity within the mold may cause anisotropy in the strength of the molded product or a decrease in the strength of the weld part. Furthermore, when molding is performed at high temperatures to improve fluidity, problems arise with the thermal stability of the TPS or EVA used in the present invention, and the effects of the present invention, particularly impact resistance and adhesion strength of the coating film, are insufficient. You won't be able to get it.
The molding conditions for obtaining the molded product of the present invention are as follows:
The resin temperature is preferably 265°C or lower. The TPS used in the present invention is a copolymer consisting of a hard phase of polystyrene, a soft phase of polybutadiene or polyisoprene, and a basic molecular structure consisting of teleblock, triblock, star block (also called radial block), or multiblock. . (Plastics Vol.30, No.3
P6-23, (1979)) The TPS used in the present invention preferably has a styrene content of at least 20% by weight. If it is less than 20% by weight, the degree of decrease in the flexural modulus of the molded article of the present invention is large, and a synergistic effect between the adhesion strength and the flexural modulus of the coating film cannot be obtained, which is not preferable. Further, the mixing ratio of TPS in the resin composition of the molded article of the present invention must be in the range of 5 to 30% by weight, and more preferably in the range of 15 to 25% by weight. 5% by weight
Impact resistance and coating adhesion will be poor in the following cases:
If it is more than 30% by weight, the effect of improving the adhesion of the coating film will be almost the same as if it is less than 30% by weight, but rather the flexural modulus will be significantly lowered, which is not preferable. In the present invention, EVA refers to a thermoplastic resin made by copolymerizing ethylene and vinyl acetate. There are no particular limitations on the type and mixing ratio of EVA used in the present invention, but it is necessary to ensure that the VA content is in the range of 2 to 10% by weight in the resin composition of the molded article of the present invention. More preferably 2
-5% by weight. The type and amount of EVA used can be appropriately selected depending on the purpose and application of the molded product of the present invention, but the synergistic effect of the adhesion and flexural modulus of the coating film of the molded product of the present invention can be selected as appropriate. To obtain the lowest limit, it is preferable to use EVA with a VA content of 30-45% by weight. In the resin composition of the molded article of the present invention, if the VA content is less than 2% by weight, the effect of improving the adhesion of the coating film will not be sufficiently exhibited, and even if it is more than 10% by weight,
The effect of improving the adhesion of the coating film is almost the same at 10% by weight or less, and on the contrary, the flexural modulus and impact strength of the molded article are significantly lowered, which is not preferable. Note that the VA content is a value measured by the method specified in JIS K6730-1973. In order to obtain the resin composition of the molded article of the present invention, it is preferable to mix each resin component in a heated molten state using a commonly known kneader before manufacturing the molded article. When kneading is carried out using a hot roll, Banbury kneader, extruder, etc., it is preferable to knead the resin composition used in the present invention at a resin temperature of 240°C or lower, preferably 220°C or lower. When the temperature is 240° C. or higher, even if the molded article of the present invention is manufactured using the resin composition, a sufficient improvement effect in terms of impact strength cannot be obtained. Further, the melt flow rate of the resin composition is 240
It is significantly lower than when kneading at temperatures below ℃,
When molding the molded article of the present invention, particularly when injection molding is used, problems arise in molding processability, which is not preferable. When manufacturing the molded product of the present invention, it is most preferable to use a compound obtained by melt-kneading each resin component before molding. However, the PP resin and TPS are first melt-kneaded and then molded. Occasionally
There is no problem even if a method of adding a predetermined amount of EVA is used. Naturally, it will be necessary to further improve the various performances of the molded article of the present invention depending on the intended use. Furthermore, EVA or TPS used to obtain the molded article of the present invention has a problem that its thermal stability or weather resistance is inferior to that of PP resin. Therefore, it is preferable to add various stabilizers. It is preferable to manufacture the molded article of the present invention while taking into consideration the synergistic addition effects of various stabilizers as described below depending on the purpose of use and required performance. Examples of ultraviolet absorbers include salicylic acid esters, benzophenones, benzotriazoles, and metal chelates. Radical chain inhibitors include mono-, bis-, and trisphenols and aromatic amines. Peroxide decomposers include mercaptans, mono-, di-, and polysulfides, dithiocarbamates, osphites, phenothiazines, and thiodifatty acid dialkyl esters. Metal deactivators include aromatic amines, acid amides and hydrazides. Also included as synergistic agents are dialkylphosphonates, dialkylphosphines, dialkylaldines, and the above-mentioned peroxide decomposers. In addition, pigments, flame retardants, lubricants, antistatic agents, etc. can be added, but many of the additives mentioned above reduce the adhesion performance of the paint film, so be careful when using them. is preferred. There is no problem in adding inorganic fillers depending on the intended use. PP resin is a crystalline resin, and the method of adding a nucleating agent is used to promote the generation of crystal nuclei, generate a large number of nuclei, make the crystals finer, and speed up the crystallization speed. It is publicly known. Nucleating agents include fine inorganic powders such as silica and talc, aliphatic and aromatic carboxylic acids and their sodium,
Potassium, magnesium, and aluminum salts are commonly used. By adding these nucleating agents, the transparency of the molded product is improved, the molding cycle is shortened in injection molding, and the degree of crystallinity is increased in terms of physical properties, thereby improving yield strength and bending rigidity. However, while the above-mentioned merits are usually obtained, it has been conventional wisdom that this results in a decrease in elongation and a decrease in impact strength, which is undesirable especially in applications requiring impact resistance at low temperatures. However, in the molded product of the present invention,
By adding this agent to the resin composition used to obtain the molded product, the bending rigidity is improved and, surprisingly, the impact strength at low temperatures does not decrease as much as when PP is used alone. The desired effect can be obtained. Therefore, even when no nucleating agent is added to the molded article of the present invention, as mentioned above, a synergistic effect is obtained in the relationship between coating film adhesion and flexural modulus, and impact resistance is improved, but when no nucleating agent is added, By adding the nucleating agent, the impact resistance was the same as when no nucleating agent was added, only the flexural modulus was further improved, and the adhesion of the coating film remained unchanged compared to when no nucleating agent was added. It is very preferable to use it as a nucleating agent in the molded article of the invention. The synergistic effect of coating film adhesion and flexural modulus, which is a feature of the present invention, can be further increased without reducing impact resistance. However, the amount of the nucleating agent added is preferably 1 part by weight or less in the case of an inorganic fine powder, and 0.5 part by weight or less in the case of an organic acid and its metal salt, based on 100 parts by weight of the composition of the molded article. Table 1 summarizes the features of the present invention with and without the addition of a nucleating agent.

【table】

[Table] When painting the molded product of the present invention, as a pretreatment step, the surface of the molded product is wiped with an aromatic solvent such as toluene or xylene, or a chlorinated hydrocarbon solvent such as trichlene, or soaked in the solvent. The adhesion of the coating film can be made very strong by dipping or spraying, but in the case of the molded product of the present invention, it can be used as a normal industrial part even without the above-mentioned pretreatment process. A feature of the present invention is that it provides the adhesion of the coating film required when used as a coating material. Primers used when painting the molded products of the present invention include chlorinated polyolefin, EVA,
Aromatic petroleum resins, modified alkyd resins, alkylated amino resins, etc. may be used alone or in combination in an organic solvent. As paints that can be used in the present invention, all conventionally known paints such as urethane-based, acrylic-based, and epoxy-based paints can be used. The present invention will be further explained below with reference to comparative examples and examples, but the present invention is not limited to these examples. Comparative Example 1 Ethylene-propylene block copolymer (melt flow index 2.0 g/10 min, flexural modulus
8100Kg/cm ² , ethylene content 12% by weight) and olefin thermoplastic elastomer (Sumitomo Chemical, Sumitomo)
TPE1600) was added in various proportions and melt-kneaded at a resin temperature of 220°C using an Osaka Seiki extruder (65 m/mφ, 2-stage full-flight screw, L/D = 25, CR = 3.0). Ta. The obtained resin composition was injection molded to prepare test pieces for measuring coating film adhesion and measuring mechanical strength. 150 x 90 x as a test piece for measuring paint film adhesion
A 2 mm flat plate was molded. For measuring mechanical strength and for bending rigidity.
A 127 x 12.7 x 6 mm rod was used for Izotz impact strength measurement by molding it into a 63.5 x 12.7 x 6 mm rod. In addition, since the impact strength of injection molded products differs significantly between the flow direction of the resin and the direction perpendicular to it, we used a bar flow mold to create molds with a width of 20 mm, a thickness of 2 mm, and a thickness of 2 mm.
A molded product with a length of 380 mm was created and used as a sample for measuring die stud impact strength in the flow direction of the resin and in the right angle direction. For the paint film adhesion test, P-3 primer manufactured by Kashiyu Co., Ltd. was spray-painted on the above flat plate surface without any surface treatment, and after drying to the touch, Micron #4001 manufactured by Kashiyu Co., Ltd. was spray-painted. After drying to the touch, spray paint the topcoat paint Strony Ace PB-2 manufactured by Kashiyu Co., Ltd. to a film thickness of 20μ, and after setting for 15 minutes.
Baking was performed at 80°C for 30 minutes. Use a safety razor blade to coat this coating film in a 10× grid pattern at 1 mm intervals vertically and horizontally.
A total of 100 cuts of 10 mm were made. Make these 100-divided cuts in 5 places on the surface of one flat plate, apply Nichiban's 24mm cellophane tape to each cut with your fingertips, and peel it off suddenly in a 90° direction to check the adhesion. Examined. Evaluation was performed using three molded products (flat plates) having the same resin composition. The adhesion rate was determined by the non-peeling rate of 1500 1 mm square cuts. Measurement of flexural modulus is carried out for at least 48 hours after specimen preparation20
It was used after being conditioned in a constant temperature room at 65% humidity. Measurements were carried out in a constant temperature room under the same conditions. Measurements were made using Toyo Seiki Tensilon UTM-1/500, span distance 100mm, thickness 6mm, width 12.7mm.
Pressure was applied to the center of the rod at a speed of 2 mm/min.
(Based on ASTMD790-66) Izotsu impact strength test is JIS K-7110-1977
It was carried out in accordance with the . Dine stud impact strength test was conducted at 140mm and 315mm from the gate of bar flow molded product.
Length 20 from the point in the resin flow direction and in the perpendicular direction
Cut out a test piece with a width of 10 mm and a length of 20 mm up to the center (10 mm position) on the support stand of the testing machine.
The impact position is the thickness of the test piece (approximately 2 mm) from the fixed part.
The hammer was struck at a raised angle of 120° on a 10 mm wide surface of the specimen. The impact velocity is 335 cm/sec. (Using a universal impact tester manufactured by Sankyo Seiki Kogyo Co., Ltd.) As for the impact strength, the lowest value among the impact strengths obtained from four locations was used. Both the Izot impact test piece and the Dynstat impact test piece were left in a constant temperature bath at -30°C for 2 hours or more, and the impact strength at -30°C was measured. The injection molding conditions for each sample are shown in Table 2.

[Table] The results obtained are shown in Table 3. Comparative Example 2 The procedure was exactly the same as Comparative Example 1, except that a styrene-based thermoplastic elastomer (manufactured by Asahi Kasei Corporation, Toughprene styrene content: 25%) was used instead of the olefin-based thermoplastic elastomer used in Comparative Example 1. Then, the resulting resin composition was melt-kneaded and injection molded to prepare test pieces for evaluation. The results are shown in Table 3. Comparative Example 3 Instead of the olefin thermoplastic elastomer used in Comparative Example 1, an ethylene-vinyl acetate copolymer (Ebatate R5011 manufactured by Sumitomo Chemical, VA content 41% by weight, melt index 60 g/10 minutes) was used. Except for this, the resin composition obtained by melt-kneading was injection molded in exactly the same manner as in Comparative Example 1, and test pieces were prepared and evaluated. The results are shown in Table 3. Comparative Example 4 The surfaces of the flat plates for measuring paint film adhesion prepared in Comparative Examples 1 to 4 were spray-coated with EPX2179 manufactured by Fujikura Kasei without any surface treatment, and after drying to the touch, coated with R257 manufactured by Nippon B Chemical Co., Ltd. After spray painting and drying to the touch, spray paint the top coat R258H (manufactured by Nippon B Chemical) to a film thickness of 30μ, and after setting for 15 minutes, heat at 80℃.
Baking was performed for 40 minutes. A coating peeling test was conducted on these coatings in exactly the same manner as in Comparative Example 1. The results are shown in Table 3.

[Table] As is clear from Comparative Examples 1 to 4, when TPR, TPS, or EVA is mixed with polypropylene resin, the coating adhesion of the resulting injection molded product improves as the mixing ratio increases, but On the other hand, the flexural modulus decreases. Figures 1 and 2 illustrate the relationship between paint film adhesion and flexural modulus, and it is clear that there is a constant relationship between paint film adhesion and flexural modulus even if the type of paint is different. I understand. Also, when comparing the coating adhesion with the same flexural modulus, the non-polar
It can be seen that the coating adhesion is better when TPS or EVA is mixed than when TPO is mixed. Also, when TPO or TPS is mixed, the impact strength increases as the mixing ratio increases, but
When EVA is mixed, there is almost no change in the isot impact strength, but when compared with the die-stud impact strength of molded products obtained from a bar flow mold, which can express the anisotropy of mechanical strength during injection molding.
It can be seen that as the EVA mixing ratio increases, it shows a decreasing tendency. Example 1 Instead of the olefin thermoplastic elastomer used in Comparative Example 1, a styrene thermoplastic elastomer (Tuffprene) and an ethylene-vinyl acetate copolymer (Evatate R5011) were used at the same time in various proportions. Melt-kneading was performed in exactly the same manner as in Comparative Example 1, and the resulting resin composition was injection molded to prepare test pieces for evaluation. The results are shown in Table 4. Example 2 Comparison except that the flat plate for measuring paint film adhesion created in Example 1 was used instead of the flat plate for measuring paint film adhesion created in Comparative Examples 1 to 4 used in Comparative Example 4. Coating was performed in exactly the same manner as in Example 4, and a coating peel test was conducted. The results are shown in Table 4.

[Table] Comparative Example 5 Ethylene-propylene block copolymer (melt flow index 1.6 g/10 min, flexural modulus
9800Kg/cm ² , ethylene content 22% by weight), test pieces for measuring paint film adhesion and mechanical strength were prepared by injection molding under the same conditions as in Comparative Example 1, and in the same manner as in Comparative Example 1. We conducted an evaluation. The results are shown in Table 5. Comparative Example 6 80% by weight of the ethylene-propylene block copolymer used in Comparative Example 5 and 20% by weight of the styrene thermoplastic elastomer (Tuffrene) were melt-kneaded in the same manner as in Comparative Example 1, and a test piece was injection molded. created and evaluated. The results are shown in Table 5. Comparative Example 7 Comparative Example 6 was evaluated in exactly the same manner as Comparative Example 6, except that 0.3 PHR of aluminum salt of aromatic carboxylic acid was added as a nucleating agent during melt-kneading. The results are shown in Table 5. Comparative Example 8 The ethylene-propylene block copolymer used in Comparative Example 5, the ethylene-vinyl acetate copolymer used in Comparative Example 3, and the nucleating agent used in Comparative Example 7 were blended in various proportions to produce Comparative Example 1. The samples were melt-kneaded in the same manner as above, and test pieces were made by injection molding and evaluated. The results are shown in Table 5. Example 3 The ethylene-propylene block copolymer used in Comparative Example 5, the styrene thermoplastic elastomer (Tuffrene), the ethylene-vinyl acetate copolymer (Evatate R5011), and the nucleating agent used in Comparative Example 7 were mixed with various The resin compositions were blended in the same proportions and melted and kneaded under the same conditions as in Comparative Example 1, and the resulting resin composition was injection molded to prepare test pieces for evaluation. The melt flow index of the resin composition obtained after melt-kneading was measured by the method of JIS K6758-1977. At the same time, Comparative Examples 5 to 8 were also measured in the same manner. As is clear from Table 5, by using a nucleating agent in combination, the molded product obtained according to the present invention can improve the flexural modulus without reducing the adhesion of the coating film, and can also maintain good impact strength. This characteristic is found. Example 4 75% by weight of the ethylene-propylene copolymer used in Comparative Example 5, 20% by weight of the styrene thermoplastic elastomer (Sorprene T414 manufactured by Asahi Kasei), and 5% by weight of the ethylene-vinyl acetate copolymer used in Comparative Example 3 Then, 0.3 PHR of the nucleating agent used in Comparative Example 7 was melt-kneaded in the same manner as in Comparative Example 1, and test pieces were prepared by injection molding and evaluated. The results are shown in Table 5.

[Table] Comparative Example 9 80% by weight of the ethylene-propylene block copolymer used in Comparative Example 5, 10% by weight of the styrene-based thermoplastic elastomer used in Comparative Example 2, and surface-treated calcium carbonate (Shiraishi Calcium Co., Ltd., Hakuenka Co., Ltd.)
DD) was blended at a ratio of 10% by weight, melt-kneaded in the same manner as in Comparative Example 1, and test pieces were injection molded and evaluated. The results of the peel test of the paint film showed that the adhesion rate was 99.87% and the flexural modulus was 8600 Kg/ ^cm2 , but the die-stat impact strength was 12 Kg. cm/ ^cm2 , which was very low.

[Brief explanation of the drawing]

FIG. 1 shows the results of Comparative Examples 1 to 3 in terms of the relationship between coating film adhesion and flexural modulus. FIG. 2 shows the results of Comparative Example 4 in terms of the relationship between coating film adhesion and flexural modulus. Figure 3 shows comparative example 5.
The results of Examples 1 to 8 and Example 3 are shown in terms of the relationship between coating film adhesion and flexural modulus to more specifically illustrate the characteristics of the present invention.

Claims (1)

[Claims] 1 Consisting of 60 to 93% by weight of polypropylene resin, 5 to 30% by weight of styrene thermoplastic elastomer, and ethylene-vinyl acetate copolymer;
The amount of vinyl acetate copolymer is such that the vinyl acetate fraction in the resin composition is 2 to 10% by weight.The resin composition is molded with excellent mechanical properties and excellent paintability. A manufacturing method for polypropylene resin molded products.