JPH0464536B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a polypropylene resin foam with excellent closed cell properties by extrusion foam molding. (Prior Art) When polypropylene resin is used alone, its extrudability is significantly inferior to other polyolefin resins such as low density polyethylene, and a foam with a high closed cell ratio cannot be obtained. The reason for this is that due to the crystallization properties of polypropylene resin, the appropriate foaming temperature range is extremely narrow and it is difficult to perform foam molding.In addition, the large amount of heat generated during crystallization and the lack of melt strength cause the bubbles to collapse immediately after foaming. This is because Therefore, attempts have been made to improve the extrusion foamability by adding melt elasticity to the polypropylene resin by mixing an elastomer or introducing a crosslinked structure. As an example of mixing such elastomers, JP-A-55-1999 uses polybutadiene.
40739 and JP-A-56-60233, as well as JP-A-Sho which disclosed a mixture of ethylene-propylene rubber.
No. 57-1603, and JP-A No. 161671-1989, or JP-A No. 49-1989 mixed with ionomer resin.
Publication No. 74264, etc. However, none of these conventional methods can be said to be sufficient in terms of extrusion foamability, heat resistance and thermal stability of the obtained foam, and production cost. Further, as an example of introducing a crosslinked structure, Japanese Patent Application Laid-Open No. 57-24221 discloses a method of imparting melt elasticity to a foam by providing a crosslinked structure to the foam. However, since this method involves single-stage crosslinking and foaming, there are problems with stability and continuous moldability.
Moreover, due to the use of antioxidants, the resulting resins lack long-term heat resistance. The methods disclosed in JP-A-58-17127 and JP-A-58-49730 commercialize open-celled extruded foam, and can only provide a single grade product. . (Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the prior art, and its purpose is to produce a polypropylene resin foam with excellent closed cell properties and a high expansion ratio. The purpose is to provide a method. Another object of the present invention is to provide a method for obtaining a polypropylene resin foam inexpensively and stably by extrusion foam molding. (Means for Solving the Problems) The present invention is based on the inventors' knowledge that a polypropylene resin composition containing a partially crosslinked polypropylene resin can provide extremely good foamability and foam quality. It was completed. The partially crosslinked polypropylene resin of the present invention is obtained by melt-kneading a polypropylene resin, a crosslinking initiator such as an organic peroxide, and a crosslinking aid such as an oxime compound by extrusion or the like. Polypropylene resin requires a crosslinking aid because the decomposition reaction takes precedence when organic peroxide alone is used. The polypropylene resin is not particularly limited, and for example, a propylene homopolymer, a random copolymer or block copolymer of ethylene or other α-olefin containing propylene as a main component, etc. are appropriately selected. . Regarding crosslinkability and foamability, the copolymer composition is slightly better. Various organic peroxides are used as the crosslinking initiator. Among these, from the viewpoint of crosslinking efficiency, those having a half-life of 1 minute or more at a temperature higher than the melting point of the polypropylene resin used are preferred. This is to prevent the organic peroxide from being decomposed before the polypropylene resin is melted in the extrusion foaming method. When using an extruder, the organic peroxide is added directly to the polypropylene resin; organic peroxide alone or dissolved in a crosslinking agent or other solvent is added to the extruder. A method such as supplying the mixture from the middle of the process; or using a masterbatch obtained by kneading in advance at a temperature below the decomposition temperature of the organic peroxide is appropriately selected. Examples of such organic peroxides include dicumyl peroxide; t-butyl peroxide; di-t-butyl peroxide; α・α′-bis(t-butylperoxyisopropyl)benzene; -dimethyl-2,5-di(t-butylperoxy)hexane; 2,5-dimethyl-2.
5-di(t-butylperoxy)hexane-3;
Di-t-butyl diperoxyisophthalate;
Examples include 2,5-dimethyl-2,5-di(benzoylperoxy)hexane. The number of parts of these organic peroxides added varies depending on the resin and other compositions, but is usually 1 part by weight per 100 parts by weight of the resin.
It has a sufficient effect even if the amount is less than 1 part by weight. As the crosslinking aid, polyfunctional arylate compounds, acrylate compounds, or vinyl compounds are generally used, but in the present invention, oxime compounds are used. This is because the oxime compound has the effect of suppressing the decomposition reaction of the polypropylene resin caused by the organic peroxide in a small amount compared to other crosslinking aids. Moreover, in the case of extrusion molding, molding stability is excellent. Examples of this include p-quinonedioxime or p・p′-
Examples include dibenzoylquinone dioxime, among which the latter is preferably used. Further, as a crosslinking aid, an oxime compound and the above-mentioned polyfunctional compound may be used in combination, and in the case of extrusion molding, the molding stability may be better when used in combination. These crosslinking aids are supplied in the same manner as the method for adding the organic peroxide described above. A sufficient effect can be obtained when the amount of addition is 1 part by weight or less per 100 parts by weight of the resin. In addition to the melt-kneading method using an extruder, resin crosslinking methods include azide crosslinking, radiation crosslinking, and silane crosslinking, but all of them have drawbacks such as high cost. Melt kneading by extrusion is the most economical method. As the melt-kneading method, in addition to an extruder, it is also possible to use a kneader such as a Banbury mixer. When a partially crosslinked resin is obtained using an extruder, the gel fraction (xylene insoluble fraction at 110° C.) of the resin is preferably 50% or less. Gel fraction is 50%
Extrusion molding becomes difficult when the temperature exceeds . Gel fraction is 0
%, extrusion reaction molding is possible as long as there is a significant decrease in melt index (MI), that is, a significant increase in melt viscosity. Next, the obtained polypropylene resin mixed composition containing the partially crosslinked polypropylene resin in a proportion of 5% by weight or more and less than 50% by weight and a volatile foaming agent are supplied to an extruder to obtain a uniform molten mixture. Then, this molten mixture is extruded and foamed using an extruder. At this time, an antioxidant may be added as appropriate in view of the thermal stability during foam molding and the heat resistance of the resulting foam. In the mixed composition of a partially crosslinked polypropylene resin and a non-crosslinked polypropylene resin, the partially crosslinked polypropylene resin accounts for 5% by weight or more and 50% by weight of the whole.
It is necessary that it be included within the range below. 5
If it is less than % by weight, the viscoelasticity required for foaming during melting will be insufficient, and a foam with excellent closed cell properties will not be obtained. Preferably, the content is 10% by weight or more. Additionally, the melting point difference between partially cross-linked polypropylene resin and non-cross-linked polypropylene resin is 10°C.
It is desirable that it be within If the melting point difference exceeds 10°C, it becomes difficult to adjust the viscosity during extrusion foaming, and a foam with excellent closed-cell properties cannot be obtained. Preferably 5
It is best to keep it within ℃. Partially crosslinked polypropylene resin
If more than 50% by weight is used, the surface of the resulting foam will slightly lack smoothness. As the volatile foaming agent, those used in ordinary foam molding of low-density polyethylene resins and polystyrene resins are appropriately used. For example, hydrocarbons such as propane, butane, pentane or hexane; methyl chloride, methylene chloride, ethyl chloride, ethylene chloride, trichlorofluoromethane,
Halogenated hydrocarbons such as dichlorodifluoromethane, difluorochloromethane, 1,1,2,2-tetrafluorodichloroethane, 1,1,2-trifluorotrichloroethane; or CO ₂
and inert gases such as _N2 . These volatile blowing agents may be used alone or in combination of two or more. Extrusion foam molding is carried out in the same manner as for ordinary low-density polypropylene resins or polystyrene resins. The extruder used is appropriately selected from a single-screw extruder, a twin-screw extruder, or an extruder made by connecting a plurality of these extruders. First, the above-mentioned partially crosslinked polypropylene resin mixed composition, or a mixed composition obtained by adding a foaming nucleating agent or the like as necessary, is supplied to an extruder and melted. Next, a volatile foaming agent is press-injected through a press-in hole provided in the middle of the extruder and sufficiently melted and mixed with the above composition to prepare a uniform molten mixture. Next, this molten mixture is extruded from an arbitrary mold provided at the outlet of the extruder and foamed to obtain a foam. Since this extrusion foam molding does not involve any chemical reaction, arbitrary additives may be used as appropriate. Examples include hindered phenol-based, thioether-based, organic phosphoric acid-based or amine-based antioxidants, metal deterioration inhibitors, and ultraviolet absorbers. The foam thus obtained had a high closed cell ratio and exhibited a good expansion ratio of about 35 times. (Example) The present invention will be described below with reference to Examples. Example 1 Melt index (MI) is 10.0g/10min.
and 100 parts by weight of a propylene-ethylene block copolymer with a crystallization temperature of 163°C as measured by DSC,
After uniformly sprinkling 0.1 part by weight of dicumyl peroxide (DCP) and 0.3 part by weight of p.p'-dibenzoylquinone dioxime (DGM) dissolved in acetone, the mixture was left at room temperature to volatilize the acetone. Next, this mixture was supplied to a twin-screw extruder having a diameter of 65 mm and L/D=25, and the temperature of the cylinder in the extruder was set to 200° C. for melt-kneading. Then, the melt-kneaded product was extruded from a strand mold having 10 small holes with a diameter of 3 mm to obtain a partially crosslinked propylene-ethylene block copolymer. The partially crosslinked propylene-ethylene block copolymer obtained was
is 1.5g/10min., gel fraction is 20% and melting point is
It was 163℃. Next, 30 parts by weight of a partially crosslinked propylene-ethylene block copolymer, 70 parts by weight of a propylene homopolymer having an MI of 1.8 g/min. and a melting point of 164°C, and a hindered phenol antioxidant (manufactured by Ciba Geigy; Irganox 1010) were added. ) 0.1 part by weight, thioether antioxidant (manufactured by Ouchi Shinko Co., Ltd.; Nofrac 400)
0.1 part by weight and 0.1 part by weight of talc as a foaming nucleating agent were uniformly mixed and supplied to a single screw extruder having a diameter of 65 mm and L/D=32. Then, 22 parts by weight of 1,1,2,2-tetrafluorodichloroethane was injected as a blowing agent into the extruder. The diameter of the mold is 5mm
Extrusion foam molding was carried out using a nozzle-shaped device at a temperature of 155°C. The obtained foam had good surface properties, and no abnormal cells such as voids were observed. When the density and closed cell properties of the foam were measured, both showed good values. The results are shown in the table below. Example 2 A foam having good foamability was obtained in the same manner as in Example 1, except that the mold temperature during extrusion foam molding was 150°C. The closed cell ratio of the obtained foam was higher than that of Example 1. The results are shown in the table below. Example 3 A foam having good foamability was obtained in the same manner as in Example 1, except that the mold temperature during extrusion foam molding was 145°C. The closed cell ratio of the obtained foam was higher than that of Examples 1 and 2. The results are shown in the table below. Comparative Example 1 Propylene homopolymer was used without using a partially crosslinked propylene-ethylene block copolymer.
Extrusion foam molding was carried out in the same manner as in Example 1 except that the amount was 100 parts by weight. The obtained foam was thin due to gas leakage, and large cavities were observed. The closed cell ratio was extremely low. The results are shown in the table below. Comparative Example 2 A propylene homopolymer was produced without using a partially crosslinked propylene-ethylene block copolymer.
Extrusion foam molding was carried out in the same manner as in Example 2 except that the amount was 100 parts by weight. In the obtained foam, abnormal cells were observed in some places, and the closed cell property was also extremely low. The results are shown in the table below. Comparison row 3 Propylene homopolymer without partially crosslinked propylene-ethylene block copolymer
Extrusion foam molding was carried out in the same manner as in Example 1 except that the amount was 100 parts by weight and the mold temperature was 147°C. The appearance of the obtained foam was almost good, but the closed cell ratio was at a low level. The results are shown in the table below. Comparative Example 4 Using propylene homopolymer without using partially crosslinked propylene-ethylene block copolymer
Extrusion foam molding was carried out in the same manner as in Example 3 except that the amount was 100 parts by weight. The surface of the obtained foam lacked smoothness, and the closed cell ratio was considerably inferior to that of Example 3. The results are shown in the table below. Example 4 A partially crosslinked propylene-ethylene block copolymer having an MI of 1.3 g/10 min. and a gel fraction of 0% was obtained in the same manner as in Example 1 except that DCP was 0.06 parts by weight, and then Example 1 Extrusion foam molding was carried out in the same manner as above to obtain a foam having good foamability. The results are shown in the table below. Example 5 A partially crosslinked propylene-ethylene block copolymer having an MI of 0.3 g/10 min. and a gel fraction of 35% was obtained in the same manner as in Example 1 except that DGM was 0.6 parts by weight, and then Example 1 Extrusion foam molding was carried out in the same manner as above to obtain a foam having good foamability. The results are shown in the table below. Example 6 Extrusion foam molding was carried out in the same manner as in Example 1 except that 10 parts by weight of the partially crosslinked propylene-ethylene block copolymer and 90 parts by weight of the propylene homopolymer were used to obtain a foam having good foamability. Ta. The results are shown in the table below. Example 7 Extrusion foam molding was carried out in the same manner as in Example 1 except that 50 parts by weight of the partially crosslinked propylene-ethylene block copolymer and 50 parts by weight of the propylene homopolymer were used to obtain a foam having good foamability. Ta. The results are shown in the table below. Example 8 As a propylene homopolymer, MI is 1.5g/
Extrusion foam molding was carried out in the same manner as in Example 1 except that a foam having a min. The results are shown in the table below. In Examples 4 to 8, the mold temperature during extrusion foam molding was appropriately set at a temperature that gave the best appearance and increased the closed cell ratio.

[Table] (Effects of the Invention) According to the production method of the present invention, a polypropylene resin foam that is stable and rich in closed-cell properties can be obtained in a wide extrusion temperature range. Therefore, there is no need for strict temperature control as in the conventional case. The resulting foams have excellent heat resistance, thermal stability, non-water absorption and elasticity, and these foams can be obtained at extremely low cost.

Claims (1)

[Claims] 1 (1) A step of melt-mixing a composition containing a polypropylene resin, an organic peroxide, and an oxime compound to obtain a partially crosslinked polypropylene resin; (2) the partially crosslinked polypropylene resin. 5% by weight
a step of supplying a polypropylene resin mixed composition containing at least 50% by weight and a volatile foaming agent to an extruder to obtain a uniform molten mixture, and (3) transferring the molten mixture from the extruder to a low pressure zone. A method for producing a polypropylene resin foam, which includes a step of foaming while extruding the foam.