JPH02269128A - Thermoforming of polypropylene sheet - Google Patents

Abstract

PURPOSE:To improve sagging of polypropylene sheet during thermoforming by melting, extruding and molding a composition containing PP resin, inorganic filler, bismaleimide and lubricant in a specific ratio but not an organic peroxide and thermoforming. CONSTITUTION:A PP resin composition which does not contain a substantially effective amount of organic peroxide and comprises (A) 80-20 pts.wt. PP resin, (B) 20-80 pts.wt. inorganic filler (e.g. talc or sllica), (C) 0.05-3 pts.wt. (based on PP resin) bismaleimlde [e.g. N,N'-(methylene-di-p-phenylene)bismaleimide] and (D) 0.1-1 pt.wt. (based on PP resin) lubricant (e.g. stearic acid or stearyl alcohol) is melted, extruded and molded to give a sheet, which is thermoformed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of molding a polypropylene resin composition by a so-called thermoforming method of vacuum and pressure molding.

Conventionally, polystyrene sheets, polyvinyl chloride sheets, and the like have been widely used as thermoplastic resin sheets for aged molds, but these do not have sufficient heat resistance, oil resistance, and acid resistance as packaging materials. On the other hand, although polypropylene sheets have excellent heat resistance, oil resistance, and acid resistance, they have the disadvantage that they tend to sag during thermoforming. At present, it is not normally used because it causes a significant drop and causes wrinkles in the resulting product, and there is a danger that the sheet may come into contact with the heater in an electric pigeon coop and cause a fire.

Techniques for improving the sagging of polypropylene sheets during thermoforming include a general method of blending a polypropylene resin with a polyethylene resin, and a method of using a composition made by blending an inorganic filler and a maleic anhydride-modified polyolefin with a polyolefin ( Japanese Patent Publication No. 5L-69553)
, a method using a composition formed by blending an inorganic filler and a silane-modified polyolefin with a polyolefin (JP-A-5
2-15542), etc., but all of them had insufficient effects.

On the other hand, as a method for producing a polypropylene foam having high elasticity, 0.00% per 100 parts by weight of amorphous polypropylene is used.
A method of producing a foam by mixing 4 parts by weight of an organic peroxide such as dicumyl peroxide, 5 to 3 parts by weight of a bismaleimide such as N+N'-m-phenylene bismaleimide, and a foaming agent and heating the mixture is also particularly applicable. Although it is known from Japanese Publication No. 47-14027, even if this method is adopted without using a blowing agent, a polypropylene sheet with improved sagging during thermoforming cannot be obtained.

On the other hand, methods for improving rigidity by adding various inorganic fillers to polypropylene are disclosed, for example, in JP-A-4739150.
It is described in Japanese Patent Application Laid-Open No. 48-45540.

In the method of JP-A-47-39150, a composition consisting of polypropylene, a bismaleimide compound, and glass fiber is
The method of JP-A-48-45540 discloses a composition consisting of polypropylene, mica, and a bismaleimide compound, but these were obtained by adding a bismaleimide compound to polypropylene with an inorganic filler. The purpose is to improve the mechanical properties of polypropylene resin compositions, and to solve the difficult technical problem of improving sag during secondary processing of maturing sheets as in the present invention. It is not stated,
When a sheet is manufactured from a composition consisting of polypropylene and an inorganic filler, and the resulting sheet is vacuum-formed or pressure-formed, the resulting product may be wrinkled due to sagging during ripening, as in the case without the inorganic filler described above. At present, it is not normally used because there is a risk of the sheet contacting the heater and causing a fire in extreme cases.

Furthermore, when inorganic fillers are added, in addition to the above-mentioned sagging problem, the smoothness of the products obtained by vacuum forming or pressure forming is poor, making it impossible to obtain products with good appearance and commercial value. There was a point.

In view of the above-mentioned circumstances, the present inventors conducted intensive studies with the aim of providing a polypropylene sheet containing an inorganic filler that has significantly improved sagging during thermoforming. (1) Polypropylene resin 80-20 Parts by weight, (2)
Inorganic filler 20-841 parts, (3) bismaleimide 0.05-3 based on polypropylene resin
By heat exchange molding a sheet obtained by melt extrusion molding a polypropylene resin composition containing 0.1 to 1 part by weight of agent based on the weight of the polypropylene resin, no sagging occurs during heat molding, and We have discovered a method for forming product grooves with good smoothness, and have arrived at the present invention.

In the present invention, only 0.05 to 3 parts by weight of bismaleimide is added to the polypropylene resin without adding a substantially effective amount of organic peroxide. The polypropylene sheet of the present invention can be obtained by melt-extrusion molding a resin composition that does not contain substances that lower the molecular weight of polypropylene resin during processing at high temperatures of 200°C to 300°C, such as organotin compounds. Especially necessary.

The polypropylene resin used in the present invention is not only a polypropylene homopolymer but also a polypropylene homopolymer.
Ethylene block or random copolymers can be used as well.

The bismaleimide compound used in the present invention is a compound having the general formula (where R is aromatic or aliphatic)
For example, N, N'-(methylene-di-P-phenylene) bisfrey, N, N-m-phenylene) bismaleimide, N, N'-hexamethylene bismaleimide, N, N'- (oxy-di-p-phenylene)bismaleimide, N,N'-(methylene-di-3-methyl-P-phenylene)bismaleimide, and the like.

Further, the amount of bismaleimide added to 100 parts by weight of the polypropylene resin in the present invention is in the range of 0.05 to 3 parts by weight, more preferably 0.1 to 1 part by weight, 0.0
If it is less than 5 parts by weight, the effect of improving sagging will not be sufficient, and if it is added more than 3 parts by weight, the melt index of the resin composition will be abnormally lowered, making it difficult to extrude the sheet, which is not preferable. .

In the present invention, the inorganic fillers used are talc, silica, calcium carbonate, barium sulfate, and other known inorganic fillers added to powdered polypropylene. It can be placed.

Furthermore, in the present invention, polyolefin 1001i18fl
A lubricant is added in an amount of 0.1 to 1 part by weight.

As lubricants, (1) saturated or unsaturated higher fatty acids with an abnormal number of carbon atoms of 12, such as stearic acid, myristic acid, arachidic acid, etc., (2) 12 carbon atoms! (3) Esters derived from (1) or (2) above, such as ethyl stearate, butyl stearate, etc. (4) +1 above
1 fatty acid, Li, Mg, Ca, Zn, ^11
1 selected from Pd, Cr, Mn, Sn, Fe
(5) partial esters of fatty acids and polyhydric alcohols, stearic acid monoglyceride, oleic acid monoglyceride, and the like.

In the present invention, the resin composition that does not substantially contain an effective amount of organic peroxide refers to the effective amount of organic peroxide disclosed in Japanese Patent Publication No. 47-14027, that is, 0.41
! According to the findings of the present inventors, the effect of the method of the present invention is significantly inhibited even by an amount of organic peroxide of about 0.1 part by weight, for example. be.

In carrying out the present invention, bismaleimide is usually added to polypropylene resin by adding the compound together with additives for polypropylene resin such as an antioxidant and a hydrochloric acid catcher, and after premixing with a Henschel mixer etc., an extruder is used. This is carried out, for example, by pelletizing the resin at a temperature of 210 to 270°C. Further, the inorganic filler may be added in any of the above steps.

Sheeting using this resin composition is carried out by melt extrusion molding using an extruder, for example, at a resin temperature of 210 to 270°C, in the same way as sheeting of ordinary polypropylene resins.

The sheet thus obtained is subjected to thermoforming such as vacuum forming and pressure forming. In thermoforming, the sheet is clamped and heated to 150 to 170°C from the top, bottom, or top using an infrared heater or ceramic heater, and then the sheet is vacuumed from the mold or compressed from the opposite side of the mold. However, compared to ordinary polypropylene sheets, the sheet according to the present invention sags significantly less when heated, making it easier to ripen, and the surface of the thermoformed product is smooth and extremely beautiful. You can get

Compared to conventional polypropylene sheets, the polypropylene sheet with improved sag in the aged form of the present invention has less sagging during the aged form, so the resulting product does not have wrinkles and can be molded well. can get. In particular, good products can be obtained for large molded products such as refrigerator door banks as well as polystyrene sheets and polyvinyl chloride sheets.

The present invention will be explained in more detail with reference to Examples below.

Examples 1-2 and Comparative Examples 1-2 N, N''-( Methylene-P-phenylene) bismaleimide 31 [Iell and 0.5 Il part of calcium stearate were mixed, mixed well in a Henschel mixer, and pelletized at a resin temperature of 240°C using an extruder with a screw diameter of 3ON. After drying the pellets at 100°C for 3 hours in a Dryhofbar, the pellets were melt-extruded at a resin temperature of 250°C using an extruder with a screw diameter of 4ON to produce a sheet with a thickness of 0.5 mm and a width of 300 U.The sheet was 270 x 270 nm. Cut into inner diameter 2
After fixing in a frame of 50 x 250 m, the upper and lower surfaces of the sheet were heated with an infrared heater at an ambient temperature of 210° C., and the tension time from when the sheet was stretched until it sagged was measured. In this case, the longer the sheet tensioning time, the better the ripening formability. The results are shown in Table 1.

Claims (1)

[Scope of Claims] Does not contain a substantially effective amount of organic peroxide and is based on (1) 80 to 20 parts by weight of polypropylene resin, (2) 20 to 80 parts by weight of inorganic filler, and (3) bismaleimide polypropylene resin. Te 0.
05 to 3 parts by weight (4) A molding method characterized by hot air molding a sheet obtained by melt extrusion molding a polypropylene resin composition containing 0.1 to 1 part by weight based on the lubricant polypropylene resin. .