PEELABLE PROTECTIVE FILM COMPRISING METHACRYLATE COPOLYMER

Abstract: A peelable protective film molded from a composition comprising 100 parts by weight of a copolymer of ethylene and 5 - 20 wt% of methyl methacrylate copolymer, 0.01 to 0.1 part by weight of an inorganic filler of particle size less than 10 µm (e.g. silica), and 0.01 to 1.0 part by weight of a slip agent, such as an organic amide or ester, especially a fatty acid amide (e.g. oleic acid amide). An antioxidant can also be included. The film, when wrapped around rubbery articles having a tacky surface, exhibits a good adhesion to the substrate but has a low peeling strength and so can be peeled away as required.

Description: The present invention relates to a peelable protective film made from a composition comprising an ethylene/methyl methacrylate copolymer. Peelable protective films are used to protect rubber, metal, plastic, or other articles so that their surfaces are not contaminated, scatched, corroded, or otherwise damaged during their shipment and storage. After they have served their purpose, they can be readily peeled away from the substrate. Peelable protective films of the type described above are conveniently made of polyvinyl- or polyolefin-based polymers such as polyvinyl chloride, high-density polyethylene, low-density polyethylene, polypropylene, and ethylene/vinyl acetate copolymers. Japanese Patent Publication No. 45974/83 describes a polyolefin-based peelable protective film made of an ethylene/1-butene random copolymer. Further, Japanese Patent Publication No. 47993/84 proposes an improved dual layered film formed of a layer of a mixture of an ethylene/ethyl acrylate copolymer and an enthylene/vinyl acetate copolymer and a layer of a polyolefin. The films disclosed in the above-mentioned patents are chiefly intended to protect the surfaces of metal articles, and the property that is principally required of these films is good adhesion to the substrate. When substrates to be protected have tackiness or adhesion, as with rubber articles, there have been proposed methods in which the substrates themselves are coated with antiblocking compositions such as hydrocarbon-based resin compositions or anionic or nonionic surfacants (see Japanese Patent Publications Nos. 10860/76 and 50047/77 and Japanese Patent Application (OPI) No. 78945/77). The term "OPI" means an unexamined published application. However, there have been no reports at all that a film can be used as a protective film which itself has good peelability to such tacky substances. Therefore, one had had to be satisified with use of low-density polyethylene films or other films as a protective film of, e.g., a rubber viel, though they are poor in peelability. US-A-4,394,474 describes extruded films of 100 parts of a copolymer of ethylene and an alpha-beta-ethylenically unsaturated 3-12C alkene, 0.02 - 2 part of an inorganic mineral (e.g., silica) and 0.05 - 1.5 part of a secondary fatty acid amide (e.g., oleyl palmitamide or oleyl erucylamide); the films have reduced block and increased slip characteristics and are used as heat-sealable films for general commercial purposes. There are no suggestions of ethylene/methyl methacrylate copolymers and substrates around which the films may be wrapped. An object of the present invention is to provide a protective film which not only has good adhesion to tacky substances such as rubber articles but also can be readily peeled away from a substrate to be protected. According to the present invention we provide a peelable surface protective film made from a composition comprising 100 parts by weight of an ethylene/methyl methacrylate copolymer having a methyl methacrylate content of from 5 to 20 wt%, from 0.01 to 0.1 part by weight of an inorganic filler, and from 0.01 to 1.0 part by weight of a slip agent. The ethylene/methyl methacrylate copolymer which is used in the present invention can be prepared by radical copolymerization of ethylene and methyl methacrylate in the presence of a free radical-initiator such as an organic peroxide or oxygen. The copolymerization between ethylene and methyl methacrylate is typically carried out at a temperature of from 130 to 300°C and at a pressure of from 490 to 2950 x 10⁵ Pa (500 to 3,000 kg/cm²). The ethylene/methyl methacrylate copolymer used in the present invention has a methyl methacrylate content of from 5 to 20 wt%. If the methyl methacrylate content is less than 5 wt% or exceeds 20 wt%, the resulting film has such strong adhesion to, for example, a block-like butyl rubber, that its peeling strength is high, whereby the peelability is not improved. The ethylene/methyl methacrylate copolymer used in the present invention preferably has a melt flow rate of from 0.1 to 20 g/10 min, more preferbly from 0.5 to 10 g/10 min. Melt flow rate is an important factor for processing a composition into a film. If the melt flow rate of the ethylene/methyl methacrylate copolymer is less than 0.1 g/10 min, the molten composition has such a high viscosity that it imposes an excessive load on the motor for driving an extruder. If the melt flow rate of the ethylene/methyl methacrylate copolymer exceeds 20 g/10 min, the formed film suffers sagging, deteriorates in terms of efficiency of handling, and has a low mechanical strength. A film processed from the copolymer of ethylene and methyl methacrylate can be prepared by any molding methods in which the copolymer is melt extruded through an extruder to form a molten resin in the thin film-like state, which is then solidified by quenching. A preferred method is, however, a blown molding or T-die molding method. The molding temperature is typically within the range of from the melting point of the ethylene/methyl methacrylate copolymer to 300°C and preferably from 120 to 250°C. The protective film of the present invention must contain from 0.01 to 0.1 part by weight of an inorganic filler, particularly a fine particulate inorganic filler having an average particle size of no more than 10 µm, and from 0.01 to 1.0 part by weight of a slip agent based on 100 parts by weight of the ethylene/methyl methacrylate copolymer. Examples of the fine particulate inorganic filler are silica, feldspar, zeolite, talc and kaolinite. Examples of the slip agent are organic amides or esters, with organic amides being preferred. Among them, saturated fatty acid amides and unsaturated fatty acid amides or bis-fatty acid amides are particularly preferable. The slip agent is incorporated into the protective film of the present invention so as to impart good slipperiness to the films to be loaded and packed after being used for wrapping rubber articles or the like, to thereby ensure efficient loading operation and smooth recovery of the articles during unpacking operation. In order to ensure good stability of the composition at the film processing, conventionally employed antioxidants such as 2,6-di-t-butyl-4-hydroxy-toluene, stearyl-β-(3,5-t-butyl-4-hydroxyphenyl)propionate, tetrakis[methylene-3-(3',5'-di-t-butyl-4-hydroxyphenyl)propionate]methane, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene diphosphonite, and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite may be incorporated in the protective film of the present invention. The film processed from the composition of the present invention is used for the surface protection or adhesion prevention of rubber substances. Examples of such rubber substances are vulcanized or unvulcanized products of natural rubbers, synthetic rubbers (e.g., styrene/butadiene rubber, butyl rubber, ethylene/propylene rubber, polybutadiene rubber, isoprene rubber, chloroprene rubber, and nitrile rubber), and mixtures of these rubbers. The film of the present invention comprising an ethylene/methyl methacrylate copolymer has not only an advantage of easy peelability but also an advantage that it can be used in plants manufacturing rubber articles without introducing any modification to the existing packaging facilities. The following Examples and Comparative Examples are provided for the purpose of further illustrating the present invention but are not limiting. EXAMPLE 1 AND COMPARATIVE EXAMPLES 1 to 3 Films were prepared from the following copolymers: Ex. 1 a copolymer of ethylene and methyl methacrylate ("Acryft" CM 2001 of Sumitomo Chemical Company Ltd), incorporating 0.2 part per hundred of fine particulate silica as filler and 0.2 part per hundred of oleic acid amide. Comp. Ex. 1 low density polyethylene ("Sumikethene" F101-1 of Sumitomo Chemical Company Ltd). Comp. Ex. 2 a copolymer of ethylene and vinyl acetate ("Evatate" F1103-1 of Sumitomo Chemical Company Ltd). Comp. Ex. 3 a copolymer of ethylene and ethyl acrylate ("Unicar" EEA 6170 of Nippon Unicor Co., Ltd). Each of these materials was formed into a film of 30 µm in thickness by means of a blown film processing machine (50 mm; made by Modern Machinery Company) at a blow-up ratio of 1.8. The film processing temperatures used are indicated in Table 1. The peelability of the resultant films from a butyl rubber in the block form can be evaluated on the actual products, but may be determined more conveniently by the following method. Peeling Test: (1) Preparation of Butyl Rubber Sample About 60 g of a butyl rubber sample BP-1066 of Japan Butyl Co. is passed several times through a roll kneader (surface temperature: about 150°C) so as to form a tacky rubber sheet having a thickness of about 4 mm. This rubber sheet is sandwiched between polyester films and compressed to a thickness of about 2 mm with a hot press at 150°C. The rubber sheet held between the polyester films is left to cool on a flat table and cut into squares having a length of 15 cm on one side. (2) Bonding of Copolymer Film to Butyl Rubber Sample The polyester film on one side of the butyl rubber sample prepared in step (1) is peeled away, and a resin film to be tested is slightly attached to the same side of the sample. The assembly is compressed by passing through rollers so that no wrinkle or separation between layers takes place. The assembly is then sandwiched between glass layers and held in an oven at 80°C for 2 hours while applying a load of 10 kg. Thereafter, the assembly is taken out of the oven and left to cool. (3) Peeling Test Each sample prepared in (2) is cut into a size of 25 mm W and 150 mm L . The adhesion strength between the rubber sheet and each test resin film is measured with a tensile tester at a tensile speed of 300 mm/min. The results of measurements of peeling strength by the procedures described are shown in Table 1. EXAMPLES 2 TO 6 AND COMPARATIVE EXAMPLE 4 As in Example 1, films were processed from Acryft CK 1004, CM 4005, CM 4006, CM 4001, CM 4004 and CM 5007, each being an ethylene/methyl methacrylate copolymer produced by Sumitomo Chemical Co., Ltd., and subjected to the afore described peeling test. The results are shown in Table 2. Not only CK 1004 but also the other copolymers were modified by incorporating 0.2 pph of silica as the fine particulate organic filler and 0.2 pph of oleic acid amide as the organic amide. Thus, when a peelable protective film of the present invention is wrapped around articles having a tacky surface such as rubber articles, the film exhibits good adhesion to the substrate and has a low peeling strength and, therefore, can be readily peeled away as required.

Claims: A peelable protective film prepared from a composition comprising by weight (i) 100 parts of a copolymer of ethylene and methyl methacrylate having a methyl methacrylate content of from 5 to 20 wt%, (ii) from 0.01 to 0.2 part of an inorganic filler, and (iii) from 0.01 to 1.0 part of a slip agent. A peelable protective film according to Claim 1 wherein said ethylene/methyl methacrylate copolymer has a melt flow rate of from 0.1 to 20 g/10 min. A peelable protective film according to Claim 1 or 2, wherein said slip agent is an organic acid amide or ester. A peelable protective film according to Claim 3, wherein the slip agent is a fatty acid amide. A peelable protective film according to any preceding claim, wherein said filler has an average particle size of no more than 10 µm. A peelable protective film according to any preceding claim, wherein said filler is silica, feldspar, a zeolite, talc or kaolinite. Use of a film as claimed in any one of the preceding claims for wrapping or packing a rubbery substance.

Inventors: EGAMI, YOSHIO, HONMA, TOSHIO, MIYAZAKI, KOHZOH, OOWATARI, YOSHITAKA, YAMADA, KUNIO
Applicants: JAPAN BUTYL COMPANY LIMITED, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1987
Main classification: C08J5
IPC codes: C08K5, C08K3, C08J5, B65D65, C08K13, C08L23