JPH0211617B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for surface modification of non-polar plastic films or sheets such as polyethylene and polypropylene. Adding polarity to the surface of non-polar films or sheets is useful in improving adhesiveness, oil resistance, and the like. Conventionally, methods have been used for this purpose, such as oxidizing the surface of polyethylene films or sheets by electrical discharge or oxidizing them with chemicals, but such oxidation methods deteriorate the underlying film or sheet. There was a drawback. Another method was to react a compound with a polar group on one side of the film or sheet, but it lacked chemical bonding properties with the substrate and was easily peeled off, making it difficult to fully demonstrate its performance. It was hard. The present invention aims to provide a surface modification method different from the above-mentioned conventional methods, and its gist is that a non-polar plastic film or sheet such as polyethylene or polypropylene has a polar group on at least one surface. By applying a composition comprising a monomer containing a mixture of dialkyl peroxides and/or peroxyketals and diacyl peroxides and/or peroxyesters as a polymerization initiator, and then heating and polymerizing the composition, A method for surface modification of plastic films or sheets, characterized in that a layer having a polar group having a thickness of 1 μm or less is provided on at least one surface of the film or sheet. That is, in this invention, a monomer having a polar group is applied to the surface of a film or sheet, and the monomer is thermally polymerized using a specific polymerization initiator, thereby forming a polar group that is chemically strongly bonded to the surface. With this method, there is no need to worry about deteriorating the underlying film or sheet, and since the bonding strength between the polymer layer and the underlying material is high, the polymer layer will not peel off during handling. It won't cause any problems if it falls off. Therefore, the film or sheet whose surface has been modified by the method of this invention can take advantage of the feature that the inside is non-polar, and the excellent properties imparted by the polar groups introduced to the surface. It can also take advantage of properties such as adhesiveness and oil resistance, and can be used extremely effectively in various applications that require these properties. Furthermore, by providing a polymer layer only on one side, it is possible to obtain a film or sheet in which one side is non-polar and the other side is polar, and thereby the front and back sides of the film have completely different properties. It can also be used as a sheet, such as a highly adhesive release film or a film that is both water repellent and hydrophilic. Typical non-polar plastic films or sheets applicable to this invention include polyolefins such as polyethylene and polypropylene;
Parameter) is 8 or less, it can be widely applied. Note that the above SP value means a value calculated from the contribution value of the attraction constant of the atomic group proposed by Krevelen. The monomer having a polar group used in this invention may be one having an SP value (same meaning as above) as a homopolymer of 10 or more, and a specific example is a monomer having a hydroxyl group such as hydroxyethyl acrylate. Examples include acrylic esters having a carboxyl group such as acrylic acid and methacrylic acid, and monomers having a nitrile group such as acrylonitrile and methacrylonitrile. As a polymerization initiator to be added to the above monomer,
Mixtures of dialkyl peroxides and/or peroxyketals with diacyl peroxides and/or peroxy esters are used. That is, the latter diacyl peroxides or peroxy esters are very effective as polymerization initiators for the monomers, but
These compounds alone have poor cross-linking properties to films or sheets, and in order to avoid this drawback, the former dialkyl peroxides or peroxyketals are used in combination, thereby improving the bonding properties to films or sheets. and polymerization reactivity. Examples of dialkyl peroxides used here include dicumyl peroxide and t-butylcumyl peroxide, and a representative example of peroxyketals includes bis-t-butylperoxycyclohexane. . Representative examples of diacyl peroxides include dibenzoyl peroxide and dilauroyl peroxide, and examples of peroxyesters include t-butylperoxypivalate. Of course, the present invention is not limited to those exemplified above, and any of the various commercially available peroxides included in each category can be used. The amount of the polymerization initiator used may be in the range of 0.2 to 5.0 parts by weight based on 100 parts by weight of the monomer, and dialkyl peroxides and/or peroxyketals and diacyl peroxides and/or
Alternatively, the ratio of the combination with peroxyesters is preferably such that the weight ratio of the former to the latter is within the range of 1:1 to 1:20. In this invention, a composition containing the above-mentioned monomer having a polar group and a polymerization initiator is coated on at least one surface of the non-polar plastic film or sheet, and then the composition is heated at a temperature depending on the type of polymerization initiator, usually from 60 to 60°C. Polymerization is performed by heating at 180° C. to form a polymer layer having polar groups on the entire surface. The thickness of this layer should be 1 μm or less; if it becomes too thick, the characteristics of the underlying film or sheet will be impaired, which is not preferable. Next, examples of this invention will be described. In the following, parts mean parts by weight. Example 1 A solution prepared by mixing 100 parts of hydroxyethyl acrylate, 0.2 parts of dibenzoyl peroxide, and 1 part of diwalnut peroxide was applied to one side of a 50 μm thick polypropylene film, and heated at 80°C in a nitrogen stream. Thereafter, the mixture was further heated to 160° C. for polymerization to form a 1 μm thick polymer layer on the entire surface. Example 2 On one side of a 100 μm thick polyethylene film,
100 parts of acrylic acid, 0.3 parts of t-butyl peroxypivalate and 2 parts of t-butyl cumyl peroxide.
60 to 60% in carbon dioxide gas.
The mixture was heated to 80°C and then further heated to 90°C for polymerization to form a 0.5 μm thick polymer layer on the entire surface. Example 3 A mixture of 100 parts of methacrylonitrile, 0.3 parts of dilauroyl peroxide, and 2 parts of dicumyl peroxide was coated on one side of a butyl rubber sheet with a thickness of 500 μm, and a mixture of 60 to 80 parts of dicumyl peroxide was applied in a nitrogen stream.
C. and then further heated to 170.degree. C. for polymerization to form a 1.0 .mu.m thick polymer layer on the entire surface. Example 4 100 parts of methacrylic acid and 0.5 parts of dibenzoyl peroxide were applied to one side of polyethylene with a thickness of 100 μm.
and bis-t-butylperoxycyclohexane
A mixture of 1.0 part and 1.0 parts was applied and heated at 80°C and then further heated to 110°C to polymerize, forming a 0.5 μm thick polymer layer on the entire surface. The modified surface of each film or sheet modified by the above method was adhered to a steel plate using a neoprene adhesive, and the adhesive strength (Kg/25 mm width) was measured at 20°C. The results are shown in the table below. It was exactly as expected.
In the table, A indicates the results of each example, and B indicates the results without treatment.

[Table] As is clear from the above table, it can be seen that the modification method of the present invention can greatly improve the adhesive strength between a non-polar plastic film and an adherend.

Claims (1)

[Claims] 1. On at least one surface of a non-polar plastic film or sheet such as polyethylene or polypropylene, dialkyl peroxides and/or peroxyketals and diacyl peroxides and/or peroxy esters are added to a monomer having a polar group as a polymerization initiator. A plastic film characterized in that a layer having a polar group having a thickness of 1 μm or less is provided on at least one surface of the above film or sheet by applying a composition containing a mixture of the above films or sheets and then heating and polymerizing the composition. Or surface modification method for sheets.