JPS6128533A - Improvement of adhesiveness of polyolefin - Google Patents

Abstract

PURPOSE:To obtain a polyolefin having good workability at room temperatures and a sufficient adhesive force and being excellent in water resistance and high- temperature properties, by coating the surface of a polyolefin with a specified primer. CONSTITUTION:A polyalkylene glycol (e.g., polypropylene glycol) of a MW of 400-2,000 is reacted with diphenylmethane diisocyanate at an NCO/OH ratio >=1.2 in the presence of a urethane formation catalyst to obtain a primer comprising an isocyanato group-terminated urethane prepolymer. Next, the surface of a polyolefin surface-treated with flame, corona electric discharge or a bicromate/sulfuric acid mixture of a polyolefin containing 5-50wt%. at least one member selected from among vinyl acetate, (meth)acrylate esters, maleate esters, fumarate esters, and unsaturated alcohols is coated with the above primer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the adhesion of polyolefins. For more details, apply polyurethane resin, epoxy resin, etc. to the surface of polyolefin,
This method improves the adhesion of polyolefins during molding.

In recent years, polyolefin resins such as polyethylene and polypropylene have come to be used in large quantities in steel structures for purposes such as corrosion prevention and base protection.

Polyolefin resin has excellent water resistance such as water absorption and moisture permeability, and also has better corrosion resistance than other resins. However, it has poor adhesion to other resins or the same resin, making it difficult to repair scratches or unpainted areas. For these repairs, methods have been developed in which the same material is pasted by heat fusion, but this method is not only unsatisfactory, but also causes damage to the adhesive surface due to the difference in thermal expansion coefficient between the melting polyethylene and the base material. The coating film peels off. Conventional adhesives for polyolefins include hot-melt and reactive adhesives. The former hot-melt type has the advantage of instantaneous adhesive strength and good adhesive workability by cooling the adhesive surface, but on the other hand, the adhesive strength at high temperatures is extremely low due to its viscoelastic properties; Since the adhesive must be melted before application, it has the disadvantage of poor application workability. Although reactive adhesives do not have the same initial adhesive strength as hot melt adhesives, the adhesive strength does not decrease much at high temperatures, and the adhesive can be applied at room temperature.

In addition, there are emulsion-type and solution-type adhesives, but both have the drawback that adhesive strength cannot be obtained unless water or solvent evaporates, and that the adhesive strength is relatively weak.

The repair of polyolefin for coating steel structures not only requires high adhesive strength and good workability at room temperature, but also the adhesive strength decreases even if it is immersed in water for a long time or exposed to high temperatures. Therefore, it is difficult to achieve sufficient adhesion, good workability, and long-term durability with conventional polyolefin adhesives.

The present inventors have focused on the above points and have provided a method for adhering polyolefins that has good workability and sufficient adhesive strength at room temperature, and has excellent water resistance and high-temperature properties.

That is, (1) By applying a primer made of a urethane prepolymer containing an isocyanate group at the end obtained from a polyalkylene glycol having a molecular weight of 400 to 2,000 and an excess of diphenylmethane diisocyanate to the surface of the polyolefin resin, Method for improving adhesion (2) Method (1) above in which the surface of the polyolefin is treated with flame, corona discharge, or a dichromate/sulfuric acid mixture (3) When the polyolefin is vinyl acetate, acrylic ester or/and 5-50% methacrylic acid ester
This is the method of (1) above.

Polyalkylene glycol (hereinafter referred to as P) used in the present invention
Abbreviated as AG. ) is a compound with a molecular weight of 400 to 2,000 obtained by addition polymerizing an alkylene oxide such as propylene oxide or ethylene oxide to a compound containing two or more hydroxyl groups using an alkali hydroxide or the like as a catalyst.
, preferably a compound having a molecular weight of 600 to 15,000 and having a hydroxyl group at the end. Compounds containing two or more hydroxyl groups include ethylene glycol,! , 2-propylene glycol, 1,3-propanediol, 1°4-butanediol, 1,6-hexanediol, hydroquinone, bisphenol A, diethylene glycol, dipropylene glycol, glycerin, trimethylolpropane and the like.

If the molecular weight of FAG is less than 400, the reaction-cured primer will not have flexibility, and cracks will occur on the adhesive surface, which is likely to cause poor adhesion.If the molecular weight is more than 2,000, the strength of the adhesive will be weak and it will not be sufficient. Adhesive strength cannot be obtained.

In order to obtain stable and strong adhesive force, it is preferable to use FAG with a molecular weight of 800 to 1,500.

Diphenylmethane diisocyanate (hereinafter abbreviated as MDI) used in the prepolymer is pure MD1. coarse MI)
It is commercially available in the form of I, liquid MDI, etc., and excellent adhesive strength can be obtained no matter which MDI is used. Other incyanates such as tolylene diisocyanate (TDI) and hexamethylene diisocyanate (CHMDI) cannot provide sufficient adhesive strength. The cause of this is M.D.
This is presumed to be because I has better reactivity when made into a prepolymer than other isocyanates, and because the urethane groups derived from MDI have a higher cohesive force than those of other incyanates.

When preparing a prepolymer, the equivalent ratio of incyanate groups to hydroxyl groups of PAG must be such that incyanate groups are in excess. Specifically, it is preferably NGOloH-1, 2 or higher. If NC010H is 1.0 or more and less than 1.2, the viscosity of the prepolymer becomes too high and cannot be coated. If the viscosity of the prepolymer is higher than NC010H-1,2, high adhesive strength can be obtained even if a solvent is added to adjust the viscosity to a level that makes it easy to apply. Solvents added to the prepolymer include aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate,
These include chlorinated hydrocarbons such as methylene chloride and trichloroethane.

The present invention's one-component brimer is a one-component type, and when applied to the adhesive surface of polyolene, moisture in the air reacts with the isocyanate groups in the prepolymer and cures, so it has a pot life similar to a two-component resin. It is not subject to any restrictions and has excellent workability. If it is desired to increase the curing speed, it can be accelerated by adding a urethanization catalyst to the prepolymer. As a urethanization catalyst, triethylamine,
Triethylenediamine, dimethylethanolamine, N
, N, N', N'-tetramethylethylenediamine,
Tertiary amines such as N-methylmorpholine, organic tin compounds such as dibutyltin dilaurate, dibutyltin diacetate, stannath octate, etc. can be used.

The polyolefins used in the present invention are monopolymers or copolymers of ethylene, propylene, butene, butadiene, etc., and copolymers of the above monomers and ethylenically unsaturated monomers.

Since polyolefins will not adhere if no polar groups are present on the adhesive surface, it is necessary to introduce polar groups into the adhesive surface.

The methods include (1) treating the surface of the polyolefin, (2) copolymerizing an olefin with an ethylenically unsaturated monomer having a polar group, and (3) mixing the polyolefin with a polymer having a polar group.

The following methods can be used to treat the surface of polyolefin.

(1) Flame treatment A method of partially oxidizing the surface of polyolefin by exposing the surface of polyolefin to flame for a short period of time. In the case of flame treatment, oxygen radicals, hydroxyl radicals, etc. in the flame react on the surface of polyolefin. and carbonyl group,
Adhesion is improved due to the introduction of hydroxyl groups, hydrogen peroxide groups, etc. As for the treatment time, it is preferable that the flame is applied to the surface of the polyolefin for a time of 1 second or less.

If too much flame is applied, the polyolefin may melt and become deformed due to the heat, or the surface may deteriorate, resulting in poor adhesion. This is the simplest and most practical surface treatment method.

(2) Method using corona discharge In this method, oxygen radicals, ozone, etc. generated by corona discharge react on the surface of polyolefin to introduce polar groups. When the polyolefin film is thin, flame treatment causes deformation of the film due to the influence of heat, which is inconvenient, so it is preferable to perform the treatment by corona discharge treatment.

(3) Treatment with a dichromate/sulfuric acid mixture. Dichromates such as potassium dichromate and sodium dichromate generate active oxygen during the process of converting into chromate in the sulfuric acid mixture. When the polyolefin is brought into contact with this mixture, the surface of the polyolefin is oxidized. Large polyolefin-coated objects such as steel structures cannot be immersed in the mixed solution and must be applied to the surface of the polyolefin.In this case, since repelling occurs on the surface of the polyolefin, add Aerosil etc. to the mixed solution. It is possible to prevent splashing. .

Since dichromate is hexavalent chromium, care must be taken when using it.

As a method of modifying polyolefin itself, a method of copolymerizing an ethylenically unsaturated monomer having a polar group and an olefin is known. Ethylenically unsaturated monomers with polar groups include (1) vinyl acetate (2) acrylic esters such as methyl acrylate and ethyl acrylate (3) methacrylic esters such as methyl methacrylate and ethyl methacrylate (4) ] Maleic acid esters such as dimethyl maleate (5) fumaric acid esters such as dimethyl fumarate (6) unsaturated alcohols such as allyl alcohol, etc. can be used.
By copolymerizing with an olefin monomer so as to contain 5 to 50% by weight of polyolefin, polar groups can be introduced into the polyolefin itself, thereby improving adhesiveness. Generally, a copolymer with vinyl acetate is often used.

Furthermore, even when a polymer of polyolefin and the above-mentioned ethylenically unsaturated heptamer having a polar group is mixed in such a manner that the content of the ethylenically unsaturated hetamine having a polar group is 5 to 50% by weight, the adhesive properties are still low. Improvements are visible.

Possible methods for applying the brimer to the surface of the polyolefin include spray coating, /\ke coating, suction coating, roll coating, and the like. When applying or molding urethane resin after applying the brimer, if the urethane resin is not applied after the brimer is dry to the touch, it will be difficult for moisture to penetrate to the brimer surface and the curing of the brimer will be delayed.

As described above, a method for improving the adhesiveness of polyolefins with excellent workability and adhesiveness could be obtained.

This will be explained in detail below using examples. Note that parts and percentages in Examples and Comparative Examples are based on weight.

Examples and Comparative Examples Predetermined amounts of polyalkylene gellicol and polyisocyanate were weighed into a resin flask with an internal capacity of 80 to 100.
The reaction was carried out at °C until a predetermined amount of free NGO was reached. If the viscosity of the prepolymer was high, a solvent was added to lower the viscosity = the resulting prepolymer was applied thinly to flame-treated low-density polyethylene or ethylene/vinyl acetate copolymer, and after drying it was made into a two-component type. Polyurethane paint (MacF 1e
x105, manufactured by Daiichi Kogyo Seiyaku ■) was applied and cured at room temperature for 7 days. The adhesive strength was determined by measuring the T-peel strength using an autograph tensile tester at a tensile speed of 50 s+layer/min.

The results are shown in the table below.

Ta. As a comparative example, a test was conducted using a polyurethane adhesive.

The adhesive strength is T peel strength (kg/25mm).

Example 6 The sample of Example 1 was immersed in distilled water at 80° C. for 23 days, and changes in adhesive strength were observed. Adhesive strength is 8.4 kg/2
5 intestines (■), and no significant decrease in adhesive strength was observed.

Patent applicant Dai-Kogyo Seiyaku Co., Ltd. Procedural amendment November 12, 1980

Claims (3)

[Claims] (1) Improving the adhesion of polyolefin by applying a primer consisting of a urethane prepolymer containing terminal isocyanate groups obtained from polyalkylene glycol with a molecular weight of 400 to 2,000 and excess diphenylmethane diisocyanate to the surface of polyolefin. how to. (2) The method according to claim (1), wherein the surface of the polyolefin is treated with flame, corona discharge, or a dichromate/sulfuric acid mixture. (3) Claim (1) wherein the polyolefin contains 5 to 50% by weight of at least one of vinyl acetate, acrylic ester, methacrylic ester, maleic ester, fumaric ester, and unsaturated alcohol. Method.