GB2131443A

GB2131443A - Unsaturated polyester resin adhesive for bonding thermoplastics

Info

Publication number: GB2131443A
Application number: GB08322303A
Authority: GB
Inventors: Tetsuo Tajima; Noboru Terunuma; Makoto Kito; Hitoshi Yokono; Noboru Mitsugi; Akira Kageyama
Original assignee: Hitachi Chemical Co Ltd; Hitachi Ltd
Current assignee: Hitachi Ltd; Showa Denko Materials Co ltd
Priority date: 1980-09-26
Filing date: 1983-08-18
Publication date: 1984-06-20
Also published as: GB2085464B; GB2085464A; GB2131443B; GB8322303D0

Abstract

An unsaturated polyester resin adhesive which contains a larger than usual amount i.e. at least 3.5% based on the weight of the resin, of an organic peroxide. This gives good adhesion for thermoplastics and is particularly useful to bring about good adhesion to cases or bobbins of flyback transformers produced by insulation treatment with the unsaturated polyester resin adhesive.

Description

1

SPECIFICATION

Unsaturated polyester resin adhesive for 65 bonding thermoplastics and method for producing flyback transformers Background of the Invention

1. Field of the Invention

This invention relates to unsaturated polyester 70 resin adhesives for bonding thermoplastics and to a method producing flyback transformers (hereinafter shortened as FBT) which comprises insulation treatment of an FBT assembly employing bobbins and a case both of which were 75 formed from a thermoplastic polyester resin, with an unsaturated polyester composition.

2. Brief Description of the PriorArt

Unsaturated polyester resins are generally 80 produced by reacting a polyhydric alcohol such as ethylene glycol, diethylene glycol, propylene glycol, hexamethylene glycol, or neopentyl glycol etc. with polybasic acids composed of an unsaturated dibasic acid such as maleic anhydride or fumaric acid etc., a part of which may be substituted by a saturated dibasic acid such as phthaiic acid or adiplc acid etc., followed by addition of a polymerizable unsaturated monomer such as styrene, vinyltoluene, diallyl phthalate, an acrylic acid ester, or a methacrylic acid ester. The reaction product can be polymerized to be hardened by adding an organic peroxide such as benzoyl peroxide or methyl ethyl ketone peroxide etc. as polymerization catalyst.

These unsaturated polyester resin compositions are widely used as adhesives because they yield no volatile matter during polymerization hardening and are inexpensive.

However, they are disadvantageous in that they 100 exhibit poor adhesive strength when used for bonding thermoplastics so that the range of application thereof is extremely limited.

On the other hand, FBTs used in TV sets are each constructed of components including a primary coil wound devidedly around a plastic bobbin having plural partition walls, a secondary coil wound dividedly around a plastic bobbin analogously to the primary coil with one or more diodes being wired, a plastic case, and condensers. These assembled components are made up through an insulation treatment to a finished F13T.

For this insulating material, unsaturated polyester resin compositions are favorably used, which are rapidly curable, of high productivity, and inexpensive, as compared with silicone resins, epoxy resins, etc. In this case, however, thermoplastic polyester resins such as poly(butylene terephthalate) and poly(ethylene terephthalate) which are almost insoluble in unsaturated polyester resin compositions, are used as the bobbin or case material, and the conventional unsaturated polyester resin compositions are deficient in adhesiveness to these thermoplastic polyester resins, so that the unsaturated polyester resin compositions cast into GB 2 131 443 A 1 FBT cases to insulate the electric parts contained therein is liable to peel from the cases or bobbins by effects of heat cycles and moisture absorption.

Summary of the Invention

The first object of this invention is to provide an unsaturated polyester adhesive for bonding thermoplastics which is free from the disadvantages of the prior art and gives good adhesion for thermoplastics.

The second object of the invention is to provide a method for producing FBTs by insulation treatment with an unsaturated polyester resin composition which is free from the disadvantages of the prior art and gives good adhesion between its hardened composition and the cases or bobbins of FBTs.

As a result of many elaborated studies made on unsaturated polyester resin compositions in order to ach ieve the first object, the present inventors have found that enhancement of the amount ratio of organic perioxide added versus unsaturated polyester resin to a large extent is effective, and that it is important for achieving the second object to use, as the insulating material, an unsaturated polyester composition which contains an organic peroxide and a hardening accelerator in amounts of at least 0.2 and 0.01 part by weight, respectively, per 100 parts by weight of the resin.

That is to say, the unsaturated polyester adhesive for bonding thermoplastics, which is the first object of this invention, is characterized by organic peroxide contents therein being 3.5 parts or more, preferably 3.15-10 parts, by weight per parts by weight of unsaturated polyester resin which is a mixture of polymerization product of polybasic acid and polyhydric alcohol, and polymerizable unsaturated monomer. Such an unsaturated polyester adhesive is free from the disadvantages of the conventional adhesives of analogous types and exhibits an excellent adhesive strength for bonding thermoplastics.

Organic peroxides added to unsaturated polyester adhesives have hitherto been considered as a polymerization catalyst, and accordingly their contents are as low as 0. 1 - 3 parts by weight per parts by weight of unsaturated polyester resin. In contrast, the organic peroxide content in the adhesive of this invention is as high as 3.5 parts by weight or more per 100 parts by weight of unsatured polyester resin. On heating to harden such an organic peroxide-rich unsaturated polyester resin composition, the excess of organic peroxide unconsumed for the hardening reaction presumably oxidizes the surface of thermoplastic resin articles and makes the surface highly adherent, this being a new phenomenon unfound in the prior art, resulting in a remarkably high adhesive strength.

The unsaturated polyester resin composition used for achieving the second object of this invention contains an organic peroxide and a hardening accelerator in amounts of at least 0.2, preferably 3.5-15, parts by weight and at least 0.01, preferably 0.5-7, parts by weight, 2 GB 2 131 443 A 2 respectively, per 100 parts by weight of the resin. The organic peroxide contents higher than 15 parts by weight results in too short pot life, much heat generation during hardening, deterioration of heat- or crackresistance of the hardened products, and high costs.

A marked improvement in the adhesion to the bobbins and cases of thermoplastic saturated resin when FBTs are subjected to insulation treatment with said composition of unsaturated polyester resin is considered to be caused by production of free radicals from the organic peroxide in larger amounts than would be the case with no hardening accelerator, and by oxidation of the surface of bobbins and cases due to these free radicals.

The impregnation of the composition into the coils can be effected by adjusting the amount of hardening accelerator added or adding a polymerization inhibitor, without detracting adhesion characteristics of the composition.

Next, the materials used in this invention are explained.

The unsaturated polyester resin to be used in the invention can be prepared by reacting a polyhydric alcohol with polybasic acids composed of an unsaturated dibasic acid, a part of which may be substituted by a saturated dibasic acid, followed by adding a polymerizable monomer.

The unsaturated dibasic acids usable in this invention are malelc anhydride, maleic acid, fumaric acid, mesaconic acid, tetraconic acid, itaconic acid, chlorinated maleic acid, and dimethyl esters of these acids. They are used separately or in combination.

The saturated dibasic acids usuable in this invention are phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetra hydrophtha lic acid, halogenated phthalic anhydride, succinic acid, adipic acid, and dimethyl esters of these acids. They are also used separately or in combination.

The polyhydric alcohols usable in this invention are ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, hexamethylene glycol, hydrogenated bisphenol A, 2,2di(4hydroxypropoxyphenyi)propane, 2,2-di(4hydroxyethoxyphenyl) propane, ethylene oxide, and propylene oxide. They are also used separately or in combination.

The polymerizable monomers usable in this invention include styrene, vinyltoluene, chlorostyrene, divinylbenzene, p-t-butylstyrene, diallyl phthalate, acrylic acid esters, and methacrylic esters. They are used separately or in combination.

The organic peroxides used in this invention include benzoyl peroxide, methyl ethyl ketone peroxide, t-butyl peroxybenzoate, t-butyl peroxyoctoate, t-butyl peroxy-2-ethyihexanoate, dicumyl peroxide, cumene hydroxyperoxide, and cyclohexanone peroxide. They are used separately or in combination.

The effective hardening accelerators used in this invention include cobalt naphthenate, manganese naphthenate, lithium naphthenate, cobalt octanoate, tin octanoate, solutions of these compounds in solvents, aliphatic amines, and aromatic amines. Further, some additives such as anti-shrinking agents, coupling agents, flame retardants, colorants fillers, etc. may be blended.

Thermoplastics which can be bonded with the adhesive of this invention are polyethylene, poly- (ethylene terephthalate), polypropylene, polybutylene, poly(butylene terephthalate), poly(vinyl chloride), poly(vinyl acetate), poly(vinyl alcohol) poly(vinyl acetal), polytetrafluoroethylene, polyacrylonitrile, polystyrene, polyacetal, polyamide, polycarbonate, ethylene-vinyl acetate copolymer, styreneacrylonitrile copolymer, and styrene- acrylonitrilebutadiene copolymer. Among them, particularly suitable are poly(ethylene terephthalate), poly(butylene terephthalate), poly(vinyl chloride), polystyrene, polycarbonate, and styreneacrylonitrile-butadiene copolymer. These thermoplastics are suited not only when containing no special additive but also when containing some additive such as filler, flame retardant, or colorant.

The adhesive of this invention hardens within 5 minutes to 24 hours at 202001C.

In the method for producing FBTs of this invention, a saturated polyester is usually employed as a material of the bobbin and case. This saturated polyester may also contain filler, flame retardant, or colorant.

Brief Description of the Drawings

Fig. 1 is the graph showing the relation between amounts of benzoyl peroxide added and tensile adhesive strengths on the unsaturated polyester resin compositions of Example 1 and Fig. 2 is the graph showing the relation between amounts of benzoyl peroxide added and gelation time on the same unsaturated polyester resin compositions.

Fig. 3 is the graph showing the relation between amounts of t-butyl peroxy-2- ethylhexanoate added and tensile adhesive strengths on the unsaturated polyester resin composition of Example 2 and Fig. 4 is the graph showing the relation between amounts of t-butyl peroxy-2-ethyihexanoate added and gelation time on the same unsaturated polyester compositions.

Fig. 5 is the graph showing the relation between amounts of benzoyl peroxide added and adhesive strengths under shear on the unsaturated polyester resin compositions of Example 3.

Fig. 6 is the graph showing the relation between amounts of t-butyl peroxy-2ethylhexanoate added and adhesive strengths under shear on the unsaturated polyester resin compositions of Example 4.

Fig. 7 is a sectional view of an FBT, and Figs. 8 and 9 show the resulting adhesive strengths in Examples 5 and 6, respectively.

ji 3 GB 2 131 443 A 3 Detailed Description of the Invention

This invention will be illustrated in more detail 65 by the following examples: In the examples, "part" means part by weight.

EXAMPLE 1

Compositions were prepared each by adding benzoyl peroxide, an organic peroxide, in an amount of 1, 2, 3, 4, 6, 9, 15 or 18 parts to 100 parts of an unsaturated polyester resin composed of 70 parts of an unsaturated alkyd resin obtained by reacting isophthalic acid, propylene glycol, and maleic anhydride and 30 parts of styrene monomer. Then, tensile adhesive strength test pieces (11.3 mm diameter and 1 em' bond area) made from a thermoplastic, poly-(ethylene terephthalate) (WNN-1030, manufactured by Teijin Ltd.), were bonded by using the above unsaturated polyester resin compositions severally. The thermal hardening conditions were 80IC-1 hour plus 1051C-3 hours, for all test pieces.

The tensile adhesive strength change with the varying amount of benzoyl peroxide added is shown by the graph of Fig. 1. As is apparent therefrom, the adhesive strength begins to increase markedly when the organic peroxide content exceeds 3 parts.

Fig. 2 is the graph showing the gelation time change with the varying amount of benzoyl peroxide added. The gelation time was measured by the hot plate method. As can be seen from Fig. 2, the gelation time no longer tends to decrease significantly when the organic peroxide content exceeds 3 parts. This means that the portion of organic peroxide in excess of 3 parts does not effectively act as polymerization catalyst.

EXAM P LE 2 Compositions were prepared each by adding t-butyl peroxy-2-ethyihexanoate, an organic peroxide, in an amount of 1, 2, 3, 4, 6, 9, 15 or 18 parts to 100 parts of an unsaturated polyester resin composed of 60 parts of an unsaturated alkyd resin obtained by reacting terephthalic acid, propylene glycol, and maleic anhydride and 40 parts of styrene monomer. Then, tensile adhesive strength test pieces (the same dimensions as those of Example 1) made from a thermoplastic, polystyrene (Styron 666, manufactured by AsahiDew Company) were bonded by using the above unsaturated polyester resin compositions severally. The thermal hardening conditions were the same as those in Example 1.

The tensile adhesive strength change with the 115 varying amount of tbutyl peroxy-2- ethylhexanoate added is shown by the graph of Fig. 3. As is apparent from Fig. 3, the compositions of organic peroxide contents exceeding 3 parts exhibit markedly increased 120 adhesive strength.

Fig. 4 shows the gelation time change with the varying amount of organic peroxide added. The gelation time was measured by the hot plate method. As can be seen from Fig. 4, the gelation 125 time no longer tends to decrease significantly when the organic peroxide content exceeds 3 parts. This means that the portion of organic peroxide in excess of 3 parts does not effectively act as polymerization catalyst.

EXAMPLE 3

Compositions were prepared each by adding benzoyl peroxide in an amount of 1, 2, 3, 4, 6, 9, 15 or 18 parts to 100 parts of an unsaturated polyester resin composed of 49 parts of a cyclopentadiene-modified unsaturated alkyd resin, 45 parts of styrene monomer, and 6 parts of a polystyrene. Using these compositions, test pieces (100 X 25 X 2 mm and 2. 5 em' bond area) made of a thermoplastic, poly(vinyl chloride) (Geon 103 Ep, manufactured by Nippon Geon Co., Ltd.) were bonded for testing adhesive strength under shear. The thermal hardening conditions were the same as those in Example 1.

The change of adhesive strength under shear with the varying amount of benzoyl peroxide added is shown by the graph of Fig. 5. Therefrom, the same conclusion can be derived as from Figs. 1 and 3.

EXAM P LE 4 Compositions were prepared each by adding t-butyl peroxy-2-ethylhexanoate in an amount of 1, 2, 3, 4, 6, 9, 15 or 18 parts to 100 parts of an unsaturated polyester resin composed of 60 parts of unsaturated alkyd resin obtained by reacting terephthalic acid, diethylene glycol, and maleic anhydride and 40 parts of styrene monomer. Using these compositions severally, test pieces (100 X 25 x 2 mm and 2.5 em' bond area) made of thermoplastic, styrene-acrylonitrile-butadiene copolymer (Styrac 101, manufactured by Asahi- Dew Company) were bonded for testing adhesive strength under shear. The thermal hardening conditions were the same as those in Example 1.

The change of adhesive strength under shear with the varying amount of tbutyl peroxy-2-ethyl- hexanoate added is shown by the graph of Fig. 6. Therefrom, the same conclusion can be derived as from Figs. 1 and 3.

As can be seen from the foregoing illustration, the unsaturated polyester resin compositions of this invention are excellent as an adhesive for bonding thermoplastics, in comparison with conventional unsaturated polyester resin compositions.

EXAMPLE 5

In order to evaluate the adhesiveness between unsaturated polyester resin composition and poly(butylene terephthalate) (Planack ST2030S, manufactured by Dainippon Ink and Chemicals, Inc., was used), tensile adhesive strength was measured on 10 specimens for each sample composition in the following way and the mean values were determined.

An unsaturated polyester compound was prepared by adding, as flame retardants, 40 parts of aluminium hydroxide and 12 parts of red 4 GB 2 131 443 A 4 phosphorous and, as a filler, 70 parts of silica to 65 an unsaturated polyester resin composed of 45 parts of a dicyclopentadiene-modified unsaturated alkyd resin, 49 parts of styrene monomer, and 6 parts of a polystyrene. Sample unsaturated polyester compositions were then prepared by adding benzoyl peroxide in different amounts of 1, 2, 3,4, 5 and 8 parts with or without further adding cobalt naphthenate in amounts of respective one half the amounts of benzoyl peroxide, separately, to each 100 parts of said unsaturated polyester compound. Test pieces (11.3 mm diameter and 1 cm' bond area) made of said poly(butylene terephthalate) were bonded by using the sample unsaturated polyester resin compositions severally. The hardening conditions 80 were 8WC-3 hours plus 1051C-3 hours, in the case of the compositions containing no cobalt naphthenate, and were 201IC-1 5 hours plus 105OC-3 hours, in the case of the compositions containing cobalt naphthenate.

Measured values of tensile adhesive strength were shown in Fig. 8. While the compositions containing no cobalt naphthenate but more than 3.5 parts of benzoyl peroxide exhibit much high tensile adhesive strength as shown by curve 9, the 90 compositions containing cobalt napthenate and more than 3.5 parts of benzoyl peroxide exhibit further high tensile adhesive strength as shown by curve 10.

Secondly, the same compositions were poured each into the case 8 of an FBT of which sectional view shown in Fig. 7 constructed of components including a primary coil 2 wound dividedly around a plastic primary coil bobbin having plural partition walls 3, a secondary coil 4 wound dividedly around a plastic secondary coil bobbin 5 analogously to the primary coil with diodes 6 being wired, plastic case 8, condenser 7 and casting resin 1 which casts abovementioned assembled components, and hardened by heating under the same conditions as the above after the case had been evacuated to 10-20 torr for 10 minutes. FBTs insulation-treated with the compositions in this way were subjected to a heat cycle test of 60 times repetition of cooling to -500C for 2 hours and heating to 1 001C for 2 hours. Results of subsequent running tests and of appearance tests of the dismantled FBTs showed that the compositions containing cobalt naphthenate and 2 PHR or more of benzoyl peroxide caused neither bond disruption between the case or bobbin and the hardened composition nor corona discharge.

EXAMPLE 6

An unsaturated polyester compound was prepared by adding, as flame retardants, 40 parts of aluminium hydroxide and 12 parts of red phosphorous and, as a filler, 70 parts of silica to an unsaturated polyester resin composed of 49 parts of an unsaturated alkyd resin prepared by reacting isophthalic acid, propylene glycol, and maleic anhydride and 51 parts of styrene monomer. Sample unsaturated polyester compositions were then prepared by adding t-butyl peroxy-2-ethyihexanoate in different amounts of 0.5, 1, 2, 3, 4, 5, 6, 8 and 10 parts with or without further adding tin octoate in amounts of 0.5 and 1.0 part, separately to each 100 parts of said polyester compound. Test pieces for tensile adhesive strength (11.3 mm diameter and 1 crn' bond area) made of a poly(ethylene terephthalate) (WNN-1 030, manufactured by Teijin Ltd.) were bonded by using the sample unsaturated polyester compositions severally. The hardening conditions were 80IC-3 hours plus 1051C-3 hours, in the case of the compositions containing no tin octoate, and 20OC-1 5 hours plus 105OC-3 hours, in the case of the -compositions containing tin octoate.

Measured values of tensile adhesive strength were shown in Fig. 9. The compositions containing 0.5 and 1.0 part of tin octoate (curves 11 and 12) exhibit higher adhesive strength than those containing no tin octoate (curve 13).

Then, the same heat cycle tests, running tests, and appearance tests as in Example 5 were conducted by using these unsaturated polyester compositions. The compositions containing tin octoate caused neither bond disruption nor corona discharge.

Claims

1. An unsaturated polyester resin adhesive for bonding thermoplastics, which adhesive contains as essential components an unsaturated polyester resin and at least 3.5 parts by weight of an organic peroxide per 100 parts of the resin.

2. An adhesive according to claim 1, containing

3.5 to 10 parts by weight of organic peroxide per 100 parts by weight of the resin. 100 3. An adhesive according to claim 1 or 2, wherein the organic peroxide is at least one compound selected from benzoyl peroxide, methyl ethyl ketone peroxide, t-butyl peroxybenzoate, t- butyl peroxyoctoate, t-butyl peroxy-2- ethylhexanoate, dicurnyl peroxide, cumene hydroxyperoxide, and cyclohexanone peroxide.

4. An adhesive according to claim 1 substantially as hereinbefore described with reference to any one of the Examples.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1984. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

New claims or amendments to claims filed on 26th January 1984 Superseded claims 1 to 4 New or amended claims:- 1 to 4 as follows 1. An unsaturated polyester resin adhesive for bonding thermoplastics, which adhesive contains as essential components an unsaturated polyester and at least 3.5 parts by weight of an organic peroxide per 100 parts of the unsaturated polyester.

2. An adhesive according to claim 1, containing 3.5 to 10 parts by weight of organic peroxide per 100 parts by weight of the unsaturated polyester.

3. An adhesive according to claim 1 or 2, wherein the organic peroxide is at least one compound selected from benzoyl peroxide, methyl ethyl ketone peroxide, t- butyl peroxybenzoate, 7 GB 2 131 443 A 5 t-butyl peroxyoctoate, t-butyl peroxy-2- ethythexanoate, dicurnyl peroxide, cumene hydroxyperoxide, and cyclohexanone peroxide.