CA1287322C

CA1287322C - Coating and irradiating reaction product of prepolymer and antistatic quaternary ammonium salt

Info

Publication number: CA1287322C
Application number: CA000474993A
Authority: CA
Inventors: Allen Henry Keough
Original assignee: Metallized Products Inc
Current assignee: Metallized Products Inc
Priority date: 1984-03-12
Filing date: 1985-02-22
Publication date: 1991-08-06
Anticipated expiration: 2008-08-06
Also published as: FR2560887A1; GB8506095D0; NO850944L; MY101967A; SE8501190L; GB2156362A; JPH0461009B2; JPS60221414A; GB2156362B; DE3508804A1; KR930005678B1; KR850006441A; SE466349B; SE8501190D0

Abstract

ABSTRACT OF THE DISCLOSURE
An antistatic resin composition which is the electron radiation cured reaction product of an electron radiation curable prepolymer, preferably an acrylated epoxy oligomer, and an electron radiation reactive antistatic agent soluble in the prepolymer, preferably a saturated quaternary ammonium compound. An antistatic laminate is made by applying a mixture of the prepolymer and antistatic agent to a substrate and then contacting the mixture with electron radiation.

Description

l~o ~ ~,c,~

Back~round of the Invention m is invention relates to resin compositions having antistatic characteristics. ~re particularly, this invention relates to resin cnmpositions co~prising an electron radiation cured product of an electron radiation curable resin precursor and an electron radiation reactive antistatic agent. In other aspects, the present invention relates to a method of making an antistatic resin cGmposition and further to substrate sheets coated therewith. Plastics such as polyethylene, polyprcpylene and the like are poor conduct~rs of electricit~f and have a tendency to develop and retain electrostatic charges which attract and hold dust particles. This kendency can have a detrimental ef~ect on the appearance of the plastic, but is especially detrinental for plastic films which are used as packaging materials for delicate electronic devi oe s, such as floppy discs for computers, or are used for hospital operating room .supplies. For these k~nds of uses f electrostatic charges can have a detrimen~al eff.ect on the function of the plastic material. It is, of course, also well known that the build up of eleetrostatie charges in plastic films leads to handling and other problems in manufacturing or converting prccesses, espeeially where plastie fil~s are transported at high speed.
One method whieh ean be used to reduee the build u.p of statie eleetricity in plasties is to add a nonreaetive antistatie additive, such as a quaternary a~monium compound or earbDn, when compcunding the pl.astie matrix. The additive exudes to the ~uxface of the plastie dhring proeessing and re~lees the build up of static electricity at the "

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surfaoe of the plastic. miS method, however, offers only short term antistatic protection. Ano~her method for reducing static build-up involves providLng a light vac~um metallized film on the pla~tic resin.
mis meth~d, however, suffers from the disadvantage of environmental instability since the metal used to provide the canductivity characteristics is susceptible to attack by isture and or other corrosive oonditions.
Thus, it would be highly desirable to provide a resin composition having a reduced tendency to form static charges both before and after fabrication and to provide antistatic laminations ccmprising the resin co~position. It also wDuld be highly desirable to develop a more permanent method involving copolymerizing or cross-linking an antistatic agent with a resin to provide long lasting antistatic characteristics throughout the resin.
In accordance with the present invention, it has been found that resin compositions h~ving desirable antistatic properties ccan be provided by electron radiation curing a composition compri~ing an electron radiation curable resin precursor and an electron radiation reactive antistatic agent. The antistatic conposition can be used to coat a substrate sheet to provide an antistatic lamination. Further understanding of the present invention will be had from the following disclosure wherein all parts and percentages are by weight unless otherwise indicated.

Summary of the Invention ~ n accordance with the present invention, an antistatic resin oomposition comprises the electron radiation cured reaction product of:
lA) an electron radiation curable prepolymer; and (B) an effective a~ount of an electron radiation reactive antistatic agent soluble in said prepolymer. In accordance with the me~hQd of the present invention, an antistatic resin ~omposition is made by: (A) muxing an . ~ .

~L213~322 electron radiation curable prepolymer and an effective amaunt of an electron radiation reactive antistatic agent to form a mixture thereof;
and (B) contacting said mixture with electron radiation in an amrunt sufficient to cure said mixture. Further in accordance with the present invention the antistatic resin may be provided as an antistatic coating on a substrate, such as a metallized substrate sheet. Preferably the antistatic agent is a quaternary ammoniu~ salt.

escri~tion of the Invention The antistatic resin composition of the present invention broadly co~prises the reaction product of a radiation cur~ble precursor and an effective amount of a radiation reactive antistatic agent. In accordance with the method of the present inventicn, the antistatic resin composition is made by mixing a radiation curable resin precursor and a radiation reactive antistatic ag~nt to provide a mixture thereof.
The reacti~e antistatic agent is employed in an amount which is effective to bbtain the desired antistatic properties. ~he mixture is then oontacted with electron radiation in sufficient amount to cure the mLxture. During radiation curing, the antistatic agent reacts with the radiation curable resin precursor to form a polymerized resin having long lasting antistatic characteristics.
The antistatic resin compositions of the present invention are especially useful as coating materials and in one e~bodiment of the present invention, an antistatic ooating of the present invention is provided on a substrate material such as paper, polyethylene, polypropylene or the like. A preferred embodiment of the present invention comprises a su~strate material having a continuous thin layer of conductive metal such as aluminum deposited thereon and a oontinuous thin layer of the antistAtic resin oomposition of the present invention overcoating the thin la~er of aluminum~

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~IL2~373~2 Radiation curable resin precursors suitable for use herein are commercially available and well known in the art. Generally speaking, the radiation curable precursor comprises a mixture of at least one oligomer and mono and/or multi-functional mDnomerS. Generally speaking, the oligoners constitute the backbone of a radiation curable c~at mg and largely determine the ultimate performance of the finally cured coating.
Mbny oligomers are based on acrylate chemistry because of ease of synthesis and cost. For exa~ple, suitable oligomers include the epoxy-acrylate, polvester-urethane-acrylates, polyether-acrylates, and polyester-acrylates. Acrylated-epoxy resins tend to have gcod adhesion and chemical resistance properties. Acrylated-urethane-polyesters tend to cure to hard, tough, flexible chemica}ly resistant coatings.
Acrylated-polyethers tend to cure to tough, abrasion resistant coatings, and are generally of lower viscosity than pol~rethanes and epoxies.
Arrylated-polyesters tend to have law visoosity and good weather-ability.
Oligomers, however, when used by themselves, may shrink excessively on curing and/or have an unworkable application viscosit~.
mus, monomers and other additives, such as flow control agents, will be generally used in combination with oligomers to provide a ra~iation curable prepolymer. Backbone oligomers can be us~d in conjunction with a wide variety of monomers, both mono- and nLlti-functional :Ct will be appreciated by those skilled in the art that prcper selection of monomers contributes to the final cured coating properties by controlling the cross-link densi~y, hardness, flexibility, cure speed, etc., and, hence, the particular monomers selected will depend upon the .inal coating properties desired. Generally, comhinations of ~ono- and mLlti-functional m~ncmers will be preferred ~o achieve the desired results.
Examples of useful mono-functional nomers include:
n-vinyl-2-pyrollidone, 2~phenoxyethylacrylate, n-isobutoxynethyl-,i 32~
acrylami~e, i~cobornylac~late, 2-ethoxyethoxyethylacrylate, and tetrah~drofurfuI~rlacrylate. N-vinyl-2-pyrollidone is especially useful kecallse of its abrupt viscosity reduction in small a~unts~ and high response to electron baam radiation.
S~itable multi-functional m~ncmers include: 1,6-hexanediol diacrylate, tripropyleneglycoldiacrylate, tri~ethylolpropanetri-acrylate, pentaerythritoltriacrylate, and tetraethyleneglycol-diacrylate.
P~tistatic agents suitable for use herein are antistaticagents whic~ are electron radiation reactive with the radiation curable resin precursor and which are soluble in the resin precursor. It has been foundl that useful agents for use herein are quaternary a~monium salts such as triaIkylalkyletherammonium salts. A preferred salt is a trialkylalk~.ethera~.onium salt wherein each of the trialkyl groups has from 1 to a~out 3 carbon atoms, the alkylether group has an alky] group having frcm about 4 to about 18 carbon atoms, and the ether group is selected from the group consisting of ethylene oxide ~nd propylene o~ide. An exa~ple of a preferred salt is tliethylalkyletherammonium sulfate, csEo~rcially available as Emerstat 6660*frcm Emery Industries.
The antista~ic agent is muxed with the radiation curable resin precursor in an amoun~ effective to obtain the desired antistatic characteristics for the resIn composition upon curing thereof. The exact amourt will vary from ~esin t~ resin, antistatic agent to antistatic agent, and intended use for the resultm g product.
One advantage of the antistatic resin compositions o the present i~venti.on is that they are especially suitable for use as coatings upon substr~tes. Substrates contemplated for use m co~bination ~7ith the ccmpositions of the present invention include w~bs, sheets or films such as paper, glass, polymer coated paper, w wen and n~n-woven sheets of ~arious materials, various polymeric films such as polyethylene film, polypropylene film, polyethvleneterephthalate film, * Trade Mark ~5-.
' lL2l3732;2 polyvinyl chloride film, ionomer resin film and the like, and includemetallized substrates.
Coating of the antistatic compositions of the present invention onto a substrate can be done in any conventional nanner.
Generally speaking, the ooating composition will be applied to the substrate surface in the form of a prepolymer and antistatic agent mixture and then cured in situ by means of electron beam radiation.
Generally speaking the coating need be applied and cured on only one side of the substrate. Both sides of the substrate generally benefit~
in obtaining antistatic characteristics even though the suhstrate has been coated with the antistatic composition on only one side so long as the substrate is not too thick and a sufficient dosage of radiation is employed to cure the coating. miS phenomenon can be observed on substrates of thicknesses at least as great as 10 mils and can be observed not only on polymeric films such ~s polyethy]ene film, polypropylene film, polyethyleneterephthalate fi~m, polyvinyl chloride film, ionomer resin ~ilm and the like, but also on paper, glass and other webs such as can be made from various woven and non-w~ven fibrous materials. Furthermore, these substrates can have a continuous thin layer of conductive metal such as aluminum deposited thereon as hy a conventional vacuum metallizing process and the coating can be applied to the metallized or non-metallized side of the substrate.
e coating can be applied by dip coating, air-knife coating, roll coating, gravure coatin~, reverse gravure coating, extrusion coating, bead coating, curtain coating, use of wire wound coatin~ rods, and so forth. The coating deposited on the subs~rate is effective even as a thin coating having a thickness on the order of from 0.1 to 0.5 mils. Of course, the viscDsity of the coating composition can vary widely depending upon the method of coating which is chosen and the desired end results. Typical viscosity of coatings may ran~e from 50 to about 1000 centipoise.

~L2~73~2 Apparatus and methods for curing of the radiation curable antistatic resin co~position are well kncw~ and any suitable radiation curing process and appa~atus can be used in carrying out this invention.
Suitable apparatus are co~mercially available from Energy &iences, Inc.
of ~burn, ~ssachusetts under thetrade ~ark ~lectrocurtain . EXamples o~ suitable app2ratus are disclosed in U.S. Patents No. 3,702,412, Nove~er 7, 1972 to ~uintal; ~o. 3,769,600, October 30, 1973 to Denholm et al; and No. 3,780,308, December 18, 1973 to Nablo. High energy ionizing radiation such as electron beam radiation should he used in sufficient intensity to penetrate substantially all the way through the coating oGmposition to cure the same. lypically dosaaes in the range of from about 1 to about 6 megarads are e~,ployed. Upon contacting the antistatic resin composition with radiation and sufficient intensity to cure the s~ame, the ccm~osition used in the present invention is sub-stantially cQmpletely converted to a solid product.
In a preferred e~bodiment of the present invention, a continuous ~hin laye~ of conductive metal is sandwiched between a substrate and the antistatic coating of the present invention. Thus, a metal layer can be first applied onto a surface of a substrate and t~en a continuous coating of the antistatic co~position is applied to overcoat the metal layer to provide a lamunate having especially gc~d antist~tic properties. Generally speaking, the antistatic coating ~ill be appiie~ to the metal in the form of an uncured muxture of prepolymer and antistatic agent and then cured m situ on the netallic layer~
Suitable metals include aluminum, copper, gold, silver, ancl t~e like.
lhe metal layer is preferably deposi~ed in a c~n~entional vacuu~
metallizing step. A resin coated paper with metallized layer thereoi especially suit2ble to be overc~ated with an antistatic resin composition of this inv~tion is taught in U~S. Patent 4rl77,310 Dece~ker 4, 1979 to Steeves :'.
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~28~7322 The antistatic resin compositions of the present invention are useful in several T~S of products. For example, the coating may be used as an overcoating for photographic film or as a packaging film for electronic devi oe s, floppy discs for computers, hospital oper~ting rocm supplies, and the like.
T~e present invention is further illustrated by the following ex~ples:

E~D?T,F. I
The following ingredients were muxed with stirring:

InqredientParts by Weight ra~iation curable uret~hane acrylate oligomer based coating ~S-9384*from Raffi and Swanson) 95 parts triethylalkvlet:hera~nonium sulfate (E~erstat 6660*
from Emery Industries~ 5 parts ~ H~r the triethylalkyletherammonium sulfate was completely dissolved, an about 0.3 mil thick coating of the mixture was applied on the al~minum ~acuum metallized side of a sheet of 5 nul thick polyethylene terephthalate film by a no. 4 wire wcund rod. The coating ~as cured by a 2 ~egarad dose of electron beam radiation.

EX~MPLE II
The ~ollowing ingredients were mixed with stirring:
~ Par_ h~ ei~ht radiation curable urethane acrylate oligo~er based coating ~S-9384*from Raffi and Swanson) 90 parts triethylaIkyletheramm~nium sulfate (Emerstat 6660*
fr~n 3~ ry Industries) 10 parts Afte~ the triethylalk~letherammGnium sulfate was cc~pletely dissolved, an about 0.3 mil thick coating was ap;plied on the aluminum * Trade Mark -8-~L~8~3~2 vacuu~ metallized side of a sheet of 5 mil thick polyethylene terephthalate and cured as in Exa~ple I.

. EX~MPLE III
The follcwing ingredients were muxed with st~Lrring:
Inqredient Parts Weight radiation curable urethane acrylate oligom~r based ccating (S-9384*fro~ Raffi and Swanson) 85 parts triethylalhyletherammonium sulfate (Emerstat 6660*
fr~m Emery Industries)15 parts A~ber the triethylalkylethera~monium sulfate was completely dissolved, an about 0.3 mil thick coating was applied an the aluminum vacuum metallized side of a sheet of S mil thick polyethylene terephthalate and cured as ~n Example I.

EX~MPIE IV
A Resistivity half-life test was u~ed to evaluate the products of EXamples I-III. Each product was suspended between t~o pol~s of an electrode. A 100 volt charge was placed on cne of the poles and the ti~e for half of the voltage to discharge was measured. q~,e follc~nng results were obtained:
Product of TLme to Half Discharge Exa~ple I 0.4 Example II 0.1 E~a~ple III 0.3 *Trade Mark ~9-.' , ', - . .
' ~ ' "': ' `

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' ' ' EX~ V
~ radiation curable coating vehicle w~s preFared f.rom triprcpylene glycol diacrylate, 70 parts; a diacrylate este~ prepared ~ro~ the di~lycidyl/ether of bis-phenol A and acrylic acid (Celrad 3600*
Celanese Resins Co.) 15 parts; an acrylate urethane ~ased on an arc~atic i~ocyanate, (CMD 6700* Celanese Resins Co) 14.7 parts; and a silicone ~ype sNrface active agent ~DC-l9~, ~cw-Corning Corp) 0.3 part.
To 85 parts of the above vehicle there was added ~S parts of the triethylAlkvletherammonium sulfate of Exa~ple 1. me resultant clear liquid coating having a viscosity of 120 cps was applied ~y an offset gravure 03ating station just prior to an electI~n beam radiation curing unit. The coating was cured with electron bea~
ra~iation on the follcwing substrates at the coati~g weights shcwn.

-*rrrade Mark -10-Substrate Coat ~. (Ibs./3000 ft2) _ 1 1/4 mil low density polyethlyene 1.6 60 Ib. C2S Paper 5 1/2 mil metallized polyethylene 1.3 (Coating on terephthalate film side) 1/2 mil metallized polyethylene 1.3 (Coating on terephthalate metal side) 1 1/4 mil metallized lcw density 1.6 (Cbating on polyethylene metal side) Resistance measurements made with a megohm meter (General Radio) shcwed that all coated surfaces had antistatic properties with readings in the range of 109 to 101 ohms/sq.
A coupling effect was noted when the antistatic coating was applied over metallized surfaces. Readings on an ohm meter were 1~3-34 ohms/sq. on the coatings on the metal on the metallized 1/2 mil polyethylene tereph~halate, and 150-200 ohms/sq. on the coating on the m~tal on metallized low density polye~hylene.

~2~373;~2 E~A~PLE VI

An antistatic electron beam curable coatin~ was preFared by mixing with stirring the following ingredients:

Inqredient Parts by Weight triprcpylene-glycol diacrylate 58.6 epoxy acrylate oligomer (Celrad 3600*) 12.4 urethane acrylate oligomer (C~6700*,Celanese Specialty Resins) 12.2 ga~a-Methacryloxypropyl-trimethoxysilane 1.3 silicone surface active agent (D~-193*)Dcw Corning) 0.5 triethylalkylether atnm~niunt sulfate (Emerstat 666~,Emery Industries) 15.0 .

Ihe above coating was applied by an offset gravure coat~tg station to a substrate of 1 1~4 mil low density polyethylerte film at a coatirtg weight of 1.6 Ibs./3000 ft2, and ~ured at a speed of 200 ft./mirl. by electron beam radiation at a dose rate of 3 negarads.
The surface resistivity of the coated side of the abcve coat~d polyethylene filnt was measured at 8.75 x 108 ohm/sq. at 100 volts and 6.7 x 108 oh~s/s~. at 300 volts. The surface resitivity of the uncc~tted side o~ the filnt measured 1.2 x 109 ohms/sq~ at 100 volts and 1.0 x 109 ohms/sq. at 300 volts.

*Trade Mark -12-~287;~22 EXAMPLE VII

The antistatic electron beam curable ccating of Example Vl was applied by an offset gravure coating station to the metallized side of 0.5 mil polyester film (polyethylene terephthalate which had beæn vacuum metallized with aluminum) at a coating weight of 1.3 Ibs./3000 ft.2, and cured at a speea of 100 ft./min. wqth electron keam radiation at a dose rate of 3 megarads.
Ihe surface resistivity of the coated side was measured at 2.2 x 105 ohms/sq. at 100 volts and overloaded (too conductive) at 300 volts. The Æ face resistivity of the uncoated side measured 1.3 x 1012 ohms/sq. at 100 volts and 1.6 x 1012 ohms/sq. at 300 volts.

EXPME~E VIII

Example Vl was repeated except that the substrate was 60 Lb.
tper 3300 sq. ft.) clay coated both sides paper. ~le surface resistivity of the coated side was 1.1 x 101 o~ms/ sq. at 100 volts and 1.2 x 101 at 300 volts. The surface resistivity of the unc~ated side measured 3.8 x 101 ohms/sq. at 100 volts and 3.5 x 101 ohms/sq~ at 300 volts.

EXAMPLE IX

Example VI was repeated except that the polyethylene substrate was first metallized hy vacuum deposition of aluminum and the coating was applied over the metal. The surface resistivity of the coated side was measu~ed at 1.5 x 105 ohn~s/sq. at 100 volts and overloaded ~too conductive) at 300 vol s. The surface resistivity of the uncoated side measured 1.9 x 1012 ohms/sq. at 100 volts and 6.2 x 1011 ohms/sq. at 300 volts.

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8732;~
E~E X

Example Vl was repeated except that the substrate was 3 mil lay flat low density polyeth~lene tubing. The outside of the tubing was coated at a weight of approximately 1 Ib./3000 ft.2. The inside of the tubing was found bo have an antistatic surface.

Claims

1. An antistatic laminate comprising:
(A) a substrate; and (B) a continuous coating on said substrate, said continuous coating comprising the electron beam irradiated reaction product of:
(1) an electron beam curable prepolymer; and (2) an effective amount of a saturated quaternary ammonium compound antistatic agent soluble in said prepolymer.

2. The antistatic laminate of claim 1 wherein said quaternary ammonium compound is a trialkylalkyletherammonium salt.

3. The antistatic laminate of claim 2 wherein each of said trialkyl groups has from 1 to about 3 carbon atoms and said alkylether group has an alkyl group having from about 4 to about 18 carbon atoms and said ether group is selected from the group consisting of ethylene oxide and propylene oxide.

4. The antistatic laminate of claim 3 wherein said quaternary ammonium compound is triethylalkyletherammonium sulfate.

5. The antistatic laminate of claim 1 wherein said prepolymer comprises an acrylated epoxy oligomer.

6. The antistatic laminate of claim 1 wherein said prepolymer comprises an acrylated urethane oligomer.

7. The antistatic laminate of claim 1 wherein said substrate is a film comprising polyethylene.

8. The antistatic laminate of claim 1 wherein said substrate is a film comprising polypropylene.

9. The antistatic laminate of claim 1 wherein said substrate is a film comprising polyethylene terephthalate.

10. The antistatic laminate of claim 1 wherein said substrate comprises paper.

11. The antistatic laminate of claim 1 wherein said substrate is a metallized substrate.

12. The antistatic laminate of claim 1 wherein said substrate is a metallized resin coated paper.

13. The method of making an antistatic laminate comprising the steps of:
(A) mixing an electron radiation curable prepolymer and an effective amount of a saturated quaternary ammonium compound antistatic agent soluble in said prepolymer to form a solution thereof;
(B) applying said solution as a continuous coating onto a substrate; and (C) subjecting said coating to electron beam radiation sufficient to cure said coating.

14. The method of making an antistatic laminate of claim 13 wherein said quaternary ammonium compound is a trialkylalkyletherammonium salt.

15. The method of making an antistatic laminate of claim 14 wherein each of said trialkyl groups has from 1 to about 3 carbon atoms and said alkylether group has an alkyl group having from about 4 to about 18 carbon atoms and said ether group is selected from the group consisting of ethylene oxide and propylene oxide.

16. The method of making an antistatic laminate of claim 13 wherein said quaternary ammonium compound is triethylalkyletherammonium sulfate.

17. The method of making an antistatic laminate of claim 13 wherein said prepolymer comprises an acrylated epoxy oligomer.

18. The method of making an antistatic laminate of claim 13 wherein siad prepolymer comprises an acrylated urethane oligomer.

19. The method of making an antistatic laminate of claim 13 wherein said substrate is a film comprising polyethylene.

20. The method of making an antistatic laminate of claim 13 wherein said substrate is a film comprising polypropylene.

21. The method of making an antistatic laminate of claim 13 wherein said substrate is a film comprising polyethylene terephthalate.

22. The method of making an antistatic laminate of claim 13 wherein said substrate comprises paper.

23. The method of making an antistatic laminate of claim 13 wherein said substrate is a metallized substrate.

24. The method of making an antistatic laminate of claim 13 wherein said substrate is a metallized resin coated paper.