CA1133177A

CA1133177A - Adhesive composition and process for bonding

Info

Publication number: CA1133177A
Application number: CA309,188A
Authority: CA
Inventors: Pallavoor R. Lakshmanan
Original assignee: Gulf Oil Corp
Current assignee: Gulf Oil Corp
Priority date: 1977-11-03
Filing date: 1978-08-11
Publication date: 1982-10-05
Also published as: JPS5472239A; DK489878A; JPS6247223B2; IT7829367A0; AU3905178A; US4167433A; DE2861082D1; EP0001878B1; FI782990A; EP0001878A3; IT1101286B; EP0001878A2; NO783547L

Abstract

ADHESIVE COMPOSITION AND PROCESS FOR BONDING
(Case B) Abstract of the Disclosure An adhesive composition effective in bonding low-energy plastic surfaces to each other which provides improved low tempera-ture performance containing the following components: (1) a first ethylene-vinyl ester copolymer having from about 4 to about 35 weight percent of a vinyl ester; (2) a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester; (3) a tackifier selected from the following group (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene-phenolic resin and (e) a rosin-modified phenolic resin;
and (4) a polyethylene wax having a molecular weight of about 600 to about 3000 and a process for bonding low-energy plastic surfaces to each other.

Description

* * *
BACKGROUND OF THE INVENTION

1. Field of the-Invention -- ~, _ .
The present invention is useful in bonding low-eneryy plastic surfaces to each other, for example, in construetion, ~automotive applications, plastic fabricating, packaging, structural foam bonding, etc. The adhesive composition described herein is effective in bonding low-energy plastic surfaces to each other which provides an improved low.temperature performance containing the following components: (l) a first ethylene-vinyl ester copolymer having from about 4 to about 35 weight percent of a vinyl ester, (2) a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester;
(3) a tackifier selected from the following group (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene~phenolic ' resin and (e) a rosin-modified phenolic resin, and (4) a ~33~77 polyeth.ylene w.ax having a molecular we~yht o~ about 600 to about 30Q0 and a process ~or ~onding lo~-~energy plastic surfaces to each other.

2~ De:scripti.:on o~ the Prior ~rt Ordinarily, adhesive bonding of low-energy plastic sur~aces to each other requires some form of surface treatment prior to application oX an adhesive to obtain high bond strengths between the surfaces so contacted. Low~energy plastic surfaces bbnde.d to each.other ~thout prior sur~ace treatment, such as by lQ relatively weak, tacky adhes:i~es, are inadequate for many purposes sucfi as those requiring strengths ~n a range in excess of several hundreds or th.ousands of pounds per square inch gauge of bonded area.
For strong bonds involving :Low-energy plastic surfaces, some form of surface treatment or etching is required prior to application of an adhesive. Surface pretreatment of low-energy plastic sur~aces, for example, involves either acid etching with sulfuric, nitric, chromic acids or mixtures thereof, or flame treatment, corona discharge treatment, treatment with plasma jets or low and high energy radiation.
Adhesive compositions which.may be used for bonding low-energy plastic surfaces, but requiring surface treatment, include polysulfide-rubber modified epoxies, epoxy-polyamides, nitrile-phenolics and polyesters. These compositions, may additionally, require long hours of post-cure and/ox clamping at temperatures substantially higher than room temperature.
Often at least two of the components of these adhesive composi-tions must be premixed prior to application.
Consequently, a need exists for an adhesi~e composi-tion and much simplier process for bonding low-energy plastic ` - v 33~L7~

surfaces to each other for low temperature performance. In accordance with the present invention a novel hot melt adhesive composition is provided which requires minlmal heating of the surfaces to be bonded together and maxlmum bond strength is obtained in a matter of minutes or a few hours without resort to elaborate post-curing procedures. Further, the adhesive composition of the present invention can be applied in its melt form to low-energy plastic surfaces in such a manner to provide rapid assembly of components and immediate handling of the assembled parts. Another advantage of the present invention is that the bonds can deliver improved tensile lap shear strengths at low temperature.
Applicant is unaware of any prior art relevant to the invention defined and claimed herein.
SUMMARY OF THE IN~'EN~ION
, I have discovered a unique adhesive composition effective in bonding low-energy plastic surfaces to each other which provides improved low temperature performance which comprises:
(1) a first ethylene-vinyl ester copolymer having fxom about 4 to about 35 weight percent of a vinyl ester; (2) a second ethylene-vinyl ester copolymer having an excess o,f 35 weight percent of a vinyl ester; (3) a tac~ifier selected from the group consisting of (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene-phenolic resin and (e) a rosin-modified phenolic resin;

and (4) a polyethylene wax haYin~ a~olecula,r we~ht o~ ~bout 6QQ to ~x~t 3QOQ, and at 25C, haYmg a penetration in the ~an~ Qf 0~25 to 1,5 an2 a 2en$~t~ ~n the range of 0.93 to O.97.
Further I have discovered a process for bonding low-energy plastic surfaces having a critical surface tension of about 24 to about 37 dynes per centimeter to each other which comprises~

(A) heating said surfaces that will be bonded to each other to ~ -3-7~

a temperature of at least about 50C., (B) applying an adhesive composition effective in bonding low-energy plastic suraces to each other which provides improved low temperature performance, said adhesive composition comprising (l) a first ethylene-vinyl ester copolymer having from about 4 to about 35 weight percent of a vinyl ester; (2) a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester; (3) a tackifier selected from the group consisting of (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene-phenolic resin and (e) a rosin-modified phenolic resin;
and (~l a p~olyethylene wa~ ~Y~n~ a~olecu~a~ ~e~ht Qf a~out 60Øto about 3QQQ~
a penetrat~on.at 25C in t~e ran~e of 0.25 to 1.5 an~ a ~.ens~tv At 25C in the ran~e of 0.93 to 0;97, to at least one of said surfaces and wherein said adhesive ~osttion ~s ~n ~ t~nperature ranse of about 140 to about 240C. at the time of application and then (C) bringing said surfaces in contact with each other.
DESCRIPTION OF THE INVE:NTION
The adhesive composition of the present invention contains two specific ethylene-vinyl ester copolymers, having varying vinyl acetate contents, a tackifier, and a specific polyethylene waxO
First Ethylene-Vinyl Ester Copo~mer Ethylene-vinyl ester copolymers that can be used herein include vinyl esters having from 2 to 4 carbon atoms. Examples of suitable ethylene~ :
vinyl ester copolymers are ethylene-vinyl acetate, ethylene-vinyl formate, ethylene-vinyl propionate, ethylene-vinyl butyrate and mixtures thereof. The first copolymer can contain from about 4 to about 35 weight percent, preferably about 6 to about 28 weight percent, of a vinyl ester, and can have a rnelt index as measured by ASTM 1238-52T of about 0.5 to about 200, preferably 2.0 to about 100. These copolymers can be prepared by any method generally employed in the art, for exarnple, preparation such as ~ -4-~3~

-that tau~ht in U.S. Patents Nos. 2,200,429 to peXxin et al and 2,7Q3,794 to RoedeO In the present invention blends, or mixtures, of et~ylene-vinyl ester copolymers are sometimes used to obtain a melt index ~ith.in the desired range. For example, if blends or mixtures o~ ethylene~vinyl ester copolymers are emplo~edf individual ethylene-vinyl ester copolymers can be used even if th.ey do not have the mel~ index defined above, provided the resultin~ m~xture has a melt index ~ithin the defined range.

. .
S'econd E:th:~len'e:~Vinyl:Es'te:r'Copolym'er Ethylene-~ ._ lQ vlnyl ester copolymers that can be used in this portion of the ~nventi.on here.in include vinyl esters having ~rom 2 to 4 carbon atoms. Examples of suita~le eth~lene-vinyl ester copolymers are eth~lene-vinyl acetate, ethylene-vinyl formate, ethylene-vinyl propionate, eth~lene-vinyl butyrate and mixtures thereof.
The second copolymer can contain in exce.ss of 3S wei~ht percent of a vin~l ester, prefexablY about 36 to about 48, and most pre~erably a~.out 38 to about 45 weight percent of a vinyl ester.
A preferred copolymer used in the experiments herein contained 40 weight percent of a vinyl ester. Ethylene-vinyl copo].ymers 2Q employed in th.is portion o~ the invention can have a melt index as measured by AST~ 1238-52T of ~out 0.5 to about 200, preferably 2.Q to about 100. These copolymers can be prepared by any method generally employed in the art, for example, preparation such as that taught in U.S. Patents Nos. 2,200,429 to Perrin et al and 2,703,794 to Roedel.
Tacki'~iers As contemplated in the present invention suitable tackifiers can be selected from the group consisting of (a) a rosin, (b) a rosin ester, l.c~ a terpene resin, (d) a terpene-phenolic resin and (e) a rosin-modified phenolic resin.
Tackifiers wh~ch are present in the adh.esive composition serve ~,! .~.~

~33~L~7~
to extend the adhesive properties o~ the eth~lene-vinyl estex copolymers. Tackifiers ~or use ~n the present in~ention have a softening po;nt in the range of a~out 4a to about 15Q C., prefera~ly about 65 to about 135C. Small amounts of tacki-fiers ~aving a softening point of less than 40 C., or higher than 150C. can ~e mixed or blended ~ith tackifïers in the de-s~red ran~e to gi~e desira~le results; however, tackifier hlends having a tack~er ~th a softening point o~ less than 40a C. or hi~her than 15QC. are not prefexred in the invention a5 set foxth. Examples of rosins and rosin esters in the hot melt system include both natural and modified rosins, such as for example, gum rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, disproportionated rosin and polymerized rosin; glycerine and pentaerythritol e-sters of rosin, including stablized~ hydrogenated, polymerized, disproportionated, dimerized and unmodified rosin. Terpene resins, sometimes called polyterpene resins, result fxom poly-merization of terpene hydrocarbons, such as bicyclic monoter-pene known as pinene, in the presence of a Friedel Crafts cat-alyst at moderately low temperatures. Terpene resins effectivefor the adhesive composition have a softening point as measured by ASTM E28-58T of from about 40 to about 135C. Another example of a suitable terpene resin is a polymerized beta-pinene.
Terpene-phenolic resins can include, for example, the product resulting from the condensation of bicyclic terpene, in an acidic medium and/ or texpene alcohol with phenol. Rosinmodified phenolic resins can include, for example, the reaction products of rosin with phenol-formaldehyde condensate. Rosin and rosin esters can be prepared, for example, according to the methods described in Encyclo'p'edia of'P'o1Vmer'S'cl'ence'and Technology, Interscience Publishers, a Division of John ~iley & Sons ~' ~3 7~

~Ne~ York: 1964), Volume 12, pp. 139-164; terpene resins can be prepared, for example, according to the methods described in Volume 13, pp. 575-596 of the same publication. Terpene phenolic-resins and rosin-modified phenolic resins can be prepared, for example, according to the methods described in .

Organic Coating'Techh'ology, H. F. Payne, 3Ohn Wiley & Sons (Ne~ York: 1954~, Volume 1, pp. 183~184 and 168-170, respectively.
.. .. . ..
Polye't~y~lene~ax ~ polyethylene wax is employed to reduce the melt viscosity o~ the hot melt adhesive composition without apprec~a~ly decreasing the adhesive bonding. Suitable polyethylene ~axes in the present invention have an average molecular we~ght of about 600 to about 3Q00, preferably about ~Q0 to about 25QQ, and most preferably about 90Q to about 2000.
Polyet~ylene ~axes useful ln the present invention are essentially linear, that is, at least 70 percent of the molecules are linear or paraffinic; preferably at least 90 percent are linear. The n-paraffin or n-alkane content of hydrocarbon eaxes can be determined by molecular sieve adsorption or by urea adduction.
The penetration or hardness of the wax at 25C~ is about 0.25 to about 1.5, perferably about ~.7S to about l.Q0 as determined by ASTM-D 1321~ The density at 25C. of the polyethylene wax em-ployed in the present invention is about 0.93 to about 0.97, preferably about 0.94 to about 0.96. Each of the enumerated parameters are interrelated as is readily apparent to one of ordinary skill in the art. Polyethylene waxes can be obtained, for example, by the low pressure polymerization of ethylene using Ziegler catalysts.
If de~ired, other components ~enerall~ added to an adhesive composition for a particular purpose can also be present in an amount of about 0.1 to about 5, preferably about .j~
..,~,~, 7~

0.2 to about 2, weight percent based on the weight of the final compositon. An example of such an additive is an antioxidant such as butylated h~droxy toluene~
For purpose o~ the present invention a low-energy surface ~s defined as one which has a critical surface tension (yc~ of between about 24 to about 37 dynes/cm (mN/m). For example, polyethylene ran~es from about 25.5 to about 36 dynes/cm, and polypropylene ran~es from about 24 to about 34 dynes/cm.
In general, the adhesive composition defined and claimed herein can ha~e the following components in the following amounts as set ~orth in Table 1.

. ~
Table 1: Adhesi~e Composition Broad Range,Preferred Range, wt ~ wt%
First Ethylene-Vinyl Ester Copolymer 10 to 40 20 to 40 Second Ethylene-Vinyl Ester Copolymer 5 to 15 5 to 15 Tackifier 25 to 45 25 to 40 Polyethylene Wax5 to 55 5 to 50 . . __ _~ . __ . _ The adhesive composition can be prepared in any conventional manner. Thus, for example, a preferred procedure involves the use o~ a so-called melt mixing techni~ue in which the wax ~diluent), together with an antioxidant, if used~ is maintained in a stirred molten $tate at a temperature between about 13Q to about 230C., preferably between about 140 to about 170C., during which time the tackifier is added, followed by the addition of the ethylene-vinyl ester copolymers. ~ixing is continued until a ho~ogeneous mixture is obtained, approximately after about 15 minutes to about 4 hour$.

~ !L33~7 The adhesi~e compos,ition o~ the present inVention is used to bond low~energy surfaces having a critical sur~ace tension o~ about 24 to about 37 dynes pex centimetex to each other. The proces$ in~ol~es heating said surfaces which are to be bonded to each'other to a temperature of at least about 50C., preferabl~ about 6Q to about 130C. r followed by an application of the adhesive composition o~ the present invention, while the adhes~ve ~5 in a temperature range o~ about 14Q to about 240C., preferabl~ about 16a to about 22QC. to at least one of the suxfaces. Then saLd sur~aces are brought in contact with each other. After assembly the bond reache$ maximum tensile strength in a matter o~ minutes or few hours. Mo post-curing is required and therefore, rapid assembly and handling of assembled parts is possible.
By low temperature as used hexein is meant temperatuxes of about lQC. and lower, that is, temperatures ranging from about lQ to about -3QaC., preferably from about 0 to about -25C., most preferably from about Q to about ~2QC.
DE$CR~PTION OF PREFERRED EMBODl'MENTS
2Q The invention will be ~urt~er described with reference to the exper~mental data.
The' adhesive compositions in the present invention were prepared as follows: A polyeth~lene wax, in an amount sufficient to make a 2Ql-gram batch o~ adhe~ive, was mixed with an antioxidant, butylated hydroxy toluene. The wax-antioxidant mixture was placed in a jacketed 4Q0-ml capacity Brabender Plast~corder and kept hot by an oil bath heated to approximately 145 to about 155C. At a slow, 5Q rpm blade settin~, the wax-antioxidant mixtuXe was melted and then the tacki~iex was added 3Q while mixing continued. Continued mixing produced a fluid wax-antioxidant-tacki~ier mixture. Ethylene-vinyl ester copolymers ~9 _ ,,j,.

~3~3~7~7 were added to the fluid wax antioxidant-tackifier mixture in the order of high melt index copolymer followed b~ low melt index copolymer. Mixing was cont~nued at a top speed setting of the ~lades at approximately 150 rRm for approximately 10 to about 15 minutes until homogeneity occurred, and then the speed was decreased to 100 rpm and the compositlon ~as mixed for approximately 5 minutes. On completion of mixing, the torque generally le~eled-off and the adhesive composition ~as ready to be poured. Total m~xing time was about 15 to about 20 minutes~
Low energy-plastic test specimens were prepared in accordance with the follo~ing procedure. Test strips having a dimens;~on of 1 x 3 x 1~8 in. (2.54 x 7.5 x a. 31 cml or 1 x 3 x

3/16 in. (2.54x 7.5 x Q.47 cm) were used in the preparation of tensile lap shear strength test specimens. The strips werè clean-ed with acetone rinse and wiped dry. The test strips (two for each test spec~men~ were then exposed to an in~rared lamp to heat the surface areas to be bonded to between about 90 to about 95C.
~olten adhesive at temperatures bet~een about 176 to about 190C.
was applied as a 1/8 in. (0.31 cm) bead over a square inch (6.45 cm ) area on one of the test strips. A lap shear strength specimen was prepared immediately following application of the adhesive composition by quickly placing another strip over the adhesive with the heated side o~ the strip on the adhesive to provide a square inch (6.45 cm2) lap. Manual pressure was used to spread the adhesive over the bonded area. A 5Q0 -gram weight was then placed on the bonded area and left for about 5 minutes, to maintain contact of the surfaces during initial coolin~, after which it was removed~ The specimen was cooled to 23C. and excess adhesive was removed. The specimen was stored o~ernight ~3~

prior to testing. At least two specimens w~re p~epared for each evaluation and the values reported as an average of the two ~or a given test run.
T~e method used ~or testing the adhesiYe bond strength was the tensile lap shear method with modifications as described in U.S. Patent wa~ 3,393,175 at columns 2 through 3. The values for lap shear ~ere measured by determining on an Instron the force required to ~reak the bond. As a-modification employed herein, the rate of extension was 2 inches (5 cm~ per minute.
lQ The force divided ~y the area of the bond gives the lap shear in pounds per square inch.
Several xuns ~ere carried out using the adhesive compositions set foxth in the upper portion of Table 2 to demonstrate improved tens~le lap shear strength at low temperatures. It can be seen that the addition of a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester in Run No. 2 resulted in an improved tensile lap shear strength at low temperatures. In fact, note that the tensile lap shear strength greatly increased up to a temperature of -10C. Although the tensile lap shear strength decreased at a temperature of -30C., it was still higher than the same adhesive ~ut w~thout the second ethylene-vinyl acetate copolymer.

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3~'7~7 Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An adhesive composition effective in bonding low-energyplastic surfaces to each other which provides low temper-atrue performance which comprises: (1) a first ethylene-vinyl ester copolymer having from about 4 to about 35 weight percent of a vinyl ester; (2) a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester; (3) a tackifier selected from the group consisting of (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene-phenolic resin and (e) a rosin-modified phenolic resin and (4) a polyethylene wax having a molecular weight of about 600 to about 3000 and at 25°C having a penetration in the range of 0.25 to 1.5 and a density in the range of 0.93 to 0.97.

2. An adhesive composition according to claim 1 wherein said first and second ethylene-vinyl ester copolymers are sel-ected from the group consisting of ethylene-vinyl acetate, ethylene-vinyl formate, ethylene-vinyl propionate, ethylene-vinyl butyrate, and mixtures thereof.

3. An adhesive composition according to claim 1 wherein said first copolymer contains from about 6 to about 28 weight percent of a vinyl ester.

4. An adhesive composition according to claim 1 wherein said first and second copolymers have a melt index of about 0.5 to about 200 as measured by ASTM 1238-52T.

5. An adhesive composition according to claim 1 wherein said first and second copolymers have a melt index of about 2.0 to about 100.

6. An adhesive composition according to claim 1 whrein said second ethylene vinyl ester copolymer contains from about 36 to about 48 weight percent of a vinyl ester.

7. An adhesive composition according to claim 1 wherein said second ethylene-vinyl ester copolymer contains from about 38 to about 45 weight percent of a vinyl ester.

8. An adhesive composition according to claim 1 wherein said second copolymer contains about 40 weight percent of a vinyl ester.

9. An adhesive composition according to claim 1 wherein said tackifier has a softening point of about 40 to about 150°C.

10. An adhesive composition according to claim 1 wherein said tackifier has a softening point of about 65 to about 135°C.

11. An adhesive composition according to claim 1 wherein said rosin is selected from the group consisting of gum rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, and polymerized rosin.

12. An adhesive composition according to claim 1 wherein said rosin ester is selected from the group consisting of glycerine and pentaerythritol esters of stabilized, hydrogenated, polymerized, disproportionated, dimerized and unmodified rosin.

13. An adhesive composition according to claim 1 wherein said terpene resin is selected from the group consisting of polyterpene and polymerized beta-pinene resins.

14. An adhesive composition according to claim 1 wherein said terpene-phenolic resin is the condensation product of phenol with terpene alcohol or alpha-terpinene.

15. An adhesive composition according to claim 1 wherein said tackifier is a rosin-modified phenolic resin.

16. An adhesive composition according to claim 1 wherein said polyethylene wax has a molecular weight of about 600 to about 2500.

17. An adhesive composition according to claim 1 wherein said polyethylene wax has a molecular weight of about 900 to about 2000.

18. An adhesive composition according to claim 1 wherein said polyethylene wax is composed of at least 70 percent linear molecules.

19. An adhesive composition according to claim 1 wherein said polyethylene wax is composed of at least 90 percent linear molecules.

20. An adhesive composition according to claim 1 wherein said polyethylene wax has a penetration as measured by ASTM-D 1321 of about 0.25 to about 1.5 at 25°C.

21. An adhesive composition according to claim 1 herein said polyethylene wax has a penetration of about 0.75 to about 1.00 at 25°C.

22. An adhesive composition according to claim 1 wherein said polyethylene wax has a density at 25°C. of about 0.93 to about 0.97.

23. An adhesive composition according to claim 1 wherein said polyethylene wax has a density of about 0.94 to about 0.96.

24. An adhesive composition according to claim 1 wherein said first ethylene-vinyl ester copolymer is about 10 to about 40 weight percent; said second copolymer is about 5 to about 15 weight percent; said tackifier is about 25 to about 45 weight percent; and siad polyethylene wax is about 5 to about 55 weight percent of the total composition.

25. An adhesive composition according to claim 1 wherein said first ethylene-vinyl ester copolymer is about 20 to about 40 weight percent; said second copolymer is about 5 to 15 weight percent; said tackifier is about 25 to about 40 weight percent; and said polyethylene wax is about 5 to about 50 weight percent of the total composition.

26. A process for bonding low-energy plastic surfaces having a critical surface tension of about 24 to about 37 dynes per centimeter to each other which comprises: (A) heating said surfaces that will be bonded to each other to a temperature of at least about 50°C., (B) applying an adhesive composition effective in bonding low-energy plastic surfaces to each other which provides improved low temperature performance, said adhesive composition comprising (1) a first ethylene-vinyl ester copolymer having from about 4 to about 35 weight percent of a vinyl ester; (2) a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester;
(3) a tackifier selected from the group consisting of (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene phenolic-resin and (e) a rosin-modified phenolic resin; and (4) a polyethylene wax having a molecular weight of about 600 to about 3000, a penetration at 25°C in the range of 0.25 to 1.5 and a density at 25°C in the range of 0.93 to 0.97, to at least one of said surfaces and wherein said adhesive composition is in a temperature range of about 140 to about 240°C. at the time of application and (C) then bringing said surfaces in contact with each other.

27. A process according to claim 22 wherein said heating of said surfaces that will be bonded to each other is to a temperature of about 60 to about 130°C.

28. A process according to claim 22 wherein said low-energy plastic surface is polyethylene.

290 A process according to claim 22 wherein said low-energy plastic surface is polypropylene.

30. A process according to claim 22 wherein said adhesive composition is in a temperature range of about 160 to about 220°C at the time of application.