There are a few types of plastic cement, according to the active ingredient:
Methyl ethyl ketone (MEK):
Testors (both liquid red tube)
Plastruct PlasticWeld (a mix of MEK and dichloromethane, see below)
Pros: slower acting than dichloromethane, so gives better repositioning time
Cons: Slower setting and cure time means the joint takes longer to set to handling or full strength, doesn't penetrate plastic as aggressively, so bonds can sometimes be superficial, high toxicity, works on a narrower range of plastics.
Special notes: The most toxic of the three in terms of chemistry. Produces strong smelling fumes. Also sold as a paint stripper/degreaser in some hardware stores, which will be cheaper by volume than the wee hobby repackaged bottles. It's literally the exact same stuff, so if you favor MEK liquid cement, ignore the hobby brands and buy the hardware store stuff instead.
Dichloromethane, AKA methylene chloride (DCM)Tenax
Ambroid ProWeld
Weld-On 4
PlasticWeld
Possibly Mr. Cement C, though no MSDS has been released as yet, and I've never handled the stuff myself
Pros: extremely fast acting and fast setting, aggressive penetration so bonds are almost always very solid.
Cons: highly volatile (i.e. evaporates lightning fast), aggressive solvent action can easily marr or damage parts if applied liberally, and you can/will lose a notable percentage of a bottle just to evaporation in the course of a bottle's lifetime.
Special notes: chemically less toxic than MEK, but high volatility means it produces a much larger volume of fumes in a shorter time frame, so in large amounts can actually be more dangerous (though we're talking much larger amounts than hobby glue use). Like MEK, is sold as a stripper/degrease in some hardware stores, though sales for stripping purposes specifically are banned in some areas (such as the EU) do to contractors killing themselves by hotboxing themselves with the fumes (doing mind bogglingly stupid things like trying to strip enamel bathtubs in-situ
)
LimoneneAnything labeled "non toxic"
Testors green tube, Testors non-toxic liquid
Pros: Non-toxic and therefore best for small children, low aggressiveness makes it ideal for tiny/thin parts that would be damaged by MEK or DCM.
Cons: slow acting, poor penetration, weak bond strength.
Butyl acetateTamiya cements (actually a mix of butyl acetate and acetone)
Can't really say much about this, as to my knowledge only Tamiya uses it, and I've never had the opportunity to try it myself, so I don't know how it handles. From reading about it, it seems to fall towards the "non toxic" end of things (safe, though not completely non toxic like limonene), although Tamiya cement should not be considered non toxic because it includes acetone, which is toxic.
Personal opinions:After using trying/using most of these over the last 20 years or so, I'm solidly a big DCM fan. The stuff just plain always works, and always works fast, and always produces a good bond. The aggressiveness actually can be a tool, as you can selectively overload a joint and squish it to fill/eliminate gaps. For normal applications, in which you apply it sparingly via capillary action, the aggressiveness doesn't make it dangerous, it just makes the bond more secure.
Pro-weld is IMO slightly better than Tenax due to some additives, but is impossible to get anymore. Tenax is going that way too, and to be honest, is just straight DCM with no additives, so you might as well just get a larger bottle of pure DCM instead of hunting for Tenax: it'll be cheaper and easier to source. I recently got some Weld-On 4, which is the workhorse for professional plastics fabricators, and discovered it's their favorite for a reason. It's got some additives that make it even more aggressive and cure even faster than straight DCM, but without raising its volatility. Takes a light touch to use, but it produces VERY solid bonds VERY fast.
MEK IMO is very "meh". It was my go-to before I discovered Tenax and Pro-Weld, but I've now been spoiled by DCM's superior adhesion, turnaround time, and range of applicable plastics that I'll never go back to the stuff. It's crap now in my eyes.
Limonene I never use. I'd recommend it to people with inquisitive small children, and maybe for extra delicate parts like tiny antennas. I've gotten good enough at applying DCM with a spotter brush that I don't really need that functionality though.
Haven't tried the Tamiya stuff, so can't comment on Butyl acetate.
Some old geezer like to use lacquer thinner or acetone as liquid cement. They'd definitely work, but probably only somewhere between limonene and MEK in terms of aggressiveness and bond strength, I'd guess. In any case, they'd be more toxic, on the level of MEK or worse. Probably only worth it if you're the sort who gets more satisfaction out of feeling clever/resourceful than from the quality of your work.
Plastruct PlasticWeld is rubbish IMO. It has some dissolved monomer/polymer in it that creates a slick of weakened plastic inside the join, making the join less secure. It also means that excess will marr surfaces worse than pure solvents, as it leaves a blob of it's own plastic deposited on the surface instead of just leaving a minor matt spot. I've been told the adhesion weirdness is deliberate, as Plastuct's stuff was originally formulated for architectural modelling, where models would be broken down and materials reused after a project. Anyone who's worked with Plastruct brand plastic stock knows it doesn't take glue/paint right either, so this explanation seems consistent.
Similarly I've found that Testors red tube cement doesn't produce bonds as strong as pure solvent due to the large amount of dissolved plastic that makes it thick. That dissolved plastic is actually pretty brittle by itself when it dries, so bonds don't actually benefit from it, only positionability. If you need a that goopyness or working time, you can just overload one or both surfaces with liquid solvent before pressing them together (instead of capillary wicking with the parts already touching), and that'll get you the same effect, but with better bond strength and a shorter time between setting and curing. This is one of the things Weld-On 4 is REALLY good at, which is why I've come to really like it in the short time I've been using it. Weld-On 4 is very versatile, acting like Tenax with capillary bonds, and Testors red tube with overloaded bonds, but with better adhesion and turnaround time than either. An overloaded Tenax bond sets in 5 minutes or so and has to sit overnight to reach full strength, Testors red tube sets in hours, and has to be left overnight to reach full strength. Overloaded Weld-On 4 sets in a minute, and reaches full strength in less than half an hour. Enough time for careful positioning, but not so much it puts the project on hold.
There's also Mr. Color's Mr. Cement line, another Japanese brand which is relatively new in the west. Haven't tried it myself, and the company reportedly refuses to make their MSDS public. Heard good things, but refusal to publish an MSDS is a massive red flag IMO.
26 February 2013, 08:24:35 AM
