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LF Technology - unique epoxy foil

What is LF Technology?

The LETOXIT® Foil Technology (LF Technology) is our unique patented technology, which allows dry way of laminate production based on the impregnation of reinforcement with LETOXIT® foil resin at increased temperature and pressure.

LF TECHNOLOGY is epoxy resin in the form of flexible foil, which softens at increased temperature and it is able to impregnate originally dry reinforcement and cure in one step.

Prepregs are materials used for years, but they are very expensive and many prepreg types are necessary, if composite structure should be optimised well. RTM is a relatively cheap method, big parts can be manufactured. The main problem is impregnation of the reinforcement. Therefore only special types of the reinforcement have to be used and the result is relatively low reinforcement content in a final composite part. In recent years, technology called RFI – Resin Film infusion appeared. The production cycle is performed usually in the autoclave under increased temperature and pressure, where the fibre infiltration and the composite consolidation occur in a single step process. Typically, the RFI element consists of a thermoset resin film placed between one side of a metal tool and a dry textile fibre preform. Problems with conventional RFI appear if sandwich structures are manufactured; honeycombs are filled with resin and foam prevents from impregnation of the sandwich skin in opposite site of the resin layer.

Concerning these disadvantages of conventional processes and a need of universal low cost technology, 5M s.r.o. developed and patented a very efficient technique of production of sophisticated and relatively cheap composite structures, which is called Letoxit Foil Technology (LF Technology).

During manipulation, production and curing doesnt release any hazard vapours and foil is very friendly to use.

LF Technology allows the application of various types and numbers of layers at different places of the construction.

The products made by the LF Technology are comparable with products made by the prepreg technology. In comparison with prepregs has LF Technology big advantage in variability, i.e. in production can be used dry fabric as required (the same like in usual hand lay-up) and that saves money, because there is no need to store huge amount of prepregs in freezer.

Advantages:

substite for prepregs with better logistics conditions - reinforcement you can choose, in freezer store only resin
variability of reinforcement
dry way of lamination
3x faster production compare with liquid resins
impregnation and curing in one step
great ratio resin/reinforcement (40:60)
very nice and smooth surface
no hazard vapours
very friendly to use
accurate defined composite structure in everyposition in the final product

Epoxy foil resins Letoxit

Resin LETOXIT	Basis	Curing (°C) (min)		Tg (°C)	Max. Tg (°C)	Characteristics
LFX 023	epoxy	120	60	95	100	universal type
LFX 035	epoxy	120	60	122	125	universal type for carbon
LFX 038	halogenated epoxy	120	60	127	135	self extinguishing (FAR 23)
LFX 040	mod. cyanoester	150	180	190*	250	high temperature resistance
LFX 044	mod. epoxy	120	60	95	105	high impact strength
LFX 054	epoxy	120	60	130	155	higher temperature resistance, for carbon
LFX 055	epoxy	120	60	130	155	higher temperature resistance, low stickiness
LFX 056	epoxy	120	60	120	125	self extinguishing (FAR 25)
LFX 060	epoxy	120 (80)	20 (240)	120	125	fast curing, for carbon
LFX 062	phenolic	120	45	80	103	self extinguishing (DIN 5510-2)
LFX 162	epoxy	120 (80)	20 (240)	95	100	fast curing universal type
* cured 3 h at 140°C, post - cured 4h at 200°C + 4h at 250°C

Technical data

Resin LETOXIT	Density (g/cm3)	Peak (120°C, min.)	Max. flexural stress (MPa)		Flexural modulus of elasticity (GPa)		Impact strength of pure resin (kJ/m2)
Resin LETOXIT	Density (g/cm3)	Peak (120°C, min.)	Pure resin	Composite	Pure resin	Composite	Impact strength of pure resin (kJ/m2)
LFX 023	1,19	4,65	120 - 125	540**	3 - 3,1	18,9**	45 - 50
LFX 035	1,19	5,5	120 - 125	580**	3,2 - 3,3	17,1**	30 - 35
LFX 038	1,39	10,5	100	610**	3,2 - 3,3	19,5**	12
LFX 040	1,21	2,3*	-	425**	-	20**	-
LFX 044	1,14	8,5	85	417**	2,2 - 2,3	12,2**	55 - 60
LFX 054	1,15	10,2	83	703***	3,9	21***	6,5
LFX 055	1,15	10	-	535***	-	16,2***	-
LFX 056	1,35	6	110	480***	3,3 - 3,4	15***	22
LFX 060	1,19	4	145	487***	3,2	14***	24,7
LFX 062	1,19	9,4	-	-	-	-	-
LFX 162	1,28	3,7	-	540**	-	18,9**	-
12 layers glass fabric 163 g/m2 twill + 5 layers Letoxit LFX 300 g/m2. Resin content 44% * 12 layers glass fabric 163 g/m2 twill + 8 layers Letoxit LFX 200 g/m2. Resin content 50%

The foil can be stored for 1 month at temperatures up to +20°C, for 3 months at +5°C and up to 1 year at -18°C without any change of its properties. Be sure not to exceed +30°C at transport and storage.

Accessories

Name		Item			Characteristics
Letoxit PFL 122		fixing agent			fixation (temporary gluing) of dry fabrics into moulds. After curing non visible, doesnt make stains.

Application

LF Technology is suitable for any composite structure, where balanced weight and mechanical properties ratio are required. Typical applications are tin shell structures with high reinforcement volume, locally added reinforcements and/or with different required local properties (for example reinforcement orientation) because these structures cannot be manufactured by conventional technologies without highadded cost of material and work. The conventional composite structures, originally made by RTM, VARTM, Hand-lay up, are possible, of course. but due to lower requirements on mechanical properties on parts made by these conventional technologies, economy of LF technology (RFI) must be taken into account.

Potential applications are: