Лако-красочные материалы — производство

Hydroxy functionality is introduced into the back bone of the acrylic via hydroxy functional monomers such as:

• Hydroxy ethyl acrylate (HEA)

• Hydroxy propyl acrylate (HPA)

• Hydroxy butyl acrylate (HBA)

• Hydroxy ethyl methacrylate (НЕМА)

• Hydroxy propyl methacrylate (HPMA)

Additionally, ethylene oxide and propylene oxide extended variants of some of these monomers are used to modify solubility and compatibility characteristics of the polymer as well as film performance (e. g. to increase flexibility).

Another route to the production of hydroxy functional acrylic is via a carboxy functional acrylic, which is subsequently post reacted with the glycidyl ether of Versatic acid (Cardura® E10, Shell chemicals), see Figure 4-3.

c=o

I

0

1

CH2

I

CHOH

I

CH2

I

0

1

c=o

I

R2-C—R,
R,

Figure 4-3

In Situ Production of Hydroxy Functionality

Although this hydroxyl group is secondary and sterically hindered, the introduction of the Versatic ester group to the polymer produces resins which have excellent compatibility, pigment wetting, flow and levelling properties.

Hydroxy functional acrylics are normally cured with amino resins or amino/epoxy resin combinations at temperatures ranging from 120°C to 150°C. Typical crosslinking reactions are shown in Figure 4-4.

i) Cure with a butylated melamine formaldehyde resin

+ C4H9-0-CH2-NH-(Melamine resin))

OH OH

4T(H) _ 6 w

120 C

OH OCHj-NH-(Melamine resin) + C4H9OH

AT 150 C

OH 0-CH2-CH-(Epoxy resin)

Figure 4-4

Crosslinking Reactions for Hydroxy Functional Acrylics

Since the hydroxy/amino reaction is catalysed by the presence of acidic groups, the hydroxy acrylic polymer normally contains some carboxy functionality. Under these conditions crosslinking reaction proceeds quickly at 120°C. It is possible further to reduce the curing temperature through the use of external catalysts such as acid butyl phosphate, para toluene sulphonic acid (PTSA), acid butyl maleate or phthalic acid. When such a catalyst is incorporated into the paint, curing temperatures as low as 90°C can be obtained.

Acrylic/butylated melamine blends typically contain 20-30% of the melamine resin (based on total solid binder). The higher the content of melamine resin, the harder and the more brittle the coating becomes.

The choice of amino resins is discussed in more detail below.

2. Carboxy Functional Acrylics

In single pack heat cured coating systems, carboxy functional acrylics can be crosslinked at elevated temperatures with amino and epoxy resins, as shown in Figure 4-5.

i) Carboxy/Hydroxy

/VW*|A*VV*Ywv*a + HO/WW OH

COOH COOH
ДТ.

COOH COO/VvWvOH + H2o

ii) Carboxy/Amino

+ СдНдОСН^НСО*****(Amino resin)

COOH COOH

ААА/уЧАЛЛЛЛ^ЛАЛА

COOH COOCH2NHCOASMA(Amino resin) + C4H9OH

iii) Carboxy/Epoxy

(Epoxy resin)

COOH COOH

Д T

catalyst 150 C

COOH COO-CH2-CH***A(Epoxy resin)

I

OH

Figure 4-5

Crosslinking Reactions for Carboxy Functional Acrylic Resin

However, the major use for heat cured, carboxy functional acrylics is in combination with either Bisphenol A based glycidyl ether epoxy resins, or hexamethoxy methyl melamine resins, for metal decorating applications, where their flexibility and deep draw properties are essential.

3. Choice of Co-reactants

As we have seen in the last section dealing with the cross linking reactions of thermosetting acrylics, a number of types of resins or oligomers can be used to modify and indeed enhance the properties and performance of thermosetting acrylics.