HYDRAULIC FLUIDS IN PLASTIC INJECTION MOLDING PROCESSES

Abstract

The present invention relates to the use of hydraulic fluids in plastic injection molding processes. Thereby it was surprisingly found that the use of hydraulic fluids with the right combination of physical parameters like the viscosity grade, the viscosity index, the density and the dispersancy allows for significant energy savings in plastic injection molding processes (PIM). The PIM process is an industrial process to manufacture plastic parts at well controlled temperatures, pressures and cycle times. The energy consumption of the process became more important over the last years, however, other parameters like process stability and accuracy of plastic part parameters as well as machine protection and long oil drain intervals have to be satisfying.

Claims

1. A hydraulic fluid composition used for reducing the energy consumption of a hydraulic system, comprising a hydraulic fluid, in a plastic injection molding process, wherein the hydraulic fluid composition comprises (i) a polyalkyl(meth)acrylate viscosity index improver comprising monomer units of a) 5 to 40 wt. % of one or more ethylenically unsaturated ester compounds of formula (I) ##STR00005## wherein R is equal to H or CH.sub.3, R.sup.1 represents a linear or branched alkyl group with 1 to 6 carbon atoms, R.sup.2 and R.sup.3 independently represent H or a group of the formula —COOR′, wherein R′ is H or an alkyl group with 1 to 5 carbon atoms, b) 50 to 95 wt. % of one or more ethylenically unsaturated ester compounds of formula (II) ##STR00006## wherein R is equal to H or CH.sub.3, R.sup.4 represents a linear or branched alkyl group with 7 to 15 carbon atoms, R.sup.5 and R.sup.6 independently represent H or a group of the formula —COOR″, wherein R″ is H or an alkyl group with 6 to 15 carbon atoms, c) 0 to 30 wt. % of one or more ethylenically unsaturated ester compounds of formula (III) ##STR00007## wherein R is equal to H or CH.sub.3, R.sup.7 represents a linear or branched alkyl group with 16 to 30 carbon atoms, R.sup.8and R.sup.9 independently represent H or a group of the formula —COOR′″, wherein R′″ is H or an alkyl group with 16 to 30 carbon atoms, and d) 0 to 10 wt. % of at least one N-dispersant monomer, and (ii) a base oil selected from API group I, II, III or IV base oils or mixture thereof, wherein the formulated hydraulic fluid has a fresh oil viscosity index of at least 160, a viscosity at 40° C. of 15 cSt to 51 cSt, a density at 15° C. of 800 kg/m.sup.3 to 890 kg/m.sup.3.

2. The hydraulic fluid composition according to claim 1, wherein the industrial hydraulic application is a plastic injection molding process or is a process carried out in a hydraulic press.

3. The hydraulic fluid composition according to claim 1, wherein the weight average molecular weight (M.sub.w) of the polyalkyl(meth)acrylate viscosity index improver (i) is 20,000 to 100,000 g/mol.

4. The hydraulic fluid composition according to claim 3, wherein the weight average molecular weight (M.sub.w) of the polyalkyl(meth)acrylate viscosity index improver (i) is 40,000 to 70,000 g/mol.

5. The hydraulic fluid composition according to claim 1, wherein the hydraulic fluid has a viscosity index of at least 180, a viscosity at 40° C. of equal or less than 36 cSt and a density at 15° C. of less than 860 kg/m.sup.3.

6. The hydraulic fluid composition according to claim 5, wherein the hydraulic fluid has a viscosity index of at least 250, a viscosity at 40° C. between 19 cSt and 28 cSt and a density at 15° C. of less than 840 kg/m.sup.3.

7. The hydraulic fluid composition according to claim 1, wherein said N-dispersant monomer is of the formula ##STR00008## wherein R.sup.10, R.sup.11 and R.sup.12 independently are H or an alkyl group with 1 to 5 carbon atoms and R.sup.13 is either a group C(Y)X—R.sup.14 with X═O or X═NH and Y is (═O) or (═NR.sup.15), where R.sup.15 is an alkyl or aryl group, and R.sup.14 represents a linear or branched alkyl group with 1 to 20 carbon atoms which is substituted by a group NR.sup.16R.sup.17 where R.sup.16 and R.sup.17 independently represent H or a linear or branched alkyl group with 1 to 8 carbon atoms, or wherein R.sup.16 and R.sup.17 are part of a 4 to 8 membered saturated or unsaturated ring containing optionally one or more hetero atoms chosen from the group consisting of nitrogen, oxygen or sulfur, wherein said ring may be further substituted with alkyl or aryl groups, or R.sup.13 is a group NR.sup.18R.sup.19, wherein R.sup.18 and R.sup.19 are part of a 4 to 8 membered saturated or unsaturated ring, containing at least one carbon atom as part of the ring which forms a double bond to a hetero atom chosen from the group consisting of nitrogen, oxygen or sulfur, wherein said ring may be further substituted with alkyl or aryl groups.

8. The hydraulic fluid composition according to claim 7, wherein said dispersant monomer e) of polymer (i) is at least one monomer selected from the group consisting of N-vinylic monomers, (meth)acrylic esters, (meth)acrylic amides, (meth)acrylic imides each with dispersing moieties in the side chain.

9. The hydraulic fluid composition according to claim 7, wherein said N-dispersant monomer is at least one monomer selected from the group consisting of N-vinyl pyrrolidone, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylmethacrylamide.

10. The hydraulic fluid composition according to claim 1, wherein the polyalkyl(meth)acrylate viscosity index improver comprises a polydispersity index of between 1.5 and 2.5.

11. The hydraulic fluid composition according to claim 1, wherein the polyalkyl(meth)acrylate viscosity index improver comprises monomer units of a) 5 to 20 wt. % of the compounds of formula (I), b) 70 to 90 wt. % of the compound of formula (II), and c) 5 to 25 wt. % of the compound of formula (III).

12. The hydraulic fluid composition according to claim 1, wherein the hydraulic fluid composition comprises 70 to 95 wt. % of the base oil selected from API group I, II, III or IV base oils or mixture thereof and 5 to 30 wt. % of the polyalkyl(meth)acrylate viscosity index improver.

13. The hydraulic fluid composition according to claim 12, wherein the hydraulic fluid composition comprises 80 to 95 wt. % of the base oil and 5 to 20 wt. % of the polyalkyl(meth)acrylate viscosity index improver.

14. The hydraulic fluid composition according to claim 1, wherein the hydraulic fluid composition comprises a Dispersant-Inhibitor (DI) package, comprising antioxidants, antifoam agents, anticorrosion agents and/or at least one Phosphorous or Sulfur containing antiwear agent.

15. The hydraulic fluid composition according to claim 2, wherein the weight average molecular weight (M.sub.w) of the polyalkyl(meth)acrylate viscosity index improver (i) is 20,000 to 100,000 g/mol.

16. The hydraulic fluid composition according to claim 2, wherein the hydraulic fluid has a viscosity index of at least 180, a viscosity at 40° C. of equal or less than 36 cSt and a density at 15° C. of less than 860 kg/m.sup.3.

17. The hydraulic fluid composition according to claim 2, wherein said N-dispersant monomer is of the formula ##STR00009## wherein R.sup.10, R.sup.11 and R.sup.12 independently are H or an alkyl group with 1 to 5 carbon atoms and R.sup.13 is either a group C(Y)X—R.sup.14 with X═O or X═NH and Y is (═O) or (═NR.sup.15), where R.sup.15 is an alkyl or aryl group, and R.sup.14 represents a linear or branched alkyl group with 1 to 20 carbon atoms which is substituted by a group NR.sup.16R.sup.17 where R.sup.16 and R.sup.17 independently represent H or a linear or branched alkyl group with 1 to 8 carbon atoms, or wherein R.sup.16 and R.sup.17 are part of a 4 to 8 membered saturated or unsaturated ring containing optionally one or more hetero atoms chosen from the group consisting of nitrogen, oxygen or sulfur, wherein said ring may be further substituted with alkyl or aryl groups, or R.sup.13 is a group NR.sup.18R.sup.19, wherein R.sup.18 and R.sup.19 are part of a 4 to 8 membered saturated or unsaturated ring, containing at least one carbon atom as part of the ring which forms a double bond to a hetero atom chosen from the group consisting of nitrogen, oxygen or sulfur, wherein said ring may be further substituted with alkyl or aryl groups.

18. The hydraulic fluid composition according to claim 8, wherein said N-dispersant monomer is at least one monomer selected from the group consisting of N-vinyl pyrrolidone, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylmethacrylamide.

19. The hydraulic fluid composition according to claim 2, wherein the polyalkyl(meth)acrylate viscosity index improver comprises a polydispersity index of between 1.5 and 2.5.

20. The hydraulic fluid composition according to claim 2, wherein the polyalkyl(meth)acrylate viscosity index improver comprises monomer units of a) 5 to 20 wt. % of the compounds of formula (I), b) 70 to 90 wt. % of the compound of formula (II), and c) 5 to 25 wt. % of the compound of formula (III).

Description

[0058] FIG. 1: Description of a typical injection molding cycle

[0059] The cycle begins when the mold closes (Step 1), followed by building up a pressure (Step 2a) which is required to keep the mold closed during injection. After moving the extruder to the mold (Step 2b), material is injected (Step 3) and a working pressure is maintained to compensate material shrinkage during molding (Step 4). Optionally, the work piece can be coated with a CoverForm® process step (Step 4.1, applied in Cycle A). The extruder is moved back when the cooling phase has started (Steps 5 and 6). At the end of the cooling phase the mold is opened (Step 7) and the work piece can be removed (Step 8).

[0060] Table 2 shows the differences in energy consumption (savings are negative values) found for cycle A, cycle B and an evaluation of Step 1 and Step 2 taken from cycle A data.

Step 1+Step 2 (2a+2b)+Step 4.1+Step 7+Step 8   Cycle A

Step 1+Step 2 (2a+2b)+Step 7+Step 8   Cycle B

[0061] Within this cycle, Steps 1, 2, 4.1, 7 and 8 are independent of the material which is injected. Consequently, the energy savings are independent on the plastic material properties.

[0062] The coating step 4.1 is optional and part of the CoverForm process. Cycle A (with coating) and cycle B (without coating) evaluate the influence of this step on energy savings.

TABLE-US-00003 TABLE 2 Differences in energy consumption with investigated hydraulic fluids Comparative Comparative Ex 1 Ex 2 Ex 1 Ex 2 Ex 3 Ex 4 Δ energy consumption versus reference oil [%] Cycle A — 3.6 −4.9 −7.5 −6.7 — Cycle B 2.5 5.1 −5.4 −7.9 −5.2 −9.5 Step 1 + Step 2 — 2.1 −7.0 −8.6 −5.7 — Cycle A: process steps which are material independent, with CoverForm ® process step Cycle B: process steps which are material independent, without CoverForm ® process step Step 1 +Step 2: fully material independent steps before material injection

[0063] On the basis of the above results, it is clearly demonstrated that physical parameters of the base oil in combination with a viscosity index improver as defined in claim 1 are crucial in order to observe energy savings in an hydraulic system used under the high pressure conditions of a plastic injection molding process.

[0064] Although illustrated and described herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope of the claims.